Simple RF Transmit and Receive

[dhouston]

The FM transmitter/receiver pair you're working with are rather costly for this type application, especially if you are planning on several sensors. You can reduce the cost by using ASK modules like those I list on my web page (or those designed/sold by Ioannis, one of the regulars here) and using a simple protocol like the one I've posted an example of in the Code Examples forum.

• http://www.picbasic.co.uk/forum/showthread.php?t=6261

[koossa]

Thx Dave!

I was actually looking for a cheaper option, but did not know what to look for.

[koossa]

What is a typical application for a FSK chip?

[koossa]

I have updated my circuit to monitor the CD pin on the Receiver
If high, I turn on an LED, but the LED switch on about every 10 seconds while the transmitter is still switched off?

[dhouston]

I have updated my circuit to monitor the CD pin on the Receiver
If high, I turn on an LED, but the LED switch on about every 10 seconds while the transmitter is still switched off?

I'm not sure what you're saying. If you are using the recommended circuit (p6 of the PDF), the /CD signal goes low when there is a signal.

[koossa]

Oops!!
I must have missed it and just assumed it must be high, sorry!

Will this code do the job to just test the CD pin functioning?
<code>
........
&nbsp;IF CDPin = 0 THEN
&nbsp;&nbsp;&nbsp;&nbsp;HIGH LEDPin
&nbsp;&nbsp;&nbsp;&nbsp;Pause 1000
&nbsp;&nbsp;&nbsp;&nbsp;LOW LEDPin
&nbsp;&nbsp;&nbsp;&nbsp;PAUSE 1000
&nbsp;ENDIF
.......
</code>

[dhouston]

Pin 3 (CD) probably doesn't have enough swing to be sensed directly by a PIC pin. That's why the transistor is needed. In effect, it amplifies and inverts CD.

I'm not sure what you want the LED to indicate. I would just capture and decode the RXD pin whenever /CD is low. What you get on RXD should match what you send with the transmitter.

The PDF file says the CD signal has a fast response but doesn't say how fast. Instead of trying to use serin/serout I would first just look at the pulsetrain to determine if CD is fast enough that you won't miss bits.

[dhouston]

What is a typical application for a FSK chip?

FSK is needed when higher data rates are desired. The pair you're using can go as high as 160kbps while ASK modules are usually limited to 4-8kbps. In simple terms, ASK is like AM radio which is subject to interference while FSK is like FM which has better noise rejection.