Kinda late on this week’s entry but life goes on.
Lets talk about Logic Probes and Pulse Probes.
This handy dandy devices are a bit old school but still come in handy if you don’t have a logic analyzer or oscilloscope. They are used for probing digital circuits for the boolean 0 – 1 or “high and low” states of a digital chip. Since everyone is on the AVR route of things this devices come in handy for quick troubleshooting before resorting to looking at code to see if you missed something. Most Logic probes can be set for TTL (transistor-transistor logic) or CMOS (complementary metal-oxide semiconductor) states. The probe has three LEDs. One for High status, one for low status and one for a NOID like light for pulse. A pulse probe is pretty much a logic probe but you can send out a pulse and have a logic probe pick it up to test a chip or even a transistor to make sure it still works. Some higher end probes have piezo buzzer that will give off different tones for high and low pluses. The Pulse Probe or Pulser for short is capable of clocking digital circuits – the signals are at LOGIC LEVEL.. The Pulser can also be called a SIGNAL INJECTOR however the term Signal Injector normally refers to an audio or RF signal injector and these have a low output (amplitude) and the waveform will not (may not) clock a digital circuit.
You can even build a simple logic probe with some resistors and LEDs. However that is more of a test NOID light and doesn’t work as well. If you really want to build a decent one try this schematic.
I built one a while back and used a 2n2222 instead of a 2m2219a transistor.