SparkFun Forums

[kingmu]

Hello all,

I have followed the walk-through and it appears to me that I have everything hooked up correctly:

On my transmitter, I can see 1400 baud at DATA coming in from the microcontroller. I also have regulated 6v at VCC.

My receiver is being powered by a 5v 1A switching power supply. I see the correct levels at the +5V pins. I placed the transmitter about 20 feet away. I have connected a scope to my receiver and all I see is noise. I do not see a change in the signal whether or not I am transmitting.





What am I doing wrong?

[saipan59]

Move the xmtr and rcvr much closer for now. You want to see the rcvr respond to the xmtr, even if the data is garbled.
Just drive the xmtr input with a switch/wire. With the xmtr off, you should see random noise coming from the rcvr. But with the xmtr on, the rcvr should go 'quiet', at least for a short time.
If you can't get this to happen, then perhaps your xmtr or rcvr is dead.
Or, consider the possibility that they are not tuned close enough to the same frequency. Some of the modules have a frequency adjustment (which is unfortunate for most folks, because if you mess with it, it may be hard to get it back to the right place unless you have the right test equipment).

Another way to verify rcvr operation: Depending on your neighborhood and such, if you watch the random data from the rcvr on your scope, you may periodically see a burst of 'clear' data bits. This means that someone nearby has a wireless device that is sending a signal (such as a car, or a wireless thermometer, etc.). Many of these things are on the 315 Mhz band.

Pete

[kingmu]

Thanks for the reply, Pete.

The xmtr and rcvr are close now. This is what I see when I just drive the xmtr with a wire coming from Vcc. My voltage source is causing xmtr to toggle possibly? I have a 5.2V 400mA wall wart running through an AN7806 regulator..



Thanks,
Sam

[saipan59]

So I gather you are *not* giving the xmtr that signal? It appears to be around 120 Hz. Perhaps the power driving your xmtr is not clean. Do you have a bypass cap between Vcc and Gnd, close to the module?

Pete

[kingmu]

The capacitor fixed that problem! Thank you for helping me so quickly. Now I see a clean signal when I drive the xmtr with vcc.

Now I have another issue. When I am grounded to my STK500, I can see my transmission cleanly at the data pin of the xmtr. But when I am grounded to the xmtr circuit, I only see noise at the data pin. I'm sure this is because these two circuits do not share a common ground, but I don't know what to do about this -- other than put all the components on the same circuit.

Sam

[saipan59]

I don't know what an STK500 is, but I assume it's the thing that provides the serial data to drive the xmtr?
Anyway, the xmtr module *must* have a common ground with whatever circuit is providing the serial data. They don't have to be on the same exact board, but you do need a clear and direct ground path between them.
If the ground path has to go through all sorts of wiring or other equipment, then the RF signal will be superimposed in all the wrong places, and the effective antenna impedance may be screwed up, etc.

Pete

[kingmu]

Yeah, the STK500 is the development board I'm using. I just connected its ground to my xmtr's circuit ground and now it's transmitting my data!

Thank you,
Sam