So, after getting the idea from some forum members, I have decided to design and build a SoloPro TX module. There are all sorts of practical benefits of this (model memory from the host TX, no need to use the cheep SoloPro TX any more), but mostly it's just fun to do

The SoloPro uses the Nordic nRF24L01+ 2.4GHz transceiver chip for the TX<->RX comunication. Datasheets of this chip can be found here: http://www.nordicsemi.com/eng/Produc...z-RF/nRF24L01P

The chip only comes in QFN package, so hand soldering it with an iron is almost impossible. But there are several options for getting a module with the supporting circuit:

1) Get a SoloPro TX and use the module inside it. It shouldn't be too difficult to get it out. This of course, destroys the TX. You can also use the module from the TX of a Solo or Kestrel. It looks like they all use the same chip. The new line of Nine Eagles helis does not use this chip any more.

2) The module is also sold in some European model shops as a spare for the Merlin Tracer 180/240 TX (rebranded Nine Eagles Kestrel). Product code is ML47050. A google search for the code brings up many links. This version has a duck antenna.

3) Get a module with a PCB a antenna from ITead. http://iteadstudio.com/store/index.p...products_id=53 Even though the range of this module should be less than the one with an external antenna, it is still very good. I did a test and the heli is responsive at 85 meters. The PCB on this one is just a little too big to fit inside the module case, but it can be sanded down without damaging the PCB traces, and then it fits into the case perfectly.

Important note: The Nine Eagles Module runs on 3.3V!!! Supplying it with 5V will probably destroy the chip. However, the SPI pins of the chip are 5V tolerant, so as long as you feed it 3.3V you can communicate with it with 5V signals.

The 2.4GHz trasceiver is controller by an Atmel AVR controller. The circuit is designed around an ATmega168, but the firmware is only around 3kB, so an ATmega8 or even an ATmega48 would be just as good.

The software is capable of binding to the RX and flying the bird. It reads the PPM signal that the TX outputs, then converts the stick positions into the SoloPro's protocol and sends it over to the RX. It also has a Copy TX ID feature, which will copy the ID of your stock TX instead of using it's own. This is useful if you use the stock TX and the TX module but want to avoid binding the heli back and forth between the stock TX and the module too often.

The nRF chip has a feature called auto ACK (acknowledge). This means that after sending a packet, the TX expects a confirmation from the RX that it received that packet and notifies the microcontroller about whether the confirmation was received. So I thought I could use this for a sort of a poor man's range test.

You can activate this range test by holding the bind button while neTX is working. If nRF gets the ACK packet, neTX will turn on the bind LED indicating that the heli has sent the confirmation. If there is interference on the channel you will notice that the LED is flickering, and if there is no connection, the LED will be off. All this is active only while you hold the bind button.

Adding EPA and subtrim is also possible, but considering the lack of interest in this project, it's not very likely that I will do that too. But, the hardware supports it, so I can always change my mind.

I still have 3 blank PCBs and parts for a few units, so if anyone wants an assembled and programmed module, let me know.

I've attached the schematics and the source code. The circuit is called nRF TX because I have plans to make this into a general short range TX module with telemetry support. Maybe some day...

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Flashing instructions (Windows only at the moment):

1. Download the flashing frogram from here: http://vusb.wikidot.com/project:hidbootflash

2. Plug a USB cable into the USB port on neTX while holding down both the copy TX ID and the bind buttons.

3. The three LEDs should start flashing successively indicating you entered the bootloader on neTX.

4. Look for the model number of the AVR microcontroller on your neTX. It can be either ATMEGA168 or ATMEGA88PA.

5. Run the HIDBootFlash.exe program you downloaded in step 1.

6. Press the 'Find Device' button. Just under the button it should say 'HIDBoot detected'

7. Press the 'Open .hex file' and select the appropriate HEX file from the archive below depending on the microcontroller model you have. Either neTX_atmega168.hex or neTX_atmega88pa.hex

8. Press the 'Flash device' button and wait a few seconds.

9. You should get a ':-) Finished flashing the device' message in the window below.

10. Unplug the USB cable and enjoy!

Good to know that the module is available as spare part, had I known this yesterday...

