Servo - January 2014

Decision #1: How to interface 5V inputs and outputs to the 3.3V GPIO pins.

I wanted to interface 5V servos and 5V digital sensors to the Pi safely and as simply as possible for the lowest possible cost.

The Broadcom processor on the Pi has 3.3V GPIOs, and while servos can be controlled by a 3.3V signal, we should limit the current the servo can draw from the Pi to guard against damaging the GPIO.

What is cheaper and simpler than passive components?

We have to handle:

1) Input — Reading a 5 VDC signal safely with a

3. 3 VDC Pi GPIO.

A. A voltage divider is a great approach.

B. We can use a nice SIP bussed resistor for the resistors to ground.

2) Output — Controlling devices that expect a 5 VDC control signal.

1. Most such devices can be driven by a 3.3V signal.

2. The only potential concern is drawing too much current from the Pi's GPIO. 3. A current-limiting resistor solves that.

SPRITE

Simple Pi Robot Interactive Testbed for Experiments

I have been following the Raspberry Pi since before it was available — other than the sheer

"WOW" factor of a credit card sized $35

computer, I've been wanting to use a Pi as the

"cerebral cortex" for some of my robots.

What I really like about using the Raspberry Pi as a robot brain is that I can easily have a Wi-Fi connection to it using an inexpensive USB Wi-Fi adapter and SSH into the robot, or even run the desktop remotely. Cutting the programming cord is a huge leap forward.

Think about it — programming your robot, on your robot, from any computer, iPad, iPhone, or Android device!

I decided to make a robot controller for the Raspberry Pi that would be as simple as possible for students and hobbyists to build — one that can be used as a testbed for experimenting with robotics, and expanded as needed.

By William Henning

mikronauts@gmail.com

Post comments on this article and find any associated files and/or downloads at www.servomagazine.com/index.php/magazine/ article/january2014_Henning.

In this article, I will show you: • How to build a simple robotics add-on shield for your Raspberry Pi using an inexpensive prototyping shield and a handful of parts.

• How to set up your Raspberry Pi so you can connect to it over Wi-Fi.

• How to write code for your Wi-Fi Pi robot.

There are many ways of building a robot (and robot controller), so I will list each major decision point, then show the alternatives I considered and the choice I ultimately made.