Energy Harvesting Wristwatch Uses a Versatile Photodiode

There’s some interesting technology bundled into this energy harvesting wristwatch. While energy harvesting timepieces (called automatic watches) have been around for nearly 240 years, [bobricius] has used parts and methods that are more easily transferable to other projects.

Unlike early mechanical systems, this design uses the versatile BPW34 PIN photodiode (PDF warning). PIN photodiodes differ from ordinary PN diodes in that there’s a layer of undoped ‘intrinsic’ silicon separating the P and N doped layers. This reduces the utility of the diode as a rectifier, while allowing for higher quantum efficiency and switching speed.

They are typically used in the telecommunications industry, but have a number of interesting ‘off label’ applications. For example, the BPW34 can be used as a solid-state particle detector (although for detecting alpha particles you’re better off with something in a TO-5 package such as the Hamamatsu S1223-01). The fast response speed means you can send data with lasers or ambient light at high frequencies – a fun use for an LED lighting system or scrap DVD-RW laser.

Some common solar panels are essentially large PIN photodiodes. These are the brownish panels that you’ll find in a solar-powered calculator, or one of those eternally waving golden plastic neko shrines. They specifically offer excellent low-light performance, which is the basis of the energy harvesting used in this project.

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Attack on the Clones: A Review of Two Common ESP8266 Mini D1 Boards

ESP8266-based development boards have proliferated rapidly. One favorite, the WEMOS Mini-D1 is frequently imitated and sold without any branding. As these boards continue to ship to hobbyists and retailers around the world, we thought it might be interesting to conduct a little experiment.

There are a few ESP8266 development boards available, and the most popular seem to be the NodeMCU ‘Amica’ board. Of course, there are dozens of other alternatives including the WiFiMCU, Sparkfun’s ESP8266 Thing, and Adafruit’s HUZZAH ESP8266. Given that, why is this review limited to the Mini D1 boards? Because the Mini D1 is the cheapest. Or was, until it was cloned.

We took a look at some of these ‘clone’ boards to figure out the differences, find out if they work as intended, and perhaps most importantly, are these clone boards shipped out reliably. What are the results? Check that out below.

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Conflict Escalates Between Brilliant Rat and 555 Timer

After [Casey Connor] captured and relocated a number of unwanted rodents in his home using commercially available live traps, he was presented with a problem: a rat had learned to avoid them.

In an epic, and adorable, conflict caught on video (and embedded below),  he documents the  designs used and how the rat escaped them by either recognizing the trap, or sheer agility. We can only tip our hat to the determination of both parties.

All the trap mechanisms are based on a 555 monostable solenoid triggering circuit that ensures that a pulse of sufficient duration is sent to the solenoid to trigger the trap correctly. This way even intermittent contacts will trigger the trap rather than just causing the solenoid to twitch without fully actuating. This is the same technique used to debounce a switch using a 555 timer.

A Raspberry Pi Zero detects motion using an IR camera to film the interesting parts. This is also a good indicator for when you’ve trapped your quarry – if you’re trying be humane then leaving it in a trap for days is counterproductive.

With the time and effort we spend building better and more complex rodent traps, we sometimes wonder who has cleverly trapped whom.

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