ee pulse - EEWeb

EEWeb 

PULSE 

EEWeb.com 

Issue 51 

June 19, 2012 

Tamara 

Schmitz 

Intersil 

Electrical Engineering Community


Electrical Engineering Community 

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TABLE OF CONTENTS 

Tamara Schmitz 4 

INTERSIL 

Interview with Tamara Schmitz - Applications Manager for Optical Sensors 

Featured Products 10 

Illogical Logic - Part 3: D-Type 

Flip Flops 

BY PAUL CLARKE WITH EBM-PAPST 

Understanding the most common logic blocks in today’s computers and digital electronics - the 

edge-triggered D-Type flip-flop. 

Arduino for Mere M0rtals: Part 4 16 

BY ROBERT BERGER WITH RELIABLE EMBEDDED SYSTEMS 

This installment will take a closer look at the blinking LED Arduino sketch for processing 

programming. 

12 

RTZ - Return to Zero Comic 20 

EEWeb | Electrical Engineering Community Visit www.eeweb.com 3 

TABLE OF CONTENTS

INTERVIEW 

Tamara 

Schmitz 

How did you get into 

engineering and when did 

you start? 

It sounds silly, but the spark came 

from my Grandpa. His nickname 

was “Sparky” and he was an 

electrician for Pullman Railroad 

Tamara Schmitz - Applications Manager for Optical Sensors 

Intersil 

company. Also, a freight train line 

had tracks just beyond our back 

fence and I used to run outside 

when I heard the train coming so I 

could wave at the engineers, count 

the cars and see if anyone was in 

the caboose. (Trains don’t seem 

to have cabooses anymore.) When 

I graduated from wanting to be a 

firefighter, I told people I wanted to 

be an engineer. I meant the train 

kind, but most others assumed the 

science/math/problem solver. Over 

the years I guess it just stuck. I do 


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love solving problems, so becoming 

an engineer was the right fit. Most 

people just don’t start by wanting to 

drive a train. 

As for electrical engineering, 

that’s much clearer. Mechanical 

engineering made sense 

because bridges could withstand 

earthquakes. Chemical 

engineering made sense because 

material science helped me see that 

durable paints could be developed 

for cars. Electrical engineering 

spanned a wide array of topics, but 

I was fascinated by one: how did 

radio waves travel through the air? 

I wanted to understand what magic 

was sending signals around and 

through me. It seemed that whoever 

controlled those would have 

disproportionate amounts of power 

to affect people for entertainment, 

for medical diagnosis and even 

for dangerous exposure. I wanted 

answers and access to this amazing 

field. Besides, it made “Sparky” 

proud. 

What are your favorite 

hardware tools that you use? 

I’m going to assume you mean in the 

lab. My favorite tool is the spectrum 

analyzer. It breaks apart a signal 

into its frequency components 

and grants me insights that can be 

hidden in the time domain. 

What are your favorite 

software tools that you use? 

I really like Matlab. And, of course, I 

have to mention SPICE. The ability 

to simulate circuits and systems 

is incredible—and improving 

constantly. Since I’m in an optical 

sensors group now, I’m finding a 

great appreciation for SolidWorks 

and FRED. 

What is your favorite 

debugging tool? 

The human body. Think of all of 

the tools that you have for free. Skin 

is a temperature sensor. Eyes and 

ears are bandpass filters. Noses 

are fantastic over-current detection 

devices. Tongues are decent battery 

testers, but I don’t recommend that 

unless you are stranded on an 

Follow your dreams. 

I know it sounds 

corny, but find 

something you love to 

do. Jobs these days 

stretch way beyond 

40 or 50 hours. 

There are times 

when my driving 

time, my evenings 

and my dreams are 

still churning away 

on a problem. 

island or something. Fingers are 

crude capacitances; touching a 

node can add 100pF or so which 

might help you quickly figure out a 

compensation problem. These are 

the kind of observations and tools 

engineers don’t usually record in 

their lab notebooks. 

