I need to wirelessly transmit an ON/OFF state that is very slow to change (many seconds to minutes between state changes). Essentially I need the wireless equivalent of a momentary push-button switch with no limit on how long the button can be held down.
Will a simple OOK/ASK TX and RX give me this functionality? More specifically, if I supply a DC +V to the data line on the TX, will I get a DC +V on the RX data line? I see lots of articles about transmitting data with OOK (bytes), but I’m new to OOK/ASK and I haven’t found anything discussing using it in the way I need to use it.
Amplitude shift or on-off keying is very susceptible to interference. If you want reliable data transmission (even if the data values are just on or off) you will have to digitize the data and use a packet data transmission protocol that checks for and corrects errors.
If you can get away with occasional change-of-value transmissions, just send those signals rather than continuous stream of “on” or “off” transmissions. A change-in-value transmission would also be susceptible to interference and would need to be encoded with an error-checking protocol. If it is important to know the time of the transition, the time could be part of the transmitted information packet.
Thanks for your reply. Maybe I can find a pre-made TX/RX pair that already handles error detection/correction. The signal that I’m detecting on the TX side also powers the TX, so when the signal is gone the TX turns off. For this reason I cannot send a change-of-state signal to OFF when the signal is gone. The only thing I need to know is when the signal is on. Basically when there is power detected on the TX side, the RX side will turn on another device. When the TX side looses power, the RX side will turn its device OFF too. They don’t have to be perfectly timed, even a difference of a couple of seconds is fine. I’m at the proof of concept stage at the moment (low budget, low time…) so the less design work I have to do at the moment, the better. I will look for a pre-made TX/RX pair that already handles errors, any suggestions are also welcome.
There is an I/O repeater application for the Wixel (from Pololu) which just copies input bits from a port on one unit to output on the port of another unit. This would appear to do just what you want. What distance range do you need?
Along the lines suggested by waltr, see http://www.rentron.com/PicBasic/RemoteControl.htm (especially the cheap 4-bit kit). If the sending and receiving units could be visible to each other, you might also consider a 38KHz modulated IR transmitter/receiver pair.
Thank you everyone for the replies. @jremington, your solution does look just about perfect for the proof of concept, I’m going to order it thanks! Here’s the direct link:
If this works, I’ll try switching to an ultra low power receiver like this one so our smallish receiver batteries will last many months (mostly idle time):
