Electronics > Beginners
How to wire this setup?
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james_s:
You'd need a 12V source and a buck converter, or a 5V source and a boost converter. Generally buck converters are more efficient than boost, so I would go with a 12V source regardless of whether you use a buck converter or linear regulator. Your 500mA unit ought to be enough for testing but might not have quite enough capacity.
Youkai:
I drew a basic circuit diagram. Please take a look and let me know if you see any problems/issues. Points to note:

* 12V power source goes to the LED strip through transistor from Arduino.
* 12V power source goes through buck converter to reduce to 5v.
* 5V powers both Arduino and Servo directly (as opposed to servo being powered from 5v pin on Arduino).
* I only drew one transistor but in reality there will be three beacuse it's an RGB LED strip. I didn't bother this time for the sake of simplicity. (Actually probably 6 because there will be two strips in different locations and I will probably want to control them independantly)
* Also there will be 3 servos. Extras were again left out for simplicity.
* The Arduino will likely not have enough PWM pins so there will be a PWM IC in the final. I think since none of the driving power goes through Arduino (only switching logic) the PWM chip should be able to handle it; but please let me know if you think I'm wrong.
Also I tried to diagram this in LTSpice but I couldn't find a "microcontroller" component (not surprising) or a Servo component. Is it possible to diagram this circuit in LTSpice?
KL27x:
All kinds of wrong.

The transistor (which shall be NPN, I presume; you're missing an arrow) probably needs the emitter connected directly to ground. It's a 12V unit, right?

The servos need to be connected to both 5V positive rail and to ground. You have no ground connection on them.

The buck converter should have its Vin connected to the 12V supply rail.
KL27x:
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You of course will need some extra caps for both the buck regulator in/out and some decoupling caps might (definitely) be needed on the 5V rail closer to the servo and Arduino supply pins.
Youkai:

--- Quote from: KL27x on May 10, 2018, 03:29:08 am ---The transistor (which shall be NPN, I presume; you're missing an arrow) probably needs the emitter connected directly to ground. It's a 12V unit, right?

--- End quote ---
Ok so maybe I have the transistor on the wrong end of the LED. Either way the transistor's collector and emitter has to be in series with the LED strip and run from + to ground, right? So I fail to see how the diagram is fundamentally wrong in that respect. Please elaborate or provide a sample diagram.



--- Quote from: KL27x on May 10, 2018, 03:29:08 am ---The servos need to be connected to both 5V positive rail and to ground. You have no ground connection on them.

--- End quote ---
The servo is connected to the buck converter (positive) and the ground (negative). The triangle symbol is ground isn't it? At least it is in LTSpice. Additionally the control wire goes to the Arduino.


--- Quote from: KL27x on May 10, 2018, 03:29:08 am ---The buck converter should have its Vin connected to the 12V supply rail.

--- End quote ---
I think it does. There is a wire from the 12v+ directly to the buck converter. What am I missing?
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