MrOnion's OnionBoard - GP IO/Power PCB (requires CPU board)

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Dan
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Re: VW Golf -89 Street/Trackday Car with ELMicro CardS12

Post by Dan »

Ravage - idle code hasn't been written yet. . . .
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Re: VW Golf -89 Street/Trackday Car with ELMicro CardS12

Post by Fred »

MrOnion, we need to skype :-p
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Re: VW Golf -89 Street/Trackday Car with ELMicro CardS12

Post by MrOnion »

Ok guys, I've come to a point I need some quick help reviewing something I've worked on. My initial plan to get a running system with a separate cpu module was to use several different break out boards etc. Later I started to look at the jaguar and ravage schematics and maybe come up with some custom stuff. The trouble I got myself into now is my scribble of a single I/O-board with almost all the external stuff I need for my setup and I ask your help to see if there is anything wrong with it before I decide to make any of these ;).

First of all I'm no HW engineer so there can be something very obvious in there so feel free to comment. Because of that I didn't do no soloing and all the pieces on the board are copied from jaguar/ravage schematics except the single power supply. Nothing fancy is implemented and tried to keep it as simple as I can.

Heres a list of things on the board:
  • Power supply with single LM2940/29150 reg, 2x filter caps on both sides, 1x varistor on input, 2x vref outputs with polyfuses, 1x 5V6 Zener clamp on 5V output
  • 6x Autofet outputs as in jag/rav, splitted as 4 injector channels and 2 accessory.
  • 4x Ignitor channels with mosfet drivers. 2x TL4424 chips with 5/12V selectable input voltage as in jag/rav.
  • 8x A/D inputs with BAT54/72 schottky protection. 4 with and 4 without bias resistors. Copied from jag/rav.
  • 2x Switch inputs with schottky and zener diodes like in jag/rav.
  • 1x BRV with own solder pad to get unfiltered voltage in.
  • 2x VR inputs and headers for external brickrpm board. Footprints for shunt and pullup resistors.
  • 2x Ground loop monitors for injector and accessory fets.
  • 10-pin header for autofet/mosfet channels, 10-pin header for A/D inputs, 12-pin header for CPU module connection.
  • 4-pin header for load/run switch/jumper and CEL.
Thats about it. Just the bare minimum to get my engine up and running. I know the zener clamp on the 5V rail is pretty crappy thing to use and should be replaced with a shunt regulator or similar (like in rav). Need to check the thread about it to fully understand why ;).

Also after the first draft Fred was kind enough to enlight me with LOTS of ideas. Like separating the groundplanes on the fets and add the groundloop monitors. Also to move the fets far as possible from the brickrpm VR inputs. Also the voltage jumper on the ignitor drivers, and and and... Thanks man for your time and help!

Few questions comes to mind that are the fact that the ground and power traces are both on the bottom layer. I don't know if this is a huge crime but tell me is it might cause trouble. There is one 5V trace that goes around the ground plane and the A/D schottky pairs are connected to it as it goes along. Finally it ends up powering the mosfet drivers if used with 5V.

Second question is that where should be a good place to put a solder pad for the sensor ground. There is space between the regulator and switch circuits. Should It be just connected to the groundplane or maybe run separate ground traces from the connection point to A/D circuits or is it overkill?

Enough ranting, here is a screenshot from Eagle:
Image

And here is the schematic which looks like shit but better than nothing:
Image

I have not put any part values in the schematic as they are the same as in jag/rav or some compromise between them. And if you want to see the the top and bottom layers separately for easier viewing please let me know.

So, if you see something in there that needs correcting please let me know, I would highly appreciate it. And to get some of this feeling of uncertainty of my back ;).

Thanks!
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Re: VW Golf -89 Street/Trackday Car with ELMicro CardS12

Post by Fred »

MrOnion wrote:Thanks man for your time and help!
You're most welcome! You scratched my back, I will continue to scratch yours! Any time! Always a pleasure! :-)
Few questions comes to mind that are the fact that the ground and power traces are both on the bottom layer. I don't know if this is a huge crime but tell me is it might cause trouble. There is one 5V trace that goes around the ground plane and the A/D schottky pairs are connected to it as it goes along. Finally it ends up powering the mosfet drivers if used with 5V.
If you do need to power them from 5V then they will inject noise onto that rail. You should probably put some beefy decouple cap(s) right on the fet driver ICs. However IMO you won't need to use 5V anyway, and if you do, it'll be at low current, so it won't be a problem. One thing I didn't notice until now: output current limit resistors on the FET drivers. Where? Inline? They are quite high power potentially (1w to 2w). I don't see anywhere to put them. Another challenge to solve? or inline them in the loom?
or maybe run separate ground traces from the connection point to A/D circuits or is it overkill?
Not overkill, just plain wrong. Think of your ground at a single point, that point is the middle leg of the regulator. All things flow back to there, cpu, sensors, etc, included. You are better off putting them in that gap than next to each input. Put enough to match the quantity of inputs, though. It's convenient to have one each. http://en.wikipedia.org/wiki/Multipoint_ground

Hope that helps. Sorry it took me till 2:30am to do it. Got on the phone to John for an hour and ran him out of battery :-)

Fred.
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Re: VW Golf -89 Street/Trackday Car with ELMicro CardS12

Post by andg »

My Dad was a VW mechanic. I would say they would be a great fit for Free EMS this is a great fit!

