I got my prototype circuit boards and have done a little testing. I have trim pots to calibrate the circuit (no software) to set the gauge needle on the full line with 0% duty cycle and the empty line with 100%. The gauge shows 1/4 full with 46.1% duty, 1/2 full with 25.4% and 3/4 full with 12.3%. I was hoping the half full would be 50% so the duty cycle would be a linear function.
Now I'm going to try my second fuel gauge and see if those values hold pretty close.
After I finish the gauge driver testing, I will start testing the sender tests. Then I have to start writing software to link the two (sender and driver). I will probably just have some tables for the link since I'm using a basic micro without complex math functions.
FYI: The gauge has a lot of filtering itself. It takes about 30 seconds to move the needle close to match the duty cycle. The readings near full seem to have more filtering (takes longer). It still will take software filtering to prevent "gas slosh" from moving the needle. It would take a longer filter to prevent a 5 or 10 minuet hill climb or hill drop moving the needle. Not sure how much filtering will be best for most users.
I ran my circuit on the other spare fuel gauge I have. This gauge does not quite hit empty with zero ohms on the sensor input. The other gauge did go a little below the empty line. There is nothing I can do about that gauge not hitting the empty mark (it's really close).
One other thing is the resistor on the back of the first gauge is Yellow and it's resistance is 88.45 ohms. The second gauge the resistor is Green and it's resistance is 90.84 ohms. The resistor goes from the +12 pin to the sensor pin. So as expected after I swapped the resistors all it changed the full scale position a little bit.
Anyway the second gauge read a little lower (about a needle width) then the first gauge at the 3/4, 1/2 and 1/4 marks driving the same duty cycle as the first gauge was tested.
So with test of two units so far it seems the sensor would just need an offset calibration to bring it reading the same as the first gauge.
I had to delay work on this new project since this last month a flood of orders of my other products came in. I had to build up my depleting inventory.
Anyway I bought a new daily driver. A 2018 Toyota Camry. One thing I note on it's gas gauge is after I fill up the needle is maxed about two needle widths above the full line. Then it stays at that point until 105 miles average 35.8 MPG. So it looks like the fuel senders all max out at full way before the tank is topped off. I guess you would need a tank with an indent so the sender can just max out when the tank is really full.
Maybe car companies did this to avoid customers from feeling like they have to absolutely top off the tank every time to get to the full line. I have an original sender in mine and it's VERY rare (or difficult) that I get it on the Full mark if I fill the thing up completely. I think the tube style sender usually has some air trapped above the float to where the float will sit just below full extension. I don't think this is an issue at all with modern swing arm floats their movement isn't physically damped by air anyways. It would be great if users could determine their full point based on their "full" tank sender position.
Originally Posted by Bitsyncmaster
I had to delay work on this new project since this last month a flood of orders of my other products came in. I had to build up my depleting inventory.
Anyway I bought a new daily driver. A 2018 Toyota Camry. One thing I note on it's gas gauge is after I fill up the needle is maxed about two needle widths above the full line. Then it stays at that point until 105 miles average 35.8 MPG. So it looks like the fuel senders all max out at full way before the tank is topped off. I guess you would need a tank with an indent so the sender can just max out when the tank is really full.
I have been able to get some time to do work on my circuit. I have production boards arriving next week and have the software finished to deliver one unit to my most critical customer. This customer is using a Bosch pump unit that has a 250 ohm full to 40 ohm empty sender. So this unit is designed for that unit only. I think other senders will be no problem to implement but I plan so far to only ship the units with one sender operational. The software and a few components will need to be changed to use some other senders.
I came up with a double type of filtering of the fuel gauge movement. First is I filter the sender readings by taking 256 readings spaced at a software timing interval. Then that summed result is divided by 256 to get the average. Then I only let the gauge move one step each time I get the sender average. The gauge has 256 steps from empty to full.
The low fuel light I have set to come on at 1/8 tank level.
I was looking at senders and it looks like the most common one is 33 ohms full and 240 ohms empty. That sender should only take a simple software change. I think the DMC pump combo uses that sender.
I have an extruded aluminum box the circuit board slides into. I think I will just have the 5 wires exit one end of that box so the user will have to splice some wires. Where the box gets mounted will be up to the user. I think if it's mounted near the tank you would need to use the pump voltage to power my box or run a new 12 volt power wire to that location. The problem with the pump power is it only has power when the engine is running (and has a lot of electrical noise). I like the idea of seeing the fuel level before starting the engine.
Last edited by Bitsyncmaster; 12-21-2018 at 07:02 PM.
I was wondering the way you install your pump (orientation), if that affects the fuel sender. I guess the bottom of our tank is level so it would only matter if the sender float was at the rear or front if your tank shows full going up a hill or down.
I was wondering the way you install your pump (orientation), if that affects the fuel sender. I guess the bottom of our tank is level so it would only matter if the sender float was at the rear or front if your tank shows full going up a hill or down.
Dave M vin 03572
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Originally Posted by Bitsyncmaster
