Hi Paul

That 555 gets better all the time.

I trying to emulate your circuit on CircuitWizard, the nearest components
included in the software don't cross reference very well. And I am not very
component savy either, so that a bit of a handy cap.

I have substituted an IRF540 for the power fet it seemed the closest and as
I have Bosch EV6 injectors, they seem to need less power, to drive anyway, a
comso drill pwm Maplin catalogue no.RN31U will drive one of these but not
the EV1, and can be ramped up on the pressure if needes.


In the simulation I am using a 12v relay.
A function generator set at +/- 18v 60 Hz, in place of the E- shaft trigger.
Digital voltmeters for the Fuel Flow and also added another to monitor the
MAF voltage the LM358 seems ok.


C1 R1 and 1N2004, and the extra diode on the trigger and the other capacitor
values would be a great help, when I run the simulation I get a lot of on
screen components blowing mostly the these ones.

House prices are terrible here too.

Clive C

What is the resistance of the Bosch injector. It should be around 10 ohms
to work in this circuit.

C1 is .1 ufd
and R1 is 10K

What is the pulse width of the function generator? It should be less than
1 msec. Also keep the voltage down to less than 15 volts as 18 might
blow the TLC 555.

Paul Lamar

Hi Paul

Thanks, I was using the sine wave +9-9 total of 18volts.

The function generator is basic but if I set it to 80% duty cycle the scope
pattern looks similar to what you have, when it measured at pin 2, just cuts
off the + and keeps the negative part.  I have only had the program week and
think I'm going approx the general vicinity of the right direction.

Will play with it will come back when I've made some progress.

The Bosch EV6 is 14.8 ohms do you think this would be too much?

Clive C in the UK

No that is fine for the injector resistance. Early peak and hold injectors
had about 1 ohm so initial current was 10 amps or so.
Those have pretty much disappeared.

I think the output impedance of the function generator may have something
to do with it. I used an actual ABS sensor set up on the bench.
The higher the RPM the higher the voltage from the ABS sensor so I was worried
it might kill the 555 so I put the conditioning circuit in there with a pull up
resister. It seemed to help at lower RPM.

I am not that far ahead of you.
Let me know if you need any help.

----------------------------------------------
Hi Clive,

I added a 10K pull down resister on pin 5. Seemed to make it
even more stable across the RPM range.

High RPM
The scope is set to 1 ms per division.
7 ms period 8500 RPM.
0.9 ms pulse width at near zero control
voltage (mass air flow sensor out).
6.7 ms pulse width with 5 volts control voltage.

Low RPM.
30 ms period 2000 RPM
1 ms pulse width at near zero control voltage.
7 ms pulse width at 5 volts control voltage.
Kind of academic as the engine will not
see that much air flow at only 2000 RPM.

This TLC 555 is an amazing device.

There is a bit of control voltage shift with RPM
but it may have something to do with the 10K pull down
resister. I need to implement the op amp to be sure.

The scope was blinking pretty bad as it is
not a storage scope so I have no pictures
under those last conditions. In both cases supply
voltage was 12 volts.

I think we can reduce the minimum pulse width with some
more trigger conditioning work. The ABS sensor puts out
a wider pulse than the Mazda RX8 trigger. Perhaps
I need to space the ABS sensor further from the steel trigger
wheel. Of course not all injectors will fire with pulse
widths less than 1 ms.

Next project is to work on the fuel flow circuit.
I may get that done in the next could of days.
Plenty of room on the circuit board for the few required
parts. I am also working on a new iteration of the PC board.
I needed to fix a problem with the injector coax connector anyway.
Major screw up on that one :)

Paul Lamar