27Mhz - Radio Ideas

I wonder if the module could be removed from something like this
https://aliexpress.com/item/32685982784.html

i can find new controllers but not receivers, i expect they are eol
https://www.nitrotek.co.uk/heng-long-receiver.html

found some in stock, so 27mhz hardware must still be in production somewhere.
https://www.aliexpress.com/item/1005002069562240.html

It has got to be worth a go - although I suspect that its specification will be nothing like as good as the Radiometrix module.

I tried to order one, just now, for trials but the site wouldn't take my order. (I have an account with Aliexpress but maybe they are out of stock now?)

If anyone gets one and tries it in a sub perhaps they could report back.

David

david f wrote:It has got to be worth a go - although I suspect that its specification will be nothing like the Radiometrix module.

I tried to order one, just now, for trials but the site wouldn't take my order. (I have an account with Aliexpress but maybe they are out of stock now?)

If anyone gets one and tries it in a sub perhaps they could report back.

David

they are still showing as in stock, it could just be aliexpress having issues. I agree that I also doubt these will be as good as the radiometrix modules, those are essentially industrial radio modules being compared to a cheap toy from china. but from what i can tell, they are 4 channels plus some aux functions with crystals to select proper channels. the main problem is the lack of servo output as its designed to run a tank. i believe there is a separate rf module in the case that might be used as a standalone receiver or can be used with an arduino to generate servo output from its output.

geofrancis wrote: the main problem is the lack of servo output as its designed to run a tank. i believe there is a separate rf module in the case that might be used as a standalone receiver or can be used with an arduino to generate servo output from its output.

or just build a sub that somehow mimics a tank

I have been having a bit more of a look at the ax5043 which does look like an economical contender for the "27Mhz global model submarine radio" challenge!

https://www.onsemi.com/pdf/datasheet/ax5043-d.pdf

However:

- It would need quite a complex external antenna matching circuit:

https://www.onsemi.com/forum/t/faq-how-to-operate-ax5043-at-27-mhz-custom-matching-networks-for-ax5043/274

And if driven by an Arduino - there is no library available. The suggested microprocessors would seem to require quite expensive test kits.

https://forum.arduino.cc/t/axsem-ax5043-rf-transceiver/213439

Further development beats me, Guys. Any ideas? A Christmas challenge?

Have a good Christmas anyway.

David

The matching circuit for the antenna is certainly a bit of a monster though the link you included does seem to have a lot of detail in it. Bear in mind that it looks as if the matching is to match to a standard 50 ohm so good for testing with a software radio & PC combo, but you would also need to match from 50ohm to an antenna, particularly if you want use to pass data back to the Tx (if the Tx antenna does not match the Tx then you can get high voltages/current that can damage the chip).
The alternative to the arduino is the raspberry Pi pico. This has a more powerfull/faster processor than the arduino but does require the use of python as a language rather than c though thats not too difficult as they have many similarities. They are also very cheap about £3 I think. I ended up using an arduino as they do a 3.3v version with was a good fit with the UHF RF module I use, but I didn't notice what this RF module is.
I would guess you could use a lot of the Arduino libraries low level functionality as a start since all the various modules seem to use the same MOSI/MISO I2C type protocol though I ended up getting rid of most of the arduino libraries as it took up too much memory and just got in the way of a simple implementation.
A good project for dark nights :)

my opinion: the advantage the arduino has over the pico (currently) is the thousands of additional libraries, and the IDE. if you need the horsepower of the pico over a standard 8 bit arduino, you could use stm32 boards, esp32 boards, or Teensy 32bit boards.

Underwater range trials with simple 27MHz TX & RX.
I ordered these before Christmas and they arrived a week ago.
They are very simple (and cheap) I am not looking to use them for any serious use but I wanted to get acquainted with 27MHz . (I am too young to remember 27MHz r/c equipment!)
I don't know anything about the details of the circuits and I am not even sure that they use crystals. (I can't see any crystals on the boards.)
I don't know what power was being transmitted but I measured the quiescent current as 27 mA and the power on transmit  as 82 mA at 6 volts. Perhaps someone can give an idea of what power this represents? (Based on TX efficiency??)
I don't even know the legal status of using the 27MHz Citizens Band.



Purchased from AliExpress
4CH RC Remote Control 27MHz Circuit PCB Transmitter and Receiver Board with Antenna Radio System for Car Truck Toy Q81A
US $3.10US $4.70-34%
Shipping: US $1.48



I used the very basic aerials provided:



I used my trusty underwater trials rig (Plenty of empty tonic water bottles available! (Gin bottles don't float so well.)) which allows the RX to be submerged to 0.5m



This is the satellite map of the lake. The rig was submerged to 0.5 m at point 2.



This is the maximum underwater range at 0.5m depth (1.5 feet). (Point 9.)



This is the maximum surface range. (Point 6)



My conclusion from this basic test is that  even simple gear will give an acceptable underwater and surface range for model subs at 27MHz.

david f wrote:

My conclusion from this basic test is that  even simple gear will give an acceptable underwater and surface range for model subs at 27MHz.

thats very cool, im surprised its working as well as it is for just a cheap toy transmitter and receiver.

