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MultiMeter Reading Wacked? My brain wacked? Answered

Ok so I just bought a new meter and I decided to test it out on my new circuit, but I was much surprised! The circuit is identical to this one: https://www.instructables.com/file/FSKP1NOHS18BW4T/?size=MEDIUM
except for instead of 4 leds on rows 1 & 2 it has 8 leds per row. 

Since I didn't want to type it all up heres the video.

So all help is appreciated! Thanks!


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Downunder35m
Downunder35m

6 years ago

You can't measure fluctuating amps with a slow digital multimeter ;)

In the videos you see the amps changing with the flashing of the LED's.

If your multimeter has a peak-freeze function use it to see the highest reading, otherwise you will need a very fast analog meter.

There is still the option of measuring the average amps using a big capacitor, let's say 0.5F, through the discharge rate but this involves a few calculations.

If you add a good electrolytic capacitor parallel to the power supply and measure the amps between power supply and cap - the circuit connected after the cap - you should be able to see more steady measurements on your multimeter.

With access to an oscilloscope you can also measure the voltage drop across a shunt, usually 1Ohm, to see the current consumption in real time.

When feeding a pulse width modulated signal to the LED this might be your only chance of accurate readings.

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HavocRC
HavocRC

Reply 6 years ago

I could understand for when the LEDs are flashing but what about when they are going from angalogWrite(0) to 255 over a course of 5 seconds or so. Is that not enough time for the meter to measure?

Thanks!

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Downunder35m
Downunder35m

Reply 6 years ago

It depends how the power is applied and how fast the meter can sample.
Most do one or tests a second and expect a more or less steady signal.
If the signal is PWM you still have only very short pulses.

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HavocRC
HavocRC

Reply 6 years ago

Ah thanks very much! I'll try just connecting all the bases of the transistors to +5v and bypass the chip. That should do it! Again thanks!