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25/2/2015 Arduino’s AnalogWrite – Converting PWM to a Voltage 

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Arduino’s AnalogWrite – Converting PWM to a 

Voltage 

By SCOTT DANIELS | Published: JUNE 15, 2011 

DA_converter 

When I first started working with the 

Arduino platform (it was also my first 

experience with microcontrollers), I was 

a little surprised that analogWrite didn’t 

actually output a voltage, but a PWM 

(pulsewidth modulated) signal. After all, 

the ATmega had a AD (analog to 

digital) converter along with Arduino’s 

analogRead. The complementary 

analogWrite function was there, but no 

DA (digital to analog) converter on the 

AVR chip itself. Fortunately, there is an 

easy way to convert a PWM signal to an 

analog voltage. To do so you only need 

to implement a simple singlepole low 

pass filter. Does it sound complicated? It 

isn’t. There are some great online tools 

to help. Once you learn how to make one, you can quickly and easily output analog 

voltages from not only the Arduino, but PICs as well as any other microcontroller 

that has PWM output. 

PWM Primer 

Pulse width modulation (or PWM as it is most commonly known), is a way of 

encoding a voltage onto a fixed frequency carrier wave. Commonly used for radio 

controlled devices, it is similar to FM (frequency modulation) or AM (amplitude 

modulation) in what it accomplishes. Each type of modulation scheme has its own 

advantages and disadvantages. AM modulation was the first type of modulation 

used for radio transmissions. It is the most simple modulation scheme to 

implement, requiring only a single transistor or vacuum tube amplifier as was done 

in the early days of radio. However, it suffers from excessive noise and therefore, 

FM modulation was invented. In this modulation technique, the voltage signal is no 

longer related to the strength of the signal. That is why FM radio has superior noise 

and fidelity qualities over AM radio, though it is not as simple to implement in 

circuitry. 

With the need for digital communication, a new modulation technique was 

invented – PWM. This technique shares the same noise immunity as FM, to which 

it is very similar. The biggest difference is the simplicity and digital nature of the 

modulation. Instead of varying the modulation frequency with voltage, an output is 

merely switched on and off at a fixed frequency. The percentage of the ontime is 

in proportion to the signal voltage. To see better what this means, let’s examine 

what a PWM signal looks like for various levels. In the following image, the duty 

cycle is the output value from the PWM pin of an Arduino divided by 255: 

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PWM outputs (curtesy arduino.cc) 

For the Arduino, you write a value from 0 to 255 on a PWM pin, and the Arduino 

library will cause the pin to output a PWM signal whose on time is in proportion to 

the value written. 

When it comes time for us to actually write an output voltage, the 0255 value 

lacks meaning. What we want is many cases is a voltage. For our purposes, we will 

assume the Arduino is running at Vcc = 5 volts. In that case, a value of 255 will 

also be 5 volts. We can then easily convert the desired voltage to the digital value 

needed using simple division. We first divide the voltage we want by the 5 volts 

maximum. That gives us the percentage of our PWM signal. We then multiply this 

percentage by 255 to give us our pin value. Here is the formula: 

Pin Value (0255) = 255 * (AnalogVolts / 5); 

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Modulating a Signal 

In addition to just setting the output voltage, you may need to actually modulate a 

signal. To modulate a signal, we simply call analogWrite with the value 

corresponding to our signal voltage. One way to do this would be to read the 

voltage at an analog pin, and then write it back out. For example: 

int pwmPin = 9; // output pin supporting PWM 

int inPin = 3; // voltage connected to analog pin 3, e.g. a potentiometer 

int val = 0; // variable to store the read value 

float volt = 0; // variable to hold the voltage read 

void setup() 

{ 

pinMode(pwmPin, OUTPUT); // sets the pin as output 

} 

void loop() 

{ 

val = analogRead(inPin); // read the input pin 

volt =(5.0 * val) / 1023; 

val = 255 * (volt / 5); 

analogWrite(pwmPin, val); 

} 

Now in this example, we obviously won’t be need to convert our output voltage 

back to a voltage, but will instead transmit our modulated signal as it is. If you 

have an oscilloscope, you can attach it to the output, and a potentiometer to the 

input and watch your PWM signal change with the input value. There are many 

applications for PWM modulation, the most commonly being control of servos – 

either directly by wire or by radiocontrol. The Arduino has a nice library that 



handles creating the correct PWM signal for servos. For more information, see the 

Arduino Servo Library. 

Changing the Modulation Frequency 

Most microprocessors permit you to change the modulation frequency for PWM 

pins. The Arduino has its own set default values. For pins 3,9,10,11 it is 

approximately 488 Hz. For pins 5 and 6, it is about 977 Hz. These values are for a 

stock Arduino running at 16MHz. You can change these frequencies easily by 

writing new values to the appropriate timer register. For example, to change the 

frequency of timer 2, which controls pins 9 and 10, to 3,906 Hz, you would set its 

register like so: 

TCCR1B = TCCR1B & 0b11111000 | 0x02; 

On the Arduino website, there is a nice tutorial on setting timer frequencies and 

their ramifications. 

Low Pass Filtering 

Now that you understand how PWM works and can even change the frequency, it is 

time to take a look at how to implement a simple low pass filter. This simple piece 

of circuitry will convert your PWM output into a voltage corresponding to the 

percentage of the PWM waveform. You will then have a complete DA converter for 

your Arduino or other microcontroller. 

If we examine the circuit on the left, when a voltage 

is applied to the input of R, the capacitor C will 

begin to charge. When it is charged, it will cease to 

conduct current and the voltage at the output of 

this circuit will match the input (assuming a high 

impedance load). If you remember that capacitors 

block DC currents, but pass AC currents, you can 

RC Low Pass Filter 

see that any DC voltage input will also be output, 

but high frequency AC voltages will be shorted to 

ground. For anything in between, i.e. lower frequency AC voltages, they will be 

filtered according to the R/C time constant formed by the resistorcapacitor 

network. 

While this circuit is very simple, choosing the appropriate values for R & C 

encompass some design decisions – namely, how much ripple can we tolerate and 

how fast does the filter need to respond? These two parameters are mutually 

exclusive. In most filters, we would like to have the perfect filter – one that passes 

all frequencies below the cutoff frequency, with no voltage ripple. While no such 

ideal filter exists, we can achieve close to it by using a multiple pole filter. Such a 

filter would incorporate many components in a ladder configuration. While such a 

filter has wonderful performance characteristics, its complexity and cost is 

unnecessary for simple DA conversion. 

