Powering an Arduino Uno R3 in an automotive application

I'm working on a vehicle related project where my Arduino Uno R3 will be opening/closing a couple of mosfets on a daughter board that a friend and I put together. It's not a lot of heavy lifting. We tested it while running on power from the USB port and so far, so good. Now that we're ready to install it in the car and power it from the 2.1mm power plug, I am shopping for a DC/DC step down converter that can deliver the necessary 9V and won't allow the car to burn the Arduino during normal operation.

I was looking at these two models and was hoping that the forum could help me decide or tell me if I'm missing the mark entirely:

http://www.powerstream.com/dc6.htm http://www.powerstream.com/daa-1209.htm

Would either of these do the trick? Is one better than the other?

*My background is in CS/CE so I'm learning this as I go. **I searched before posting this question and I couldn't find anything that pointed to a specific product and that had a general consensus.

The only trouble with something like that is you're essentially paying "too much" for your application. Since the Arduino already has its own regulator, you don't need such tight tolerance on the output. They can also supply a lot more current than you would ever need if you're powering the daughter board separately.

Where do you plan on locating it? You could look at cigarette lighter USB chargers. You could get a couple of them from eBay for $5 and if need be you can hack one up to wire it directly instead of having to plug it in inside the car.

Why not connect the car's 12v supply directly to the Arduino's barrel connector? - that can take a max of 20v.

Alternatively I have an Atmega 328 running off a 12v battery charged by a diesel engine - when charging the voltage can be 14.9v. I just have a 7805 voltage regulator IC to drop the voltage. It's been working for a few years now. You can power an Uno through its 5v pin PROVIDED you have a regulated 5v supply.

...R

So you use the buck converter to knock 12+V down to 9V for whatever you're powering and that 9V feeds into the Arduino regulator?

You can take the worst spikes out with some caps across power and ground on the car side of the converter.

I got buck converters with 3A max output (good for half that steady I guess) for a bit over $2 ea.

Hi,
Why not buy a car to USB power adapter and power the lot of the 5V, just like you are doing with the PC USB port.

Tom… :slight_smile:

USB adapter.jpg

Just find a place to solder it in or road bumps may reset the board.

Thanks for the responses. The daughter card mounts to the Arduino and requires no additional/external power. It is going to be installed in the driver side footwell(not on the floor though). Powering it from the cigarette lighter is not an option since I want the installation to be in a discrete location without any exposed wiring. I am tapping vehicle power from a junction under the dash.

My concern was with protection and possible voltage spikes but It sounds like hacking a 12V to 9V car charger is the way to go. I will do some looking.

Woah! You don't need 9V for something? 5V will do?

I've been informed before that cheap buck converters will fluctuate output with fluctuating input and haven't tested that. If true then crank it down to 7.5V or 8V and feed that to the Arduino power jack... or just skip the converter, it will run warmer so make sure it gets air flow/is not in a sealed box.

If your Uno has a DIP ATmega328P (as opposed to surface mount chip... but I think that's the 'Uno Pro' model) and you have one or more bootloaded 328P chips then if you do burn the chip you can replace it, load the sketch and get back on working. It's one of the things I like most about Unos is the replaceable chip. Bare 328P DIP chips can be gotten for under US$3 if you shop (Futurlec wants US$2.20 ea).

Here's a full tutorial on bootloading/programming the chip on a breadboard with your working Arduino or an FTDI cable with full optional paths and wayyyy better/easier to use than the official Arduino site sketch to do the same:

www.gammon.com.au/breadboard

I luv this chip family; besides power and ground all you need is a bypass cap to get one running up to 8MHz. You need to add more, a resonator, or crystal and 2 caps, to run much faster but there on that one chip is everything needed but the bypass cap and power. If you're not going to use many pins or close external parts then you can build the project on a socket (no board) and pop the programmed chip into that. One project page (O'Baka Arduino) even shows bare 328P chips with parts soldered directly to the chip legs yet still breadboard-pluggable but I'd never dare since I'd for sure overheat pins/chip, can't do that to an empty socket.

