[Efi332] H/W - S/W Question about triggering MSD type ignition box

[bowtievette at aol.com]

Hi Paul,
Lemme make sure I understand your configuration. It appears that you want to use one TPU channel per cylinder and effectively join or "or" all these signals together into a single transistor switch which will in turn trigger a single Crane Ignition amplifier and then on to a distributor. To answer your question directly, you will need to provide some form of isolation between the TPU pins to get it to work, and to avoid drawing too much current from the channel that happens to be driving high while all the others are low. Diode "steering" should work but an OR gate IC with however many channels you need would work best. I use the OR gate method on one configuration of my xfi box (I need a new name since FAST stole this one already) for an application that requires a closely spaced complex pattern of triggers.
 
That said, I'm unclear why you would want the complication of 8 TPU lines (for an 8 cylinder) when they are essentially driving a single channel output. Perhaps this is just for an interim test configuration and you intend to go to multiple coils down the road. But if you plan to run your target this way you could just use a single TPU channel and drive all 8 signals with it as is done with the efi332 software. The PSP function is set up to interrupt on the falling edge of the current cylinder's trigger signal and the ISR then re-assigns the trigger angle for the next cylinder in the firing order. You still have individual control over each cylinder's timing (if required) and avoid the addition of the OR gates and such. Works like a damn to rpms well past 10000 rpm at least.
 
-----Original Message-----
From: Paul Helmuth <PaulHelmuth at SprintMail.com>
To: efi332 at diy-efi.org
Sent: Sat, 11 Jun 2005 00:27:45 -0500
Subject: [Efi332] H/W - S/W Question about triggering MSD type ignition box


All (all three of you),
 
I have be swapping some email with Jeff to get some idea of where each of us were in the development process. Development that is, of projects similar to the original EFI-332 project, but based on the MPC555 chip (and in particular on the Phytec SBC - though I am not utilizing any resources that aren't directly on the MPC555).
 
Per my exchanges with Jeff, I'm posting this query to the list.
 
I am pretty close to doing some "ignition trigger only" testing, but would like to check a few things with some of you that have more experience than I.
 
1) I have set up individual TPU channels with the PSP12 function to generate the timing pulse for each of the cylinders. I have set them up in the Angle-time mode. This seems most appropriate since the external trigger isn't controlling the "dwell", just providing a timing signal. I'm reasonably confident of this, but if I'm wrong, please set me straight.
 
2) In order to provide the timing signal to the external ignition box (in my case a Crane Fireball system), I need to ground one of the wires going in to the control box. Since I have one TPU pin for each cylinder and I want to use the high signal from each of them to "energize" the base of a transistor (in order to "switch on" a connection to ground) - do I need to "isolate" the individual TPU pin outputs (like running them through an OR gate, or putting diodes in between each pin and the transistor base) or can they all be directly connected to the transistor base? My first concern is any potential damage to the TPU channel pins. Secondly, I wonder if having all of them common would effectively "pull down" the high signal that each of them will be generating in sequence.?.?
 
Thanks,
Paul
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