Open source PCB design

[dcb]

I think the project could use an open source PCB design to go along with it for folks who want a real easy and tidy assembly.

I'm playing around with the free version of EAGLE currently: http://www.cadsoft.de/freeware.htm which some companies can actually take and produce boards with. Or if you want to do the DIY laser printer etchant thing too that would be cool too. So I will play around with EAGLE and post something unless a more experienced person beats me to it

Requirements:

1. it MUST be pin compatable with the mpguino as defined. Otherwise we will have too much explaining to do and other support.maintenance headaches.

2. It should work with the top pin LCDs, the Edge pin ones are optional, but would be nice if we could get those wired up too. You should be able to solder it directly to the back of a LCD with some header pins.

3. It should be as small as possible, and still provide for programming, via rs232 or usb adapter. (edit: leaning towards USB, but lack of standards here is frustrating)

4. Of course, it has to hold all the other components necessary to call it a guino

Any other requirements?

If enough folks want a kit then maybe we can get something together. But probably not for another month or so.

There might be seperate USB and rs232 versions, or just two versions of an external programmer that you build, don't know.

[jmonroe]

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

[awillard69]

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, .

[dcb]

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

[awillard69]

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!

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?

[dcb]

Originally Posted by awillard69

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

[awillard69]

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.

[MilesPerTank]

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.

[dcb]

FYI: eagle is pretty cool, you start with a schematic then layout the components on a board.



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.

[MilesPerTank]

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!

[dcb]

Need is a strong word, and it is a little specious to suggest the failure mode of andrews LCD AND to go from "person" to "people", but nonetheless...

On the one hand, there are plenty of examples of 7805's in automotive service in the homebrew/diy niche, where it is deemed "good enough" with a couple capacitors on it. With the standard LCD we are barely at 1/5 the capacity of the regulator.

On the other hand, there are a couple examples where they go to great lengths to protect the voltage regulator, the megasquirt comes to mind, but its schematic seems to be something of a paradox in itself.

Tell you what, Sourcing a 30 volt zener isn't terribly bad, it adds a component, but I cannot believe that there isn't a common 5 volt voltage regulator in existence designed for automotive use. Can somebody mouse around and see if the 7805 should be obsolete for automotive use and replaced with something better?

[dcb]

One power conditioning design I did see that made a lot of sense to me was a large capacitor on the input and positive was connected to automotive power "in case the starter tries to drain the capacitor" For some reason I have a real hard time putting a voltage regulator (zener) on a voltage regulator, but a large capacitor should smooth things out and reduce/eliminate brownouts, which the atmega definately doesn't like, especially with a diode there. Thoughts? Is that a reasonable compromise between DIY "good enough" and "clean room" mentality and complexity? Which would also add a fair degree of reliability to the power supply at the same time?

edit: updated schematic/board in post 9. Also note futurelec sems to have very reasonable prices for no-frills prototype boards, especially single sided. Any others? I have zero experience here.

Also what about buttons? I wind up custom fabbing them to keep the front profile to a minimum, but what are the options there? Also I like pressing down on them since it doen't test the strength of my velcro so much.

[MilesPerTank]

Originally Posted by dcb

With the standard LCD we are barely at 1/5 the capacity of the regulator.

At ambient room temperatures maybe. Our end goal has this device powered by a 13-14V alternator inside a hot car. 14V * 200mA is 2.8W (LDO). We only use 5V * 200mA = 1W . That's 1.8W burned in the regulator.

The way I have mine mounted is non heat sinked with no airflow. I admit I've got it in a project box pretty sealed up which isn't the best idea. Its 100 degrees ambient this week (~36C , North Carolina) not counting any solar loading.

http://www.fairchildsemi.com/ds/LM/LM7805.pdf

Max junction is 125C with a RthetaJA of 65 C/W. Using the above 1.8W*65C/W = 117 C. You can see if our 200mA is correct we are already in violation of the max temp even under a 25C air conditioned lab when using the cars voltage range. Anyone got some good temperature probes at home to mount to one of these? I'll take the board into work tomorrow and try to get some load current measurements.

