Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Electronic fuel gauge.

Status
Not open for further replies.

stuee

Member
Hi all.
I have just put this fuel sender in my underground boat tank
https://www.wemausa.com/instructions/WEMA_SENDING_UNIT_INSTALLATION.pdf

i would like to make a 10bar led display for it as i have no room for a gauge.
I have been reading a little about the lm3914n controller to a 10bar led. (i have purchased both)
i now need to know how to hook this up if someone could assist me (the boat is using a standard 12v deep cycle battery)

thanks in advance.
stuart
 
ok, not sure if i was doing something wrong but i connected to my multimeter with it disconnected from the power, i set to 2000k and it hovered around 700-820?
 
Ok lol, it was still connected neg on the battery that must have been causing odd reading.

it now ready 243ohm empty
 
That would do it. I at least knew what half-full and half-empty were. :D

So, it makes things a bit more complicated. You need to invert and offset as well.
 
It would have been easier if you had a sensor that went the other way 30 (empty) to 240 full.

I hope someone comes along and helps because I'm extremely swamped with real work. I hang around here to relax, bedtime or whatever. I should be sleeping right now.

I.m not too familiar with the bar graph display, but a constant current source, say 10 mA across 240 ohms would be 2.4 V. A part such as this (AD8226) https://www.analog.com/en/specialty...ation-amplifiers/ad8226/products/product.html can invert by switching the input leads. By applying a reference of 2.4V, the output would be zero. (assuming a gain of 1). But, the offset needs to be a little lower than that. 0.01*20 or 0.2 V lower.
So, now you have a signal that's 0 to 2.2 V. (which isn't likely the right number)

This is just an example and not design equations, but it uses simple numbers to get the point across. Many IA's (Instumentation amps) nned to be driver with a low impeadance source (not sure about this amp). 2.5 is a standard reference voltage, otherwise that may have to be variable and buffered. The LM431 might be a good choice here: https://www.google.com/url?sa=t&rct...Nb3WsPEx8KXVyz9vZ0GYexQ&bvm=bv.77161500,d.b2U

You may need an OP amp to buffer the reference.

The LT3086 https://www.google.com/url?sa=t&rct...RVGD3t77CWkkcWsXl-jZtNQ&bvm=bv.77161500,d.b2U might not be a bad choice for a current regulator.

So, tweaking the current source adds gain. I didn't take into account lots of things. I didn;t look at the LM3815, for instance. I just assumed 0-2.2 V.
The "other" components aren't covered for power supply protection and/or regulation or the possible selection of a buffer amplifier.

You can get www.proto-advantage.com to mount a surface mount package to a DIP header that they make.

So, a lot more work.
 
I think this can be done without opamp and voltage reference . LM3914 has a voltage reference.
It's output and offset can be programmed with a few resistors.
If the fuel sender is the upper part of a voltage divider the voltage from the divider will move in the right direction.
You need a voltage regulator, maybe 8V, to which the voltage divider will be connected.
 
The instructions for the sender say:
Connect ground (pink) wire from the WEMA sending unit to a common grounding hook-up.
Connect (black) wire from the WEMA sending unit to gauge hook-up. If your gauge has color coded hook-ups, maintain this coding as you connect the sender and ground wires.
Can you confirm that both the pink and black wires of the sender are (or can be) electrically isolated from any metal-work (sender body or tank)? This would be necessary to adopt the approach suggested by Jjw.
 
Last edited:
For safety you will need a high value resistor in series with the sender and measuring circuit, also you might need to look at the reference voltage supply to the sender too, if theres a short you do not want a spark, or glowing resistor track.

You might also find the sender isnt linear, take some resistance measurements with the float in 10 equal positions from empty to full, to see if they are linear, or at least give you some idea of the non linearity.
 
Below is a circuit using the LM3914 with the sensor grounded. This circuit assumes the resistance changes fairly linearly from empty to full. An op amp is used to invert and scale the signal so that minimum resistance (tank full) gives maximum voltage to the LM3914.

R8 and R9 may need to be adjusted for the full scale and offset voltage going to the LM3914 input to give the desired readout.

R3 determines the LED current which is about 20mA for the 620 ohm value shown.

Gas Gauge.gif
 
thanks for all your replies,
I have checked the continuity and neither are connected to the metal mount.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top