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!

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?

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.

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 :).

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.

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.

http://opengauge.org/diympggauge/scratch.JPG

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?

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

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.

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.

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 :)

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. :)

FYI, added eagle files to the repository. There's no onboard programmer or programming adapter due to lack of standards. Use an existing duino to program the chip.

Revision 51: /trunk/mpguino

Just want to make sure I have this straight...

This would be an all-in-one unit, leaving me with my RBBB to play with as needed. If I needed to update the code, I'd pop the chip out of the 'guino and set it in my RBBB, programming however I like.

And it'd be hella slick and small.

Is that it? If so, I want one! I like the idea of a kit format that I solder myself... I'm not yet skilled enough for a total DIY, and all those leads intimidate me.

Correct, in this scneario you would program your rbbb or iduino or any DIP based duino/clone as "normal" with the latest mpguino code, then swap chips with the guino.

I didn't notice this thread before, but I was thinking of making an Altoids tin-sized PCB for the OBD MPGuino, and looking at the code for the OBD one and comparing the schematic of the mainline one, there doesn't seem to be much of a reason that both designs can't share a PCB. Maybe we should look into making a unified design and make a volume order? :) (Personally, the OBD one is very appealing to me, since I have two OBD-II enabled cars...)

7805 Automotive Replacement
 

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?[/QUOTE]

The LM2940.. was designed by National Semiconductor for auto applications with attendent power interruptions and spiking and is available with a 5v output. I'm not sure which temp. spec you're interested in, but in general the T0-220 variety runs just under $2 from DIGI-KEY.

I've watched the development of this project and am ipressed with the progress. Keep up the good work!

G. Taylor
Honda PC800 50mpg

I'd be more interested in LM2940T because I can easily see the inside of my car being below 0 C ;)
Definitely looks like the right part for the job though. Thanks!
If you're only ordering 1 and need to go Mouser (due to other parts in the order, etc.), they have NTE1951 as a replacement part for LM2940CT.

Oh, excellent, a PC rider! I miss my PC terribly, and someday hope to convert one to electric.


Tim

Has anyone compiled a list of all the parts that are needed for this project? I think a parts list with links to sources would be really handy. If all the parts could be gotten from one source, that would be even better since it saves on shipping. Just a thought.

Suggestion for Connectors
 

How about using RJ45 connectors? My Guino is on a breadboard now. To connect to the car, I put an RJ45 jack on the breadboard and found an RJ45 terminator at Lowes for the other end. I made the cable by crimping RJ45 plugs on each end of 8 conductor telephone wire. So I've got 8 wires to work with and a simple way to connect to them elsewhere in the car.

Here's the terminator:
http://img246.imageshack.us/img246/9...45conn1us5.jpg
http://img246.imageshack.us/img246/9...45conn2fr3.jpg

(UPDATE: These connectors are called RJ45 Keystone Jacks. Good price here http://www.monoprice.com/products/su...05&cp_id=10513)

The connector comes with a little plastic punch-down tool. I used it to push 3 solid copper wires into place. In this case, I connect to the wires with alligator clips. It makes a very neat installation.

There are RJ45 jack templates in the Eagle libraries. Jacks can be had for $0.85 at AllElectronics.com.

RJ45 for Onboard Power and for Programming
 

If a second RJ45 is provided on board it could be used to power the Guino in the car. This cable provides only +12V power and ground.

A programming cable could be built with an RJ45 plug on one end and a USB to TTL serial on the other. It provides +12V power, ground and programming signals. Power and ground fed through the same pins as the onboard power cable.

Remove the onboard power cable from the Guino. Plug in the programming cable. Program the Guino. Swap the cables back. Walla! New code.

If current carrying capacity is an issue, use 2 wires for power and 2 wires for ground. The remaining 4 are available for programming signals.

I am currently using the Iduino for the MPGuino, (I use a telephone cord ($1.99) with a wall mount jack ($0.99) mounted to the car for the quick disconnect.) I would like to re-build my MPGuino in the manner of DCB's prototype board (For neatness) and be able to use the iduino to program the chip if I ever need to.

DCB: Do you have some detailed photos of both sides of your single board prototype? And, couldn't you change the pin settings to make the chip / LCD connection easier? (Yes, I know that this will make it not compatible with the currently constructed 'Guinos and could cause a branch in the software or can possibly be handled with a #define switch)

I just took a look at the datasheet for the LM2940, and as I read it, there's no spike protection (but, since I'm an embedded software guy, with only modest hardware knowledge, I might be mistaken). I believe the "automotive thang" was the low dropout so the 5V wouldn't go squirrelly during crank.

