I have created a little gadget, based on a tiny single chip
that will read the value from the sender, look it up in a user
programmable table, and drive the gauge to the desired reading.
As a DeTomaso Pantera owner, I'm "blessed" with italian
Veglia gauges, connected to american Ford senders. Neither of which are
particulary high quality.
To solve the problem with inaccurate readings, extremely dark
illumination, glass fogging, I decided to replace all of the small
gauges with higher quality VDO gauges and senders. The only problem
with this is the fuel tank sender, which is seriously hard to replace
with one that would work properly with the VDO gauge.
I found a document that said that the sender has a resistance of
0Ω when full and 200Ω when empty.
VDO has some special US tank gauges which are 33Ω full and 240Ω
empty, and I ordered such a gauge from Summit Racing. I figured that
adding a 33Ω resistor in series would work out nicely for both full and
empty, and hopefully also for intermediate levels. Unfortunately the
200Ω at empty proved to be around 300Ω in reality, so the choices I had
was to add the resistor and have it accurate at full tank, but be off
scale when empty, or skip the resistor and have it indicate above full
when full, and below empty when empty. Initially I opted for the latter
As far as I know it will work with most 12V negative ground automotive
gauges, using resistive senders that works by being resistive to
That includes tank level, various temperature gauges, various pressure
It allows up to 16 key/value pairs to be programmed and it will
interpolate any intermediate values.
It also has an integration mode that will smooth and slow down fast
There are several unique features with this solution:
- Can use mismatching senders and gauges, i.e. Veglia tank sender
with a VDO tank gauge.
- Can compensate for irregularly shaped tanks.
- Can improve precision of stock senders and gauges.
Calibrating your gauge
As the Gauge Calibrator interpolates between data points, it is very
important that the values at the extreme ends of the scale are
There are gauges and senders where the resistance decrases with
increasing value, and others have increasing resistance with increasing
value. It is particularly important to set the extreme values if you
are using a sender of increasing type with a gauge of decreasing type,
and vice versa.
The first step is therefore to determine what type of sender you have.
Normally temperature senders have decreasing resistance with increasing
Pressure senders come in both varieties, VDO pressure senders have
increasing resistance with increasing pressure, while the Veglia oil
pressure gauge used in the Pantera have decreasing resistance with
The same goes for tank senders, most VDO senders have increasing
resistance with increasing fuel level, and the Veglia tank sender in
the Pantera has decreasing resistance with increasing level.
Connecting the Gauge Corrector
The Gauge Corrector is shipped with spade connectors on all leads.
Connect the black wire to the gauge ground input.
Connect the red wire to the gauge +12V input.
Disconnect the sender/sensor wire from the gauge and connect the green
to the gauge's sender input.
Connect the yellow wire to the sender/sensor wire.
Make sure all connections are correct before applying power.
The maximum sink capability of the corrector is about 0.5A.
Calibrating the Gauge Corrector & gauge
If the corrector has not been shipped with a proper calibration, or
the application has changed, the correctors memory should first be
cleared. This is done by holding the Store button depressed while
applying power. All calibration data is then irretrievably lost, and
the corrector must be reprogrammed by the user.
The first steps are to adjust the corrector to show the correct result
with the sender lead open (unconnected) and shorted to ground. The
order of these two steps is not important.
After this, the correct value at maximum and minimum scale should be
adjusted. Notice that some of these may be the same as one or both of
the first step.
After this, I recommend that the values for 1/8 and 7/8 of the scale
is checked and programmed. This will make the initial linearity much
better and reduce the numer of required additional data points.
The adjustment is then stepwise refined until the gauge is correct
over the entire scale.
Adjusting one data point is done in the following sequence:
If the "Hold" button is released before the new value has been stored,
the new setting is lost and has to be repeated.
- Set the correct input value, either using a sender with a known
quantity, or using resistors with the nominal resistance.
- Press and hold the "Hold" button.
- Adjust the gauge reading using the "+" and "-" buttons. Notice
that the gauge may move in the opposite direction, depending on the
gauge type. Wait a few seconds after obtaining the correct reading to
allow the gauge reading to stabilize. Tapping the gauge slightly may be
a good idea.
- When the correct reading is obtained, press the "Store" button.
- Release the "Hold" button. The gauge should now hold the set
value as long as the sender value is kept constant.
The gauge will likely be at either max or min scale when the corrector
is first connected and powered up. Depending on the gauge it may take a
long time (~30 seconds) holding the + or - buttons down before the
gauge starts to move. The value wraps around, so after the corrector
has reached its max value, it will drop down to the minimum value, and
the gauge needle should move over the scale. It also wraps going in the
Notice that it is not possible to remove a single data point, and it is
almost impossible to select exactly the same input value again to
redefine the value, so if there has been an error in the input, it is
best to clear the EEPROM and start over.
There is space in the EEPROM for up to 16 data points, which should
normally be more than adequate.
The Gauge Corrector has an optional integration mode, which will slow
down fast moving gauges. This is perhaps most useful for tank gauges
where the gauge moves around due to fuel sloshing in the tank.
The integration mode is enabled or disabled by pressing and holding the
Hold (H) button while switching on the ignition.
Obtaining the Gauge Corrector
This is just a hobby project of mine, and I have created a few for
friends and needing car nuts, including one owner of an old Ford that
had a broken sender, but a new OEM type sender was impossible to get.
He used the Gauge Corrector to connect his new style sender to the
original gauge in the car.
The boards were a bit expensive, and I have set a price at US $60 for
the board, plus US $5 for shipping to most of the world.
If you're interested in the Gauge Corrector, please drop me an email to
firstname.lastname@example.org for availability
and payment options.
If you have comments or suggestions, email me at thomas@Hax.SE
Last update: 2005-07-22