Atmel AVR motor development board
This document specifies and describes a development board for Atmel Atmega168 and compatible 28-pin microcontrollers. The board is designed specifically with motor control in mind, with dedicated headers for RC servos and DC motors, including dedicated connections for H-bridge control, quadrature encoder and current sense. The board also supports serial communication (SPI, I2C, USART) .
The board provides easy connection to both RC servo motors and DC motors (including H-bridge, encoder and current limit pins) via dedicated headers.
RC servo motors
Dedicated headers for two DC motors are available on the board. The headers are standard 100mil-headers.
Headers for each DC motor
Connector 1, to motor amplifier/H-bridge. This connector has pins for common signals used in H-bridge IC’s and motor amplifiers.
Ground connector to amplifier.
Programming and debugging
Standard 6-pin ISP header with Atmel-ICE.
The LEDs are routed directly to the i/o pins via a series resistor.
Value of series resistor
Note that the absolute maximum rating for DC current per output pin is 40mA according to data sheet.
A red LED has a Vf at about 2,2V and should have a current of about 20mA. With a high level of 5V, this corresponds to a resistor value of
R = (5-2,2V)/20mA = 140Ω
To keep some safety margin and limit the current a 330Ω resistor is selected. Anywhere between 200 – 500 ohms should be OK (Williams).
The LEDs and series resistors, load the ports to some extent, whether or not they are actually used. The LEDs should therefore be considered disconnected if the port is programmed to be used for other purposes.
Switch as input to digital pins
The switch output should be connected (strapped) from the point “Switch output” on the PCB, to the input pin of choice.
The switch can have two different configurations, for pulling the input high or low when the button is pushed. The pull-up resistor (if used) need to be soldered in the appropriate place on the PCB, together with a correct strap. See user codumentation for details.
The resistor values values should be large to minimize currents, at least 10k and up to 100k.
For pulling the input low when pushed, the internal pull-up can be activated, which eliminates the need for an external pull-up resistor.
Analog to Digital Conversion (ADC) inputs.
There are four dedicated headers for ADC inputs. these can be used for potmeters or other analog sensors.
The ADC module needs supply voltage on the AVCC pin. There are two ways to provide the supply voltage:
The PCB also has dedicated holes for a decoupling capacitor for improved noise immunity, as recommended in the data sheet.
In any case, the voltage on AVCC must be within +/- 0,3 volts of Vcc.
Two dedicated connectors for serial communication is provided (in addition to the SPI programming header).
General serial communication header
A general, proprietry header for serial communication is provided, with the following serial modes, depending on configuration in the application software:
An FTDI-compatible header is provided for easy communications with FTDI-based serial to USB converter cables, for use with direct connection to a computer (terminal programs or other).
Routed to RXD/PD0 and TXD/PD1.
Power pin is disconnected, but if needed can be strapped to Vcc via dedicated holes in the PBC.