Back in the 1980s and 1990s, I used to do a lot of work with a friend who is a real EE, developing systems for (mostly automotive) engine control. The power input circuit he always used (with great results: he had pretty near zero units get smoked in the field) was:

1. A series diode (to protect against reversed wires during installation, and negative spikes that can occur in some vehicle electrical systems). Any old 1N4000 series will do. Since I'm not personally building a million of these, I'd spring the extra 2 or 3 cents, and go for a 1N4003 or better: it's cheap insurance.

2. A series resistor to help absorb spike energy, and dissipate some heat instead of the regulator doing it all. About 10 Ohms, since the MPGuino peaks at about 200mA.

3. A 1/2W Zener in the 25-30V range.

4. An input filter cap. The 330uF already specified might be okay, but I'd probably go for a smaller one, and use a tantalum (there are some formulas around for picking the value). Make sure its voltage rating is similar to the Zener's, since it will have to absorb spikes of up to the Zener voltage.

The output from this network went into an ordinary 3-terminal regulator (like a 7805 or an LM317).

Maybe the newer vehicles that most folks are building for have cleaner electical systems, but I wouldn't think of putting even a $40 MPGuino in my old-enough-to-vote vehicles without this sort of circuit.

Ran

Ok, I ordered some PCBs, hopefully in time for Christmas :) Been wanting to try this manufacturing thing for a little bit.

Here's the latest layout, has extra capacitance on the supply line and on the crystal and optional vss pullup/pulldown resistors (for noisy reed switch cars). Also went to 50k ohms. Will try it out and put some units together if it works.

http://opengauge.org/diympggauge/mpguino-pvb-v1.0.JPG

Hi DCB,

I'm quite new to this mpgUino project. I think my soldering and building skills are up to it but I want to build a small neat unit that doesn't look too homebuilt so this is good news for me.

Hi DCB!
good work!
Is this layout still latest PCB? Is it possible to get Eagle file for this PCB?

Sorry for stupid question, but that power supply part looks strange - near IC2 voltage regulator, there is C3 capacitor - shouldn't it be between two upper pins (Out and Gnd) on IC2 rather than Input and Gnd?
I looked this layout about 20minutes and still dont figure it out why it is like it is - all other places in internet (breadboard arduino) that power supply part is differently.
Can you comment this please.

Meelis

To "MilesperTank": Have you thought of designing an open-source DC to DC converter for an electric car? 144 volt in, 14.5 volts out. Maintenance-free batteries are charged to 14.5, not 13.8v. Measure any car. In fact, anyone running a DC to DC converter (purchased) at 13.8 volts may find poor battery capacity. (90 amps out would be nice.) I am also an analog designer, and I could design and build the (massive?) power transformer.

meelis11, I think this may be the answer to your question, though I'm completely new here (first post)

I realize that the layout above was posted quite some time ago (2 years), but...
also wondering if there's an update, or is the information, schematic, PCB at THIS website current?

I really like the idea of it being so small, with the LCD on one side, the PCB on the other. Very nice.

here is the latest schematic for the prebuilt: (note: I'm using a 20mhz crystal, not 16, and the zeners are both 5.1 volts, and I'm using an atmega328 currently and not a mega8), more descriptions here, i.e. switched to npn transistor for lcd and I don't try to keep the backlight running if the power dips.
http://ecomodder.com/forum/showthrea...tml#post171793

http://opengauge.googlecode.com/svn/...no/mpguino.png

With that "latest schematic" - does it come with a "latest PCB layout/design" or still use the one from here -->> opengauge.googlecode.com/svn/trunk/mpguino/
? Or...shall we use Eagle to generate a new PCB from this updated schematic? (my Eagle skills are non-existant)

I added MPGUINO13 eagle files to the repository, though a couple things to note:

It is not compatible with the working but deprecated arduino pde. The original MPGUINO files and schematic should be though. Arduino is a great learning platform, but I had really pushed it beyond arduinos meta-limits here and it wasn't sustainable (hence the arduino version 0011 dependency)

It is only compatible with mpguino.cpp version .83 and above (just released .86 with metric display option which needs an atmega328 for space), so you will need to sort out making hex file and isp programming.

It is not single sided, turns out that none of the board houses offer any price break for single v/s double sided so I lost interest in maintaining the extra complicated one-sided layout. If you just need one, I suggest other prototype construction methods, i.e. what is in post 15

http://opengauge.org/diympggauge/scratch.JPG

Great advancement! I've been waiting for the KM/L (L/100Km) possibility.:)

I don't understand a lot about the details you've posted, but am certainly interested in tackling it, as are a couple of others of us "north of the border".:rolleyes: