Infrared photodiode & scope - where to start?

Beginners
#1

I’m looking to get https://www.littlebird.com.au/products/photodiode-5mm-led to use with a simple oscilloscope (am I allowed to link to non-LB products here?) to read the signals from an old remote.

Two questions:

  • Is there a kit I’d be better off buying instead of paying shipping for a single tiny part? Happy to get a few other bits and pieces

  • Can I just connect the photodiode directly to the scope or is there an additional circuit I need to build?

#2

I’m not speaking for LB, but many LB products are sold to interoperate with many other products, so I don’t see why you can’t link to non-LB products here.

The photodiode you reference may work with an oscilloscope, but the result may not be as square as using an IR Receiver module. LB has several of these, do a search for IR Receiver. They contain a preamplifier, and greatly increase range. Three pins; voltage supply, ground, and data output.

For decoding old remotes, you don’t need range, so I won’t go into the precise selection process.

Also, it can be much easier with an old remote to use two other methods of hooking up to oscilloscope;

  • direct connection to the transmitter LED, using tack-soldered wires. This reads the voltage across the IR LED.
  • direct connection to the battery terminals, using wires jammed between the battery terminals and the battery case. This reads the voltage drop, so you should invert the waveform. It works because of internal resistance of the battery.

For related kits; https://www.littlebird.com.au/products/sparkfun-wifi-ir-blaster-esp8266 is an ESP8266 CPU on a board with IR LED and receiver. For many situations, it can be used to extend an IR remote control service through WiFi. I was able to control one of my Daikin air conditioners with it.

#3

The scope I’m using is this: https://espotek.com/labrador/product/espotek-labrador-board/

I will try this first and then move up to something like the ESP8266 module you’ve linked. Thanks!

#4

My guess is that product should show something. I would try in this order; the battery, the LED, and the IR Receiver. I would also use a phone camera to make sure I could see some flashing from the LED. There’s nothing like reverse engineering a device that isn’t working. :grin: