×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Fuel Guage Anti-Sloshing Circuit

Fuel Guage Anti-Sloshing Circuit

Fuel Guage Anti-Sloshing Circuit

(OP)
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.

RE: Fuel Guage Anti-Sloshing Circuit

Place a large cap across terminals 2 & 4.

RE: Fuel Guage Anti-Sloshing Circuit

Aw melone, you made it too easy for him.

RE: Fuel Guage Anti-Sloshing Circuit

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

RE: Fuel Guage Anti-Sloshing Circuit

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

RE: Fuel Guage Anti-Sloshing Circuit

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)

RE: Fuel Guage Anti-Sloshing Circuit

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?

RE: Fuel Guage Anti-Sloshing Circuit

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources