Transcript
An EMDRC construction project by Ralph Parkhurst, VK3LL
Prototype version PCB shown
Version 2.11 6th May 2016
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 (and optional audible) 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) PCB and pre-programmed PIC 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
There are two small pilot holes on the PCB - in the exact centre of the PTT-Switch and the On-Air LED, to aid drilling the front panel. Firstly, use a small PCB drill bit to drill pilot holes in the case, then widen using a 9mm drill bit for the PTT switch and a 3mm drill bit for the LED.
Component Layout
All parts mount on the double sided PCB using “through hole” components for easy assembly*
*SKILL LEVEL: Constructors are advised that this project should be considered “Intermediate Level”.
Enclosure Drilling Guide
Side view of case shown. You need to cut out an area for the RJ45s and drill one hole for the microphone socket. 27.0mm
16.0mm
17.5mm
Drill 6.5mm hole for microphone socket here
37.0mm
35.5mm NOTE: This diagram is NOT drawn to scale.
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 PIC18F1320-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 3mm LED (“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 RITEC RL-6215F ABS enclosure (Altronics H0121) 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 v2 1 x PIEZO speaker for audible output (Altronics S6140) 4 x 6mm M3 PCB threaded standoffs
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 LM78L05 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 PIC18F1320 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). 8. To install the PCB into the case, the board is designed to be mounted onto the enclosure’s “lid” using 4 x 6mm malefemale brass standoffs. The threaded male end of the standoff is screwed into the plastic lid, and four M3 machine screws then hold the PCB in place. 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 wish, you could also connect an optional piezo speaker to the “PIEZO” pins on the PCB for an audible alert (e.g. Jaycar AB3440 or Altronics S6140). If you’d like to change the timeout period from the default, 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 (factory 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 Digital radios like 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.
