Adding MQTT To A Solar Powered PIR Light

The size and price of the ESP wifi modules have quickly made them into one of the preferred building blocks for IoT devices. Unfortunately they are not particularly well suited for very low power applications.  [LittlePetieWheat] wanted to add MQTT to a cheap PIR solar light, so he paired an ESP with an Attiny85 to hold it to a strict power budget.

Most of these lights contain some sort of no-name microcontroller that monitors the analog PIR sensor, and turns on the LEDs as required. [LittlePetieWheat] replaced the PIR sensor with one that gives a digital output for simpler interfacing. The Attiny serves as the low power brains of the project. Its tasks include reading the solar panel and battery voltages, and PIR output. When movement is detected by the sensor, it activates a clever little latching power circuit to power on the ESP01 just long enough to send a MQTT message. The LEDs are only turned on if there is no power coming from the solar panel. The solar power is stored in a 18650 battery.

The Attiny85 might not be a powerhouse, but it is perfect for simple, low power applications like this. We’ve also seen it pushed to its limits by running tiny machine learning models, or receiving software updates over I2C. Continue reading “Adding MQTT To A Solar Powered PIR Light”

Teardown And Analysis Of A Cheap Solar Lamp

If you walk the aisles of a dollar store one constant that you will see worldwide is the Chinese solar lamp. Your dollar gets you a white LED behind plastic, mounted on a spike to stick into the ground, and with a solar cell on top. It charges in the sunlight during the day and then lights the LED for a few hours at nightfall. They are in gardens everywhere, and no doubt landfill sites are full of them because they do not last very long. [Giovanni Bernardo] had one that stopped working, so he subjected it to a teardown to find out what was up, and what made it tick (Italian, Google Translate link).

As expected, the culprit proved to be a leaking and corroded 1.2 volt NiMh cell, and its replacement with an AA cell brought the lamp back to life. But the interesting part of this tale comes from his teardown and analysis of the lamp’s components. It’s centered around a YX8016 battery charger and power management chip. The device has an amazing economy of design with only four components including the solar cell and the LED. The final component is a small inductor that forms part of the boost converter to keep the LED lit as the battery voltage falls. The chip switches at 580kHz, and produces a 3.2 volt supply.

If this is a subject that interests you, don’t forget to take a look at the power harvesting challenge we ran a while back.

Solar nightlight

Nocturnal Solar Light Bulb Saves Your Lungs

India has a bit of a problem with electricity. In fact, over 74 million rural households live without power altogether. Instead they rely on burning fuel for light — and coincidentally, inhaling harmful smoke. Not to mention fuel isn’t cheap. [Debasish Dutta] wants to change this — so he came up with yet another solar powered light that is a low-cost alternative.

It’s a very simple light made out of a cheap Tupperware container, a 2V solar panel, a white LED, a rechargeable AA or AAA battery, a photo diode and a Joule thief (voltage boosting IC). One day of charging can provide approximately 20-22 lumens for the entire night of operation. While it doesn’t seem like much, a typical kerosene lamp puts out less than half that brightness.

And with the photo diode, it automatically turns on at night, and off during the day. A coat hanger doubles as both a stand for charging, and a hook for hanging it at night.

[Dabasish] says this is just the beginning and has a website dedicated to creating green energy and sharing it with the world. Video below.

Continue reading “Nocturnal Solar Light Bulb Saves Your Lungs”