[sdiy] 74HC165 vs CD4021..

[brianw]

For me, the choice is first determined by voltage supply needs. It's rare to need more than 5V, but there are a few applications. If high voltage is needed, then options are limited.

The second choice is price. If multiple parts meet the voltage requirements, then I'll just choose the cheaper one, or the more available one. With today's supply chain issues, availability might be the number one concern.

Brian

p.s. I've seen analog multiplexer designs where the analog voltages actually exceeded the mux chip ratings and caused lockup of the part. In this product, the manufacturer did not pay close enough attention to the voltage requirements. I'm assuming that their supply rails did not exceed the chip specs, but the input voltages from external equipment still exceeded the ratings. You're probably not in this situation, but it does explain why old technologies like 4000 series continue to be manufactured today, and sometimes there are even improvements to the voltage handling beyond what 4000 series could handle, originally.


On Oct 14, 2022, at 11:31 AM, René Schmitz <synth at schmitzbits.de> wrote:
> On 14.10.2022 19:52, Tom Wiltshire wrote:
>> I can't speak to the reliability question, but I'd choose the far-more-modern and more-available 74HC part over the ancient-history 4000-series CMOS.
> 
> 4000s have their place, say when you need to interface with 12V or 15V directly. Here I would also choose the HC series. More vendors, easier to get.
> 
>> I learned about logic circuit using 400-series circuits and a 9V battery on my breadboard about 40 years ago. They must have come up with something better since then, right?!?
> 
> HC have been around for 40 years by now. But 4000s are still older, 1968...
> 
> 
> Best,
>  René