Hi
Just a question on setting up a logic circuit, to see if I am doing it correctly.
I have a 74HC42N BCD to decimal decoder
http://www.nxp.com/products/logic/decoders_demultiplexers/74HC42N.html
I am basically after probing its logic just to watch it working
I dont really know how to figure these circuits out so I am trying to use the same resistor pull up values that I used for my other 74HC logic ICs.
I add it to my breadboard with 5v regulator, I then add 4 buttons for inputs and on the buttons I use 10k resistors as pull ups.
I do not know how this value is determined exactly, I was following a schematic when I made the last circuit I did, but since that I read this article:
https://learn.sparkfun.com/tutorials/pull-up-resistors/what-is-a-pull-up-resistor
I am not rightly sure how to determine the input impedance then go a 1/10th less. But it does state 10k as a loose rule.
I then decide to leave the outputs floating like I did with the 74HC00.
With the 74HC00 I only had to pull down the inputs, so I am hoping this is normal practice?
I am expecting the inputs to dictate each output pins state, so are the outputs even floating?
Then I was hoping to be able to power on and test the state of the pins using logic probe and pressing the switches.
Does this seem reasonable?
Thanks
Just a question on setting up a logic circuit, to see if I am doing it correctly.
I have a 74HC42N BCD to decimal decoder
http://www.nxp.com/products/logic/decoders_demultiplexers/74HC42N.html
I am basically after probing its logic just to watch it working
I dont really know how to figure these circuits out so I am trying to use the same resistor pull up values that I used for my other 74HC logic ICs.
I add it to my breadboard with 5v regulator, I then add 4 buttons for inputs and on the buttons I use 10k resistors as pull ups.
I do not know how this value is determined exactly, I was following a schematic when I made the last circuit I did, but since that I read this article:
https://learn.sparkfun.com/tutorials/pull-up-resistors/what-is-a-pull-up-resistor
I am not rightly sure how to determine the input impedance then go a 1/10th less. But it does state 10k as a loose rule.
I then decide to leave the outputs floating like I did with the 74HC00.
With the 74HC00 I only had to pull down the inputs, so I am hoping this is normal practice?
I am expecting the inputs to dictate each output pins state, so are the outputs even floating?
Then I was hoping to be able to power on and test the state of the pins using logic probe and pressing the switches.
Does this seem reasonable?
Thanks