Nitro low fuel warning experiment!

One of the things that bugs me slightly with my nitro cars is the very limited warning you get when they are about to run out of fuel. As it starts to suck air into the tank you get the surge of power as it runs lean but that only  gives you a few seconds to point it back in your direction and come off the throttle before the fuel is used up completely.

What I want is some way of knowing 30 seconds or so before the tank is dry to give me time to bring the car fully back to where I am standing or give me the option of a quick splash and dash with the fuel while the engine is still running.

For my work I have used some simple PIC circuits to monitor the levels of liquids and so I thought... why not try one in my RC car!

Previously I have been using the circuits to monitor water levels using two probes. For this application the system would be looking for a small current flow between the probes. The probes themselves will be positioned with one touching the bottom of the tank, the other around 5mm from the bottom. The idea being that once the fuel drops below this 5mm level the current flow will be lost and the circuit will flash some LEDs and sound a buzzer. All well and good in theory but will it work?

To find out I setup a simple test circuit using an 18-pin PIC circuit board. I don't need all of the functions of the 18-pin but decided that I wanted as many LEDs flashing as possible for the test.

Here is the board I used-

and here it is populated with the test components...

I still need to add on a suitable power source, which currently I'm thinking will be a 3 cell AAA NiMh pack or 2 cell lithium, and the probes themselves which for the purpose of the test will simply be 2 lengths of wire with the ends stripped bare.

I'll run the circuit as it is simply placed in either my RS4 or Hyper 12 and if it works I'll look at making it a more permanent solution with a case and off board LEDs, maybe even integrate them into the shell in some way. What I would like to do with the RS4 eventually is add some rally spot lights which are illuminated but then flash when the fuel level drops.

Anyway, lets see if it works first!