Hmm where to start.

I've read this entire webpage, where it outlines how to wire up the VB921 to the Top of R26. This is connecting straight into the output on the CPU from what I understand.

http://megasquirt.sourceforge.net/ex...tup-wheel.html

I understand if I wire the circuit that way, I will need to set spark output inverted.

If I just tag the VB921, onto the end of the LED, like outlined in the FAQ, ie like you would wire the BIM024 Bosch Ignitors I'm using atm, or the stock Gen2 ignition, do I just leave spark output to normal (ie NOT inverted).

I just want to be 100% sure before I risk burning a chip trying this, as there will be enough other variables to worry about, ie my heatsinks, new wiring, etc.

Thanks!

 

If someone could explain what the actual CPU pin does for Ignition triggering that would help greatly too.

I understand that PNP Q6 means that Voltage/Current on the base switches the transistor off.

 

I've been looking at the circuit a bit more, and I'm starting to think that I will need Spark Output Inverted selected either way.

Is this correct?

 

Have you read the RX-7 FAQ?
https://www.rx7club.com/showthread.php?t=466051
No VB921s in the ignition circuit at all.

 

yeah I have read the FAQ, I'm thinking of just wiring it the way outlined on the extra website

 

You cannot run trailing ignition, at least not in FC mode if you're using the wiring in the msextra documentation... The rotary trailing code does not work with inverted spark outputs.

 

I will be using FD mode.

4x VB921 and 4x Bosch Coils

Maui can you explain what will happen if I wire the VB921 to be connected where my current ignition module is? Or should I take the output direct from the CPU, instead of using the PNP transistor between?

PS On a side note, I think I worked out a way to get non-wasted spark on the leading ignition.

What you will need is

2x FC trailing coils, and you would wire the Trailing coil for the leading spark with the signal you normally use for wasted spark, and you would wire the "Front/Rear" Rotor switch wire in parallel with the same wire that normally goes to the trailing module

 

So I guess it doesn't invert anything, I would like to know why the external style ignitors like an input like this.

These are *ideal* plots with default parameters, but it still gives a good idea.

 

** whops double post

 

Yeah, that's what it looks like on a scope... the stock ignitors use the leading edge of the +5v square wave to start dwell, and the falling edge of the +5v square-wave to fire spark.

If you have an oscilloscope, check that inverted spark outputs work in FD mode.

What you're looking for is for leading to fire once every 180 degrees, and each trailing to fire every 360 degrees. Just make sure the signals are nice clean square waves.

Ken

 

In that plot the green line is the voltage coming out of the CPU pin, and the red line is the voltage right before the 11k ohm load (just a randon guess at what the input impedance of the ignitor would be)

Does this change anything, because the signal that is actually triggering the ignitor is changing between ~3V and ~4.5V not between 0V and 5V.

I realise you probably just had a really quick look tho.

Don't have a scope but i will be sure to test that before i try installing it on my car.

Look forward to your response!

 

I didn't even really notice that there were two plots...

This is odd because if you're monitoring the right places on the circuit with the scope, then 1) the signal going to the ignitors is inverted from the signal from the CPU, and 2) the signal is 0-5v... I don't see either of these things in the picture you posted.

I think that 11k resistor to ground is creating a voltage divider... I'm not really an expert, but that's the only thing I can come up with.

Ken

 

Still does it without the 11K resisitor there, (that just pulls the output down more)

I won't be learning about PNP structure parameters for a few more weeks, I will have a play with it later.