Hi!
Kind of a noob question, but after thinking about this for a couple of hours I am stuck, and really would appreciate some input from others.
Scenario: I have an existing tank level sender and analog gauge. The analog gauge is fed +12V when the start key is in position 1. I want to digitally be able to determine the tank level regardless of the start key position. I don't want the analog gauge to show a incorrect tank level when engine is running. (See attached illustration)
The basic idea is to get a high level reading of the current flowing through the circuit based on the variable resistance in the tank sender, and there by calculate the tank level.
How would YOU complete the circuit to get the desired result, and why?
I'd just create a voltage divider based on 20V. Supply the divider with the sending units voltage, send the tap to an analog in, and convert to a tank reading of some sort.
I'd find what the full reading is and the empty reading is from the sensor to develop a range of values to depict the various fuel levels.
If you want you can bypass the switch and feed 12V all the time to the sensor, which will help drain the battery quicker.
Idahowalker:
I'd just create a voltage divider based on 20V. Supply the divider with the sending units voltage, send the tap to an analog in, and convert to a tank reading of some sort.
I'd find what the full reading is and the empty reading is from the sensor to develop a range of values to depict the various fuel levels.
If you want you can bypass the switch and feed 12V all the time to the sensor, which will help drain the battery quicker.
The why is your part of the assignment.
Thanks, but that was also my initial idea. The problem is that the voltage divider would influence the gauge. The idea to use a INA219 was to measure the current with minimal influence over the gauge. I'm just confused how to connect the VIN-/VIN+ the best way.
bluejets: How would YOU complete the circuit to get the desired result, and why?
Sounds like homework question to me........
I just didn't want to influence you with my thoughts and ideas as I'm not at all sure that they are correct. There are devices like this, and I want to understand how they work. For example see Tank Adapter: Connect resistive type fluid level sensor to NMEA 2000 (yachtd.com)
I guess that they are reading the current that is flowing through. Could anyone confirm that the attached setup would give me the correct result?
I doubt it.
If you take the time to see how the INA219 works , and there are spec sheets out there that explain everything, then the first thing you would see is a shunt resistor.
This is currently now connected ....where...?
The simplest method to measure the fuel level was laid out in post #1. You don’t need an INA219, just some resistors. But then there is a larger problem with your original post:
I want to digitally be able to determine the tank level regardless of the start key position.
So if the key is off, there is no voltage or current to measure. I’m not sure if you have overlooking that fact or you’re ignoring it. Which is it?
There is of course the resistance of the sender. But the INA219 is current and voltage measurement sensor. See the problem yet?
anho:
I just didn't want to influence you with my thoughts and ideas as I'm not at all sure that they are correct. There are devices like this, and I want to understand how they work. For example see Tank Adapter: Connect resistive type fluid level sensor to NMEA 2000 (yachtd.com)
I guess that they are reading the current that is flowing through. Could anyone confirm that the attached setup would give me the correct result?
Quote from: anho Sun Mar 28 2021 06:45:49 GMT+1100 (Australian Eastern Daylight Time)
Unfortunately it won't work the way you want it to.
Here is the equivalent circuit of the 1NA219, it is a very low value resistor, so all you will be doing is bypassing current around the gauge and not measuring the current through it.
Thanks for clarifying!
The best idea I have had so far is to do it like this:
When doing a reading (Every hour or so), if voltage measurement of INA219 is zero (start key is in position 0), I pull a relay (on the right) to get power flowing through the circuit, and then do the current reading, and finally release the relay. If power is there (start key in position II), just do the current reading. Not a very elegant solution as I probably will get somewhat different measurements if the start key is position I or II, but I guess it would be possible to correct that in software.
JCA34F:
Are you saying the fuel gauge does not work with the engine running?
It is only working when the ignition is on or engine is running. I want to be able to digitally do measurements of the tank level even if no key is in the ignition. But when the ignition is on, or the engine is running, I also want to be able to do measurements.
I realize it sounds a bit like having the cake, and eating it too, but I'm confident that there is a solution for that somewhere out there..
WattsThat:
The simplest method to measure the fuel level was laid out in post #1. You don’t need an INA219, just some resistors. But then there is a larger problem with your original post:
So if the key is off, there is no voltage or current to measure. I’m not sure if you have overlooking that fact or you’re ignoring it. Which is it?
There is of course the resistance of the sender. But the INA219 is current and voltage measurement sensor. See the problem yet?
Of course there would need to be power flowing through the circuit. I intentionally left some parts out to see what possible solutions people could come up with. I can't say that I am very experienced with electronics or that familiar with voltage dividers, but wouldn't a 1.3KOhm resistor mess up the reading of the analogue gauge? Perhaps I have misunderstood voltage dividers somehow?
Actually not bad at all.. My first thought was that it would be an "ugly" solution as it would trigger the gauge, and that it would require a lot of cabling, but when i give it a second thought it actually could be quite neat. No different current whenever engine is running or not, and only a few wires. Thank you! I will give it a try.
