27Mhz - Radio Ideas

Hi David,

I am going to do the lottery tonight :) - 5 mins in and I have read AX5043 register values - so the journey starts....

Is it possible that you tested the boards you sent me with some other software?

See image and code below

Code:


// ***********************************************************************************************
//  Name:       SPI_readRegs_003
//  Date:       10 May 2022
//  Brief:      Crude SPI test - read write
//  Author:     Jonathan Askey
// ***********************************************************************************************

/*  SPI connections
 *  Uno/Nano      AX5043
 *  MOSI  11      17
 *  MISO  12      16
 *  SCK   13      15
 *  SS    10      14
 *  3.3v          23
 *  GND            6
 */


#include <SPI.h>

uint8_t slaveSelectPin=10; // CS Chip Select

uint8_t regAddr;
uint8_t regVal;


void setup() {
 
  digitalWrite(slaveSelectPin, HIGH);
  pinMode(slaveSelectPin, OUTPUT); // set the SS pin as an output
  SPI.begin();         // initialize the SPI library
  SPI.beginTransaction(SPISettings(14000000, MSBFIRST, SPI_MODE0));
  
  Serial.begin(9600);
}

void loop() {

  digitalWrite(10, LOW);            // set the SS pin to LOW
  
for (uint8_t regAddr = 1; regAddr <= 0x0F; regAddr++)
  {
  
    SPI.transfer(regAddr & 0x7F); // send address + r/w bit
    regVal = SPI.transfer(0);
    

    Serial.print(regAddr, HEX);
    Serial.print(" - ");
    Serial.print(regVal,HEX);
    Serial.print(" - ");
    Serial.println(regVal,BIN);
  }

  digitalWrite(10, HIGH);           // set the SS pin HIGH
 }



Regards
Jonathan _._

Fantastic result!
I will try again with exactly that software.
Once they start talking it can take off!
Well done!
David

Thanks again. I can confirm that the chips give the same result at my end



I don't actually know what went wrong with my earlier tests. Having the SPI test software means that I can do basic tests on the chips.

I have just tried them all with the same results above. However one chip gave the result below.



This one also doesn't give out any RF output. It presumably is a fault with my soldering. I wonder if I was unlucky and this was the one I tried the tests on?

David

Just some feedback on this (long-term!) project:

https://github.com/rdforrest/27MHz-using-AX5043

Very puzzling but TX circuit does not seem to transmit on full power. I am not quite sure if this is hardware or software. (The module current is about 2mA, but should be about 50mA from data sheet.)

It's slow progress on this project - still not sent any data or transmitted at usable power. But it is very interesting to delve into. Beats Sudoku!

Any suggestions most welcome!

David

https://github.com/pascallanger/DIY-Multiprotocol-TX-Module/discussions/711#discussioncomment-3222101

Hi David,

Have you set TX register TXPWRCOEFFB?

I think this is register number'ish

169 TXPWRCOEFFA0
16A TXPWRCOEFFB1

What are these reigters set to?

Regards
Jonathan

Hi Jonathan ,
16A is set to 40 and 16B is set to 96. ( As per "Ax5043 not Black Magic " instructions.
David

This looks very interesting. Rob Schuckman has been using an AX5043 successfully for underwater communication.

https://www.electronicsworld.co.uk/building-and-evaluating-an-underwater-rf-communications-link/33705/

Does anyone know how he can be contacted? I have found his LinkedIn profile but it is all in Dutch and I have never joined LinkedIn.

David

Contact form on bottom of his website home page

https://www.robschuckman.nl/

Regards
Jonathan

Thanks, Jonathan.

I have sent Rob a message and a link to this forum. (I suggested that the ability to transmit through the air/water interface at 27MHz was more important to us than transmission through water. I also suggested that the use of 27MHz for radio control could be a worldwide market for someone (him?)

David

Hi David,

Have you seen this resource

https://gitlab.com/librespacefoundation/ax5043-driver

And this appears to be a full tx/Rx example @ UHF

https://github.com/alanbjohnston/CubeSatSim/blob/master/afsk/ax5043.h

Regards
Jonathan

Thanks for the information, Jonathan.

