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I want to add a notification LED to my digital multimeter which i need to glow with the multimeter`s inbuilt speaker (piezo/buzzer/beeper) while in Continuity testing mode.

MM Model : DT830D

If i have no other option except to replace the speaker with the LED then also please guide.

If i have to add any additional circuit to my MM then also please guide.

To make it simple i was thinkng to built something that will be connected in parallel or series with the MM`s speaker.

or is this possible to built a circuit that will only glow the led when the MM beeps.

Thanks in advance.

Amit Kumar Agrawal
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    If the meter is to be used for commercial purposes, be sure to check your local laws on equipment modification. Tampering with a multimeter in any way will likely void both warranty and all certifications. – K H Aug 25 '18 at 00:53

1 Answers1

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This may be tricky as you have no circuit schematic and have provided no evidence of investigation.

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Figure 1. A piezo oscillator circuit. Source: Electronice Circuits.

Suggested approach:

  • Measure the voltage on each terminal of the piezo while silent.
  • Measure the voltages while beeping.

Even with only a multimeter you should be able to detect a difference.

When you've found the one that oscillates you'll need to monitor that with your LED circuit. This may require a high impedance input to avoid loading the piezo so much that it doesn't work.

Transistor
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