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Audible Logic Probe/Indicator (1N914)

2016-10-22 05:26  
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This article describes the Audible Logic Probe / Indicator (1N914). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: 1N914.

Logic indicator circuit / logic probe is used to identify logic level at any point of logic circuitry. The indicator can be visual (using LED, LCD, of 7 Segments) or auditory (using beeper or speaker). This circuit has a audible indicator, with the help of ?a loudspeaker to produce indication tone. ?Using the opamp,U1, as schmitt trigger, the Audio oscillator Q3-Q1-Q2 is isolated from TTL. Beside that, the op amp also acts as high input impedance inverter. The R8-R9 is used to set reference level at 16.6V which is a midway between low and high logic level. The Q3-Q2 will generate tone that indicate a high logic when the probe voltage is above 1.6V. If the probe voltage is below 1.6V then the ?OP-amp output will saturate the Q1 and disables Q3-Q2 to cut off tone. Here is the schematic diagram of the circuit:

Audible Logic Indicator circuit schematic


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