DC Power is glitching to Servo

I recently bought this reader: https://www.priority1design.com.au/rfidrw-e-ttl.pdf
and am reading it with my Arduino Uno and then controlling a servo (Amazon.com: 4Pcs SG90 9g Micro Servos for RC Robot Helicopter Airplane Controls Car Boat: Toys & Games) depending on what the RFID reads.

I have it working when connected to my PC to power the arduino.

(Servo getting powered by 5v arduino pin, rfid reader getting powered by plugging into the top pins on here with 5v: https://www.amazon.com/gp/product/B08JYPMCZY/ref=ppx_yo_dt_b_asin_title_o02_s01?ie=UTF8&psc=1 plugged in with wall adapter: Amazon.com : R-Tech12V 1A Switching Power Supply Adapter 5 Pack - Black, UL-Listed : Power Converters : Camera & Photo)

When I upload try to use an external power source for the servo, the power seems to glitch in and out to the power supply. I was reading a bit that this is due normally to issues of overloading, but I am a bit confused where my issues lies.

Here's the voltages my project includes:
RFID Reader: System power input line. +5.5 to 15V DC
Servo Motor: 4.8-6V

Power supply: output: 3.3V 5V

Here's how I have it setup in the breadboard powered with the 12v adapter.

I'm assuming my issue possibly is that the RFID reader is taking more than 5v from the power supply and causing issues with the servo, but I'm not sure how to confirm that. I can plug in my RFID reader alone with the 12v power supply, but I'm not sure how to connect those wires to pins on the board, so help with that would be appreciated if that is the issue.

Thank you in advance!! :slight_smile:

Please read the first topics telling how to use this forum, how to get best from this forum.
No helper is happy to download pdf. Post it here.
Powering problems.... Post a wiring diagram and links to the items in use.
Without a posted code, in code tags, more things are unclear.

Do you have a DMM to read some of the voltages?

Thanks.. Tom... :smiley: :+1: :coffee: :australia:

Hi there, I'm sorry - I'm not familiar with what a DMM is - can you explain what that stands for?

That is a mistake. The servo draws too much current for safe operation. It will overload the voltage regulator, and motor electrical noise can even damage the Arduino.

Use a separate servo power supply (e.g. 4xAA battery pack), and don't forget to connect the grounds.

Avoid tutorials that suggest it is OK to use the Arduino as a power supply.


Digital MultiMeter, to measure your circuit components and voltages.

Tom.. :smiley: :+1: :coffee: :australia:

Obligatory tool for all electronics work.

Sad mistake, imagining that the "barrel jack" or "Vin" on a UNO (or similar boards) is usable for providing power.

It is not.

Not at least, for any real project - such as one using a servo. :astonished:

Depend on the type of servo, I have no issues controlling a single 9g servo with a arduino Uno over USB. And I can almost stall it (before the voltage drops)

Assume it's those stupid (and bigger) "metal gear" servos, I think 500mA on Arduino still holds plenty of juice.

That is USB. We were/ I was discussing how inappropriate it is to use the on-board regulator.

If he pull the power for the servo from Vin, he will be fine.
The on-board regulator provide ... ugh.
(checks Arduino Uno schmantics)
Well, it says that the NCP1117-d have 1A of output. And the power regulator appears beefy enough for supplying 1A of power (it's a step-down, so size is small)

HOWEVER, he says that his RFID reader need 5.5V to 15V to work. And the 5V ain't going to pump out 5.5V.

You should connect the red wire from the RFID reader to the VIN pin instead of the 5V pin. The VIN pin is unregulated and fed with 12V from the barrel jack. Connect the servo to the 5V pin, but only if it is a small (9g servo).

No, never do that.

For just a few seconds while it overheats. :roll_eyes:

For those of you that indeed think there will be a problem, the fact is that I have run them like this forever and there are never any problems.
Do I need to pull out my multimeter (and perhaps infrared thermometer) and show you how much current the servo draws?
I've been designing shields that feed battery power (4.2V) directly to the 5V rail, even on 3v3 boards. And they get away with perfect for hours (until the battery dies), and recharge the battery with USB 5V fed from the rail (diode clamp on battery + charger IC). And I don't think the fact that he connected the servo to the 5V is the reason he is complaining about it.
Of course, it depend on what type of servo he gets. If it's one of those 995 servos, I will recommend him to get a 5V source. But if it's a 2g servo (trust me I had one of those earlier), it will do.

So I hooked my 9g servo to the Arduino Leonardo that I have and have it run the "servo sweep" sketch. Then I powered the entire thing with 12V and tasked my multimeter with the task of figuring out the current drawn by the servo.
The result shows that the servo draws about a cozy 50mA.

Blocking current is ... well, I can't block it, because otherwise the plastic gear will be destroyed (because it happened before). But you get my idea.

And the servo is being supplied with PURE DC? Right?

Hi all - I appreciate the input regarding powering from the Arduino - however, my main question comes from powering both the servo and RFID reader from the external powersource in the picture.

Can someone help provide input regarding why the power cuts in and out from the DC power supply?

The problem with your picture is that it doesn't show any servo or RFID reader. And it doesn't show the connections to any of your components. So it's not exactly helpful. A schematic would be a lot more useful.

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Here’s some more images of my setup:

[Uploading: 0CFFE72E-81C9-4FF1-A4EC-6646B505BA47.jpeg...]

Nylon carpeting is a great way to generate static electricity and zap your electronics.

Thanks, I’m aware of this. Can you please provide help regarding the actual question I’m posting about?

This forum is littered with posts about Arduino failures, due to following your terrible advice, or the terrible tutorials on the web, suggesting that it is OK to power motors and servos from the 5V output.

We also understand the reasons for those failures, and could care less that it just happened work for you, so far.

@hackergirl69420: Servo twitching is almost always due to an inadequate servo power supply (like the 5V Arduino output), or using breadboards for servo power connections. Breadboards are for low power logic circuitry and the tracks will burn and fail if exposed to motor currents.

A much less frequent cause of servo twitching is timer and interrupt conflicts with some libraries. Post your code, using code tags, and we can tell you if the latter could be the case.