Open source PCB design
 

Have you given any thought to simply designing it as a shield for the *duino that could be removed and re-attached.

The advantages I see are
- less to design
- USB or RS232 independent
- *duino can be reused for other things
- already retains all *duino functionality

disadvantages
- probably larger
- more expensive to build the entire project from scratch

You should consider a size as well. Something that can fit a basic project box would make it easier to get common parts.

Consider the buttons also. Without a good board design and enclosure, the geometry of the buttons and placement will be have to be custom build, deviating from the "kit" mentality.

What about the wiring? How should someone connect to the automobile? You wouldn't want it hardwired in. That dictates some common form of connector, what kind, how much, how easy to get, etc... This will allow pulling it for upgrades, or use in a different vehicle.

How to program the Guino, with a pass through connector to the enclosure? If not, maybe some way to mount the Guino so that it easily snaps out of the enclosure for reprogramming.

I don't think it will ever be as small as a SGII, but we should at least try. Looking at my pictures, outside of the Arduino and LCD, my components are quite small, a PCB would help here. My homemade connectors for easy dis/connect are large because I didn't have something more appropriate.

A good PCB would go along way to shrinking my whole unit.

With the exception of the LCD, buttons and inputs, would one of the generic project/proto shields work? Perhaps a custom shield? You would still need some custom connector to the LCD and external buttons. But, since those will mount to the enclosure, maybe it's better that way.

This is definitely a good idea, and has sorta been my perspective from the beginning. But, maybe a DIY-scrounge-for-yourself-on-the-cheap or a more easily utilized kitted version. Worth investigating once it is stable and usable, which seems to be now, ;).

re: size, good point. My guiding principal is no bigger than a 2x16 lcd and as thin as possible. I was able to make a guino from a rbbb kit and an lcd that was 60% the size of a scangauge, should be able to beat that with a custom board.

Re: shield, if someone locates an arduino board template for Eagle, I can slap a PCB diagram together. Also, you *could* pop the guino chip in your 'duino and program it that way, then put it back in the guino. Actually that helps build the case for keeping the programmer seperate.

re: car wiring, possibly just solder if you are up for it, or use the red trailer wiring clips if not. I found stripping the wire in place then soldering to be about the same effort and a whole lot more reliable. I heard mention of other types of taps, can someone research that a bit more?

re: programming, don't know. It was an issue before we even got here. I think the safe thing to do is to include the couple transistor rs232 circuit adapter, and have some folks try their usb adapters on that. Or use an existing 'duino to program the chip.

Anywhoo, here is my first stab at pcb design, don't laugh :) I have not added a voltage regulator or programming interface yet.

Edit: added regulator. With a pre-programmed chip it just might work :)

http://opengauge.org/diympggauge/pcb.GIF

Ok, I admit that maybe I misunderstood. I thought you meant create some sort of peripheral card for the Arduino, one that performs the MPGuino functions as an add in shield module to a Freeduino/Arduino module. More of a snap together assembly from available parts.

From your design, it seems that you are adapting the ATM168 and creating a single purpose unit for the MPGuino. That can be good for the long term, and I agree, with a programmed chip, it could work! :thumbup:

Maybe add tie points for the 4 inputs: VSS, Injector, ground, +12v. Either through some buss bar, or solder holes, and point labels.

Don't forget the MPGuino name, board version, etc.

Does the Eagle software maintain a parts list?

It does in fact, dont take this list literally though:

Partlist

Exported from MPGUINO.brd at 5/30/2008 9:51:08 AM

EAGLE Version 5.0.0 Copyright (c) 1988-2008 CadSoft

Part Value Package Library Position (inch) Orientation

C1 20p C025-025X050 rcl (1.95 1.75) R270
C2 20p C025-025X050 rcl (2.7 1.75) R270
C3 C025-025X050 rcl (2 2.6) R0
C4 20p C025-025X050 rcl (3.3 1.85) R180
C5 20p C025-025X050 rcl (3.05 1.7) R0
C6 20p C025-025X050 rcl (3.05 1.85) R0
D1 ZTK DO35Z10 diode (1.1 2.3) R0
D2 ZTK DO35Z10 diode (1.1 2.55) R0
DIS1 TUXGR_16X2_R2 TUXGR_16X2_R2 display-lcd (1.85 2.3) MR0
IC1 MEGA8-P DIL28-3 atmel (2.15 2.2) R0
IC2 78XXL v-reg (3.15 2.2) R0
Q1 16M HC49/S crystal (2.35 1.85) R180
Q2 2N3906 TO92 transistor-pnp (0.5 2.7) R0
R1 10k 0207/7 rcl (1.6 2.6) R180
R2 0207/12 rcl (0.6 2.55) R0
R3 0207/12 rcl (1.5 1.7) R180
R4 100 0207/7 rcl (2.65 2.75) R180
R5 2.7K 0207/7 rcl (0.4 2.1) R90
S1 SKHMPUE010 SKHMPXE010 switch (0.9 3.05) R0
S2 SKHMPUE010 SKHMPXE010 switch (0.45 3.05) R0
S3 SKHMPUE010 SKHMPXE010 switch (1.35 3.05) R0
SV1 MA04-1 con-lstb (0.7 1.85) R0

Well, that's a start. Now we just need a kit of parts (minus the board) from some supplier.

I received my proto shields today. I'm gonna migrate my crude interfacing and wire gobs to a shield, then try to stack my prototype generator to yet another shield.

Sure, it won't be uber-tiny, but probably more compact and safe for a smaller enclosure. The shield will also make it a more pluggable design.

I would prefer to use surface mount parts. It isn't that much harder to solder them.

Also please add a fuse to the input.

FYI: eagle is pretty cool, you start with a schematic then layout the components on a board.
http://opengauge.org/diympggauge/schematic.GIF
http://opengauge.org/diympggauge/pcb.GIF

re: fuse, you can certainly add it to where you tap into the power supply, it wouldn't hurt if you are using smaller wire than the existing circuit protection will provide for, but it doesn't really belong on the board itself (most devices do not have such a fuse). The 100k resistors will prevent calamity on the signal lines.

If you plan to run this in a car you really need a surge clamp on the input. People have been experiencing LCD s fail and its nice to just rule a surge out of the equation.

Almost every single piece of electronics I have ever taken apart have a fuse on the input (or that I've designed at work).

I'm a hardware engineer by day that designs DC/DC converters so if I come off sounding rude I apologize. I don't work in the automotive industry but rather tel com so my surges are lightning induced and a surge clamp is mandatory!