Logic probe

Posted on Jun 3, 2012

The probe indicates a high or low at 70% and 30% of V+ (5 to 12 V). One section of the voltage comparator (LM393) senses V in over 70% of supply and the second section senses V in under 30%. These two sections direct-drive the appropriate LEDs. The pulse detector is a CMOS oneshot (MC14538) triggered on the rising edge of the LM393 outputs through 1N4148 diodes

Logic probe
Click here to download the full size of the above Circuit.

With the RC values shown, it triggered reliably at greater than 30 kHz on both sine and square waves.

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