wireless module problems

[transistorboy32]

I'm having a bit of trouble using the TX/RXM-900-HP-II modules which I bought a couple years ago. I have a Basic Stamp 2P24 attached to the transmitter and a PIC18F452 to the receiver. I'm just trying to do basic testing, but the data seems to come across wrong. I have a code in the PIC that samples the USART (using the usart.h library) and retransmits it to the serial port of my computer, where I'm running HyperTerminal. Everything is set up at 9600 baud, and at 5 volts (spare the serial port but I use a MAX232). I'm transmitting (0xFF, 0xFF, 0xFF, 0xC, "ECHO1", 0xFF) from the Stamp. The PIC doesn't seem to grab the info correctly. However, when I hook the receiver module directly up to pin 2 of the serial port on my computer, it comes across perfectly (minus some occasional noise after, but I can remove that in code). This seems weird since the RX module is running at 5 volts and the serial port is at 12 volts. In fact, when I route the receiver through the MAX232 and then to the serial port, the output is jumbled again. I read another post that said you have to use Manchester encoding to do data transfer wirelessly. But then why does the data come across perfectly when I hook the receiver right up to my serial port? I think my error is somewhere in the PIC code and the interface to the USART functions. Has anyone else had this trouble? How would I go about fixing it? Thanks,

-Seth

 

[Oznog]

MAX232 inverts the signal. Would this cause what you're seeing? Perhaps the PIC was configured for the wrong polarity.

 

[tkvenki]

I had a similar problem....
THe problem you described is usually a hardware problem.

Try the following things:

1. Reducce the length of serial port cable if it is long.
2. Check wheather u have connected 4 caps to MAX232...( Long back i had connected 3 capacitors and i had the same problem)
3. If u have a CRO check the voltage levels of the signals you receive....If they are getting attenuated, u may have a problem there.

All the best