For beginners, the 595 series Shift Register isn’t easy to grasp. I’ve written an interactive 595 simulator so you can learn out the 595 works without having to wire one together. Play around with it. See if you can get it to produce the output you expect.
“Wait a minute! How does this work? I don’t get it!”
Picture a box that has a hole on either side. Inside it has 8 spaces you can fill up. Those spaces can either hold a zero (0) or a one (1). To fill up a space, you just push a new 0 or 1 into the left-hand side. When you do, the last space in the box gets pushed out the right hand side. At any time, you can open up the box and get all 8 values at once in the order you put them in there.
That’s kind of how a shift register works. You use the Serial In Value to tell the chip if you’re going to put a 1 or a 0 in. You use the Register Clock to tell the chip you’re pushing in a value on the left hand side. You use the Latch (or Shift Register Clock) to tell the chip you want to see all the values in the box.
Try the following:
- Click the Serial Input Toggle button so that the SER pin goes red (that means it’s “HIGH”)
- Click on the Clock button (Notice the SRCLK pin goes HIGH)
- Now look at the Storage Register on the right. You’ve added a 1 to the beginning of the list!
- If you click Clock again, you’ll see another 1 added to the left side.
- Click the Serial Input Toggle again and the SER pin will go LOW.
- Click Clock, now you’ll see a 0 added to the left side.
- Now click on the Latch button. The values in the Storage Register are pushed out to the Shift Register. Now the output pins on the chip are also showing HIGH or LOW corresponding to the Shift Register. Lastly, you’ll see the 7-segment display has lit up as well.
- Press the Storage Register Reclear button and press Latch. Now both registers are clear.
Now try those steps again, except press the Latch button after each Clock press. Notice what’s happening. Once you get the hang of it. see if you can make some numbers on the 7-segment display. Figure out which segments correspond to which pins on the shift register chip.
Here are a couple of characters for the 7-segment display to get you started:
At least one person was looking for part numbers for 595 shift registers. Here are a few:
What’s the difference?
Similar part numbers usually suggest compatibility between manufacturers. The specific part number may denote a variation. For instance, the 74HC595 differs from the 74HCT595 in that it can handle a wider variation in input voltage. For beginners, the variations usually aren’t particularly important. Check the data sheet for a particular chip.
If you’re looking for one and aren’t sure where to start, I’d recommend going to SparkFun. It’s not going to be the cheapest option, but they’ll give you the right chip if you’re uncertain.