What is the hardest/trickiest 

bug you have ever fixed? 

Whichever one I’m working on 

right now. Bugs aren’t usually so 

complicated that it takes a team 

of geniuses to find them. It’s like 

finding Waldo. If he’s half an inch 

tall, he’s easy to spot on a baseball 

card. However, if he’s half an inch 

tall and he’s somewhere on a wall 

mural, it’s probably going to take a 

lot longer. 

The tricky part is finding the bug. 

Too many people guess without 

a plan. The best thing to do is to 

“draw a box around the problem”, 

to quote one of my colleagues, 

Ken Dyer. Then you know the 

bug is somewhere in the box. 

Methodically go through the system 

and verify whether each block is 

working properly. Eventually, you 

will be able to shrink the box around 

the problem area and focus your 

efforts more efficiently. 

The exception to this method is 

the case where you have loads of 

experience. Experience can inform 

you of the most likely places to look. 

In those cases, I’d start there. 

What is on your bookshelf? 

Some old databooks that I haven’t 

recycled yet, a copy of my PhD 

thesis on RF CMOS low phase noise 

oscillators, the Art of Electronics, 

the ARRL Handbook, a picture of 

me pretending to pitch to a full-size 

statue of Babe Ruth at the Baseball 

Hall of Fame, various textbooks, a 

roaring Godzilla doll and a photo of 

my 3 dogs. 

Do you have any tricks up 

your sleeve? 

It’s all about the basics. Start 


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simple. Power and ground. Check 

the voltage on every node/pin. Don’t 

assume anything. Once the basics/ 

bias checks out, start varying over 

ranges. Do min and max input get 

expected output? Then follow the 

signal through the system. 

What has been your favorite 

project? 

My favorite project was constructing 

a horn antenna to be used at the 

“Big Dish” on Stanford University’s 

campus. The operating frequency 

was 330MHz, so the horn was 

about the size of a coffin. I soldered 

copper clad pieces together and 

built a wooden exoskeleton for 

support. It was awesome to see the 

mathematics come to life, to test the 

antenna response in a warehouse at 

SRI, and then to mount it on that big, 

beautiful dish and see it work! Well, 

it worked until a bird decided that 

it was a wonderful place to build a 

nest. 

Do you have any note-worthy 

engineering experiences? 

I’m particularly proud of the Test 

Development Engineering Program 

I championed at San Jose State 

University. After noticing that 

electrical engineering students 

were finding jobs as apps, test and 

product engineers, I joined with a 

team of folks from Agilent, National 

Semiconductor, Teradyne and 

Intersil to put together a program 

to teach skills needed for these 

areas. Students spent the spring 

semester learning lab techniques 

like measurement and soldering. 

They designed a PCB to test an IC 

and presented their work to a panel 

from the supporting companies. In 

the summer they had internships 

with the sponsors. In the fall, they 

returned to school and proceeded 

in their work—this time on ATEs. 

Along the way, they learned a 

lot about the semiconductor 

industry and where they would fit 

in. Every student got a job. They 

even nominated me for an IEEE 

certificate of appreciation. Cool 

stuff. 

If I was to tell you some of the cool 

things I work on now, it would break 

customer confidentiality. Let’s just 

The global work 

force is adjusting 

its footprint. 

While it might be 

advantageous to 

use cheaper labor, 

the time, cultural 

and communication 

differences are a big 

stumbling block for 

projects that span 

multiple continents. 

say that it’s fun to walk around Best 

Buy and see all of the products that 

use an IC from Intersil—especially 

one of the light sensors. 

How is academia different 

than industry? 

Huge difference. From the students 

perspective, you learn a lot of 

math in college. You can solve 

KVL and KCL with Thevenin and 

Norton equivalents. You can take 

derivatives with respect to time 

and to voltage. In industry, the 

derivatives are with respect to cost 

and to customer interest. It’s hard 

to put those into matrices (yet MBAs 

and economists do it all the time). 

