RC 27 MHz transmitter and receiver help

Discussion in 'The Projects Forum' started by programmer6502, Jan 1, 2016.

  1. programmer6502

    Thread Starter Member

    Feb 1, 2014
    126
    6
    Hi,

    I have an RC kit that I've been building that didn't come with any electronics so I've pieced together some of my own. I decided for the time being to use the old 27MHz radio system and I have a 1980's circa Nikko 2-channel transmitter, labeled to be running on 27.145MHz frequency. So I ordered a Traxxas #2015 2-channel 27MHz receiver, along with a 27.145MHz crystal to match the channel of my Nikko transmitter. (Just to make things clear, I know trying to reuse the old Nikko transmitter isn't the practical thing to do, but it's what I want to do anyway.)

    So with the Traxxas receiver in a standalone setup for testing, it will receive my Nikko transmitter, but I'm not getting the kind of output that it should be. No matter how the sticks are positioned, the two receiver outputs are either a high signal (around 4-5v) or a low signal (0v), but nothing in between. So clearly, this wouldn't be able to drive any motors/servos properly. I know for sure that the transmitter works because I've tested it with the RC that it came with.

    Does anyone have experience with Nikko and Traxxas to give me some input? Of course the easy and simple solution is to get a proper Traxxas transmitter, but I have faith that there's some way to get the Nikko to work. ;)

    Thanks!
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,151
    3,058
    Is the output voltage you are measuring supposed to be an analog voltage or a PWM signal, and how are you measuring it?
     
  3. programmer6502

    Thread Starter Member

    Feb 1, 2014
    126
    6
    I initially did a simple mutimeter test just to give me some numbers, which of course isn't a great method. So I later connected the servo outputs to my Arduino with it's built-in A/D converter and had it print integer values to the console ranging from 0-1023 (0-5v). I got similar results to the multimeter, either high(ish) signals or low signals and nothing in between. In the Arduino's case, integer values 0-1, or 844-845.

    One day I'll have an oscilloscope ;)

    Edit: Servo outputs would be PWM wouldn't they?
     
  4. programmer6502

    Thread Starter Member

    Feb 1, 2014
    126
    6
    Well in the case of PWM, then maybe it is working correctly? Cause it's just a bunch of pulses.
     
  5. sailorjoe

    Member

    Jun 4, 2013
    361
    63
    Programmer, go back to your Arduino setup and put a 0.01uf capacitor from the ADC input pin to ground. Now see if you get numbers between 0 and 844. This isn't an ideal value for a low pass filter, just a simple test case. Low pass filters can convert PWM to analog voltage.
     
  6. programmer6502

    Thread Starter Member

    Feb 1, 2014
    126
    6
    Thank you sailor, I'll give that a try.

    As a backup solution ahead of time, I salved the circuit board and transmitter from another (but much newer) Nikko RC that had seen better days, but is still 27MHz. I've determined that the receiver has been integrated onto the same board as the motor controller and have disabled the motor controller since I'm only interested the receiver portion. I also determined that transmitter and receiver are using a simple 2-chip interface provided from Pericom Semiconductors. The receiver chip is faded, but it seems to make out PTNRX7300. I've been unsuccessful in finding a datasheet, but I assume it's functionally similar to the PT8A978B found in this datasheet due to the functions of the transmitter (including turbo). However, although they have the same pin count, my chip seems to make it's reference to ground on pin #7 instead of pin #2. So they don't seem to be the same on that aspect. Does a PTNRX7300 ring a bell for anyone? It could be a little off since the chip is faded, but I'm pretty sure it ends in 7300.

    Anyway, not giving up on the 1st method, just though I would mention the 2nd ahead of time just in case.
     
  7. programmer6502

    Thread Starter Member

    Feb 1, 2014
    126
    6
    Alright, the capacitor didn't fix the problem, but I have been reading the PWM with the digital pins of my Arduino instead and am getting better results. Without a doubt, neutral works. So that's a good start. I will admit that I haven't actually tried a servo yet because I've been waiting for some in the mail. But they'll be here today so I'll see what happens. I was just curious to see if that Nikko transmitter would even work period which is seems to do, now I just need to make sure it works properly.

    Stay tuned....
     
    Last edited: Jan 2, 2016
  8. programmer6502

    Thread Starter Member

    Feb 1, 2014
    126
    6
    Alright, servos came and tried them out. Very intermittent with the only thing working being neutral like I said before. I'm not really sure what to do next. I guess I'll keep digging for the data sheet so I can maybe use the salvaged Nikko receiver.

    Thanks.
     
  9. programmer6502

    Thread Starter Member

    Feb 1, 2014
    126
    6
    Just dropping by to report that I successfully hacked the salvaged Nikko receiver with a multimeter and the general information given in the datasheet from the similar chip. I'm now running the output signals from the board to a microcontroller which opens a lot of exciting possibilities. So I guess I didn't really need help after all? Patience is a virtue I guess. ;)

    Thanks all for the help anyway, you guys have given me some good information and guidance in the past,
    Have a good one!
     
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