JOB OFFER: Automotive Application

[VlaDeMaN]

hi everyone,

i'm in a bit of a time bind and i need help building a box to remedy a problem i have with my car. I only have until march 14th.

Fuel Level reads 0-50ohm (empty to full) for a 12V fuel gauge.

Motor was swapped and new car computer (ECU) needs to read fuel level as well, but it needs 50-250ohm over 5V signal.

I need to split fuel level sender into 2 outputs: #1 for the fuel gauge, as the sensor reads it, and #2 for the ECU, as a ratio of the sensor resistance, unless you have a better idea.

I can put it all together but I need the design and programming. I already have an arduino which i think could be helpful, but not sure what else I will need.

Let me know your $ requirement.

Thanks!!

 

[4pyros]

hi everyone,

i'm in a bit of a time bind and i need help building a box to remedy a problem i have with my car. I only have until march 14th.

Fuel Level reads 0-50ohm (empty to full) for a 12V fuel gauge.

Motor was swapped and new car computer (ECU) needs to read fuel level as well, but it needs 50-250ohm over 5V signal.

I need to split fuel level sender into 2 outputs: #1 for the fuel gauge, as the sensor reads it, and #2 for the ECU, as a ratio of the sensor resistance, unless you have a better idea.

I can put it all together but I need the design and programming. I already have an arduino which i think could be helpful, but not sure what else I will need.

Thanks!!

I think you would be better off posting in general electronics chat.
Mod please move.

 

[VlaDeMaN]

figured this was the right place, i forgot to mention i'm willing to pay

 

[4pyros]

Your header looks like you are applying for an automotive job.

 

[alec_t]

Fuel Level reads 0-50ohm (empty to full) for a 12V fuel gauge.
Motor was swapped and new car computer (ECU) needs to read fuel level as well, but it needs 50-250ohm over 5V signal.

A single sender unit can't have both a 0-50 Ohm range AND a 50-250 Ohm range.
Which range will you use?
Is your gauge a crossed field (twin coil) type or a bimetal type?

it needs 50-250ohm over 5V signal.

?? Does the ECU actually expect a signal in the 0-5V range linearly related to the 50-250 Ohm variation?

 

[VlaDeMaN]

i believe it is a bimetal type.

i'm aware the sender won't have a dual resistance. i need to use BOTH ranges for TWO different devices, which is why i was suggesting an intermediary controller, such as arduino.

 

[4pyros]

A single sender unit can't have both a 0-50 Ohm range AND a 50-250 Ohm range.
Which range will you use?

I think you need to keep the existing fuel gauge system and tap off of it and convert it for the new ECU. Right?

 

[VlaDeMaN]

I would rather start the split right at the sensor, instead of tapping it at the gauge... mainly because i already ran a harness lol.

i have to confirm the type of gauge, because if it is a bipole then i should expect some decent current running thru it, right? because such current may not be supported by a controller? thinking out loud over there.

 

[KeepItSimpleStupid]

Fuel Level reads 0-50ohm (empty to full) for a 12V fuel gauge.

No way can this be a 12 V gauge. I = 12/Zero blows up. That also means ~2.9 W minimum power: 12*12/50 from P= V^2/R.

It can be 0-50 ohms, but it can't have 12 V across it.

 

[picbits]

It can have 12 volts across it but it is current limited (fed through a resistor) at the dashboard. When the sender is open circuit they can quite often read 12 volts.

You can either modify that dashboard with an appropriate current limiting resistor to suit depending on the dashboard or use something like a microcontroller driving a MOSFET in a closed loop to emulate the 50-250R based on the output from the existing fuel gauge. I managed to emulate something similar using opamps for a specific application but didn't test it on a vehicle in the end.

I've done both successfully but both on a commercial basis so I'm not at liberty to share any schematics I'm afraid.

 

[VlaDeMaN]

that's what my idea basically was, a micro controller working an input to the right output. I wouldn't imagine sharing schematics would be necessary, this doesn't seem like that big of a deal if you know what goes where... right?

 

[picbits]

Basically PWM from the microcontroller based on a ratio from the input voltage, convert this to a DC voltage using a simple RC filter then use an opamp to drive a mosfet to ground the dashboard signal to a level appropriate to the second dash reading.

I can't say much more than that and it will only work on dashboard with a regulated feed to the gauges (i.e. gauges which form a potential divider). Some dashboards don't use a regulated supply for the gauges and compensate for any vehicle voltage running differences internally.

 

[VlaDeMaN]

i thought it would be easier to put the controller before the gauge, so i wouldn't have to worry or work around the gauge's personality because the fuel sensor is just a simple resistor.

 

[alec_t]

Why does the ECU need to know the fuel level? Isn't just the presence of fuel sufficient information? I was under the impression that these days the fuel gauge had its own micro which checked the sensor and received pulses from the ECU indicating instantaneous fuel injector consumption.

 

[picbits]

i thought it would be easier to put the controller before the gauge, so i wouldn't have to worry or work around the gauge's personality because the fuel sensor is just a simple resistor.

There isn't an easy way to emulate a simple resistor though - you can use digital potentiometers but they are very low current compared to the currents that get passed through the fuel sensors (the old Vauxhall Astra GTE shoved 200mA short circuit current through the tank sender)

 

[VlaDeMaN]

Why does the ECU need to know the fuel level? Isn't just the presence of fuel sufficient information? I was under the impression that these days the fuel gauge had its own micro which checked the sensor and received pulses from the ECU indicating instantaneous fuel injector consumption.

Typically nowadays the ECU reads everything and the dash is connected to the ECU via serial. I need the ECU to know fuel level in order to begin operating EVAP. It's a legality thing too. I could very well bypass and remove the programming completely, but in this case, factory programming reads level constantlyish, and I can't modify anything. Has to work as factory.

There isn't an easy way to emulate a simple resistor though - you can use digital potentiometers but they are very low current compared to the currents that get passed through the fuel sensors (the old Vauxhall Astra GTE shoved 200mA short circuit current through the tank sender)

I noticed digital pots do have low current and less than ideal, but acceptable, resistance steps and ranges. Is it possible to hook up multiple pots in series or parallel? i'm unfamiliar with the effects it would have.

 

[KeepItSimpleStupid]

Well, just saying: You can use a fixed resistor for the fuel tank sensor to get through inspection (Maybe, unless the ECU is super smart). If that's what the deadline is,

Below 200 ohms it's probably a bit harder to emulate. I have a project on the back burner where I want to emulate a much higher and nonlinear resistance.

 

[VlaDeMaN]

yeah, the referee is cool too, but he's not too hot on doing that. i just didn't want to cheat on this one, wanted to be legit because I also want to share the results and process. LS1 in an S14, done before, never legal in Cali.

 

[KeepItSimpleStupid]

There are some measurements that won't hurt.
ECU
Open circuit voltage (I'm assuming 5V)
With a 50-250 ohm potentiometer (50 ish ohms in series with 200 ohm pot) see what the range of voltage is.
Adjust so voltage is 1/2 and measure the resistance of the POT out of circuit.

You kinda also have to do a similar thing and simulate the "original gas gauge sensor" with the gas gauge.
Pay some attention to linearity

 

[shortbus=]

I know you want to do it yourself, but, what is your time and car worth? Is it worth burning up the wireing harness and possibly the car? Is it worth more than the cost of one of these?
http://docskustom.com/shop/viewcategory.php?groupid=38