FreeEMS hardware feature wishlist (your suggestions here!)

[Fred]

With regards TO220 vs. DPAK some of my concerns were about heat management. I had forgotten about adhesive heatsinks. Here are some examples that would make it ok for high heat producing items (i.e. items that switch often, or have to handle flyback transients internally)

http://nz.farnell.com/jsp/displayProduc ... ku=4302280
http://nz.farnell.com/jsp/displayProduc ... ku=4302400
http://nz.farnell.com/jsp/displayProduct.jsp?sku=175006

I still think if possible TO220 might be better, but perhaps a mix of the two is possible as well.

Admin.

[Fred]

Have a look at the way this OEM EMS handles having two boards, and where it puts its high powered drivers, and what case style they are. Granted, its a fairly old EMS, but still interesting none the less.



Admin.

[AbeFM]

LOTS of catching up to do before I start contributing, but I wanted to point out a thread or two I think will nicely compliment the discussion here:

One all about inputs for cam/crank/etc angle sensors. This is the actual physical design of them, not the logic of how to run the motor.
http://www.diyefi.org/forum/viewtopic.p ... &sk=t&sd=a

Physical circuits aside, as far as triggers are concerned, two things I would like to see (though they hardly matter, perhaps could be ignored, would be a "signal propagation delay" which you can't make up for with a degree offset, my circuits have been in microsecond range, with big caps the delay could be higher. Of course, this works out to be well under one degree of error, but it could be watched anyway if there's processing power to spare.

The second is logic is NEEDED to deal with missed pulses, some computers "giving up" because of a missed pulse is dumb! It should be *logged* that pulses are being missed, but the motor should know when to expect the next pulse, and if it sees one impossibly early, impossibly late, missing or double, it should be noted so folks can fix their wiring/electronics.


The issue of when to start fueling, when to start sparking, and how, is another close to my heart.
http://www.diyefi.org/forum/viewtopic.p ... &sk=t&sd=a

Lastly, I would really like to see more options for warm up...
http://www.diyefi.org/forum/viewtopic.p ... &sk=t&sd=a

More to be added once I catch up. Sorry if I'm repeating stuff that has already been discussed.

[Fred]

Thanks Flacid,

The LM339 thread will be a valuable addition to the information in this forum :-)

I moved the other threads to the firmware subforum as that's where I believe they belong. The links appear to still work though.

All good information.

Admin.

[Fred]

This device contains circuitry protecting against damage due to high static voltage or electrical fields;
however, it is advised that normal precautions be taken to avoid application of any voltages higher than
maximum-rated voltages to this high-impedance circuit.

From page 1241 of the MCU datasheet.

I guess my decision to order a large number of 5.1 Volt zeners was warranted :-)

The consequence of that statement is that all Input pins should be clamped to 0V with a normal diode to protect from -0.6V or more, and clamped to OV with the 5.1V zeners too. Current to those devices should be limited with a series resistor of an appropriate value.

The doc shows the current for a single pin in full drive as 4mA given that, and an external voltage of up to 15V gives a conservative value of 3750 Ohms, and using 5V we get 1250 Ohms. Considering that Tech Art use a 2k resistor with an LED in series, if we assume that the LED drops 2.0V then they would likely choose :

2.7k for driving transistors and 3.3k or greater on 5v inputs. Time to go and pay through the nose for 50 of them.

Admin.

[AbeFM]

I suppose I should shut up about this, but I figure if I keep talking it gives you a chance to be the bigger man and ignore it.

Actually, I'm just excited because I never saw all this before.

http://digi-key.dirxion.com/Main.asp?fr ... index=1798

Fig 1 is self explanitory, and so is figure 2, they just save space, disspate heat better, etc.
Fig3 I don't get what it's good for, like a parallel voltage divider?
Fig4-6 are just DIP versions.

But the big thing: 15 resistors, even 24 of them (you'd want two per 50 channels, plus a couple discretes) are... $0.30-$1.20 a set. 8 discrete resistors for 0.60, so you could buy ten of these and never have to worry. Still, I want to look more into useing them for something cool, like a dip-switch-based pull up/pull down.
-Abe.

[Fred]

Dip switches are a great idea for configuration that changes and testing etc, but in a car environment, I'm not sure they are a plan, esp when you typically want a particular config and nothing else.

The way it should be approached is to design your total engine management package as a system and configure it per the detailed design (much like we are going to do with the software for FreeEMS) at which point you have everything set in stone. You are less likely to unsolder and change something than you are to flip a switch (either by accident or on purpose) rendering something dysfunctional and hours of fault finding because a dip switch ended up somewhere it shouldn't have been.

Anyway, suggestions all noted and appreciated :-)

Admin.

[AbeFM]

Apparently all these future users are afflicted with some form of "sanity" which I lack. Nothing suits me more than changing something that already works.

In an ideal world, you could put in a DIP switch bank, or jumper block, then solder those connections when things are finalized. Certainly jumpers across the back are easy enough. I guess removing an entire block is tough though.

The other thing I see on production boards is staking of dips. Not the easy, flip/tilt kind, but the hard-to-change slide kind where you need to move it with a pin.

I'm becoming more of a fan of jumper blocks as they do make it easy to try things out (leave them open, short them, or wisk the signal off somewhere for 'processing', then it's easy to solder a bridge across it when you're happy with it.

With any luck, a final board could keep the spacing between jumper holes at .100" so those could be optionally installed.

[Fred]

Digital pots:A local friend of mine (big thanks Mark) had suggested using cheap digital pots (something like these) for non-time/resolution-critical analog outputs like temperature.

Nice idea for analog outputs. just blip a pin briefly to inc or dec the pot :-) the init sequence could involve resetting them to zero and winding them to where you want. If feedback was used with the controlled device, you wouldnt even need that.

[Fred]

http://nz.farnell.com/1453664/semicondu ... ID5001NT4G
http://nz.farnell.com/1453667/semicondu ... ID6002NT4G
http://nz.farnell.com/jsp/Semiconductor ... ku=8165416

A few more mosfet solutions.

I have to admit, I'm starting to be pulled around to gearheads way of thinking. I may have been unrealistic.

Additionally, SMD parts like that are more reliable in operation because of their mounting. i.e. no dry joints.

Admin.