[klodolph]

What was the answer?

I’m just curious at this point about what the quality of the answer is, just because you made a point about LLM use not turning your brain into mush.

I’ve not really used LLMs to answer questions, since it hasn’t gotten me the answers I wanted, but maybe I’m just set in my ways.

[peteforde]

I'm actually pretty thrilled that you asked, because I think that this chat is an extremely solid example of LLM usage in the EE domain, and I'm happy to share.

https://chatgpt.com/share/69a184b0-7c38-8012-b36d-c3f2cefc13...

I definitely led some questions to try and squeeze new-to-me perspectives out of it; for example, there could be tricks that make the active high variant more useful in some scenarios.

I think it does a good job of surfacing adjacent questions you might not realize you were eager to ask, as well as showing how it's able to critically evaluate real-world part suitability. I do find that ChatGPT in particular does better with a screengrab of the most likely parts vs a URL to the search engine.

[klodolph]

I see the chat, but it looks like you’re not actually considering using TTL anywhere, and ChatGPT isn’t giving any explanations about TTL?

> I would definitely like to understand HCT vs HC (CMOS vs TTL) much better than I do, which currently isn't at all.

I think what ChatGPT should have explained at the beginning is that both HCT and HC are CMOS logic families, it’s just that HCT is designed to interface with TTL (receive TTL signal levels as inputs). The outputs are the same (CMOS outputs are rail to rail, which you can feed into TTL just fine).

Actual TTL logic, like the 7400 series and the variations (LS is one of the more popular variations), uses NPN transistors as inputs and to pull output signals low. It uses resistors to pull the signals high. The result is a lot of current consumption and asymmetrical output signals… maybe a good question to ask ChatGPT is “why does TTL use so much current?” CMOS, by comparison, uses a tiny amount of current except when it is switching.

I would probably choose AHC first as a logic family these days. It’s a slightly better version of HC, but it’s not so fast that it will cause problems.

Just peeking at one of the recommendations in the chat, if you search for 74HCT125 or 74AHC125 on Mouser, you’ll see that the AHC has more options available and more parts in stock. That’s a sign that it’s probably a more popular logic family than HCT, which is something I consider when buying (more popular = better availability).