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DESIGN IDEAS - CMOS IC Makes Low-Cost Digital Potentiometer - Power Management In The ST62 - Automatic Power-Off Circuit Saves Battery - Simple PC Smart Card Reader Enhancement - Digital Position Encoder Does Away With ADC - Single-Supply RS-232 Transmission Without Level-Translator ICs - ΅C Controls Charge Pump As Background Task - Clock Multiplier Circumvents PLL - Drive Smart Cards With A Low-Cost MCU's UART - Wireless Battery Energizes Low-Power Devices - Harvest Energy Using A Piezoelectric Buzzer - Drive A Single-Coil Latching Relay Without An H-Bridge Circuit DESIGN CONTESTS ARTICLES
CONTACT
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HARDWARE
DESIGN
The hardware design is built around the Atmel AVR ATmega168 microcontroller. It has the small footprint required for this application with a large flash memory.
The
hardware design is powered through the USB port, so that it is not
necessary to use an external power supply or a battery. The
smart card interface is a special socket needed to interface the smart
card to the USART0 of the ATmega168. It uses a 4,9152 MHz oscillator to
get a communication baud rate of 12711 bps on the I/O line of the smart
card. The
LCD module is a standard 2 lines by 16 characters display compatible with
the industry standard Hitachi LCD controller. It is connected to the
ATmega168 using a 4-bit bus configuration to save I/O lines. The
USB interface is accomplished through software emulation. USB lines DATA+
and DATA- must be wired to the same I/O port. Line DATA- must be wired to
bit number 0. DATA+ must also be connected to INT0. DATA- requires a
pull-up of 2.2KΩ
to 5 volts to be identified as low-speed USB device. DATA+ is used as
interrupt source instead of DATA-, as it does not trigger on keep-alive
and reset states. No UART, timer, input capture unit or other special
hardware is required (execept one edge triggered interrupt). Additionally
the ATmega168 must be clocked at 12 MHz, so it is necessary to specify the
speed grade of the microcontroller when ordering it. It is also possible
to make overclocking with low-speed AVR devices, but it is not recommended
since there are high-speed components available for a reasonable price. There
is an activity LED to signal data transmission on the I/O line of the
smart card. Finally,
there is an ISP (In-System Programming) port for updating the flash if
further updates or enhancements are planned in the future. Following is the block diagram and the schematic of the board designed:
BLOCK DIAGRAM The hardware block diagram is below:
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