connect to a remote control buttons

I'd like to control my air conditioner units with Arduino but after spending some time on reverse engineering their IR codes, I found they have much longer codes than other devices, so they are too difficult to replicate. I think it could be easier to simulate a key press of each button. As I like to control 4-5 buttons and not the entire remote control, do you think a 74HC595 shift register and a TIL116 opto isolator for each button are enough? There is also a nice reset button on the remote, so I could reset it every time and don't care the last mode set.

Thank you for all the suggestions :)


the TIL116 might work, depends on the input resistance for the buttons on the remote control, but for what reason do you need the shift register? I think there are enough output pins on the arduino to use one output for each button. Mike

You're absolutely right Mike, the reason is that it will be part of a home automation system, there will be an ethernet shield plus I'd like to have some spare output pins for future applications. Do you think I can measure this resistance with a cheap tester?

I understand the shift register accept a serial input and transforms it in a parallel output. Does exist a chip that accepts as a input just high and low states? With 3 digital pins you have up to 2^3 combinations. It could use then standard digital.write functions.

Does exist a chip that accepts as a input just high and low states?

Try a 74LS151. This has 3 input / data select lines that control the routing of a logic level to one of eight outputs.

Thank you Mike, you always have the right answer! I can't find the TIL116 on RS. Maybe it's discontinued. Is it suitable a 4N25 optocoupler? Can I use this approach to control other digital appliances like a fridge or a dryer by hooking to their UI buttons?

Just had a quick peek of the data sheet and it looks like the 4N25 is actually a better one, from the point of current transfer that is.

Hello everybody, I'm writing again to this topic because I found that 4N25 is a bit expensive and maybe it's better to use dual or quad optocouplers since remote controllers don't have much free space inside.

However I don't understand much the datasheets. Take this as example What's the optimal voltage for the photodiode? How much current does it take to work? How much current can it switch? The input I have can provide max 20mA, 0.4V when it's in low state, 4.7V when it's high.

Thank you for the help!