injectors - [56k beware page 2]

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jharvey
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Re: injectors - [56k beware page 2]

Post by jharvey »

The hall I'm purposing is a switch, so a digital input 0V - 5V on a high impedance input. It would tell you if you screwed up before you break something. I think the first proto has some extra crap, like the 0R that allows you a test point with out cutting traces and such. I think this test point might be handy to simulate the tolerances you can encounter in the real world.

I would say PCB / schematic goals should be

-- keep cost reasonable
-- make it functional (fuel first, but why not stab at ignition),
-- make a proto in a reasonable amount of time that meats a min set of requirements.

I think the min set of requirements was well laid out in another forum. I seem to recall something like 6 injector drivers, tach input, temp input, MAP input, ect.

I feel that feed-back from our sensors has been extremely important. Looking at a gauge and seeing the RPM's at 1K when you might think it's running at 1K is very handy. However, I don't know anyone with direct feed-back about outputs from the ECU. Say you're running a motor at 50% power and you expect that to be a 50% duty cycle on the injector. Just because the ECU tells the circuit to do 50% duty, doesn't mean the injector is at 50%. Tossing that information in a graphical readout similar to what you would have for RPM, ect, would be quite handy. If you see it's at 70%, you know somethings wrong.

I know you can add test equipment for troubleshooting, but then your changing the system,. If it's an intermittent problem you won't have the tool on hand, ect. It's just a pain. I'd rather pay $6 to know determine if the problem is ECU related, or engine related.

How often have you had that intermittent problem, that only happens on occasion. I think $1 per injector to have feed back telling you that the device is most likely working OK is cheap and will increase the robust nature of freeEMS.
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jharvey
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Re: injectors - [56k beware page 2]

Post by jharvey »

Here is my purposed schematic.

Image

I believe those values should work, and it should allow for the PCB creation. However the NPN symbol isn't entirely accurate for a hall symbol. The base is really V+ not base, and the real base is saturated when the inductor makes a current creating a magnetic field. Data-sheet for this hall device can be found here

http://search.digikey.com/scripts/DkSea ... 80-2002-ND

Thoughts? Feel free to criticize I won't cry. I know Fred isn't for the extras because he believes in KISS, and Delta prefers the ISC version because of heat concerns. Any other debates, please chime in now.
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Fred
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Re: injectors - [56k beware page 2]

Post by Fred »

Delta wrote:If those are the goals then yep thats exactly what you need, no more no less.
Cool. Hey, btw, I'm not deciding what anyones goals are for a particular implementation here. I have a set of goals of my own for the first general use design, and I have a set for a first testing design (this one?) but if I'm not doing it, it's none of my business :-) At the end of the day if I don't like what you guys come up with I can build my own. One major reason for this site existing remember ;-) Another was to try to get everything "right" first time by public discussion. I think this thread is a good illustration of that principle.
I'd be using IGBT's for ignition drive.
And I'd be using OEM ignitors and small autoFETs to drive those just to protect the CPU but considering there is no actual ignition code at the moment and producing a solid fuel only setup is high on the list, I think the little autoFET idea is a better one to keep things simple.
Mosfets for on/off/pwm channels. Depending on cost, I'd use these new protected fets for all your general outputs + injectors, as they won't die if someone stuffs up their wiring.
2 - 10USD each depending on how grunty/weak/brand etc. I think it's well worth it.
<Snip>

Or am I mad??
No, you're not mad, but this is really just to get the ball rolling and have something that supports a minimal config on one board. We also don't have any GP code or any way to assign pins just yet, but it's all in the grand master plan for sure :-)
jharvey wrote:How often have you had that intermittent problem, that only happens on occasion. I think $1 per injector to have feed back telling you that the device is most likely working OK is cheap and will increase the robust nature of freeEMS.
It may only be $1 for the components, but it's a wopping 1 ADC channel per injector, and if you do those you do the coils too and you have 8 gone on a 4 cyl just like that. Remember this is a first prototype that will have early prototype code running on it. There won't be any fancy icing code for a while. All the work is going into foundation stuff to benefit everyone first and foremost. Once the basics work well, the focus from me will be on all those "extra" features that make an EMS usable :

idle
boost
fans
etc

Jared, move the resistor and cap for damping out of the extra area and put the resistor from FET input to ground back in place how you originally had it before I opened by big mouth :-) If the man says we need a fast diode to make it an "engineering solution" rather than a hack that will work, then I say include it.

