Hey, look, i built something! Neds MicroEMS

All home-built FreeEMS implementations without a forum of their own, usually TA-based.
DonTZ125
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Re: Hey, look, i built something! Neds MicroEMS

Post by DonTZ125 »

Hi, Ned.

Very nice! I do have a few questions / comments:
1. I don't understand the point of R83, and the comment about removing either R13 or R83. I can understand a 12v pull-up on a logic input, so long as the series resistor is sufficient to allow the shunt diodes to break down the voltage, but I don't understand having both a 12v and 5v pull-ups. Removing R13 leaves the input broken; do you mean R12?

2.Having pull-up / bias resistors on ADCs makes them useless for 0-5v inputs. While this doesn't much matter for a DIY design built for your purpose, if this ever becomes a device for the masses, I would suggest that solder jumpers should be included.

3. That USB6B1 is a chunky beast; have you considered the much teenier NUP4201MR6? It does the job and takes up less real estate. (I assume this is why you went with the FT230-XQ, not the more common FT232RL.
a. What are the red symbols between the USB socket and the USB6B1?
b. Why a big honkin' USB-B socket? A micro-B socket is easier to fit in, AND can be had in IP67.

4.I like the way you've handled the USB / RS232 combo. I don't recall ever seeing an AND gate for that purpose.

5. As with the pull-up / bias resistors in #2, the shunt resistors in the VR circuits should use solder jumpers. From discussions on the forum for the "EMS That Shall Not Be Named" (Voldesquirt?), adding the shunt resistor to a MAX9926 input when it isn't needed can actually cause issues.

6.You might consider switching your Tach pull-up to 12v, allowing the circuit to directly drive a lot of tachs.

7. The power supply. Ummm ... I assume the multiple caps is an artifact of your opinion of tants?
a. Instead of the LTC4411, consider a 3A SOT23 P-channel Mosfet at the 12v input pin, installed with the body diode pointing towards the power supply and the gate grounded. This gives battery-reverse protection with near-zero Vf.
b. Why do you have a 6.8v Zener, vs 5.6v?
c. How are you going to see the fuse light?
d. Why the heavy filtering on the VRef?
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Re: Hey, look, i built something! Neds MicroEMS

Post by Ned »

Cool, questions, i like questions :)

ruzki wrote:Ned !
You may could tell us some more about the PCB design ?
I personally would like to know how such dense PCB design is done ? How many Layer´s did you use ?
How does your mixed signal grounding looks like ?
So the PCB is only 2 layers. I was thinking about 4, and it m,ight still be the way to go but i thought i'd try 2. There arent many tracks on the bottom layer except for power and ground. Just a few little bits like the silly USB coms lines and some some jumpering. The design isnt very complicated, its pretty simple, so the components could generally be laid out so that they all connected via the top layer.

Ground wise, as you can see, the only things on PGND is the injectors and the low side drivers. They are all placed physicaly close to the PGND pins so that section of PCB could get poured with a PGND ground plane on top and bottom layer for a nice solid connection. The rest of the board is all SGND
DonTZ125 wrote:Hi, Ned.

Very nice! I do have a few questions / comments:
1. I don't understand the point of R83, and the comment about removing either R13 or R83. I can understand a 12v pull-up on a logic input, so long as the series resistor is sufficient to allow the shunt diodes to break down the voltage, but I don't understand having both a 12v and 5v pull-ups. Removing R13 leaves the input broken; do you mean R12?

2.Having pull-up / bias resistors on ADCs makes them useless for 0-5v inputs. While this doesn't much matter for a DIY design built for your purpose, if this ever becomes a device for the masses, I would suggest that solder jumpers should be included.

3. That USB6B1 is a chunky beast; have you considered the much teenier NUP4201MR6? It does the job and takes up less real estate. (I assume this is why you went with the FT230-XQ, not the more common FT232RL.
a. What are the red symbols between the USB socket and the USB6B1?
b. Why a big honkin' USB-B socket? A micro-B socket is easier to fit in, AND can be had in IP67.

4.I like the way you've handled the USB / RS232 combo. I don't recall ever seeing an AND gate for that purpose.

