Infrared reception with discreet digital logic

There shouldn't be reasons today to build a remote control reception circuit with discreet digital logic. However, some time ago microcontrollers weren't so versatile as nowadays: almost all were OTP, expensive and with just a few peripherals. That's why it was 'logic' to use discreet digital logic circuitry. Afterall, the concept of counting time between signal edges is still used with microcontrollers.

The proposed circuit is based on a counter connected to a shift register. By means of NAND and inverter gates coupled with R-C networks, it is possible to detect the transitions at the output of the infrared receiver.

When a high-to-low transition is detected, the counter value is charged over the shift register and it starts to be sent  through the serial port. Almost at the same time, the counter is reset. This way, during the next high-to-low transition, the value of the counter charged over the shift register will be proportional to the elapsed time between the last two transitions and therefore we obtain a measure of the signal period.

Complex? Maybe taking a look to the schematic and the time diagram of the signals (not to a scale) will help a little bit.

You can also take a look at the received samples obtained from different remotes to appreciate the repeatability achieved. To make it possible, it is very important to adjust the clock frequency well to 19200Hz.

There is room for improvement in the edge detection using the scheme contributed by Robert Mauser. It is also his contribution a circuit to obtain power directly from the serial port and also avoid U6.

Return to the do-it-yourself page for more options...

 

Bill of materials

• U1 - 74HC14
• U2 - 74HC132
• U3 - IR receiver module
• U4 - 74HC393
• U5 - 74HC165
• U6 - DS14C232/MAX232
• R1,2 - 1K ohm
• R3 - 22K ohm
• C1,2 - 1 nF
• C3 - 4.7 nF
• C4-7 - 1 uF
• Serial port connector (RS232 info)
• Power supply 5 volts / 20 mA (example circuits)