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Old 02-04-2009, 12:01 AM   #303 (permalink)
RussEnterprises
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Quote:
Originally Posted by cmags View Post
I'm planning on using the iDuino too. Looking over the schematic, the only trouble I see is that the Arduino is powered by the OBD connector's 12V line. This is convenient for having one less plug to come into the circuit, but the iDuino does not have a built-in regulator, and requires a regulated 5V.

Question: Can we power the iDuino from a separate 5V source, allowing the 12V line from the car to power only the MC33290 on pin 1?

It would be the same 12V from the car's system as it is coming in over the OBD line, so I don't see why not.

I could put a regulator on the aux. board (requires 4 components: 7805, .1uf cap, 330uf electrolytic cap, 1n400x diode), but I'm trying to save board space for a small enclosure. Plus I was running into heat issues with my MPGuino so I'd like to keep the reg out of the box if possible. My plan is to build an external 5v regulator and run it into the USB port of the iDuino, and use that to power the board and the VDD of the MC chip. Seems viable, anyone see a reason this won't work? The MC already has a separate ground (signal GND vs chassis GND) so it already looks power isolated.
There should be no problem with using a separate 5v source, as long as the 5v source shares a ground with the 12v source. Chances are if your 5v source is powered from the cars electrical system, that will be the case, but I'd probably connect the ground from the iDuino to the MC33290 ground just to make sure.
For my prototype, I'm using 3 wires from the obdii plug (+12, gnd, K-Line) to a small piece of perfboard with the 33290, pullup resistor, and a 7805, then 4 wires to my arduino clone (tx, rx, gnd, +5). If I do a final version, I may be able to build the perfboard into the hood for the obdii plug, or I may just put it in a small box and leave it inline.

Russ
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