Go Down

Topic: CMOS chips with ardiuno (Read 1 time) previous topic - next topic


I was going to play around with some shift registers the likes of which can be bought very cheap on ebay...


(no that's not me or anyone I know)

...then I read that the 74HC series cannot be used reliably at this link  http://www.kpsec.freeuk.com/components/74series.htm but this link http://www.arduino.cc/en/Tutorial/ShiftOut from the arduino site seems to imply that it is ok.

Can someone fill me in on what will work and what won't with cmos chips and ardiuno?


then I read that the 74HC series cannot be used reliably at this link

No, there are probably 1000-billion 74HC chips being used in the field. This is what your
link actually says,
Note that 74HC inputs cannot be reliably driven by 74LS outputs because the voltage ranges used for logic 0 are not quite compatible,

74LS devices are very old style bipolar [NPN,PNP] chips and work at TTL-levels, while 74HC
chips are CMOS and work at CMOS levels, which is basically all you find anymore.

For background, research what TTL and CMOS voltage levels mean.


The AVR chip in an arduino is CMOS and will interface with any +5volt logic chip family there is. The input voltage switching states are .3 or lower of Vcc for a LOW and .7 or higher of Vcc for a HIGH, and they are of very high input impedance, so no +5 volt logic chip I'm aware of should have trouble driving an arduino input pin. And the AVR output pins are of very high current capacity and are both active high and active low so it can drive the snot out of any +5 volt logic chip family. Where you have to be careful is when you start mixing digital chips that are operating at different Vcc voltages, then there needs to be careful look at the datasheets for compatibility or take steps to convert the voltage levels.



Thank you very much retrolefty and oric_dan.  I appreciate it!

Go Up