5. As with the pull-up / bias resistors in #2, the shunt resistors in the VR circuits should use solder jumpers. From discussions on the forum for the "EMS That Shall Not Be Named" (Voldesquirt?), adding the shunt resistor to a MAX9926 input when it isn't needed can actually cause issues.

6.You might consider switching your Tach pull-up to 12v, allowing the circuit to directly drive a lot of tachs.

7. The power supply. Ummm ... I assume the multiple caps is an artifact of your opinion of tants?
a. Instead of the LTC4411, consider a 3A SOT23 P-channel Mosfet at the 12v input pin, installed with the body diode pointing towards the power supply and the gate grounded. This gives battery-reverse protection with near-zero Vf.
b. Why do you have a 6.8v Zener, vs 5.6v?
c. How are you going to see the fuse light?
d. Why the heavy filtering on the VRef?
multi part questions and some good ideas in there, i like it! I also like that you obviously really looked at the PCB and not just glanced at it, appreciated!

1. So because this project was done mainly for me, not for the general public, my documentation is super super shit. Let me explain what happens there. Fred had a big hissy fit about measuring 12V battery being one of the most important things in this world, and he hated that the voldesquirt measured the 12V on its input feed, and he was dead keen on being able to measure the battery voltage seperately, so for the sake of one extra track and one resistor, i gave him that option. If you populate R83 and remove R1, as well as remove R13, then SPARE3 will become the battery V input and gets rerouted to the same BattV pin on the micro and spare3_adc gets left unconnected.
You dont actually need to remove R13 if you dont want to, the protection circuit will take care of it, but its best to remove it. R12 can stay, it will just draw 3mA but thats ok. You really just need to move the 3K9 from R1 to R83 to move the battery sense pin.
Does that make more sense?

2. guessing you mean having the 2K49 resistors from 5V to the input are no good for things like a MAP sensor? i understand, but things like a MAP sensor that have an actual driven output SHOULD have enough output current to completely negate a 2K49 pullup. Thats only 2mA afterall. I agree that its a part thats not needed, and in a perfect world not wanted, but its also not worth putting a solder blob on the board for it because it should operate fine with it.
The other thing is that a machine cant place solder blobs, unless its on the bottom side of the board during wave soldering and then you need an extra step (peel able solder mask) if you want solder blobs to be open by default. You make a valid point though because it wouldnt work with another TPS for example. Actually, even that you could make work by only using the bottom bin and the wiper on the TPS. Signal size would go down but it would still operate fine.

3. that USB6B1 sure is big! and there is a simple reason why i picked it... i already had the footprint etc for it haha. I have 2 units i use, the USB6B1 (nice and bit and simple and easy) and the ESD7383, which is tiny and little and awesome but 'impossible' to hand solder. It's a BGA and i can fit 7 of them in the same space as your NUP4201MR6 suggestion ;) but thats a volid suggestion, and i probably should actually have changed to a smaller device really...
I actually picked the FT230 for the same reason, had the footprint so used it as thats the part i normally use. Its harder to solder, but actually easier than the micro if you ask me... It's also 1/2 the price...
3a. the squiggles are markers in altium to say those are differential tracks, so i can use the differential track router. It lets me route both tracks at once through the same places and keep track and gap constraints etc etc.
3b. simple reason, if i trip over the cord, i am less likely to ruin a USB B port, but will 100% rip the little micro USB socket off the board. It's just a robustness thing really. People like fred have complained to no end and say they dont even have that cable anymore, but i still use them every day on a bunch of hear i have here. It really is the right choice if you ask me. I never tried to make this board small, so it wasnt an issue.

4. the NAD gate is on the 'top' schematic where all the green blocks interconnect. Not sure if that works yet because i think the MAX chip shutdown pins are set so it Hi-Zs the output and i didnt put on pullups so that may require some work still... but its nice being able to use either setup and there being no code changes for using different serial ports etc

5. yeah, a solder blob wouldnt be a bad idea, but i just wanted to stay away from that for this revision because again, a machine cant place a solder blob.

6. i was thinking about having 2 pullups. One to 12V and 1 to 5V, that way you could choose. You could also put an inductor in place of the resistor to the 12V that way and actually create a big spiking high voltage to drive an old school tacho thats normally fed from the -ve of the coil... but figured an external circuit works well and keeps the high voltage noise out the ECU case.

