ESP8266 Community Forum

- Fri Jun 10, 2016 10:07 pm #48965 Hi, I am using the nodemcu v2 board with a 16x2 serial lcd. All is working well with a separate 5v supply, but i was wondering if its alright to draw current from Vin while the esp is powered by a usb supply. The lcd just needs 5v for its power then the 3.3v serial is high enough to work on its input. I have tried it already and it does work, just wondering if there is any problem with this.

- Sat Jun 11, 2016 2:24 am #48972 the i2c pullups on the adapter board are connected to 5V, so the esp i2c pins theoretically see "overvoltage".
But in reality this does work. If you want to be 100% sure insert a i2c level converter.
Regarding the current draw it is ok, too. The LCD and the converter just draw about 10mA. The backlight might add signifficantly more current but still within reason.

- Sat Jun 11, 2016 8:16 am #48989 Just to be clear the display is not using i2c, but rather uart. So just using the tx pin works to communicate, and there are no pull ups. This lcd backlight does draw around 100mA, but that should be drawn only from the usb, when I have it connected to Vin. At least this is what I'm trying to confirm.

- Sat Jun 11, 2016 9:26 am #48993 yep, this is correct.
According to schematic, USB V+ is connected to Vin via a diode.