In such cases, we only need a simple single pole filter as shown above. We can 

achieve a reasonable voltage ripple for a single price – a low cutoff frequency. A low 

cutoff frequency has two ramifications. First, it limits the speed by which we can 

vary our output voltage. Second, there is a response delay when changing the 

voltage until the steadystate voltage is reached. For many of the more common 

applications, this tradeoff is perfectly acceptable. Let’s now look at an example. 

First, let’s choose our maximum ripple voltage. When we filter this high frequency 

PWM signal, a small component of it will always make it through the filter. That 

happens because our capacitor is too small to filter it out entirely. We could choose 

a very large capacitor /resistor combination that would get a very high proportion 

of it, but then it would take a long time to reach the proper output voltage as the 

capacitor charges. That would greatly limit how fast our signal can change and be 

seen at the output. Therefore, we need to choose a reasonable value for the ripple 



voltage. A popular application would be to change the voltage of a MOSFET. Since 

MOSFETs are voltage controlled devices, we can easily drive them with our 

microcontroller with PWM and a lowpass filter. Any ripple voltage present at the 

input would also be present at the output. For this example, assume the MOSFET 

will be driving a noncritical load such as a high power LED. In this instance, we 

merely need to stay within reasonable limits so the peak current in the LED will not 

be exceeded. In this case a 0.1 volt ripple would be more than adequate. 

Next we choose a capacitor value. While it would seem the next step would be 

choosing a cutoff frequency (and it normally would be), there are additional 

considerations such as output load and capacitor cost. If we were only driving the 

gate of a MOSFET, there would be no output load to speak of. In such case, we 

could choose a cheap ceramic cap such as 0.1uF and then choose the resistor we 

need to achieve the cutoff frequency desired. If, on the other hand, we need some 

current from our output, then we will need a smaller resistor and a correspondingly 

larger capacitor. For a recent circuit, I found I needed a 2.2uF capacitor to prevent 

my modest load from altering the output voltage too significantly. Designing this 

circuit for nontrivial loads is beyond the scope of this article. If you find yourself in 

such a need, the best approach would be to start with at least a 1uF capacitor and 

then test how your output voltage changes with load. Increase your capacitor until 

the load has a low enough effect to be acceptable. Another way to look at this 

circuit would be to think of it as a poorly regulated power supply. It only meant to 

convert digital signals to an output voltage; not to drive a load as well. Buffer the 

output with an opamp or a FET first. Then drive your load. 

For our example, let’s choose a capacitor value of 1.0uF. For driving a MOSFET, you 

can use something even smaller, but this size will let us have a small load. Next, 

we need to choose a cutoff frequency or response time. These two parameters are 

related but not the same. For simple things like driving LEDs, we are more 

concerned with a response time. Our response time can be pretty generous. Let’s 

choose a settling time (to reach 90% of the final value) of 0.1 seconds, which 

would require a resistor of 15K ohms. 

You may be wondering how to calculate these values, or others of your own. Rather 

than delve into a lot of equations, I have found something better. This excellent 

online calculator does all the hard math for you, calculating cutoff frequency, 

response times, voltage ripple and other values. It even draws a transient analysis 

graph for you – displaying your ripple and how the voltage ramps up over time. 

Here is the output graph for this example: 

RC Low Pass Filter Time Response (curtesy http://sim.okawadenshi.jp/en/PWMtool.php) 

Conclusion 

You are now armed with the knowledge you need for creating and using your own 



digital to analog circuit. Such circuits are incredibly useful. My favorite is driving 

MOSFETs and opamps. By sampling a current or voltage somewhere, you can then 

determine what voltage you need to output to create the level of current or voltage 

you need. By means of such a simple system, you can make your own voltage 

regulators, current regulators, LED drivers, etc. The possibilities are endless. 

If you have any questions about this article, please drop me a note in the 

comments. If you have any improvements, corrections or additions, please let me 

hear about them as well. 

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John 12 

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Posted 

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2 June 16, 2011 at 2:09 pm | Permalink 

Simple, 12 

2 

clear, concise…an excellent tutorial. Thank you. 

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G Lewis 

Posted April 7, 2013 at 3:58 pm | Permalink 

Send via Shareaholic Mail 

A great Print Article with PrintFriendly 

very usefull indeed. 

Im on the Highway to Pedhell with ADC/DAC 

http://www.youtube.com/watch?v=Trb3UAXWNn8 

Reply 

Ian Crane 

Posted November 10, 2013 at 1:23 am | Permalink 

Scott, where do you get the little DA Conv PCBs? 

Reply 

High Energy Rob 

Posted June 16, 2011 at 6:08 pm | Permalink 

Nice article. Great job. 

Reply 



wilcimar 


Hi, I´d like to know if I could use this circuit to convert a frequency to 

voltage signal from a ignition cable of my car ( by capacitive coupling), for a 

reliable RPM measuring. thanks. 

Reply 

High Energy Rob 


I think you can buy frequencytodigital converters that would probably work 

better for a tach. Im also fairly sure that I have seen guages that do this 

automatically and just require a frequency input. The problem with this 

circuit is that the signal from the coil on your car is not pulse width 

modulated, the pulses are always the same length so it wont really work. 

You could pretty easily turn an arduino into a tach using this circuit on the 

output though. 

Reply 

Mike 


What is the point to this? Most motors handle the PWM just fine. And for 

applications that need an analog voltage, well…this is only capable of 

sourcing a small amount of current. 

Reply 

Scott Daniels 


That’s a good question. For some applications such as the ones you 

describe, PWM may be just fine. For others, PWM is not acceptable. In 

these cases you need a lowripple voltage. When you buffer this 

voltage with a highimpedance amplifier such as a FET or an opamp, 

you can drive any load you like. This application is intended to drive 

such high impedance loads only. 

One example for this type of circuit is driving high intensity LEDs. For 

these devices, you can’t just apply a full voltage to them without some 

sort of current regulation, no matter how short the pulse is. They will 

burn up. You must create some kind of constant current driver. One 

way is to use the circuit described and apply this voltage to the gate of 

the FET. By monitoring the current going through the FET, you can set 

it to whatever value you like by varying the pulse width. 

