Author Topic: Problem with RC circuit *images*  (Read 2236 times)

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Offline jman571Topic starter

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Problem with RC circuit *images*
« on: April 27, 2008, 01:21:56 PM »
Okay, so before I continue, I'm going to say that what I've done I here I know I SHOULDN'T HAVE DONE but I did it anyways, because I wanted to test out all the components before I even did any soldering, so yes, instead of doing soldering, I just kind of connected some cheap wires I found in my house to the motor and battery leads by sort of wrapping it around them  :-[ Well...now that we've got that over with, here's my problem.

The above picture shows the simple RC control circuit that I wanted to make, it essentially the same as what Dimension Engineering did here: http://www.dimensionengineering.com/appnotes/simple_robot/simple_robot.htm

And if you read this thread: http://www.societyofrobots.com/robotforum/index.php?topic=3173.0 you'll get some background on what I'm trying to do here.

So everything seems to be connected properly to my motor controller, and yet I am unable to control the motors when my transmitter is on. I think the problem resides with the receiver as everything else seems to be working fine. Below are two pictures, one is a picture of the transmitter crystal, and one of the receiver crystal. As far as I know they are both Channel 88 (75.95MHz) and so should be able to communicate.


EDIT: The weird thing about the reciever crystal is that on the other side it does say CH88 75.950, but on the side I took the picture of, it says 75CH88 75.495 GWS

Here's what I DO know:

  • 1.)I turn on my transmitter first, then turn on my receiver like you're supposed to. I am not able to control the motors whatsoever, however the motor controller's status LED shines bright blue, indicating it is connected to a receiver source. No attempts to straighten the receiver antenna or improve the proximity to the transmitter have worked.
  • 2.)When I turn off the transmitter, and the RC circuit is still powered, the motors jerk around a little, turning back and forth, seemingly randomly, this seems to continue for a while. When I turn the transmitter back on they cease to move. I think they're moving because the receiver is just getting interference from somewhere. This leads me to believe two things, 1: my motors are working, and 2: there is something wrong with the receiver/transmitter/motor controller.
  • 3.)When the RC circuit and the transmitter are both powered, and I remove the transmitter crystal, the motors jerk around again.

So there's my problem in a nutshell. When the transmitter is turned on, nothing at all happens. When it's off, stuff happens, but I can't control it.

To add insult to injury I think I may have overcharged my NiMH battery, because when I picked it up from charging last time, it was very hot (hot enough that I couldn't hold it for more than a few seconds right after charging) :( It's kinda my fault because this little piece that I removed from the charger, was the reason the battery wasn't charging, and so I assumed it would take a full charge after putting the piece back in (a little over 3 hours set to 0.9A mode), but the thing finished charging in less than an hour for some reason  :o Must've came pre-charged, I'm sure...

Anyways, any assistance would be appreciated on this matter. If you need some more detailed pictures, or more information, feel free to ask. All the pictures I have can be found here: http://www.flickr.com/photos/12017635@N07/sets/72157604699684442/

One more thing, I unfortunately do not have a multimeter, but I think my uncle might, as he is an electrician, so I may be able to obtain one.

« Last Edit: April 27, 2008, 02:25:05 PM by jman571 »

Offline AndrewM

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Re: Problem with RC circuit *images*
« Reply #1 on: April 27, 2008, 09:26:10 PM »
Do you have anything else you could connect to the receiver to see if it is working correctly, like a servo?  Barring that, you will need to check the pins on the receiver for ground, power and signal with a multimeter.  I imagine you don't have another crystal pair to try?
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Offline jman571Topic starter

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Re: Problem with RC circuit *images*
« Reply #2 on: April 27, 2008, 09:36:23 PM »
Do you have anything else you could connect to the receiver to see if it is working correctly, like a servo?  Barring that, you will need to check the pins on the receiver for ground, power and signal with a multimeter.  I imagine you don't have another crystal pair to try?
I don't have another crystal pair right now, but I realize they're cheap, so I wouldn't be too upset if I had to go out and buy new ones (the only problem I can see is finding the particular brand I have, unless they're pretty much universal).

