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Originally Posted by Occasionally6
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).
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So, of that list, I won't have any problems (at least for this project)? Some DMMs I have found say 20M ohms, is that going to cause a problem? You mentioned with the voltage divider, having more than 10M ohms could cause an issue with the circuit being too resistive. Would this be the same problem with a 20M ohm DMM?
Quote:
Originally Posted by Occasionally6
You'll need to put together a schematic design and work out what they should be first.
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See attachment. I think if you open it in a new window, it might be a little easier to see. Let me know if any of it is wrong. It assumes a Mega2560 board (more about that later, see below
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Quote:
Originally Posted by Occasionally6
Do you still need the Mega when using I2C, given that I2C will only need two digital pins rather than 6 analog pins?
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I am going back and forth between the Mega and Uno. I am trying to figure out if all of my future projects will take up all the pins of the Uno, thus necessitating the Mega. The other reason why I would want the Mega is processing power/memory, being that it has more of it. I am also worried about having too much total current, thus possibly necessitating 2 or 3 Uno boards. This page says the Mega can handle 800mA, but I'm not so sure about that.
Total Current (The Uno is on top, the Mega is at the bottom). It's possible I am just misreading it, but it seems to be able to handle more amps. If the total amps is indeed 800mA, then I might go with the Mega, just for the reason of not overpowering the board.
Quote:
Originally Posted by Occasionally6
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.
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I have a cigarette lighter USB adapter. If I power the Arduino through that, will that be good enough to supply power without over-supplying it? (i.e. 7-12V and <200mA). That would certainly be a lot easier than any other option.
Quote:
Originally Posted by Occasionally6
I can't recall the last time I bought a relay anyway. They're usually free from the junkyard, especially if purchasing something else.
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Would a junk relay work with the Arduino? Would a typical car relay be able to be switched from an Arduino without overpowering an I/O pin (i.e. 40mA to make the connection switch)? I was thinking something like this, if need be:
Arduino Relay
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Are voltage drop and forward voltage the same thing? I can't seem to find the answer anywhere.
I've been watching a few of these videos (just to get the basics)
Youtube Arduino Basics Luckily for me he reviews DMMs too
On the voltage divider, I'm thinking I might use a 10M resistor and a 5M resistor, that way if the ECM is supplying 14V, it will be less than 5V (so I don't destroy the Arduino) and if it is supplying 11V, it will be more than 3.3V (which will mean it has enough voltage to read properly).
This page helped me with the transistors and associated resistors.
Transistor Diagram He mentioned using a 4.7k resistor, but I am still a little confused about how I figure out what I would need for my application.
Alas, I stop here feeling like I have forgotten something...