7. multiple caps is because ceramics just arent perfect, but adding lots of physically big, lower value caps, you get a good end result, so thats why that is.
7a. the ideal diode isnt there for reverse polarity, its there purely to not back-feed 5V from the USB into the regulator when the reg isnt powered. A lot of regs wont like that.
7b. The problem with clamping diodes is that they start conducting too early, and a 5V6 will likely conduct at well below 5V and wanted to avoid that.
7c. put a light pipe in the case if you want, but basically you're not, but i like having at least a power LED on a board and 1 to a micro pin because just that is enough to test a lot of stuff with.
7d. the heavy filtering is just to get the micro noise and other switching noise out of the ADC. The Jaguar board uses a complete second reg for this purpose, but i opted for a few little passives.

I never set off making this board small. It was made with big components where i could so it was easy to manufacture and make it not massive. This board could shrink down to a lot lot lot smaller if i really tried...
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Re: Hey, look, i built something! Neds MicroEMS

Post by DonTZ125 »

Ned wrote:Cool, questions, i like questions :)

Ground wise, as you can see, the only things on PGND is the injectors and the low side drivers. They are all placed physicaly close to the PGND pins so that section of PCB could get poured with a PGND ground plane on top and bottom layer for a nice solid connection.
Good stuff - that's how I like to do mine.
The rest of the board is all SGND
I had one design where I ran out of pins, and had SGND and PGND on the same pin. PGND was the bottom plane snuggled against the header, while SGND was the top plane. The only place they met was at the pin.
Ned wrote: multi part questions and some good ideas in there, i like it! I also like that you obviously really looked at the PCB and not just glanced at it, appreciated!
8-)

1. So because this project was done mainly for me, not for the general public, my documentation is super super shit. Let me explain what happens there. Fred had a big hissy fit about measuring 12V battery being one of the most important things in this world, and he hated that the voldesquirt measured the 12V on its input feed, and he was dead keen on being able to measure the battery voltage seperately, so for the sake of one extra track and one resistor, i gave him that option. If you populate R83 and remove R1, as well as remove R13, then SPARE3 will become the battery V input and gets rerouted to the same BattV pin on the micro and spare3_adc gets left unconnected.
You dont actually need to remove R13 if you dont want to, the protection circuit will take care of it, but its best to remove it. R12 can stay, it will just draw 3mA but thats ok. You really just need to move the 3K9 from R1 to R83 to move the battery sense pin.
Does that make more sense?
I had to read that 3 times, looking back and forth at the schematic, before it sank in. Batt_ADC remains Batt_ADC, whether it comes in through the power supply pin or SPARE3 header pin. Spare3_ADC is taken out of service if SPARE3 is the VBatt sense pin - right?

