Use LED VU meter as Tachometer?

Hi, i want to share and ask something.  

Somedays back i bought a digital tachometer with dial and needle. I wanted to test it, so i connected its power terminals (12V) and connected the Tach input wire to audio speakers output (+ve) terminal and played a loud song. 

I saw Tach needle going up at certain frequencies.

I want to ask that if tach can detect audio signals SAME AS a VU audio meter does. So, CAN A LED VU METER BE CONNECTED SAME IN PLACE OF TACHOMETER  to detect car RPM signals.?

Plz help and guide.

frollard5 years ago
The tachometer counts the number of pulses per second and represents those on a scale.

A vu meter adds up the total power (amplitude) in the signal, and represents THAT on a scale.

They are 2 completely different things, one (the audio signal) happens to have a frequency in it to count, but that's not fundamentally what its for. The other, (the tach signal) is just pulses, and a vu meter wouldn't respond to just a variable frequency, because it isn't changing in amplitude with changing frequency.

You need either a frequency counter circuit, or some equivalent that counts and represents that frequency as a decaying sum (or voltage in analog terms) for the vu meter to display.

There are plenty of projects on ibles and otherwise (I know I've seen them) that use leds as a tachometer.
waqasjamil (author)  frollard5 years ago
Thanx for info.
p.s. I added some keywords to your question; 'tachometer, led, rpm, gauge, vu, metter'

...with those in there, the related column

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has several projects you may be interested in.