Importantly though, ensure that the return paths for injectors grounds and the diodes power feed dump back are isolated from the cpu/sensor/sensitive power and ground. Also give us a separate reference line and filtration setup for battery voltage measurements.

That's at least 3 +ve feeds and 2 ground feeds potentially using more than one conductor each to lower inductance.

Also, although the FETs for injectors and pumps and relays etc may not need heatsinking the Vreg DEFINITELY will. This CPU draws quite a bit to make the MIPS it does :-)

Fred.
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jharvey
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Re: injectors - [56k beware page 2]

Post by jharvey »

Fred wrote:It may only be $1 for the components, but it's a wopping 1 ADC channel per injector
No no no no. Whine sniffle, scuff dust on the ground. The hall signal uses a high impedance digital input, no ADC required. 0V and 5V. I know it's an NPN, but it's internal circuitry either saturates or not. There is no middle ground on this device.
Fred wrote:Jared, move the resistor and cap for damping out of the extra area and put the resistor from FET input to ground back in place how you originally had it before I opened by big mouth :-) If the man says we need a fast diode to make it an "engineering solution" rather than a hack that will work, then I say include it.
Perhaps a race is in order. He who breaks his first looses :D I've put the resistor back in, to allow for normal FET's. I think the ISC is easy enough to add, so probably don't need to be shown on the schematic? I can add it if we like.
Fred wrote:Importantly though, ensure that the return paths for injectors grounds and the diodes power feed dump back are isolated from the cpu/sensor/sensitive power and ground. Also give us a separate reference line and filtration setup for battery voltage measurements.
I just posted some pictures of the overall structure that I'm planning on. I plan on taking care of grounding and traces to each sub circuit at this level. That can be foundd here

http://www.diyefi.org/forum/viewtopic.php?f=9&t=333

I think this schematic is about done, I've started looking into input signal(s). I was thinking of the thermistors first. Mostly because I've got some work done on them already. Don't comment about thermistors here, I'll start a different thread about that.

If the zener fails, then you are still protected with a 2K resistor. I think the potential path through the hall circuit is safe enough. Also if it did double fail, you'd likely only blow the port, causing that input to stop working.
Fred wrote:Also, although the FETs for injectors and pumps and relays etc may not need heatsinking the Vreg DEFINITELY will. This CPU draws quite a bit to make the MIPS it does :-)
I'd agree, even if it only makes a little bit of heat, it should still be heat sinked. If it doesn't require the sink, that's just better design.
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Re: injectors - [56k beware page 2]

Post by Fred »

jharvey wrote:I can add it if we like.
I think so assuming ISC = the fast diode to protect the FET and clamp the spikes.
Fred wrote:Also, although the FETs for injectors and pumps and relays etc may not need heatsinking the Vreg DEFINITELY will. This CPU draws quite a bit to make the MIPS it does :-)
I'd agree, even if it only makes a little bit of heat, it should still be heat sinked. If it doesn't require the sink, that's just better design.
Oh no, it puts out far more than a little bit of heat, it needs sinking and sinking well. This is no MS2 cpu ;-) It's got significant processing power! 14.4 - 5 = 9.4, 350mA x 9.4V ~= 3.5W

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Re: injectors - [56k beware page 2]

