Power Supply Check Request

Projects General Guidance
1

Hi all,

I'm designing a moving sculpture, and think I have all my required power supplies figured out, but as I'm totally new to circuitry, I'd greatly appreciate any warnings/checks before I finish the project and potentially fry my equipment. Thanks!!

I will be using three small servos (two Reely S-0008s and a Modelcraft MC-410), an HR-SC04 sensor, a breadboard, and a LED light string (looking at this one: https://www.amazon.com/VISDOLL-Individually-Addressable-digital-Non-waterproof/dp/B017D2TGTS).

The servos all require 5V, as does the LED string. There is only a very light load placed on each servo, so I am estimating at most a current draw of 1A per servo, for a total of 3A. This LED string uses 0.3W, which I believe places its full need at 3A, as well. The sensor's schematics claim that it needs only 2mA. The LED will be turned off when the servos are moving, and vice versa. The sensor runs on a timed program. So I shouldn't be using much more than 3A at any given time.

Considering background power needs to all these components for their control circuitry, I'm planning on purchasing a 5V 4A external DC power supply, as well as a female DC barrel power adaptor to attach the power supply directly to the breadboard, from which I will power all of the other components, except for the Uno board, which will be USB-powered, though its ground pin will be connected to the breadboard ground.

I've read that I shouldn't need a resistor between the Uno and servos, especially as my power supply is their needed voltage, but I'm unclear if this is still the case since I will be switching them 'on' and 'off'.

Am I correct in thinking that I do not need resistors, or a regulator, for the servo?

Is it correct that I should still place a 220-440 Ohm resistor between the Uno and LED?

Because so much switching is happening, even though this is a fairly low-power project, should I look into a transistor?

Does this seem good to go?

Thanks y'all! Appreciate your time, here.
(It's maybe a more clumsy setup than if I were to solder my equipment, but money is a bit tight at the moment, so I'm trying to stay solderless.)

2

We like details because one persons "small" is another's "oh they're huge". So what exactly are your "small servos".

It's generally not a good idea to power servos through a breadboard. Breadboards are only intended for very low currents so you may have problems getting good enough connections for the power the servos need. You can give it a try but it may not be reliable. Similarly I wouldn't use a barrel connector for 3-4A but you may get away with for a while. Soldered connections are so much more reliable though.

Also I doubt if you will really be switching the servos on and off. You'll more likely be moving them to a position then holding them in that position then moving them somewhere else. So they will be using at least some power all the time though probably not very much unless they're having to hold something in position against some other force, like maybe gravity.

You shouldn't need resistors for the servos. And the resistors for the LEDs should already be built in.

Steve

3

Thank you for your reply! I had no idea that breadboards were better off left at a low amperage. And I've edited the original post to show the servos (two Reely S-0008s and a Modelcraft MC-410).

Regarding the overly high amperage for the breadboard, would a servo driver (like the Adafruit PCA9685) be a good idea? Just attach the servos and LED to the power supply through the driver, and leave the sensor on the breadboard?

Thanks again! That was really helpful.