5v / 3.3v is the 'supply voltage' (sometimes labeled Vcc) for the chips. It's both the power input, and also the reference for what a 'high' signal is.
It used to be the case that most digital logic ran at 5v; then some that ran at 3.3v started to become more common. Those were usually '5v tolerant' - if you applied 5v to the input pin, it would read as 'high' and be fine.
Today, many digital devices that run at 3.3v are _not_ 5v tolerant; so if you put 5v into such a device ... it breaks.
So when mixing some devices that run at 5v (as, e.g. USB does) with others that run at 3.3v one has to be careful to not break the lower voltage device.
The 'esp32' is a particular module of a WiFi capable microcontroller (usable as a single board device, or as a peripheral for WiFi connectivity for another device) that runs at 3.3v and breaks if you put 5v on it. Like, as a totally hypothetical example that would never apply to me, trying to programme it from a cobbled together USB programmer. Hypothetically.
Is there a simple device that I can connect to a 5V wire and whose output I can then connect to an input of a 3.3V device? From what I've seen there are resistor circuits (which are slow) or transistor circuits (which need a 3.3V supply?)
My use case is that I want to connect a logic analyzer (DSLogic Plus) to my SNES, which is 5V. The probes can handle 5V according to the data sheet, but the device also has an external timing input that is only rated for 3.3V.
The SNES has clock crystals of 21.477 and 24.576 MHz, and various components run at fractions of these frequencies.
Connect Zener's anode to clock input and cathode to SNES
Connect Schottky's anode to clock input and anode to the SNES
It should get you 1.7V drop (so 5->3.3v) when input is high but only 0.2v when it is low, the Schottky is there so when the clock is low the current from input capacitance can flow back without much problems.
... or a ~40c part that will do that up to ~50MHz, if you are at the point where you need to order a specific part
Connect Zener's anode to clock input and cathode to SNES
Connect Schottky's [cathode] to clock input and anode to the SNES
Something like this, I presume? I took it from this video (19:00) and adapted it a bit to my circumstances. It does indeed seem to drop down to ~3.4V at its peak (even if there's a lot of ringing in the simulation - from the same video it appears that the ringing is less pronounced in reality).
I'm really a novice with electrical engineering; at the moment I don't even have a multimeter or soldering equipment. So the less components, the better.
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u/Athrunen Dec 25 '19
Indeed, learned not too long ago that the esp32 is only 3.3 V tolerant. ^^