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Old 05-17-2008, 11:59 AM   #9 (permalink)
EcoModding Apprentice
Join Date: May 2008
Location: South Dakota
Posts: 117

GMC Sonoma - '94 GMC Sonoma
90 day: 36.97 mpg (US)
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Originally Posted by dcb View Post
That's really cool Greg! Would you be kind enough to hack up a schematic in paintbrush and a parts list? Maybe a little description of what to do with the potentiometers?
The pots are to set the voltage range that the LED drive will see. I set VR1 so the first LED lights up when the car is warmed up and idling. This turns out to be about 1 mili second of ON time of the injectors. I then set the total range, using VR2, such that each LED represents another 1 mili second of ON time. This of course requires an O'scope. What I did was monitored the actual fuel injectors with a scope while driving, then I made a circuit (555 timer IC) to replicate the range of square pulse width modulated waves for use on the bench (it's harder than hell to build and test a circuit while driving!).

EDIT: The schematic does not show it but the anodes of the 10 LEDs are connected to the car's 14.x volts. The shotkey diode (D1) can be any diode, I used it because it has a lower voltage drop and that made adjusting the pots easier, to get a range (completely arbitrary) that I wanted to be in.

for instance, If I floor the pedal all 10 LEDs will light, and beyond. I wanted a good resolution with the mere 10 distinct voltage ranges that the LEDs can show so I chose to have the 10th one lit at the 24% injector duty cycle. The engine will go as high as 45%, at least that's what the scope appeared to show while I was driving hard and watching its display, and the road, at the same time.
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Last edited by Gregte; 05-17-2008 at 12:45 PM..
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