Running a 7v shift register from arduino 3.3v

Question

Im trying to learn some electronics, so im not that confident with some of these systems,

I recently bought a load of the alphanumeric displays from Sparkfun but foolishly read the data sheet for the red, then bought the blue. The difference is the operating voltage is 7v instead of 5v which is making things difficult.

I have also some shift registers, eg 74HC595 but they are rated only up to 6v, I have found other shift registers that take a higher voltage, such as the cd4006b, but they look like the clock and latch pins etc. also need to be at the higher voltage, so driving them from an Arduino is proving difficult.

Can someone give a simple solution or suggestion that im missing for keeping this simple?

• I. Wolfe: The red display is 2 bucks... Easiest solution is to buy the correct display. I also wonder if Sparkfun would take a trade for the correct displays if you paid a restocking/shipping fee.
• Dan: Majenko has the best answer. I have used TPIC6C595 shift registers too (Note no constant current tho, 5V supply) because it is available in a DIP form factor. 74HC595 is not ideal because it will source current (not sink) and its max continuous current Vcc to GND is 70mA

Answer 1

You want a proper LED driver shift register. These are normally a constant current sink, and can accept up to around 30V usually.

One example is the STP16CP05

• sherrellbc: What is the context of the word "proper" here? What makes the 74HC595 improper?
• Majenko: "Proper" as in "Designed for the purpose".