From a professor standpoint, you 

are trying to get as many students 

through the system as possible. 

There is so much that could be 

taught, but there are also so many 

regulations about teaching (think 

ABET accredited). Many professors 

teach the same material because it 

is approved. It’s a lot of work to put 

a class together and it is too easy to 

use the same material “one more 

time”. Besides, the point of school 

is to learn the basics, right? The 

basics don’t change much. Still, 

the motivation and end goals do 

change. Our university classrooms 

are not at the forefront of technology. 

(One could argue that the research 

labs at a university house the 

forefront of technology. Yes, a ittybitty 

slice of it.) Remember, though, 

that engineering is growing and 

changing every day. University 

curriculums, therefore, must 

theoretically teach more and more 

each year. Students don’t stay in 

school longer, so sacrifices have to 

be made. Often that means tough 

choices. 

I, personally, prefer the “real world” 

where the technological innovation 

creates a product or device that 

enables product differentiation or 


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new platforms. People use money 

to say what they like and don’t 

like. It is impossible to survive in 

the semiconductor industry if you 

produce the same product year 

after year. This ever-present drive 

to improve and innovate is what 

makes it fun. 

What are you currently 

working on? 

I am the new manager for the 

applications group focused on 

optical sensors. (These are ambient 

light or proximity (IR) sensors.) I 

have the privilege of leading a 

talented team of engineers as we 

work with the greatest electronics 

manufacturers around the world. 

Sensors are special because it isn’t 

just an electrical system. It’s an 

optical and mechanical one, too. 

Will the device be behind some kind 

of glass? Will there be plastic with 

a hole to allow access for the light? 

How much light can bounce around 

inside the product? How reflective 

is an object you want to target? 

(Black hair happens to be very 

non-reflective, yet the cell phone 

manufacturers want to turn off the 

touch screen before you bring the 

phone to your ear. They don’t want 

it to only work for blondes…) 

What direction do you see 

your business heading in the 

next few years? 

Sensors are growing like crazy! 

Consumer devices want to interact 

more naturally with their users. 

They want to save us power by 

turning down the backlight of a 

screen in low-light conditions, so we 

can enjoy longer battery life. They 

want to understand our questions 

and interpret our gestures. They 

want to anticipate our desires and 

prepare. They want to help camera 

understand what kind of lighting 

conditions they operate in so we 

can take better pictures. There are 

so many more examples. 

What challenges do you 

foresee in our industry? 

There are lots of challenges. The 

global work force is adjusting 

its footprint. While it might be 

advantageous to use cheaper 

labor, the time, cultural and 

communication differences are a 

big stumbling block for projects 

that span multiple continents. Still, 

money is a stronger driving force 

(especially in the limping recession) 

so we are willing to accept the 

challenge. 

Another challenge is “the next big 

thing”. Cell phones kept getting 

smaller and then acquired touch 

screens. They have great cameras 

and organize our personal and 

professional lives. Really, though, 

we haven’t seem much that is new. 

The platform seems to be moving 

from hardware to software. It’s not 

“What can the silicon do”, but more 

“What can we do with the silicon?” 

Almost everyone has a cell phone. 

What is the next device everyone 

will have? 


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Is there anything that you 

have not accomplished yet, 

that you have your sights on 

accomplishing in the near 

future? 

My goals have morphed over the 

years. I wanted to be a professor 

and achieved that goal. I wanted to 

show that I was a real engineer and 

could contribute in industry. I have 

achieved that goal, too. (And it pays 

much better than the professor gig.) 

At times I get frustrated with upper 

management and have a desire 

to see if I could do better. Ok, I 

have that desire even when I’m not 

frustrated with upper management. 

