Decoupling Capacitor in Arduino Starter Kit Projects 05 and 10

Other Hardware General Electronics
1

Hi,

I just finished Projects 05 and 10 from the Arduino Starter Kit and I was wondering, why there is no decoupling capacitor necessary in Project 10 for the DC Motor?
Also, is there a way to calculate the capacity of the decoupling capacitors in Project 05?

Thank you very much
Kind Regards
Bernhard

2

In project 05, the servo motor is powered from the 5V pin of the Uno. This means that the Uno's microcontroller is subjected to the voltage fluctuations caused by the motor. That could interfere with the working of the microcontroller, so it's important to reduce them.

In project 10, the DC motor is powered by a dedicated 9V battery, while the Uno is powered by its own power line (e.g., the power from the USB cable). So the voltage fluctuations caused by the motor only affect the motor.

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3

Thank you very much for your quick reply Pert!

I was not aware that the capacitors are protecting the Arduino rather than the servo motor.
Isn't one decoupling capacitor around the motor enough then?

thanks again
All the best
Bernhard

4

Hello Bernhard,
General rule with decoupling capacitors is if in doubt add them. They might not do any good but they won't do any harm. They should be wired as close as physically possible to the device being powered.

5

I'd strongly recommend always using separate power for any servo or motor. Sharing the Arduino's 5V
rail with a high current noisy component such as a motor/servo is asking for issues like drop-outs, spikes and
spurious resets of the microcontroller.

And to drive a motor from a small 9V battery is overloading the battery, so it will rapidly drop in voltage
and won't be able to get much torque from the motor. Small 9V batteries typically struggle above 100mA.

6

pert:
In project 05, the servo motor is powered from the 5V pin of the Uno.

Which, I'd like to add, is OK for testing out and playing a bit with a very small servo, like the little blue ones commonly seen in Arduino kits, and then only when the Arduino is connected to the USB for power, not a higher voltage supply through the barrel jack connection.
For any permanent project, or any more serious servos, or more than one of those little servos, a dedicated power supply is in order (that power supply may in turn power the Arduino as well, of course).

7

Thank you very much for your replies and sorry for my late reaction: I couldn't log in for some time..

My plan is also to use a dedicated power supply for motors as I also fear that a battery will lose degrade very quickl. I was thinking of using something like this: %product-title% kaufen

Unfortunately, the homepage is in German but to sum up, it is possible to vary the output voltage and it is possible to provide up to 1.5 A (which is more than enoguh I guess).
However, I would have also used that supply to power the arduino via the Vin pin. (The pump I want to run is the following https://www.amazon.de/-/en/SGerste-Machifit-JT80SL-Microhorizontal-Submersible/dp/B07HK69MTK/ref=sr_1_7?dchild=1&keywords=pumpe+6v&qid=1610719984&sr=8-7)
I would presume that I can power both: the pump and the arduino with 6V.

What do you think.

Thanks a lot
All the best
Bernhard

8

Dig into your drawer with disused mobile phone chargers and likely you have something that can produce 5V with sufficient current, and power both in one go. Use the 5V pin, not the Vin pin (which needs at least 6.5V to guarantee a 5V supply on the Arduino board, 6V is a horrible voltage for an Arduino).

9

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