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Comment by criddell | Hacker News Reader

Using an AVR128DA48 feels using a 747 to go get my mail from the mailbox.

Why not use actual logic gate chips? I made a board like this a long time ago with 74xx-type chips. It was neat looking at a datasheet[1] and seeing exactly how the pins correspond to the gates.

[1]:https://datasheetspdf.com/datasheet/7411.html

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Got curious how big a front yard would be required to fit a 747.

A 747-100 is 70m long,

Wingspan ~60m.

(I am not saying everyone has a mailbox accessible through a front yard, or even has a front yard, or necessarily a mailbox. Just want to make that clear to the whole internet.)

Consider also Boeing's minimum runway length official reference which states an additional 4000m will be needed to cover your heaviest mail deliveries in wet conditions (for example, two consecutive rainy days with a bout of Amazon shopping). https://static1.simpleflyingimages.com/wordpress/wp-content/...

For the love of God... both of you.

I was thinking about using the fuselage as a corridor because that was the most charitable.

The article says he wanted the gates to be configurable. But yeah, seems like a missed opportunity to not familiarize with the 74 series. That having been said, the AVR chips are probably a lot more useful to learn as a newbie these days. Not many people using discrete logic ICs anymore :(

That having been said, the AVR chips are probably a lot more useful to learn as a newbie these days. Not many people using discrete logic ICs anymore

I dunno. I mean, there's no question that they are less widely than in their heyday. But I think there might be a surprising number of uses where they are used for some small (very small) bit of functionality where even the smallest microcontroller is overkill.

In my own experience, I had something recently where I literally needed a single AND gate to switch a transistor on or off based on whether one or both of two power rails were HIGH. A discrete 74xx chip turned out to be the simplest way to implement that.

I'd say that pretty much every schematic I've reviewed in the last few years has a handful of logic on it. Often we need to guarantee that something is off or disconnected if the CPU fails or software crashed, etc. Hard-wired logic is good for that kind of thing.

Ti have long had "little logic" for this kind of thing (I've been out of that game for a while, maybe something has taken its place?)

2018 link (PDF): https://www.ti.com/lit/pdf/scyt129

Hey, thanks, I did not know about the "little logic" stuff until just now. I'd always looked at the 7400 series chips (or 4000 series chips) as my "goto's" for one-off individual logic gate kind of stuff.

s/widely than/widely used than/

How the heck did I just leave an entire word out? sigh

Why use 6 chips when you can use one? It's not like those discrete chips would be cheaper in total

For me, the ideas become a little more concrete when I see a discrete package and can exactly map these inputs to that output.

Otherwise, why use one chip when you can use none? This could all be little virtual switches in a web app.

> Otherwise, why use one chip when you can use none?

Because you're actually designing a hardware product to sell.

You could also use 0 chips and create an app that does the same thing.

I think you'll find an app needs more than zero chips to run...

In theory, if you have the source code (it is the easiest), you can run the app in your head, so no chips needed.

Those 6 discrete chips will probably use less power.

They probably would be, actually. In quantities of 1, a discrete logic chip is around 50 cents, while that microcontroller is $2.50. In higher quantities the logic gets cheaper faster. For this project, you would need:

1 quad NAND gate

1 quad NOR gate

1 quad XOR gate

1 hex inverter

The cost isn't the main thing here, though. A better reason to go with discrete logic is that the MCU also requires an entire software and hardware toolchain to create and load firmware.

Never underestimate the cost of adding nonvolatile memory to your system.

> In quantities of 1, a discrete logic chip is around 50 cents, while that microcontroller is $2.50

The article also mentions that ATMEGA809 should work here, and costs about $1.53 in singles https://www.digikey.com/en/products/detail/microchip-technol...

> I built two prototypes, one with an AVR128DA48, and one with the older ATmega4809 which is pin compatible, and their performance was indistinguishable. The program only uses about 1500 bytes, so an ATmega809, ATmega1609, or ATmega3209 should be fine

For the record, you could also use a much cheaper MCU like e.g. an STM32F030C6 which costs around $0.60 for a single chip and around $0.45 for 30 chips at LCSC the moment. Of course this is completely irrelevant if you build a small number of boards like here, because then you'll probably waste most time with programming the chip and you need the necessary programming connector + tools too.

It would be fun to redesign this board for the lowest manufacturing cost with machine assembly and compare it to how much more expensive it would be to use discrete logic chips.

In this case the behavior is not equivalent, I know the author said it's close but with polling the inputs I doubt it would replicate various feedback configurations faithfully.

It would indeed disappoint the user hoping his CMOS fedback inverter gets faithfully destroyed.

Whereas less destruction of electronics -> more faithful "experimenting with and learning about logic" as per the device's purpose.

I recently designed a board using discreet components but I replaced those chips with a single STM8 MCU because it was significantly cheaper. While designing using gates is fun, it doesn't make economical sense, even for a simple hobbyists like me.

edit: one exception is using the venerable 555, but while it's a discreet component it's not a gate.

> Why not use actual logic gate chips?

Surely that would have greatly increased the assembly work. And possibly cost too.

I don’t know. You can buy a solderless breadboard, some pre-cut wires, and a lot of 74xx chips for the $99 that the the bare board costs.

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