I like looking at choices, defining 

challenges, setting goals and 

inspiring a team. I believe a good 

leader is a good listener, is a wise 

businessman and can bring out 

the best in people. Engineering 

is a spectacular skill and medium 

we share. We can learn to deliver 

premium products and the highest 

quality service for a fair price. It’s 

a win-win. 

Any advice you would like 

to give the engineering 

community? 

Follow your dreams. I know it 

sounds corny, but find something 

you love to do. Jobs these days 

stretch way beyond 40 or 50 

hours. There are times when my 

driving time, my evenings and my 

dreams are still churning away on 

a problem. If I don’t love what I do, 

I’d be exhausted and miserable a 

lot. I might be exhausted at times, 

but I’m proud of my team and my 



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www.eeweb.com/register 

work. That satisfaction is important 

to me. I want to own a house, drive 

my truck, take my dogs to the beach, 

take care of my aging parents, enjoy 

the time with my coworkers and 

make some kind of difference. I 

feel like I can do that here at Intersil. 

I hope you find your place, too. ■ 


FEATURED INTERVIEW

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GD 

110 

EN 

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CS 

PGND 

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100 

90 

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I_CH3 

SDI 

SDO 

COMP 

80 

/CS 

70 

I_CH1 

EN_VSYNC OVP 

60 

I_CH4 

CSEL 

50 

ISET1 

ISET2 

OSC 

PWM_SET/PLL 

CH1 

CH2 

CH3 

CH4 

40 

30 

20 

10 

0 

0 20 40 60 80 100 

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CHANNEL CURRENT (mA) 

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TECHNICAL ARTICLE 

Illogical Logic 

Part 3 - D-Type Flip-Flops 

Paul Clarke 

Electronics Design 

Engineer 

When it came to illogical logic circuits, I must say, I was always 

scratching my head at edge-triggered D-type flip-flops. These are one of the 

most common logic blocks in today’s computers and digital electronics. It’s 

a bit like saying the transistor is the most common component in modern 

electronics—but how many of us understand how a D-Type works? 

To begin the voyage to the edge-triggered D-type flip-flop, we will start with 

the common element that’s used inside it: the SR flip-flop. 

This is the simplest flip-flop to understand as it only contains two logic gates 

and NAND gates. It is also the easiest to see a common issue in digital 

electronics, the ‘race condition’ or a glitch. These states occur when the 

logic output of a circuit is undefined for a few brief microseconds. We have 

to remember that logic gates are, after all, analog circuits full of transistors. 

These circuits take time for the charge on the devices, like FETs, to rise 

or fall. This means that the voltage thresholds are not clear and transistors 

may or may not be switched on. Within the gate, this means that a clear 

decision about output levels has not been made – hence undefined. This 

also happens during changes to the input as it takes time for the gate to 

react and generate a new output, if one is required. 

So in our SR flip-flop there is a race condition at switch on where the gates 


TECHNICAL ARTICLE


Set 

H 

Reset 

H 

Figure 1: SR FLIP-FLOP 

power up and try to work out their output state. This 

becomes more complex as the outputs are fed back to 

the inputs. This means that the output is affecting the 

input, hence the decision making and hence the output 

itself. Confused? Well thats how the gate feels. However 

after a few microseconds the gate settles and a stable 

state persists. 

S R Q 

0 0 ! 

0 1 1 

1 0 0 

1 1 X 

Figure 2: SR TRUTH TABLE 

Q 

L 

Q 

H 

The truth table for the SR flip-flop is therefore as follows: 

The most interesting states are the Set and Reset states 

and the Do Nothing state—so remember these for later. 

The next thing to add is our clock input, which is done by 

adding two more NAND gates to the front end of our SR 

circuit. This becomes a gated SR flip-flop. The Set and 

Reset still work as before, but as the name suggests, it’s 

gated so the output only happens at certain times, when 

the clock input is high. This is all very good, however, 

it’s possible for the circuit to change its output multiple 

times during a clock high, which is not what we want at 

all. It’s also not a D-type yet. However, this is easy to fix 

by adding a NOT gate between the S and R inputs and 

renaming the S input as D (Figure 3). 