Another example would be creating a programmable linear voltage or 

current regulator, again by using a single FET. You can even create a 

constant power regulator using this technique. 

Do these examples make more sense of this article now? 

Reply 

Hello.. 

Eddie 

Posted May 3, 2013 at 1:03 pm | Permalink 

by modulating a signal, 


int inPin = 3; // voltage connected to analog pin 3, e.g. a 

potentiometer 



if i use accelorometer.. how about the coding? i dont use 

potentiometer. 

Thanks 

Reply 

Navid 

Posted July 1, 2011 at 10:52 pm | Permalink 

Thanks alot – your answer solved all my problems after several days 

struggling 

Reply 

Art k 


Great article. Do you mind a question. 

I am using the arduino to take two input signals to output a 05 volt analog 

control signal. No real load. Respons time is probably the most critical. What 

cap and resistor do you recommend? 

Thanks again for a great lesson!!!! 

Reply 

Scott Daniels 

Posted December 6, 2011 at 4:29 pm | Permalink 

That all depends on what timing you need. Go to the RC calculator 

referred to determine them. 

Reply 

Magnus 

Posted November 11, 2011 at 3:25 pm | Permalink 

Could you use this to convert an audio signal to pwn to control a laser which 

will send the impluse to a photo diode? 

great tutorial 

Reply 

Scott Daniels 


Yes, although you probably just want to send the PWM directly to the 

laser. Usually lasers are pulsed, not attenuated. 

Reply 

Tomas 

Posted August 29, 2014 at 4:28 am | Permalink 

NO! Lasers are delicate components that can not be driven by 

PWM. They will – as oposed to LEDs, transistors etc. – suffer 

from “COD” (Catastrophic Optical Damage) in nanoseconds; that 



is – long before they die from thermal overheating in for 

instance a critical junction. 

Reply 

Hi, 

RodP 


I’m looking for a circuit that will interpret a signal that changes in pulse 

frequency and amplitude to drive a small peristaltic pump to deliver a very 

small amount of liquid. The pulses come from an lpg injector system, namely 

Prinns. I have a picture of a scope readout showing an example of the pulse 

but it doesn’t look like I can post it here. Please could you let me know if this 

might help me with what I’m looking for? 

Many thanks in advance 

RodP 

Reply 

Scott Daniels 


It sounds like you will need to read your input via an analog pin, do 

you signal processing on it via code, and then output straight PWM. You 

won’t need the filter specified in this article at all. Pumps like other 

motors are usually controlled by being turned on and off, not by 

sending a reduced voltage. 

Reply 

JStoski 

Posted January 17, 2012 at 6:56 pm | Permalink 

Perfect. Knew I had to buffer the pulses and smooth them out in order to 

measure the current going through the FETs. Have to control the current 

_smoothly_, not just max value and off using PWM. Thanks for the link to the 

single pole filter calculator. 

Reply 

Hannah Herbert 

Posted January 27, 2012 at 10:09 am | Permalink 

Thank you for an excellent tutorial! 

Reply 

Hannah Herbert 


Scott, do you think I could sum digital audio samples using an Arduino 

and output this value using PWM and the filter you have suggested. Do 

you think this would suffice to generate a percussion sound like a bass 

drum or a snare drum? 

Please let me know your thoughts or if you have any better 

suggestions. 



Reply 

Scott Daniels 


If you are fast enough . You must be able to do your signal 

processing in time to output your value above the Nyquist rate 

which is usually considered to be 40kHz for high fidelity music. 

The top frequency for the Timer2 of an ATmega 168 series is 

62.5k according to the spec sheet, so as long as you can do your 

signal processing fast enough to keep up. That would be the 

trick. Of course you want to make your output filter to be just as 

fast as well. Lastly you’ll want a high impedance load such as an 

opamp or MOSFET in order to make a fast filter. 

I hope that answer makes sense and isn’t too technical. I would 

begin by designing a filter you think would be fast enough and 

try doing some tests – both with an oscilloscope and your ears. 

— Best wishes on your project. 

Reply 

Ajay 

Posted February 20, 2012 at 2:29 pm | Permalink 

Looking for circuit or suitable instrument which can convert vehicle tach/rpm 

impulses to analog voltage, i.e. output value of tach/rpm needs to get 

converted to analog voltage as our hardware takes input from 0 to 5v or 

even up to 20v. 

Reply 

Scott Daniels 


What you need is a frequency to voltage converter. Something like this 

one or similar. If you are using a micro already, you can also count the 

pulses and then output a voltage as my article describes. 

Reply 

Ajay 


Thanks for the info Scott…..is any ready made Micro board 

available for PWM to Analog converter? 

Reply 

Asaph 

Posted February 24, 2012 at 5:34 am | Permalink 

Thanks for the PWM insight. 

I would wish to use it for triggering mosfets in a variable frequency inverter. 

Could you shed some more light on the same. you could forward some 

similar work on the same. 



I will appreciate our help 

Reply 

gusti 

Posted March 7, 2012 at 4:03 pm | Permalink 

Thanks for that great tutorial. Especially for the link to the japanese site. 

Reply 

Scott 

Hello Scott, 

Posted March 25, 2012 at 10:32 am | Permalink 

I have 8bit digital signal coming in from photodiode (the song that is being 

transmitted from LED and captured by photodiode). Now I want to convert 

that 8bit signal back to analog and recover the song. Would your circuit 

work for it? Or should I just use the PWM signal as an analog input to the 

muencoder? 

Reply 

Scott Daniels 


This circuit will work, provided your digital signal is using PWM 

modulation. Also, make sure response time of the filter is fast enough. 

For audio, 24K sampling is fine for moderate quality (think cassette 

tape) audio. For high fidelity, sample at 40K. Also, note for the 8bit 

output, your dynamic range will be about 48 decibels. Give it a try and 

see how you like it (be sure to buffer the filter’s output with an opamp). 

Reply 

vipul 


Hi Scott, 

I am using the arduino and xbee radios with current transducers to monitor 

realtime power. 

