Hands Free Mobile Instructions.pdf - Emdrc.com

An EMDRC construction project
by Ralph Parkhurst, VK3LL
Prototype version PCB shown
Version 2.0
10 th Jan 2011

Why hands free
• Safety – keep both hands on the
steering wheel whilst operating your
radio transceiver
• Improved TX audio – the electret
microphone is at a constant distance
from the user’s mouth and tailored for
optimum frequency response within
your particular vehicle
• No more curly cord – a tiny (8mm x
15mm) microphone can be discreetly
installed to provide a neat and tidy
installation – XYL approved!

From humble
beginnings...
This is an updated design
from an earlier construction
project described in
Amateur Radio Action
magazine in the early ’90s
and now features a PIC
microcontroller, so it is now
even easier to build.

Features
• Adjustable microphone gain control
• Adjustable bass and treble audio equalisation
• All adjustments are made using 25-turn trim-pots for
fine ‘tweaking’
• 8 choices of on-board timeout duration (0.5min, 1min,
2min, 2.5min, 3min, 4,min, 5min, 10min)
• Two RJ45 connectors - one to the radio’s mic socket
and the other for microphone loop-through
• Momentary pushbutton PTT switch used to provide
greatest versatility

Features (continued)
• Flashing LED provides “on-air” indication
• Visual indication 10 seconds before imminent timeout
• Low cost of parts
• Easy construction on a single, high quality PCB
• All ‘thru-hole’ parts, no SMD soldering required
• Uses a low cost electret microphone (supplied in the kit)
• Complete kits readily available from EMDRC
• No adjustments or mods inside your radio are required
• Designed to work with just about every radio transceiver,
using jumper pins on a 16-pin header...

Header Jumpering: Examples for common radios*
*IMPORTANT: Constructors are reminded
that they must verify the strapping to suit
their own specific radio transceiver.

Power connection
• Many modern radios provide +8v or +9v at the mic connector – this will
power the hands-free-board directly from the mic socket with a single
cable to suit your radio (e.g. RJ45 to RJ45, or RJ45 to 8-pin round etc.).
• Radios without +DC power at the mic socket can still be used - in these
cases 13.8V is applied separately to the board’s “EXTERNAL POWER”
connector (note that off-board 13.8v DC power filtering and suitable
fusing is recommended).
• The PTT to the radio is an “open collector” output that is driven logic
low (i.e. to ground) as required by most amateur transceivers. In the
rare instance you need to invert the sense of the PTT line, you can
solder a wire jumper on the PCB at position OPT1 which will invert the
PTT line to the radio.

Schematic
Low parts count for easy construction - just two ICs, one transistor, one
regulator, and a handful of resistors and capacitors

Quality PCB provided in the kit
Double sided, silkscreened with soldermask (50mm x 75mm)

Component Layout
All parts mount on the double sided PCB using “through hole” components
for easy assembly*
IMPORTANT: This
resistor (R4) is marked
on the silkscreen overlay
of some Printed Circuit
Boards as a 33k resistor.
This is incorrect - it
should be a 3k3 resistor,
as shown here.
*SKILL LEVEL: Constructors are advised that this is relatively densely populated board,
so the skill required to solder this project should be considered “Intermediate Level”.

