[Diy_efi] RE:Photocoupler?

Mark Bowers & Family mbalntel at cfw.com
Sun Feb 23 18:36:02 GMT 2003


Hi Tony,

Bruce interpreted the initial statements the same way that I did: the you
were going to put the LED of the photocoupler IN SERIES with the injector.
In that configuration, the high current of the injector would flow through
the LED. Well, maybe for few msec, then poof!

I looked at Steve's PW meter circuit and see that he is hooking the LED, and
a current controlling resistor in seires with the LED, in parallel with the
injector. That's OK, and should work just fine, and will have no effect on
the injector operation. This is an A-OK way to do what you want by
monitoring the drive to the injectors. Bruce does make good comments about
the reverse spikes when the injector drive is turned off; these DO need to
be suppressed. But most existing drive circuits have spike suppressors
already, so you are probably OK. (If you want an explanation, I can write
and crudely draw something up to explain....)

I think your second question is how to possibly go back to the controller
that is driving the injector, and monitor off that point. If this controller
is a regular TTL or xCMOS type of technology (which it probably is), you can
add what is called a non-inverting buffer chip to the existing logic lines,
and this will give you buffered logic level drives to your monitoring
device. (With some technologies, you don't even need the buffer, but to be
safe, do it any way.) The chips I would look at are:
74AHC04 which is a hex (6 buffer) package that inverts the logic
74AHC240 which is an octal (8 buffer) package; it's companion part is the
74AHC244

Can you tell us what the part designation is on the driving micorcontroller
chip that you are trying to monitor??

Regards,
Mark B.


----- Original Message -----
From: Tony Petroski <tp11 at uow.edu.au>
To: <diy_efi at diy-efi.org>
Sent: Sunday, February 23, 2003 5:45 AM
Subject: [Diy_efi] RE:Photocoupler?


> well, first of all i wanted to use the photocoupler to make my own
> pulse width meter. Yes, the idea of using the photocoupler came from
> you Steve. I am not an electronic expert but i just don't know any
> other ways of being able to tap into the injector circuit in the
> effort to workout pulse widths without affecting the performance of
> the injector. Looking at the datasheet, the photocoupler doesnt seem
> to use much current. The photocoupler i was gonna use was not the
> bipolar one because i can't find it in australia. Only the single
> polar direction. And because i thought it doesn't use much current i
> wanted to apply it to the OEM injector circuit. Now using the
> photocoupler opens up the idea of using it to drive extra injectors on
> a separate ciruit. But i mostly need it to generate a TTL signal that
> can be interpreted by a micropic chip.
>
> Now that Steve has replied, i have contracting reports. Steve states
> that his design pw_meter.jpg the photocoupler is ok.
>
> Yet Bruce Roe states....
>
> I hope you are not planning to use a photocoupler input
> diode in series with a fuel injector.  The current may blow
> it up, if not the turn off spikes.  The voltage drop across an
> LED is rather high; probably will affect injector operation.
>
> Could someone clear this up ? Or provide alternate ways in generating
> TTL signals from existing circuits ? i.e. like to log. Say we have to
> microchips communicating between TX/RX 0-5 Volts, & i want to log the
> traffic over teh data lines via a third microchip. What can i use to
> tap into the circuit without affecting (minially) the circuit?
>
>
>
> eagerlt awaiting reply,
>
>
>
> tony
>
>
> -----------------------------------------------
> Tony PETROSKI (Postgraduate)
>
> Bachelor of Engineering in Mechanical (BE Mech)
> Master of Computer Studies (MCompStd)
> University of Wollongong NSW 2522 Australia
> Mobile: 0402 297 106 Email: tp11 at uow.edu.au
> -----------------------------------------------
>
>
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> Diy_efi mailing list
> Diy_efi at diy-efi.org
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>


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