I plan to mount a nice sized power resistor in front of the 7805. It will help current limit and burn some of the initial 14V .

[dcb]

I'd suggest a metal project box that would double as a heatsink if you are going to box it. You shouldn't have any problems with 200ma then. FWIW, my open air installations haven't complained yet about the heat, I haven't even noticed the regulator getting warm.

We do need to wait on the autopsy report on Andrews before deciding on a course of action there. I really want to keep the final product as simple and inexpensive as possible.

Edit: I should also mention that it isn't *really* necessary to run the backlight at 200ma, I run it on its lowest setting day and night without a problem. I turned down the brightness values a bit in the sourcecode, that is far easier than changing the circuit.

[hank freid love]

This is nice and all, but the one thing I'd like to see is a tutorial on how to properly lay out a circuit board in one of these CAD tools. All of these PCB how-to's assume that you know how to find the mechanical specifications for a specific chip into a proper pad placement and size in these CAD tools.

[dcb]

Here is a proto-prototype for the pcb version (I needed another guino for testing anyway). It was a PITA, took some planning, but it is loosely based on the pcb planform above and uses the same schematic. Playing with the layout in eagle helped out a bit.



For some reason this lcd isn't turning off all the way, no biggie. But need to figure out why.

The onesided preprogrammed version currently only has one airwire, and needs some tweaking yet. But I just checked futurelec and their price per board just took a big jump?!? 10 single sided boards would be $39 shipped. And that is with doing your own custom buttons. Where are we with the buttons anyway? I've gotten pretty good at fabbing them and tucking them into the LCD border, but that doesn't make it the best solution.

Also don't know about programming headers or onboard usb/rs232 chips. I'm comfortable using my existing freeduino to program a "headless" guino chip and pop it in to the socket, especially if the software gets pretty stable. I could crank out quite a few of them for friends and family who would never have need for either the usb chip or a programming header. Is assuming the builder has an arduino at their disposal to program the chip setting the bar to high?

[ConnClark]

Originally Posted by MilesPerTank

http://www.fairchildsemi.com/ds/LM/LM7805.pdf

Max junction is 125C with a RthetaJA of 65 C/W. Using the above 1.8W*65C/W = 117 C. You can see if our 200mA is correct we are already in violation of the max temp even under a 25C air conditioned lab when using the cars voltage range. Anyone got some good temperature probes at home to mount to one of these? I'll take the board into work tomorrow and try to get some load current measurements.

I plan to mount a nice sized power resistor in front of the 7805. It will help current limit and burn some of the initial 14V .

We are supposed to be saving energy here ;-)

Here is a Switching 7805 drop in replacement project
http://www.narwani.net/neil/tech/elec/78SWxx/index.html

Also for an OpenSource layout and schematic program look at kicad. It supports Linux/Unix and windows.

[jmonroe]

When a PCB design gets finalized, is anyone planning on putting together a kit with the board, components, and LCD un-assembled in a bag and selling that? I would be interested in at least one of those.

I am sure there would be room in that to make profit.

[dcb]

I can look into it, but need to understand the intended audience better, so let me get some feedback here:

The first run as it stands would be:
The above schematic, zeners, big old capacitor power supply, atmega with a bootloader and the then current version of the code, header pin interface with the car with a small female plug you solder your wires too, LCD, IC socket so you can update the software, single sided PCB, etc.

Not included:
Exact instructions for your vehicle
fuses for power lines
fancy wiretaps, you strip and solder to your own wires or come up with something.
A chip programmer or header, use an existing DIP duino to update the software and swap in the updated chip, or come up with something.
Warranty, or any liability on my part.
Solder, tools, skill, nerve.

Rough guess would be $25ish +- 20% depending on quantity and using the current parts set. Might be a month before the software is really ready for pre-loading.

If you are interested let me know, I've not done this before so be forewarned

[SVOboy]

I'm DIYing it, but if you're interested, dcb, I'm sure the site would be willing to help make it a reality so that the project is more accesibly for those who need it.