I will be going over to my uncle's tomorrow and will test the pins on the receiver with a multimeter, thanks for the suggestion.

Just to be clear, did it matter which way I inserted either crystal? Because there is no polarity distinction, and I would have no idea how you would figure that out anyways. :-[ ???

« Last Edit: April 27, 2008, 09:40:25 PM by jman571 »

Offline AndrewM

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Re: Problem with RC circuit *images*
« Reply #3 on: April 28, 2008, 12:05:58 PM »
I believe RC Crystals are nonpolarized, so it doesn't matter which way you plug it in.
blog: www.iamwhen.com
Saving the world from humanity one robot at a time.

Offline Steel_monkey

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Re: Problem with RC circuit *images*
« Reply #4 on: April 28, 2008, 03:30:34 PM »
Are the the crystals taken from same RC bundle ( transmitter+receiver) ? As I can see, they are, so receiver-transmitter pair should work. If this receiver-transmiter are PPM ( see documentation) you can see reaction on you transmitter input visually. If you don't have o-scope like me, you can use your soundcard to check the receiver output reaction on transmitter. Make simple resistor divider 1/50  ( only 1 part of 51 from input signal will reach the soundcard input, it is made for its safety), solder wires to it from input and microphone jack to the output ( GND is the closest to cord terminal as I remember).
Check everything twice!!
Power receiver from battery pack or PC which you are using for -scope role, don't power from wall adapter
Then, plug jack into PC microphone port, connect groinds of receiver and your new cable ( it should have two wires- signal, which goes to the divider input, and grund, which goes to divider ground). Now, you have two options- hear for input from you speakers/headphones ( sound will change as you move transmitter joysticks), or download one of numerous free soundcard-oscilloscope programs, or just sound record program. On the record you should see pulses on the output change their length. If you are interested, I can explain clearer.

Offline jman571Topic starter

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Re: Problem with RC circuit *images*
« Reply #5 on: April 28, 2008, 08:09:15 PM »
Thanks for that method to test my receiver/transmitter Steel_monkey, but I think I will first ask a friend to borrow his transmitter and crystals, to determine where the problem is originating from. He's also making an RC robot like myself. I've now soldered what I needed to in my circuit, so wiring being a problem is out of the question. I've now narrowed down to what could possibly be the problem.

  • 1.)The transmitter/receiver crystals are not functioning, and thus, no signal is being recieved/sent.
  • 2.)The transmitter/receiver crystals are not on the same frequency, or the transmitter can't handle that frequency. This theory came about because the transmitter is listed as supporting frequencies of 35 , 36 , 40 , 41 , 72 , and 75MHz. But since I'm using frequency 75.95MHz, perhaps this is too close to 76 MHz, and the transmitter cannot use this frequency.
  • 3.)The transmitter is broken.
  • 4.)The receiver is broken
  • 5.)The motor controller is not sending enough voltage/amperage to the receiver to allow it to function. I was unfortunately not able to check out this theory today as I did not have a multimeter.

I didn't want to include this in my theories, because if it holds true I'm downright screwed. That is: my motor controller is broken/doesn't do as adverstised, and simply the signal is going from my transmitter to my receiver, and to my motor controller, where then it gets lost forever, and the motors don't move.

Offline Admin

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Re: Problem with RC circuit *images*
« Reply #6 on: May 03, 2008, 05:34:57 PM »
Quote
The weird thing about the reciever crystal is that on the other side it does say CH88 75.950, but on the side I took the picture of, it says 75CH88 75.495 GWS

odd . . . it sounds like you have mismatching of crystal frequencies. If the transmitter crystal and receiver crystal aren't the same frequency, it won't work:
http://www.societyofrobots.com/remote_control_robot.shtml#RFrefchart

Other than that, use a multimeter on your entire circuit to trace the problem.

 


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