Activity board question

danielstritt

I am going to order an activity board tomorrow, and I was wondering, if I hook up a battery pack to the power socket, and also hook up USB for debugging, and I want to run servos, will the servos run off the batteries, or the USB? Because I heard its a bad idea to run servos off of USB power.

Thanks

Daniel

Mike Green

First of all, there are jumpers near the servo sockets that allow you to select which power source is used, the power socket (Vin) or the regulated 5V supply. The regulated 5V supply comes from either Vin or USB, whichever is available. If you set the jumpers to Vin (see the Activity Board documentation for details), the battery pack will supply the servos. If you set the jumpers to Vdd (+5V), the voltage regulator(s) will supply the servos. USB is limited in how much current can be supplied, so Vin will also be used if there is enough current demand from the servos. Keep in mind that servos can draw up to 1A each peak, like when they start moving and there's some mechanical resistance. USB can supply only about 500mA at most. The Vin voltage regulator can only supply about 1.5A with a 6V battery pack, less with higher voltages due to heat dissipation. It's best to use a 6V battery pack and set the jumpers so Vin is supplied to the servos.