A precaution when using a logic probe is to

A precaution when using a logic probe is to

• A. Never connect the leads to a DC source
• B. Never apply leads to an AC source
• C. Always use direct battery power
• D. Always connect to a signal generator

Answer: (B)

Logic probes are built to detect static high or low levels for digital signals, using voltages within the circuit’s DC range and with a common ground reference. Applying an AC source would continuously swing the voltage above and below those levels, potentially exceeding the probe’s input limits on the peaks and driving current through its protective circuitry. This can damage the probe or the circuit and also produce unpredictable, flickering readings that don’t reflect stable logic states. If you need to observe signals, stay within 0 to Vcc and keep a solid ground connection; for true AC behavior, use an instrument suited for AC waveforms, like an oscilloscope with proper coupling.

Logic probes are built to detect static high or low levels for digital signals, using voltages within the circuit’s DC range and with a common ground reference. Applying an AC source would continuously swing the voltage above and below those levels, potentially exceeding the probe’s input limits on the peaks and driving current through its protective circuitry. This can damage the probe or the circuit and also produce unpredictable, flickering readings that don’t reflect stable logic states. If you need to observe signals, stay within 0 to Vcc and keep a solid ground connection; for true AC behavior, use an instrument suited for AC waveforms, like an oscilloscope with proper coupling.