In a previous post I wrote about the importance of accurate measurement, and how it is not always straight forward. That post introduced the first part of a video series on how to accurately measure temperature with a micro:bit. In that video I talked about the basics of thermistors and demonstrated how a voltage divider circuit works. This circuit is how we will convert temperature to voltage so that a micro:bit can measure it.
Part two of the video series is now available on the Platypus Technical YouTube channel. It shows how to design a voltage divider circuit that measures the range of temperatures that you are interested in. In the video I show the process for designing a simple circuit to measure the ‘weather temperature’. However, you can a design a similar circuit to measure other temperature ranges. Try using the voltage divider layout and the equations in the video for your own design.
Choosing a range
Importantly, you should also think about what you don’t want to measure. Trying to measure the biggest range possible is an interesting exercise, but not actually that useful for designing an accurate device. Measuring a largeer range than you need can make the project more expensive and more difficult. Later in the series we will see how designing a circuit that only works over the range you need makes the project easier, and often improves accuracy.
Try to think of some examples of other thermometers, digital or analogue. Notice that most only work for a limited range. Medical thermometers work between about 30 and 45 degrees Celcius. They have to be accurate and precise over this range to detect fever. However, but are pretty useless outside that narrow range. Cooking thermometers often only work at high temperatures because they are used for measuring hot things. The thermometer that I am designing and building in this series will measure the weather temperature in Canberra, Australia. So it needs to be accurate between about -20 and 50 degrees Celcius, but not outside that range.
In Part 3 it’s time to connect the thermistor voltage divider to the micro:bit and take some measurements.
Dr Lee Walsh the founder and director of Platypus Technical Consultants. Lee is an electrical and biomedical engineer, physiologist, technical consultant and science communicator. He has over a decade of experience in measurement, instrumentation and analysis, particularly in clinical settings, physiology and medical device testing.