Arduino Pro Mini 5v and HTU21D sensor - SUPPLY problem

Other Hardware Sensors
1

Hello,

I make a project with Arduino Pro Mini collecting data from temperature and humidity sensor and printing this on Serial monitor. Arduino operating voltage is 5v and sensor is 3.3v. I supply the sensor from Arduino vcc pin through regulator.

Everything works fine when i power the Arduino through Arduino UNO (which i used as a programmer). When i want to switch to battery power i don't get any results on serial monitor, althought led on Arduino is lighting and it's printing some control text. I tried to use many combinations of batteries like 6x1,5 AA batteries to RAW pin, 1x9V to RAW, 4x1.5v AA to VCC, 3x1,5V to VCC etc. I tried also to power regulator separately from battery but always with the same result. Voltage behind the regulator and current taken from battery is the same as from Arduino UNO. When i power it back from Arduino UNO everything works again.

I'm quite new to Arduino so sorry if it's some obvious question but i have no more ideas where can be the problem.. Thank you for help!

2

If your Mini is the 5V version, the VCC pin is 5V, 5V Mini does not have a 3.3V regulator like Nano and UNO, so you're connecting your 3.3V sensor to 5V. Where are you getting power when powering from UNO?

3

Thank you for reply.
I am using external voltage regulator, it's LD33V. When i power it from UNO i use 5v and GND pin and connect it to vcc and GND of Mini and also to input and GND of regulator. Then with output and GND of regulator I go on sensor. This works fine. When i change only the 5v and GND from UNO to some battery - it's gone..

4

Is your Pro Mini a 3.3V or 5V version?

For your Serial communications, do you not only have TX/RX but also the grounds connected?

5

Yes, connecting GND of both Arduinos was the point
Thank you a lot!