Arduino Pro Mini with ROB-14450 Motor Driver

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1

Hey Everybody,

I am currently using an Arduino Pro Mini 5V microcontroller with a small DC gearmotor.

Is there an “easy” way to measure the current draw from the DC motor while using the ROB-14450 Motor Driver from Sparkfun? I have also purchased the Sparkfun Current Sensor Breakout SEN-13679, but I am looking to simplify.

Can I place 2 resistors in parallel with the motor like what I show in the attached image? V=IR. So if there is a large torque load on the motor (i.e. drawing a large amount of current), then less current should flow through the parallel resistors and the voltage at Vout should be nearly 0V. With little torque on the motor, more current will flow thru the parallel resistors and Vout will be nearly 5V.

The value of the first resistor is 10K. In order to get a voltage drop of 8.5V across the 10k resistor and then the remaining 5V across the second resistor, the second resistor had to be 5.87k.

TIA,

–Neal

2

Ideally, you measure current in series with the load (motor).

But any resistance you put in series will increase the overall resistance so what you use must be small.

Measuring the voltage across the measuring resistor will allow you to calculate the current.

(0.3 V / 1.0 ohm = 0.3 A)

Then there’s the issue of ensuring that your voltage is compatible with the Arduino input.

You’re better off buying something like the Adafruit 904 BOB for $10:

https://www.adafruit.com/product/904