Code: Select all

{url: andrewgauger.com, skype: andrgaug, email: andg@andrewgauger.com, car: 25, fb: facebook.com/DonatoArrighi, github: andg.github.io, assets:https://s3.amazonaws.com/3400}
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Re: VW Golf -89 Street/Trackday Car with ELMicro CardS12

Post by DeuceEFI »

A few thoughts about your board:

1. You need current limiting resistors on the outputs of the TC442x drivers just as Fred mentioned. I used 100 ohm resistors on my Jaguar board.
2. For your 12v power feed to the voltage select jumper for the TC442x drivers, it would be better to branch that off from the MOV rather from the decouple capacitor to the regulator. If you want to decouple the 12v input to the drivers, place another pair of capacitors closer to the driver supply line (the 5v/12v jumperable line) and the driver ground.
3. Try to keep the positive voltage runs primarily on the top side of the board by the regulator instead of on the bottom with the ground plane. It looks like you have plenty of room to re-route the 5v traces on the top side. With a two sided PCB, I try to run the low power 5v and the signal traces on the same side when possible and the ground on the opposite side. Also try to run the 5v supply traces at 90 degrees from the signal traces to help with noise reduction on the signal traces if you route them on the ground plane side of the PCB.
4. Another idea for the voltage regulator and the 5v capacitors, slide the regulator closer to the VR inputs and move the output capacitors up to below the PolyFuses to keep the 5v supply lines away from the VR inputs.
5. You will want to use a mica insulator between the regulator heat sink and the board to keep from burning the board in the event that one of the 5v accessories is shorted or tries to draw 0.5A for any amount of time before the PolyFuse opens the circuit. This will also act as a electrical isolator between the traces and the heat sink if you route any 5v traces under the heatsink (but I don't recommend this routing).
6. I agree with Fred on the A/D grounds, don't separate them.

Other than the above thoughts it looks good :-)
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Re: VW Golf -89 Street/Trackday Car with ELMicro CardS12

Post by Fred »

BIG +1 for point 2.

2. also reminds me of this: You should take your 5V to the ignitor drivers directly from the supply, not from the tail end after the other stuff has its share. Star power, if you like. Much like star grounding.

Unsure how feasible 3. is, if attempting it, branch! Branch == easy return if failing.

Unsure how 4. would work, even after asking Andy :-) However this reminds me that you have 5V between the inputs of the VR traces down the bottom. If that could be reworked to keep the trace away. If you're using VR and the pull ups are not installed, then that trace would be isolated. You could keep it as is and put a solder bridge where it joins the main wire like I showed you the other night. IE, just a thin cut through the trace near the 5V rail.

Not sure that I agree with 5. I'd tend to put some copper under it instead and use the board to sink more heat away.

Thinking about 3 some more, I reckon you could do it by dipping down into the ground area and using little bridges to hop over/under other traces. This wouldn't make your ground plane ineffective, and would help the routing a lot. Ground plane may even be better and bigger with this approach.

Thanks for taking a look, Andy! :-)

Fred.
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Re: VW Golf -89 Street/Trackday Car with ELMicro CardS12

Post by DeuceEFI »

#3 was more of an observation and what I TRY to do (it doesn't always work out that way, you know how that goes...)

Another thought regarding the voltage regulator and the capacitors for the regulator circuit, why not use SMD components to:
1. save space and,
2. allow for more ground plane/heat sink area

The above is just a thought to save on space and to allow the traces to be routed a little differently.

I used a Diodes Inc part# ZLDO1117G50TA Low Drop Out regulator 5V 1A SOT223-3 package for my TCU prototype, with the supporting 0805 SMD capacitors it only occupies 14mm x 14mm of board space.

ON Semiconductor part# 1SMB5919BT3G Zener Diode 5.6V 3W SMB is available to keep the power supply all SMD if you choose to do so.

I would stay with the through hole mounted PolyFuses, they have lower internal resistance and I would keep the through hole MOV as well.
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Re: VW Golf -89 Street/Trackday Car with ELMicro CardS12

Post by DeuceEFI »

One additional thought about routing traces...
I generally route supply voltage first, then signal traces and finally let the CAD program fill in the ground plane at the end.

With that said I normally route the traces manually (by hand) instead of using an auto-router...
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Re: VW Golf -89 Street/Trackday Car with ELMicro CardS12

Post by Fred »

If you use an SMD reg, be prepared for the PCB to get a bit toasty. No big deal, but it will be warm.
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