[Diy_efi] schematic critique

[Bill Washington]

J,
    I'm just back after a hectic w/end & today was pretty busy with 
meetings also.
    Sorry to hear that the circuit (7?) didn't work, there could be a 
variety of reasons, and I must apologise that I was a bit rushed in my 
comments on Friday, and over looked a couple of points that were 
elequently made by others.
    One that springs immediately to mind is that yes the NPN Transistor 
emitter should be connected to ground and the relay coil should be fed 
from +12V (assuming a 12V (automotive) relay). Sorry, I should have 
picked that one!!!
    Also the idea of a filter circuit on the sense voltage is a good 
idea because as the fuel sloshes around when that side is nearly empty 
it will tend to switch the pump on and off.
    If you would like to look at the circuit further, could you please :
1. Measure the supply voltage to the Opamp (should be 8V)
1. Measure the reference voltage.(as someone else suggested you can use 
your 47k pot with one end connected to your 8V supply and the other to 
ground and the wiper to the sense input).
2. Monitor the output voltage and the input voltage.
3. Raise the input sense voltage from 0V to 1V higher than the reference 
voltage and observe what happens to the output voltage.
4. log your observations to the list.

    If you would prefer to try Mark's circuit instead, that also is fine.

Regards
Bill



>
>Date: Sat, 22 Feb 2003 23:21:28 -0500
From: "Toyota Supra" <turbosupramk3 at hotmail.com>
>To: diy_efi at diy-efi.org
>Subject: Re: [Diy_efi] schematic critique
>Message-ID: <BAY2-F160O8qPLlxw0000001c20 at hotmail.com>
>Content-Type: text/plain; format=flowed
>MIME-Version: 1.0
>Precedence: list
>Reply-To: List for general do-it-yourself EFI talk <diy_efi at diy-efi.org>
>Message: 2
>
>hey mark!
>
>you should be able to email to this email address
>
>turbosupramk3 at hotmail.com , it can receive up to a meg if i remember 
>correctly.
>
>thanks for taking the time out, i was just about to give up, as i built the 
>other circuit, and it does not work
>
>tty soon!
>
>-j
>
>
>
>
>
>
>
>  
>
>>From: "Mark Bowers & Family" <mbalntel at cfw.com>
>>Reply-To: List for general do-it-yourself EFI talk <diy_efi at diy-efi.org>
>>To: "List for general do-it-yourself EFI talk" <diy_efi at diy-efi.org>
>>Subject: Re: [Diy_efi] schematic critique
>>Date: Fri, 21 Feb 2003 23:39:59 -0500
>>
>>J,
>>
>>I have finally gotten around to the schematic, drew it by hand, and have
>>scanned it for you, into a 750k .jpeg file; it a bit fuzzy, but readable.
>>Let me know where I can email this, and you can put it in your schematic SW
>>and post.
>>
>>Items to note about this circuit:
>>1) Includes an input buffer resistor on the 12v supply to the 7808; this
>>prevents the input filter cap from trying to filter out all the noise on 
>>the
>>car's 12v system, which will dry out the cap in short order and make it
>>useless
>>2) Adds filtering on the line from the fuel level sender, plus a slow time
>>constant (several seconds) to smooth out any "wiggling" of the sender
>>output. The noise filter is important as you will ground the sender near 
>>the
>>tank, and the gound for the control circuit may be in a different location
>>in the car. If so, you will need a noise filter.
>>3) Feeds the fuel sender from the 8v bus; this will be a MUCH more stable
>>circuit, rather than feeding the sender form the car's 12v syste, If you 
>>use
>>the 12v system to feed the sender, without running cvia the dash units
>>regulator, the switching point of the circuit will vary widely as the car's
>>12v system voltage varies. (Hence why the put soem soret of regualtor in 
>>the
>>dash!)
>>4) Implements the hystersis you wanted of approx 0.1v; you can increase 
>>this
>>by DECREASING the 220k feedback resistor, within reason
>>5) Uses a simple NPN output driver
>>
>>Things to note:
>>a) Assumes that the fuel sender will present about 55 k ohms resistance at
>>the point that you want the pump switched off; this can be changed by
>>varying the pot connected to pin 5.
>>b) The output drive transistor can support about 100mA max current, and
>>still be saturated. (Which means it will turned on hard, and there will not
>>be much heating in the transistor.) This means your relay coil resistance
>>needs to be about 1200 to 1500 ohms. It is important that you measure this.
>>If it is much lower, then the FET driver circuit that was espoused by one
>>fellow should be used.
>>c) Assumes that the fuel guage will NOT be connected to the sender; this is
>>important.
>>
>>I took a quick look at the schematic 7 and I can't see it working at first
>>glance; I lost the link so I can't look at it more..
>>
>> And, my apologies for the long time to work on this; gotta work for a
>>livin' !
>>
>>Regards,
>>Mark B.
>>
>>
>>
>>
>>_______________________________________________
>>Diy_efi mailing list
>>Diy_efi at diy-efi.org
>>http://www.diy-efi.org/mailman/listinfo/diy_efi
>>    
>>



_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi