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Is this practical? small modification to code on 12f and 18f chips

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Triode

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So a friend of mine has asked if I can mod something for him, I'm not sure if it's easy, hard or impossible. He has a jet engine for a model jet, and it has a 12F629 on the rotation sensor, and a 18F26-something on the controller, I'll check these and update when I get it home and open it. The modification he needs is small, on starting it kicks up to a high speed of around 110k rpm, he had customized his jet engine (very skilled in machines, not in electronics) and needs the controller to only start-boost to 50k rpm. I have a Microchip ICD 2, and an Easy Pic Fusion v7 which has their version of the ICD built in. The boards both have a RJ12 which appears to be wired to program the chips. They don't seem to be read protected. I've never pulled code from a chip, I know this will need to be disassembled, and a little online research shows that I will probably need to replace the precompiler settings. I wouldn't be surprised if this is one of those tasks that seems small and is actually huge and not worth the effort, but I thought I'd seek advice here before saying I can't do it.
 
Darn it. I am on my laptop as my desktop mouse died. I just lost everything I had written.

A buddy of mine is quite active with jets. That is the extent of my knowledge about the electronics. So, beware. My impression is that it is a relatively small fraternity. So, my first action would be to call the controller's manufacturer and ask whether the chip can be customized. It might even share the firmware with you.

Failing that, and if the board is ICSP programmable, you could take a look with your ICD2. What you will get is disassembled "whatever" was used to write it. My understanding is that disassembled C or higher languages is not as readable as disassembled Assembly. So, it might be a real problem interpreting how the rpm advance table is set up.

John
 
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I'm back. It was a really difficult problem. I had to find a new battery and get it installed correctly.:) It just died instantly. No warning.

If you strike out with the company, let me know the model jet controller your friend has. My buddy here may know more about it and have contacts.

John
 
The ECU is a:
EvoJet Jettronic-Vx
Can't find a part number beyond that

The speed sensor says
EvoJet 2009 and the chip is a 12F683

I know how it is with the dropped post. I've written some 5 pagers helping someone out just to have it blink out and post "I can't rewrite all that, I'll help you later" Haha
 
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The owner of the device told me that he had tried configuring it. I'll have to get more details on why it wouldn't work, maybe it doesn't go down to 50kRPM, though here in the manual it looks like it does.
 
Please keep us updated.

Have you ever seen the thing fly? They sound, smell, and gulp fuel like their big brothers. We happen to have a grass runway, and we can always tell the next day when the jets have been there. :)

John
 
It looks like the parameters we will want to change are in the Limits menu on page 21, options 30 and 31. For 30 he'd like to lower limit at 25,000, I believe it's 34,000. And 31 he'd like the lower limit at 45,000, it's currently 75,000.

I've contacted EvoJet to see if they can help, maybe by just giving me updated code if I'm lucky, I doubt they'll give me the code to update myself.

I've actually never seen one of these run in person, I'll probably get to see this one once it's all fixed up.
 
Just out of curiosity: why do you actually need to change (decrease) those limits? Are you trying to avoid going out of control?

Isn't it safer to keep them as they are?
 
He said that the engine can't run at the minimum speed it will allow. I don't really know exactly why, but he seems to know what he's talking about.
 
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