The location and desire to be discrete has absolutely nothing to do with just using a cheap phone charger. Hardwiring such a buck board is your simplest option, I have no idea why you're so eager to make it more complicated. You're literally saying "I want to step it down to 9V, which requires a device. But I don't want to use an identical kind of device that would just step it down to 5V because reasons"

INTP: The location and desire to be discrete has absolutely nothing to do with just using a cheap phone charger. Hardwiring such a buck board is your simplest option, I have no idea why you're so eager to make it more complicated. You're literally saying "I want to step it down to 9V, which requires a device. But I don't want to use an identical kind of device that would just step it down to 5V because reasons"

Like maybe the converter won't hold 5V when the car system voltage varies? If it will then sure, it's more efficient, adjust it down to 5V. If it gets to 6V then get a new board. If you only want to use 1 device and don't mind a little waste then the regulator is a sure thing.

INTP: You're literally saying "I want to step it down to 9V, which requires a device. But I don't want to use an identical kind of device that would just step it down to 5V because reasons"

Stepping down to 5V means using the 5V rated USB-B port and wholly relying on the voltage regulator/protection provided by the "cheap phone charger". It may be all for nothing but as a newcomer, that was my concern.

Stepping down to 9V means using the 9-12V rated 2.1mm barrel port. The barrel port has the onboard voltage regulator. That additional protection seemed like a good idea in this application.

brothermatt: Stepping down to 5V means using the 5V rated USB-B port and wholly relying on the voltage regulator/protection provided by the "cheap phone charger". It may be all for nothing but as a newcomer, that was my concern.

Stepping down to 9V means using the 9-12V rated 2.1mm barrel port. The barrel port has the onboard voltage regulator. That additional protection seemed like a good idea in this application.

Meanwhile millions of people plug in their $800 phones without incident.

The onboard voltage regulator is linear. It throws off heat. The more work it has to do, the hotter it gets and the lower your current cap from the board. If you think that's preferable, by all means let your newcomer concerns guide you, full cup and all.

INTP: Meanwhile millions of people plug in their $800 phones without incident.

The onboard voltage regulator is linear. It throws off heat. The more work it has to do, the hotter it gets and the lower your current cap from the board. If you think that's preferable, by all means let your newcomer concerns guide you, full cup and all.

No need for the attitude, INTP.

"The onboard voltage regulator is linear. It throws off heat. The more work it has to do, the hotter it gets and the lower your current cap from the board."

That is the kind of useful information that I was looking for.

If the project isn't doing any heavy lifting, just how much loss do you think you'll get in mA?

Current cap... Arduino Uno max total current is 200mA. What chance that a CAR can't provide enough current to meet that?

I wonder if those $800 (and cheaper) phones don't have a 3V regulator and/or power protection circuitry?

The buck converters I got have an adjustment screw to set the output voltage with. If I wanted to feed the Uno power jack I'd give it 7.5V. If I wanted 5V then I'd put regulated 5V in the Vin hole (end of the power header near A0) and ground in GND.

IF you go with a buck converter (more needed with small batteries and minimal power sources) then test it out in the car with a meter while you do things like rev the engine or turn the brights on and off, stereo full to low, etc. If it stays at 5V then good news.

Serious, Matt, look into bootloading your own 328P's as once you have spares you have less to fear trying things out. DIPMicro sells bootloaded 328P's for around $5 ea last I checked while bare chips were more like $3. Once you set up a breadboard to do one, any more should take a minute to two each. The Arduino Uno was made to develop the program on then pop the chip out and run it stand-alone. You keep the comparatively expensive dev board for your next effort.

That's not how to advertise here.

Things powered through the 12V Aux socket tend to reset when the car hits a bump. It's a PITA when the music changes, I'd hate to think of letting anything important rely on that source.