Hello all, even though I started out with electronics building radios (like many here, it seems), I quickly moved on to other areas that interested me more (stuff that makes noise controlled by me :). Now it's time to go back to the roots... I need to design a simple RF system. With all the modules out there that doesn't seem to be too difficult. My problem is to get the various constraints under one hat, and especially the certification. Here's what I need to do: - Main function is to transmit the states (on/off) of two switches over up to a few meters, usually less than a meter. There will be two transmitters (two switches each) and one receiver. - The transmitters are battery-powered and need to be small. As small as reasonably possible, and the battery should last a year or more. I calculate with 1M switch state changes in that period. (The receiver is not critical, neither power nor space.) - The system needs to be inexpensive, with smallish quantities at least initially; maybe 20...50 per month. - It's sold to consumers in the USA (automotive application), so I think FCC certification of the transmitter is required. Here's what I've been thinking (and asking myself without finding answers...): - For all I know, I need FCC certification of the transmitter. Due to the small quantities (and the lack of experience I have with this), it seems to me that getting my own is not going to make much sense. OTOH, it seems that with something like these Laipac or Linx modules , the certification might be rather straightforward. Does anybody have experience with getting a simple design based on these or similar ready-made modules FCC certified? How much does this typically cost? Is it as straightforward as they (almost) claim it is? - I'm not sure whether one-way transmission will be good enough. I want to get close to 0 false positives at the receiver, and false negatives should ideally be less than 1 in 1M. Is this realistic with one-way transmission? Or would I need transceivers and a protocol? (In this I'm not considering concurrent presses of switches connected to the two transmitters.) - In case running my own FCC certification doesn't make sense, the only small pre-certified module I've found so far is a MaxStream ZigBee module . But it's bigger than I'd like it, it uses more current than I'd like it to use, and it's more expensive than simpler solutions. Are there any smaller and/or less power-hungry and/or cheaper pre-FCC certified RF modules out there? - The other question about this MaxStream ZigBee module I haven't yet answered is related to the protocol. How long does a typical ZigBee information exchange take, between power-downs of one device? My doubt is about resyncing with the mesh. Can a station wake up and start transmitting right away? What's the typical time for a complete protocol exchange of very little data (1 byte is enough in my case -- if the protocol takes care of error checking etc)? - I'm thinking about using Lithium coin batteries (like CR2354 or so, size depending on what I end up needing for the transmitter/transceiver). Is this a good idea? Any better suited alternatives? They should be user-replaceable. I'm not sure how important it is that they are readily available, but it would be a bonus if they didn't have to order the batteries from us. - Last not least is the antenna question. I'd like to come by without any antenna external to the (very small) enclosure. The MaxStream module comes in a version with what they call a "chip antenna". Its performance seems to be just fine for my needs. Is this more than just a skillfully placed track? Thanks for any info or pointers, Gerhard -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist