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What can a logic probe tester be used for?
A logic probe tester is a very cheap and simple item of test equipment. It is able to provide a quick but very basic test for many logic circuits. However it is not nearly as flexible as an oscilloscope or a logic analyzer. A logic probe can be used for quick testing, whereas for more in-depth testing more sophisticated test equipment is needed.
How is a logic probe in a TTL circuit?
This circuit is a Logic Probe. It indicates the logic state of the node of any TTL logic circuit. To do that, we have to supply the probe with the same power of the circuit that we want to analyse: same Vcc and same GND. To check the logic level, we must connect the “Test” wire of the probe to the desired node of the circuit that we want to check.
What kind of probe is used to test digital circuits?
The logic probe or digital tester is normally a low cost handheld probe contained within a pen-like tube with indicator lights to show the state of the line being probed. Typically logic probes are used to test digital circuits like those using TTL or CMOS logic.
What should the probe read on relay logic?
On some logic systems, the probe would read up to 48V for a logic “1” on relay logic, and perhaps +/-12V on other systems. Many systems have existed, most are now gone, relay, DTL, ECL and so on.
What happens when logic probe is not connected?
When the logic probe is either connected to an invalid logic level (a fault condition or a tri-stated output) or not connected at all, none of the LEDs light up. Another control on the logic probe allow selection of either TTL or CMOS family logic.
What kind of logic probes are used in CMOS?
They can be used on either TTL (transistor-transistor logic) or CMOS (complementary metal-oxide semiconductor) logic integrated circuit devices, such as 7400-series, 4000 series, and newer logic families that support similar voltages. Most modern logic probes typically have one or more LEDs on the body of the probe:
Can a logic probe be used on surface mount boards?
Most logic probes will not work with these ICs as the logic levels cannot normally be accommodated. Additionally it is often difficult to probe surface mount boards as there is a real danger of shorting pins. With power applied to the circuit under test and the logic probe, it is possible to use it to probe various points on the circuit.