Friday, July 1, 2016

Bee hive monitor

Using an ESP8266 v01 a single-wire DHT11 monitors temperature and humidity and logs to thingspeak channel:

The hive is about 100' from wifi access so am using an open-mesh AP that simply has a more powerful 20mW antenna and appears a reliable connection.  Android app "Wifi analyzer" is good at measuring signal strength.

There are lots of online examples of logging ESP8266 data onto a thingspeak channel, so the only apparent novelty is using a $6 solar-cell battery charger.  It is built for recharging 5V USB cell phones, but the battery is a 3.7V li-ion.  At first I was planning an LDO to get the 3.3V directly from the 5V, but the unit appears to turn off power if significant current (i.e.1A) is not being drawn. Currently the direct battery connection is driving the 3.3V ESP8266.  Current 20 second sensor updates consume more power than solar recharge, so a USB recharge is needed weekly.  Need to figure if simply lowering sample rate fixes this, or if special low-power states are needed.

ESP module was $1.78, sensor about $1, extra bypass cap, and a pullup resistor, so total unit cost <$9.

"Weather protection" is a milk carton.  Power is delivered from left and sensors go into top of hive for center air vent location.

Solar cell charger is under an old window for protection, even though it cuts down recharge rate.

ESP8266 module with DHT11 sensor.