Answered! Powering 2 servos and a laser diode from 12V battery

Other Hardware Motors, Mechanics, Power and CNC
1

I am running two servos and a laser diode through an Arduino Uno.

One servo is this 360 degree and one servo is this 180 degree. I'm using the Adafruit Motor Shield for easy servos hookup.

This is the laser diode I'm running. I have it hooked up to a mosfet transistor with a 1.5ohm resistor.

I got all my components/programming working separately when powered through the USB cord, but when I tried hooking it all up together, there wasn't enough power and everything flickered and had trouble moving through programming.

My final plan is to power it from a 12V deep cycle marine battery through the DC port.

My question is, can the Arduino handle regulating that type of battery for a long time (several weeks) without a buck converter (I've got some 12v to 5v), and can it provide enough power to all of the components?

I guess part of my confusion is that I can run two servos at the same time, with their operating voltage both 4.8-6v, which I thought the arduino wouldn't be able to supply that voltage for them both through the USB (5V?). And maybe it was having issues and it wasn't noticeable to me. They aren't moving heavy loads.

And if it can't provide enough power, is there a way I could hook both the arduino and the laser up to the same power supply? I know it isn't recommended to do so for motors because of electrical noise, but I don't need precision from the laser. It just needs to be on and off when programmed. I'm not sure if the noise would affect the lasers brightness or something like that. I guess an alternative would be to hook servos and laser up to the 12v battery (maybe through motor shield) and power the board from a separate battery.

2

You cannot power 2 servos AND a 300mA laser from Arduino 5V pin if you are powering it through the barrel jack or VIN pin, you need a separate buck converter from 12V battery down to 5V at 3 Amps minimum.

My question is, can the Arduino handle regulating that type of battery for a long time (several weeks) without a buck converter (I've got some 12v to 5v)

Use one for the Arduino and one or two for the other parts, battery life will depend on load, less use, longer life. Be sure to connect all grounds together.

3

You cannot power 2 servos AND a 300mA laser from Arduino 5V pin if you are powering it through the barrel jack or VIN pin, you need a separate buck converter from 12V battery down to 5V at 3 Amps minimum.

I figured that might be the case. I didn't check the current needs of the servos and just assumed the board could provide enough.

I will need a buck converter for the arduino for sure.

Use one for the Arduino and one or two for the other parts, battery life will depend on load, less use, longer life. Be sure to connect all grounds together.

Would I need to run the servos off a separate power? The board seems to run them fine at the same time although looking at specs, it seems that running it for a long time with both might not be good for the board.

Wiring wise, I can split the positive line to go to two buck converters, one for arduino, one for laser (assuming servos run from board for now). The negative line would also be split, to the two buck convertors. I'm assuming I would still run a wire ground from transistor into the arduino, correct? Then all of my grounds should be wired together since the buck convertor has a ground that goes to the transistor. Ah, I did some different searches and it looks like I should do that!

Okay, thank you for your help! I'm going to look into running the servos from either this battery or another battery. Right now I guess I could do the same thing and split the line again for the servos. Maybe the best bet would be to run the servos and the laser from the 12v battery and have the arduino run from something smaller. Then I could eliminate the motor shield since it's just being a convenient plug in for the servos. I'll think about it, thank you again!

4

dukekyler:
Would I need to run the servos off a separate power? The board seems to run them fine at the same time although looking at specs, it seems that running it for a long time with both might not be good for the board.

If a small servo with no load is connected to the 5v pin, it usually works without problem.
As soon as you add more load, either through additional servos or attaching something to the servo so that it has to do work to move, you overload the regulator and it shuts down.

I believe that the tutorial is specifically constructed to lead new users to an early failure involving the power supply. This permits greater success if the new user learns early on that specs and power requirements are real and must be given proper attention.

It sounds like you have developed an appreciation for power requirements.

5

You should never attempt to power servos or motors of any sort from the 5V pin.

They inject random electrical noise that causes program malfunctions and can overload the regulator, destroying the Arduino.

Pololu has a great series of very efficient buck converters. Choose one that can supply at least 1 Ampere times the number of servos.

6

Your servos and the laser should be powered from the 12v battery (with suitable voltage regulation) independently of the Arduino.

Don't draw power through the Arduino for motors or other devices needing large currents (say over 100mA).

...R

7

If a small servo with no load is connected to the 5v pin, it usually works without problem.
As soon as you add more load, either through additional servos or attaching something to the servo so that it has to do work to move, you overload the regulator and it shuts down.

I believe that the tutorial is specifically constructed to lead new users to an early failure involving the power supply. This permits greater success if the new user learns early on that specs and power requirements are real and must be given proper attention.

It sounds like you have developed an appreciation for power requirements.

It's interesting, because I haven't seen issues with running both servos at the same time, but they aren't really doing too much and it had only been for short periods of time. I hadn't realized that both servos were hooked to the 5V through the motor shield because I had no idea what I was doing. I know slightly more now.

I'll get them hooked into their own buck converter.

I actually had gotten my entire project working "properly" with a tiny laser 5mW, 25mA type because the larger laser took a while to ship in. Once I added the bigger laser, I ran into a whole host of issues that I obviously hadn't realized were there, just that the arduino was compensating enough to make them not visible, like the servos. So I had to do a lot of learning!

It's a work in progress and my next version will have some improvements over this one. Not sure if I'll get to some of the really complicated stuff (on a timer! adjusting timer via bluetooth! more randomized laser!) immediately but I think I can get it figured out in the next few months or so.

You should never attempt to power servos or motors of any sort from the 5V pin.

They inject random electrical noise that causes program malfunctions and can overload the regulator, destroying the Arduino.

I guess the motor shield was handling some of the electrical noise or something, I'm not sure. I didn't seem to have any issues with the servos or the arduino. But I'm moving them off it anyway, since it doesn't look like it is good long term for the board.

Thanks everyone!