An Epic Tale Of Thermistors: Tricks For Much Better Temperature Sensing

For years [Edward] has been building professional grade underwater sensing nodes at prices approachable for an interested individual without a government grant. An important component of these is temperature, and he has been on a quest to get the highest accuracy temperature readings from whatever parts hit that sweet optimum between cost and complexity. First there were traditional temperature sensor ICs, but after deploying numerous nodes [Edward] was running into the limit of their accuracy. Could he use clever code and circuitry to get better results? The short answer is yes, but the long answer is a many part series of posts starting in 2016 detailing [Edward]’s exploration to get there.

Orange is 12 bits, red is 24

The first step is a thermistor, a conceptually simple device: resistance varies with temperature (seriously, how much more simple can a sensor get?). You can measure them by tapping the center of a voltage divider the same way you’d measure any other resistance, but [Edward] had discarded this idea because the naive approach combined with his Arduino’s 10 bit ADC yielded resolution too poor to be worthwhile for his needs. But by using the right analog reference voltage and adjusting the voltage divider he could get a 20x improvement in resolution, down to 0.05°C in the relevant temperature range. This and more is the subject of the first post.

What comes next? Oversampling. Apparently fueled by a project featured on Hackaday back in 2015 [Edward] embarked on a journey to applying it to his thermistor problem. To quote [Edward] directly, to get “n extra bits of resolution, you need to read the ADC four to the power of n times”. Three bits gives about an order of magnitude better resolution. This effectively lets you resolve signals smaller than a single sample but only if there is some jitter in the signal you’re measuring. Reading the same analog line with no perturbation gives no benefit. The rest of the post deals with the process of artificially perturbing the signal, which turns out to be significantly complex, but the result is roughly 16 bit accuracy from a 10 bit ADC!

What’s the upside? High quality sensor readings from a few passives and a cheap Arduino. If that’s your jam check out this excellent series when designing your next sensing project!

Underwater Laser, Just Add Shark

underwater-laser-beam

[iskor12] put together a blu-ray laser that is waterproof and packs quite a punch. At 182 mW there is enough power here to pop dark colored balloons (see the video after the break). To make this happen, he found an LED flashlight that has rubber o-rings for waterproofing. Although small, there is enough space in the case to house the battery, driver, and laser diode. A thick ring of aluminum is placed around the laser diode to act as heat sink.

We’ll admit, we don’t know that much about lasers. This is probably the wrong question to ask, but now that he has this what do you do with it? Leave us a comment about your plans for this diabolical creation.

Continue reading “Underwater Laser, Just Add Shark”

Naval Academy’s AUV Team Project

auv1

[Daniel] sent us over to the blog for the Naval Academy’s Autonomous underwater vehicle entry for the AUVSI competition. You can follow along as they design, build, and test this years entry. It really looks like it would be fun to be the guy who gets to swim with them, like in the latest post in their blog. Their entry, named “Awkward turtle” can be seen above in orange, pictured with their 5th place winning previous entry.