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Help with a LM3914 gauge with cascaded chips and a photocell for brightness

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madmen

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I'm looking for a little help with a circuit that has two LM3914 cascaded chips and a photocell to control brightness. My supply is 14.8v DC my input signal is 0.5-4.5v DC and I would like the led current to go from 17ma in the day to 6ma at night.

I built a circuit that works but I set the led current at 19ma but I can't figure out how to change the current on both chips at the same time, let alone how to add a photo cell.

Thanks,
Bob
 

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madmen

New Member
So I'm reading and rereading the application paper for the LM3914,
LM3915, LM3916 and I'm more confused then ever. I also read the "LM3914n Woes" thread on here and I think I understand how to setup one chip. But in the LM3914 application paper I read it to say that I need to us a unity gain buffer (LM310) to control brightness and not effect the range setting. Then I read LM3915 application paper and on page 14, figure 9 they have a circuit setup that has independent adjustment of reference voltage and led intensity for multiple LM3915s (same thing for the LM3916 page 15, figure 12) so I'm not sure do I need a unity gain buffer circuit? I have built some simple circuits before but I'm not sure how to apply the series parallel math to the circuits from the LM3915 and LM3916 papers.

I'm new to building from scratch, I have built a tube amp from a kit and I'm reading some books on tube amps but this hobby can really make you feel stupid.

Thanks,
Bob
 
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