How to use a 74HC595 Shift Register with a AVR ATtiny13

Picture of How to use a 74HC595 Shift Register with a AVR ATtiny13
If you have been playing with microcontrollers and electronics then you have likely seen LED dot matrix displays and other projects that use shift registers like 7-segment displays and more. This instructable goes over a quick intro to the 74HC595 8-Bit Serail to Parallel Shift Register with Latch and how to interface it to an AVR ATtiny13 to flash some LEDs.

What you need:
1 - Breadboard
1 - Power Source - 7805 or some other 5v source
1 - ATtiny13 and a way to program it ( I'm using the AVRISP mkII with AVRStudio 4.17 w/ WinAVR)
1 - 74HC595 Shift Register
1 - 100uF cap
1 - 0.1uF cap
1 - 10K resistor
8 - LEDs
8 - 470ohm resistors
~15 - hookup wires

What is a Shift Register?

Serial to Parallel Shift Registers are ICs that allow "serial" data to be clocked in on 1 pin and stack up in a register which is output on 8 parallel pins (in the case of a 8-bit shift register). As data is clocked in, it shifts all the other bits over one position with the end one falling off. Common shift registers are 74HC164 and 74HC595.
There's a couple of good online tutorials about these with animations.

The 595 has another feature which is cool. It's called a latch. It allows the outputs to show the current bits which have been latched in the Latch Register while new data is shifted into the Shift Register. Then toggle the latch pin and the new data is copied into the Latch Register.

Here's a link to the 74HC595 Datasheet:

Check Out a Youtube Video of the Circuit in Action

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FreakErn1 year ago
Where can I download the code?
roznerd (author)  FreakErn3 months ago

Download the package at the end of Step 3.

contrechoc made it!1 year ago

Thank you for the very elaborate and accurate code wth all the comments...

(I used an attiny85...same code.)

First I made a breadboard test. Then I made the LED (smd) in a circle. My idea was to make an interactive etching. I added a bit of code for an LDR. If it sees light change, it reverses the way the light is turning around the circle.

I had to skip the ENABLE PIN, made this HIGH on the 74HC595 and had a free adc PIN on the Attiny85.

All works on a 3V lithium battery.

Normally I use the LED matrix code with interrupts, with this shift register you have less wires...

I'll make another circle for use in a sweater!

roznerd (author)  contrechoc3 months ago

Awesome!!! I'm glad you had some fun with it.

gussmith2 years ago
My Bad! I just plugged in another SN74HC595N and now I see led8 blink too.
Just a bad pin.
gussmith2 years ago
I use an ATTINY85 and a SN74HC595N with the exact wiring and example code.
When running
I put a delay in the loop of option 1 and only see the leds 1 to 7 blink but not led 8.

Can't figure out what I'm doing wrong.
opticalaser2 years ago
hi my friend first thank you a lot
but my compiler is Basic may be you can tech-me how i can write program
by basic


lefam4 years ago
what is the total amount of current that the 595 shift register can sink and source?
roznerd (author)  lefam4 years ago
Thanks for the question. The 595 is able to source or sink 20mA on each output, however the catch is that the total current for the chip is 70mA, so you have to consider that. Alot of guys get away with running dot matrix leds and stuff directly off the 595 because they are multiplexing and the average current works out to be be less than the max. I think the 595 has some internal over-current protection on the outputs too.

There's a good discussion about this at this link:

I hope this helps. Thanks
lefam roznerd4 years ago
thanks. it helped a lot...
arthur927104 years ago
Hi, this code is very helpful. I have a question, it uses a for loop to fill the register from an array, how can I send a binary or hex code. I am using this to build a 10 x 10 matrix.
roznerd (author)  arthur927104 years ago
I'm glad you found this tutorial helpful. The for loop and array was used to make it easy to show, but as you know, its not really practical for most useful applications.

I understand what you are getting at with the application for a dot matrix. You want to individually clock in the bits of an 8 bit byte. This could be in bin or hex, it makes no difference.

I have done this before for using a 595 to drive a 4 digit multiplexed 7 segment display. Here's the excerpt of code I used to take the byte (in hex in my case) associated with the digit I wanted to display and get it clocked into the 595 without using an array.

It uses whats called a bitmask. I describe it in the comments of the code below. I tried to be very thorough because I know how hard it is looking at someone elses code and trying to figure out what's going on. Hopefully this is helpful for you. Thanks for the feedback - roznerd

for (k=0; k<8; k++)
// you have to loop 8 times to clock in all 8 bits in the byte to display, makes sense.

//Your byte will replace the "digit" byte. if the 7th bit of the byte "digit" is 1 then set Data pin high for 595 and toggle clock to shift it in. If the 7th bit of the byte "digit" is not 1 (i.e. 0) then set Data pin low and toggle the 595 clock pin.

if (digit & 0x80)

// this is the bit mask, by AND-ing the 8-bit byte you want to display with a "mask" that overlays all bits except the 7th bit (0x80 = 10000000) you get to differentiate whether the 7th bit is a 1 or 0 by the outcome of the AND. IF 1 & 1 = 1 (data pin high) ELSE 0 & 1 = 0 (data pin low).
Then you shift the bits in your byte to the left << 1 position and compare again.

Data_H; // defined in header to set data pin high
Shift_Clk_H; // defined in header to set shift pin high
Shift_Clk_L; // defined in header to set shift pin low

Data_L; // defined in header to set data pin low

digit = digit << 1; // shift the bits in your byte to the left 1 position
} // end for

// after all 8 bits in the byte "digit" are clocked in, toggle the latch to show on the display

Thanks! This will help me a lot!
SuperFlyGT4 years ago
Thanks for the quick tutorial. I was looking at using this part for a personal project and this helped to clear up some questions I had.

Out of curiosity, why ground Pin 9 (serial data out / QH')? If the output is of QH is high (and by extension Pin 9), you're shorting a high output to ground.

Another version of the datasheet (for HC595, not HC595A, lists a clamping current of +/- 20 mA max which I suspect is saving the chip from blowing. It would be safer to either leave this output floating in this application or put a resistor to ground.
roznerd (author)  SuperFlyGT4 years ago
I'm glad the tutorial was helpful for you. In retrospect, I would have left the Pin 9 floating or pulled it down with a 10K resistor. I think connecting Pin 9 to GND for breadboarding is probably ok, since it's probably internally clamped to prevent over current, but in a design, I would handle it differently. Good catch, thanks
tissit4 years ago
avrdude is not a compiler.
ju1ce4 years ago
Thanks for this tutorial - I really like your clear way of presenting things.