The Incredible Shrinking Coin Cell Battery Pack

How’s it going with your project for the coin cell challenge? You can only use a single one, but Hackaday alum [Jeremy S Cook] has a great way to package coin cells into a sleek little power packs whether you need one, two, or even four.

[Jeremy] is building a wireless Wii nunchuk, so he needs a small battery that won’t short out or get punctured in the confines of the controller body. A single coin cell holder is already a bit bulky, and he needs to use two in series. He thought, why not try shrink wrapping them together? The only downside here is that the biggest tube that came with your average heat shrink multi-pack is probably a bit too tight to fit around them, so you might have to buy more (aw, shucks!).

After trying a few ways to make a good connection between the leads and the bare coin cell faces, [Jeremy] settled on generously stripping stranded wire and wrapping the long strands around the end to form a conductive swab. This slides in nicely between the coin cell and preshrunk tube. A little more heat will make a good connection, and some hot glue secures the wires. Click past the break for his build video and the other connection methods he tried. Have you come up with something better? Let us know in the comments.

Stray a bit further from the bench and you might come up with something like this googly eye battery holder we saw a few months ago.

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Hackaday Prize Entry: A PCB To Emulate Coin Cells

The Coin Cell Emulator CR2016/CR2032 by [bobricius] homes in on a problem some hardware developers don’t realize they have: when working on hardware powered by the near-ubiquitous CR2016 or CR2032 format 3V coin cells, power can be a bit troublesome. Either the device is kept fed with coin cells as needed during development, or the developer installs some breakout wires to provide power from a more convenient source.

[bobricius]’s solution to all this is a small PCB designed to be inserted into most coin cell holders just like the cell itself. It integrates a micro USB connector with a 3V regulator for using USB as an external power source. The board also provides points for attaching alligator clips, should one wish to conveniently measure current consumption. It’s a tool with a purpose, and cleverly uses the physical shape of the PCB itself as an integral part of the function, much like another of [bobricius]’s projects: the Charlieplexed 7-segment LED display.

Edge-lit Pendants Show Two Layers are Better Than One

Engraved acrylic lights up nicely with LED lighting. Simply engrave clear acrylic with a laser engraver, then edge-light the acrylic and watch the engraving light up. This badge made by [Solarbotics] shows how they used this principle when creating some pendants for an event that performed particularly well in the dark.

The pendants they created have two engraved acrylic panels each, and that’s about it. Two LEDs and a CR2032 battery nestle into pre-cut holes, and the engraved sides are placed face-to-face, so the outer surfaces of the pendant are smooth. By using some color-cycling RGB LEDs on one panel and blue LEDs on the other panel, the effect is that of an edge-lit outer design with a central element that slowly changes color separately from the rest of the pendant.

The design stacks the LED leads and coin cells in such a way that a simple wrap of tape not only secures things physically, but also takes care of making a good electrical connection. No soldering or connectors of any kind required. [Solarbotics] found that CR2032 cells would last anywhere between a couple of days to a week, depending on the supplier.

This design is great for using a minimum of materials, but if that’s not a priority it’s possible to go much further with the concept. Multiple layers of edge-lit acrylic were used to make numeric 0-9 display modules as well as a full-color image.

 

Asynchronous fireflies use few parts

led-firefly

[Karl Lunt] wrote in to share his LED firefly project. His goals for the project were to develop a low-power, low parts count module that can sense when it’s dark and then mimic the blinking patterns you’d associate with its biological namesake.

We like his design which uses a coin cell battery holder as the chassis for the project. The ATtiny13 driving the hardware is held in place by the two power wires. This lets him flash new firmware by rotating the chip and plugging in a little adapter he build. The LED connection might look a bit peculiar to you. It has a resistor in parallel, which doesn’t satisfy the normal role of a current limiting resistor. That’s by design. [Karl] is driving the LED without any current limiting, which should be just fine with the 3V battery and short illumination time of the diode. The resistor comes into play when he uses the LED as a light sensor. Past firefly projects included light dependent resistors to detect light and synchronize multiple units. [Karl] is foregoing the LDR, using the LED with a resistor in parallel to combat the capacitive qualities of the diode. As we mentioned, this senses ambient light, but we’d love to see an update that also uses the LED to synchronize a set of the devices.

MSP430-based wristwatch project

[Nav] is working on a scratch-built wristwatch. Although it is based on an MSP430 microcontroller, it’s not the ready-to-hack ezCronos that you might be thinking of. Instead, [Nav] started with a different TI development tool that we’ve looked at before, the ez430-F2013.

The breakout board for the F2013 is small enough to meet his needs, but still provides easy soldering with 0.1″ vias that break out each pin. To make sure the timepiece is accurate he added a 32.768 kHz clock crystal. A small, square, LCD screen acts as the face of the watch, but we didn’t find specific part information for the display.

Currently the watch can run for a few days on the CR2032. We’d bet some work with sleep modes for the microcontroller can help with that. The watch has a couple of buttons that let you control it, and [Nav] discovered that he could fit everything into the watch case for an iPod nano. That’s creative!

We’ve seen other hacks with tiny batteries. The next logical step here would be to swap out the disposable coin cell for something that can be topped off with an external charger.

Extending the battery life of LED dominoes

[Fede.tft] wrote in to tell us about some work he’s been doing to save battery life for LED dominoes. He originally got the idea after reading this post about the electronic gaming pieces. That project was aimed at the 555 timer contest and therefore, used a 555 timer. [Fede.tft] calculates the battery life for the CR2302 battery in the 555 circuit at no more than about 80 days. That’s if you never use them and the LEDs are never illuminated. It makes sense to remove the batteries from the device when not in use, but a redesign to increase efficiency is definitely worth the effort.

This rendition does away with the 555 chip in favor of a CMOS chip. By building a circuit around four NAND gates of a CD4011 chip, the standby lifetime of the battery is calculated to increase to about 4.5 years. Not bad! Add to this the fact that replacing the 555 timer didn’t increase the component count, the price for the chip is similar to the 555, and you didn’t need to resort to a microcontroller. Yep, we like it.

Button cell connectors for breadboarding

We’re working on a project that has a battery backup, but we don’t have any more coin cell holders on hand. No problem, we remember seeing a double pin header used for this. But when we tried to shove the CR2032 battery in between the pins it was a no-go. We could swear we’d featured a project that does this but couldn’t find it here at Hackaday. After much searching we came up with the Guerrilla battery holder which is seen on the left. No wonder it wasn’t working, the CR1212 in that picture is a much smaller package. So we figured we’d have to come up with something else, until inspiration struck.

There must be some other way to configure the pin header to work with a fatter cell body. On the right you can see that a diagonal orientation works like a charm. Join us after the break for a couple of close-ups of that connector and our thoughts on using this with a variety of different cells.

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