rickhar...@gmail.com said: > I would like to triangulate a position of a device which moves using 3 fixed > positions devices of known location. The idea is to have these operate on > 915mhz or 434mhz or 2.4ghz or appropriate frequency.
> I'd like a range of 150 feet or better and accuracy of 3 feet or better. > I know the time accuracy is the key to count time = feet, 1ns. > How to make it "inexpensive" is key. how inexpensive, very ;-) I think it's going to be tough to do it at low cost. The low cost transmit/receive chip sets you can get for 915 MHz are low bandwidth. That will turn into noise on the on/off transition that you need for timing. I'd suggest getting a pair of demo boards and running some experiments. The first simple sanity check would be to wire them up to a couple of uProcs and send messages and see if they work at your required range. Play around to learn the error rate vs baud rate. > -device response ASAP on different frequency Not with low cost. But you don't need to use a second frequency. My straw man would be something like this: Only one station transmits at a time. Wire up the transmit and receive lines to counter/timers. On both the transmit and recv side, grab the time on each data-level change and average them to figure out when the packet started. Look at the NTP protocol. It collects 4 time stamps. From that, you can compute the time of flight. The time at the remote server drops out. The sequence would be something like this: fixed->remote: long timing packet. (with lots of 1/0 transitions to feed data to the timer hardware) remote->fixed: long timing packet. remote-> fixed: packet with 2 time stamps first from the receive side, second from the transmit side I'd put a CRC on the packets as a sanity check. Handwave time: Assume the counter/timers run at 100 MHz. That's 10 ns. So you'll have to do lots of averaging to get below 3 ns. But that's assuming the RF units work well and that the averaging works. You could build a (much) faster counter/timer in a FPGA. I'm not sure that will help. Get a pair (or 2 pairs) of units and see how well they work. I'd expect FSK to work slightly better than ASK (on/off), but I'm not enough of an RF geek to turn than into numbers. I'll say more if that will help. We should probably take it off list. ------------ One probably crazy idea... Setup a directional antenna with a motor to aim it. Scan for the best signal. -- These are my opinions. I hate spam. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.