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Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
I found this schematic as a base to go off of, but I want to make sure this is the proper way to do it. I have 20 leds I want to use on 2 chips. In the diagram,IC3 pin 1 would be another led, so I have 20 total.
Would R8 and R9 be pots, so i can fine tune their range? I need these chips to be able to have a reference value of 2V..which means chip 1 reference must be 1V, chip 2 must be 2V. Then I will be feeding a signal, which will be 0-2V. Is this diagram set up to do this? or is there stuff missing?
Also, if i have LEDs that run with resistors at 12V 470ohms (i think they are 4.5V 30mA leds) Do i need resistors? I ask because the diagram shows 12V to leds, not many leds can handle straight out 12V, and i recall this chip did have internal current limiting. Below I posted what I would do, but I would like some feedback! All im looking for is a 20 led meter that can do 0-2V, where 2V is full bars. Thanks!!
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
The circuit that you show has a pre-amplifier and a full-wave rectifier, it's for low-level audio ( ac ) It would work but is over complicated for your requirement of dc input.
Look at the LM3914 datasheet and you will see a 20-led circuit for 0 to 2.4 V .. quite simple. You could add an op-amp to give a gain of 1.2 for exactly 0 to 2.00 v range.
It's always worth reading manufacturers datasheets as they need your circuits to work properly !
the tinkering/no math barbarian way would be to use a pot as a divider, set a power supply to 2 volts and adjust the pot until it lights all the way. what are you bar graphing?
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Need some help with LM3914