The voltage output of the current sensor is wirelessly transmitted as adc 

value((01024) to a xbee receiver which is connected to arduino uno board. 

This board basically maps the adc value received via xbee(01024) into a 0 

255 range pwm signal. But this mapping causes loss in resolution, which 

affects the system, because i am not actually generating a steady voltage 

equal to the one i read using the current sensor. 

Do you think a low pass filter circuit will solve this issue by generating 

accurate voltage from pwm signals coming out of arduino analoque write(). 

Thanks in advance 

Reply 

varsha 

Posted April 24, 2012 at 9:40 am | Permalink 

Hi Scott, 

we are making project with the help of arduino kit ATmega8, so we need 

difference between 8051 micro controller and arduino. 



Thank you! 

Reply 

Mark Murray 

Posted May 27, 2012 at 4:47 am | Permalink 

Nice article, i would like to drive a model train with PWM [0 to 100%] at 

about 4V up to 1/3 throttle then linearly run up to 12V. I have an arduino and 

was wondering how to use PWM and then control the output voltage. 

Reply 

Scott Daniels 


For driving motors, you can use PWM directly – you don’t have to filter 

it to a voltage. Basically, use the PWM output to turn a MOSFET on and 

off, switching the full voltage. The motor will coast during the off 

phase, and the result will be a reduction in torque and speed that is 

correlated to your PWM percentage. 

Reply 

Tobi Broger 


Hi Scott. 

Thank you for this excellent tutorial; for me as a Arduino/Electronic beginner 

really helpful! 

Probably you can help me with some hints on this: 

I would like to drive a tunable lens 

(http://www.optotune.com/images/products/Optotune%20EL1030.pdf) with 

my Arduino ADK. For this purpose I need DC: 0…300 mA. The manufacturer 

of the lens proposes some LED Driver Modules. Would the following one 

(http://www.thorlabs.com/Thorcat/0000/LD1255RManual.pdf) work together 

with the Arduino PWM output? Does that work straight away or do I need the 

low pass filter your described? Do you know cheaper possibilities (this one is 

123 Euros) to do something like that? 

Thank you for your valuable advice! 

Tobi 

Reply 

Tobi Broger 


Found a cheaper one and decided to just try it 

(http://www.ebay.com/itm/WavelengthElectronicsWLD3343Laser 

DiodeDriver22AFastAnalogModulation/271026157095? 

pt=LH_DefaultDomain_0&hash=item3f1a6af627#ht_554wt_1093) 

Reply 

sri 

Posted October 6, 2012 at 1:33 am | Permalink 

thanks for the article besides that let me ask you one thing, i don’t 

understand the use of potentiometer to vary the duty cycle .my point is that 

by varying the bit sequence in our program with specified delay we can 

change the duty cycle of our pwm just like any other pin isn’t it? 



Reply 

Scott Daniels 

Posted October 24, 2012 at 1:55 pm | Permalink 

The use of a pot is just an example of how to change the duty cycle. 

You can change the duty cycle of any PWM capable pin using 

analogWrite getting the value for that function anywhere. You don’t 

have to read it from a pot. 

Reply 

repairs laptop 


Interesting site I’m very glad I stumbled here through google, Gonna have to 

add this one to the old bookmark list 

Reply 

sam 

Posted October 20, 2012 at 1:00 am | Permalink 

Nice article, is it possible to drive peltier element from the output of low 

pass filter 

Reply 

Scott Daniels 


Since you would need to have a driver of some sort to drive any high 

power device, I don’t see why you would want to change the voltage 

into the driver. Just using PWM would suffice. The main exception 

would be in making your own constant current source using a MOSFET. 

In that case, you drive the FET with the low pass filter. 

Reply 

sam 


Hi Scott, 

Thanks for the reply ,am a beginner in electronics ,am using a 

opamp h bridge circuit to drive the peltier . Can i give PWM 

signal from a atmega32 to a driver circuit for peltier element? 

Reply 

Josh 


Hey Scott, 

I am trying to decide if the Arduino is right for me. I am 100% a beginner to 

this kind of stuff but I have a few things I would like to make that I can not 

just go out and buy, or so it seems. I have a 12v sensor that outputs a 

frequency. I want to take that frequency and convert it to a linear 05v 

output that will not be driving anything, its just for data accusation. I also 

have a pwm output that has a constant frequency and I would like to take the 



duty cycle and convert that to a 05v output for the same use. My question is 

the Arduino the right thing to use? Maybe just a low pass filter and a 

frequency to voltage converter would be simpler, I’m just not sure if that will 

fit my needs of getting both signals to be 05v. 

Thanks for your time and your help. 

Reply 

Josh, 

Scott Daniels 


I like your spirit regarding making the stuff you need and want to 

encourage you in that direction. You can do what you want without an 

Arduino or microcontroller. It really depends on what your needs are. 

As far as cost, an ATtiny chip costing $1 will do what you want for less 

than the freqvolt chip, but you will need to program it. If you actually 

use an Arduino in a permanent placement, that would of course be 

fairly expensive. As an alternative you can use the Arduino for 

prototyping (which is what it is best at), and then switch to just an 

ATmega328 chip or even program an ATtiny as I said. 

The only real disadvantage to using a microcontroller is the need to 

program it. Are you a beginner in electronics or microcontrollers? If 

you are new to electronics, then microcontrollers can actually be 

easier for you since they greatly simplify the electronics involved. 

They kind of convert the messy analog world into the tidy digital 

realm. If you are new to microcontrollers (and not electronics), then I 

recommend adding this category to your repertoire. It opens a new 

world of possibilities. 

In either case, I recommend getting your application running using the 

Arduino – it is beginner friendly and makes electronics beginner 

friendly as well. When you need to deploy your application, you can 

burn an ATmega or ATtiny chip using your Arduino and pop it into your 

final project for only a few dollars. 

Lastly, the other advantage the Arduino offers is intelligence. Your 

circuit does not need to be ‘dumb’, meaning it can only do simple 

things like an analog circuit can. You can program in extra features, 

complex decision making, etc. Smart electronics is the wave of the 

future. 

