CubeCell AB02 with MH-Z19 CO2 sensor on Vext

does anybody have experience with CubeCell AB02 and a MH-Z19 sensor connected via a 3.3 to 5V step-up device HW-668 connected to Vext?

My sketch from the MHZ19 library does not work, if the step-up device is connected to Vext. The initial serial connection (based on SoftwareSerial.begin) only works, if I connect the step-up device to VDD, not to Vext.

The MH-Z19 sensor is a not very accurate!

Any 3V3 microcontroller should work with a 5V device with a level converter!


I have included a StepUp converter, which is connected via a P-MOSFET to VDD and switched ON/OFF with the P-MOSFET via pin 14 in OUTPUT mode. Now it is working.