Weekly timer-thermostat with LCD

* Project under development *

Main features:

After presenting the Portable Thermometer, we present this multifunction weekly programmable thermostat with LCD 20x4, in addition to the normal functions of a programmable thermostat we decided to add some functionality.
A normal weekly programmable thermostat allows you to set the desired room temperature, normally one hour intervals and with the possibility of diversifying times and temperatures on the various days of the week.
We thought we would use a fine watch that is, the DS3234 from Dallas / Maxim with SPI bus with lithium battery for data retention, the same battery keeps the data in ram 23LC1024 always with SPI bus. As temprature sensor 18B20 always took the Dallas / Maxim as it has very good accuracy and an extended range of temperatures from -55 ° C to +125 ° C.
We opted for the 230V ~ power supply so as not to be tied down with battery and transformer "Block" integrated. This does not take away the possibility of eliminating the transformer and the rectifier bridge and power the thermostat, for example by batteries (6V)
The relay used is with exchange NO and NC max 250V, 5A
The LCD display is 20x4 so you have a good view of the data and we also added a 4-pin connector with +5 V, GND and two outs programmable for controlling external devices like GSM / SMS etc ... to send remote alarms, horns, etc. ...
On the pcb there are 2 connectors for programming the micro; ICSP Microchip and mikroProg (only front connector) and 5 buttons for programming and data visualization.

The software:

We thought we would make this thermostat as versatile as possible with different modes of operation:
1) Operation as a thermostat for the daily management of heating, is handled in this mode the temperature from 0°C to 40°C.
2) Operation as weekly programmable thermostat for heating management, is handled in this mode the temperature from 0°C to 40°C using different every day.
3) Operation as industrial thermostat for cooling and cold storage environments. In this mode the relay will drive a contactor for the management of the refrigeration unit.
In all modes you can program the response threshold of the internal buzzer and individually out of the two for the management of external devices, the programming is handled over 24 hours in 15 minute steps, ie step 4 per hour. Storing the minimum and maximum temperature with the event date.
Hysteresis programmable as -3°C ~ +3°C in steps of 0.1°C.
USB interface for programming the thermostat directly from your computer.

Wiring diagram

PCB and positioning components

PCB Top e Bottom

Schema elettrico in formato pdf (A3) Schema Elettrico.pdf (29k)