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Old 4th April 2010, 01:16 PM   #1
Ricco is offline Ricco  Italy
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Default Problem with LM3916 dotmode..

When I take off the supply on the pin N.9, all led lightly on, but no visualize dot mode! In bar mode it's all ok! I don't understand!

The circuit is this:
http://www.pctunerup.com/up/results/...schematics.jpg

Mic preamp is this:
http://www.electro-tech-online.com/a...mic-preamp.png

thanks to all!
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Old 4th April 2010, 02:28 PM   #2
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Well , you're lucky ! When I built it with a homemade Pcb , it didn't work . It resulted some kind of ESP tracer ...the leds were following my hand's movement !!
Building it with a well made pcb ( I think it got some instability issues ) should work at first shot , even in the dot-mode.
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Old 4th April 2010, 02:35 PM   #3
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I looked at the datasheet and didn't see any obvious answers but there would be some basic suggestions. That IC is pretty much a comparator network and I don't believe that it could be absolutely reliable without supply bypass and good attention paid to layout even though it's not Supposed to be doing anything high speed. It could oscillate, and if you really have it on a breaboard there could be enough capacitance from node to node to cause some "undocumented features". I don't think any comparator circuit can truly work with open inputs so there must be an internal divider that allows floating the mode pin. You should check to see the voltage on that pin when open and see if it makes sense compared to the voltage levels outlined in the datasheet text. There are several "hidden" things going on in that circuit that would be quite a bit more obvious if they would simply print a real schematic of it, but you would likely figure out what it's doing if you read the entire datasheet closely. An oscilloscope might help a lot.
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