Hacking color and battery life on a solar powered garden light

Give your garden lights a little bit more life by changing out the LEDs. In the process, you can also choose a different color if you like. It really is as simple as cracking it open and replacing the stock LED, but a bit of a change may also prolong the stored charge.

These garden lights consist of a small solar cell and an LED, both controlled by a small PCB powered from a NiMH rechargeable battery. Sure, you could try to put in a battery that has more potential, but if you replace the single LED with two of them in series, it drops the current consumption and increase the battery life. Just make sure to use super bright LEDs and the intensity change will not be all that noticeable. That comes partly from the fact that our eyes don’t detect intensity changes as well when a light is already very bright. And since it’s two LEDs, mixing colors is an option as we see above.

[Thanks Ken]

Garden sensors measure soil moisture and greenhouse temperature

[Andy] is getting his garden up and running. This year it’s been pretty cold so he decided to get small plastic domed tunnel which acts as a mini greenhouse. To help monitor that environment he built this sensor array which displays temperature and soil moisture readings.

Temperature is quite simple. He’s using a TMP36 sensor which is held a few inches above the soil. The moisture sensor is of his own design. It uses two building screws embedded in foam. These are pushed into the soil and a resistance reading indicates moisture level. By driving voltage on one screw, and measuring voltage on the other he gets some useful data. It’s not a standardized value, but observation over time will let him know how the scale relates to dry or wet soil.

During the build process he found that he needed a pull-down resistor on the probe used to take the moisture measurement. He also uses an I/O pin to drive the other screw. This gives him a way to shut off the juice when not taking a reading. We just hope he’s either got a current limiting resistor, or is using a transistor to drive it high.

Adding mobile control to your gardening

[The Cheap Vegetable Gardener] wanted to check in on his garden from the road so he wrote a control app for his WinPhone. The hardware work is already done; having been built and tested for quite some time.

The implementation comes in two parts, both shown in the chart above. The grow box is behind a firewall as you don’t want random folks turning on the water and grow lights on a whim. The first part of the interface takes care of this separation by providing a set of functions on the host machine. The second portion is the phone app itself which calls those functions and displays all the pertinent information from the status of the lights, heater, exhaust, and water pump, to the current temperature and humidity. He’s even used Google Charts to graph data over time. The app itself took about two hours to code with no prior experience, a testament to the level of approachability these tools are gaining.

Automated entry for a garden gate

[Dan McGrath] tipped us off about a solution for a problem that most people don’t have. He built a web-based entry system for his garden gate. This isn’t quite as original as that chain and sprocket dorm room system, but it does use a keypad for entry. [Dan's] already got a web server and home automation box that is always running. He coded a webpage that presents a virtual keypad for code entry. If the right code is input the system unlocks the electronic strike on the other side of this gate. Since the interface is a web page you can load if from any web browser (an iPhone is used for demonstration purposes after the break). But if you don’t have internet access you’re in trouble; there’s no physical keypad. But we guess you could always just jump the fence.  [Read more...]

Lawnbot 400: an update to an update

Driven by the relentless nagging encouragement of the Hackaday commenters, [Johndavid400] has improved the Lawnbot 400. No longer does it just sport a makeshift wooden shelf. he now has a wheel barrow attachment. It looks quite sturdy as long as that front hinge holds out. There is an actuator coming in the near future for dumping the contents as well. Also, we suspect that might be a shovel in this picture.