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0-90ohm fuel sender to xf (volatge) gauge PROJECT

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On 2017-6-2 at 9:20 AM, Stu5766 said:

I had a similar issue when I fitted the mustang tank to the XD.

I used a peel unit interface to convert from ohms to capacitance.

i have a couple of 0-90 units here if anyone is interested.

cheets stu.

I need one that does 2 ohms to 190 ohms which is the value of my new sender unit.

 

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Got this mostly sussed out now. Using an emitter follower amp with discreet components and a 33-240ohm sender as they seem to be most common on eBay. Going to bypass the added complexity of inverting the signal by mounting the float arm backwards (essentially operating the reostat/sender upside down)

The downside is if the sender brakes the gauge will read full. 

Will do a walkthrough once It's complete but I was prototyping the circuit last night and it was working. Uses a 9v supply chip, 2 bjt transistors, 1 pot and 4-5 resistors so it will be well under 10 dollars doos. 

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THIS IS A PROTOTYPE. Function is not guaranteed. There ARE mistakes. I've already noticed a couple.
(zd1 value should be 1n4733 5.1v, Output voltage should be 4.5v when full, not 5.1v. Value of r2 and r7. c1, etc. These things still need finalizing.)

This is about as far as i'll go till till i actually fit it to the car. It's been physically assembled and tested on the bench with a digital x-fal cluster using a pot to simulate the 33-240ohm fuel sender. Works good.
C1... I'm not sure if it will be needed, But im expecting a bit of noise to be generated by the float's rheostat as it bobs around so a sufficiently large cap to dampen transients may be needed.  Note it is drawn wrong in the diagram, It will need to be from Q1 emitter to ground. Not across Q1 Re as showen.
Edit: oh, And ignore the part number on Q1, Q2. that's just default from the software, I'm using BC547.

R4 is just for biasing, adjust as needed. R6 is current limiting if cluster wire is shorted to ground or circuit faults and sends Q2 into saturation.

ZD1 and LED1 is just there for circuit protection. The idea is if the fuel level sensor goes open circuit the gauge will read Full. Assuming your an astute drive, you'll notice you've done too many KM without the fuel level dropping. You can check the box, If the red LED is on BRIGHT, you know something is wrong.

pcLCNbz.jpg

IzglNb3.jpg

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On 30 March 2015 at 9:38 PM, Lord_fahrquhar said:

Testimonials:

 

Unfuckit stopped that whinging Scotsman that he canna get more power. Unfuckit gave us great readings on the level of he dilithium crystals so much so I don't understand why on a fucking starship they used an antique capacitance based fuel gauge

I believe engineers at the time felt it would be more reliable to not use a float with moving parts, but they did not take into account the way fuel changed in chemical composition and the reaction it had on the components, as for my design, primitive yes but functional also. Digital is good too but I fail to see the reason to over engineer the shit out of a fucking Guage interface unit. A capacitor works as well as a timer ic and is cheaper and more than likely avalable as a replacement component for allot longer. Have too big a shed build at the moment going on right now so the old girl is side lined for now safely in a mates garage. Will resume when I finish the build.

 

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6 hours ago, Crazy2287 said:

THIS IS A PROTOTYPE. Function is not guaranteed. There ARE mistakes. I've already noticed a couple.
(zd1 value should be 1n4733 5.1v, Output voltage should be 4.5v when full, not 5.1v. Value of r2 and r7. c1, etc. These things still need finalizing.)

This is about as far as i'll go till till i actually fit it to the car. It's been physically assembled and tested on the bench with a digital x-fal cluster using a pot to simulate the 33-240ohm fuel sender. Works good.
C1... I'm not sure if it will be needed, But im expecting a bit of noise to be generated by the float's rheostat as it bobs around so a sufficiently large cap to dampen transients may be needed.  Note it is drawn wrong in the diagram, It will need to be from Q1 emitter to ground. Not across Q1 Re as showen.
Edit: oh, And ignore the part number on Q1, Q2. that's just default from the software, I'm using BC547.

R4 is just for biasing, adjust as needed. R6 is current limiting if cluster wire is shorted to ground or circuit faults and sends Q2 into saturation.

ZD1 and LED1 is just there for circuit protection. The idea is if the fuel level sensor goes open circuit the gauge will read Full. Assuming your an astute drive, you'll notice you've done too many KM without the fuel level dropping. You can check the box, If the red LED is on BRIGHT, you know something is wrong.

pcLCNbz.jpg

IzglNb3.jpg

 

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Thanks for another idea, though of incorporating a couple of transistors into my design also but the voltages were so close with a simple voltage divider and 7805 reg that I did not bother. The sender unit I am using is not 0 to 90 ohm though. Have written it down somewhere but dont remember right now. It's a factory xg - xh tank and sender unit with pump and all evap system to satisfy those peski engineers which is another discussion I will have at a later date.

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V1.0

X series capacitive fuel level cluster interface to normal resistive fuel level sender.

THIS IS A PROTOTYPE. 
Function is not guaranteed. There are probably mistakes.

This uses a normal emitter follower amp so it is non inverting. When setting up the rheostat on the sender it must read high resistance when full. You can either flip the reostat, or install the float arm on the other side.

If this is not possible you'll need to sort out an inverting stage into the circuit.

It's been physically assembled and tested on the bench with a digital x-fal (Star wars) cluster using a pot to simulate the 33-240ohm fuel sender. Works good. Further testing shows it would work fine with any restive fuel level sender up to about 500ohm, At which stage you'll need to replace R6 with a larger resistance.

R6 sets the output voltage and needs to be configured. Set your fuel level sender to its maximum resistance, or simulate it's max with a potentiometer. Then connect the output to your instruement cluster, or simulate the cluster by placing a 265ohm +-10% resister on the output, to a ground. Then measuring the output voltage, adjust R6 till 4.5v is seen on the output. This is then the gauge will read "Full" (Reminder: This is on a digital cluster, but i assume they are all the same?)

R4 is just for biasing, adjust as needed. It sets the output voltage about 0.5 volts. Adjustment of this value will dictate out much "Reserve" fuel you'll have when the gauge reads empty. It is also dependent on the sender you use.

R5 is current limiting if cluster wire is shorted to ground or circuit faults and sends Q2 into saturation. An 1/2watt resister is needed here as it will pass significant current if Q2 emitter is shorted to ground. 1/4 or 1/8w resisters are sufficient in all other locations.

S1, D1, D2, D3, F1 and C3 are all optional. mainly for circuit safety.

S1 is a momentary test switch, when applied it grounds Q1 base, driving it off, sending Q2 Base high. D3 will illuminate brightly and the fuel gauge will read full. If D3 does not illuminate, the circuit is faulty, or not powered.

D1 is reverse polarity protection (If you wire the circuit in backwards.)

D2 is for voltage limiting, protecting the cluster from overvoltage. If the LED (D3) is illuminated brightly, it's an indicator that the circuit has failed or the sender is open circuit/not connected. If open circuit failure occurs causing the gauge to read full, assuming your an astute driver, you'll notice you've done too many KM without the fuel level dropping. You can check the box and the test switch, If the red LED is on BRIGHT, you know something is wrong.

D3 will illuminate dim, when gauge is full in normal operation, this is leakage currant past D2, to test, press the test switch, if the led gets brighter, then the circuit is operating normally. If intensity is consistent, then there is an error.

F1 id over current protection. The circuit should draw reasonably low current (Up to about 25mA). If something goes horribly wrong, F1 is there to protect the circuit.

C3, I'm not sure if it will be needed, But i'm expecting a bit of noise to be generated by the float's rheostat as it bobs around in the fuel so a sufficiently large cap to dampen transients may be needed.

31404118_976603209159906_813718914859217

 

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