Honestly, I really don't see the difference; the nominal VBatt tap is upstream of all the power supply filters and protective components, so I don't see how one circuit would interfere with the other.
Fred? This was done at your behest; can you un-confuse me? ;)
2. guessing you mean having the 2K49 resistors from 5V to the input are no good for things like a MAP sensor? i understand, but things like a MAP sensor that have an actual driven output SHOULD have enough output current to completely negate a 2K49 pullup. Thats only 2mA afterall. I agree that its a part thats not needed, and in a perfect world not wanted, but its also not worth putting a solder blob on the board for it because it should operate fine with it.
The other thing is that a machine cant place solder blobs, unless its on the bottom side of the board during wave soldering and then you need an extra step (peel able solder mask) if you want solder blobs to be open by default. You make a valid point though because it wouldnt work with another TPS for example. Actually, even that you could make work by only using the bottom bin and the wiper on the TPS. Signal size would go down but it would still operate fine.
The thing is, the MACHINE isn't putting down a solder blob. It's an open solder jumper, filled in by the end user if needed.
3b. simple reason, if i trip over the cord, i am less likely to ruin a USB B port, but will 100% rip the little micro USB socket off the board. It's just a robustness thing really. People like fred have complained to no end and say they dont even have that cable anymore, but i still use them every day on a bunch of hear i have here. It really is the right choice if you ask me. I never tried to make this board small, so it wasnt an issue.
Take another look at that uB connector. Especially if the board is in the housing such that the socket & gasket are wedged against the housing like it should be, you'll probably rip the connector off the cable first!
5. yeah, a solder blob wouldnt be a bad idea, but i just wanted to stay away from that for this revision because again, a machine cant place a solder blob.
Again, the end user should be placing the blob. You want it open from the factory. This is how the Micro-Volde-squirt does it, and it is effective.
6. i was thinking about having 2 pullups. One to 12V and 1 to 5V, that way you could choose. You could also put an inductor in place of the resistor to the 12V that way and actually create a big spiking high voltage to drive an old school tacho thats normally fed from the -ve of the coil... but figured an external circuit works well and keeps the high voltage noise out the ECU case.
Again with the selecting solder jumpers ... :lol2:
7. multiple caps is because ceramics just arent perfect, but adding lots of physically big, lower value caps, you get a good end result, so thats why that is.
Fred made a comment about watching the various and cumulative ESR. How does an array like this affect his point?
7a. the ideal diode isnt there for reverse polarity, its there purely to not back-feed 5V from the USB into the regulator when the reg isnt powered. A lot of regs wont like that.
Gotcha. The point of using a small P-mosfet still stands.
7b. The problem with clamping diodes is that they start conducting too early, and a 5V6 will likely conduct at well below 5V and wanted to avoid that.
That's why you use 1% zeners in SOT23 cases (or 0.2% PolyZen devices), not 20% units in SMA boxes ... ;)
7d. the heavy filtering is just to get the micro noise and other switching noise out of the ADC. The Jaguar board uses a complete second reg for this purpose, but i opted for a few little passives.
Interesting point, but the majority of the switching inside the housing is small, Hi-Z and (presumably) low-capacitance Mosfets. How much noise is generated, and how much comes off the uP, compared to what the VRef wire picks up as it travels into the Great Outdoors (tm), where it's suddenly surrounded by injectors, ignition coils, and PWM-ing solenoids? Not arguing, genuinely curious.
I never set off making this board small. It was made with big components where i could so it was easy to manufacture and make it not massive. This board could shrink down to a lot lot lot smaller if i really tried...
Heh - I've looked at some boards with 0102 resistors and caps, or 01005(!) - I can barely SEE the damn things, never mind put them on a board with a set of tweezers! :?
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Re: Hey, look, i built something! Neds MicroEMS

Post by Ned »

DonTZ125 wrote: I had one design where I ran out of pins, and had SGND and PGND on the same pin. PGND was the bottom plane snuggled against the header, while SGND was the top plane. The only place they met was at the pin.
Fred doesnt like this and threw a big tantrum about grounding. He's so so so so scared of noise that boy, but i think he's just not used to rubbish hardware/installs that are noisy. He made some good points but 75% of his points were shit (in my opinion)
DonTZ125 wrote: I had to read that 3 times, looking back and forth at the schematic, before it sank in. Batt_ADC remains Batt_ADC, whether it comes in through the power supply pin or SPARE3 header pin. Spare3_ADC is taken out of service if SPARE3 is the VBatt sense pin - right?
thats exactly it, you got it (i should have re-read my shitty explanation and cleared that up better)
DonTZ125 wrote: Honestly, I really don't see the difference; the nominal VBatt tap is upstream of all the power supply filters and protective components, so I don't see how one circuit would interfere with the other.
Fred? This was done at your behest; can you un-confuse me?
the difference is that Fred has this 'ideal' scenario in his head that isnt actually how life works haha. If fred had his way, every single thing would be fed directly from the battery, and grounded directly to the battery etc. His arguement is that he wants to get an accurate battery voltage reading to control dwell and injector timing etc based on battery voltage, and he doesnt want that on the main feed line due to voltage drop of the cable etc.

