heres a continuity tester dave jones would probably be proud of

[williefleete]

after getting a few parts from dick smith electronics, a 5 pack of 555's and various coloured (and size) LED's
i have made up an audible continuity tester using 2 of the good ole tripple fives, one as a pulse extender/debouncer and the other as a plain oscillator

the  first one acts as a fast monostable which keeps the output pulled high if the switch/device under test is making all sorts of noise while the probes are making contact and keeps the beeper reasonably stable and reduces the staticy sounding beep while responding to fast pulses and extending them
the other one is just a plain astable oscillator which is running fast enough to produce a tone
how it works:
when the device under test (the push button) closes, it will remove the voltage from the trigger pin (pin2) triggering the first 555 and allowing the capacitor to charge and setting the output pin on applying voltage to the RESET pin (pin4) of the second triple 5 which starts the audio oscillator going, the output pin stays on until the trigger pin goes back up to supply voltage and the capacitor fully charges when the probes are released in which the reset pin goes zero, halting the audio oscillator triple 5 the beep staying on longer with the probes released with a larger capacitor or resistor, 100k resistor and a 1µF capacitor sets the debounce values nicely
performance wise it will pick up short pulses on the probes and extends them to about a 50 - 100mS beep pulse, comparable to a good multimeter continuity tester.
bonus features: you can use it to audiably test diodes and most LEDs and polarity, the probes are attached to the TRIGGER pin of the first 555 with a 10k pull up to 9 volts so it can be used to supply 0.9 mA which is enough to slightly light an LED to at least see what colour it glows and if it glows. and it also provides enough juice to test transistor and diode junctions and polarity, audibly beeping if the diode or C/B E/B junction is conducting
once i can find my card reader i will take some pictures of the unit but heres a schematic

[timofonic]

Hello.

I'm not able to see the schematic image in Tapatalk and the mobile.web browser. Are you attaching it in the forum or using an external URL? Despite Dave might hate it due to database space growing, I prefer the first approach

I collected some forum threads about continuity testers:

• Continuity tester with glitch capture
• Latching continuity tester with an auto reset
• Advanced continuity tester?
• Low-voltage, low-current continuity tester
• Looking for a specific continuity tester
• Simple ATTiny-based Contuinity Tester/Multimeter
• What is your ideal continuity tester?

Regards.