A RC servo motor consists of a small motor, a potentiometer, some gears and a drive circuit. Upon receiving a PWM square wave, it rotates to specific angles. The angle depends upon the pulse width of the wave.

Buy it then test it

http://www.sparkfun.com/commerce/product_info.php?products_id=9065

For example this servo has the following specifications

Operating Voltage: 4.8 v ~ 6v

Min. Control Pulse: 0.9 ms

Max. Control Pulse: 2.4 ms

Pulse Refresh Rate: 50 Hz

Rotation Angle: +90 to -90 (Approx.)

Output Torque: 1.4 kg-cm

How it will work?

RC servos require a PWM signal to rotate.

For the RC servo as above a 0.9 ms signal width will make the servo to go at +90° and a signal of 2.4 ms width the servo will go to the -90°. The mid-point or the 0° will be achieved by the mid-point of the signal width. i.e. 1.65 ms. In this way, we can achieve almost any value of angle in between +90° and -90° by simply changing the pulse width.

We will make a test circuit to give signal to run the servo. The microcontroller is PIC 16F877A with CCS C Compiler.

Circuit (Proteus ISIS 7)

To simulate our circuit we will be using Proteus ISIS 7.

Make the circuit as above. The servo signal pin is connected to the PIN C1 of the PIC microcontroller. For the actual connections:

C Source Code (written in CCS C Compiler)

We are using 50 pulses at an interval of 20ms for each cycle. In first while loop, the servo will rotate to -90°. And for the second while loop, the servo will rotate +90°. The value 50 (no. of pulses) is not always set to be constant; it is just to provide continuous stream of pulses until the servo achieves its rotation command.

Note: We have to provide continuous pulses rather then just a single pulse; otherwise the servo will not achieve the angle. We have to maintain the frequency of 50 Hz for this servo.

Simulate this project with the C source code in Proteus ISIS 7.

These little devices are of great robotic applications.

Click here to download.

Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It’s intended for artists, designers, hobbyists, and anyone interested in creating interactive objects or environments.

This platform is powered by Atmel’s AVR microcontroller. Arduino takes inputs from the environment using different sensors attached to it. It can control motors, lights and actuators upon receiving the inputs from the environment.

Arduino has its own programming software which makes easy to write code and upload to the I/O board.

Arduino has lots and lots of learning examples and techniques how to implement the I/O board for your applications.

These are some of the basic control commands.

• If Statement (Conditional): how to use an if statement to change output conditions based on changing input conditions.
• For Loop: controlling multiple LEDs with a for loop and.
• Array: A variation on the For Loop example that demonstrates how to use an array.
• While Loop: how to use a while loop to calibrate a sensor while a button is being read.
• Switch Case: how to choose between a discrete number of values. Equivalent to multiple If statements. This example shows how to divide a sensor’s range into a set of four bands and to take four different actions depending on which band the result is in.
• Switch Case 2: A second switch-case example, showing how to take different actions based in characters received in the serial port.

Buying the Adurino

Thanks to the Arduino team to develop such a wonderful learning platform.

http://arduino.cc/

Buy:

http://www.sparkfun.com/commerce/product_info.php?products_id=8691

Note: Xbee Series 2 will not communicate with Xbee Series 1

Some of the key features of Xbee modules are:

• 3.3V @ 40mA

• 250kbps Max data rate
• 2mW output (+3dBm)
• 400ft (120m) range
• Built-in antenna
• Fully FCC certified
• 6 10-bit ADC input pins
• 8 digital IO pins
• 128-bit encryption
• Local or over-air configuration
• AT or API command set

Aim:

We will design a simple wireless communication system. A microcontroller will wirelessly send data to a PC. We will use “HyperTerminal” on pc to see the data from microcontroller. What ever microcontroller sends on its TX pin, it is received on the RX pin of the other XBEE. Simple.

Now, the first feature is a little tricky for some of us who have the habit of using 5v Logic devices. Xbee is not 5v tolerant means no 5v to Xbee.

So, the first step in making a circuit will be a voltage translator. We need to convert the 5v signals to 3.3v signals so that Xbee remains happy (works).

If you hate to solder, sparkfun has a good translator board. Otherwise please refer to the schematic on the sparkfun page below.

Logic Level Converter:

http://www.sparkfun.com/commerce/product_info.php?products_id=8745

For the schematic

http://www.sparkfun.com/datasheets/BreakoutBoards/Level-Converter-v10.pdf

Programming Xbee to talk to each other

When we buy the Xbee pair, the modules doesn’t know the each other. So to make them recognize each other for communication we need to program the Xbee modules.

This is a small circuit which will be used to program the Xbee.

Or if you want to buy the board, it’s the Xbee Explorer.

http://www.sparkfun.com/commerce/product_info.php?products_id=9111

After that you need software to program and configure the Xbee modules.

It’s the X-CTU.

X-CTU Download

Now that you have all the hardware connected we will proceed to the programming steps.

Connect the programming circuit (serial explorer) to your PC through serial port or the USB (if you have the USB explorer).

-  Select the com port (Communications port for serial and USB for    USB explorer)

-   Set the baud to 9600, Flow control None, Data bits 8, Parity none, and stop bits to 1

-   Press Test/Query button. It show you the version of your Xbee in the dialogue

-   Goth to modem configuration tab and press Read button

-   It will import all the settings of the Xbee

You have 2 Xbee modules. Set one module to Zigbee Coordinator AT and other to Zigbee Router/End Device AT

-   PAN ID of both Modules should be same

-   DL and DH of one module should be the SL and SH of the other module respectively (See photo)

Now press the Write button to start burning the parameter in the Xbee module

Testing the Chat

Connect one Xbee module using the serial or the USB explorer to a pc. Connect the other Xbee module to another pc.

Open Hyper Terminal. Set the communication settings to

Baud: 9600

Parity: none

Data bits: 8

Stop bit: 1

What ever you type in the hyper terminal will appear at the hyper terminal of the other pc. It will check your Xbee configuration.

Microcontroller – Xbee – PC

To interface the Xbee with a microcontroller, use the logic level converter.

Be sure to connect TX of microcontroller to the RX of the Xbee and vice versa

using the level translator.

NOTE: Xbee is not 5v tolerant place the logic level translator between Xbee and the microcontroller.

And connect the other Xbee module using USB or serial explorer to a PC.

Whatever microcontroller transmits on TX pin will be received by the PC and shown on Hyper Terminal.

Enjoy the high-quality wireless communication.

Please let me know if I could be of further assistance.