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» Lab » Infra Red Scope via BitStream
| Project: | Infra Red Scope |
| Source Code: | None |
| PIC: | None |
| Interface: | BitStream + SerialPIC |
| Author: | Ravi Deo |
| Last Updated: | 7th April 2005 |
Project Description
This sample project demonstrates how to use BitStream to capture and display the infra red
data signal transmitted from the remote control of a consumer device (eg TV remote control)
which uses a 38kHz carrier.
This project uses an infra-red filtered detector (Mitsumi B0L12) as input to the BitStream module which
transmits the captured waveform using a wired SerialPIC interface. Although it is
possible to use an IrTx interface as the final transmitter (in isolation to PDA), the SerialPIC interface
was used to prevent possible infra-red interference from the monitored source.
Most modern infra-red remote controls for household appliances, use a 38kHz carrier onto which the
bit stream data signal is modulated. The infra red detector in use, filters out the 38kHz carrier wave
to leave the data signal. The output signal of the infra red detector is normally high (+5v)
during data inactivity. Hence, the BitStream module is set to a negative trigger. The sampling rate for
the filtered data signal has been set to 10kHz (samples every 0.1ms).
With the above BitStream settings, and SirPic configured for Serial Port (9600,N,8,1)
the data capture is started by pressing the "Go" button.
This is followed by pressing the TV remote control button towards the infra red detector.
This triggers the data capture (after which a 5 second timeout occurs on BitStream), followed by
the transmission of the captured waveform.
The following captured waveform diplays the signal transmitted on pressing the "sky" button on the satellite
remote control. Notice that the waveform is transmitted three times for a single button press (data actually overlaps
in the screenshots).
Armed with this information, it is possible to re-generate the same infra red signal from your own custom PIC
remote transmitter (PIC+IrTx). I shall leave that as an excercise for the reader, possibly another lab project!
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