The custom design circuit description

IR transducer U3 receives the modulated IR (infrared) signal, which produced by remote control. This transducer contains circuit who’s capable to demodulate received signal and produce square wave (the envelope of IR modulated signal). The inverter U1-a converts the output of U3 from low logic to high.

The C1-R1 net is a high pass filter (it’s effect on T(off) of inverted signal). The U2-a is a simple inverter; his output signal drives the shift register (positive edge).

Figure 1:Main signals

In the normal state the output of U2-a is high when the signal appears on his input the output drops down and rise back to high state, this activate the shift register. This signal also supplied to U1-b C2 R2 U2-b net that holds and inverts this signal. The normal state of U2-b output is low, his high logic level resets the counter U4. Free running oscillator generates the clock for counter and the shift register.

Steady state explanation:

As we can see when the shift register (U1-b) pulse appears the “reset counter” signal is in the low state so counter is counting.

During 8 clock cycles the shift register sends to the serial port (through RS-232) 8-bit number, in this way every cycle of U2-b signal represents by 8-bit number and theU2-b signal is actually represents original IR signal from remote control. Every 8-bit number is relative to Ton Toff times of each cycle of the IR signal.

For instance:

IR signal received in serial port is a group of 8-bit numbers:

125 254 153 155 217 124 127 185 205 203 210 150 123 165 154 215 217.

Improved circuit

Explanation to improved circuit:

Instead of using 2 chips NOT and AND , I replaced 2 AND gates by NOT in single ship 4049.

Why the original custom design circuit will never work:

In this circuit the shift register signal (U2-a) and the “reset counter” signal (U2-b) come at the same time so the counter is still zero when the shift register sends him to the port.

In my improved circuit I use U1-b as a shift register signal and it solve all problems.

Another solution for oscillator circuit

If you have any problems with NOT gate based oscillator you may build this simple oscillator circuit.

5v DC circuit

Those two capacitors are very important don’t discard them.