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by HeyLaughingBoy 679 days ago
Be careful with assumptions though. Being 5V tolerant doesn't mean that your 3V output can sufficiently drive an input that expects 0-5V levels correctly.

I ran into this problem using an ESP32 to drive a Broadcom 5V LED dot-matrix display. On paper everything looked fine; in reality it was unreliable until I inserted an LS245 between the ESP and the display.
2 comments
irdc 679 days ago
> Being 5V tolerant doesn't mean that your 3V output can sufficiently drive an input that expects 0-5V levels correctly.

It's fine for TTL (like your 74LS245 is), which registers voltages as low as 2V as a logical 1. Being able to directly interface with TTL eases up so many retrocomputing applications.

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HeyLaughingBoy 679 days ago
Which was... exactly the reason I chose it?
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lloydatkinson 679 days ago
> LS245

Do you think that would be a good IC to drive these with a RP2040? https://www.analog.com/en/products/max7219.html

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HeyLaughingBoy 679 days ago
A better question might be why anyone is using a MAX7219 on a new design in 2024. There are so many other choices for displays than a 20 year-old IC from a company that's gone through two changes of ownership since.

Anyway, a 74LS245 isn't a level shifter, it's an octal buffer. It just happened to be the right choice for my needs. In your application, I'd suggest an actual level shifter. You can find level shift breakout boards at Sparkfun and Adafruit.

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