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Topic: CD74HC4067 Multiplexor. Is Resistor important? (Read 2884 times) previous topic - next topic

Laktica

hi everyone

just a quick question, specifically about a multiplexer but may just be a 'rule of thumb' for many ICs

with the  CD74HC4067E PDIP

Ive got a 100nF cap accross the power  

but do i need a resistor along the 'enable pin to ground' connection

the schematic on the single SMD CD74HC4067 board here:  http://www.sparkfun.com/products/9056
has a 10k resistor

but the same chips here on a 3 chip board dont: http://mayhewlabs.com/products/arduino-mux-shield

is this resistor important??

tried searching and people mention building your own mux ect but no specifics on the resistor

thanks everyone

Grumpy_Mike

#1
Nov 03, 2011, 11:10 pm Last Edit: Nov 07, 2011, 02:19 pm by Grumpy_Mike Reason: 1
Logic chips like this can have the pins directly connected to either voltage rail. However a 10K to ground makes it look like a logic zero but allows you to easily pull it high later if you want to connect a signal to it.

Laktica

Thanks! so I know its not essential, I'm just going to connect them direct to ground for now, as thats ok

but if I decide I want to enable/disable the chips for some reason, I add a resistor to ground ( is 10k enough for two chips?)  so its enabled by default but use a 5v 'digital out pin to 'HIGH' to this enable wire to dissable the chips?

have i got that right?


Grumpy_Mike

Yes that is right.  :)

Quote
( is 10k enough for two chips?)

Well if it was me I would use 1K resistors to pull down.

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