This simple circuit allows you to record any IR remote control signal on your PC, and then play it back. This is particularly useful if you want to control appliances such as TVs, VCRs, CDs etc. from your computer. The device simply connects to the parallel port of your PC. You can also use this circuit to analyze the waveform from any IR remote control.
The circuit consists of two parts. The first part is the IR receiver made up of a OP-505 IR photo transistor. This signal is buffered and squared up by the Schmitt trigger inverters (74HC14). The output of this inverter goes directly to the Acknowledge line (pin 10) of the parallel port. The software polls this line in the recording mode and stores the incoming data sequence.
The transmitter consists of a clock generator (555) set to run at 80Khz followed by a 74LS74 D flip-flop. The flip-flop divides the clock signal by 2 giving a precise 50-50 duty cycle on a 40Khz signal. This is then used as a carrier for the transmitter section of the circuit. In playback mode the software turns the D0 line of the parallel port on and off at the same rate that it recorded the signal at. This is used as a gate signal for the 40Khz carrier. The gate action is achieved by controlling the Clear input of the D flip-flop. If the clear line is low, then the Q output is also held low.
This gated signal is then used to drive the IR LED via the driver section. The IR LED driver section consists of a 7405 hex open-collector buffer. All the outputs of the 7405 are tied together to give enough current to drive the IR LED. The two 1N4001 diodes are used to step down the voltage to around 3V for the IR LED. This may seem as an overkill but you can drive several IR LED's simultaneously.
The 555 frequency can be adjusted for remote controls whose carrier frequency varies from the standard 40Khz.
The record/playback software can be obtained free of charge from GKDesign. Please email us to get a copy of the executable and source code. The software allows you to record/playback and view any IR remote control signal. The real fun begins when you write your own software to control your house. For example, a program can be easily written that automatically programs the clock on your VCR, TV and anything else.
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