This design uses a smart card to enable a relay. It fires a relay when a card with the correct code is inserted. A Nutchip recognizes its mating smart card among thousand similar ones and the smart card sends a digital code among thousands different codes.
This card-activated realy requires just an handful of parts and is very simple. The active components in addition to the Nutchip are a 74HC00, a reset generator (IC3) and a transistor for relay switching.
Thereset integrated circuit IC3, an MC34064 from Motorola, guarantees a clean Nutchip RESET even in presence of electric noise coming from the power network. Its duty consists of discharging the capacitor C2 as fast as possible when a power drop is detected.
The Nutchip (IC1) is the heart of the device. Nutchip output OUT1 drives an LED (LD1) which is in series to a current-limiting resistor (R3). A separate output is used for dirving the relay (RELAY1) through a transistorized relay driver stage (TR1, R2, D1). The transistor works as an electronic switch, amplifying Nutchip output current from tenths of mA to tens of mA – a level suitable for driving the relay coil. Diode D1 protects the circuits from high voltages that are induced on the coil during switchoff.
But let’s introduce the smartcard. We choose a “Funcard Purple”: this is the usual name for a card embedding a powerful processor, an Atmel AT90S8515, and a serial EEPROM memory. Other “Funcards” similar to the “Purple” are the “Funcard Prussian” and “Funcard Prussian 256”: these should be theoretically compatible, although more expensive. However, please note that we have not tried them, so take our word at your own risk.
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