Well for those who have followed this saga, we are now in the final stage. The PIC turned out to be the key to pulling it altogether, using the PIC I'll have battery life options from several weeks to 6-8 months, just depends on the mode. Talk about scope creep, this project has been the poster boy for it, but I guess that is normal when you go into a project blind.
The final design came out as a TX-433 smd style transmitter (433MHz), an 8 pin dip PIC12C509 control device, and an 8 pin smd PIC12C508 based receiver that draws only microamps. This is all powered by 2 coin style 3VDC Li-On batteries in series, the size of the collar device is 1"dia by 1" deep in it's plastic case, not being a drug dealer I don't own a scale that can measure it's actual weight, but it is pretty light.
I should note that only a rough prototype of the collar has been put together, the final programming for the control chip us underway now thanks to Rob who saved the day on the battery life problem.
The tracker side is a Ramsey DR1 Direction Finder, whip style Yagi antenna and an alternative Loop antenna (contributed by another person here), The loop antenna has the added benefit of high attinuation from behind it making it harder to be 180 degrees out in direction. This is hooked to a Uniden Scanner (any scanner will do). In addition to a
433MHz code-lock transmitter, incorporated into the DF1 case.The heart of the system is the PIC control chip, the PIC in the transmitters and receiver are for the most part, just parts savers, in that it has the encoder/decoder for the code-lock parts, and of course the core of the transmitter/receiver electronics. The contol PIC chip in the collar is what does the real magic in that it conserves batteries.
The control program keeps the PIC in "sleep" most of the time, drawing only a few uAmps. The control PIC wakes up every 5 seconds for 50mS and keys the transmitter to send basically a beacon blip, then each 5 minutes it wakes up and does a 30 second transmit, then repeats this forever.
The PIC powers down the tranmitter any time it is not actually transmitting taking it's 2mA a idle load to 0mA. The 50ms beacon only draws .87mA an the 30 Second transmit period draws just under 4ma, but only for 30 seconds of each 5 minutes. If I am within 150 feet of the collar, I can transmit a code-locked signal to the receiver in the collar and this will wake the Control PIC that will initiate a 5 minute transmit cycle, drawing about 8ma. This will only happen when I am very close, so while it will hit the battery, I will easily find him long before I would run them dead.
Control Program rational
Transmitting to the collar would seem the obvious choice, but it is not reliable, even with a better transmitter, if I stay inside of Part
15 of the FCC rules then there is no way make it 99.9999% reliable.The automated blip (50ms ever 5 seconds) lets me know I am in range, and 50ms is just long enough for the DF1 to get some tone and left/right indication at 600 feet. This is not enough to determine true direction, just general direction.
I found it took me on average 20 seconds with the DF1 to find the direction of a transmitter withing a few degrees, when the transmitter was keyed solid. So we went with the 30 Second every 5 minutes.
As soon as I close the distance to about 150 feet I am in range for the transmitter on my side to reliably be received by the receiver in the collar. Remember that antenna considerations in the collar offer addional constraints on range and power, all far from ideal shapes and orientation. The receiver antenna is a 3/4" dia 8 winds of 30 guage wire, the collar transmitter antenna is 6.3" of 22 guage laminated wire that does long winds around the collar to use up the length in
2/3rd's of the collar dia. I needed room for a break-away link in the collar, the breakaway link is a weak link in the collar that the cat can break by pulling hard if the collar or collar transmitter were to get caught on something he was crawling through.that is inside 600 feet of the beast, the longer transmit time lets me nail down the direction, then when I am within 150 or so feet, the code lock transmitter in the tracker will trigger the code lock receiver in the collar, and that will wake the control PIC up and cause it to key the transmitter for 5 solid minutes, at this point battery life will not be an issue as I will be real close. With a solid transmit, the DR1 has proven very effective in determing the transmitters direction and loacation.
The final addition to the control chip logic was the ability to set it into several modes, these are full mode where it does the beacon blip each 5 seconds and the 30 sec transmite each 5 minutes, and wake and transmit for 5 minutes triggered from the collar receiver. The next mode only does the beacon, and the final mode only does the 5 minute
30 sec tranmit. The 5 minute transmit can also be diabled by just not hooking up the receiver to the wake up pin or not transmitting to it.