by Rusivan @ instructables.com:
In this article I will try to tell you about the gift I made for my girlfriend!
The basis of the scheme is a microcontroller Atmega8, 1K resistor, selected in such a way as not to overload the microcontroller ports. SMD resistors and diodes, size 1206.
On the reverse side of the board, there are two batteries CR2032, two capacitors, voltage regulator LM7805, and the power button with latching.
DIY SMD LED heart – [Link]
Embedded legend Jack Ganssle tackles the question of how much juice you can pull from a coin cell. He writes:
About a year ago I wrote of my on-going experiments to determine how coin cells behave. This was motivated by what I consider outrageous claims made by a number of MCU vendors that their processors can run for several decades from a single CR2032 cell. Some vendors take their MCU’s sleep currents and divide those into the battery’s 225 mAh capacity to get these figures. Of course, no battery vendor I’ve found specifies a shelf life longer than a decade (at least one was unable to define “shelf life”) so it’s folly, or worse, to suggest to engineers that their systems can run for far longer than the components they’re based on last.
Conservative design means recognizing that ten years is the max life one can expect from a coin cell. In practice, even that will not be achievable.
There’s also a war raging about which MCUs have the lowest sleep currents. Sleep current is, to a first approximation, irrelevant, as I showed last year.
But how do coin cells really behave in these low-power applications? I’ve been discharging CR2032s with complex loads applied for short periods of time and have acquired millions of data points.
How Much Energy Can You Get From A Coin Cell? – [Link]
karllunt @ www.seanet.com writes:
This is pretty much one of those required projects; everyone builds a datalogger in an Altoids can. But each is different and I enjoyed making mine.
Uses ATmega328P (low power, 32K flash for lots of program space)
Uses Maxim/Dallas DS1337 Real Time Clock (uses I2C)
Logs data to microSD flash card, readable on PC (uses FAT32)
Runs on two AAA alkaline batteries
Low power draw (exact consumption varies based on SD card used)
Supports RS-232 for entering commands
Uses CR2032 lithium coin cell for RTC backup
Uses Analog Devices TMP36 for temperature sensor (not shown, it gets wired to the green four-position terminal shown below)
Uses SparkFun 3.3VDC boost converter to provide stable voltage even as batteries die
Datalogger in an Altoids can – [Link]
This Design Idea describes a simple two-chip CMOS circuit that can sort capacitors into 20 bins over a wide range (100pF to 1μF), using 10 LEDs to display the value range. The circuit is power efficient and can be run using two CR2032 cells. As such, it can be built into a handheld probe. by Raju Baddi
Simple capacitance meter bins parts – [Link]
Planning on powering that next über-low-power board of yours from a measly CR2032 coin cell? Read this app note to understand exactly what the limitations of coin cells are: [via]
When designing a small wireless sensor node to be powered by the popular CR2032 coin cell, some sources claim there is a 15mA “limit” and that drawing more current is not possible or will “damage” the battery. This may give the impression that at 15mA everything works perfectly and battery capacity is great, while at 16mA nothing works. There is little public information available to explain why such a limit exists (if it indeed does exist), and little information explaining why 15mA would be a “magic number”.
Understanding Coin Cell Limitations – [Link]
Sergei Bezrukov writes:
A digital clock with a LED display should be designed for being powered from a wall power supply, as the display draws a lot of current. However, such clock needs a reset after every power outage if no backup battery is provided. Usually commercial clocks use a 9V backup battery. Such batteries take a lot of space and are relatively expensive. If the clock electronics works from 3-5V, a lot of battery energy is dissipating for nothing.
This clock uses a cheaper and much smaller CR2032 battery as a backup. It is based on a Texas Instruments MSP430F2101 16-bit microcontroller, which can be purchased just for $1.50. If the display is off, the microcontroller itself draws about 14 μA in average due to being kept in sleep mode for most of the time. The input voltage in the range 5 – 15V is converted into a 3.6V by a linear voltage regulator MIC5209-3.6. The average current drawn from an external power supply is about 35 mA, depending on the digits shown on the display.
Digital clock with backup battery – [Link]
If you design circuits powered by CR2032 batteries here’s an article located by Joe Desbonnet which you should consider: [via]
This is an interesting article on how the performance of a cell/battery under pulsed loads can vary dramatically depending on period, peak current, duty cycle and other factors. The article discusses the performance of a CR2032 button cell driving low power wireless protocols such as ANT+ and Bluetooth v4.0.
The impact of high pulse drain on CR2032 coin-cell battery capacity – [Link]
This “Annoyer” basically emits a high pitched “beep” randomly every 2-15 minutes. The beep is very high pitched so it is impossible to find where this beep is coming from. No matter where you walk around the room, because of the pitch of the beep, you cannot tell if you are closer, farther, or even what direction it is coming from. The beep is just loud enough to annoy anyone near it -just ask my wife It runs off of a 3v cr2032 coin cell battery. I don’t know exactly how long the battery will last, but mine has been going for 2.5 months in my co-worker’s office and is still going strong (yes, I am evil :0) The Annoyer is based on a Pic10f202 microcontroller. This is a very cheap uController (about $.50). This project has very few parts as most of the work is done in software.
Mini sound annoyer – [Link]
This project uses RGB LEDs to create a clock face. Each hand is assigned a colour and as the hands overlap on the face of the clock it mixes the colours.
The clock uses a single AA battery to power the display which is boosted to 5 volts with a switching mode power supply. The power supply should be able to use any AA battery that is at 0.7 volts or higher, which means that it should still work fine with AA batteries that may be “dead” when used in other devices.
The heart of the clock is a DS1307 realtime clock with a CR2032 coin cell battery backup. The battery should be sufficient to keep the time for at least a couple of years.
LED Desktop Clock – [Link]
Nokia 3310 LCD is still very popular among small embedded projects. It is low power (can run from a single CR2032 motherboard battery) and easy controlled Graphical LCD with 84×48 pixel resolution. Hardware construction is based on another project (3310 temperature probe). You can get LCD setup source code here. Couldn’t find the game code of this project that would be interesting to see and even to try it. Anyway project is great for learning basic Nokia 3310 interfacing. [via]
Nokia 3310 LCD game project – [Link]