Ordinary IR remote control circuits have one big drawback, they easily get disturbed by stray external frequencies, and thus produce spurious toggling of the load. The circuit discussed here eliminates this issue, and detects only the specified IR frequency from the given remote transmitter unit.
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.
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.
Parts List
R1 22K 1/4W Resistor
R1 22K 1/4W Resistor
R2 1 Meg 1/4W Resistor
R3 1K 1/4W Resistor
R4, R5 100K 1/4W Resistor
R6 50K Pot
C1, C2 0.01uF 16V Ceramic Disk Capacitor
C3 100pF 16V Ceramic Disk Capacitor
C4 0.047uF 16V Ceramic Disk Capacitor
C5 0.1uF 16V Ceramic Disk Capacitor
C6 3.3uF 16V Electrolytic Capacitor
C7 1.5uF 16V Electrolytic Capacitor
Q1 2N2222 NPN Silicon Transistor 2N3904
Q2 2N2907 PNP Silicon Transistor
Q3 NPN Phototransistor
D1 1N914 Silicon Diode
IC1 LM308 Op Amp IC
IC2 LM567 Tone Decoder
LED1 Infa-Red LED
RELAY 6 Volt Relay
S1 SPST Push Button Switch
B1 3 Volt Battery Two 1.5V batteries in series
MISC Board, Sockets For ICs, Knob For R6, Battery Holder
RELAY 6 Volt Relay
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