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Old 06-12-2013, 06:27 AM   #60 (permalink)
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Originally Posted by jeff88 View Post
Looked up some DMMs, but I am still stuck on what will be of benefit (for this project and general purpose uses).
I don't think you are too far off, no. I wouldn't like to pick one out though. I think that should be your decision (sorry).

Also, I have added links to the exact items I am going to get in my parts list. Can you just double check to make sure I am getting the correct items before I order them? I want to order them this week or next, but want to make sure I get the right things first.
Current limiting resistors for the display and for the transistors? You'll need to put together a schematic design and work out what they should be first.

Do you still need the Mega when using I2C, given that I2C will only need two digital pins rather than 6 analog pins?

I put a relay on the list originally, but now am wondering why I did so. Can you think of a reason at this point why I would need one?
Not really. Maybe there's some benefit to keeping the unit isolated from other circuits in the car to avoid noise. The current it draws (it needs to be under 200mA total to protect the Arduino) won't be enough to require a dedicated circuit and it can be connected into an ignition switched supply. I'd (will) try it without one first.

I can't recall the last time I bought a relay anyway. They're usually free from the junkyard, especially if purchasing something else.

Should I get some male to male pin headers to make soldering the wires on easier or can I just attach the wires directly to the board (I assume this might be difficult in the long run as the wires might come out with vibrations and whatnot, plus the headers would make taking the wires out easier, if need be)? Is there a special Arduino pin header or are all pin headers the same (other than # of pins)? I assume I should be looking for a pin header for less than a dollar a piece (or maybe literally just a few pennies a piece)?
I used the pin headers to make the connection between the shield and the Arduino. The pins are soldered to the shield and a push fit into the female sockets on the Arduino. There are a few tutorials around on doing that. Adafruit has (at least) one. That means the shield is easy to separate from the Arduino and there's no permanent alteration to the Arduino.

They are not locked in any way but are a pretty solid friction fit (there are 28 of the pins and sockets).

The header pins are a standard 0.1" spacing.

I have the wires soldered directly to the shield, in the through holes.

If you want to be able to separate the wires from the board, you could use PCB mount friction locking header connectors.

Like this:

5 Position 0.1" Straight Friction Locking Header: Industrial & Scientific

plus the corresponding female part. There are 90 degree versions of the male connectors if that packages better.

One part is soldered to the board, the socket terminals are crimped or soldered to each wire, pushed into the second part and the two parts snap together.

What you use is up to you.

How should I mount the Arduino and accel/gyro? Can I just drill some holes in the veroboard and screw them directly to the board, or should I mount it to something else, like a piece of aluminum or wood with some bolts and nuts and maybe some rubber washers (for vibration control)?
As you may recall (or can check in the images) I have the accelerometer board mounted solidly on the shield, held in place solely by the soldered wires, so I only have to figure out a single mount for the Arduino plus shield, and one for the display. It will all end up in what is currently a storage slot in the dash.

Doing it again, I would not solder the connecting wires with the accelerometer board resting on the shield. That makes the accelerometer board difficult to remove (should that be necessary) by soldering the solder pads on the two boards together. A better way is to space it off the board with a thin, flat insulator eg. a scrap of bench top laminate.

While I have some idea, I haven't fully thought out how to mount mine yet. Worst case, there's always epoxy adhesive .

I am not anticipating vibration to be a problem and something I think I can deal with in the sketch if it is.

It probably won't hurt to rubber mount the parts but most automotive electronics are solidly mounted.

The accelerometer board at least already has holes in it for the purpose of mounting it to something. You can certainly drill holes in Veroboard.
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