We know exactly what [Dan] is going through. We also bought a cheap wireless doorbell and are plagued by the batteries running down. When that happens, the only way you know is when people start pounding on the door because you’re not answering the bell. Well no more for [Dan]. He built a backup system which monitors the voltage of the batteries on the chime unit.
You can see the small bit of protoboard he used to house the microcontroller and the UI. It’s an ATtiny13 along with a green LED and a single push button. The idea is to use the chip’s ADC to monitor the voltage level of the pair of batteries which power the chime. When it drops below 3V the green LED will come on.
First off, we wish these things would come with better power supply circuits. For instance, we just replaced the CR2032 in an Apple TV remote and measured the voltage at 2.7V. That remote and the chime both run from a 3V source. Can’t they be made to work down to 1.8V? But we digress.
In addition to monitoring voltage [Dan’s] rig also counts the number of times the chime has rung. Every eight seconds it flashes the count in binary, unless he presses the red button to clear the count. This is shown in the video after the break. We guess he wants to know how many times this thing can be used before running the batteries down.
Seriously though, for a rarely used item like this how hard would it be to use ambient light harvesting to help save the batteries? Looking at some indoor solar harvesting numbers shows it might be impossible to only power this from PV, but what if there was a super-cap which would be topped off with a trickle from the panels but would still use the batteries when that runs down?
Continue reading “Wireless doorbell battery monitor”
[Kaj] wanted to help out an aging family member by building them an electric tricycle during international Hack Day back on August 11th. He mixed in some reused parts with some new ones and ended up with bike that lets the rider troll other cyclists. Apparently when serious riders see an older man on a trike gaining on them they pedal like mad to make sure they don’t suffer the embarrassment of being passed. But there’s enough power and range to overtake the strongest of non-powered competitors.
Many of the parts came from a non-functional electric bike sold on Craig’s List. [Kaj] reports that the bike was trashed, but the motor system was mostly salvageable. He replace the batteries and charger and hooked up the motor to the rear axle. The initial install placed everything but the motor in the basket behind the rider. The weight and placement made the thing unstable when cornering. The solution was to house the batteries in a tool box and strap it below the basket. The lower center of gravity makes sure the trike is easy to handle, and now there’s still room in the basket for your groceries.
This would make a perfect platform for some road messages printed in water.
[Woodporterhouse] must deal with regular power black outs in his area. He recently converted a rack-mount uninterruptible power supply to feed a portion of his mains wiring. This one is not to be missed, since he did such a great job on the project, and an equally remarkable job of documenting it. It’s one of the best examples we’ve seen of how to use Imgur as a project log.
The UPS still needs to have a case, but it doesn’t need room for batteries as he’s going to use a series of high-end sealed lead-acid batteries. So he cut down the enclosure to about half of the original size. That’s it mounted just above the new batteries. For this to work you need some type of transfer switch which can automatically patch between incoming line voltage, and the battery backup. He already had one of these switches in place for use with a generator, that’s it in the upper left. The entire system powers a sub-panel responsible for his essential circuits — the electronics in the home and a few lighting circuits (we’d assume this includes utilities like the refrigerator).
One really great feature that the reused UPS brings to the project is a monitoring card with a NIC. This way he can check the server to see if the UPS is being used, and how much of the 14 battery life remains.
[Thanks Ross via Reddit]
Being the smart consumer he is, [Denis] usually looks at the price per pound when comparing similar products at the grocery store. When it came time to buy a few AA batteries, he didn’t have any data to go on. To solve his little conundrum, [Denis] decided he would test several brands of batteries and see which one gives him the most bang for the buck.
After bringing home a haul of a dozen different brands of AA cells, [Denis] broke out the Arduino and starting designing a circuit. To test how much energy each brand provides, the Arduino measures the voltage across a load every second until the battery reaches 0.2V. The elapsed time, as well as the voltage, Watt hours, Joules, and ambient temperature are logged on an attached LCD screen and sent over a USB serial link to automate the data collection process.
What’s the verdict? Unsurprisingly, words like ‘super,’ ‘max,’ and ‘ultra’ didn’t connotate a better battery. The best bang for the buck came from an off-brand called RS Power Ultra. The worst battery was the Panasonic Evolta cells that came in at about $1.50 USD per watt-hour.
If you’d like to verify [Denis]’ work, all the code is up on Github along with the schematic.
Here’s another circuit that can be used to squeeze the remaining potential from supposedly dead batteries. Just like the AASaver, we see this as a useful prototyping tool, providing juice for a breadboard even though it’s not reliable enough for long-term use (the batteries are just about through after all).
First off, the image above shows rechargeables instead of alkalines. We don’t recommend this as the circuit has no cutoff feature and the 0.7V input for the boost converter surely is below the recommended low-voltage limit for those cells. But that aside, we like the diminutive board which solders onto the end of a battery pack. It uses an SC120SKTRT which is a variable boost regulator capable of outputting 1.8-5V depending on resistor choices. You can leave the resistors off and it will default to 3.3V, set the output explicitly, or roll in some potentiometers and use your multimeter to tune the output.
This regulator costs more than the MCP1640 used in the AASaver, but it appears to use less passive components making for a smaller footprint. At a total of $3.50 plus the PCB (which will be a snap to etch at home) this is another great option to top off your next parts order.
[Roy] over at GeekDad had a dead laptop battery on his hands, and decided he would disassemble it to see what useful things he could do with the cells inside. He mentions in his article that even though your laptop might be convinced that its battery is toast, more often than not just one or two cells are damaged. This may not be news to all of our readers, but is worth pointing out to those who might not be aware.
With the bad cells separated from the good, [Roy] thought up a couple of different uses for his newly acquired batteries. His initial idea was to power an LED flashlight that was made to run on the 18650 cells he recovered from his laptop – not a stretch of the imagination, but definitely useful. The second use he came up with was to pair two of the cells together in order to simultaneously power an Arduino and some small Lego motors.
[Roy] lays out all of the standard caveats you would expect regarding the care and feeding of the lithium cells, and even suggests rebuilding the laptop battery as an option for the more skilled members of his audience.
Now we understand that dismantling and re-using old laptop cells is not necessarily groundbreaking, but it’s definitely something that’s worth a bit of discussion. [Roy] admits that his two ideas fall far short of the “18650 Things” his article title suggests, so how about adding a few of your own?
If you have stripped down some laptop batteries to salvage the cells, let us know what you did with them in the comments – we would be interested in hearing about it.
Forget the Tesla Roadster, we want an electric car like [John Wayland’s] White Zombie!
If it wasn’t plastered with sponsor stickers and the like, you would never realize that this otherwise unassuming ‘72 Datsun 1200 is an absolute beast of a car. The gas engine that used to provide a mere 69 horsepower was swapped out for a pair of custom-built electric motors which propel the Datsun to 60 miles per hour in under two seconds.
The electric motors supply 500 horsepower and a staggering 1250 foot pounds of instant torque, providing one hell of a ride. The car is powered by 12 custom 29.6V battery packs which provide 2,400 Amps of current each! Aside from laying down a quarter mile in under 11 seconds, White Zombie can make a 90 mile trek before requiring a recharge.
Needless to say, this impressive car takes plenty of people by surprise each time [John] hits the track. Continue reading to watch one poor sap learn the hard way that his brand new Maserati is no match for White Zombie.
Continue reading “Engine Hacks: Electrified Datsun is the ultimate engine swap”