LM3915 as LED fuel gauge?
Electronics Forum Index Electronics
Circuits, theory, electrons and discussions.
 
 FAQFAQ   MemberlistMemberlist     RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
 
Google
 
Web ElectronicsHelp.net
LM3915 as LED fuel gauge?

 
Post new topic   Reply to topic    Electronics Forum Index -> Basics
Author Message
Glenn Ashmore
Guest





Posted: Thu Feb 03, 2005 1:25 am    Post subject: LM3915 as LED fuel gauge? Reply with quote

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

Back to top
petrus bitbyter
Guest





Posted: Thu Feb 03, 2005 3:04 am    Post subject: Re: LM3915 as LED fuel gauge? Reply with quote

"Glenn Ashmore" <gashmore@cox.net> schreef in bericht
news:mO9Md.113838$Wo.54030@lakeread08...
Quote:
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 Andy´s 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
Back to top
Glenn Ashmore
Guest





Posted: Thu Feb 03, 2005 5:36 am    Post subject: Re: LM3915 as LED fuel gauge? Reply with quote

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@reducespamforchello.nl> wrote in message
news:SfbMd.77134$PH1.68849@amsnews05.chello.com...
Quote:

"Glenn Ashmore" <gashmore@cox.net> schreef in bericht
news:mO9Md.113838$Wo.54030@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 Andy´s 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



Back to top
 
Post new topic   Reply to topic    Electronics Forum Index -> Basics All times are GMT
Page 1 of 1

 
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum



Home & Living New Topics
Powered by phpBB