In one of previous posts I have discussed a simple IR remote control circuit which operates quite well, however the circuit is not completely immune to external electrical disturbance generations such as from appliance switching etc. which results in false operations of the circuit causing lot of annoyance to the user.
The circuit design included here efficiently overcomes this problem without incorporating complex circuit stages or microcontrollers.
The solution comes easily due to the inclusion of the versatile IC LM567. The IC is a precise tone decoder device which can be configured to detect only a specified band of frequency, known as passband frequency. Frequencies not falling within this range will have no effect on the detection procedures.
Thus the passband frequency of the IC may be set precisely at the frequency generated by the transmitter IR circuit.
Shown below are the Tx (transmitter) and the Rx (receiver) circuits which are set precisely to complement one another.
T1 ad T2 along with R1, R2 and C1 in the first Tx circuit forms a simple oscillator stage which oscillates with a frequency determined by the values of R1 and C1.
The IR LED1 is forced to oscillate at this frequency by T1 which results in the transmission of the required IR waves from LED1
As discussed above, R5 of IC2 in the Rx circuit is adjusted such that its passband frequency precisely matches with that of LED1 transmission output.
When the Tx IR waves are allowed to fall over Q3 which is an IR photo transistor, a subsequent order of varying positive pulses is applied to pin#3 of IC, which is basically configured as a comparator.
The above function generates an amplified output at pin#6 of IC1 which in turn gets induced across the input or the sensing pin out of IC2.
IC2 instantly latches on to the accepted passband frequency, and toggles its output at pin#8 to a low logic level, triggering the connected relay, and the preceding load across the relay contacts.
However the load would stay energized only as long as Tx stays switched ON, and would switch OFF the the moment S1 released.
In order to make the output load latch and toggle alternately, a flip flop circuit will need to be employed at pin#8 of IC2.
R1 22K 1/4W Resistor