Pointed out that indoor air quality measuring instruments are terrible

'The industry is in a state of collapse, and if the product is garbage, few customers will notice it, so they don't care,' said Hales, an electronics designer by trade, about products that measure indoor air quality. .

Many indoor air quality sensor products are a scam (temperature, humidity, pressure, CO2, TVOC)

Mr. Hales posted to the forum of the Linux distribution 'OpenWRT' used as firmware for embedded systems, 'I want to measure the temperature and humidity in the room, but all four devices give different values. I'm seriously worried about what to do.'

According to Mr. Hales, who makes a living as an electronic designer and also handles temperature and humidity sensors, creating devices that measure temperature, humidity, pressure, etc., uses off-the-shelf sensor components such as the BME280 and 2SMPB-02E, and Wi-Fi It is easy if it is placed on a microcontroller with Fi or a PCB with a chipset.

These sensor components are extremely excellent because the manufacturer guarantees accuracy, but the problem is that 'I have never seen them used correctly in devices,' said Hales.

First, the temperature sensor must be placed on the board away from any other power-hungry electronics for proper temperature measurement. Due to the microcontroller and Wi-Fi chipset, even 0.5W of heat can affect the sensor. The error in the measured temperature is a few degrees Celsius if nothing is done, and less than 0.1°C if there is forced air flow around the sensor. Since the error changes even with a gentle breeze, it is impossible to simply adjust the numerical value.

And since the humidity display is based on the 'maximum moisture capacity of the air at the current temperature', temperature deviations lead to humidity deviations.

Pressure sensors also need their own temperature to correct their internal readings and display the correct value. For this reason, they have built-in temperature sensors, but some can self-heat. The data sheet describes the method for correction, but there are cases where the wrong method is selected.

In addition, although there is no problem with the relative value of the carbon dioxide sensor, the place where the carbon dioxide value is the lowest is automatically set as the 'minimum measurement value' on the premise that it is in contact with fresh air once a day. Sounds like you have a case to fix. For this reason, Hales pointed out that it will not work properly in an office that is closed and air-conditioned all the time.

``Consider the device is a fraud unless accompanied by documentation demonstrating product accuracy and reliability, expected lifespan, and proper use,'' advises Hales.