in previous air freshener entry, i mentioned about my implementation attempt of esp8266 based esp-01 board to a basic security system. it wasn't worked but i figure out the problem later and started to build a remote telemetry probe for my next set of crops.

esp-01 is controllable via serial AT commands. even you can make http requests like multi-purpose gprs modems. first of all, i was stuck at the network scanning part. that's related with power consumption. it's hitting to 200ma while scanning & connecting to wifi networks which is close to supply limit of arduino board. i fed it with an external +3.3v power supply and solved this one.

second problem is uart noise, obviously that board got the firmware from early esp days and not accepting the bitrate set command. i applied a cloud update command which is seen in reference document and completely bricked the device. i was assuming a firmware update will bring these advanced commands and fix that issue by minor a tweak. reviving the module is another story, i mentioned at this instructables entry.

first tests was based on arduino mini pro decided to go with uno r3 to accelerate software development part after few write cycles, plug-in & plug-out on each upload is literally a torture. got a stable sketch after 4-5 revision.

currently it's sending me the outdoor temperature, soil humidity and outdoor light level. same as previous setup, my personal assistant software judith handling the http posts and notifies me if soil getting dry or outdoor temperature drops below lettuce's acceptable range. an 12v/7ah ups battery powering it about 8 days with 30 minutes of send interval. planning a solar charger with li-ion battery for it in my next spare time.

Cost table
+ ESP-01 wifi board: $5
+ Arduino Uno R3 (clone): $3
+ HL-69 soil moisture sensor: $2
+ ds1621 thermometer module: $2
+ light resistive diode: $0.5

took 3 days to develop, 3 weeks to fix errors. for sake of time don't buy chinese clones of esp8266. an extra $5 can save your whole month. if interested, source code available in devzone section and github