Mega Board

MegaBoard is a Robot Control Board, with an AVR ATMEGA1281 microcontroller, 6 High Power H-Bridges (5A DC capacity), & ULN2803 

Downloads: Circuit Schematic ,
SimpleTest Code,
and Quick Start Manual(N/A)

Contest Start: March 2, 2008
Contest Ends: May 5, 2008
Board Reaches the Winner: May end, 2008
Contest open to Robot hobbyists living in India only.

Win MegaBoard Contest

The winner of this contest shall receive a MegaBoard (AVR ATMEGA1281 Microcontroller Based Robot Control Board), and a CD containing sample-code/datasheets. This page describes the background of this contest, and the technical specifications of the MegaBoard

So What is This About?

Many budding Robotics hobbyists need a good electronic control board to control their robot. The "Megaboard" is such a board, with an AVR ATMEGA1281 Microcontroller. All you need to do is start writing your robot control software in C. Before that, however, you need to know the capabilities of the Megaboard, and also be aware of the Software Tools you shall use to program the Megaboard. This page gives all the details you would need to know and do, to use Megaboard. 

It must be noted that the Megaboard might not be suitable for "absolute" beginners. Prior knowledge/reading of any Microcontroller Programming would be necessary to fully enjoy using this board. The link to the application for the Contest can be found below on this page.

This kind of board is also being used currently by Chetan (who is a past contest (XVIBoard) winner) for Robocon-2008.

MegaBoard Features and Summary

Block Diagram:

Block Diagram of ATmega1281 Board
Fig. 1

MegaBoard Specs:
Component Features Details
MCU: AVR  ATMEGA 1281 Maker Atmel , Part No. ATMEGA1281-16AU
Core AVR, 8Bit , 16 MHz
Memory Flash: 128KB, RAM: 8KB, EEPROM 4KB
ADC 10 Bit, 8channels. Speed: upto 15kSPS
Timers & PWM Two 8-bit, Four 16-bit, Real Time Counter with Separate Oscillator
– Four 8-bit PWM Channels
– Six PWM Channels with Programmable Resolution 
Serial Asynchronous UART- Rx/Tx : Converted to RS232 level by MAX232 for link to PC serial port. 
H-Bridge L9929 (6 Motor Driver ICs) Voltage Rating 4.5V to 28V
Motor Current 5A DC Max WITH HEATSINK. (Please read below about how you would have to make the heatsink yourself)
Protection Over Current (short to VB & GND), Short between Terminals, Over Temperature Shutoff
Uses Can drive 6 DC motors, or 3 Bi-polar Stepper Motors (2coils each)
Open-Colletor
Driver ULN2803 		Voltage rating 50V peak (includimg clamped voltage of motor coil)
Motor Current 500mA each coil or output
Uses Can be used to driver 2 small stepper motors (unipolar) (eg. from old floppy drive.), or other small loads. This IC is NOT MOUNTED on MegaBoard. If you need to use it please buy and mount it yourself. Please read below for mounting details.
Debug LEDs  3 LEDs driven by CPU ports for debugging etc.
Push-buttons  2 Push-buttons for debugging etc.
Flash Writing  Using Serial Download, via AVR ISP, by Pony-Prog software on PC
Size  95mm x 75mm
Power Supply VB0 Supply for 5V regulator and ATMEGA. Min 8V, max 35V. Try to keep as near as possible to 8V to minimize heating of the LM7805. But if you are running everything of a single 12V battery, its ok to make it common with VB1 & VB2
VB1 Supply for Motors M1, M2, M3 & ULN2803. Min 4.5V, max 28V. Could be common with VB0 & VB2.
VB2 Supply for Motors M4, M5, M6. Min 4.5V, max 28V. Could be common with VB0 & VB1.

Participation

Click here for the Online form, and quiz:>  MegaBoard Contest Application (but please do read below completely before applying)

Frequently Asked Questions (FAQ)

What kind of person would probably Win the Board? Beginner , Intermideate, or Advanced ?

