For anything related to the 'official' Speeduino boards (Eg v0.3, v0.4 etc)
#29651
Hi all,

I'm very new to Speeduino, and was wandering through the schematics, and noticed the MOSFET drives for your Injector outputs are all inverting type buffers - switching the INJ*-CPU pin high turns on the MOSFET, and pulls the INJ-*-OUT line low (also illuminating the LED via the 680R).

Is this so the injector drives can be either PWM'd for Peak and Hold, or just on and off for Saturated (High Impedance) injectors?

Either way, just wondering about the rationale behind the inversion of logic levels between uC output and board output.

Highly tempted to build a very tiny board to suit Teensyduino 35, without requiring the adapter board...

W.
Last edited by w1g3y on Thu Oct 18, 2018 11:26 pm, edited 1 time in total.
#29656
Hello W. The outputs are inverted as that is the common and simplest way to ground the injectors when necessary. If an alternate method was available that was simpler, cheaper, or more effective, Speeduino would probably use that instead. ;) The injectors are active when the output is 'active', e.g., the injectors flow current only when the uC output is high. I'm not sure I understand your question. It's a low-side MOSFET switch, so . . .
:?:
David
#29671
PSIG wrote: Thu Oct 18, 2018 4:43 pm Hello W. The outputs are inverted as that is the common and simplest way to ground the injectors when necessary. If an alternate method was available that was simpler, cheaper, or more effective, Speeduino would probably use that instead. ;) The injectors are active when the output is 'active', e.g., the injectors flow current only when the uC output is high. I'm not sure I understand your question. It's a low-side MOSFET switch, so . . .
:?:
David
Hi David, makes sense to low-side switch now that I think about it. Thanks for your informative post!

W.
#29673
theonewithin wrote: Thu Oct 18, 2018 12:51 pm Just high Z. No PWM.

Just checking the wiki would have told you that.

https://speeduino.com/wiki/index.php/Ha ... #Injectors
Ah poop, I did see that mentioned in the Wiki, but really should have taken more notice!! :)

I just thought it was interesting that the actual circuitry (presuming that the corresponding uC pins are PWM equipped) could be used to implement "Peak and Hold" if there were time during firing to change the PWM values...

(Warning: Pseudo firmware code ahead)

//setup for this brand of injectors
set pwrInjectorPeak = 70;  // Required to open the injector
set delayInjectorSettle = 10;  // Required to allow injector to settle before 'hold'
set pwrInjectorHold = 20;  // Required to hold injector


// In the fuel delivery routine:
// Peak the Injector...
analog.write(pinOut,pwrInjectorPeak);

// Settle the injector
delay(delayInjectorSettle);        // Yeah, non-blocking delay would be nicer

// Hold the Injector
analog.write(pinOut,pwrInjectorHold);

// Now run magic code to determine how much fuel to pump in...
Thanks for the response, and apologies for being under-informed - this really is a fascinating project, and excited about learning more!!

W.
#29674
Ah, yes I also forget there is a common assumption that Speeduino powers stuff. In most cases, the components are powered, and Speedy just grounds it to make an active circuit. Exceptions are the temperature and some trigger sensors (use 5V bias pullups on the signal line), ignition output signals (5 or 12V), and stepper IAC outputs. PWM injector control could be done (and I'd be happy to see it), but needs one of the timers that we don't have any extra of. ;) In testing, we have also found that inline resistors on low-Z injectors works as well ( I can verify that repeatedly), and there's always the option to do add-on P&H control in various ways, so it's not a priority item ATM.

David

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