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Brymen BM789 continuity tester response

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slavoy:
I'm currently using the Sanwa PC7000, and I am considering switching to the Brymen BM789. I'm particularly interested in the continuity tester's speed in this multimeter. In the Sanwa, the continuity measurement is the fastest I have seen, practically without any limitations with no latching. It responds almost instantly, and the buzzer's operating speed goes into kHz. I love it, and I really need it in my next multimeter. Has anyone conducted such tests for the BM789 with a signal generator?

shapirus:
The manual says:


--- Quote ---Response time < 100μs

--- End quote ---

The BM869s (which I think is built on the same platform as your Sanwa) manual says the same, so I guess it's safe to say that the 789 is not worse.

joeqsmith:

--- Quote from: slavoy on January 20, 2024, 12:48:20 pm ---In the Sanwa, the continuity measurement is the fastest I have seen, practically without any limitations with no latching.
--- End quote ---

You never state how fast is fast and for all I know, your Sanwa may be the only meter you have seen.  So here's my low cost UNI-T UT90A in action.  Is your Sanwa this fast?

shapirus:
Lol, challenge accepted.

Direct feed from the headphone jack into the meter. I believe the audio quality could be improved by feeding it into a comparator that compares the signal against an adjustable reference voltage and then using its output to control a mosfet switch, whose resistance would be measured by the meter, but that would need more time. Besides, this track doesn't really sound all that better with normal speakers anyway :)

(once again, I believe this is essentially the same meter as the mentioned Sanwa)




That Uni-T is impressive though. I didn't know they actually had good continuity response.

shapirus:

--- Quote from: shapirus on January 20, 2024, 06:51:17 pm ---I believe the audio quality could be improved

--- End quote ---
...and indeed it can!

It requires two things: a) a signal polarity detector to turn on a switch when the wave is positive (or negative, doesn't matter) and off when otherwise; b) a high-pass input filter with cutoff frequency around ~2-2.5 KHz, close to the buzzer's own frequency. Maybe a preamp would also be helpful, since I found that increasing volume on the music output side helps, and on top of that filtering by signal level (by raising the polarity detector's threshold) to prevent low-volume component and noise from activating the buzzer.

Compressed recordings (I'm looking at you, metallica!) should sound better than those with high DR :)

As silly and funny as it is, it creates food for thought: think and experiment on how to produce multi-frequency sound with a mono-frequency buzzer, how to make it sound better, and how to design a respective circuit.

This reminds me of those old attempts of producing DAC-like sounds on the dumb mono-frequency PC speaker of early PCs when a proper sound card was a rare animal and cost a fortune. That sounded better, though, than my DMM :).

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