Here's a little more about the wireless doorbell. I'm kind of excited about this because it could have lots of remote control applications and was really easy to do.
Here's the transmitter and receiver opened up and bareing all on my train wreck of a worktable. The receiver/ringer part runs on two AA's. That would be 3 volts with standard batteries but I used NiMH so it was only seeing 2.4 volts... and working. Since it will be mounted along side the heliostat control board which has the micro on it which needs 5 volts, I wanted to know if it could run at 5. So I ran the receiver at 5 volts from the bench supply. It was quite happy. The Simpson is set to 15ma full scale. With 5 volts Vcc, the receiver draws a mere 2.5ma
A regular LED draws about 20 to 30ma! When activated, the current jumps to 5 ma for just a moment and then drops back to 2.5ma. Clearly, a couple of alkalines would run this thing a long time. Or a small pv panel could run it. It might have drawn a bit more current had I not disconnected the little speaker. I could have my choice of 24 melodies to listen to every time the heliostat made a correction, but I opted out on that.
As I said in the above post, I found a point in the receiver circuitry that goes high when it receives a signal from the transmitter. With 5 volts Vcc, this point goes to 2.6 volts. It will be a simple matter to run that through an 10k resistor to an input on the micro.
The transmitter runs on 12 volts. The $1 price tag included
a 23A 12 volt Alkaline which came with the unit. The transmitter draws zero current on standby and here too, only a very few milliamps when the button is pressed.
Here's the transmitter hacked to be triggered by three water clear gallium phosphate (green) LED's. I have soldered their leads in series and glued them together with a gob of gorilla glue (kind of hard to make out in the picture, but that's what you are looking at). In strong light, they generate .7 volt, enough to forward bias the 2SC945 NPN transistor which then turns on the 2SD837 high gain NPN Darlington transistor. The 2SD837 is a high current device and was overkill, but it was handy and it worked.
This thing is set up so that the battery is disconnected until the button is pressed. The button presses on a micro lever switch, which connects the battery to the circuit, so it was simple to let the Darlington supply the circuit.
I was planning to make a little circuit board for the sensor components, but since it turned out to require so few parts, I just soldered their leads together and will probably mount them in a tube and pot them in resin or epoxy. I'd just gob hot glue all over them if they wern't going to be in the sun. The tube will extend out as a hood and help keep ambient light from affecting the LED's. That's the plan, anyway.
The seller claims the unit will work up to 70 meters. With NiMH batteries in the receiver, my unit was getting about 100 feet. I think the voltage in the transmitter would have a much larger effect on range. But 100 feet is plenty for what I want (to keep from having to run wires from my solar collector hot box to my heliostat controller).
So. Now you know more than you ever wanted to know about wireless doorbells. Put your thinking cap on and I'll bet you can find a use for it in your project.