Post by Fred »

jharvey wrote:No no no no. Whine sniffle, scuff dust on the ground. The hall signal uses a high impedance digital input, no ADC required. 0V and 5V. I know it's an NPN, but it's internal circuitry either saturates or not. There is no middle ground on this device.
OK, so what does that tell you then? That the injector is ON or OFF ? and if so, what good does that do you? I'm looking to find motivation for this desire here. You may have a good reason that I can't see yet afterall :-)

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Re: injectors - [56k beware page 2]

Post by jharvey »

It's either to hard for me to explain or it's simply a less important idea. You're not the first to question me about why I feel there should be smaller loops in a feedback system like this. I simply feel that many times you can either add test equipment for diagnostics and hope to catch the problem, or you can have it built in, so you don't have to drag around a bunch of equipment. The first time I have to connect a scope, to confirm the injectors are working correctly, I would have saved the $6 it cost to add this test equipment on-board.

For example, why do you have an RPM gauge, if the engine is OK you shouldn't care right? However, most vehicles have a RPM gauge, even when it's an automatic. Seems like it's simply a valuable piece of diagnostics equipment to have on board. I think measuring the real duty of the injector is one of those situations. Low cost, and easy to implement. So why not do it.

The bottom line, is that either you have to increase the quality of your craftsman ship, ensuring you have good crimps, properly sized wire, ect, or you have to increase the robustness and cost of the brain keeping track of such things. Picture TCP/IP with out error detection and correction, you know like UDP. Close the loop, fix the problem.
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Re: injectors - [56k beware page 2]

Post by Fred »

Sure, but what exactly are you going to do with this information in the ECU that is going to help the situation?

I think placing too much trust in a code and wiring poorly to match is a VERY bad idea. Even if it's my code ;-)

You have to partition a system like this and say the following :

"what are my assumptions"
  • When I set a bit in a register the pin associated with it follows suit
  • When I provide current to a FET it is on
  • When the FET is on the injector is on
  • When the injector is on fuel is flowing
etc.

I think it's a vastly false economy to spend a heap of time (far greater than hooking up the scope) coding for such events and implementing circuits etc to cover "all" bases when you simply can't.

The failure modes for the above list include :
  • Pin on CPU dead OR pin on CPU overloaded and "stuck" temporarily
  • Board trace is burnt OR component in signal path failed
  • Connector at ECU is faulty OR wiring is faulty OR connector on injector is faulty
  • Injector is blocked, fuel pump has failed, fuse is blown, injector is stuck
More reasonable remedies include :
  • Include current limit resistor to ensure neither occur
  • Use suitable trace widths and components such that the chance of failure is minimal
  • Use decent connectors, ensure they are plugged in properly, use strain relief on wiring, use appropriate wire gauge
  • Have injectors flow tested and cleaned before installation, use a good fuel filter, fuse appropriately, run reasonable pressure to ensure locking doesn't occur
Reality says that 9/10 you assemble such a device it works perfectly, if that isn't your ratio, you need to be way more careful soldering ;-)

Thoughts?

Fred.
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Re: injectors - [56k beware page 2]

Post by Delta »

Just out of interest why the PIP3104?

It has a continuous current rating of 8A - which seems overly high, and an average short circuit clamping current (protection) of 12A!!!!

Now lets assume we don't have anything below the MOSFET in the current path.....then all is ok, and the MOSFET survives etc etc....what happens if you DO have something in the return path even a 0.1 ohm resistor is going to have to dissipate around 14W at 12A...just seems a little excessive to me. I'm assuming there was a reason for choosing this FET in particular?? TO-220 package...cheap...protected seem like its pros.

A TO-251 IPAK fet with a 5A limit would probably be more appropriate unless your planning on driving multiple peak and hold injectors per channel???
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Re: injectors - [56k beware page 2]

Post by jharvey »

I think the other factor is that Fred has them in hand. I think multi-sourcing this FET is an option.

What's the clamp voltage of the one you recommended?
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