Maikrt Embedded Thermal Printer 1224V Micro Thermal Receipt Printer Serial Port Microcontroller Secondary Development MCU Printing Module TTL/RS232, C209H, 82*58*44MM, Black

I got this for a project that uses an ESP32, and I had no trouble sending data via TTL-level UART and getting a print-out. It does come with a roll of paper, and there's even a print-out with some technical details (one detail being the serial baud rate).Tip for Arduino users: while you can print simply by using `Serial1.print()` (or `Serial2` or even SoftwareSerial), the "adafruit/Adafruit-Thermal-Printer-Library" on GitHub makes printing a lot easier!But this loses one star for the documentation being incomplete and confusing...First, the product description says the model is a C209H, but the label says MC206H. Not sure if that matters, but figured I'd mention it in case it's important to someone else. Regardless, put either of those into Google to look for more detailed information, and you'll find nothing.The product description says it's TTL or RS232 level, and that RS232 is the default. However, the document that came in the box with mine said it's already set to TTL-level (which is what I wanted anyway). The description also says "If you need to switch, you can and we will tell you how to switch" -- why must I contact someone to know how to switch between TTL and RS232? Why not provide that in the instructions?On the bottom is a tiny hole (see photos) over a micro slide switch -- could this be the magic TTL/RS232 switch? I removed the bottom cover to have a closer look at the PCB, and it's not labelled. So this kind of worries me; it's not labelled, and the product description says "defaults to RS232" and the instruction sheet that came with it says "set to TTL" -- how do I know what's right?My ESP32 didn't fry, so it must be in TTL mode. If I make the time, I'll attach my oscilloscope to the RX and TX lines to see what the signal levels are.Also, the serial header includes a DTR pin, which is informational to the host and not needed to make it print -- if the printer is idle, it's ready. However, in TTL mode, I measured 5.5V on this pin instead of the expected 3.3V -- glad I didn't connect this to my ESP32, or I might have fried a GPIO!Overall, this is a nice module; it's not a commercial-grade unit, but it doesn't feel like cheap junk either and seems reasonably priced. But the secretiveness and confusion around the RS232/TTL switching and the documentation not being very thorough is a disappointment.