The first reference an "OS-independent implementation for the AX5043" looks interesting but I don't think I have the depth of knowledge ( I am just a keen amateur) to make use of it. Will it develop into something which we can use easily?

The second one also looked promising and I tried it on a Raspberry 4. As usual with all the AX5043 C programs I have tried on the Raspberry I couldn't get it to compile! I don't have much knowledge of the Raspberry and I'm using Visual Code as an editor I have had a little more success using AX5043 Python routines using the Thonny IDE but still without getting the AX5043 to run.

It is very slow progress on this project.  I have still not sent any data or transmitted at usable power.

I am still not sure that I have the hardware working properly. (AX5043 connections and RF filter.) The low current draw indicates a problem. The AX5043 oscillator does function at 16MHz but any RF I have picked up on my SDR may just be harmonics.

However I'm sure that a simple Arduino based approach is right for our r/c model submarine application. (Need for small size and low power. The Raspberry Pi doesn't really fit the bill.)

If anyone else would like breakout boards suitable for the AX5043 (I also have two boards with AX5043 chips already mounted by me) I can let you have them for free as long as you let us know how you are getting on with them on this Forum. (Please PM me if you would like boards.)

David

P.S I have had a reply from Rob and he will reply in full shortly.

Rob phoned me last Wednesday night.

He was very helpful and wanted to see how he could help.

He stressed that he was primarily developing methods of underwater communication for high data rates within water i.e no air/water interface. So this was somewhat different from our radio control application which he was interested to find out more about. I mentioned the need for low(ish!) costs and the use of existing transmitters probably using the trainer plug (ppm) signal.

He has already developed a working board using the AX5043 at 27MHz but he thought that  these were probably more complex and expensive (and maybe physically larger?) than the sort of board we needed.

He suggested that an RF front end using an AX5043 could be the way to go and he will put together an outline specification.

He wanted to say that he was interested in submersibles and model submarines but all the work he was doing was in his own personal time. He was interested to hear about other Associations - the SubCommittee and Sonar-ev.de, in particular. (He lives in Holland, I think. His English is perfect!)

David

Hi,

CALLING ALL US MODELLERS?

As a humble Brit, can you confirm that these links summarize the available R/C channels for you in the States?

https://www.fcc.gov/wireless/bureau-divisions/mobility-division/radio-control-radio-service-rcrs

https://www.law.cornell.edu/cfr/text/47/part-95/subpart-C

In particular, does anyone in the US actually use the 27MHz channels and are CB radio enthusiasts still active in the States? (They are more or less defunct over here.)

David

a better list of available frequencies.

https://www.liveabout.com/radio-frequencies-in-the-us-for-radio-controlled-vehicles-2862530

the 50mhz frequencies require a HAM technicians license for legal use.

the 72mhz frequencies are reserved for aircraft use only
the 75mhz frequencies are reserved for ground use only

the rest are shared


not listed are the 433mhz and 915mhz frequencies, 433mhz also requires a HAM tech license.

as to CB use here in the states... I don't know of anyone that still uses them, but that is just me. i am not a long haul trucker, so i have no idea if they are still used in that situation.

Bad news!
I've just got back from holiday to find that the AX5043 radio transceiver chip and its variants are going to be discontinued for manufacture.
I've been in touch with Rob in Holland who confirms that this will prevent any larger scale commercial manufacture.
It is a shame because this seems to be the only modern chip which can work down to 27MHz. The only alternatives will be earlier types of hardware with coils etc and all rather "home-brewed"!
So yet again we have a lot of development work wasted and no way ahead for 27MHz - which IS a useful frequency for r/c model subs.
So our UK/US options are still second  hand 40/75MHz or home built 433/458MHz or 915/868 MHz or 2.4GHz with exposed antenna.

David
M7DYP
73

Yes, that's not good news on the AX5043, I had been considering playing around with it sometime.

