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 wantwww.kpsec.freeuk.com/components/74series.htm
164 is the model number for this chip, there is a large chart of them on wikipediaen.wikipedia.org/wiki/List_of_7400_series_integrated_circuitsNext, 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)
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
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)