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document updated 5 days ago, on May 19, 2024

cheap sensors

Sometimes you need to be able to measure some basic information, but don't need those measurements to be particularly accurate

integrate the information here into this article

sensors present in smart phones

Many Android phones have four sensors that can be read by apps, however not all sensors are present in all phones:

An ambient light sensor, usually used only to automatically adjust the screen brightness.

An ambient humidity sensor.

An ambient pressure sensor, used to supplement the phone's altitude measurements.

An ambient temperature sensor.

Reads all available sensors:


If you have a meat thermometer, many of those are capable of working as an ambient temperature thermometer. Just check its specified temperature range to ensure it can also read lower temps. Optional: crumple up a small aluminum foil ball over its tip.

You could keep a few thermometer strips on hand, as they're cheap and very compact.

airflow, indoors (anemometer)

To measure the direction and magnitude of airflow, you'll need a smoke generator. Then, observe which direction the smoke drifts, and roughly how quickly it drifts away.

length (smart phone) — TODO: trim this section, after evaluating these

Apps that guesstimate length using the camera:

Apps that will display a mostly accurate ruler on-screen:

Similar measurements:

length (physical)

There are lots of things that are near you every day that you can use as ad-hoc length gauges, since they come in standard sizes:

But for me, the most useful one is the size of a playing card, since I always have them on-hand.


point distance from top edge distance from top edge
top ◆ #1 3/8" 7 mm
center ◆ #1 11/16"   (~5/8") 16 mm
center of gap #1 1" 25 mm
center ◆ #2 1 3/8" ...
gap #2 1 3/4"
center ◆ #3 2 1/8"
gap #3 2 1/2"
center ◆ #4 2 13/16"   (2 7/8")
bottom ◆ #4 3 1/8"
And then there's the width of certain spans:
feature distance between points distance between points
height of diamond 5/8" 16 mm
width of diamond 1/2" 12 mm
two ◆s vertically, from top of ◆ to bottom of ◆ 1 3/8" ...
three ◆s vertically, from top of ◆ to bottom of ◆ 2 1/8"
far left edge of a ◆ to the far right edge of a ◆ 1 11/16"