The article explains a simple, accurate sound activated remote control circuit that will work on a particular sound frequency. Therefore it's perfectly foolproof since it won't be disturbed through other unwanted sound or noise. The idea was requested by Mr. Sharoj Alhasn.
The Sound Sensor Circuit
The figure shows the circuit of a sound activated sensor circuit which can be effectively converted into a remote control, triggered using a sound generator handset.
We have already learned a lot regarding this wonderful frequency decoder LM567 IC. The IC will lock-on into any frequency that's fed across its input and which exactly matches the frequency fixed across its pin5 and pin6 via the relevant R/C components.
The formula for determining the latching frequency across pin5/6 may be calculated using the following formula:
F = 1/R3xC2, where C is in farads, R is in Ohms while F is in Hz.
Here it's set to around 2kHz.
Pin3 is the input of the IC which tracks, responds and locks on an frequency which may be reaching the 2kHz figure.
Once the IC detects this, it produces a zero logic or an instant low at its output pin8.
This low at pin8 sustains as long as the frequency at the input pin stays active, and becomes high as soon as it's removed.
In the discussed sound triggered remote control circuit, a MiC is configured across pin3 of the IC.
An external matching frequency (2kHz) in the form of an audible sound or whistle is pointed toward the mic such that the sound hits the mic starighton.
The mic converts the sound into electrical pulses corresponding to the received frequency at the relevant input pin of the IC.
The IC immediately acknowledges the matching data and reverts the output into a low for the necessary actions.
The output may be directly connected with a relay if only a momentary toggling is required or only for the time the input is active.
For an ON/OFF switching the same may be configured with a FLIP-FLOP circuit.
Sound Activated Remote Transmitter Circuit
The following circuit may be utilized for generating an audible frequency for the above described sound remote receiver circuit.
The circuit is based on a simple AMV concept using a few ordinary transistors and some other passive parts.
The frequency of this transmitter circuit must be first set to the receivers matching frequency which is calculated to be 2kHz. This may be done by suitably adjusting the 47k preset and monitoring a latching response from the receiver simultaneously.