Our new D-Type works just like the SR flip-flop as it’s 

possible to change the output while the clock is high 

multiple times during that period. We need a circuit that 

only latches in the D signal when the clock edge is rising. 

To simplify this to begin with, let’s think about the ability 

to generate race conditions—or in this case, a glitch. 

If there was only a way to make the clock pulse really 

really small on the positive duration, then there would 

not be enough time to switch back (Figure 4). 

L 

Figure 3: D-TYPE FLIP-FLOP 

Figure 4: GLITCH CIRCUIT 

This circuit uses the idea that it takes time for the gates to 

switch. Let’s assume for a moment that the input is LOW. 

One side of the AND gate is set to LOW as per the input 

and the other is logic HIGH because the NOT gate has 

inverted the input. In a perfect world, if the input changes, 

the NOT gate would change instantaneously and this 

input to the AND gate would swap and the output remain 

unaffected. However, because it takes time for the NOT 

gate to react and drive the output, there is, in fact, a small 

moment in time were both the inputs to the AND gate are 

HIGH. This sets off the chain reaction in the gate that will 


H 

D 

CLK 

Q 

L 

L 

TECHNICAL ARTICLE


CLK 

H 

D 

Figure 5: D_TYPE EDGE TRIGGERED CIRCUIT 

drive the output from LOW to HIGH. Moments later, the 

NOT gate output changes state and the AND gate reacts 

to the new stimulus. However, the chain reaction is still in 

place and what we see at the output or the AND gate is 

a HIGH equal to the time it took the NOT gate to switch. 

This may look great, but it’s not a defined period of 

time—other gates may not even react quickly enough to 

it and we are relying on the analog side effects of the 

gates. So what we need is a nice stable version of the 

glitch generator. We could, for example, have a much 

higher speed clock running somewhere that could help 

us process the signals, but then that would need higher 

speed clocks too… 

The answer, however, is in our original SR flip-flops. 

These react to the change of input only once when the 

input change is applied. With both inputs at LOW, a HIGH 

signal on one of the inputs generates a fast reaction and 

latches in a new output if one is required. The interesting 

effect is the DO NOTHING condition where setting both 

inputs HIGH will not change the output. Changing an 

input as LOW will then either Set or Reset the SR latch. 

However, driving the signal up and down as much as we 

want will not affect the output. If we were to connect a 

clock input to this circuit, then Setting or Resetting the 

latch would happen only on the falling edge of the clock. 

We are now getting close, but still not quite there. We 

have a circuit that responds to the edge of the clock—the 

wrong edge—but we can only connect this circuit so that 

it Sets or Resets. We need both. 

Q 

H 

In order to have both, you need two SR flip-flops that act 

as Set and Reset circuits. By connecting these circuits in 

opposite modes, it’s then possible to use the data input 

to decide which one latches and holds and which one 

flips back and forth with the clock input (Figure 5). 

First thing to notice is that the NOT gate that was used 

on the SR to turn it into a D-Type is simplified by using 

the NOT Q output on one of the SR flip-flops (in this case 

the bottom one). This lower flip-flop generates this NOT 

signal as a feedback or input to the top flip-flop, which 

in turn generates a NOT signal back to the first. This 

causes the two SR flip-flops to latch in opposite modes. 

The clock signal is also fed to both SR flip-flops and 

because of this the lower flip-flop need to have a three 

input NAND gate. The overall effect is that these two flipflops 

generate a very useful signal. One will, as I said, 

latch and the other flip with the clock input. These two 

signals can then be used to drive a third SR flip-flop that 

functions as before with the DO NOTHING condition, 

only changing its output once the D-signal has changed 

and when the clock edge is seen, in this case, on the 

rising edge. 

