High range LED meter display
built by sv3ora
There are a lot of times where you need a
meter display that is insensitive to vibrations and mechanical stress.
Analogue needle meters and LCD-based meters are
very prone to such things. But LEDs are immune to mechanical stress and
vibration, so the good old LM3914/LM3915 is the solution to the
problem. However, these displays lack the range we need when measuring,
as they can only accomodate 10 LEDs. However, more than one chips can
be cascaded to form a greater range display. The schematic above, shows
how four LM3915 can be cascaded in bar-mode to form a larger meter
display. If you want to save power you can try the dot-mode as well.
Each LED in the display shows a 3dB increment and the display has 40
LEDs, so this is a total of 120dB that can be shown by this display.
The input voltage range is 0-5v and if you want to measure larger
maximum voltages you can use a simple resistor potential divider. I
have used tiny Russian bargraph displays that come into packs of 5 LEDs
but you can use any common anode 10-LED bargraph display. In this case,
you would need only one 39 ohm resistor per LM3915. If you use the
LM3914 instead, you can have a linear display instead of a logarithmic
one, without any other changes to the circuit.
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