I have been planning to build an air quality measuring device using the Honeywell HPMA115S0 and an Arduino.
There are a few tutorials out there on how to do it, such as this one Arduino: measuring PM2.5 and PM10 with Honeywell HPMA115S0
The thing that makes things slightly complicated is that the Honeywell HPMA115S0 needs a 5V power supply, but its UART interface only accepts 3.3 volts.
So the interface cannot be connected directly to an Arduino UNO, because it has a 3.3V logic level interface
The author of the above tutorial solves this by using an Arduino Due, which has a 3.3V logic level interface.
But that's a fairly expensive solution, so I want to see if there is a cheaper way to do it.
My idea was to use an Arduino Pro Mini 3.3V with an integrated USB connector.
As far as I can figure out, the RAW pin on the Arduino supplies 5V when the board is plugged into USB, since there seems to be a direct connection between the 5V on the USB connector and the RAW pin. At least, that's what I gather from this post: RAW power and USB at the same time? - SparkFun Electronics
I suggested the following solution to the author of the above tutorial:
I use an Arduino Pro Mini 3.3V version,
Pin 2 (Vcc) goes to the RAW pin on the Arduino board (which is at 5V, since the Arduino is powered via USB).
Pin 6 (UART TX) goes to the RX pin of the Arduino board. This pin uses 3.3V logic level (since this is the Arduino Pro Mini 3.3V version).
Pin 7 (UART RX) goes to the TX pin of the Arduino board.
PIN 8 (GND) goes to GND pin of the Arduino Board.
The author replied that this won't work, but I don't see why.
Can anybody help me verify his conclusion?