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Mega Plan



I2C and SMBus

I2C is a 5V, 2-wire, synchronous, multi-master serial bus created by Phillips Electronics. It is used on many types of microprocessors for interfacing with other integrated circuits. Various modes allow 100kbps, 400bps, and 1mbps operation. I2C has four wires: power, ground, SDA (data) and SCL (the "clock"). Two pullup resistors connect SDA and SCL with power. SMBus is a variant of I2C.

You can think of I2C (or IIC) as "USB for robots" and is used in conjunction with USB to extend their capabilities. It typically connects a master with up to 127 slaves. Masters send data to slaves and initiate data requests from slaves. We are using I2C to drive the Matrix Orbital LCD display; but other I2C devices could be similarly connected. Devices on the I2C bus are assigned a 7-bit address which uniquely identifies each device.

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Servos are motor devices which are designed to turn to a specific angle in response to an incoming signal (in the form of a square wave). Servos can usually turn between -90 and +90 degrees, and the angle depends on the duty cycle of the square wave (how long it is "up"). We use servos to tilt the camera and to move the gripper.

An internal potentiometer attached to the servo's geartrain tells it at what angle it's turning. The speed at which a servo turns is proportional to how far it presently is from its desired angle. This makes possible the use of servos as regular motors: replace the potentiometer with a fixed-value resistor so the servo always thinks it's at a certain location no matter how much it turns. Also, remove limits on the servo so it can spin freely 360 degrees. Now the angle difference you specify translates into how fast the servo turns. We use servos pre-modified in this manner for wheel motors.

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IR Range Sensors

IR range sensors use an infared beam to determine distance to an object using an emitter and receiver. The emitter emits a short IR pulse which is either reflected by an object, or continues into space. Any reflected waves are picked up by the receiver, and form a triangle with the sensor and the object. The receiver contains a very precise lens and CCD element which is used to determine the angles of the triangle. Using these angle, the distance to the object is determined. Due to sensor's design, each sensor has a minimum and maximum range at which it can detect objects.

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Wireless Sensor Networks (WSN) (802.15.4)

A new protocol for low-powered and lossy networks has emerged as IEEE 802.15.4. Like Wi-fi (802.11), this protocol operates over the 2.4GHz ISM bandwidth, providing the ability to transmit packets between devices over the air. This protocol is specifically designed for very low-powered devices to communicate small data packets, which are typically sent to a single destination node.

The flockbots communicate with WSN devices (Tmote Sky or Zolertia Z1 motes) through a USB connection, using the termios system library for serial communications. The devices use the Contiki Operating System and implement the Routing over Low Powered and Lossy Networks (RPL) routing protocol to form ad-hoc DODAG networking configurations. The power of using these devices is that data collected can be aggregated on one or more master robots, regardless of the present configuration of these mobile devices.

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Page last modified on February 20, 2014, at 03:24 PM