Difference between revisions of "Continuity Tester"
From Hackstrich
(Implemented proper latch timer) |
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** <s>Will add another 555 in the next revision and add a real timer for the latching functionality</s> | ** <s>Will add another 555 in the next revision and add a real timer for the latching functionality</s> | ||
** <s>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</s> | ** <s>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</s> | ||
| − | * Current draw idle is a bit higher than I'd like, should try to optimize this further | + | * <s>Current draw idle is a bit higher than I'd like, should try to optimize this further</s> - Optimized in Rev002 |
| − | ** Switching to a comparator that draws <1uA instead of 165uA will help somewhat | + | ** <s>Switching to a comparator that draws <1uA instead of 165uA will help somewhat</s> |
| + | ** <s>Optimizing resistor dividers in front of the comparator should help a lot</s> | ||
* Duty cycle control isn't really useful, should reevaluate need for it in Rev002 | * Duty cycle control isn't really useful, should reevaluate need for it in Rev002 | ||
| − | * Comparator input offset is 7mV and sensing voltage is 7mV, should increase the sensing voltage somewhat to make this reliable | + | * <s>Comparator input offset is 7mV and sensing voltage is 7mV, should increase the sensing voltage somewhat to make this reliable</s> - Fixed in Rev002 |
* <s>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</s> - Fixed in Rev002 | * <s>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</s> - Fixed in Rev002 | ||
Revision as of 19:21, 16 January 2018
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.
Status
- 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.
Features
- 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
Rev001 Issues
Holes for jacks are way too small (addressed in ECO A)- Fixed in Rev002Footprint for trimmers fits, but is way way oversized- Fixed in Rev002LED footprints are backwards (anode/cathode swapped, addressed in ECO B)- Fixed in Rev002Beeper/LEDs respond "analogly" due to the capacitor on the TRIGGER line- Fixed in Rev002Will add another 555 in the next revision and add a real timer for the latching functionalitySecond 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 Rev002Switching to a comparator that draws <1uA instead of 165uA will help somewhatOptimizing 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
Comparator input offset is 7mV and sensing voltage is 7mV, should increase the sensing voltage somewhat to make this reliable- Fixed in Rev002Switch 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.
Current Draw
- Rev001 w/ ECO A+B
- Idle - 465uA
- Beeper - 1.5mA
- LEDs - 3mA