though discussions about wiring and grounding and noise should be had with Fred in a different thread because he'll talk about it until the cows come home
DonTZ125 wrote: The thing is, the MACHINE isn't putting down a solder blob. It's an open solder jumper, filled in by the end user if needed.
thats true, but in a perfect world, the ECU should be able to be used by any and all configurations of car, without opening the case after it leaves the factory
DonTZ125 wrote: Take another look at that uB connector. Especially if the board is in the housing such that the socket & gasket are wedged against the housing like it should be, you'll probably rip the connector off the cable first!
you're right, it's a good connector, but also the only one of its kind, and is a non-stock item with a 6 month lead time ;) so i'm glad i went with the standard USB-B that i can get from any parts place, any day of the week...
DonTZ125 wrote: Fred made a comment about watching the various and cumulative ESR. How does an array like this affect his point?
by simply not caring about cumulative ESR. We're not building precision control gear here. It's just a car ECU. again, this is where me and fred differ and clash heads a lot. I'm a binary person, he's a decimal guy. For me shit is a 1 or a 0. It works or it doesnt. If it works, i'm happy as larry. Fred is a 0-10 guy, he wants everything to be a 10, anything under a 10 is shit and doesnt deserve his time of day... and this is how i built an ecu in 3 weeks, and FreeEMS hasnt had a public commit since June 2014.
DonTZ125 wrote: Gotcha. The point of using a small P-mosfet still stands.
Yeah, for sure, that works, but so does the diode thats there. That provides reverse polarity already. Plus its pretty hard to reverse polarise something with 1 supply and 5 grounds. Much more likely to short it probably :)
DonTZ125 wrote: That's why you use 1% zeners in SOT23 cases (or 0.2% PolyZen devices), not 20% units in SMA boxes ... ;)
Yeah, for sure, there is always better gear out there, and better solutions. Quite frankly, i just copied some other designs that had one and called it a day. It's just there to stop the rail from coming up too far, and even at 5V6 thats technically over the max input v of the devices so both options are shit in real life anyway haha
DonTZ125 wrote: Interesting point, but the majority of the switching inside the housing is small, Hi-Z and (presumably) low-capacitance Mosfets. How much noise is generated, and how much comes off the uP, compared to what the VRef wire picks up as it travels into the Great Outdoors (tm), where it's suddenly surrounded by injectors, ignition coils, and PWM-ing solenoids? Not arguing, genuinely curious.
you actually make a fantastic point, and that reason is why you SHOULD (i dont) probably run shielded cable for the TPS and other stuff that uses the 5V Ref... but it should be pretty hard for noise to be induced that way though when it's a supply that has quite a bit of grunt. An input pin with little/no filtering is a different story though, but i doubt you'll be able to induce much noise into it... as long as you keep it away from the HT side of the coil of course ;)
DonTZ125 wrote: Heh - I've looked at some boards with 0102 resistors and caps, or 01005(!) - I can barely SEE the damn things, never mind put them on a board with a set of tweezers! :?
It sure does get hard! the stuff i build at work (concussion sensor for rugby players) all uses 0201 stuff and its gets quite hard changing components and hand soldering etc
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Re: Hey, look, i built something! Neds MicroEMS

Post by DonTZ125 »

Ned wrote:
DonTZ125 wrote: The thing is, the MACHINE isn't putting down a solder blob. It's an open solder jumper, filled in by the end user if needed.
thats true, but in a perfect world, the ECU should be able to be used by any and all configurations of car, without opening the case after it leaves the factory
Sure, that's perfect for a model-specific device, what the Brits call "bespoke". For a generic unit meant to be sold to people using something else, there has to be some degree of customization. The simplest way to do this in a SMT box is solder jumpers.
DonTZ125 wrote: Take another look at that uB connector. Especially if the board is in the housing such that the socket & gasket are wedged against the housing like it should be, you'll probably rip the connector off the cable first!
you're right, it's a good connector, but also the only one of its kind, and is a non-stock item with a 6 month lead time ;) so i'm glad i went with the standard USB-B that i can get from any parts place, any day of the week...
Wot the ... ?! I really did not notice that - I thought they were available off the shelf. Too new, apparently ... :oops:
DonTZ125 wrote: Fred made a comment about watching the various and cumulative ESR. How does an array like this affect his point?
by simply not caring about cumulative ESR. We're not building precision control gear here. It's just a car ECU. again, this is where me and fred differ and clash heads a lot. I'm a binary person, he's a decimal guy. For me shit is a 1 or a 0. It works or it doesnt. If it works, i'm happy as larry. Fred is a 0-10 guy, he wants everything to be a 10, anything under a 10 is shit and doesnt deserve his time of day... and this is how i built an ecu in 3 weeks, and FreeEMS hasnt had a public commit since June 2014.
*snerk* But you are using the FreeEMS firmware in your toy?
DonTZ125 wrote: Interesting point, but the majority of the switching inside the housing is small, Hi-Z and (presumably) low-capacitance Mosfets. How much noise is generated, and how much comes off the uP, compared to what the VRef wire picks up as it travels into the Great Outdoors (tm), where it's suddenly surrounded by injectors, ignition coils, and PWM-ing solenoids? Not arguing, genuinely curious.
you actually make a fantastic point, and that reason is why you SHOULD (i dont) probably run shielded cable for the TPS and other stuff that uses the 5V Ref... but it should be pretty hard for noise to be induced that way though when it's a supply that has quite a bit of grunt. An input pin with little/no filtering is a different story though, but i doubt you'll be able to induce much noise into it... as long as you keep it away from the HT side of the coil of course ;)
The problem with running shielded VRef wire is tapping into it. Unless you plan on tapping in and splicing into both the wire and shield multiple times, you'd have to run a dedicated shielded wire out to each sensor, with a ganged splice and termination point for the various wires. Actually, if you're going to do that, you may as well use two-lead wire to the TPS and MAP, and run the signal return back inside the shield.

