Open source PCB design

[dcb]

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

[slogfilet]

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.

[dcb]

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.

[ishiyakazuo]

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...)

[pcrider]

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

[ishiyakazuo]

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.

[Clev]

Originally Posted by pcrider

G. Taylor
Honda PC800 50mpg

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


Tim

[wyatt]

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.

[rmccomiskie]

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:



(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.

[rmccomiskie]

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.

[ac7ss]

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)

[Ran_Talbott]

Originally Posted by pcrider

The LM2940.. was designed by National Semiconductor for auto applications with attendent power interruptions and spiking and is available with a 5v output.

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

[dcb]

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.

[scubascooby]

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.