I'm trying to identify the cheapest shift register for a 3 digit 7 segment display.
How about no shift register? Just 10 output pins, 7 resistors, clever multiplexing so only 1 LED segment at a time is driven.
I want to use an attiny.
An Attiny2313 has 17 IO pins
Will it be possible to daisy chain 2 74hc595 shift registers to an attiny 85? I want to have a pin left over on the attiny85 for an input.
Sure. ATTiny has SPI pins? SCK to HC595 Serial Clock (SCLK) MOSI to HC595 Serial Data in SS to HC595 Register Clock (RCLK) Connect all 3 in parallel to both devices.
On each chip: HC595 OE to Gnd, MSTR CLR to +5.
q7/ of chip 1 to Ser Data of 2nd chip.
0.1uF from +5V pin on both chips to Gnd.
To send out data:
digitalWrite (SS,LOW); SPI.transfer (byte1); SPI.transfer (byte2); digitalWrite (SS, HIGH);
This will be helping you http://zugiduino.wordpress.com/2012/07/11/how-to-drive-4-seven-segments-using-ic-74hc595/
I bought 3 IC shift register 74HC595 (phi) for only 1buck, very saving cost.
depends on which you want, they even have 74HC2999, 8 bit Universal for 85 cents. Only takes 2 pins if you only want to read or write, but 4 to do both. And they can chain.