DIY LTCC or similar system for LT1s

[vilefly]

sorry about the late response. Your plan B with the old oscilloscope should be done with a capacitive voltage divider probe to keep from zapping the oscilloscope. It is like a resistor voltage divider, but uses capacitors instead.
this is a link to a pdf document showing you how to make one. see page #5
https://www.princeton.edu/ssp/tiger_..._waveforms.pdf

oscilloscope probe diagram.png

The clamping ends of the probes are clothespins hot-melt glued to split pieces of tubing. You probably could use foil also, but is less consistent.
Hope this sheds some light on secondary ignition probes. The capacitors are 1000pF.
Don't forget that the signal will be inverted as it is a measurement of negative voltage.

[spfautsch]

Interesting read but I think I've moved past that. I was able to get a good enough picture of the coil discharges with my hillbilly inductive pickups to tell me sequencing looked good. I may be proven wrong on that, but chasing other demons now.

I ran it for a few minutes yesterday with the test cylinder (#4) being fired from the arduino. I may test more in this configuration tomorrow just to verify it was actually hitting (most of the time).

[vilefly]

Curses! Too late, again!

[lionelhutz]

Wow, it's impressive how well you're making out.

If you need some help with the noise issues let me know. I might be able to come up with some ideas that help. I also might be able to help if you have any circuit questions.

[spfautsch]

It's hard to put a finger on what all the issues might be, so I can't say positively that noise is one of them but it's highly likely. I unwrapped the right bank upper harness and tapped the 14ga pink wire for power Sunday. In the process I created a small rat's nest of wire that could be contributing also.

It doesn't help that I'm only getting about 90 minutes a day to work on it, and those are usually distracted minutes. Words cannot describe how anxious I am to get this nailed down and move on to yanking the engine and fixing the oil leak, etc. I'm sure that impatience isn't helping.

I managed to get an order placed yesterday with digikey for some rc filter parts, a spare boarduino kit and a couple proto boards. Hopefully I'll have that this weekend and can try cleaning up my wiring mess. Between chasing noise / count errors and soforth I've been contemplating how to package the thing for underhood conditions - would love to hear ideas here. Mine is going to be dead simple - potting the whole thing in epoxy. Possibly an external m+f weatherpack connector set for the power, uart and inputs (10 pins total if memory serves) and then either 10 or 16 loose-ended pigtails (8 ttl pins and either two or eight ttl grounds) for the coil igniters coming right out of the epoxy.

Work's been busy lately so I haven't had much time to research and audit code. Today I was hoping to look for a wiring diagram because the info at http://chevythunder.com/lt1_electrical_page.htm isn't close to what my Y body has - there is no tach wire on my black coil connector.

[vilefly]

What I am going to suggest might seem obvious, but it could be a lot of the problem. I suggest twisting the positive and negative voltage supply wires around each other. I remember the early fuel injection computers having issues with their injector drivers until they did that. Twisting the input signal wires around each other is a good idea, too. (5v signal + gnd). Twist all inputs and outputs if nessesary, but start with the heavy current users 1st.
I was putting together my Rostock MAX 3D printer 3yrs ago, and noticed in the forum that they have feedback issues, so I twisted all my wires in +/- pairs, and never had a problem. So from then on, I twist everything. ABS wheel speed sensors have twisted wires going to them as well, as they are touchy amplified inputs to begin with.

Worth a shot.

How about some PCM pinouts?
95 corvette pinvoltage chart1.jpg95 corvette pinvoltage chart2.jpg95 corvette pinvoltage chart3.jpg95 corvette pinvoltage chart4.jpg
95 corvette ignition schematic.png

[lionelhutz]

I would have to say potting can have it's downsides, especially with a hard material like epoxy. I have been involved with some items at work that were potted and failures were happening due to the potting and components expanding and contracting with temperature at different rates. Components were breaking and solder joints were getting damaged. Then, it can't be fixed either. Just saying, it's great to seal but can still create problems.

Now, if you can find a silicone based material that remains soft then you might be better off. Still can't fix it, but at least it avoids mechanical thermal stresses.

[vilefly]

I think a light layer with RTV silicone followed with epoxy for the rest of the cavity would balance the need for speed (curing time) and retain some degree of toughness. If it were fast, I'd use 100% RTV silicone, but it would take too long. Silicone dielecric grease would be nice(thermal conductivity), but may leak out before it "dries out" in high temps. A nice "chewy" potting material would be perfect, like the potting material used in Ford TFI ignition modules, and such. Chewy=tough.

[dzidaV8]

Have a look at ELASTOSIL products, I have used their two component curing silicone before with great results. I don't remember the exact number, but you mixed it with hardener, poured it into the case like water and it cured chemically, becoming reristant to over 150*C.
It is a german company, but I'm sure you have something similar in US :)