I just went Frankenstein on my SP TX round 1.00AM, I'm beat up, not used to stay up so late anymore

Anyway it's good to know I can buy one if mine is dead of to much heat applied from the soldering job, they really don't want you to harvest that module do they...

And thanks again for looking at the 16MHZ issue in the code, I'll try it on the arduino once this is solved, I don't want to prototype a board just for testing.

I'm gonna make some publicity for this on the SP thread, I think they would be interested, maybe it will give you enough motivation to pursue with EPA and subtrims.

Is it Kicad that you used for the schematic ?

Edit: just saw you commented the 16Mhz part even tough you have added the missing line, I'll map the ports to 328P and give it a try tomorrow, have to work late today.

subscribed!

Good job. It came across my mind to try something like this at one time or another. Glad someone actually did it.

I've added the buttons and the LEDs to the schematics. I was too tired last night, so I forgot those . I've changed to code to support both 12 and 16MHz F_CPU clock frequencies. The clock2ne macro has been upgraded to a function. It's a little more robust now.

I've also added MIN_CHANNEL_DUR and MAX_CHANNEL_DUR macros to define the range of duration of a channel in the PPM train. Different TXs have these durations set a little differently, so this can help with that.

I've replaced the attachments in the first post with new versions.

Schematics are gold. But could you also take actual photos of your work. That's invaluable for those who are good at tinkering...but don't have an EE degree.

Interesting mod, if this works out as well as intended, I'll include it in the FAQ, for those that want to use a different TX, without changing the receiver board.

Just found this site: http://arduino-info.wikispaces.com/N....4+GHz+Scanner

It is a great tool to test the setup and see if SPI communication and the nrf are working. The code works as it is on my Arduino Mini Pro and compiles with the Arduino IDE 1.0. Do not change the CE pin (PIN 9 on Arduino boards) as the code writes directly to the port.

Originally Posted by mha1

Just found this site: http://arduino-info.wikispaces.com/N....4+GHz+Scanner

It is a great tool to test the setup and see if SPI communication and the nrf are working. The code works as it is on my Arduino Mini Pro and compiles with the Arduino IDE 1.0. Do not change the CE pin (PIN 9 on Arduino boards) as the code writes directly to the port.

You just interface with computer via ftdi and listen to the right COM on a terminal ?

Thank you.

Originally Posted by blackmoon

You just interface with computer via ftdi and listen to the right COM on a terminal ?

Thank you.

Correct. And start Tools/Serial Monitor in the Arduino IDE. Make sure to select the correct baud rate in the serial monitor.

If I only knew...

http://www.befr.ebay.be/sch/i.html?_...arr%3D1&_rdc=1

I wouldn't have gutted my poor TX

Originally Posted by blackmoon

Good to know that the module is available as spare part, had I known this yesterday...

Sorry about that, I thought you guys knew

The modules from ebay you linked to have a PCB antenna. Even though they should work, their range isn't very good.

I've soldered little wires onto the module on my stock TX so that I don't have to open it every time I want to check something. I will try to figure out the EPA/subtrim protocol in the next few days.

I've attached a few images of the ATmega644 breakout and the 'shield' I use for testing the software. The shield can accept both the SparkFun and the Nine Eagles modules, so I can test with both.

Can the non plus do the 250kbps?

Originally Posted by mha1

Can the non plus do the 250kbps?

I've just checked the datasheet and it can't. Only the + can do 250kbps. That means that the both SparkFun and Nine Eagles modules have the nRF24L01+ since the communication runs on 250kbps.

My bad.

Originally Posted by kile

I've just checked the datasheet and it can't. Only the + can do 250kbps. That means that the both SparkFun and Nine Eagles modules have the nRF24L01+ since the communication runs on 250kbps.

My bad.

Can I send you my foam plane TX for analysis? I can not get hold of a logic analyzer.

Happy New Year

Michael