[Diy_efi] 555 Timer controlled EFI

Geoff Harrison geoff_h
Sun Jan 22 00:28:44 UTC 2006


It sounds like Scotty is using sequential injection. Is your 555 
free running, or triggered from ign pulses?
The simplest freq to voltage converter would be what used to be 
known as a charge pump, that used in early electronic tachos. 
It's just a diode feeding an RC network, the meter being 
connected in parallel to the capacitor. That is a low pass 
filter. The diode prevents discharge back to the circuit feeding 
it.

I think the best way to drive the 555 is ignition pulses to the 
trigger input. This provides compensation for RPM, though it 
will need a bit of help. The compensation is fed the Modulation 
pin, which allows the duty cycle to be varied. Throttle position 
is part of the RC network which sets the pulse width.

So the 555 is fed by freq (ign) and voltage (load) and its 
timing constant (which is now a variable-TPS)
(in my scheme)

Geoff Harrison
----- Original Message ----- 
From: <TheEthereal at gmx.net>
To: <diy_efi at diy-efi.org>
Sent: Sunday, January 22, 2006 5:56 AM
Subject: Re: [Diy_efi] 555 Timer controlled EFI


The flap-style AFM restricts the intake much more than any other 
MAF I'm
aware of. You don't specifically need a F-to-V converter, a low 
pass filter
set to the appropiate specs may suffice. Although it's not as 
elegant as a
555. I'm confused by now. What is better to drive the 555 
injection, a
Voltage or a frequency?

> --- Urspr?ngliche Nachricht ---
> Von: ScottyGrover at aol.com
> An: diy_efi at diy-efi.org
> Betreff: Re: [Diy_efi] 555 Timer controlled EFI
> Datum: Sat, 21 Jan 2006 13:13:16 EST
>
>
> In a message dated 1/21/06 7:13:58 A.M. Pacific Standard Time,
> kml_daniel at yahoo.com writes:
>
> Hi
> The 555 timer could be used as frequency to voltage converter 
> i   could
> send
> you a schematic of it, if you need
> Kamal Daniel
>
>
>
>
> The F-to-V converter was my reply to the person wanting to use 
> the
> Mitsubishi MAF device. I am using a Datsun Flap-type AFM which 
> has an
> antilog
> CFM-to-Voltage curve; I am applying this to pin 5 of a 555 to 
> linearize
> the  curve.
> Then processing this signal for Intake air temp. and engine 
> (cylinder
> heat)
> temp.; then passing this through a National Semi. A/D device; 
> hen with
> further
> processing, this is applied to the input of a programmable 
> 8-bit counter
> which, through rotary counters, gates, and power transistors, 
> feeds the
> injectors.
> Scotty
>

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