Audible Logic Tester Circuit


Posted on Sep 25, 2012

The tester provides an audible indication of the logic level of the signal presented to its input. A logic high is indicated by a high tone, a logic low is indicated by a low tone, and oscillation is indicated by an alternating tone. The input is high impedance, so it will not load down the circuit under test. It can be used to troubleshoot TTL or CMOS logic. The input section determines whether the logic level is high or low, and enables the appropriate tone generator; it consists of two sections of an LM339 quad comparator. One of the comparators (ICl-a) goes high when the input voltage exceeds 67% of the supply voltage.


Audible Logic Tester Circuit
Click here to download the full size of the above Circuit.

The other comparator goes high when the input drops below 33% of the supply. Resistors Rl and R2 ensure that neither comparator goes high when the input is floating or between the threshold levels. The tone generators consist of two gated astable multivibrators. The generator built around IC2-a and lC2-b produces the high tone. The one built around IC2-c and IC2-d produces the low tone. Two diodes, 1 and 1)2, isolate the tone-generator outputs. Transistor Ql is used to drive a low-impedance speaker.




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Frequency Meter
Headphone Class-A Power Amplifier
Logic probe yields three discrete states
Peak detect and hold
Noise-limiter
Crank Doorbell Circuit Schematic
tachometer circuit diagram
Interface Circuit for PC Soundcard Oscilloscope
servo motor control through keypad
Loudspeaker Protector Monitors Current
Voltage controlled sine wave oscillator



Top