Sonoff are dirt cheap WiFi AC/DC relay systems based on ESP8266 selling for about $5 with board and case. They are made by ITEAD Studio, and the company has now new versions supporting up to 16A @ 250V, and with a 2.5mm connector to connect external temperature and humidity probes.
- SoC – Espressif ESP8266 Tensila L106 32-bit MCU up to 80/160 MHz with WiFi
- Connectivity – 802.11 b/g/n WiFi with WPA/WPA2 support
- Terminals – 6 terminal for mains and load’s ground, live and neutral signals.
- Misc – 4-pin 2.5mm jack for external probes, LEDs for power and WiFi status
- Dimensions – PCB: 89.1 x 45.0 x 1.2mm
- Temperature range – -40 ℃ to 125 ℃
The company also offer two probes to connect the sensor jack: one based on AM2301 sensor for temperature (-40 to +80 °C, +/- 0.5 °C) and humidity (10 to 90%, +/- 3%), and an a waterproof temperature probe based on DS18B20 supporting -55 to 125 °C range.
The wireless relays can be controlled with eWeLink app for Android or iOS, where you can manually turn on and off the load, but also set temperature and/or humidity threshold to start and stop a device. Some technical details, most related to the hardware like PDF schematics, can be found on the Wiki.
ITEAD Studio now have a nice portfolio of inexpensive device for “smart home”. Please note that (AFAIK) none of the items have UL or TUV safety certifications, so use them at your own risks.
Sonoff-TH10/TH16 and sensor probes can be purchased on ITEAD Studio’s Sonoff-TH page with Sonoff-TH10 selling for $7.50, Sonoff-TH16 for $8.60, Sonoff Sensor-AM2301 temperature & humidity sensor for $4.30, and Sonoff Sensor-DS18B20 waterproof temperature probe for $3.50. Shipping is not included but only adds a couple of dollars, if you select the cheapest (and slowest) options.
Thank to Harley for the tip.