Fuel Guage Anti-Sloshing Circuit

[lovelesspl]

I am looking for a circuit that will provide the fuel gauge with a delayed reading. Several new cars have this and I was wanting to build one for my car. The one I have heard of are based on an opamp and a few transistors. They normally have 4 wires. This is to keep the fuel guage from eratically jumping around.

1.)Voltage in: Normally 10-12 volts DC
2.)Input from fuel sender: Range 0-90ohms 0=empty 90=full
3.)output to fuel gauge
4.)Ground


If anyone could help me with a circuti for this I would appreciate it.

 

[melone]

Place a large cap across terminals 2 & 4.

 

[Lewish]

Aw melone, you made it too easy for him.

 

[lovelesspl]

What value of capacitor would be sufficent? A single capacitor seems to easy!

 

[melone]

play with it and see what works best. becareful to supply a charge/discharge path for power on/off conditions.

 

[DeanBanks]

The capacitor approach may or may not work. Most fuel senders actually sink a reasonable amount of current out of the fuel gauge (can't remember now, but it's somewhere between 20 and 100mA). Most gauges are current-driven, not voltage driven, so you may need to reconsider your other circuit, which I expect creates a voltage divider out of the fuel sender, creates a lowpass filter with the op amp, then creates a variable current sink with the transistors to drive the gauge.

Remember: the advantage of a 'real time' fuel gauge is that when your tank is almost completely empty, you can stomp on the brake and look for the fuel slosh on the gauge. With a low pass filtered gauge, you lose that reserve! (grin)

 

[carnage]

then go with three supercaps in series. (to make it not so easy) they are 1f at 5V and are becoming common to replace bios batteries. they recharge everytime the computer is turned on.
three in series is 1f at 15v and three in paralell is 3f at 5v, or have I forgotten how they add?

 

[peebee]

Any low-pass filter will do it. Using the capacitor circuits discussed above, the time constant will be equal to RxC where R is the resistance of the meter and C is the size of the shunt capacitor (the resistance of the source may also need to be taken into account if it is roughly equal to the meter resistance, but that is unlikely). If you need to, you could add resistance to the circuit, too.

The break frequency (the frequency at which the output is reduced by 3dB or approximately 50%), is 1/RC.

There's LOTS of information on RC filters available all over the net.