# Question: Brainstorm on ways to use colored light to show sensor readings

warren asked on April 18, 2019 17:52
114 | 0 answers | #19110

In the #simple-air-sensor's default settings, we chose to show a rough sense (think qualitative, for comparison) of the PM2.5 dust sensor readings as a colored light, in part because without calibration or accounting for humidity/temperature, it's hard to know exactly how accurate the readings are. (the Simple Air Sensor includes a single #Plantower PM sensor, while two come in each #purple-air device)

Also, this opens up a lot of possibilities for using the sensor to do group projects. It was very useful in talking as a group about how sensitive they are -- using a candle, for example, with 30 people, we had one person hold a sensor a few meters from a candle, with another right next to it. The whole group was able to see how one responded sooner, and there was a lot of other useful things we could do with it.

That said, the scale is currently set from green to yellow to red, and the color choices are worth some discussion -- i'd love to hear your thoughts and input. And as with any design question, we may not find there's one clear solution.

One problem is that red and green are the most difficult colors to distinguish for people who can't see colors as well.

A second issue is that they overlap with the colors used in the US AQI system (read more here), so could be confused with a direct indication of "safe" or "not safe" - which is not what the sensor is telling us, exactly.

### How it's set up now

The actual code we're using is here: (gist link and Arduino Create link) and is as follows:

    int minVal = 0;
int maxVal = 20; // arbitrary
// map values to a portion of the 360 degree color wheel
int hue = max(0, min(359, map(data.pm25_standard, minVal, maxVal, 140, 0)));
setLedColorHSV(hue, 1, 1);


So, as marked, we can choose the top and bottom of the range.

Basically, the value of 20 µg/m3 for PM2.5 is mapped to an angle of 0 on the color wheel, and a value of 0 µg/m3 is mapped to the angle 140, which is roughly green:

### What now?

Ok, so one thing that could address the red/green issue above would be to map from blue to red.

Another could be to use blue and green, although it's becoming less clear to a majority of people what is "more".

Other options could be to use a numerical display, or multiple LEDs. Or a blinking light. Or a sound (annoying?). But it'll depend on the use case, and I'm interested in how we can make a single, simple, colored light as useful as possible.

I would love to hear input; and keep in mind, we can try a few out and see how they work, so we can discuss this a bit -- and people may opt for different solutions. Thanks!