How long can you keep an Arduino circuit running on three AA batteries? With careful design, [educ8s] built a temperature sensor that lasts well over a year on a single charge of three 2250 mAH rechargeable cells (or, at least, should last that long).
Like most long-life designs, this temperature sensor spends most of its time sleeping. The design uses a DS18B20 temperature sensor and a Nokia 5110 LCD display. It also uses a photoresistor to shut off the LCD display in the dark for further power savings.
During sleep, the device only draws 260 microamps with the display on and 70 microamps with the display off. Every two minutes, the processor wakes up and reads the temperature, drawing about 12 milliamps for a very short time.
Along with the code, [educ8s] has a spreadsheet that computes the battery life based on the different measured parameters and the battery vendor’s claimed self discharge rate.
Of course, with a bigger battery pack, you could get even more service from a charge. If you need a refresher on battery selection, we covered that not long ago. Or you can check out a ridiculously complete battery comparison site if you want to improve your battery selection.
Continue reading “It Keeps on Going and… Arduino Edition”
If you want to proclaim to the world that you’re a geek, one good way to go about it is to wear a wristwatch that displays the time in binary. [Jordan] designs embedded systems, and he figured that by building this watch he could not only build up his geek cred but also learn a thing or two about working with PIC microcontrollers for low power applications. It seems he was able to accomplish both of these goals.
The wristwatch runs off of a PIC18F24J11 microcontroller. This chip seemed ideal because it included a built in real-time clock and calendar source. It also included enough pins to drive the LEDs without the need of a shift register. The icing on the cake was a deep sleep mode that would decrease the overall power consumption.
The watch contains three sets of LEDs to display the information. Two green LEDs get toggled back and forth to indicate to the user whether the time or date is being displayed. When the time is being displayed, the green LED toggles on or off each second. The top row of red LEDs displays either the current hour or month. The bottom row of blue LEDs displays the minutes or the day of the month. The PCB silk screen has labels that help the user identify what each LED is for.
The unit is controlled via two push buttons. The three primary modes are time, date, and seconds. “Seconds” mode changes the bottom row of LEDs so they update to show how many seconds have passed in the current minute. [Jordan] went so far as to include a sort of animation in between modes. Whenever the mode is changed, the LED values shift in from the left. Small things like that really take this project a step further than most.
The board includes a header to make it easy to reprogram the PIC. [Jordan] seized an opportunity to make extra use out of this header. By placing the header at the top of the board, and an extra header at the bottom, he was able to use a ribbon cable as the watch band. The cable is not used in normal operation, but it adds that extra bit of geekiness to an already geeky project.
[Jordan] got such a big response from the Internet community about this project that he started selling them online. The only problem is he sold out immediately. Luckily for us, he released all of the source code and schematics on GitHub so we can make our own.
In the realm of low-powered desktop computers, there are some options such as the Raspberry Pi that usually come out on top. While they use only a few watts, these tend to be a little lackluster in the performance department and sometimes a full desktop computer is called for. [Emile] aka [Mux] is somewhat of an expert at pairing down the power requirements for desktop computers, and got his to run on just 10 watts. Not only that, but he installed the whole thing in a board and mounted it to his wall. (Google Translated from Dutch)
The computer itself is based on a MSI H81M-P33 motherboard and a Celeron G1820 dual-core processor with 8GB RAM. To keep the power requirements down even further, the motherboard was heavily modified. To power the stereo custom USB DAC, power amplifier board, and USB volume button boards were built and installed. The display is handled by an Optoma pico projector, and the 10-watt power requirement allows the computer to be passively cooled as well.
As impressive as the electronics are for this computer, the housing for it is equally so. Everything is mounted to the backside of an elegant piece of wood which has been purposefully carved out to hold each specific component. Custom speakers were carved as well, and the entire thing is mounted on the wall above the bed. The only electronics visible is the projector! It’s even more impressive than [Mux]’s first low-power computer.
Orientation trackers can be used for a ton of different applications: tracking mishandled packages, theft notification of valuables, and navigation are just a few examples! A recent blog post from Texas Instruments discusses how to build a low-cost and low-power orientation tracker with the MSP430.