Reply 

Jason White 


Hi Scott, 

Thank you for the article, I’m sure when I’m farther along in my education, I 

will understand it better. I am 2 to 3 month novice to electronics and 

Arduino’s, but I Love challenges, so I may have bitten off more than I can 

chew with my latest project. I guess it’s silly to go from lighting some RGB 

LEDs to trying to control a model train with a TV remote, but pardon the pun, 

that’s how I roll. I actually am doing quite well with it. I have managed to get 

all manner of speed and direction control with DPDT relays and a Darlington 

transistor, or two types of motor shield. The problem lies in all cases with 

the annoying hum generated by PWM. I am currently using Lady Ada’s motor 

shield and I have set e frequency to 64khz which I am told will make the 

Pwm in audible, but I still hear it. Do you think your low pass filter could 

help with this? Can It be placed after the motor shield, before the track? 

Testing has moved from an nscale running 12v dc at 300mA to a big Gscale 

pulling .5.75A at 16V. If this would help with the hum, could you lead me in 

some direction as to the values of resistor and Capacitor I might need to 

make my train function more silently? I have considered going back to the 

Darlington hbridge and using a tip120 to provide speed control. Would a low 



pass filter before the tip120 help with the PWM hum? 

Thank a million, Jason 

Reply 

Scott Daniels 

Posted December 6, 2012 at 10:42 am | Permalink 

Jason, 

I am not sure why you are hearing a hum. I suspect it is in the motor 

itself and not related to the actual PWM frequency. I would suggest 

trying a different frequency and see if the pitch changes. 

If you want to control the motor without PWM by filtering, you will 

need to use Nchannel MOSFETs to drive your motor. The low currents 

you mention should not be a problem with proper heat sinking. You 

would probably also need to monitor the current or voltage in order to 

determine what voltage to drive the FET with. The technical aspects of 

doing so is too much for this comment, but I plan a future article on 

the subject. 

You definitely cannot use a low pass filter either before or after 

Darlington transistors. They are for switching applications only. 

It is nice to hear about your willingness to tackle such an ambitious 

project. When facing a big learning curve it can sometimes be quite 

daunting, but with persistence the pieces eventually fall into place. My 

best to you. 

Reply 

Michael Hayman 


As an 87 years0ld dinosaur who started life with crystal sets, I have dabbled 

with electronics ever since, without ever really learning the theory; my most 

recent venture has been a poorman’s electrocardiograph (described on the 

above site). It seems to be time to update this effort, and I see the 

possibility of using one of the Burr Brown analog amps, and – I hope – a 

sampler employing an arduino device. I taught myself sufficient of several 

versions of Basic to be able to draw and printout the necessary waveforms, 

and am now battling with C and its variants. I am told that microcontrollers 

make electronics easier to grasp, but so far this blissful state eludes me. I 

am most happy to see your kindly and tolerant responses to us uneducated 

people, and just wonder if you could point me in the right direction with 

arduino? ( My field is Medicine, and my aim has been to make it possible for 

electrocardiography to be available to poor parts of the world). 

Reply 

Michael, 

Scott Daniels 


I applaud your efforts with your noble project. The best I can do to 

help you get started with the Arduino is this article – Getting Started 

with Arduino. It gives a brief overview and links to some books and 

other resources. 

I do recommend the Arduino as the best microcontroller to start with. 

It has more resources, libraries and tutorials than any other platform. 

The best way to start is to buy an Arduino and start playing around 

with the sample “sketches” (programs) and go from there. The Arduino 

website has libraries for everything you will need to do. You just need 

to use them and modify the examples as needed. 



Best wishes and keep up the outstanding effort. 

Reply 

John Ford 


Very informative. 

I need to replace a defunct HPLC gradient controller with absolute minimal 

cost (since I’m paying out of my pocket). Basically, I need to generate 

complementary sawtooth waveforms, one changing from 0 volts to 10 volts 

over 10120 minutes while the other changes from 10 to 0 volts over the 

same time interval. 

As I (mis?)understand this method, you effectively get about 8 bits of 

resolution on the conversion. Is that approximately correct? 

Thanks 

Reply 

Scott Daniels 


That is correct. On the ATmega328, Timer0 & Timer2 are 8bit, while 

Timer1 is 16bit. Therefore, it is possible to get 16bit resolution by 

using Timer1. The Arduino library does not support 16bit timer values, 

so you will need to write your own analogWrite equivalent in order to 

use all 16bits. 

Reply 

John Ford 


Thanks, Scott. I appreciate the advice. I’m thinking that an 

Arduino Due (with two 12bit DACs) would be an easier 

implementation for me. I’ve put my name on the waiting list at 

Adafruit. 

Reply 

GP 


Do you trust this method enough to use in lieu of a current limiting resistor 

for driving LEDs? The Arduino can source up to 40mA of current which is 

more than sufficient to burn out even most high mcd value LEDs; I am 

considering using this method to exactly deliver the maximum forward 

voltage to an LED based on its specifications. Good idea or high likelihood of 

magic smoke escaping the LEDs? 

Reply 

Scott Daniels 


You cannot reliably drive an LED using its nonimal forward voltage. If 

you look at an LED’s IV curve, the current takes off vertically at this 

bias point. Since the exact voltage various from device to device and 

over temperature, there is no way to do it. There are two alternatives: 

1) You can drive an LED with much less than its Vf by this method. If 



the spec says the Vf=3.2 volts and you use 2.8 volts, it will probably 

work. However, what have you gained? You must use an added 

capacitor (not very cheap) and it is still an iffy approach. 

2) Use the method to make a constant current source. LEDs need to be 

driven by a controlled current source as opposed to a voltage source. 

To make a current source (technically a current sink), use an N 

channel FET as a voltage controlled resistor. Put a small resistor 

between the source and ground and measure the current by means of 

the voltage across that resistor. The LED goes between Vcc and the 

FET’s drain. Set your analog voltage to the FET’s gate to a nominal 

value (such as 1.0 volts) and measure your current flowing through the 

resistor. Increase your analog voltage driving the FET’s gate until you 

get the current you want. You need to test and adjust your current 

constantly. This method is a fair bit crude, but it will work. A better 

approach is a strictly analog one such as using a bipolar’s constant VBE 

to provide the needed feedback or else an comparator. 

Obviously, this approach is overkill for low current LEDs, but is a 

legitimate way to drive high current ones. 

