Tag Archives: light sensor

This DIY moisture monitor

 will help keep your houseplants alive

With spring just around the corner, it’s never too early to start thinking about planting.

Writing for Popular Mechanics, Alexandra Chang explained why she recently created an open-source, Arduino-powered DIY moisture monitor to ensure that her plants received the optimal living conditions.


“My perennials always died because I watered them too little or too much, or put them somewhere too dark or too hot,” she says. 

“[So] I vowed to keep my plants alive [and] turned to Arduino. I’d been looking for an excuse to try out this microcontroller platform, which I knew could be programmed to do a lot of cool things. Why not use it to save my ailing amaryllis?”

According to Chang, the project took a single afternoon and resulted in a smart sensor that was capable of reading and displaying soil-moisture levels, light intensity and temperature. 

For the build, the Maker turned to no other than an Arduino Uno Starter Kit (ATmega328) which included the following parts:

  • Solderless breadboard ($5)
  • Assorted wires ($7)
  • Thermistor ($2)
  • Photoresistor ($1)
  • 10K-ohm resistors ($8 per pack)
  • Potentiometer ($1)
  • LCD display ($10)


After finding instructions for a number of Arduino-based plant sensors online, such as the GardenBot, the ArduGarden and Soil IQ’s solar-powered sensor, Chang converged certain elements from each to devise something that suited her own skill level and needs.

The DIY gardening device features two soil probes responsible for measuring how much the soil resists the flow of electricity — or how moist it is. By adding a photoresistor (light sensor) and a thermistor (temperature sensor), then connecting them to a programmed Arduino, she was left with a gadget that could monitor the environment of a single plant. Meanwhile, an LCD display was used to show its moisture, temperature, and light readings in variable resistance values.

Interested in learning more? Head over to the project’s official writeup in Popular Mechanics here.

Tritium Skydiving Altimeter is redefining altitude awareness

This stunning new wrist altimeter lets you know your altitude through LEDs.

For some, skydiving can be an extremely enjoyable, adrenaline-producing activity. For others, the mere thought of free-falling from the sky can cause severe anxiety. If you’ve ever soared through the sky, then you know all too well that after jumping from the plane, it becomes quite obvious that you indeed plummeting towards Earth, and that if you don’t pull the parachute soon, the end result will not be as “fun.”


In order to make the best of a skydive, it’s imperative to acquire the necessary training and tools to not only ensure your safety but to optimize the experience as well. That was the idea behind the Tritium Skydiving Altimeter, a nifty little tool that sits on your wrist and provides you with your altitude using LED lights, instead of having to read the exact number.

Created by AO(N²), the wearable device is equipped with 16 ultra-bright LEDs, each of which represent 1,000 or 100 feet depending on the mode. The LED colors are designed to change with altitude. For instance, when the light is green, you’re fine. When amber, time to break off. When red, pull the parachute.


“We find the colors make it intuitive to know when to break off, track, and pull, and we find canopy mode especially useful as the scale is easier to read than an analog altimeter,” the team writes.

The Tritium Skydiving Altimeter is built around an ATtiny85 MCU along with a Bosch MEMS barometric pressure sensor and a Sharp HDR ambient light sensor for automatic brightness control. As for power supply, the wrist-adorned gadget boasts 10 hours of continuous operation battery life and is rechargable via USB.

“Analog altimeters typically use a sealed chamber that expands or contracts based on the air pressure. This drives a spring, which turns the needle of the altimeter. Well-designed metal springs can have lifetimes of several thousand cycles, and analog altimeter failures are quite rare,”  AO(N²) adds.


Comparatively, Tritium uses a microelectromechanical system to sense the air pressure. The MEMS sensor is a microscopically etched piece of pure silicon crystal tasked with detecting the air pressure and transmitting its value to the ATtiny85. What’s more, the device is equipped with self-check features responsible for ensuring that the sensor is, in fact, working properly when on. Otherwise it will indicate a fault with flashing red LEDs. To top it all off, the minimalistic Tritium was developed with only one moving part: the power switch.

So, are you ready to bring this altimeter on your next skydive? Head over to its official Kickstarter page, where the team is currently seeking  £66,000. If all goes to plan, shipment is expected to begin in July 2015.