|GCSE Measure Current Frequency Meter >Logic Probe< Multimeter Oscilloscope Power Voltmeter|
Measure Logic Probe
The probe measures the voltage at a point in the circuit.
One or more LED indicators show a logic zero, one or open circuit connection.
This simple circuit might work but it drains quite a lot of current from the circuit being tested so it's not ideal. A separate power supply for the probe is not needed.
Here is a better circuit with input buffering. The probe needs its own power supply or battery.
Here is a more advanced probe. This one shows one LED for low signals and the other LED for high signals. If the logic line is inactive, neither LED comes on. In tristate circuits this is useful.
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