Reply 

dan 


ok im using arduino mega 2560 to control the speed of a dc motor. i want to 

vary the speed of the dc motor according to a load from a load cell off a 

digital scale. i know i have to use the pwm, to control this. however im 

completely new to this and have no ideal where to go from here. i have the 

arduino, dc fan, power supply, and very little time to do this any help will be 

greatly appreciated 

Reply 

Scott Daniels 


It sounds like you just need to use the analogRead & analogWrite 

functions as well as processing the data. Read your data from your 

scale using analogRead(), and then power your motor with an N 

channel FET, giving the PWM to its gate with analogWrite(). For small 

FETs, you can drive their gates directly or with a small series resistor. 

For larger ones, you may have to use a driver circuit. 

Reply 

Hi Scott, 

Tom 


First off, thanks very much for the great article! 

I came across this while looking for a way to convert an analogOut to 05v in 

order to control a mains dimmer 

(http://www.amazon.co.uk/dp/B001IROCTO/?tag=provideyourown120). I 

had enough of an exciting time soldering that whole assembly together! I’m 

quite a noob when it comes to electronics, so I’m a bit nervous about making 

a lowpass filter myself, for fear of getting lost in what exactly I need… I’ve 

poked around on Amazon and eBay but can’t seem to find any for sale, or it’s 

not clear whether or not they’d be suitable for my application… 

If you’ve got a spare moment, would you mind pointing me in the right 



direction? I believe I simply need a 05v signal to control the power of the 

light through the dimmer, but of course I could be way off! 

Reply 

Scott Daniels 


Just use the example given. Prototype it and measure the voltage 

output with a voltmeter. It should correspond to your PWM duty cycle. 

Provided the dimmer circuit you cited takes 0 to 5 volts, you should be 

good to go. 

Reply 

Hi Scott, 

Brian 


Wow, I love what your doing and how much your helping others. I often 

search for information for myself and very rarely share solutions. I’m glad 

someone out there does. Very inspiring. 

Keep up the good work. 

Reply 

andy 


this could be exactly what i’m looking for. i want to take a pwm signal from 

my computer’s motherboard and drive an analogue dial gauge. what 

components would i need for this? 

thanks in advance 

Reply 

Scott Daniels 


If your dial gauge measures up to 5 volts, just the resistor and 

capacitor given should work fine. If your gauge requires a higher 

voltage, you will need to drive the gate/base of a transistor hooked up 

to a voltage source matching the gauge, and then filter that PWM 

signal as before. 

Reply 

Holger 


Hi Scott, thanks for all these great thoughts, its fun reading through this 

thread! 

I have to drive a Photomultiplier (PMT) control circuitry with a 05V DC 

control voltage (CV) to generate the respective high voltage (HV) that 

regulates the PMT’s sensitivity. 

As the HV follows the CV according to the equation 

HV = CV*250 

any ripples are scaled up by a factor of 250 as well which could cause some 

additional noise on the PMT output due to sensitivity fluctuations. 



As the Arduino’s PWM output is 5V (UNO in my case), I thought of a 2 pole 

active low pass filter with an OpAmp (e.g. a LM358 at 14Vcc) to get the full 

5V back after the low pass. 

Do you think that this will produce a DC stable enough or can you think of a 

better circuitry to be driven from a PWM pin for my purpose? 

Thanks 

Holger 

Reply 

Hi Holger, 

Scott Daniels 


You may have to do some testing to see what is acceptable. Multiplepole, 

lowripple filtering is a good bet. An alternative would be to use 

an R2R resistor ladder. It would take a lot of pins, but you would have 

no ripple. 

That’s the best I can come up with. Have fun. 

Scott 

Reply 

Enrique 


Hi everyone, 

I´ve been working in DAC to drive a directional proporcional valve (0 10V), 

but I´ve got de DAC (PWM to Analog) with a AOP LM741. will I need another 

step to drive the coil of the valve? 

Reply 

Scott Daniels 


An opamp should drive a small coil, but don’t forget to add the bypass 

diode to protect against the inductive transients. 

Reply 

Jason 


I have a gear reduction motor that has its own motor controller. It has one 

analog input controlling direction and speed. +5vdc thru 5vdc, Ovdc being 

the stopped position. +5vdc full speed counter clockwise, 5vdc full speed 

clockwise. Is there a way to make the pwm output from the arduino output 

+5vdc? Thanks 

Reply 

Jason, 

Scott Daniels 


You’ll need to use an opamp configured as a noninverting amp with a 

gain of 2 and supply it with 10 volts (assuming rail to rail opamp), to 

give you the required 10 volt peakpeak voltage swing. Then use 



another opamp configured as a voltagefollower with a 5v input to 

create a ‘virtual ground circuit’ (google it for details). Use the output of 

this opamp for your ground and the first opamp for your signal. 

Reply 

Hello.. 

Eddie 




int inPin = 3; // voltage connected to analog pin 3, e.g. a 

potentiometer 

if i use accelorometer.. how about the coding? i dont use 

potentiometer. 

i use http://fr.hobbytronics.co.uk/imu5dofadxl335idg500 

thanks 

Reply 

NAcho 


I’m sorry, I didn’t read all the comments. If my question 

has been asked before, please point me to the answer and 

I’ll be grateful. 

I want to convert: PWM to Analog 05Vdc. 

Is it possible? Easily. 

Thank you. 

Reply 

sab 

Posted May 9, 2013 at 5:19 am | Permalink 

Hi Scott, 

i am wandering on how to operate and to make just a simple program for my 

6A Hbridge motor controller, here it is,http://www.egizmo.com/KIT/hbd6.htm, 

and the manual is 

https://docs.google.com/file/d/0BxdLxDCD6HidMTFJVFdfeC1pQ3c/edit?pli=1, i 

really dont understand what does the PWM means but because of this tutorial 

i think i have an idea on how to this , advance thanks =) 

Reply 

Scott, 

Chris 


A very late comment but just getting into this stuff and came across your 

excellent article. 

I wonder if you can help me. 

I am driving a PC fan through an H bridge motor controller. I send a PWM 

signal from the arduino, and can vary the motor speed. Problem is that I get 

an annoying hum, which only occurs with PWM. If I use a lower voltage (non 



PWM) on the fan I don’t have a problem. 

