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Shift registers are a very important part of digital logic, they act as glue in between the parallel and serial worlds. They reduce wire counts, pin use and even help take load off of your cpu by being able to store their data.
They come in different sizes, with different models for different uses, and different features. The one I will be discussing today is the 74HC164 8 bit, serial in parallel out, non latched, shift register.
Why? Well for one it is one of the most basic shift registers out there, which makes learning about it easier, but it just so happened to be the only one I had (lol!)
This instructable covers how this chip works, how to wire it, and interface it with an arduino including some sample sketches and led circuits.
I hope you all enjoy!
They come in different sizes, with different models for different uses, and different features. The one I will be discussing today is the 74HC164 8 bit, serial in parallel out, non latched, shift register.
Why? Well for one it is one of the most basic shift registers out there, which makes learning about it easier, but it just so happened to be the only one I had (lol!)
This instructable covers how this chip works, how to wire it, and interface it with an arduino including some sample sketches and led circuits.
I hope you all enjoy!
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Signing UpStep 1So, what are shift registers?
As mentioned earlier they come in all different flavors, and I also mentioned that I am using a 74HC164 8 bit, serial in parallel out, non latched, shift register
so what does that all mean?!?
First, the name
74 -- means its part of the 74xx logic family, and since its logic it cannot directly control very much current (16-20ma for the entire chip is common) , it only passes signals around, but that does not mean that signal is not going to a transistor which can switch a higher current load.
HC means its a high speed cmos device, you can read about that on the link below, but what you basicly need to know about that is that it is a low power device and will run from 2 to 5 volts (so if your using a 3.3 volt arduino your ok)
Also it can work properly at high speeds this particular chip has a typical speed of 78mhz, but you can go as slow or as fast (until it starts goofing up) as you want
www.kpsec.freeuk.com/components/74series.htm
164 is the model number for this chip, there is a large chart of them on wikipedia
en.wikipedia.org/wiki/List_of_7400_series_integrated_circuits
Next, 8 bit
A shift register is made up of flip flop circuits, a flip flop is 1 bit of memory, this one has 8 (or 1 byte of memory). Since it is memory, if you do not need to update the register you can just stop "talking" to it and it will remain in whatever state you left it, until you "talk" to it again or reset power.
other 7400 logic series shift registers can go upto 16 bit
serial in parallel out
This means your arduino sends it data serially (on off pulses one after another) and the shift register places each bit on the correct output pin. This model only requires 2 wires to be controlled, so you can use 2 digital pins on the arduino, and break those 2 out to 8 more digital outputs
some other models are parallel in serial out, they do the same thing but as inputs to the arduino (for example a NES gamepad)
non latched
This may be a downfall of this chip if you need it. As data enters a shift register via serial, it shows up on the first output pin, when a clock pulse enters in, the first bit shifts over 1 place, creating a scrolling effect on the outputs, for example 00000001 would show up on the outputs as
1
01
001
0001
00001
000001
0000001
00000001
If your talking to other logic devices who are sharing the same clock and not expecting this, it could cause issues. Latched shift registers have an extra set of memory, so once the data is done entering the register you can flip a switch and show the outputs, but it adds another wire, software, and things to keep up with.
In the case of this instructable we are controlling LED displays, the scrolling effect happens so fast you cant see it (except when you very first turn on the chip), and once the byte is in the shift register there is no more scrolling
We will be controlling bargraph type, 7 segment, and a 16LED 4x4 dot matrix with this chip and software on the arduino using only 2 digital pins (+ power and ground)
so what does that all mean?!?
First, the name
74 -- means its part of the 74xx logic family, and since its logic it cannot directly control very much current (16-20ma for the entire chip is common) , it only passes signals around, but that does not mean that signal is not going to a transistor which can switch a higher current load.
HC means its a high speed cmos device, you can read about that on the link below, but what you basicly need to know about that is that it is a low power device and will run from 2 to 5 volts (so if your using a 3.3 volt arduino your ok)
Also it can work properly at high speeds this particular chip has a typical speed of 78mhz, but you can go as slow or as fast (until it starts goofing up) as you want
www.kpsec.freeuk.com/components/74series.htm
164 is the model number for this chip, there is a large chart of them on wikipedia
en.wikipedia.org/wiki/List_of_7400_series_integrated_circuits
Next, 8 bit
A shift register is made up of flip flop circuits, a flip flop is 1 bit of memory, this one has 8 (or 1 byte of memory). Since it is memory, if you do not need to update the register you can just stop "talking" to it and it will remain in whatever state you left it, until you "talk" to it again or reset power.
other 7400 logic series shift registers can go upto 16 bit
serial in parallel out
This means your arduino sends it data serially (on off pulses one after another) and the shift register places each bit on the correct output pin. This model only requires 2 wires to be controlled, so you can use 2 digital pins on the arduino, and break those 2 out to 8 more digital outputs
some other models are parallel in serial out, they do the same thing but as inputs to the arduino (for example a NES gamepad)
non latched
This may be a downfall of this chip if you need it. As data enters a shift register via serial, it shows up on the first output pin, when a clock pulse enters in, the first bit shifts over 1 place, creating a scrolling effect on the outputs, for example 00000001 would show up on the outputs as
1
01
001
0001
00001
000001
0000001
00000001
If your talking to other logic devices who are sharing the same clock and not expecting this, it could cause issues. Latched shift registers have an extra set of memory, so once the data is done entering the register you can flip a switch and show the outputs, but it adds another wire, software, and things to keep up with.
In the case of this instructable we are controlling LED displays, the scrolling effect happens so fast you cant see it (except when you very first turn on the chip), and once the byte is in the shift register there is no more scrolling
We will be controlling bargraph type, 7 segment, and a 16LED 4x4 dot matrix with this chip and software on the arduino using only 2 digital pins (+ power and ground)
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thank you :)
I can easily address an individual LED to light up, but when I do I get surroundings LEDs to turn on as well ( much dimmer then the addressed LED)
I have attacked a picture to show you what is going on. I am trying to just light up and LED that is in position (1,1) but as the same time LED (4,4) is dimly lit.
here is the piece of code that I am using.
shiftOut(data, clock, MSBFIRST, B10000001);
delay(1);
Any guess as to why?
Great tutorial. Thanks for making it, it's real helpful!
I've been looking for something written like this for a while.
I now have a fully working 4x4 led matrix, that I've built myself, and got to show the patterns I want.
This is all thanks to you.
Cheers,
Mikey C
I made this with your help.
http://www.youtube.com/watch?v=3UNbvYED0bI
I have 4 or 5 of these chips laying around, and just for giggles I wired up a old 4 section 7 segment led display from an alarm clock
i got a bunch of shift regs to put to use :P