DIYEFI.org Forum

That's a fantastic story, HotCat! May I ask, do you have an "English name" or some phonetics for your name?

Thanks for taking the time to write it up. I'm sorry for causing you to be embarrassed before! It's heart warming to read your post! Thank you very much!

Fred.

Cool, and I agree you've done a good job. I like those VB325SP chips. I would like to raise some caution about the LED's on inductive loads. The 70V you'll see when an inductive load is switched off, will create about a 55V reverse potential on the LED. Most LED's will conduct in the revers with around a 20V to 30V potential. Which means the inductive spikes can cause a reverse potential issue, dumping energy into the high side rail. You'll probably want to add a shottky in series with the LED to allow a higher reverse polarity potential, before conducting in the reverse direction. If space is a concern, a LED with the resistor inside, can be used such that the 3K can be diode.

jharvey wrote:Cool, and I agree you've done a good job. I like those VB325SP chips. I would like to raise some caution about the LED's on inductive loads.

I like your solution by adding a shottky in series with the LED, space is not a concern. My friend also points out this issue and said doing so will make LED explode, but he suggests to wire a transistor on I/O pin and drive the LED. which one is better?

As much as it could be an issue, they will only see 70V if the injector kicks back that high, which it won't necessarily do. Plus, my LEDs on Puma which are not rated high enough have not failed yet, nor have they exploded :-)

Fred wrote:That's a fantastic story, HotCat! May I ask, do you have an "English name" or some phonetics for your name?

Thanks for taking the time to write it up. I'm sorry for causing you to be embarrassed before! It's heart warming to read your post! Thank you very much!

Fred.

Because English is not an offical language in China and I am not working for an international company before, So I don't have a formal English name. what a tragedy.

I've concerned FreeEMS project for 2 years, I saw a lot effort you made to develop this site, arrange topics in more intuitive way. I've benefited from your True open source spirit and feel nothing to return but keeping FreeEMS researching job

LOL @ tragedy! Thanks man! :-) I'm glad some people appreciate the effort that I put in!

HotCat wrote:I like your solution by adding a shottky in series with the LED, space is not a concern. My friend also points out this issue and said doing so will make LED explode, but he suggests to wire a transistor on I/O pin and drive the LED. which one is better?

I'm not seeing how they might explode, perhaps your friend is not thinking of OVP MOSFET's, and could benefit from looking at a page I made showing some simulations that show the differences from the snubber diode, vs the OVP topology. http://code.google.com/p/open5xxxecu/wi ... ver_theory

I don't see any real issues with putting the LED on their own parallel drive, that would provide most of the diagnostics information that you would desire from that LED. It would tell you that the circuit should be on of off, it would indicate things like injector 1, is wired to the correct cylinder, and it would let you know that the S12X pin is driving verses failing for some reason. The down side if done with a parallel drive chip is that if the OVP MOSFET fails, you won't know it by looking at that LED. A pro in doing it with a parallel drive chip, is that it allows you to change from an OVP MOSFET, to the snubber diode approach.

In my opinion the OVP MOSFET topology, is superior to the snubber diode topology. It does cost slightly more than a normal MOSFET, however from my point of view, the extra cost is not much, so it's worth it. You come from another culture, so I'm not sure if you might place the importance of a small cost like this as more important than I do. So I could see how you might want to keep non OVP MOSFET's as an option. If you would like to have more options to use more general purpose MOSFET's, I can see how you would place a higher importance on the parallel drive option.

That said, I would suggest using it as you have it drawn, but add the schottky, and use an OVP MOSFET. However, using a separate drive chip would probably work just fine as well.

HotCat wrote:But the puma.sch was not as elegant as the puma.brd, too many hierarchical sheet box all around, most of them contain only a few resistors and a couple of wires occupied the whole A4 paper. It is unacceptable when I need to print on real A4 pager.

That's largely my fault. PUMA was based on DFH, where I did that same thing. I did it to allow new designs to be schematically scaled from 1 cyl to 43 cyl by simply changing the pages called for on the top page. It also established blocks such that if you didn't like the AN protect, or DIGI protect, or what ever sub circuit, you could change out those blocks fairly easily on the top level without having to delete or modify the actual components. The design goal was to automate the design process, with minimizing the page count as a lower priority. We all felt limited by the constraints of the software.

I haven't seen people try the scaling theory as I had originally hoped, so I've stopped doing it that way, and I now draw them similar to how you did it. That's one reason why I think you did a good job in your layout.

Yep, I remember when you did it giving you a pat on the back! :-) I didn't know at the time how nasty it would make PDF output, though, and I guess neither did you?

Re the FET situation, if using normal FETs then a FET driver chip is required between the CPU and the gate. Logic level FETs without OV protection and with something on the board for that is acceptable too, and perfectly valid. Such protection is required for the normal FETs too. All can work, but the fully protected logic FETs are infinitely simpler and more compact.

Fred.

@HotCat

Very Nice Design, i too want to be the first to run freeEMS in my country.
can i ask for your contact details, i would like to ask for your advise on how to get started and get up to speed on my freeEMS project.

Thanks