[Florin] picked up a cheap multimeter in order to make multiple measurements at one time. Unfortunately, he wasn’t very good at remembering to turn it off when he was finished so he burned through some batteries. Why an auto-off feature wasn’t the first thing coded into the firmware we’ll never know, but [Florin] developed his own hardware-based auto-off circuit.

It sounds like he had all of the components necessary for this on hand already. He grabbed an AVR ATtiny25 in a surface mount package. To keep the board small, he didn’t include an ISP header, but instead made long pads that could have wires soldered to them for flashing the firmware. The microcontroller drives an NPN transistor that can cut off the ground path between the multimeter and its battery. A tactile switch is connected to one of the external interrupt pins and, when pressed, gives you 15 minutes of time to use the meter. After that, the chip kills the power and goes into sleep mode. Simple, and small enough to fit inside the case.

[via Dangerous Prototypes]

[Vassilis Papanikolaou] just finished building a gear indicator for a motorcycle. This quite a simple implementation compared to some of the other vehicle information displays we’ve taken a look at. You should be able to build and install your own without breaking the bank. An ATtiny25 microcontroller reads data from a couple of hall effect sensors and the neutral switch, then displays the current gear on a 7-segment display.

There’s a magnet on the shifter and two hall effect sensors at the position for ‘gear up’ and ‘gear down’ shifting. The AVR chip keeps track of these and even stores the last position in EEPROM when you shut the bike off. If the device somehow gets off track, it will automatically recalibrate itself next time you shift into neutral, thanks to the bike’s neutral sensor switch.

The PhorsePOV by [Julian Skidmore] almost slipped by, but we thought it was a nice easy hack for your Memorial Monday. The gadget uses an ATTINY25 to drive 6 LEDs aren’t standard characters 7 units high? Which when waved in the air produces a readable message. What we were really interested in is the use of a single button for text entry, called Phorse code, or an “easier to learn and remember” version of Morse code. While it seemed silly at first, most of us here could enter messages within a few minutes of trying.

Reader [Will R] sent in a thermostat mod for his brew fridge. His friends had found a perfectly fine bar refrigerator and wanted to repurpose it for brewing beer. A previous batch of microbrew had been mangled by the Australian heat so they wanted something that could maintain the perfect temperature. The fridge’s built-in thermostat wouldn’t rise above 5 degrees so they had to build their own. [Will] used a 10K NTC thermistor to measure the temperature. It’s connected to an ATtiny25 microcontroller that does the comparison and determines whether to turn on the compressor. He referenced SparkFun’s relay tutorial for the switching side. Although he didn’t etch a board for this project, the design file is included along with all the code on the project site.

[Bob] has a USB page hit counter that uses an ATtiny25 to run a MAX7219 which drives eight 7-segment displays. It is easy to implement USB on an AVR using just firmware, eliminating the need for any USB to RS232 conversion. The host software is written in Delphi and sits in the Windows tray. The code examples seem simple enough to expand upon into your own display programs.