[Diy_efi] SUCCESS! (was LED changes brightness)

[bcroe at juno.com]

Feel free to solder that cap in; it won't throw off calibration.  
Anyone who suspects problems should add it, a 0.1 ufd 
from pin 1 to pin 3 of D5.

I am getting together a parts list and schematic for the 
circuit that shorts out R4 after warmup.  It is set to operate 
after 55 seconds, at which time the heater should be 
ready to go over to voltage regulation if it hasn't already.  
I wired it into the spare chip position.  

This will give you another volt of battery margin.  However 
it also moves about 1.5 watts of heat from R4 to U1, so 
U1 needs to definitely have a good heat sink.  R4 can 
handle its power in any case with little or no heat sink.  

I'll FAX this as soon as I get it all together.  Looks like 
we aren't far apart (Aurora); 708 use to be my area code.

Sounds like you are loosing about 0.9V from the battery, 
not too terrible.  At the point where the LED comes on, 
you will see the heater voltage (J1, J2) is constant around 
10.3V, and the voltage across R4 starts decreasing.  

Bruce Roe

18 Mar 03 "Philip V. Glazatov" <gphilip at umich.edu> writes:
> Bruce, you are THE MAN!
> 
> I took one of those small yellow 0.1 mfd caps (C8, 9, 13, 
> 14) and connected it to D5. First I connected it wrong. I 
> connected it to pin 2 and the pin that is closer to the LED. 
> It still worked! The LED stopped blinking and started 
> shining constantly and MUCH brighter. Then I 
> reconnected the cap correctly to pins 1 and 3 and it 
> still worked just as well. The cap by 
> itself solved 99% of the problem!
> 
> Then I shorted the R4 and the LED blinded me!!! So I 
> am now typing to you blind. :-)
> 
> I did some other tests that you asked for. The voltage 
> drop across R4 was 1.32 V in the beginning. It started 
> slowly dropping to about 1.16 after the LED came on. 
> After it settled I checked the voltage across J3 and J4 
> and it was 13.42 V. I went and checked the voltage at 
> the battery (the alternator is kinda hard to reach) and 
> it was 14.32 V. Even with that good and healthy voltage
> my LED was still barely glowing and blinking periodically.
> 
> So should I now just solder that capacitor across D5? 
> Could that change the WB calibration?
> 
> I would also like to implement you other fix that 
> eliminates R4 so that I am less dependent on voltage. 
> I also need to know what tests to do to make sure that
> I do not have too much or too little current going to the 
> sensor heater. But I guess that might never bother me 
> again.
> 
> Thank you very much for finding the problem and a 
> solution. You could fax me a scheme 
> (708-585-3470) and I will post it for others to see.

> Philip

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