HC Or HCT Series - General Electronics - Arduino Forum

HC or HCT series Other Hardware General Electronics system August 26, 2012, 7:58pm 1

hello,

I want to use an 74HC595 to be driven by arduino and in turn to drive an ULN2803A from the ULN2803A data sheet I understand that it can be driven by both 74HC595 and 74HCT595, but which series is recommended for an new design with avr microcontrollers ?

thanks, razvan radu

MarkT August 26, 2012, 8:12pm 2

The difference is in the input levels and power-supply voltage - HCT are designed to interface to TTL levels (0.8V / 2.0V). In general HC are the ones to go for if interfacing to other CMOS chips (they take 2 to 6V so are voltage-agnostic). HCT will in general work fine too if your power supply is 5V. If you want a simple 3.3V to 5V level converter you can use an HCT buffer powered at 5V - its input levels of 0.8/2.0V should be happy with 3V3 drive.

system August 28, 2012, 9:53am 3

HCT are cheap, reliable, and simple. Even those considering transistor solutions would be advised to look instead at HCT family ICs just for simple interfacing. Even a single channel interface made using transistors is larger in circuit board space, more complex to build, and likely to cost more - especially so if you put a value on time. Fault finding with HCT is ridiculously simple, whereas a transistor format has multiple points for potential faults, and will take much longer to fault find, and to replace a faulty component. "Keep it simple" usually pays well in the long run!!

MarkT August 28, 2012, 10:21am 4

ipadwarrior: HCT are cheap, reliable, and simple. Even those considering transistor solutions would be advised to look instead at HCT family ICs just for simple interfacing. Even a single channel interface made using transistors is larger in circuit board space, more complex to build, and likely to cost more - especially so if you put a value on time. Fault finding with HCT is ridiculously simple, whereas a transistor format has multiple points for potential faults, and will take much longer to fault find, and to replace a faulty component. "Keep it simple" usually pays well in the long run!!

This reads like marketing. And it doesn't answer the original poster's question. And its wrong.

[edit: Oh I see, you've copy/pasted this from another reply where it did make sense - here it's not relevant since we are not talking about level-shifting to 5V]

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