Version 1.21 There has been an improved version of the solar controller. The main difference from the previous version – Arduino Nano processor with CH340G chip for connection to the computer’s USB port. There is no need of any additional programmer. The processor costs about $3 if you buy it from ebay.com. All other details are the same as in previous versions. You can install the program from here. Circuits here. The sketch has ben expanded and has the following menu items:
SETTINGS Saving of settings –>> Default Settings – >> LCD backlight
COLLECTOR temperature difference for turning the pump on – >> Temperature difference for turning the pump off – >> manual switching of the pump on / off in order to vent/bleed the collector
THERMOSTAT Temperature1 ->>- Temperature2 — >> Status heating / cooling / off
A brief explanation on how the thermostat operates: 
Temperature 1 and 2 is set using the controller keys. The third controller temperature sensor measures the temperature. Having selected the cooling mode the relay is activated if the temperature rises, the heating mode activates the relay if temperature drops. PCB board universal, it can be customized according to your needs by changing the software. The controller has a standard Arduino 5-key pad (A0), a connector for 16 × 2 LCD Screen (RS-A5, EN-D3, D4 D4-, D5- D5, D6 D6-, D7- D7), backlighting of the display, switching on/off, light intensity is adjustable through software (D9), the controller has a ENC28J60 network module connection (CS-D10, D11-SI, SO-D12, D13-SCK), three DS18B20 sensors (D2, D8, A3). A1, A2 are for relays connection. This is how the controller looks: (in the photo LED’s are connected instead of relays for the purpose of checking the controller’s operation):