Digital Logic Probe Circuits

Digital Test and Measurement Starts with Logic Probe

By Christian Taube (Own work) [CC BY-SA 2.5 (], via Wikimedia Commons

Any point in a Digital Circuit can be High, Low, Float means TriState. The High Low in a 5V CMOS circuit is just 0V and 5V. In TTL and ECL it is much different. The Test Point could also be Pulsing or have analog values and waveforms, as in Mixed Signal Chips.

Here are Logic Probe Circuits you can Build in your own Home Lab.

By Plusea (Logic probe) [CC BY 2.0 (], via Wikimedia Commons