LM3915 as LED fuel gauge?
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From: Glenn Ashmore on 2 Feb 2005 14:25 I want toadd a set of gauges to my fuel management system. It will require one for each tank and 3 standard gauges take up to much room and cost a bunch so I am going to DIY it. Follow me through on this: The sender is a variable resistor with a range of 240 Ohms empty to 33 Ohms full. If I put a 240 ohm resistor in series with the sender, feed it 3.3V and measure the voltage across the 240 Ohm resistor I will get a voltage from 1.65V empty to 2.9V full. That is a range of 1.25V in a more or less logarithmic curve. If I feed this voltage to an LM3915 LED driver I can display the tank levels on a 10 segment LED array. There is only one problem. How do I set the zero to 1.65V? -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com
From: petrus bitbyter on 2 Feb 2005 16:04 "Glenn Ashmore" <gashmore(a)cox.net> schreef in bericht news:mO9Md.113838$Wo.54030(a)lakeread08... >I want toadd a set of gauges to my fuel management system. It will require > one for each tank and 3 standard gauges take up to much room and cost a > bunch so I am going to DIY it. Follow me through on this: > > The sender is a variable resistor with a range of 240 Ohms empty to 33 > Ohms > full. If I put a 240 ohm resistor in series with the sender, feed it 3.3V > and measure the voltage across the 240 Ohm resistor I will get a voltage > from 1.65V empty to 2.9V full. That is a range of 1.25V in a more or less > logarithmic curve. If I feed this voltage to an LM3915 LED driver I can > display the tank levels on a 10 segment LED array. > > There is only one problem. How do I set the zero to 1.65V? > > -- > Glenn Ashmore > > I'm building a 45' cutter in strip/composite. Watch my progress (or lack > there of) at: http://www.rutuonline.com > Shameless Commercial Division: http://www.spade-anchor-us.com > > Use an opamp to subtract the 1.65V. An old CA3140 will do. VCC + | +-+-------+----------------+ | | | .-. .-. | ___1k | |33- | |10k +-----|___|-+ | |240 | | | | | '-' '-' | | | | | 1k ___ | |\| | | +-----|___|--+-|-\ | out | | | >------+---- +----------------------|+/ CA3140 | | |/| | | | .-. .-. | | |240 | |10k | | | | | | '-' '-' | | | | ++-------+----------------+ | === GND created by Andyýs ASCII-Circuit v1.24.140803 Beta www.tech-chat.de If your environment is noisy you can reduce the 10k resistors and/or put an elco 1-10uF parallel to the lower 10k. You can make a zero adjust with a 100-220 Ohm trimpot between the two 10k resistors, its tab to the 1k input resistor of the opamp. petrus bitbyter
From: Glenn Ashmore on 2 Feb 2005 18:36 Thanks. That should work and not be effected by minor supply voltage variations. -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com "petrus bitbyter" <p.kralt(a)reducespamforchello.nl> wrote in message news:SfbMd.77134$PH1.68849(a)amsnews05.chello.com... > > "Glenn Ashmore" <gashmore(a)cox.net> schreef in bericht > news:mO9Md.113838$Wo.54030(a)lakeread08... > >I want toadd a set of gauges to my fuel management system. It will require > > one for each tank and 3 standard gauges take up to much room and cost a > > bunch so I am going to DIY it. Follow me through on this: > > > > The sender is a variable resistor with a range of 240 Ohms empty to 33 > > Ohms > > full. If I put a 240 ohm resistor in series with the sender, feed it 3.3V > > and measure the voltage across the 240 Ohm resistor I will get a voltage > > from 1.65V empty to 2.9V full. That is a range of 1.25V in a more or less > > logarithmic curve. If I feed this voltage to an LM3915 LED driver I can > > display the tank levels on a 10 segment LED array. > > > > There is only one problem. How do I set the zero to 1.65V? > > > > -- > > Glenn Ashmore > > > > I'm building a 45' cutter in strip/composite. Watch my progress (or lack > > there of) at: http://www.rutuonline.com > > Shameless Commercial Division: http://www.spade-anchor-us.com > > > > > > Use an opamp to subtract the 1.65V. An old CA3140 will do. > > VCC > + > | > +-+-------+----------------+ > | | | > .-. .-. | ___1k > | |33- | |10k +-----|___|-+ > | |240 | | | | | > '-' '-' | | | > | | 1k ___ | |\| | > | +-----|___|--+-|-\ | out > | | | >------+---- > +----------------------|+/ CA3140 > | | |/| > | | | > .-. .-. | > | |240 | |10k | > | | | | | > '-' '-' | > | | | > ++-------+----------------+ > | > === > GND > created by Andyýs ASCII-Circuit v1.24.140803 Beta www.tech-chat.de > > If your environment is noisy you can reduce the 10k resistors and/or put an > elco 1-10uF parallel to the lower 10k. You can make a zero adjust with a > 100-220 Ohm trimpot between the two 10k resistors, its tab to the 1k input > resistor of the opamp. > > petrus bitbyter > >
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