You're going to roll your eyes when I suggest this, but you will thank
me later when you do this simple project using one:
Run the gauge with an Arduino. The version you will need costs maybe $20
and will do this job simply and easily.
Once you get a single project working using an Ardunio, (which will take
a bit of work on your part at first) you will be amazed how easy it is
to use and how many little projects will be simplified by using one.
1) Get this book and kit: https://www.sparkfun.com/sylviakit (Book is
written by a 12 year old girl.)
2) Read the book.
3) Do the simple programs and experiments with the kit that the book
tells you, step-by-step, _exactly_ how to do. (This book assumes you
know _nothing._)
4) Write a simple custom program for the board (or look up a program for
the board on line and simply download it) that solves this particular
problem.
5) Install the board in your car, connect it up, and you are done.
You can get a much smaller, cheaper, specialized Arduino to do this
specific job, but the more generic Arduino "Uno" in the kit will work.
There are Arduino's _everywhere_. For example, our Taz 5 3D printer that
has all sorts of things happening at once, like three axis motion
control, two temperature controls, a variable speed fan, a digital
display, a digital knob that controls a menu on the display, reads
commands from a computer via USB or runs commands from an SD card, plus
things I have forgotten, runs it all _simultaneously_ on an Arduino
board that costs about $80.
Trust me, if you do this you will be astounded at how simple the whole
thing has become and will never look back.
Bill Dube'
On 10/25/2016 2:05 PM, Rick Beebe via EV wrote:
I have a 1998 Ford Ranger (http://evalbum.com/4674) that I bought as a
lead-acid EV and converted it to Lithium. In the process I replaced
almost everything. I bought an AutoblockAMP from RechargeCar (sadly,
discontinued). It's a slick hall-effect current sensor that measures
current and counts amp-hours. It outputs a pulsed signal to show amps on
a tach (works great). It has another line that puts out 12v to light up
a "low battery" light at some specified threshold and a third one that,
I believe, uses PWM to ground to simulate a variable resister to drive
the fuel gauge to show SOC.
I have the service manual for the truck and indeed it shows a single
wire from the gauge to the sensor in the tank. 22ohms empty and 240ohms
full (that's from memory so don't quote me). The problem is it doesn't
work. Connecting that wire to ground through any resistance does
nothing. The engine computer (PCM) was removed during the initial
conversion. The fuel sensor wire also went to the PCM but I don't see
anything in the wiring diagram that should influence the gauge. What I
have discovered is that I can make the gauge work by supplying voltage
rather than a connection to ground. 2volts is empty and 9volts is full.
I haven't got a clue as to the piece of magic that the PCM (or some
other wire) must have provided such that the gauge is now "backwards."
So I've tried seeing if I can convert the AutoblockAMP signal. My first
attempt was to use it as 1/2 of a voltage divider and that sort-of
worked except for finding the right value to drive the gauge full scale.
Plus if, while I'm adjusting the ABAMP and I get too close to one end
of the scale the resister burns up. My second attempt, thinking it was a
PWM signal, was to use a PNP mosfet. That looked promising but isn't
driving the gauge linearly enough. It goes from full to empty in the
first quarter of the SOC.
So I'm looking for ideas. Any thoughts?
--Rick
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