Thread: Flex-fuel sensor output

After ordering a GM-style flex fuel sensor (New Flex Fuel Sensor Fit for 2012 Cadillac SRX 13577379 1219900737 | eBay), I realized that these output 50hz-150hz depending on ethanol content

In NismoTronic, the "Flex Fuel Fuel Trim" seems to accept a 0-5V signal (via breakout board)


I need to modify the hz signal to an linear analog voltage right? Already dusting off my arduino...

I'll modify this thread into a how-to when I get the hardware..

this seems like a decent solution for you if you allready have a flex fuel sensor.

flex fuel ? Dynosty

Yes, it is a 0-5 volt input for the ADC.

The V2 NEMU, which will be released shortly will have the hz to voltage converter built into the board so you can wire the flex fuel sensor directly to the board.

But for now, you will need to use a simple converter.

The Arduino will work as I built an LCD gauge a few years ago using on that converted the hz to voltage and then displayed ethanol content. So you are on the right track!

I was looking at these

Zeitronix ECA : SEMA Award Winning Ethanol Content Analyzer and Flex Fuel Sensor for E-85 and E-85/gasoline Blends

I am also in the market for a 50Hz-150Hz to 0-5v converter. After looking around I found a guy from sweeden on the FRS forums is very close to releasing an open source board that does exactly what you are looking for Dala.

He states that he will release the source code, componet list and wiring diagrams in the near future. He will also sell boards pre-maid.

It is a very cool little device and also has a bluetooth output with an adroid app to check your sensors voltage so you know what percentage of fuel is in your tank.

Opensource Flex-Fuel Ethanol Content Analyzer with Bluetooth - Scion FR-S Forum | Subaru BRZ Forum | Toyota 86 GT 86 Forum | AS1 Forum - FT86CLUB

I am currently programming, watch this space in 3 hours.

There are great solutions ready to be purchased, but they all cost a significant amount of money. Let's crack out the microprocessor!

Fiddling with my old ATMega644p, this is how it looked last time I used it.


Constructing a program atm, but I have some issues, will post updates when I get something I can show you

Development continues, but after thoroughly reading the datasheet I've come to the conclusion that the Atmega644p cannot handle D/A conversions, only A/D...

I wanted it to function like this:


I need to do some more testing, and source an external D/A converter. EDIT: Hmm, maybe I could use a PWM output, to simulate a voltage output. If that doesn't work on it's own, I will try to add a simple RC low pass filter.. Hmm..

Lots of info on PWM as D/A converter here: https://www.google.com/search?q=D%2FA+with+PWM&ie=utf-8&oe=utf-8

This piece of engineering arrived yesterday:


Time to start programming. I simulated a PWM output, and sampled it back into the microprocessor. You NEED an oscilloscope for this!


No flex sensor hooked up yet, only simulated in/out


I will share the code (for an Atmega 644P, but easy to convert to other microprocessors) once I have it on the car, and I'm 100% sure there are no bugs. I am using OC0A (PinB3) for PWM output (0-5V). OC1A (PinD5) is used for 50-150Hz input.


Once the flex fuel sensor is connected (to the return fuel line), and works, I'll share the code.

Stay tuned!