[Diy_efi] Data Logger CPU schematic and C for review

[Bernd Felsche]

On Sunday 04 February 2007 12:16, Jean Belanger wrote:

> What would also be interesting would be the ability to directly
> drive analog gauges. Since a lot of people lose some or all of the
> dash gauges when going to a non-OEM MCU, it would be nice to be
> able to restore this functionality. I don't know exactly how this
> would be done and it certainly is dependent on the vehicle but
> some type of PWM or stepper motor controller would cover some
> cases.

Reminds me...

I've toyed with the idea of using RC-servos to do the needle
positioning on stock gauges. The servos are controlled by pulse
width and (I understand) will lock when they get no further signal.
Even removing power leaves the servo locked in position.

This by-passes the need to fake various types of signal and allows
for other interesting analogue gauge functions to be programmed.
Also, pulses only need to be sent to the gauge when the indicated
value is to change.

RC servos are cheaper than traditional steppers and have the
advantage of a built-in position controller. Some have additional
limit switches. The servos have a lot of torque for their size and
are very light (for model aircraft, anyway).

Haven't got around to hooking up a servo yet to try. The idea is
that one buzzes the servo up to the bottom end of the scale
"stepping" up from the driving controller, sets that in eeprom to be
the base setting and value, then up to the next linear point in the
scale - or even the maximum scale if it's evenly spaced, and tells
the driving controller the associated value in eeprom.

The controller then does a simple ratio calculation to determine
what pulse width to send to the RC servo so that the needle points
in the right place.

Higher needle positioning accuracy and scale alignment is possible
by setting several points on the gauge.

-- 
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