I'm working on "hacking" a Skylink DM-50 Swing Door Opener. I bought it used on eBay for parts (was missing some things including the wireless remote to control the device but the motor was operational). Device User Manual. Going to integrate this device into my smart home for automation
So far, with the help of reading through other people's projects on this forum, I was able to get this dev board to simulate a button press to open/close the door (to replace the missing wireless remote). This Skylink device has an option to connect an external button to activate the door. The terminal connection on the circuit board (T3) for this has two pins; 1 pin outputs +3.92v and the other pin is the ground 0v. If you bring the +3.92v down to ground, it will activate the motor/door.
I used a NPN transistor (2n2222a), connected the collector to the +3.92v pin, the emitter to the 0v pin and the base to a 1k resistor which then connected to my dev boards digital pin. I also have my dev board grounded to the same ground as the Skylink circuit board. Now when I bring the digital pin HIGH for 1 sec, it simulates the button being pressed and activate the motor
This is where I need help
My next goal is to power this dev board by stealing power from the Skylink's board (so I don't have to supply power VIA external USB cable). My dev board runs off +3.3v but also has a Vin pin that connects to an on-board voltage regulator. This regulator can take +5v min and up to +10v max and supply a constant +3.3v.
I've already tried to connect the +3.92v to Vin but it wasn't enough to power the board. I'm afraid to connect the +3.92v to the dev boards +3.3v in fear of burning something up. Is this a valid fear?
I checked multiple points on the Skylink board but could not locate a +3.3v source. I found a terminal on the Skylink board (T2) which is suppose to be used for enabling/disabling external power source for the electromagnetic lock. The positive pin on this terminal is usually around +31v to +32v max when motor is not in operation. When I activate the motor, this voltage varies. The lowest I see it drop is about +26.5v. It varies while the motor is running (about 6 to 8 seconds) then returns to about +31v to +32v max.
I'm thinking I can use this fixed voltage regulator ua78m (datasheet) to supply it the +26v to +32v input and get +5v out in which I can use to connect to the Vin of the dev board. But looking at the datasheet and the recommended operating conditions, it seems the voltage I would use is a little too high (they show +30v max)? Would this regulator work for my needs? Do I need a different regulator? Perhaps a 10v regulator instead of 5v? Is it okay to regulate a power source twice (+32v down to +5v; then the dev board's on-board regulator going from +5v to +3.3v)? Lastly, once I have the correct regulator selected, how would I wire this up? Would I use capacitors in any fashion?
From what I've been able to research, a regulator is what I need but don't know the specifics. While not necessary, it's recommend to use capacitors as the regulators datasheet specifies. And since I see the voltage line I want to use fluctuate, I think I'll need to use capacitors, correct?
I appreciate any help at all in helping a noob get my first "hacking" project completed