In most cars the fuel level is measured by a floater connected to a potentiometer and it's quite likely that the panel is reading an analogue voltage signal coming from the fuel sender unit.

What would be the cheapest way to read that voltage, then send it via WiFi to a listening unit. (the listening unit is already finished and awaiting implementation)

I'm looking for a permanent solution, something that can be placed in the vehicle with an autonomous battery (or connected to the car battery).

Please keep in mind that i'm not an Electrical Engineer, i'm a software engineer with a hobby in this area, but i've never done anything this complex before, so if you can point out ideas or components used that be great. Fuel Tank pump

^^That is the fuel tank pump.


closed as off-topic by Dmitry Grigoryev, vini_i, laptop2d, duskwuff, Peter Smith Dec 18 '16 at 14:32

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  • \$\begingroup\$ The electric imp would serve your needs. It will require some electronic tinkering because the voltages won't match and it needs a break out board but the WiFi is effectively taken care of. sparkfun.com/products/11395 \$\endgroup\$ – vini_i Dec 14 '16 at 19:26
  • \$\begingroup\$ Great device, but I'm looking for a cheaper <$10 solution, one build it yourself kind of thing is always cheaper. \$\endgroup\$ – RonEskinder Dec 14 '16 at 19:47
  • \$\begingroup\$ Do you also want it to slice and dice? Easy to implement solutions are going to be more expensive. If you want to get true WiFi, this is the cheapest solution. \$\endgroup\$ – vini_i Dec 14 '16 at 23:45
  • \$\begingroup\$ Already found a $2 solution below... but thanks for the cheers \$\endgroup\$ – RonEskinder Dec 15 '16 at 16:03

You can use an ESP8266. It takes care of the Wifi and has a suitable ADC (10-bits which is more than good enough for gas tank level).

The level sensor (aka 'sender' in automotive parlance) will be something like a low resistance rheostat. Getting specs on it may be challenging or you could just test one. You will need a small bit of circuitry between the two.

  • \$\begingroup\$ I've been reading about the ESP8266, it comes with a wifi module and that solves the communication between Car and Server, but im kind of lost here, for instance, how do you power the ESP8266 inside the car? i've saw some tutorials on LiPo batteries but only seem to last about a day or so (maybe recharge from the car itself), also about the "low resistance rheostat" can you give me a link to that, i couldnt find anything on ebay/ Can you send a diagram of the connection between all the elements? thanks \$\endgroup\$ – RonEskinder Dec 15 '16 at 2:17
  • \$\begingroup\$ They run on 3.3V at a couple hundred mA peak (much less average typically). So it would make send to use a 12V:3.3V switching power supply. The sender characteristics would need to be researched before that part could even be approached. Automotive power supply design is a bit complex as the electrical and temperature environment can be challenging. We don't really do whole designs here- way too much like real work, I'm afraid. \$\endgroup\$ – Spehro Pefhany Dec 15 '16 at 5:56

There are very common circuits using LMC555 chips that convert a resistance value into a varying frequency square wave, or a square wave whose pulse width varies with resistance. Very simple - one chip and a few resistors and capacitors. The circuit below shows a version that has constant frequency, but varies duty cycle by varying resistor R1 and/or R2:
pulse width varies with resistance555 pulse width modulator circuit
The pulse output then drives a radio frequency transmitter...when the pulse is "high", the transmitter is on, when the pulse is "low", the transmitter is off. A companion radio receiver provides a similar logic output (high & low) that is very easy to connect to a single-bit input port of a microcontroller, computer or other digital input. These RF modules implement "on-off-keying" (OOK), like morse code:RF transmitter, receiver
It should be very easy to write microcontroller code to determine pulse width of the receiver's signal, or determine pulse duty cycle, and convert that to something more useful (like a fuel display).

  • \$\begingroup\$ This is a good implementation, im taking a ESP8266 Serial WIFI Wireless Transceiver + Voltage Divider sensor for arduino, and try to make them work together, thanks for the idea! \$\endgroup\$ – RonEskinder Dec 15 '16 at 15:43

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