Matt circuit

When the push switch is operated - the buzzer will sound and the LEDs will begin to flash. For the hearing members of the household - the buzzer acts as a regular doorbell. It also re-assures the visitor that the doorbell is working. When the push switch is released the buzzer will stop - but the LEDs will continue to flash. The length of time they will go on flashing is set by the values of R2 & C1. With the values shown in the diagram - the LEDs will flash for a further 30 seconds or so. If you make R2 a variable resistor, you can adjust the time period. If you want longer than 30 seconds - increase the value of C1 or R2. The last circuit will flash up to two groups of 3 LEDs in tandem. This circuit will flash the two groups alternately. The alternate flashing creates the illusion of movement - and makes the display more eye-catching. Note that - although I've drawn the two groups of LEDs side by side - the individual LEDs can be mounted in any pattern you like. The main diff...

Small and portable unit, Useful for old men and old women. This low-cost, general-purpose electronic hearing aid works off 3V DC (2x1.5V battery). The circuit can be easily assembled on a veroboard. For easy assembling and maintenance, use an 8-pin DIP IC socket for TDA2822M. Cheap Hearing Aid Circuit Diagram   A Low Cost hearing Aid Circuit Parts: P1 = 10K R1 = 2.2K R2 = 330K R3 = 680R R4 = 33R R5 = 100R R6 = 4.7R R7 = 4.7R R8 = 220R C1 = 0.01uF-10V C2 = 100nF-63V C3 = 47uF-10V C4 = 10uF-10V C5 = 0.01uF-10V C6 = 100uF-10V C7 = 100nF-63V C8 = 100nF-63V D1 = Red LED Q1 = BC547 IC1 = TDA2822M EP1 = Mono Earphone 32R SW1 = On-Off Switch Circuit Operation: In this circuit, transistor Q1 and associated components form the audio signal preamplifier for the acoustic signals picked up by the condenser microphone and converted into corresponding electrical signals. Resistor R5 and capacitor C3 decouple the power supply of the preamplifier stage. Resistor R1 biases the internal circuit of t...

Small and portable unit, Useful for old men and old women This low-cost, general-purpose electronic hearing aid works off 3V DC (2x1.5V battery). The circuit can be easily assembled on a veroboard. For easy assembling and maintenance, use an 8-pin DIP IC socket for TDA2822M. Circuit Diagrams:   A Low Cost hearing Aid Circuit Parts: P1 = 10K R1 = 2.2K R2 = 330K R3 = 680R R4 = 33R R5 = 100R R6 = 4.7R R7 = 4.7R R8 = 220R C1 = 0.01uF-10V C2 = 100nF-63V C3 = 47uF-10V C4 = 10uF-10V C5 = 0.01uF-10V C6 = 100uF-10V C7 = 100nF-63V C8 = 100nF-63V D1 = Red LED Q1 = BC547 IC1 = TDA2822M EP1 = Mono Earphone 32R SW1 = On-Off Switch Circuit Operation: In this circuit, transistor Q1 and associated components form the audio signal preamplifier for the acoustic signals picked up by the condenser microphone and converted into corresponding electrical signals. Resistor R5 and capacitor C3 decouple the power supply of the preamplifier stage. Resistor R1 biases the internal circuit of the low-voltage co...

When the push switch is operated - the buzzer will sound and the LEDs will begin to flash. For the hearing members of the household - the buzzer acts as a regular doorbell. It also re-assures the visitor that the doorbell is working. When the push switch is released the buzzer will stop - but the LEDs will continue to flash. The length of time they will go on flashing is set by the values of R2 & C1. With the values shown in the diagram - the LEDs will flash for a further 30 seconds or so. If you make R2 a variable resistor, you can adjust the time period. If you want longer than 30 seconds - increase the value of C1 or R2. The last circuit will flash up to two groups of 3 LEDs in tandem. This circuit will flash the two groups alternately. The alternate flashing creates the illusion of movement - and makes the display more eye-catching. Note that - although I've drawn the two groups of LEDs side by side - the individual LEDs can be mounted in any pattern you like. The main dif...