I plan to flash new firmware for a Sonoff ESP8266-based switch.
So I need a 3.3v USB to TTL for the programming. I see an inexpensive converter from China which has pinouts for
My question: I understand the 3.3v and 5v pinouts as providing constant voltage for the load (device being programmed) with the power coming from the USB port. But why isn't a switch of some sort needed so the TX line can be set to either 3.3v or 5v output?
What I am missing here? Thanks.
Why doesn't TX need a voltage selector?
Because it's a cheap, low-quality adapter that only supports one output level.
The Prolific PL2303, around which this adapter is based, can't output 5V signals. By default, it uses a 3.3V voltage standard, and will output at least 2.4V for high outputs. This will be high enough for most 5V TTL devices, but some devices may have trouble with it.
I have used cheap cp2102 converters for this, and am quite happy with them. They already work at 3.3v, and support high baudrates. The only drawback is that you can't use them with arduino, since it doesn't support 5v. But for the price, who cares? Beats accidentally frying your ESP :)
