How to use a Flip-Flop "74LS74"?

Forum 2005-2010 (read only) General Bar Sport
#1

Hi vereybody,

as i didn’t get my arduino board yet but want to build something, i
found some flip flop IC in my cupboard.They have the following
names:

DL086D = SN74LS86
DL074D = 74LS74
DL010D = SN74LS10

So, as these Parts are Flip Flops, i wanted to start understanding them
with switching an LED on and off, but i didn’t find any information on
how to use these things… I had some experience with digital
techniques at school, but nothing really usable (At least, nothing of it
has stayed in my head until now lol)

Does anybody have some elementary Information on what they do
and how they can be used for me? Can i just use a switch, an LED
and some sort of Battery or so and it works? Or is teremore needed
for my testing?

#2

for lack of a better discription, a flip flop acts like a bit of memory, from there you can do all sorts of stuff

counters
registers
dividers
???
profit

for example if you look at the logic diagram for a 74x164 shift register
(bottom of page 2) http://www.google.com/url?sa=t&source=web&ct=res&cd=1&ved=0CBsQFjAA&url=http%3A%2F%2Fwww.fairchildsemi.com%2Fds%2F74%2F74VHC164.pdf&rct=j&q=74hc164&ei=bTTmS9jNG4SKlweXlLmPDA&usg=AFQjCNGFyge6ducd8zD8hXUKD3GiX582xA

you can see its made up of 3 gates and 8 D type flip flops, your 7474 contains 2, and here is some more fun stuff to try

http://www.softwareforeducation.com/electronics/notes/AS/ttl/dtypeflipflop.php

#3

DL086D = SN74LS86 is a Quad 2-input XOR gate

So that’s 4 exclusive OR gates. Power with 5V and ground. Take one output and wire it up through a 470R resistor to an LED. Put a push switch on each of the 2 inputs with a 3K3 pull up resistor to +5V, other end of switch to ground. The LED will only light up if the state of the two switches are different.

DL074D = 74LS74 is a Dual D Positive Edge Triggered Flip-Flop with Preset and Clear.

So that is two edge triggered D type latches. Power with 5V and ground. Take one Q output and wire it up through a 470R resistor to an LED. Put a push switch on the D and the CK inputs with a 3K3 pull up resistor to +5V, other end of switch to ground. Wire pre set and clear to ground. Change the state of the D input, nothing happens until the CK input goes from a logic low to a logic high. When this happens the logic state on D is transferred to the output Q.

DL010D = SN74LS10 is a Triple 3-input NAND gate

So that’s 3 NOT AND or NAND gates. Power with 5V and ground. Take one output and wire it up through a 470R resistor to an LED. Put a push switch on each of the 3 inputs with a 3K3 pull up resistor to +5V, other end of switch to ground. The LED will be on if the any one or more switches are off.

#4

Do you have more than one 7474? The neatest thing I ever made from small scale logic like that was shift registers (your basic Kit Car blinking LEDs.) You can probably make an oscillator with the NAND gates, and 2 or more 7474s will make a decent number of blinking lights.

You’ll appreciate the arduino more that way as well…

this seems to have some of the details: http://www.docstoc.com/docs/13424256/experiment-7/

A set of bounceless pushbuttons and/or switches are handy to have as well, and should be achievable with the NAND gates. Using your three-input NANDs instead of the usual 2-input gates is left as an exercise for the student.

#5