Based on the MSP430 LaunchPad and CircuitCo’s Educational BoosterPack, the orientation tracker is very simple to put together. It can also be made wireless using any of the wireless BoosterPacks with a Fuel Tank BoosterPack, or by using the BLE Booster Pack with a built in Lithium Battery circuitry. TI provides all the necessary code and design files in their reference application for getting your orientation tracker up and running. Be sure to see the device in action after the break! This project not only involves building a low-power orientation tracker, but also showcases IQmathLib, a library of optimized fixed point math functions on the MSP430. One of the more challenging aspects of using small MCUs such as the MSP430 or Arduino is how inefficient built in math libraries are. Check out the IQmathLib, it greatly improves upon the built in math functions for the MSP430.
It would be interesting to see this project modified to be a DIY pedometer or be used on a self-balancing robot. It would also be interesting to see the IQmathLib ported to other micros, such as the Arduino. Take a look and see how you can use this reference design in your own projects!
Continue reading “Low-Power Orientation Tracker and an Optimized Math Library for the MSP430”
After being inspired by the Deciwatt Gravity light, [Steve Dufresne] decided he wanted to try making his own as a proof of concept.
The Gravity Light by Deciwatt is an innovative device designed for third world countries to help eliminate expensive lighting like kerosene lamps. It has a small weight on a pulley which can be lifted up in under 3 seconds. During its slow descent down the weight provides light for 25 minutes! It’s affordable, sustainable, and reliable. It’s also mechanically impressive, which is exactly why [Steve] decided to try making his own.
He’s using a single LED, a small DC motor, a few pieces of wood, an old bicycle wheel, some bicycle chain, and a few jugs of water. The water is connected to the chain which is looped over the smallest gear on the bike. The generator is then powered by a belt wrapping around the outside of the rim. This gives the motor enough speed to generate electricity for the LED. His current design only lasts for about 3 minutes, but he’s already working on the second iteration. Testing systems like this really give you an appreciation for the effort that must have gone into the real Gravity Light.
Stick around after the break to see it in action.
Continue reading “Homemade Gravity Light Doesn’t Last Long but Proves the Concept!”
[Josh] had a little project where he needed to keep a variable in RAM while a microcontroller was disconnected from a power source. Yes, the EEPROM on board would be able to store a variable without power, but that means writing to the EEPROM a lot, killing the lifetime of the chip. He found an ATTiny can keep the RAM alive for a variable amount of time – somewhere between 150ms and 10 minutes. Wanting to understand this variability, he decided to solve the mystery of the zombie RAM.
The first experiment involved writing a little bit of code for an ATTiny4313 that looked for a value in RAM on power up and light up a LED if it saw the right value. The test circuit consisted of a simple switch connected to the power pin. Initial tests were astonishing; the ATTiny could hold a value in RAM for up to 10 minutes without power.
With the experiment a success, [Josh] updated his project to use this new EEPROM-saving technique. Only this time, it didn’t work. The value hidden away in RAM would die in a matter of milliseconds, not minutes. After tearing his hair out looking for something different, [Josh] rigged up an Arduino based test circuit with humidity and temperature sensors to see if that had any effect. It didn’t, and the zombie RAM was still not-undead.
The key insight into how the RAM in an ATtiny could stay alive for so long came when [Josh] noticed his test circuit had a LED, but the actual project didn’t. Apparently this LED was functioning as a very tiny solar cell, generating a tiny bit of current that kept the RAM alive. A dark room with a flashlight confirmed this hypothesis, and once [Josh] gets his uCurrent from Kickstarter he’ll know exactly how much current this LED is supplying.
In what we hope is a new trend in interviewing, some of the people at [Anthony]’s place of work asked him to make some wireless quiz buttons. He took the task quite seriously, making them extremely robust and low-power.
[Anthony] is experienced in the button arts, having made this party push button for a wedding reception. His design for the quiz buttons is a little different. Each button has an Arduino Pro mini and an nRF24L01 wireless RF module. On the receiver side is an Arduino Pro micro and an another RF module. A connected PC captures the serial data and displays the pressed button’s ID. It also shows the order in which subsequent buttons were pressed and the time elapsed between them.
The really notable part of this build aside from the awesome laser-cut MDF Devo energy dome button housings is the extremely low power consumption of the transmitting Arduinos. [Anthony] has designed them to go into sleep mode which disables all on-board circuitry and only wakes on interrupt. He removed the power LED and the voltage regulator since they run on 2-AA batteries. The voltage regulator was drawing more than 25mA in sleep mode. Because of these mods, each button consumes < 1μA, which is less power than the batteries can self discharge over their lifetime.