# Logic Probe With Sound

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This logic probe can be selected to operate on TTL or CMOS logic levels, depending on switch S1. A string of resistors associated with switch S1 sets the threshold levels for a window comparator comprising IC1a and IC1b. Depending on whether the level applied to the probe is high or… Read more »

# Logic Probe for Tri-state Logics

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This is a simple circuit of Logic Probe for Tri-state Logics. This circuit can be built only in a few hours. Besides that, this circuit has some other advantages such as it is cheap, has high performance, and the LED will only light when tip of probe is touching a… Read more »

# Audible Logic Probe

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We can use NE556 timer IC to make indication of static of terminal in digital logic audible.  Audible logic probe can be very useful when we have to visually inspect a part while need to check the logic state on other point apart from the part.  Here’s the circuit diagram:… Read more »

# Logic Probe with Pulse Indicator

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A single CMOS IC is used on this logic probe. This logic probe shows three logic condition, High, Low, and Pulsing. Ind addition, there is no LED’s will glow if the probe input is neither hi or lo ( the high impedance state of tri-output logic IC’s). Here’s the circuit… Read more »

# Simple Discrete Logic Probe

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This is simple logic probe circuit. Logic probe is used to determine if a point in a circuit has high or low state when the circuit is in operation.  Here is the schematic diagram of the circuit: When the probe is not touching any circuitry, this circuit consumes no current…. Read more »

# Audible Logic Probe/Indicator

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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… Read more »

# Logic Probe with Seven Segment Display

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Logic probe is circuit that indicates  the logic state of the node of any TTL logic circuit. It will work if we must supply the probe with the same power of the circuit that we want to analyze, in other words same Vcc and same GND. The “Test” wire of… Read more »

# Darlington Transistor Pair Logic Probe

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Ideally, any testing equipment will not draw any current from the device under test. This ideal condition can be approximated by  designing a testing device with a very high input impedance for negligible loading, and this Darlington logic probe circuit could be one of this. This circuit uses two transistor… Read more »

# Coincidence Detector for Logic Signals

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This is a coincidence detector circuit. This circuit is very useful for monitoring complex logic circuits. This circuit has two inputs, A and B. if A and B are both low, red LED will be on, and green will be on when A and B are both high. The indicator… Read more »

# High/Low Voltage Probe

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Simple voltage probe circuit shown in the schematic diagram below very useful in testing, testing, or troubleshooting discrete  or integrated circuits, especially logic circuitry. This voltage probe circuit gives two indication, “high” or “low”. Here is the schematic diagram of the circuit: When the “high” condition is probed, Q2 and… Read more »