Parts List
The following parts are supplied as part of the FULL EMDRC KIT:
RESISTORS (all metal film, 2% or 5%)
5 x 10k ¼ Watt (R1, R2, R14, R15, R16)
4 x 3k3 ¼ Watt (R3, R4, R8, R11)
1 x 4k7 ¼ Watt (R9)
1 x 2k2 ¼ Watt (R7)
1 x 6k8 ¼ Watt (R10)
1 x 100R ¼ Watt (R12)
1 x 470R ¼ Watt (R13)
TRIMPOTS (all vertical multi-turn sealed)
50k TRIMPOT 25-turn (GAIN)
10K TRIMPOT 25-turn (LO)
100K TRIMPOT 25-turn (HI)
CAPACITORS
1 x 1.0uF 50volt Multilayer Ceramic (C1)
4 x 0.022uF 100volt Polyester Film (C2, C3, C4, C5)
3 x 22uF 10volt Tantalum (C6, C7, C8)
2 x 0.1uF 25volt Multilayer Ceramic (C9, C10)
2 x 470pF 50volt Multilayer Ceramic (C11, C12)
SEMICONDUCTORS and ICs
1 x TL072 Dual OpAmp 8pin PDIP (IC1)
1 x PIC18F1220-I/P pre-programmed MCU 18pin PDIP (IC2)
1 x 1N5819 Schottky Diode (D1)
1 x 1N4148 Diode (D2)
1 x LM78L05 5volt Regulator (IC5)
1 x BC548 NPN Transistor (Q2)
1 x 5mm BLUE LED with mounting clip (“ON AIR”)
OTHER
3 x IC Sockets (one each of 8pin, 16pin, 18pin)
2 x RJ45 PCB Sockets side entry (8/8pin)
2 x 2-pin polarised headers (PTT and EXT POWER)
2 x 2-Pin polarised plugs and pins
1 x ‘SERPAC’ plastic case, model 131-BLACK
1 x Electret Microphone and cable with 3.5mm stereo plug
1 x Pushbutton Switch, momentary contact (PTT)
1 x 3.5mm Stereo PCB socket (MIC INPUT)
1 x 16pin IDC DIP plug (JUMPER)
1 x 6-hole ferrite bead RF Choke (RFC)
1 x PCB coded "EMDRC HANDS FREE“
YOU WILL NEED TO PROVIDE: Solder, short lengths of hookup wire, a suitable cable from the Hands-Free Adapter to your radio, and
optionally any additional cabling if you’d like your radio’s existing microphone to be connected to the ‘loop-through’ microphone socket.

Construction
Assembly and Testing:
ASSEMBLY
1. Insert and solder all resistors, capacitors and diodes. Note carefully the polarity of the three 22uF Tantalum capacitors
(C6, C7, C8) and the polarity of the two diodes (D1 and D2). On some PCBs, R4 is shown on the PCB overlay as 33k. This
is incorrect, it should be 3k3 as per the schematic and parts list.
2. Insert and solder the three IC sockets used by the PIC processor (18pin), the OpAmp (8pin) and the Jumper (16pin).
3. Insert and solder the LED, the LM7805 voltage regulator and the BC548 transistor, taking care to orient the “flat” edge
of these parts as per the silkscreened component overlay on the PCB. Leave the LED lead length as long as possible to
allow it to be aligned into a hole in the case later –a piece of spaghetti insulation over one lead is a wise idea to keep
them from shorting out.
4. Insert the RJ45 connectors by snapping them into the PCB, then solder.
5. Insert the 3.5mm mic socket ensuring that it is properly seated on the PCB, then solder.
6. Insert the TL072 and the PIC18F1220 into their respective sockets, noting carefully the orientation of these to
components to ensure they are aligned correctly as per the component overlay (there is a tiny white dot identifying pin
1 on the PCB).
7. Do not solder anything to the OPT2 pins – this has a special purpose (discussed later).
TESTING
1. Wire and connect the PTT switch to the header on the PCB.
2. Wire and connect to the Microphone socket on your radio (user supplied cabling – refer to separate EMDRC document
titled “Jumper Diagram v2.pdf” for further assistance. DO NOT INSERT YOUR CUSTOM WIRED HEADER PLUG YET!
3. Plug into the radio and turn on. Confirm that the expected DC voltage appears on the relevant pins of the 16pin
JUMPER socket – this step is important as you do not want to short your +8v or +9v to ground as doing so may ‘fry’ the
radio’s internal voltage regulator!
4. Insert the 16pin Jumper (wired for your radio) and assemble into the case.

