Pulse Counters – The Kenwood TM-D710A keyboard hack.

I’ve got a ton of emails about the adapter for the Kenwood TM-D710A. The microphone on this unit uses a digital pulse counter based on 4017 logic IC’s to determine, over a single wire, which key is pressed.  This same principle can be use in other projects to read a keypad, control LED’s etc with on a pin or two from a microcontroller.  For reference below, are the articles on the TM-710A Adapter and associated projects.

http://www.shaneburrell.com/?p=688 – Keyboard Adapter itself – This board is line powered from the microphone cable. It effectively sits between the Kenwood radio unit and Microphone. It allows you to place a keyboard in between the two to allow functionality that Kenwood never intended per say.

Adapter Board PCB Prototype.

The theory of operation:  The microprocessor in the radio head unit sends pulses to the microphone.  On each pulse the line is pulled low which the microcontroller spies on via another pin attached to the pulse pin.  On a scope, it’s very easy to see the line being pulled low depending on the keypress.  In hacking the pulses, its just a matter of seeing what key generates what pattern.   In the TM-D710A adapter I used a AVR to talk to the microphone and read a standard keyboard. The One Signal Wire board design above was used to Emulate the mic controlled by the AVR.

Pulse Counter in Action.

Below is a video some Arduino code I initially developed to scan the microphone patterns driving the Kenwood Mic from the AVR.  If you look at the scope this should give you a good idea how the pulse counter is working.

The TM-D710A keyboard hack was a really fun project and hit multiple stages of hack/design.  The 4017 counter is a pretty neat way of reading/controlling things using on 2 pins from a micro-controller.

TM-710A Keyboard Adapter Design

Interest during the last few months is very sparse on the TM-710A Keyboard adapter.  I haven’t’ put much work into it since I’ve found other options.   I do not plan on doing any more kits for this board at this time. This is a option for anyone that did not complete an initial build.

The concept used on the board is to drive the normal mic with a AVR chip and emulate the mic on the TM-710 board which is controlled by the AVR.  Software will have to be completed to come up with something useful and this design may not be perfect.  I have used this board and the previous OSW board in my mobile setup for a long time without any issues but have switched to using a SSD based PC.
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SB710Key – TM-D710A Keyboard Adapter

Prototype boards have arrived.  I’ll be working with these for the next few weeks to hopefully finalize a line powered PS2 keyboard adapter for the Kenwood TM-D710A.  Here are some pics of the proto board.07/14/2011 – UPDATE waiting on some missing parts to arrive in mail.

07/20/2011 – All parts arrived except for the osc. It’s on backorder for at least two weeks.

07/29/2011 – Still no osc.  I’m researching alternatives.

08/05/2011 – Finally located something that should work.  2 week leadtime on this part so more waiting.

11/30/2011 – I ‘ve assembled and tested the few boards I had left and due to limited application of this I will be doing some sort of open source release of the project in December for those that want to build one of these and improve the software.

OSW 1.0D Kit TM-D710A keyboard adapter.

05/02/2011  07:12 AM – The order for the 1.0D board has been processed and passed design checks with manufacture.  We all should see boards from the group buy in the next 3-4 weeks hopefully.  Parts have already arrived.  I’ll be posting more information and documentation during those long 3-4 weeks of waiting here.  I recommend to everyone to use an AVR platform for MCU development an interface but you are welcome to use what you want.  The goal is to end up with something that is under the 100ma current of the MIC interface. Read more…

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OSW Board TM-D710A Keyboard Interface revisted.

04/21/2011  08:00PM EST

I have gotten back to this as promised tonight and almost have a prototype of something new for folks wanting to interface with there TM-D710A.  I’m am tediously taking the CPLD logic to CMOS on a board thats all hardware based.  I will post all information on this blog post as time goes on.  This will not be a complete TM-D710A keyboard adapter, however by providing your own MCU platform you will be able to accomplish the same thing.  My hope is to get this all under the 100ma rating of the 710 8V source to be in line.  The spice run on my initial schematic shows 16ma for this board which will turn the one wire protocol into something a MCU can read.  I’ll also provide a AVR hex file to play with shortly.  If you are interested in building this please let me know by simply posting a comment.  Once I get at least 10 people committed I will order boards.  They will be prototypes and I make no guarantees whatsoever that they will work and you may need some bailing wire and replacement parts so you’ve been warned.  These will very likely be my last run of boards related to this issue as I have something that works already so if you aren’t afraid of SMD and getting your hands dirty post here.  I expect the boards and parts kit be less than $40.00US.

04/21/2011 10:12PM EST

Ok here it is.  Please post if you are interested and how many you want.  Once enough people post, at least 10 boards,  I’ll start contacting those folks and put together an order.  These are prototypes so they may require tinkering.  Basically this has  PWR connections that will work with the 8V on the mic or from 12V.  You will need to make a RJ45 cable to pull out the YELLOW / PIN 8 for the one wire communications.  On the edge of the board there is a pin for each row and column which you can control with your own MCU.



5 Board commitments so far. 5 to go.  I’ll likely refine the design a bit before sending off to have them manufactured but I’ll post the final design prior to ordering boards.

04/25/2011 10:13PM EST

8 Board commitments. 2 more to go.  Here is revision C.  Everything is kitted and ready.  I’ll be contacting those that have committed and place the order after 2 more boards, maybe a few more.  THESE BOARDS WILL BE PROTOTYPES!  THEY WILL TAKE ABOUT A MONTH TO ARRIVE AFTER THE ORDER IS PLACED!!!


04/26/2011   7:00AM EST The last two boards have been committed.  Those of you that have committed I’ll be emailing details to you.  If you plan to get one of these and haven’t committed I’ll need to know sometime early today.

04/27/2011  7:00AM EST Last call for boards!!!!  I’ll be sending out for manufacturing on Monday May 2nd early in the morning. No funds, no board.  I’ve already recieved funds for over 10 boards so Monday morning is the absolute cut off date.  Below is a gerber view of the board, now is the time to ask questions if you are ordering a board.

TM-D710A Keypad Adapter.

04/28/2011 – Few changes on the SO-89 footprints after test fitting parts.  For those that have contacted me boards will be sent to board house on Monday morning.

05/01/2011  The design has went to the board house.  I won’t be adding any more to this order.  For those that ordered boards they should arrive in 3-4 weeks and I will promptly ship them and parts pack when they arrive.  Here is the final gerber view.


Kenwood TM-D710A Keyboard Adapter

First I really like my TM-D710A radio. It works great, never gives me any problems, and I use it daily.  The main reason I worked diligently on the AVR APRS display was to have a screen and keyboard attached to radio out in the field.  The TM-D710A works well for short messages but it could be so much easier with a keyboard.  I’ve started work on building a keyboard interface for a small rollup keyboard. I’ll post progress here but I’d like to know if there is more interest in this project out there.  If so leave me a comment or drop me a line.