I am attempting to build an IR remote receiver for a project I'm working on.
I decided to test to see what my Sony remote output looks like to help see, firsthand, what the carrier frequency would be, so I cracked open a Sony remote, connected the IR LED to my new Rigol scope and started hitting keys on the remote. I figured I could lock on the carrier and take some measurements to see what's what.
It wasn't that easy.
First problem, I could not get a stable carrier to appear onscreen no matter where I set my triggering line. Not sure why, this is my first issue. However, when I paused the sampling, I could take some measurements. (Please check my math)
I see an overall repeat of the cycle every 1200us (1.2ms), or 833Hz. This cycle goes through this: Voltage rises from about -1.5 volts sharply to +1.5 volts, then pulses about 24 times at 25us each for a total of 600us with +1.5V down to to +0.5V waveform. This 600us long section of pulses calculates out to be 40kHz. This completes half the overall cycle. The next half of the cycle (lassting 600us) causes the voltage to drop in a 1/4 of a sinusoldal waveform down to -1.5 volts.
The overall cycle lasts 1200us (1.2ms), or 833Hz. (Is my math correct?)
How is this an 80kHz carrier, or am I missing something? And why won't the scope get a stable triggering on this?
I'll attempt to attach a photo of the scope trace.
Thanks,
Edward