It’s quite a difficult circuit to put into words because 

of the number of states it can be in. I could post lots of 

pictures showing them, but nothing works better than an 

animation. If you have not seen this website before, then 

http://www.falstad.com is great and has a really nice 

little circuit simulator. Follow the link below to load the 

simulator and the following instruction to bring up the 

edge-triggered D-type flip-flop. 

From the menus click here, select “Circuits,” then 

“Sequential Logic.” Then click on “Flip-Flops” and then 

“Edge-Triggered D Flip-Flop.” 

About the Author 

Digital Electronics Engineer with strong software skills 

in assembly and C for embedded systems. At ebmpapst 

I’m developing embedded electronics for thermal 

management control solutions for the air movement 

industry. These controllers monitor environmental inputs 

like Temperature, Humidity and Pressure and then 

control the speed of our fans based on various profiles. 

Our controls also interface with other systems over 

RS232/485 or TCP/IP as well as a host of other user or 

control interfaces. ■ 


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Disclaimer 

The views, opinions, positions or strategies expressed 

by the author and those providing comments are theirs 

alone, and do not necessarily reflect the views, opinions, 

positions or strategies of anybody else. 

Das Blinkenlights [1] 

We’ll have a closer look at the blinking LED Arduino 

sketch we saw last time (Figure 1). 

ACHTUNG! 

ALLES TURISTEN UND NONTEKNISCHEN LOOKEN- 

PEEPERS! DAS KOMPUTERMASCHINE IST NICHT 

FÜR DER GEFINGERPOKEN UND MITTENGRA- 

BEN! ODERWISE IST EASY TO SCHNAPPEN DER 

SPRINGENWERK, BLOWENFUSEN UND POPPEN- 

CORKEN MIT SPITZENSPARKSEN. IST NICHT FÜR 

GEWERKEN BEI DUMMKOPFEN. DER RUBBER- 

NECKEN SIGHTSEEREN KEEPEN DAS COTTON- 

PICKEN HÄNDER IN DAS POCKETS MUSS. ZO RE- 

LAXEN UND WATSCHEN DER. BLINKENLICHTEN. 

Dissection of BlinkWithoutDelay [3] 

Sketch 

Programs written for the Processing [4] programming 

language are called sketches. These sketches are 

typically written using the text editor that comes with 

Processing. It has features for cutting/pasting and for 

searching/replacing text. Sketches written for Processing 

should have a .pde file extension, which stands for 

Processing Development Environment. Arduino 

borrowed this concept from Processing and programs 

that are being uploaded to and run on an Arduino board 

are called sketches as well. To distinguish Arduino 

from Processing sketches, .ino should be used as a file 

extension, which stands for Arduino (Figure 2). 

Comments 

Robert Berger 

Embedded Software Specialist 

Arduino 

for mere m0rtals - PART 4 

Everything between the /* (line 1) and */ (line 22) is 

ignored by the Arduino when it runs the sketch (the * 

(lines 8, 9) at the start of each line is only there to make 

the comment look pretty, and isn’t required). Comments 

are for people who read your code and for you and try 


TECHNICAL ARTICLE


Figure 1: Try telnet towels.blinkenlights.nl [2] 

Listing 1: BlinkWithoutDelay.ino 

/* Blink without Delay 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

Turns on and off a light emitting diode (LED) connected to a digital 

pin, without using the delay() function. This means that other code 

can run at the same time without being interrupted by the LED code. 

The circuit: 

* LED attached from pin 13 to ground 

* Note: on most Arduinos, there is already an LED on the board 

that’s attached to pin 13, so no hardware is needed for this example. 

created 2005 

by David A. Mellis 

modified 8 Feb 2010 

by Paul Stoffregen 

This example code is in the public domain 

http://www.arduino.cc/en/Tutorial/BlinkWithoutDelay 

*/ 

Figure 2 

to understand what you wrote a long time ago. They 

(hopefully) explain what the program does, how it 

works, or why it’s written the way it is. It’s good practice 

to comment on your sketches and to keep the comments 

up-to-date when you modify the code. Remember, as a 

good ”open-source citizen,” to share your code so others 

can learn from or modify/improve your code. 

There’s another style for short, single-line comments. 

These start with // (e.g on line 26) and continue to the 

end of the line. 

To delay() or not to delay()? [5] 

The delay() function mentioned on line 4 and the hint 

not to use it so other code can run already looks weird 

to someone who used a RTOS or Unix/Linux before. 

Let’s have a closer look at it. From the FreeRTOS call 

vTaskDelay(500/portTICK RATE MS) [6], you would 

expect to delay a task for 500 msec. The fact that this 

API call delays/blocks a task for 500 msec means that 

it allows tasks with a lower priority to run until the time 

expires. 

In Linux usleep(500) [7], it would block the calling 

process for 500 msec and allow processes with a lower 

priority to run until the time expires – kind of. 

Description 

The delay() function pauses the program for the amount 

of time (in milliseconds) specified as parameter. 

(Remember: there are 1000 milliseconds in a second.) 

Syntax 

delay(ms) 

Parameters 

ms: the number of milliseconds to pause (unsigned long) 

Returns 

nothing 

(Figure 3) 

Caveat 

While it is easy to create a blinking LED with the delay() 

function, and many sketches use short delays for such 

tasks as switch debouncing, the use of delay() in a 

sketch has significant drawbacks. No other reading of 

sensors, mathematical calculations, or pin manipulation 


TECHNICAL ARTICLE


can go on during the delay function, so in effect, it brings 

most other activity to a halt. For alternative approaches 

to controlling timing, see the millis() function [8] used 

on line 49 in the sketch below. Arduino veterans usually 

avoid the use of delay() for timing of events longer than 

10’s of milliseconds unless the Arduino sketch is very 

simple. 

However, certain things do go on while the delay() function 

is controlling the Atmega chip because the delay function 

does not disable interrupts. Serial communication that 

appears at the RX pin is recorded, PWM (analogWrite) 

values and pin states are maintained, and interrupts will 

work as they should. 

Author’s Comment 

From what we have seen above, the delay() 

implementation behaves like a busy loop with interrupts 

enabled. 

Variables 

A variable is a place for storing a piece of data. It has 

a name, a type, and a value. For example, the line 26 

from the sketch above declares a variable with the name 

ledPin, the type int, and an initial value of 13. It’s being 

used to indicate which Arduino pin the LED is connected 

to and since it never changes, it’s declared as const, 

which could give the linker a hint to place it in a section 

other then precious RAM. Every time the name ledPin 

appears in the code, its value will be retrieved. In this 

case, the person writing the program could have chosen 

not to bother creating the ledPin variable and could have 

simply written 13 everywhere they needed to specify a 

pin number instead. The advantage of using a variable 

is that it’s easier to move the LED to a different pin—you 

only need to edit the one line that assigns the initial value 

to the variable. 

Often, however, the value of a variable will change while 

the sketch runs (lines 29, 34, 49). Due to the lack of 

insightful comments, it’s not quite obvious to me why the 

variable in line 30 is not defined as const as well since it 

does not change. 

Functions 

A function (otherwise known as a procedure or subroutine) 

is a named piece of code that can be used from 

elsewhere in a sketch. The setup() function [9] as seen in 

Listing 2: delay-example.ino 

int ledPin = 13; // LED connected to digital pin 13 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

void setup() 

{ 

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

} 

void loop() 

{ 

digitalWrite(ledPin, HIGH); // sets the LED on 

delay(500); // waits 500 msec 

digitalWrite(ledPin, LOW); // sets the LED off 

delay(500); // waits 500 msec 

} 

Figure 3 

Listing 3: BlinkWithoutDelay.ino continued 

24 // constants won’t change. Used here to 

25 // set pin numbers: 

26 

27 

const int ledPin = 13; // the number of the LED pin 

28 // Variables will change: 

29 int ledState = LOW; // ledState used to set the LED 

30 

31 

long previousMillis = 0; // will store last time LED was updated 

32 // the following variable is a long because the time, measured in 

milliseconds, 

33 // will quickly become a bigger number than can be stored in an int. 

