I've got a circuit with LM339 driving several LEDs. LEDs are powered from a constant current source. In this configuration, the meter works in bar mode. Is there any way to make it display in dot mode? Or do I have to remove constant current source and feed the LEDs through ballast resistors (this way I can use pull-ups for dot mode, need to check this though)?
LED display with LM339, dot mode?
- Thread starter Ilya
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radardoug
Well-known member
Not easy to do. Find some LM3915/6. They will do dot or bar directly.
The easiest way to roll a dot mode display, is using cheap op amps (need active pull-up and pull-down). String the LEDs in series with individual LED and ballast resistors between op amp outputs.
When the first op amp output goes high it illuminates the first lowest LED connected between lowest and next lowest op amp. When the second (next lowest) op amp goes high it lights the second LED and extinguishes the first LED.... etc
The meter current draw is only one LED at a time so not a current hog.
JR
When the first op amp output goes high it illuminates the first lowest LED connected between lowest and next lowest op amp. When the second (next lowest) op amp goes high it lights the second LED and extinguishes the first LED.... etc
The meter current draw is only one LED at a time so not a current hog.
JR
Ok. Got this thing on the breadboard. Everything works with TL074. The only thing that I don't like is when Vref is exactly 0V (grounded), the outputs go haywire and I have the last LED in the string light up. It's possible to insert the diode or resistor to avoid it. I can't think of any other easy solution right now.
Generally you would rectify and smooth the audio into a DC voltage with attack and release time constants. The meter thresholds would be set appropriately.Ilya said:
JR
JohnRoberts said:
That's correct. But in this case I'm feeding a DC voltage from a voltage divider for a quick check. As it is now, once it sees 0V at its input, it lights the last LED in the string (that LED is for maximum level). Once the voltage is ~0.001V, the "min" LED is lit.
