I have donne a voting system with 50 remotes and a master. In that system I used bidirectional RF transmission at aprox 4600 baud. The RF modules I have used where BiM2-433 transciever modules from RADIOMETRIX (www.radiometrix.com). This modules have included a data shaper to get the audio received shaped to square wave and it works great, CD (carrier detect) pin which tells you when you are in RX mode if the transmitter it's on or off (used that to trigger the RX interrupt). Transmitter and receiver can't be at the same time on and that spares you a lot of extra components to use and it can be put in low power mode where it uses a few uA. The bad news for you should be that it is not recommended to use the USART for transmitting on RF because of the asimetry af the data. (a 0 byte will be 0V on the transmitters input for 8time slots and a 255byte will be 5V for 8time slots) and that causes the data shaper to decalibrate and that will increase the error rate a lot. The best way to do this is to write your own send and receive routines and use a simetrical data encoding like manchester, where a 1bit is a 10 transition on a time slot and a 0 is a 01 transisiton on a time slot so a 0byte will be 0101010101010101 and that is simetrical enough. You also have to calibrate tha data shaper at the begining of the tranmission by sending a burst of 0101010101010. You can use an osciloscope on the receiver and trigger the spot by CD to see when the data is stabile so you can determine the burst length accordingly to the modules you use. Happy codding, Mircea Chiriciuc EMCO INVEST sascha@go.ro ----- Original Message ----- From: "Luc Bolly" To: Sent: Monday, May 20, 2002 11:10 PM Subject: [PIC]:RF transmission Hello all I'm a newcomer in this list. I'm discovering the PIC world (more specifically PIC 16Fxxx) since a few weeks. Until now, I've found all the answers either by my own experience or by looking in the Internet. But here, I'm blocked. So if someone can help ... Description I have two PICs (16F877 and 16F628) that must communicate. I use the integrated USART on both sides and everything works great if I cross-connect TX and RX lines between each PIC. In software, I use an interrupt (Timer 1 every 50 or 60 or ... ms) to send the data at my pace (2400 bps or 4800 bps). I use another interrupt on the other side (RCIE) and that's it. Not even implemented a buffer as each transfer is completed before next data is sent. The problem Once connected via a cable, it does work. But my goal is to replace the cable via a RF system. I'm not that good in electronic (mostly a system programmer), but I work with a friend who is supposed to be good. We are using transmitter and receiver from AUREL (we also tried another brand). The signaling is correct up to the transmitter, but after, we only saw "bzzz bzzzz bzzz" - nothing usable. The question Is there some special technics to be used with RF ? Does some of you have any idea about my problem ? Do I need to add some hardware excepted the transmitter and receiver (and the antenna of course) ? Thanks for any help. Luc Bolly -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu