Android usb serial for direct read

[davidcarlson]

Hi,
Where can i get an android lib (arr) to connect an android phone directly from the Pm2.5 meter to my android phone?
Thanks

[dwhitemv (Doug White)]

What are you trying to accomplish? There’s no serial port on the PurpleAir. You can query the device directly for its readings, but you need IP connectivity to the sensor to do that, usually by WiFi.

[davidcarlson]

I code wireless interfaces to scientific meters for Safeenv.com. I’m coding an Android app for the PurpleZen to add to the 100+ meters we currently have interfaced with. See www.safeenv.com for more information.
Initially I was having difficulty connecting to the Zen with an Android phone using a USB Serial connection to complete the app. I have solved that issue. But at the time of the post I was wondering if Purple had a serial interface.

[dwhitemv (Doug White)]

Looks like I’m wrong here, they all have USB Serial capabilities, described here:

Accessing Serial Data From PurpleAir Sensors

This article covers working with serial data, which requires technical knowledge. Our How to Obtain Sensor Data article details other ways to obtain sensor data. Serial Data PurpleAir sensors collect data every second and average it into “real-time” samples (typically for a 2-minute period). These real-time samples are sent to PurpleAir over WiFi and made visible on the PurpleAir Map. Serial data provides access to both reported samples and second-by-second measurements taken by the sensor. Thi…

[davidcarlson]

Good serial doc however it’s missing the format for the gas record:

.0h16:43.322 2025/01/29T00:07:20z: p:971.71 gasR:974310.19 iaq:50.00(1) T:26.65(32.25) H:16.91(12.27) sIaq:50.00(1) Stabilization:1 Run in:1

I can guess the uptime and utc time but the p: gasR iaq: T: H: fields not sure? do you know what they mean?

[dwhitemv (Doug White)]

The serial output format is described in this post, though it doesn’t explain the gas output:

Understanding PurpleAir Serial Output

When using the PurpleAir Utility or a Classic-SD sensor modified to record SD data every second data is not in CSV format. Instead, it is in a custom format described below, which may require additional processing to use. 1-second Reports Every second, one of the laser counters will report. Five reports will be recorded from channel A, then five reports from channel B. This process repeats until the next 2-minute report. This 2-minute report is the averaged data that is uploaded to our API as “…

You can get the field descriptions from the chip’s datasheet:

• p: Pressure in millibars/hPa
• iaq: Index for Air Quality (mobile sensor), like EPA AQI
• T: Temperature
• H: Humidity
• sIaq: Static Index for Air Quality (“static” meaning “stationary” here), like EPA AQI; is not subject to the auto-trim algorithm like iaq is
• gasR: Gas resistance value (raw reading of the sensing device, may or may not be temperature- and humidity-compensated depending on which field they’re reading)

There may be more fields depending on which chip your sensor is equipped with. I linked the datasheet for the BME688, but I believe older sensors may have the predecessor chip, the BME680.