I bought one of those cheap Chinese 27mHz radio for my 1/35 tank RC conversion. It notes  5 channel,  #1- Left Forward, #2-Left Reverse; #3- Right Forward, #4-Right Reverse. Channel #5 is just a on/off switch.
https://servimg.com/view/20354514/5

redboat219 wrote:I bought one of those cheap Chinese 27mHz radio for my 1/35 tank RC conversion. It notes  5 channel,  #1- Left Forward, #2-Left Reverse; #3- Right Forward, #4-Right Reverse. Channel #5 is just a on/off switch.
https://servimg.com/view/20354514/5

I had an idea, those cheap transmitters are essentially binary off and on signals for each channel, I wonder what is switching time on the channels? could we bitbang some data over the rc channels if we can get them to switch fast enough to get a couple of proportional channels on each binary channel?

double post

An interesting idea!
This is a screenshot of the simple transmitter with the 4 channel buttons being pressed one after the other.



I am not too sure how to interpret the modulation. Do the lines on the trace indicate (audio?? ) single frequency s for each channel? A bit like the old telephone tone system?
I am not sure how practical and legal the simple TX would be. As I posted earlier I can't see any evidence of even a crystal.

Later edit. Relevant earlier discussion:

https://www.avrfreaks.net/forum/one-way-usart-data-over-27-mhz-rf-possible

david f wrote:An interesting idea!
This is a screenshot of the simple transmitter with the 4 channel buttons being pressed one after the other.



I am not too sure how to interpret the modulation. Do the lines on the trace indicate (audio?? ) single frequency for each channel? A bit like the old telephone tone system?

thats what it first looked like to me like its sending tones. i wonder if this is just a childrens walkie-talkie with a tone generator.

like this
http://www.talkingelectronics.com/projects/27MHz%20Transmitters/27MHzLinks-1.html


what would be an interesting test would be to connect a channel on your your tx and rx between some usb serial adapters and see if you can get stable serial, start at 300 baud and see if you get anything.

david f wrote:

Later edit. Relevant earlier discussion:

https://www.avrfreaks.net/forum/one-way-usart-data-over-27-mhz-rf-possible

thats cool, turns out im not the first person to think of this idea, apparently its totally possible. as for the legalities, were not changing the radios in any way were just button bashing codes into the sticks.

Another test would be to see if you can transmit a basic pwm signal to move a servo. technically, these radios are single channel multiple tones, so they can only send one command at a time, but if it can send pwm then it might be able to send ppm, if that works we have a full proportional rc system.

I ordered one of those little 27mhz radios for testing

Just following up your ideas with some experiments.

I fed one of the TX switches with a PWM  generator giving a 5v output.

The RX was picking this up. (If I set the generator to a very low frequency  (1Hz) the RX output gave this frequency.

I then probed around with a scope to try and find the input to what I assume is the tone decoder chip on the RX. Pin 16 seemed to give the same signal input as the TX.

I wound the generator up to 1000Hz with the following scope traces:

50% PWM duty



75% PWM duty



So it all looks promising but without a circuit diagram I may be barking up the wrong tree.

standard servo uses 10-20ms pulses for servo position, that might be a good first test to connect the output of a servo tester to the transmitter then a servo on the receiver output. it should give a good idea if we can use it at higher speeds for PPM.

PPM uses 1-2ms pulses, we would want at least 100point resolution over 8 channels gives around 100kz so if these are based on audio circuits it might have a hard time at those frequencies.

https://youtu.be/9CpsH4miXKk

Found these 27mhz crystal from China. Can these work with a DIY remote?

redboat219 wrote:https://youtu.be/9CpsH4miXKk

that video is just replicated the little push button 4ch remotes we are getting from china, it doesnt have proportional control.

On youtube I see a lot of homemade remotes using an arduino coupled to a 2.4ghz transmitter/receiver. Would it be possible to use these cheap Chinese remotes in lieu of the 2.4ghz unit? https://youtu.be/pjBnFZGfsjI

redboat219 wrote:On youtube I see a lot of homemade remotes using an arduino coupled to a 2.4ghz transmitter/receiver. Would it be possible to use these cheap Chinese remotes in lieu of the 2.4ghz unit? https://youtu.be/pjBnFZGfsjI

that is essentially what we are trying to do, but the only 27mhz modules that exist like those ones are the radiometrix ones I linked to in the first post that were very expensive. thats why we are now hacking the chinese toys. but those NRF24L01 2.4ghz modules are around 50 years more advanced than the 27mhz toys so we are having to radically simplify our approach at the moment to see what is actually possible with them.

I am now not sure about my statements about my PWM generator tests which I posted a couple of days ago. I still don't quite understand how these TXs work!

My latest tests are done with a scope connected to pin 16 on the "decoder chip" of the RX and I have now read your very useful source more carefully:

http://www.talkingelectronics.com/projects/27MHz%20Transmitters/27MHzLinks-1.html

The two screenshots show the text from this article on the left and my scope test on the right. Each one is with a different button being pressed on the TX board.








It is clear that the TX doesn't generate different tone frequencies but produces  "tone bursts" at a single frequency. (About 1 kHz).

I don't know what the best way of sending transmitter stick data will be? I can't see a simple way of putting a PPM stream into the TX.

I know from the work we did on LoRa that it is quite easy, with Arduino software, to put this data into digital form which we then sent through the LoRa chip in a standard way using packet serial communication.

Would we be best to do this and send digital data through the 27Mhz TX board. Using something like FSK and packet serial?

I have done some more digging and have found some more interesting material, this could be an good way around a transmitter, I had forgot about seeing it at a maker fare once where they used a pi onboard DAC to generate a wireless serial link to an old CRT text console, it works from 1-250mhz  so 27mhz and 40mhz would work. if we could get an SDR dongle working on something like a pi zero or the new zero2 then a pure software approach might be the way to go.

https://brskari.wordpress.com/2014/06/02/turn-your-raspberry-pi-into-a-radio-controller-for-rc-vehicles/