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 :)

Hi,

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 http://docs-europe.electrocomponents.com/webdocs/0d1c/0900766b80d1c757.pdf 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!