IR trace on Sony remote

• IR trace on Sony remote
  Posted by bmwm3edward on 28 Nov, 2009 03:21
• 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
  
• #1 Reply
  Posted by cybergibbons on 28 Nov, 2009 18:08
• This page here explains what is going on with the signal:
  http://www.sbprojects.com/knowledge/ir/sirc.htm
  
  You'll want to set the scope to single shot trigger to capture a signal like this. The 40kHz carrier can be seen during the 0.6ms pulse.
• #2 Reply
  Posted by dexters_lab on 28 Nov, 2009 18:32
• also might help if you rig up an IR receiver circuit, it means you can see and work with the demodulated signal and also means you don't need to hack apart your remotes
• #3 Reply
  Posted by bmwm3edward on 05 Dec, 2009 09:11
• Great stuff!  I obtained a IR receiver from sparkfun and with single-shot capture, I can totally see the sony command set, as described in the link provided by cybergibbons.  And with this codehttp://www.rtfa.net/2008/12/31/arduino-infra-red-ir-remote-control, I was able to capture the actual codes (his codes were wrong for my Sony remotes, but the code basis worked).
  
  Thanks, everyone.
  
• #4 Reply
  Posted by Raj on 23 May, 2020 07:17
• Why reinvent the wheel... The working of tv remotes he already been documented in huge amount of detail. It literally took me a day to make a simple 8 button tv remote that transmitted to a BPL tv (sanyo circuitry) and sky set top box