So i'll probably be using these to prototype before I move onto my PCB design.
However, I've got a few questions regarding their actual operation.
Neither the reciever or transmitter seem to have any special IC on them, other than a common op-amp on the reciever, no special decoder or anything.
So how do these devices actually work? Most notes seem to say they are AM, so are they just constantly outputting an AM signal, and then the serial data transmitted modulates the signal to a 0 or a 1?
I'm trying to find a schematic for these, seemingly without luck - but how do they actually send 0s or 1s? I guess when a 1 is sent, the amplitude simply increases - and stays the same as the carrier for a 0. So when an 8-n-1 serial stream is transmitted, carrier frequency = 0, and a modulated carrier = 1?
Again, schematics would help - I'd like to understand how input a logic high into the transmitter actually transmits a modulated signal.
They are OOK (on-off-keyed) dumb transceiver pair. You'd typically send an occasional packet with the TX,
and listen continuously to the noise from the receiver trying to recognise a valid packet-start-preamble.
Check out the VirtualWire library I think it is.
(The TX is just an oscillator with a logic signal to gate the oscillator - you normally just send a serial
signal at 2.4kbaud or similar according to its datasheet).
I believe it is VirtualWire yes, I have found a lot of reference to this already.
Thanks for the info though - they do appear to be crude (mainly from the price!) - however, I only intend it to use for locking/unlocking of a door, and nothing else.
When you say, "gate the oscillator" however, what do you mean?
The tranmsitter is simply a keyed oscillator, whose frequency is set by a saw resonater.
When you apply a logic 1 to the data pin , it produces an output at whatever frequency the saw filter is .
Usually 315 or 433.92 Mhz.
So data gets sent by rapidly turning the transmitter on and off.
As MarkT indicates, they are very simple and crude devices, but can be used successfully with the Virtualwire library
which does all the hard work in coding the data in such a way as to get the best results from them.