Hi all,
I am an amateur hobbyist currently messing around with Arduino/ESP8266 boards & have made a number of simple data loggers for around my house.
I found that my current DMM, a Bryman BM235 has a relatively high continuity cut-off, 30 to 480 Ohms & this has caused me an issue lately as I suspected a short in one of my loggers but this particular logger had a 150 Ohms resistor which my DMM did not even see.
Searching the net for a simple alternative I came across a straight forward schematic: Continuity Tester
Initially I constructed this circuit on a breadboard & it did not function, no sound when touching the probes together. I tried the various troubleshooting steps laid out on the page with no success. I even swapped transistors, checked all the actual resistor & capacitor values butr it still did not function.
I decided that it could possibly be an issue with the breadboard in some way & then constructed the circuit on some protoboard.
Still the same result or should I say no result, I get nothing from the tester.
Through fault finding I found that shorting between B & E of Q1 gives an audible tone but that's it so I know the buzzer is working.
I took a few readings from the circuit:
Input Voltage: 3.278v
Across Buzzer: 2.699v
Across 100R: 0.446v
On Probe: 0.758v
Base Q3: ~ 2.7v
Across Diodes: 2.055v
Probe leads resistance: 7 ohms
Can anyone see a possible glaring error with this circuit that I am unable to see.
Regards..,
Kirk
