Hack SC2262/PT2262 transmitter to send commands for each button



Applications of RF transmitters based on 2262-type chips (datasheet) are innumerable. You can find it in most remote controlled things on the market - toy cars, light switches. This one in particular came from a fog machine and was used to trigger it remotely.

 Recently I needed a way to remotely tell a robot to start and stop doing a simple task, and this thing seemed a perfect solution for this - use Lock button to stop and Unlock to start.
RF transmitters and receivers come in several flavors, most commonly 315, 433, 868 and 915MHz. To determine which one I had, I had to crack it open:


Now we got to read it somehow... Luckily for me, you can buy receivers for any frequency in China by boatloads and dirt cheap. That's what I did!

315MHz variety as marked in silkscreen table
Now hook it up to Arduino and quickly check that everything is ok... (that's the library I use BTW)
Except that when I tried to read the code for those buttons there was something unexpected in my terminal window...

2 buttons yield the same code
  Looks like optimisation in production of fog machines really came a long way - even though transmitter's enclosure implies you can send 2 commands, it actually transmits one and the same command when you press any one of those 2 buttons.

Checking the layout, my suspicions that 2 buttons are just connected to the same input were confirmed:


That's how this works: any button pressed will connect 12V to the whole circuit: VCC pin and some address pins of 2262 IC and red LED thus sending one of 3^12 address codes possible.
What you need to make 2 buttons work is separate them and make each of them send 12V to different address pins and VCC.
Time to whip out your trusty scalpel 8-)
Aand that's the result:

You can see that in order to separately provide VCC to chip, I used 2 diodes.
Now I have a fully functional remote control:


Was it worth the hassle? Hell yeah, knowledge about internal works of stuff never hurt anyone. Hope someone will find this article at least educational, and maybe even practical!

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