Clap-Sensitive Relay with ON/OFF Feature

Figure 1 

Parts List

Clapping of hands is the main idea on how this circuit was built with the acknowledgement of a relay to cause the circuit to function with ON/OFF feature.

• TS555 – a single CMOS timer which offers very low power consumption and high frequency where the timing remains very accurate in monostable or astable mode while providing reduced supply current spikes during output transitions, which enables the use of lower decoupling capacitors and with added features of high output current capability, high input impedance, wide voltage range, and output compatible with TTL, CMOS & Logic MOS
• BC550 – an NPN general purpose transistor with low current and low voltage used for low noise stages in audio frequency equipment
• BC328 – a PNP general purpose transistor in a TO-92 package, used for general purpose switching and amplifier applications which is suitable for AF driver stages and low power output stages of audio amplifiers due to its features of high current at 500 mA maximum and low voltage at 45 V maximum

During the operation of the circuit, a hand clap would activate a SPDT reed relay while a further clap will turn OFF the relay. In order to prevent unpredictable operation, the sensitivity of the circuit was reduced on purpose. This reduction of sensitivity will make sure that a loud hand clap will switch the relay to ON/OFF without failure when received from the electret microphone.

A clean output signal is being provided by the IC1 timer as it operates in a monostable mode along with a reasonable time delay so that the proper switching of the bistable circuit will be allowed. The monostable mode produces a single pulse upon receiving a trigger signal while a bistable mode produces a state of set and reset as with a flip flop or Schmitt trigger. An audio amplifier is being acted by Q1 while Q2 forms a discrete-components circuit together with Q3 and other related parts for this purpose. This formation directly drives the relay and allows the operation of a 3 V supply.

The current drain of the circuit is increased to 20 mA when the relay has been energized. However, the current consumption of the circuit will be less than 1 mA during standby or idle state. Even if the voltage supply is only 3 V, coming from two 1.5 V AA or AAA cells in series, a small DIL 5 V reed relay was still used for the circuit. This is because of the tests done on several devices of this type where it was found out that they can be powered ON with a coil voltage value in the range of 1.9 V to 2.1 V. The values of the coil resistance are varying from 140 Ohms to 250 Ohms.

The clap relay circuit may be utilized in several beneficial applications especially for elderly or disabled people where the lighting can be operated with a simple hand clap. It can also be used with other types of appliances for as long as the microphone would be capable of hearing the hand claps.

Source:redcircuits.com/Page88.htm