Frequently Asked Questions

uThing's integration

I'm using Linux and I get "Permission Denied" when I try to access the serial port

You have to give your user permission to read and write to the port. Please check here for more details.

uThing::VOC

Can I use the device outdoors?

You will need to consider 2 things:

Water-proofing. Obviously, you will have to consider how to install the board + host in a way that rain won't reach the electronics while still keeping a reasonable amount of air-flow into the sensor.

The concentration of VOCs is usually much higher indoors than outdoors, due to products like cleaning, paints and even the varnishes from some furniture. The BME680 is also relatively sensitive to CO2 from breathing, so you will notice the difference in a closed small room with a few people after a few minutes. Outdoors, the VOCs concentration is much lower in general, unless you have some factory or storage facility close-by emitting these gases. For outdoor air quality, what is usually interesting to measure is the particulate matter (2.5-10 um in size) generated by cars exhaust, dust storms, fire, and other sources. To measure particulates, the most common sensors are based on photo-optical absorption.

Why I'm seeing an offset between the reported and ambient temperature?

Regarding the temperature offsets (and humidity, since RH is highly dependant on the temperature):

Because of heat conduction through the PCB, the temperature seen by the sensor will change when you plug more devices to an USB hub, or if you have it directly connected to a Raspberry for instance, the heat generated by the CPU highly depends on its load, so a "perfect" calibration with ambient temperature will be even impossible in some cases.

The device comes with a fixed calibration performed while connected to a 4-ports USB hub, but you can use the {"temperatureOffset": -.-} command to calibrate against ambient-temperature for your specific setup.

If precise temperature values are important for your use case, the device can be connected through an USB extension instead, reducind the heat transfered from the host device. In addition, you can disable the LEDs with the command {"led":false}. The power used by the Blue LED is not much (~10mW) but is close enough to the sensor, so it may help to reduce the self-heating.

Remember that you can save the configuration in Flash to make it permanent with {"saveConfig":true}

Is there a plastic casing for the uThing::VOC?

Although there is no injection-molded case for this board, we have designed a 3D printable model which could be useful if you have access to a 3D printer or a printing service. The case consists of a top and bottom parts which snap together with small snap-fit features.

Check here for the design files.

Between multiple units, why the raw resistance seems to be quite far from each other?

The heated element (hotplate) is designed in a way that its resistance will change in a very wide range due to varying VOC concentrations (the higher the concentration of reducing VOCs, the lower the resistance and vice-versa). Since this raw signal is influenced by parameters other than VOC concentration (e.g. humidity level), the raw values are transformed to an index for air quality (IAQ) by the BSEC algorithms. BSEC keep track of the changes in this value over relatively longs period of time (days) to obtain baselines to improve the IAQ estimation.

uThing::MNL