Current calculation

Hello guys,

I need to calculate how much current my circuit gonna need in order to choose the right external battery to supply my arduino NANO, but I don't know how to do that so I'm wondering if somebody could help me with that.

OK, so I have 12 servo motors ( sg90 ), one ultrasonic sensor( HC-SR04 ) and a bluetooth module ( HC-05 ).

Here is the schematic:

And if you wanna know, I'm actually making a Quadruped robot, it's gonna be controlled using an android app and the BT module, the US module role is to avoid any collision with something in front of the robot while walking.

Thanks for your help
Steewz

Measure the stall current on one servo, then multiply by 12.

The stall current is the current a servo draws when its intended movement is blocked, i.e. you try to force the arm into a different position.

I would guess at a stall current of maybe 1Amp.

The rest of the circuit will take very little current in comparision.

The stall current of an SG90 is rated at 650mA. Your power supply needs to provide that times the number of servos that will be moving or holding a load at any time. For a quadruped robot that may be most or even all of them.

I'd go for something that can provide at least 8A at 5V. You could do it with 4 x NiMH rechargeable batteries but not really AAA or AA size. They will need to be the sort of batteries sold for RC use like https://hobbyking.com/en_us/turnigy-receiver-pack-2-3a-1500mah-4-8v-nimh-high-power-series.html

Plenty of lipos can also provide enough current but the voltage is wrong for SG90s so you'd need a DC-DC converter to get it to 5V.

Steve

With that many servos you are going to need plenty of decoupling on the supply to stop the EMI ( Electro Magnetic Interference ) from constantly resetting your Arduino and interfering with the Bluetooth module.