So I imagine that I should use a low pass filter to change PWM into 

something more like straight DC. I used the calculator to size R and C 

values, but find that there doesn’t seem to be enough voltage left after the 

resistor to drive the fan, is the fan barely runs (low speed). 

Perhaps I have misunderstood but I would assume that the resistor in the 

filter will cause a volt drop as current passes through it? 

I’m a complete beginner at this so any suggestion welcome. 

Chris 

Reply 

Chris, 

Scott Daniels 

Posted June 16, 2013 at 1:15 am | Permalink 

The problem you are seeing is the fact that the motor is putting a load 

on the filter. Such a filter needs to have a buffer between it and a 

load. Yes, the resistor is a huge voltage drop at all but the smallest 

currents, and the capacitor can store only the smallest amount of 

charge. Any kind of load at all with cause the filter to not function 

properly. 

What you need is an amplifier with high input impedance and low 

output impedance. Either an opamp or a MOSFET will serve this 

purpose nicely. Both have high input impedance (they won’t load the 

filter at all), and they both have low output impedance (they can drive 

a large load without bogging down). 

In the case of using a Nchannel FET, put your load between your 

supply and the FET. Your duty cycle will not be follow a linear 

relationship to motor speed however. If you want such a relationship, 

insert a small current sense resistor and feed the voltage across it 

back into your Arduino and scale your PWM to produce the current 

level desired. 

For a choice of FET, this one in a TO220 package will handle a couple 

of amps. If it gets too hot, just add a small heat sink. 

Reply 

Michael 


hey scott 

i was hoping someone else would ask this with all the comments… 

but no one did so it may be a bad question, but could clear this up for me. 

in your schematic of the filter what connects to the other end of the 

capacitor? the schematic shows nodes with no further indication of what they 

are connected to. my assumption is common ground or nothing as dc cant 

pass through the capacitor. 

thanks. ill be messing around with this circut to fade in and out a large LED 

array with my arduino. 

Reply 

Scott Daniels 


Yes – the lower wire with its connections is the common ground for 

both input and output. I apologize that the drawing is not more clear on 

that. 



Reply 

Greetings, 

Asterios Stamatis 


I would like your advice because i am a little bit confused. I have a project in 

which i have to dim a 10V lamp according to a digital value. I just ordered 

the arduino starter kit. I have an LPC2468 board but seems to be too 

compicated for that and the community is not that big. 

I started to read some things and it seems easy to dim an LED. But how can 

I produce voltage from an Arduino board? Is there an easy way? My project 

is supposed to read a value (luminance) from a file and dim the lights 

accordingly. In addition arduino produces PWM equal to 5 V. is there a way 

to amplify it to 10V? 

Its been a long time since the last time that i read about electronics, so plz 

make it as easy as you can..!!! 

Best Regards, 

Asterios Stamatis 

Reply 

LewTwo 

Posted August 5, 2013 at 10:09 pm | Permalink 

First: Thank you for the well written article. 

Second : There may be an excellent application for this technique … 

supplying and analog reference voltage to the Arduino’s “AREF” pin. 

This would allow the user to adjust the reference voltage through software to 

meet the needs of the signal that they were intending to read (temperature 

sensors come to mind). There is already a 32K Ohn resistor on the Ref Pin 

but that would be on the wrong side of the capacitor. Is there a convenient 

way to modify the calculation to take this into account? 

Reply 

Scott Daniels 


Since the input impedance to the AREF pin is probably quite high, you 

don’t have to worry about the effects of an additional resistor. I am not 

sure this is the best way to go about what you want to do though. 

Using a precision 2.5v reference IC is what I would suggest. It would 

be very accurate and independent of supply voltage. 

Reply 

gargoor 

Posted August 6, 2013 at 3:46 pm | Permalink 

great article . Dear i have a question . now i got a mic+amp+pot i want to 

feed it into arduino and get an output digitally and send it via a TRx RFM22 . 

do i need a buffer for it ? 

second thing , what if i use my mic+amp+pot as input , then the output i 

want to hear it via speaker . should i still use a buffer ? …. 

Do i need to divide 1023 from ADC by 4 so it can be heard properly in the 

output ? because i know the ADC reads from 0 to 1023 and the PWM from 0 

to 255 . wouldnt there be loss in data ? 



Reply 

Scott Daniels 


On the transmitter, I would have to study the spec sheet more to be 

sure, but you should just give it a try – if it doesn’t work, add a buffer. 

For output to a speaker, you definitely need a buffer. On the 01023 

input, no you don’t need to divide, but rather scale both the input and 

output. For example, if you want to do internal calculations in terms of 

percent, then scale your input from 1023 to 100, and your output from 

100 to 255. The Arduino supplies a ‘map’ function for this very purpose. 

See – http://arduino.cc/en/Reference/map 

Reply 

Manikandan Selvam 


I’m doing PWM to analog voltage conversion in my project. We are using 

second order RC low filter to convert from digital to converter. 

It would be helpful if you share the calculation to find out value of the step 

response and peak to peak ripple voltage and settling time. 

and how to make the relation between pwm input signal and rc filter in 

equation to get the output waveform. 

Reply 

tenCents 


Adequate and well explained, got me up to speed quickly. Thanks for your 

effort. I’m just getting into this Arduino stuff and loving it. Salutations! 

Reply 

David Pan 


How can I type numbers from 0255 from seiral USB keyboard to control 

PWM and analog output? 

Reply 

Hey Scott 

Ferdous Ahmed 


I’m just trying to get two Analog output from Arduino. can you give some 

guidance to do so. I have a duo device. Thanks a lot 

Ferdous 

Reply 

SJPeng 


Hi this article is fantastic!! 



And one question I would like to understand. How to convert PWM > RC 

filter to + voltage. 

ex. Here I have a PWM channel where the voltage level is 5volt. so if I use 

your suggestion, only 5 volt is available for filtered ouput. So how can I get 

negative 5 volt by using the similar manner? Many thanks for your kindly 

help. 