Construction (continued)
Alignment and Use:
ALIGNMENT
1. Initially, rotate all trimpots anticlockwise for at least 25 turns - this will ensure that they are all at their minimum value.
2. Now, wind the GAIN trimpot clockwise by 4 turns.
3. Next. wind the LO trimpot clockwise by 12½ turns – this is half way or ‘centre’ for the 25-turn trimpot.
4. Wind the HI trimpot clockwise by 12½ turns – this is half way or ‘centre’ for the 25-turn trimpot.
5. This will get the hands free adapter set to the point where you can try it on-air or into a dummy load and make finer
adjustments. Rotating the GAIN pot clockwise will increase the audio level. The LO and HI tripots are just like the Bass
and Treble controls on a HiFi amplifier, that is clockwise rotation from centre will BOOST the HIghs or the LOws, whilst
anticlockwise rotation from the centre with CUT the HIghs and LOws.
6. Adjusting the HI and LO equalisation trimpots will effect the overall gain, so you will find a degree of interaction is
needed with the GAIN trimpot to compensate. Up to 12dB BOOST and CUT is provided by the two equalisation
trimpots.
USE IN THE VEHICLE
1. Proper adjustment of the GAIN control is vital and don’t be surprised if it takes you several attempts to get it just right.
There is a fine line between effective microphone placement, GAIN trimpot setting and background road noise
transmitted, and you need to find the best balance between all three and what works for you.
2. With care you should be able to achieve great results with only a minimal increase in road noise – please note that
depending on how far your microphone is placed from your mouth and how “loud” your vehicle is, some increased
degree of background road noise is inevitable – the trick is to make these adjustments carefully to prevent background
road noise from becoming objectionable. Adjust the gain control carefully – even a ½ turn can make a lot of difference!
3. To assist further, a video is being produced which demonstrates how this hands-free mobile kit should sound when
setup correctly.

LET’S GET MOBILE!
To transmit using the Hands Free Adapter, just briefly press the PTT button (the one on the hands free adapter, not on your
microphone!) The LED will begin flashing to warn you are now “ON THE AIR” and your radio will commence transmitting.
Initially your hands free adapter will have a timeout period set for 2½ minutes – this means that after 2.5 minutes of
continuous transmission, the PTT line to the Tx will be disabled. Ten seconds before this timeout is invoked, the LED will
begin to flash at very fast rate giving you a visual cue that timeout is imminent.
If you’d like to change this timeout period, proceed as follows:
a) Turn your radio off (which also turns the Hands Free Adapter off)
b) Whilst holding down the PTT button (again, the one on the hands free adapter, not on your microphone) power on the
radio – this enters a configuration mode where you can adjust the timeout value. You can now release the PTT.
c) Each time you now briefly press the PTT button, the LED will flash a number of times to indicate the timeout setting:
1 flash = 30 seconds
2 flashes = 1 minute
3 flashes = 2 minutes
4 flashes = 2.5 minutes (default)
5 flashes = 3 minutes
6 flashes = 4 minutes
7 flashes = 5 minutes
8 flashes = 10 minutes
(after this, the configuration program rolls over, starting from 1 flash again)
d) After you count the number of flashes appropriate to the timeout period you desire, turn off the radio (and the Hands
Free Adapter), pause, and turn it back on again. The new timeout value is now stored permanently.
e) If for some reason you don’t wish to use the timeout at all, it can be disabled by soldering a wire jumper on the PCB in
position OPT2, but only do this if you have a genuinely valid reason for doing so!

FAQ
Q. Are there any circumstances where the Hands Free Adapter should not be used
A. In my opinion yes, there are two; if you have a very noisy vehicle (truck etc.) or you like to drive with the window
down, you are probably better to use the regular microphone rather than hands free - unless you can position the
microphone reasonably close to your mouth.
Q. Can the Hands Free Adapter be used on HF/SSB
A. Yes, it has been used with radios like the IC7000 (at 100 watts) and it works exceptionally well. You are recommended
not to use high levels of audio compression when driving hands free - at high roads speeds, excessive road noise can
lead to a resultant loss of intelligibility at the receiving end if the audio processing (compression) within the radio is set
higher than about 15%.
Q. Can the Hands Free Adapter be used with DSTAR
A. Yes, it has been used with radios like the ID800 and it works perfectly. Very complimentary audio reports have been
received.
Q. What is considered the best placement for the electret microphone
A. As close as possible to your mouth – typically within 30cm – for example mounted above the drivers door, on the sun
visor, in the roof headlining – anywhere that gets the microphone as close to your mouth as possible.
Q. My FM radio’s transmit audio is too soft – will this kit improve it
A. Possibly. In principle, it’s best to get your radio set up correctly first with the standard microphone – making sure that
radio’s FM deviation and mic gain are correctly adjusted first (this kit will NOT correct an under deviating FM signal –
that MUST be set within the radio). However you will have much wider control over microphone gain and hence how
“loud” your signal sounds on a correctly set FM rig. Further, you’ll be able to compensate for the often poor sounding
audio that some of the ‘standard’ supplied mics exhibit these days. For example, users of the IC7000 will be delighted
with the improved top end crispness and tailored low frequency rolloff that can be achieved with this kit after it is
properly setup.