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Power control of the EMS system 
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hmmmm

200 RPM
6 cylinders
100 CPM
1.666 CPS
10 droops per second
25% droop duty (4 stroke with only the last part of the compression stroke causing droop)
droop to 6v outside
non droop of 10v outside

25ms at 6v outside with a 1 ohm resistor separating it. you then have to maintain a hair over 6v on the input cap by the end of that period with the outer source pulling it down to 6v with the 1ohm and the regulator pulling it down feeding the load. during the other 75ms you have 10v through a 1ohm pulling it up and the regulator pulling it down. Work it out for 500mA and you have a reasonable representation of what is going on very roughly :-)

For the inside one the data sheets should suffice, or you could consider worst case is 25 pins pull 4ma each all at once at 150Hz with 50% duty.

Those ought to get us closish?

Fred.

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Wed Aug 20, 2008 2:25 pm
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The dropout voltage of the LM2940T-5.0 is 0.3V at 500mA and a temp of 50C. With the voltage drop across the series input protection diode, 6V at the battery should be just OK. The line transient response graph shows a deviation of +20mA and -25mA for an instant rise or fall of 3V on the input. Recovery time is about 5uS. It appears to be fine on paper. Suggestion - make room on the PCB for 2 caps, one electro and one non-polarized, and work out exactly what is required on the running vehicles. Maybe I could scope the output of the LM2940 on my bike, which has a 22V zener and 22uF cap on the input, and a 22uF cap on the output.

Edit - spelling mistake, should be "+20mV and -25mV"


Last edited by Brian on Thu Aug 21, 2008 12:45 pm, edited 1 time in total.



Thu Aug 21, 2008 7:55 am
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You are right again (don't make a habit of it Image) I'm being paranoid unnecessarily. Having read the data sheet for that and the ts2940 I would still like to see 3 caps on each side. Ceramic and tant take up very little space and even a 1000uF 10v cap is pretty small really. Due to the voltage requirements on the outside one and the fact that being a reservoir doesn't matter I'd say quite a bit smaller, perhaps 100 - 220uF and 35 - 50V. Putting the three different types together is good for wide band noise reduction though, so I *still* think we should have one of each of appropriate sizes there.

Scoping the mini ms2 would be interesting, but not overly representative as the CPU is significantly lighter in load than this one and can't switch as much stuff on and off either.

Fred.

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Thu Aug 21, 2008 12:22 pm
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Fred wrote:
You are right again (don't make a habit of it Image) I'm being paranoid unnecessarily. Having read the data sheet for that and the ts2940 I would still like to see 3 caps on each side. Ceramic and tant take up very little space and even a 1000uF 10v cap is pretty small really. Due to the voltage requirements on the outside one and the fact that being a reservoir doesn't matter I'd say quite a bit smaller, perhaps 100 - 220uF and 35 - 50V. Putting the three different types together is good for wide band noise reduction though, so I *still* think we should have one of each of appropriate sizes there.

Scoping the mini ms2 would be interesting, but not overly representative as the CPU is significantly lighter in load than this one and can't switch as much stuff on and off either.

Fred.


I think this is a good plan, however I would add that if the two regulators are phsically close to each other on the board then I would have only 1 set of pre caps and make the elctro 220uF, if they are far apart then 100uF each


Thu Aug 21, 2008 1:07 pm
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The have to be separate because they are powered up at different times from different sources.

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Thu Aug 21, 2008 1:28 pm
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2940 is a shunt regulator right? Why not use a switching regulator like 20242 - it might have lower thermal output than shunting and probably can respond to transients at uc speeds ......


Thu Aug 21, 2008 6:48 pm
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It's SMD though and can't be picked up at a local hobby place easily unlike the other unit. Besides, the heat isn't significant and the linear regs are silent. That unit also requires an inductor and other external parts that the linear one doesn't. I think we should definitely KISS with the regulator. LM2940 works, everyone can get it and the heat isn't an issue (it's the only hot thing anyway probably).

Fred.

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Thu Aug 21, 2008 7:07 pm
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I probably said it before, but I'd much rather see the computer just burn data to flash when you shut it down. If 'carputers' can shut down when you shut off power, so can we. Certainly there's no reason to power the cpu board, etc. We just don't need it.

And with flash, you're good forever. No weirdness pulling the computer out, and your settings are retained. It's not like flash is pricey these days, how much data are we looking at that we can't do a last second write when power falls below X and RPM go to zero?

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Thu Aug 28, 2008 7:20 am
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8InchesFlacid wrote:
but I'd much rather see the computer just burn data to flash when you shut it down.

That definitely needs to be optional, and is no use for stuff that must be recorded every time. Then it's just down to how. This statement implies that it is an alternative to constant power to do this. The opposite, to do this with ANY degree of safety and consistency and certainty constant power and a digital I/O pin are required.

Quote:
If 'carputers' can shut down when you shut off power, so can we.

How do they achieve this. I'm damn sure if I yank the plug out of the wall right now, I will lose this post among other things. If the hdd head happens to be down and writing I could lose other data too. There must be some sort of slow shut down on them.

Quote:
Certainly there's no reason to power the cpu board, etc. We just don't need it.

I'd say to do anything like that we certainly do need it.

Quote:
And with flash, you're good forever. No weirdness pulling the computer out, and your settings are retained. It's not like flash is pricey these days

Are you talking external flash to avoid erase cycles inside the cpu? We have eeprom on board that can be written repeatedly without worry. eeprom will be used if we want to persist shutdown info, or it can just live in ram for the time being with this approach.

Quote:
how much data are we looking at that we can't do a last second write when power falls below X and RPM go to zero?

Any amount. We have to blow away 1k and the write it back in, if the power falls instantly which it will with the key going off and non-oversize caps you will lose data if you try to do that.

There just isn't a clean way to reliably do thisin software without constant power without expending lots of excess memory. I can think of a way with duplicate data but we don't have the spare space to just waste like that.

Every OEM ECU has constant power, what is your problem with it exactly?

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n00bs, do NOT PM or email tech questions! Use the forum!
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Thu Aug 28, 2008 8:21 am
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