Project 026 - DMM Continuity Tester
ISCLAIMER: This design is experimental, so if you decide to build one yourself then you are on your own, I can't be held responsible for any problems/issues/damage/injury that may occur if you decide to follow this build and make one yourself.
DMM Continuity Tester V1.2
Watching YouTube videos where Multimeter reviewers reach the stage where they test the continuity beep mode of the meter by 'clicking' the probes together as fast as they can to see if they can beat the 'beep' into submission.....I thought "there must be a better way than that".
So, I immediately thought of producing a small circuit to short the probes together (p-type FET) and release in quick succession and on top of that provide a display where the timing can be adjusted. All thats required from that point is the reviewers ear to listen for the beep repeat falling apart.
An Arduino Pro Mini (5V) provides the processor, switch interface and LCD drive.
A laser cut front panel, bottom cover and a battery holder finishes it off.
Example MARK Examples (minimum) at 250ms SPACE:
- Brymen BM257 = 38ms
- Fluke 85 III = 0.9ms
- Fluke 87 = 0.9ms
- Agilent 34405A = 25ms
- Keysight 34461A - 1ms (needs Space = 300ms)
- Agilent 34401A = 20ms, but will work lower but gives continious tone
- Brymen BM786 = Better than 0.01ms
- V&A VA38 = 0.1ms (beep varies in volume to point it's hardly audible though, obviously not using a fixed beep length)
- Fluke 17B MAX = 30ms (courtesy of EEVBlog YT video)
V1.2 - I have made it all free/open source on a strictly non-commercial basis. So here's the files:
Schematic
Code
PCB Gerbers
Bottom Cover Gerbers
Front Panel (G-code & Lightburn files)
Notes:
- V1.2 offers the same same functionality as previous versions, I just added a bottom cover, integral battery holder and an on/off power switch.
- Please don't ask me to make you one, or if I have any prototypes I could sell you. Sorry!
External links:
EEVblog Forum thread: https://www.eevblog.com/forum/projects/dmm-continuity-tester-v1-0-better-than-clicking-probes-together!/
EEVblog Mailbag Youtube video (featuring the DMM Cont. Tester): https://youtu.be/Xfs0dglIVOM?t=1275
EEVblog Fluke Multimeter test (featuring the DMM Cont. Tester): https://youtu.be/UER8fiI9WrY?t=1190
The design could go a lot further I guess, here's some ideas from the EEVBlog forum thread:
- Add a microphone to measure response time.
- Increase the speed so the likes of the BM786 can be measured (Use 16bit PWM or perhaps an STM32).
- Add some arbitary type modes, i.e. mimic running along 10pins of a connector.
- Add more output FETs with various different resistances to mimic crap probes etc.
Photos: