Problem with simple rf600d circuit

[NielsE]

Hi,

I've build a simple encoder/decoder circuit, as shown in the official data sheet:

https://www.electro-tech-online.com/custompdfs/2012/06/DSA-468017.pdf

It all seems to be working fine, it's just that it doesn't really. The transmitter is transmitting something, the decoder is receiving something. The decoder can be reset, that is: made to forget all stored encoders. But I can't get it to complete the "learn" process described here:

1. Press briefly and release the learn switch
2. The status LED will illuminate while the switch is pressed and remain on when released.
3. Operate the transmitter encoder once, status LED on the decoder will extinguish
4. Operate the transmitter encoder a second time, status LED on the decoder will flash
5. After the status LED has stopped flashing the transmitter has been successfully taught to the decoder
6. This transmitter will now operate the system

I get stuck in item 3: The led never turns off. This would seem to indicate that the decoder never receives a proper signal. However, I can see on my oscilloscope that it is getting some digital signal on its input pin.

Suggestions?

Thanks!

 

[Dragon Tamer]

It sounds like you have quite a good grip on what you are doing, however you haven't quite given enough information.

-The circuit that you have built, is it the circuit on page 9 or page 10?
-Second, is your signal the full 7 bits with a stop bit?
-Finally could noise be getting into the circuit and interfering with your signal?

 

[NielsE]

Hi Dragon Tamer,

I've built the simple one on page 9. It's the same as the example in the data sheet for the RF module:

https://www.electro-tech-online.com/custompdfs/2012/06/DSA-42418.pdf

I can't really say what the signal looks like, or if it's correct. I can just see that there's a digital signal there. I can't get my scope to trigger on it, for some reason.

Noise could be a problem, I'll try to shorten the wires. Can I connect the rf600e directly to the rf600d, to bypass the RF modules?

Thanks!

 

[NielsE]

Moving wires around and fine tuning input voltages didn't make any difference. I'm probably going to try running on batteries or even moving from breadboard to a more compact layout.

Am I doing the Learn Procedure right? I'm pressing on of the input buttons on the transmitter.

 

[Dragon Tamer]

To test the transmitted and received signals, you would need a logic analyzer. There are some cheap models out there that you can look into, but getting a slightly better model will be better because it will give a more clear reading.

As for the noise, long wires will most likely pick up any stray RF signals floating around (if you're near a radio station, these will be quite profound). You did fail to mention that you were testing on a breadboard, breadboards are the least ideal platform for testing high frequency circuits. Capacitance between the pins will cause frequency drift with little to no way of correcting it.

Move to a prototype PCB and see if you have better luck, be careful not to damage the components when you place them or remove them from the board.

You can try to bypass the RF components of the board simply for troubleshooting purposes. Just be sure not to exceed any operating voltages of the two ICs.

 

[NielsE]

I don't think a logic analyzer would help me here. If I detect that some bit is missing, or whatever, that's not something I can do anything about. It would be a nifty thing to have, certainly.

I tried making a bare bones receiver circuit, with the RF module soldered directly to the decoder. No difference. I could try the same with the transmitter. I could try a 100nF on vcc. But I'm now guessing that the decoder chip is simply fried, that would be the best explanation for the symptoms. I'll order a new one.

Thank you for your helpful input!

 

[Athain]

Hi!
Did you ever resolve this issue? I am having exactly the same issue. Tried building the circuit in the datasheet. Transmitter and receiver are doing their bit but can't get the decoder to learn the encoder!

Thanks

 

[JimB]

Athain, welcome to ETO.

Sadly NielsE has not been back here since 11th June 2012.
So who knows if he ever fixed his problem.

JimB