Old radio transmitter

A friend of my club (thanks Salvador) gave me his old Radios that he used years ago. They were made by Lextronic, a french electronic company. The company still exist, but the radio are not more sold. Simple, neat and strong.

Bootloader Xmega

I received the prototype board (Stk600) for Atmel processor and started to play with it. The First step was to install a bootloader in the Xmega192a3.

Hum, that was more complex than I thought. Xmega world is still very new and I discover several problems: avrdude program (to flash the xmega) does not work under linux (pdi does not work), and bigger problem, the Xmega 192a3 has a bug which prevent its flash memory to be written directly.

So to workaround the "avrdude" problem on linux, I simply used XP and avr-studio 4.17. This is a recent version whcih support Xmega. Even if it not perfect, because the x192a3 is not yet in the compiler mcus list. But it is known in the uploader part of avr-studio.

Then for the second problem, I port on avr-studio (avr-gcc) the workaround from Atmel (application note 1008) which allows the flash to be self-written. Unfortunately, the workaround provided by Atmel was made for IAR (not avr-Gcc compiler) and was not a complete bootloader. So I had to port it and integrate in an existing bootloader port.

The first version I made did not work. Good opportunity to learn AVR assembly. So I redo and finally it worked ! Ouf , thanks to Atmel support which provided me this application note. My bootloader is here: bootloader Xmega 192a3.

The project files are included, and you need avr-studio v4.17 (free from Atmel). Serial port is port D and baud rate is 19200. See defines.h and compiler options before using. Once the bootloader has been installed, an application can be flashed with the command "avrdude -c avr109 -b 19200 ..." and other needed parameters.

ATxmega

I received the new processor that may well be the basis of the next version of RCHome. It is an atXmega192A3. This processor looks very interesting for a radio transmitter because it has:
* 16 Kbyte SRAM, which gives more spaces for the core of the software,
* ADC 12bits (Analog to Digital) converter: for a best accuracy of stick inputs
* tqfp 64 package, is "smt" technology, but should be still reasonable to solder,
* has hardware support for quadratic encoders,
* many IO pins (switch, several rotary encoder, lcd, etc...)
* several timers
* 32 Mhz clock

But it has some drawbacks also:
* can't be programmed with ISP, need PDI and there is still no low cost PDI programmer
* programmatic interface a bit different from Atmega AVR
* requires most recent version of avr-gcc tools
* has still few concrete examples on how to use

Here is the adaptor board for the stk600, I should receive the stk600 soon.

Schematic

The schematic of Rchv2 is available here. It's made with "Kicad" which is a nice open source for electronics, schematic and PCB.. See kicad home page to get it.
Thanks to Andreas Thorn for his help and contribution on this schematic.

T12Z with Assan

Some pictures of the Assan X8D module installation in a Futaba T12Z. Lock switch and led are located on the same side than antenna. PPM signal, + and - are taken from the back of the middle board which carries the trainer connector.

some thinking

Some more thought about what could be improved on most modern transmitters (including the nice new Robbe FX30):
* programming usability: Some functions you will never know what they are used for,
* no direct access to often used functions (on T12 you need to press 4 or 5times buttons just to change model),
* no global view on what's happening on a servo channel,
* limitations in switch cascading for timer function (on 12z you can't say stick high AND switch OFF = time start),
* can't have your own names for functions you like,
* lcd screen badly visible while flying, most have lcd below the stick median, no chance to look at it while flying without some gymnastic,
* simple way to tune model settings while flying,
* light and thin case for any style of pilot,
* talk when needed, useful for retransmission function: push a button and the radio will tell you the current receiver battery voltage, or give you an alarm when below some value, etc...
* a simple generic way to enter model settings with your own vocabulary

RCHome Source code

The source code is now available on sourceforge under the rcopensource project, with GPLv2 license. You can view it, or retrieve it. To view it with web, go to gitweb.

To retrieve, you'll need "git". Once "git" installed on your computer, to get it in read-only mode do:

git clone git://rcopensource.git.sourceforge.net/gitroot/rcopensource

If you want to contribute to the project, you are more than welcome. The entire project can be retrieved with:

git clone ssh://@rcopensource.git.sourceforge.net/gitroot/rcopensource

Rcopensource project page is here: https://sourceforge.net/projects/rcopensource/develop

Read the file README and COMPILE before starting.

Have fun,
Olivier