[Diy_efi] Data Logger CPU schematic and C for review

[Robert W Hughes]

>> 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.

Most late model cars use air core meters which can do 90 or 270 degree 
or more sweeps. Check out the Phillips driver SA5778D at 
http://www.ortodoxism.ro/datasheets/philips/SA5778D.pdf  for an idea of 
what is involved. This chip accepts a serial bit string to drive two 
90deg meters and one 270 with .35deg resolution and could probably drive 
the instruments in a car panel with whatever you wanted to digitize and 
send out. I think most manufacturers are using something like this in 
their panels now to cut down on wiring and connector pin count.

--
Robert W. Hughes (Bob)
BackYard Engineering
29:40.237N, 95:28.726W or perhaps 30:55.265N, 95:20.590W
Houston, Texas "The city with too much Oxygen"
rwhughe at oplink.net