Yes, the chip provides all the regulation necessary to drive the LED's. It
will run on 12 volts, but it gets a little warm at that voltage and it is
not supposed to be used continuously in bar mode because the package can't
dissipate that much heat, so a regulator like the LM7805 should be used to
drop the voltage to 5. That would keep things nice and cool and keep the LED
brightness steady, since the voltage supplied in the car will be anything
from 11 to 15 volts. It would also permit the meter to be used on a six volt
electrical system. Here is a link to a similar circuit to mine (I changed it
slightly to fit what I needed) http://pages.prodigy.net/bipes/afschem.htm
This is a Dick Bipes circuit. I have a simplified version of the second
circuit set up on a test board. I changed the input voltage to 5 to allow 6
volt use and keep the thing from melting on hot days. His circuit will be a
little iffy if used in 90+ degree weather.
http://come.to/miata
This page describes the circuit a bit better and has several others. Just
click on the techie stuff link.
You can also download the data sheet for the chip directly from national:
http://www.national.com/pf/LM/LM3914.html#Datasheet
You can figure out how to pick the resistor values from that.
I hope this stuff helps.
Regards,
Josiah
-----Original Message-----
From: GremlinGTs@aol.com [mailto:GremlinGTs@aol.com]
Sent: Thursday, April 04, 2002 8:25 PM
To: Bartlett, Josiah
Subject: Re: [oletrucks] Electronic Gadgets for trucks..LED voltmeter/
IC chip
Hey, thanks for that info on the LM3914 ! Ok, let me try to get this
straight, as I am a Repair Tech, not a Design Tech. :) I can pick a
resistor
to have a 12-volt input reduced enough to activate the LED in delayed
manner?
Meaning, by staggering the values to the input of the IC chip, I can
regulate
when it activates the appropriate 2-volt output to the LED? That WOULD be
perfect, I was having a HELL of a time trying to figure out how to drop the
12 volts ( er, 10-16 volts ) enough thru each circuit and get 2 volts to the
LEDs without frying them crispy. I have enough of these little LED strings
to
experiment with for awhile, just need to find them again. They're in some
little anti-static bag somewhere. I also have plenty of metal and plastic
housings desposed of by my job, so I could go into limited production. Maybe
sell them for $10 each. Would'nt be fancy, but would be useable.
Is this IC chip capable of handling the current load directly from the
auto volt system, or would i need to buffer it thru a current limiting
device
somehow? As I said, I'm not up on design theory, just like to dabble a bit.
Thanks for any "input" on this subject, I might could even send you one
after
I'm done creating a few of them! :)
Jerry Casper
Tempest repair/production Tech, former X.25 Data Comm Tech...
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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