Interfacing with TTL?

[barnacle]

Yup, three main suppliers: Digikey, Mouser, and LCSC (in China but don't let that put you off - they provide access to a number of Chinese parts as well as TI and Nexperia and the like). LCSC is cheapest for delivery but takes longest; Digi and Mouser are OK if you're spending more than fifty bucks.

Farnell are good for next day delivery *in the UK* but I've had issues with their Euro store; not all parts are available in Euroland (also applies to Digikey but I can't recall the exact parts; odd because Digi ship from the states anyway). RS's web store has been a pain to use for years...

One complaint about all of them is that the parametric selection is sometimes confusing...

Of course, most of my use is for smallish orders - couple of hundred bucks - for work prototyping. The other half of the job is to see whether what the board stuffers offer us as 'equivalents' actually are...

Neil

[Dr Jefyll]

Thank you, SamCoVT and barnacle.

-- Jeff

[Yuri]

AndrewP wrote:

Unhinged rant time!

O no, what HAVE I started?

AndrewP wrote:

Mouser's website is ... challenging. It's not hobbyist friendly but it is also BY FAR the best website for electronics. Digikey's is somehow worse and RS Component's is an abomination*. And that's not even counting non-electronic websites that sell ICs like Amazon or Aliexpress.

I try to avoid using Amazon and Aliexpress as much as possible for parts. I also tend to avoid Ebay if I can as well, I prefer fresh new (or at least new old stock), if I can get it. I did manage to find some 74F181s on ebay when I was thinking I might do a CPU with just 74 chips (at least as much as I reasonably could). I tested them so they are working, but yea that was the only thing I was having a hard time finding. But in general I don't trust 'em as far as I can throw 'em.

My go to vendors are usually Digikey, Mouser, Jameco (seems good for older parts), AdaFruit, and Arrow (if I remember to search there, I tend to forget they exist, IDK why)

I will admit that Mouser's site is a bit slower than Digikey's that's for sure. And yes, they were VERY challenging to find parts for when the only logic family I knew of was the "LS" series. (Searching for 74LS04 didn't yield a lot of good results..... )

I think I've more or less got it figured out now though. At any rate, one of the things that helped was just using Google to search for things like "Quad Nand Gate IC" which would provide some links to Digikey, Mouser, et. al. pages. Probably helped that I had some exposure to all of this when I was a kid in the 80's and 90's. I took more to programming (now my day job) than hardware though.

AndrewP wrote:

And there you have it. Lots of 74LVC245s. Now all you have to do is scroll through them them until you find a package and manufacturer you like. I tend to Nexperia then Texas Instruments but honestly a 74 series IC is a 74 series IC and as long as the datasheet says it does what you want it will work.

I'm a bit biased towards Texas Instruments. My paternal grandfather was a engineer there for many years (as far back as I can remember at any rate). He even got permission to let me tour the place when I was kid, I was so interested in tech back then.

ANYHOW, you are correct of course, a 74 IC is still a 74 IC for the most part. I try to let the specs help me make final decisions instead of just going straight for a brand. And price to some degree, but with a lot of 74s they're already pretty cheep to begin with, and with the very low quantities I get, a few cents doesn't make a large cost difference. If I were buying in bulk for a large product build out, then those cents would matter more. (Funny how they quickly add up when you get into thousands of units)

AndrewP wrote:

But if you didn't know a 245 would be found under bus transceivers then it's time to start clicking around Mouser's Products. Bus transceivers happen to be under Semiconductors -> Logic ICs -> Bus Transceivers but the only way to find that is to go on an adventure.

And I didn't of course. I was looking for logic level shifting, I didn't even know it was the 245s, or a bus transceiver at all!

All I could find with what I knew was stuff on AdaFruit. And don't get me wrong, I love what AdaFruit does, but they are not a good source for more than one or two parts at a time, plus they are very focused on Arduino/RaspPi stuff going through the GPIO pins, where speed isn't super critical.

(Maybe? Looking at the Datasheet again and I see the timings are in at around 18ns max. I thought I saw them at 200+ns when I looked last, maybe I'm confusing it with another part.)

AndrewP wrote:

And I'm glad I didn't have to sort and choose categories. But once you've found the exact part number using Mouser's website then do a general Google search for the exact part number (say: 74LVC245AD,118) and see if it is cheaper on Digikey or somewhere local etc... Good luck, Mousering definitely takes practice!

I've started doing this more. Particularly with the more expensive parts like the CPLDs and FPGAs I've been eyeballing.

SamCoVT wrote:

Once you've determined the part number you want, you might want to try octopart.com ...

*bookmarks* Thank you!

floobydust wrote:

As the interrupt on the 16C550 is active high, all you need is a simple mosfet and a resistor.

Thank you for this, I was going to use a diode, but I think this is a much safer circuit. Also makes me consider that maybe my hair brained idea of funneling all of the push/pull interrupts through a dedicated PIC may not be as hair brained as I first thought after all.

[barnacle]

Yuri wrote:

(Funny how they quickly add up when you get into thousands of units)

Yep, I've spent multiple weeks saving a cent or two on the BOM; on one memorable occasion a circuit change saved a buck and half which is possibly why they wanted me to come back after I retired!

Neil