Like most of his work, this tiny two-digit thermometer shows that [David Johnson-Davies] has a knack for projects that make efficient use of hardware. No pin is left unused between the DS18B20 temperature sensor, the surface mount seven-segment LED displays, and the ATtiny84 driving it all. With the temperature flashing every 24 seconds and the unit spending the rest of the time in a deep sleep, a good CR2032 coin cell should power the device for nearly a year. The board itself measures only about an inch square.
You may think that a display that flashes only once every 24 seconds might be difficult to actually read in practice, and you’d be right. [David] found that it was indeed impractical to watch the display, waiting an unknown amount of time to read some briefly-flashed surprise numbers. To solve this problem, the decimal points flash shortly before the temperature appears. This countdown alerts the viewer to an incoming display, at the cost of a virtually negligible increase to the current consumption.
[David]’s project write-up explains how everything functions. He also steps through the different parts of the source code to explain how everything works, including the low power mode. The GitHub repository holds all the source files, and the board can also be ordered direct from OSH Park via their handy shared projects feature.
Low power consumption adds complexity to projects, but the payoffs can easily be worth the time spent implementing them. We covered a detailed look into low power WiFi microcontrollers that is still relevant, and projects like this weather station demonstrate practical low power design work.
Dippy birds are the toys that teeter-totter back and forth as the beak of bird-shaped body dips into a container of water. The felt covering the beak and head picks up water and, through evaporation, cools that end of the glass tubing. The temperature changes cause the dichloromethane to either boil off, or condense, shifting the weight of the liquid thereby pivoting the glass body.
The real question is, does the temperature of the water cause the toy to move differently, and can that be measured to calculate the temperature of the water? [Craig] put that query to the test, by designing an apparatus to measure the motion of a Dippy Bird. A photointerruptor was used to measure the motion of the body, causing an interrupt each time the tail of the bird passes in between the sensor and the emitter. For control data a DS1820 temperature sensor was positioned near the felt on the head of the bird, and a relative humidity sensor captured readings at the same time. Data from the three inputs was collected over a two-day period. Although not a precise measurement, the motion of the bird did trend in the same ways that were recorded by the temperature and relative humidity sensors.
When working on battery-dependent projects you want accurate performance information where a datasheet may not be available. [E. Lelic] set out to build a device that would meter internal battery resistance but ended up with a bench tool that can do much more than that.
A PIC 16F88 microcontroller takes center stage on the meter, taking voltage level readings, monitoring a DS1820 temperature sensor, and controlling an LM2575 step-down regulator. The components provide functionality for measuring Lithium Ion, Lithium Polymer, Nickel Cadmium, Nickel Metal Hydride, and Alkaline batteries. It is capable of fully discharging and fully charging the batteries, measuring time and power consumption during this cycle, and monitoring temperature changes for the NiMH and NiCad versions.
Look for the little red ‘Download’ icon at the bottom of the post linked above. That archive includes a schematic (which we’ve also embedded after the break), board layout in .LAY format, and a HEX firmware file.
If you enjoyed this build you might want to look at this other battery capacity tester.
Continue reading “Full-featured Battery Tester Puts Them Through Their Paces”
[Eric Friedrich] needed to keep the wort warm enough for yeast to ferment it into beer. To solve the problem he built his own fermentation temperature controler using a microprocessor to turn some heating tape on and off. You can see the heating element embracing that diminutive fermentation bucket in the picture above. This was originally meant for keeping reptile cages warm. It costs less than similar products meant just for brewing and works well for [Eric]. A DS1820 temperature sensor gives feedback to an ATmega168 which then uses a relay to switch the heat on and off. The target temperature can be changed using a potentiometer on the board, with the setting displayed on a character LCD screen on the project enclosure.
[Michael] got his hands on a refrigerator that he intended to store beer in but found that it ran constantly. Instead of buying a new thermostat he and his friend [Doug] set out to build an Arduino-based controller for the fridge.
The finished project will switch 240v so they’ve used a transformer to power the logic circuitry and a solid state relay to handle the load switching, with a Dallas 1820 for temperature data. Because the Arduino offers more capabilities than the average thermostat hack they also decided to tap into its potential by adding an Ethernet shield. We see the Arduino as a prototyping device and so do these folks. Once the bugs in their first PCB prototype are worked out the circuit will use the ATmega328 and do away with the Arduino.