SJPeng 

Reply 

banz 

hi Mr. Scott, 


i wonder if our group is using the correct value for resistor and capacitor for 

the low pass filter. 10k ohm and 3.2 nF respectively for a 5khz cutoff 

frequency. this application is for our project wireless communication based 

laser with certain distance to cover.. we are using a PIC 877A for a PWM 

output, then we decided to low pass filter the PWM output to generate analog 

waveform. 

does it make sense sir? 

and one thing also i have read some forums online is that in order to acquire 

the right value for resistor we have to refer first on what input impedance 

we have in our audio amplifier, say if input impedance is 10k ohm then the 

resistor will also then be 10k ohm..BUT as far as what i have searched, 

typical input impedance say for LM386 is 50k ohm. seemed to be too large. 

what could be the right thing for this sir?. 

alternatively, we planed to use IC 555 timer to generate PWM and wire up 

the low pass filter for analog output. i wonder if what could be other 

consideration for this?. or say is this possible and applicable for our project?. 

i hope u can help us with our project. THANKS LOT and thanks for your info. 

GOD BLESS.. 

Reply 

Aydin Gulgun 

Posted March 14, 2014 at 9:43 am | Permalink 

hi, i find your project when i was searching for an audio to pwm 

transformation. 

i m trying to drive some pomps to create an equalizer graphic with water. 

i understand that what i want is kind of opposite of what you did here but i m 

wondering if you can do this, can the oposite be done? what i mean is can we 

input an audio signal and convert it into a pwm signal? if yes can you help 

me to understand the prosses. and i m sorry for my bad english. 

Reply 

Allan 


Thank you Scott. I believe you have described what I am needing which is a 

method for an Arduino to mimic the controller for a submersible Speed Wave 

DC aquarium pump. I think these pumps must have their own PWM controls 

potted into the pump. The external controller provides a steady 24 volt 

source to the pump and a 0 to 4.9 volt control signal for on/off and 6 speed 

levels. I have assumed at this point this 0 to 4.9 control signal is not PWM 

from the controller to the pump. My questions are: One, why would I care 

about cutoff frequency? I think I need to pay attention to the ripple and how 

long it takes to go from one voltage to another. Second, the OKWA calculator 

looks at 0% to X% as duty step. How can I figure the time going from X% to 

Y%? I assume this is the ramp time going from one speed to the next for the 



pump application. Thanks again. 

Reply 

Greg 


I’m sorry, I didn’t read all the comments. If my question has been asked 

before, please point me to the answer and I’ll be grateful. 

My question is: Would I be able to control sound volume (from an external 

source) through a transistor with this analog output? If not, do you have any 

suggestions? In my project space is verry limited so as few components as 

possible would be nice. 

Thank you! 

Reply 

NAcho 


I’m sorry, I didn’t read all the comments. If my question has been 

asked before, please point me to the answer and I’ll be grateful. 

I want to convert: PWM to Analog 05Vdc. 

Is it possible? Easily. 

Thank you. 

Reply 

Logan 


I’m curious of a DAC like this would work for driving galvanometers, which 

don’t like raw PWM input (At all…), for a UNOprogrammable laser light 

show. Assuming it would, any idea what changes might need to be made? 

Sorry if this is a noob question, I’m kinda new to both Arduino’s and Galvos. 

Reply 

Alannah 


Pretty! This was an extremely wonderful article. 

Thanks for providing this info. 

Reply 

Vin 


Hello Sir. I need an analog control signal ranging grom 5V to +5V. Can I use 

this approach to get 0 to 5V, and then use an amplifier with gain 2 to get 0 to 

10V, and clamp it negative by 5V to obtain 5V to +5V? 

Reply 

Bojan 


Can you make it quicker? I mean can you make time necessary for capacitor 



to charge smaller? 

Reply 

Mike Eisen 


Help Please! 

I have PWM out put from a Radio Control Receiver that i need to connect to 

an RS485 input to control the zoom on a camera any pointers you have 

would be much appreciated as i have no idea how to do it. 

Reply 

amit singh 


I am trying to build a quadcopter but i am facing problem in calibration of 

ESC. I have 4in 1 EMAX ESC. I am using Arduino UNO to calibrate the ESC. 

My code is: 

#include 

Servo esc; 

int potpin = 0;// Pot pin 

int val=0; 

void setup() 

{ 

esc.attach(9);// ESC attach to pin no 9 

} 

void loop() 

{ 

val = analogRead(potpin); 

val = map(val, 0, 1023, 0, 179); 

esc.write(val); 

} 

by using this code i have calibrated 2 ESCs (esc1 and esc2) out of 4 and they 

are working fine. but other 2 ESCs(esc 3 and esc4) are not calibrating 

properly although the ESC is giving the calibration confirmation tone but 

motors are not rotating. 

my procedure is 

1 throttle the pot at full. 

2 connect the li po and turn on the esc 

3 after exact beep sending the minimum signal to ESC (by throttling pot to 

lowest position). 

4 certain beeps come and finally calibration confirmation beep comes and 

ESC has calibrated. but motors are not rotating 

Plz help me . 

Reply 

Dennis 


Trying to eliminate the noise from a Micro when Pulse With Modulating 

“PWM” the Analog out with LED’s attached! The LED’s are mounted inside of 

an electric guitar and the pickups of the guitar are amplifying the sound of 

the Arduino Micro. I’ve tried to change the Timers 0,1,&2 frequency but 

unfortunately I was getting an error when trying to change the frequency of 

Timer #2. Are there only 2 timers on the Micro being #0 & 1? 

Reply 

Hubert Tchio 




what is the easiest way to control the PWM pulse width? 

Hi Scott, thanks for all these great thoughts. I am a beginner in Electronics. I 

have designed a switch mode power supper made up of a MOSFET to driver a 

high current LED (1.2A). My switching frequency is about 1.5Mhz. I have also 

built an analogue PWM consisting of op amps for switching the Mosfet. What 

is the easiest way to control the PWM pulse width? is it possible to use a 

common controller (P, PI, PID) to change the pulse width? if yes how? 

I will be grateful to get some hints. 

Reply 

Hello.. 

Eddie 




int inPin = 3; // voltage connected to analog pin 3, e.g. a potentiometer 

if i use accelorometer.. how about the coding? i dont use potentiometer. 

thanks 

Reply 

Scott Daniels 


You’ll have to figure out how to interpret your accelerometer data by 

studying the specs/tutorials you already have. Modulating the signal is simply 

changing your analogWrite value based on how you want to interpret your 

measured data. Does that make more sense now? 

Reply 

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