Servo - December 2014

74 SERVO 12.2014

servos. The servos would just wave around some “arms.” What we really wanted to control was the DC motor.

As a quick proof of concept, we took the Arduino module out of the equation so that the motor and servos were just connected straight to the button. Just as we had hoped, when the button was released, the servos, motor, and buzzer came to life. So, why bother with the Arduino module? If we were to implement the circuit in the robot as-is, our present defender would indeed move when the present sitting atop the pressure plate was moved. The problem was that it would only move forward at one speed.

We wanted slightly more sophisticated movement back and forth, so the bot wouldn’t try to outrun its tether. We also wanted the option to exercise more granular control if we implemented a second motor in the drive train to increase maneuverability. We wanted to achieve more than the robotic equivalent of a unidirectional domino show.

The Arduino Code

The way to achieve more was through programming with the Arduino module. As we mentioned last month, the Arduino board is equipped with three inputs (two analog and a digital) and three outputs (three digital). For those hoping for some motor control, three digital outputs may sound like a disappointment. Once again, however, we were impressed by the efficient design on display with the littleBits. Two of the output ports are paired with output switches — much like the unassuming mode switches on the servo and motor modules. The output mode switch allows you to switch the digital output to analog output or PWM output. You still have only three outputs, but with up to two PWM outputs you should be well on your way to robotic greatness. We actually prefer the switchable ports instead of having more ports coming off of the Arduino module.

Sure, the Arduino module could have its three digital outputs, and it could even have separate ports for PWM output. Or, for analog output for that matter. However, since each port would be outfitted with a magnetic littleBits connector, the module would become bulky and unwieldy with even just a few more ports. We prefer the compact simplicity with the three inputs and three outputs, and we think the output mode switch is a clever way to efficiently use circuit board real estate.