Arduino and 74x595

[wb4jfi at knology.net]

I don’t have a sketch, but I would say that you want to toggle the clock line as many times as you want, in this case probably 32 times.  Keep the data line low except for the equivalent bit that you want to turn on, and keep the latch line disabled until all 32 bits are shifted into position.  Then toggle the latch bit once (up then down).  Both clock and latch lines are leading edge.  If that makes sense?  I’m sure a Google search will also help, as the 595 is a common way to expand data I/O on the Arduinos.

Another option that only requires two lines, but does require slightly more expensive parts, would be to use I2C port extender ICs.  The PCF8574P is a very popular 8-bit extender, while the PCA9555N handles 16-bits of I/O.  Two PCA9555 (or equiv.) would do the same job.  There are many others as well.  The Arduino Two-Wire library makes using I2C devices very simple.  I’ve also use I2C 16x2 LCD displays, as that also greatly reduces the number of pins used for these displays.

I use these I2C chips all the time, as they don’t use up the limited digital I/O pins of the Arduino.  For example, on a current project I am using a PCF8574P for I/O expansion, a “digital pot” IC to control the output level of the AD9850 DDS, an EEPROM (24LC256?) for a large look-up table, a DS1307 RTC chip (for battery-backed-up RAM), and a temperature chip, all using only the two I2C pins of the Arduino Uno.

I2C, it’s a great tool!
73, Terry, WB4JFI


From: Joseph Bento 
Sent: Sunday, March 30, 2014 5:32 PM
To: Tacos AMRAD 
Subject: Arduino and 74x595

Hey all,

Been playing around in Eagle Cad today, drawing some schematics for a Arduino shield I want to play with.  I've never done much with shift registers.  Looks to be a good way to get virtually unlimited outputs with just three lines from the Arduino.

While I like to think my electronics skills are good, my programming skills are dismal.  

I want to be able to individually address a specific LED out of the 32 rather than light them in a sequence.  I think I have the data lines routed properly between the 595s in the schematic.

If anyone can share a tutorial sketch, it would be appreciated.

Thanks!

Joe, N6DGY





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