I think, a beginner with some/little background in Microcontrollers, AND some hands-on Skills would be the most appropriate user for this board. If you are an advanced robot maker, the board would not serve your needs, and it is better to let a beginner get the chance to use it. If you are an "absolute beginner" and have no Hands-On skill, I must say that this board is not best for you. I have deliberately not made the heat-sink of the Motor Drivers. And if you dont make it and attach it correctly, and if your motors take current high enough to heat the ICs till damage, the board turns useless. (The H-Bridges do have over-temperature shutdown, but nothing is guranteed in hobby use). I cannot judge your practical skills on internet, but i can get a little idea about your engineering understanding by your answers to the questions on the application. Please be fair to yourself, and judge yourself if you need this board or not.

Why are you holding this contest ? 

This contest is just to give away a board i developed for giving away to a budding robot hobbyist. I made a few boards, and 1 for winner of a past contest (Chetan), and thus am giving this out to others with talent and craze for robotics.

What is the difference between ATMEGA128 and ATMEGA1281? 

ATMEGA1281 has 8KB RAM, whereas ATMEGA128 has 4KB RAM. For details see Atmel App.Note "AVR097: Migration between ATmega128 and
ATmega1281/ATmega256"

If I don't win this contest, can I buy this board from you /somewhere?

Maybe. I do have a few more PCBs, but I cannot commit on assembling them yet. If this happens, this website shall be updated, and I shall inform you. 

Can i make this board myself ? Would you provide me with the PCB layouts ?

Yes, you may download the schematic from the links on this page, and ask me for the PCB layout.
But, i think it may be hard to find these ICs in the local market in India. I think the approximate cost of the MCU would be $14 and H-Bridge about $10 each if they are available in local market. 

Requirements

Things you need to Do before you could use MegaBoard (after you get it)

  • ULN2803 Not Mounted: This chip has not been mounted on the board. If you need this function please buy and solder a DIP Socket, the IC ULN2803, and the Zener Diode D4. D4 could be 27V, 1W (or higher wattage). D4 is used for clamping, so max voltage can be: Vz_max = 50V - VB1 (supply of ULN).
  • RS232 Header & Connector: A cable should be made with a 3 pin connector on one end, and a 9 pin D-sub (f-type) connector at the other end. This shall be used to connect the CPU to the PC Serial Communiction and debugging the code.
  • Megaboard pin ---(about 2m wire)--- 9pin D-sub pin
    1 (Tx) ------- 2 (Rx)
    2(Rx) ------- 3 (Tx)
    3(Gnd) ------- 5 (Gnd)
  • Capacitors C5 & C19: The voltage rating of Capacitor depends on your motor voltage. It should be twice or higher. So please buy 2 caps, 1000uF atleast, & 25V if your power supply is less than 12V. C5 & C19 are very necessary for good start-up performance of the motors. Please solder C5 & C19 yourself. 
  • No Sensor interfaces!: This board is more like a Motor Driver board. There are no circuits to interface to sensors. So you shall have to connect your own circuits/sensors on the free pins. Please see the schematic and plan for your use.
  • Heat Sink: If the motor current is higher than 2A, please do not use the board without adding a heat sink under the H-Bridges. There is are 2 screw-holes near each set of 3 H-Bridge ICs for the heatsink. But there is no ready-made heatsink available for this design. You will have to make one yourself with aluminum channel or bars. It has to be screwed to position Under the H-bridge IC., where there is rectangular exposed copper on PCB for good heat conduction. If used without the Heat-sink at high current (about >2A DC), the H-Bridges WILL BE DAMAGED.

    Fig. 2: Bottom side of MegaBoard.

Some tips for using the MegaBoard

  • DC Motors and PWM Speed Control: Although the Demo Program source may eventually explain how the speed and direction of the DC motors is controlled in Megaboard, here is the basic concept.
    Each H-bridge IC gets 1 PWM and 1 direction bit input from the MCU. When the direction of the motor is to be reversed, the Direction bit set to High, And the PWM is set to Active "low" duty. Figure below shows the Motor1 being run at "same speed" in opposite directions, because the PWM active duty is the same.

    PWM and Direction control of DC motors in XVI board
    Fig. 4


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Copyright: Vivek Vaid 
Last updated: 2008, Mar 2