34 

35 

long interval = 1000; // interval at which to blink (milliseconds) 

36 void setup() { 

37 // set the digital pin as output; 

38 pinMode(ledPin, OUTPUT) 

39 } 

Figure 4 

Listing 4: BlinkWithoutDelay.ino continued 

41 void loop() 

42 { 

43 

44 

// here is where you’d put code that needs to be running all the time. 

45 // check to see if it’s time to blink the LED; that is, if the 

46 // difference between the current time and last time you blinked 

47 // the LED is bigger than the interval at which you want to 

48 // blink the LED. 

49 

50 

unsigned long currentMillis = millis(); 

51 if(currentMillis – previousMillis > interval) { 

52 // save the last time you blinked the LED 

53 

54 

previousMillis = currentMillis; 

55 // if the LED is off turn it on and vice-versa: 

56 if (ledState = LOW) 

57 ledState = HIGH; 

58 else 

59 

60 

ledState = LOW; 

61 // set the LED with the ledState of the variable: 

62 digitalWrite(ledPin, ledState); 

63 } 

64 } 

Figure 5 

line 36 is called once, when the sketch starts. It’s a good 

place to configure pin modes and to initialize libraries. 

The pinMode() function [10] line 38 configures a digital 

pin as either an input or an output. To use it, you pass the 

number of the pin to configure and the constant INPUT 

or OUTPUT. When configured as an input, a pin can 

detect the state of a sensor like a “Push” button. As an 

output, it can drive an actuator like an LED, which, in 

our case, utilizes the digitalWrite() function [11] line 62 to 


TECHNICAL ARTICLE


change state (Figure 5). 

The loop() function [12] line 41 is called over and over 

and is the heart of most sketches. Both setup() and 

loop() need to be included in your sketch, even if you 

don’t need them for anything. 

Author’s Comment 

From what we have seen so far, it looks like an Arduino 

sketch behaves like a cyclic executive with interrupts. 

Stay tuned for more hands-on stuff in the next part of this 

series of articles where we’ll investigate Processing! 

References 

[1] ”Das Blinkenlights” http://en.wikipedia.org/wiki/ 

Blinkenlights 

[2] ”www.blinkenlights.nl” http://www.blinkenlights.nl 

[3] ”First Sketch” http://arduino.cc/en/Tutorial/Sketch 

[4] ”Processing” http://processing.org 

[5] ”delay()” http://arduino.cc/en/Reference/Delay 

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[6] ”vTaskDelay()” http://www.freertos.org/a00127.html 

[7] ”usleep()” http://pubs.opengroup.org/onlinepubs/009695399/functions/usleep.html 

[8] ”millis()” http://arduino.cc/en/Reference/millis 

[9] ”setup()” http://arduino.cc/hu/Reference/Setup 

[10] ”pinMode()” http://arduino.cc/en/Reference/pin- 

Mode 

[11] ”digitalWrite()” http://arduino.cc/en/Reference/digitalWrite 

[12] ”loop()” http://arduino.cc/en/Reference/loop 

About the Author 

Robert Berger is a highly respected and experienced 

embedded real-time expert and CEO of Reliable 

Embedded Systems, a leading embedded training 

consultancy. Robert consults and trains people all 

over the globe on a mission to help them create better 

embedded software. He specializes in training and 

consulting for embedded systems, from small real-time 

systems to multi-core embedded Linux. ■ 

Teamwork • Technology • Invention • Listen • Hear 

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