I’m looking for a wireless solution of some sort that can detect when I am within a general proximity of my car. The idea is that I would have a receiver attached to an arduino in my vehicle and the transmitter attached to my key ring.
I don’t need very long range … in fact <30 & >15 ft. would probably be the best. Obviously the transmitter’s size is a factor, as it power consumption, it needs to be omnidirectional (IR is out), and that I think need to drive it with out a microcontroller (or at least w/o a full size arduino). To overcome the lack of a uC, I was thinking that I could use an oscillator to control the “ping/chirp”. (Yes? No?)
Originally, I was thinking that I could emit an ultrasonic chip every few seconds or so, but I have been unable to find such a device. The only thing I can find an ultrasonic range finder which isn’t exactly what I want.
Next, I started thinking of RF. I found this [Transceiver nRF2401A with Chip Antenna which seems that it would fit the bill, but I’m unsure as to if this would work without a uC and its 60ft range is actually more than I need.
I need a very primitive product. I don’t need to transmit any complex data over the connection, just enough so that the transmitter can say “Hi”.
Interesting … The digikey stuff is a bit beyond what I wanted to spend, but the sparkfun seems possible.
My only issue is that there seems to be some disagreement on whether the uC can be reprogrammed… although the buttons are nice, I still need a autonomous chirp every few seconds so that the car can determine when I am around … any thoughts?
Size could certainly be a problem though … I suppose I could always put the PCB in another case … but then I wouldn’t be able to use any of the buttons as well.
Hook up a multivibrator using some logic gates, caps, resistors, and a breadboard that can all be purchased at Radio Shack (at least you used to be able to, not sure if you still can):
Put the output of the oscillator into the DATA pin of the transmitter. Or you can use the 555 as your oscillator. I would go with whatever is cheaper and easier.
Power transmitter and receiver appropriately and BOOM! You will see the square wave on the DATA pin of the receiver. You should get 30ft range without any external antenna, I could be wrong though, it is worth some experimentation.
There was some question about FCC certification of those radio pairs though:
ipndrmath:
Ah. See; that’s what I was originally looking for.
wootness!
ipndrmath:
I’m a little unsure of what the purpose of the multivibrator is…
It is a cheap square wave oscillator. It outputs square waves, nothing more. The on and off time is set by the RC circuit, I think the link I posted explains how to calculate the frequency you want.
ipndrmath:
Does not the 555 chip give me the on / off that I need?
You can probably get away with
waltr:
A 555 timer chip can generate a pulse every second to trigger the transmitter input instead of a button.
I can't remember if the 555 outputs a pulse or if it just switches levels or if it can do both. You have to actually send the radio transmitter a pulse to get any transmission out of it as I recall.
The 555 timer outputs a pulse because the capacitor carges up to a trip point which activates a op-amp to fire of and discarge the capacitor which will charge up again.
