I want to build a continuity tester that's fast, tiny, and can attach to a board I'm reversing so I don't need full multimeter when reversing boards away from a desk. The hardware files for this can be found on GitHub at sarahemm/continuity_tester.
- 2018-01-11: Received PCBs and parts, assembled and started testing.
- 2017-12-13: Completed PCB design, sent to OSH Park for manufacturing.
- 2017-12-11: Started putting idea together after spending lots of hours reversing for the DMS project. BOM and schematic done, PCB layout in progress.
- Fast, latching to catch quick pulses as probe is dragged along multiple pins.
- Visual/audio switchable options
- Lasts a long time on a CR2032 or similar
- Clips or magnets to a board I'm working on to save having another thing to put somewhere.
- No programmable logic, entirely simple analog/digital logic
- I almost never have projects that don't involve firmware, I'd like this to be one of them.
- Makes it easier for people to replicate without needing programming hardware/software
Holes for jacks are way too small (addressed in ECO A)- Fixed in Rev002
Footprint for trimmers fits, but is way way oversized- Fixed in Rev002
LED footprints are backwards (anode/cathode swapped, addressed in ECO B)- Fixed in Rev002
Beeper/LEDs respond "analogly" due to the capacitor on the TRIGGER line- Fixed in Rev002
Will add another 555 in the next revision and add a real timer for the latching functionality
Second 555 rather than a 556 so we can have one on always for the sensing and turn the second on as-needed for the beeper, saving battery power
Current draw idle is a bit higher than I'd like, should try to optimize this further- Optimized in Rev002
Switching to a comparator that draws <1uA instead of 165uA will help somewhat
Optimizing resistor dividers in front of the comparator should help a lot
Duty cycle control isn't really useful, should reevaluate need for it in Rev002- Eliminated in Rev002
Comparator input offset is 7mV and sensing voltage is 7mV, should increase the sensing voltage somewhat to make this reliable- Fixed in Rev002
Switch sticks out a fair ways, should either find one with a shorter actuator or move it slightly further onto the board so it's better protected from bumps- Fixed in Rev002
Rev001 ECOs =
- A - Trim legs on both jacks slightly to enable them to fit through the holes.
- B - Mount LEDs upside down to work around the reversed footprint.
- Rev001 w/ ECO A+B
- Idle - 465uA
- Beeper - 1.5mA
- LEDs - 3mA