Electronic – 1.8V UART with 3.3V UART

level-shiftinglevel-translationuart

I have Quectel EC25 module comes with GPRS and GNSS in built, this module needs supply of 3.3V and it's UART works at 1.8V (default Baudrate is 115200) – But i have a processor ATMEGA2560V running at 8Mhz on 3.3V supply.
I am trying to interface that module with my processor, I have used voltage divider circuit with 1M Ohms resistors to pull down 3.3V of processor to 1.8V, I can see some random values comes in the Serial Monitor and i am unable to send any AT commands.

How do i solve this.? is this need any more reliable Resistor divider circuit.? and i don't have source to get 1.8V to 3.3V level shifter 🙁

Please help

Thank you

Best Answer

  1. Do not use meg ohm resistors for the voltage divider from the 3.3V to 1.8V UART direction flow. Something with resistors more in the 3.3K to 10K range would be much more appropriate.

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  1. For the 1.8V to 3.3V operational direction you can easily make a level translator with a couple of transistors and resistors. 2N3906 NPN transistors will work great.

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