[Diy_efi] need schematic critique

[Toyota Supra]

thanks for the reply dave!

is this what you meant?

http://68.7.7.84:8080/schematics/schematic2.jpg
(the photoshop file is schematic2.psd)

is there an easy way to calculate hysteresis? also, i have the flyback 
connected to the positive side of the coil, should it be different?

thanks again

-j







From: Dave Harvey <hernt at mindspring.com>
>Reply-To: List for general do-it-yourself EFI talk <diy_efi at diy-efi.org>
>To: diy_efi at diy-efi.org
>Subject: Re: [Diy_efi] need schematic critique
>Date: Sun, 16 Feb 2003 20:13:42 -0800
>
>J,
>To expand on Mark's comments, I suggest that you connect the output of the 
>LM339 to the base of an NPN transistor and drive the relay with the 
>transistor. Connect a 2.2K resistor from the LM339 output to +8V. Connect 
>the transistor emitter to ground. Connect the relay between the collector 
>and +12V (use a 12V relay). A 2N2222A can handle up to 50mA for the relay 
>coil. The LM339 output will now only swing 0.6V, so reduce R3 to 10K or so. 
>With this configuration, the relay is energized when #1 > #2. If you want 
>the opposite polarity, then swap the 2 pots and adjust the feedback 
>resistor (R3) value to get the desired hysteresis. You might want to bypass 
>Pin 4  to ground with 0.1uF to filter any noise pickup. Is the 47K pot 
>located near the LM339? Also the flyback diode should connect across the 
>relay coil. When a relay (or any inductor) is denergized, the voltage 
>across the winding reverses.
>
>V = L * di/dt
>
>Feel free to contact me off-list if you like.
>
>-- Dave
>
>Mark Bowers & Family wrote:
>
>>Needs work....
>>
>>- LM339 does not have drive output capable of sinking enough current for a
>>relay drive, and it's an open collector output device so can only sink
>>current, not drive current into the relay..
>>- So you need a driver stage after the LM339, and possibly an inversion of
>>the logic.
>>
>>Didn't look at the ref schematic yet. You can write me at mbalntel at cfw.com
>>
>>Mark Bowers
>>
>>
>>----- Original Message -----
>>From: Toyota Supra <turbosupramk3 at hotmail.com>
>>To: <diy_efi at diy-efi.org>
>>Sent: Sunday, February 16, 2003 6:50 PM
>>Subject: [Diy_efi] need schematic critique
>>
>>
>>
>>
>>>hi all,
>>>
>>>i need a schematic critique on the schematic housed below, it is in .jpg
>>>format or .psd
>>>
>>>http://68.7.7.84:8080/schematics/
>>>
>>>i have included the psd in case someone wanted to edit it to something
>>>better
>>>
>>>specifics on it are as follows :
>>>
>>>variable resistor input, ranging from 0 to 3.5vDC
>>>circuit is to kill signal to normally open relay at 3.2vDC
>>>i would like approximately a tenth of a volt of hysteresis
>>>
>>>
>>>below is a link that i would like to use to control the reference voltage
>>>for pin 4 of the LM339 chip, will it work?
>>>
>>>http://www.mitedu.freeserve.co.uk/Circuits/Power/lm317.htm
>>>
>>>
>>>thanks to all that look at this
>>>
>>>-j
>>>
>>>
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>>
>>
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>>
>
>
>
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