I use 75MHZ or 6 meter band amateur for control but I really want a full telemetry link and have been testing 27Mhz (and probably 6 meter in the future) for a telemetry link with good results so far, the FCC permits limited telemetry on the 27MHz band. So far I have been using modified standard 27MHz rc components from ebay (internally modified for a microcontroller interface) but over this winter I am planning to build some new boards that will handle either 27MHz or 6M. I have been looking at the TI LMX2571 for the FSK transmitter among others .... I'll be releasing everything as open source when done.

Great to see this type of technical discussions on this forum, Khim

So after the AX5043 turned out to be a dead end, I have "grabbed the bull by the horns" and turned to the next option. The Radiometrix 27MHz modules.

Not exactly cheap (TX/RX £55/£65 + VAT respectively. As always, I have bought these with my own money.) but they are small and well made and have CE approval.

http://www.radiometrix.com/lmt0-0



I will let everyone know how I get on with the trials.

Happy Christmas to all our readers!

David
M7DYP

Hi David,

I used some Radiometrix modules many years ago for a HAB project (High Altitude Balloon) - using RTTY on UHF to transmit GPS location and altitude - they worked amazingly well...

Will follow your progress with interest - presume you are using a straight serial protocol and will need to develop your own method of a data package control structure.

PS Where did you purchase the modules?

Regards
Jonathan

aka G6SWJ - Short Wave Jammer

They were ordered over the phone from Radiometrix and delivered almost (postal strike!) the next day.
So far the Tx transmits a good carrier wave at the correct current level. The Rx gives sensible RSSI values.
I am using arduino nanos for the interface which are sending correct serial data at 2400 Baud via a hardwire connection but no correct data received yet when using the radio modules. Early days still!
I am hoping to use as much software as possible from the (quite successful) LORA project. The Tx arduino is already collecting stick position data into an array.
Hopefully more progress once the turkey has all been eaten! Compliments of the Season to you Jonathan and all!
David

A report on progress and an appeal for help.

The modules seem to be working well in that they transmit and receive but I haven't been able to interpret any data!

No correct data has been transferred over wireless but data is correctly transferred via hardwire.

For the software, I have based everything on the LORA software. The core routines for conversion of PPM to digital values at TX and RX PWM outputs to servos (6 channels) and Failsafes are in place and working but again only using a hardwire. The RSSI works and is used to trigger an LED and the failsafe on the RX. I have reduced the Baudrate to 1200.

The software is a work in progress and is over here:

https://github.com/rdforrest/27MHz--Radiometrix-module

A bit more detail:



This SDR "stick" screen grab shows the TX signal transmitting being switched on and off every 300 milli seconds (The dotted line. I assume that this is better than using continuous transmission?) and sending "some" data.  The data from the RX should be serial RS232 data. It can be displayed on a scope but can't be read as RS232 data. BUT connect the TX and RX together with a wire and data is read fine - even the servos move with the sticks.

It is obviously something to do with my attempts at encoding for WiFi. Any suggestions?

David

have you tried just direct ppm without the digital conversion?

An interesting suggestion, thanks! I have just been trying it again (I think I tried it when I first got the modules and it didn't work.

This is the scope trace. It doesn't look much like a ppm stream and the widths don't change when I move the sticks. BUT I will do some more experiments.




If it worked with just a ppm stream would that be an advantage over making everything digital?

david f wrote:An interesting suggestion, thanks! I have just been trying it again (I think I tried it when I first got the modules and it didn't work.

This is the scope trace. It doesn't look much like a ppm stream and the widths don't change when I move the sticks. BUT I will do some more experiments.




If it worked with just a ppm stream would that be an advantage over making everything digital?

making it digital opens up a lot more options like more channels, ppm isnt a very efficient use of bandwidth but its a simple signal that just relies on timing so you can usually get it across most radios.

from what I can read from the radiometrix pdf they are very basic radios almost like audio transmitters and ppm should work.

you could go even more low level and try something like a pulse, just a single off and on and see if that shows up on the other side.