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I have very limited knowledge regarding electronics. Please help me cure my ignorance on the subject of robotics.

I want to power the Arduino Uno R3, US-015 ultrasonic sensor, and the L298N motor controller from a single power source (7.2v). However, I'm not sure if this diagram is correct. If it is functional, will it last that way?

enter image description here

If this diagram is deemed wrong, please suggest alternatives with one power source.

Advance thanks to those who would reply. Elaborate answers would be very much appreciated. :D

Edit: Since it's deemed incorrect, I'm going to power Arduino through the DC barrel jack and power the L298N motor controller through the Vin and the ultrasonic sensor from the Arduino 5v output. Is it wise to do this?

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    Using a motor controller to power an Arduino or analog peripherals is probably unwise as the source is liable to be noisy. Better probably is to power Aduino from 7.2V into Vin - with a small series resistor from 7.2V to Von and a large filter cap at Vin to ground. Then power sensor from Arduino 5 V. Series R must drop < 2V - probably about 22 Ohms to start.Capacitor at Vin - the larger the better. 100 uF good. 1000 uF better. – Russell McMahon Apr 9 '15 at 18:04
  • @RussellMcMahon Why the 22ohm resistor. The voltage regulator on the arduino will smooth things to 5v. Is it like a low-pass filter? Wouldn't a diode, or inductor be more useful? – Gerben Apr 9 '15 at 18:19
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    In the diagram, there is nothing producing the 5v. – Gerben Apr 9 '15 at 18:20
  • @Gerben Presumably the motor board OUT{URS 5V on Vcc for 7.2V in - just as most Arduino's accept > 5V on Vin and output 5V. – Russell McMahon Apr 10 '15 at 4:00
  • @Gerben - the 22 Ohm resistor and large capacitor form an RC (Resistor + Capacitor) noise filter. This greatly redcues motor noise which appears on the 7.2V line. This is vry standard practice in real world installations like ythis. An inductor based filter can be better but RC should suffice. – Russell McMahon Apr 10 '15 at 4:02
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Using a motor controller to power an Arduino or analog peripherals is probably unwise as the source is liable to be noisy.

Better, probably, is to power the Arduino from the 7.2V supply via a noise filtering resistor into the Arduino's Vin terminal.
NBNBNB 7.2V input MUST be to Arduino Vin.

Use a small series resistor from 7.2V to Vin and a large filter cap at Vin to ground. Then power the sensor from Arduino 5 V output.

Voltage drop in series resistor from 7.2V to Vin must drop under 2V.
Rmz is <= Vdrop / Iload
For say 50 mA load Rseries = V/I = 2V max / 0.05 = 40 Ohms . For 100 mA R <= 2/.1 20 Ohms.
So probably try about 22 Ohms to start.
If Vdrop is > 2V a smaller R is needed.
If Vdrop is << 2V increase R.

For the capacitor at Vin - the larger the better.
100 uF good. 1000 uF better.

Resistor power dissipation is I^2 x R.
So at even 100 mA Pres = 0.1^2 x 22R = 0.22W
A 1/2 Watt resistors would suffice. A 1 W resistor would do no harm and would tolerate the heat better.


The 22 Ohm resistor and large capacitor form an RC (Resistor + Capacitor) noise filter.
This greatly reduces motor noise which appears on the 7.2V line.
This is very standard practice in real world installations like this.
An inductor based filter can be better but RC should suffice.

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