Or just accept that the filter circuit on the ADC will probably absorb more variation than the increased accuracy such a wiring plan would allow ... :D
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Re: Hey, look, i built something! Neds MicroEMS

Post by Fred »

9pm, just walked inside, yet to have dinner, or shower, alarm set for 6, so I won't reply to most of the above, tonight, anyway.

Dontz, do you have a phone number? I have many minutes per month to foreign lands, but rarely use them all up. It'd be my pleasure to discuss all of the above things that Ned has deemed inappropriate to discuss. His sentiments about me in the above posts have been repeated in person many times. We'll agree to disagree on many things, however on some of the more personal remarks about me, Ned's just wrong. He's wrong about some of the tech, and my reasoning, too.

"*snerk* But you are using the FreeEMS firmware in your toy?" < I can answer this one quickly. Not yet. Though I hope soon. Time will tell. I can elaborate over the phone if you are interested.

Ned, let me know if you make any progress and need a further FreeEMS-focussed hand.

Fred.
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Re: Hey, look, i built something! Neds MicroEMS

Post by TonyS »

Hi Ned,

Congratulations on your new design!
Please keep us informed as you progress through testing and such.

I took a look at the schematic, and if you ever decide to do a "Rev 2", I think that I could offer a few suggestions for improvement.

Do you have a BOM you would be willing to share? I am interested in looking at the specs for the passives / discretes that were selected.

Thanks,
TonyS
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Re: Hey, look, i built something! Neds MicroEMS

Post by Ned »

feel free to share them with me now :) and i'll post up a bom in the not too distant future, dont have one handy atm
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Re: Hey, look, i built something! Neds MicroEMS

Post by DonTZ125 »

Fred wrote:Dontz, do you have a phone number? I have many minutes per month to foreign lands, but rarely use them all up. It'd be my pleasure to discuss all of the above things that Ned has deemed inappropriate to discuss. His sentiments about me in the above posts have been repeated in person many times. We'll agree to disagree on many things, however on some of the more personal remarks about me, Ned's just wrong. He's wrong about some of the tech, and my reasoning, too.
I took most of Ned's comments to be one friend lighting up another, exaggerated for the purpose of humour and generally being a schmuck.

I do have a phone number; we don't all live in igloos. :D That said, a phone discussion would sorta break your own rule about discussing things in PM vs the forum, so that knowledge is shared. If you don't want to post it here, do please start a thread titled "Fred's reasoned responses to Ned's ridiculous allegations and slander."


TonyS - Share! That's the whole point behind posting the design, third-party review and input. Gods know I've found stupid errors in my own designs only after I've shipped one off to a client. Usually they're innocuous or easily remedied; I once had to replace the three units already shipped due to a fatal mistake. Designing without a second (or 3rd, 4th) set of eyes is HARD.
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Re: Hey, look, i built something! Neds MicroEMS

Post by Ned »

Thats exactly what it was :)
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