Science Olympiad – Div C – Technical Problem Solving – DIY Probes: Temperature Probe

By | January 26, 2015

It’s this time of the year again and preparations for the regional Science Olympiads are speeding up. This year, I looked a bit at the four sensors/probes to be used in the “Technical Problem Solving” event. I’m just a parent, so I don’t have ready access to the official Vernier probes or software. But with a couple of electronic components and a/some Arduino‘s, something similar can be build and easily interfaced to a computer.

The advantage of using an Arduino is that you can decide what to do with the collected data. It’s easy to print or create graphs or whatever else you want to do. It also allows a little bit more insight into how those sensors work.

I’m planning to create four posts in the next couple of days, one for each probe. All of the designs can be created with any Arduino/clone or whatever you have already. The additional parts cost less than $20/probe and you might find some in your parts-box already;-)

TempProbe1_1024This post is about the temperature probe. The official Vernier Temperature Sensor is not that expensive at $29 as long as you have the `infrastructure’.

My idea was heavily inspired by another blog post: “Building an Arduino Powered BBQ Thermometer”. There are other thermistors/temperature sensors out there, but the `food/cooking thermistor’ is designed for wet environments;-) So it can be safely used around/in liquids. I got a Polder Replacement Oven Probe for THM-362-86 from Amazon for $10. That was the cheapest I could find. But it turns out that it’s nominal resistance @ 25°C seems to be 220kΩ. So I had to adapt the resistor values accordingly.

TempProbeAside from the thermistor, we just need a resistor for the voltage divider, in my case, I use a 220kΩ resistor plus a 100kΩ potentiometer. I found that the resistor alone was a bit too small, so the potentiometer is used to adjust as needed. With some constants, I found for a similar 220kΩ variant of the VISHAY NTCLS100E3 thermistor, I got mine to within 1°C of another kitchen/oven thermometer. That sound be good enough for most experiments where the interesting part is more the temperature differences than the absolute temperature.

The sketch is very simple for now. It just reads the analog voltage every second and calculates the temperature using the formula and constants from the data sheet. It’s here: TempSensor.tar

That temperature probe should work at least from -20°C – 200°C, that should be enough for most experiments;-)

As always, have fun;-)

— Marco

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