WiFi Smart Omniscient HVAC Touchscreen Theromstat
Update 3: Did what I could with the PCB. An external sensor works best though. I'm done with the code for now as well.
Update 2: Added a picture. There will need to be a rev 1 board. The SHT21 works fine on the desk, but reaches 91°F in the box. I've moved it to an external board and not sure where to go with it now.
Update: Changes have been made in the bom.txt file. The schematic is incorrect for some resistor values. 2K2 should be used for the SHT21 pullups.
Notes about the Nextion: First, add the line bauds=115200 to the main initialize varaibles once (if using MicroSD) or send it the command over serial. This will alow it to communicate at the highest speed.
It has a 10K pullduown resistor for 5V tolerance (R13: next to the connector). Removing this allows the ESP8266 to boot normally and operate without any resistors added, or add a 10K pullup between TX and 3V3 when serial debug is not connected. I've opted for the removal of the resistor, which fixes all problems. The 5K6 on the thermostat (R17) allowed it to operate with serial connected plus the pulldown, but not without. The blue wire (data sent to the ESP) doesn't really need any resistors. The ESP can't be programmed without a 1K while both are connected, and with the 1K and debug the touchscreen won't work. So just disconnect the wire while programming and reconnect it after.
This will eventually replace the old Spark-O-Stat with a newer system using the ESP-07, with a better screen (Nextion HMI 2.8" touchscreen), 5 outputs (1 extra output for humidifier), option for SHT21 (I2C) or DHT22/11/AM2302, and anolog input for expansion.
Main and remote units are designed into the single PCB with wired 5V or USB Mini-B for the remote units, and 24VAC for main. Headers on top are for onboard serial programming of the ESP and Nextion. Only power it with 1 source at a time. (3V3 for just the ESP, encoder, and temp sensor, 5V to include the display, or 24VAC for all of it including the SSRs).
The watchdog chip (PIC10F) is unnecessary, but can be used to monitor activity and reset the ESP if it freezes. All the components used are cheap. The PCB is about $25 for 3 from OSH Park, and the Nextion display is $15 off eBay.
Remote: The Remote folder contains all the changes to the Arduino folder needed to build the remote code that handles mirroring all display data, sending commands to the main unit, and streaming temp/rh. By tapping the target temperature on the display, it will toggle transmitting the remote temperature and humidity to the main unit to use in all operations. Tapping the same item on the main unit will also end the remote temperature connection. There are notifications to indicate use as well as a flashing run indicator instead of solid.
Some screens including a keyboard and SSID chooser, but this is using the auto connect with SoftAP server (which attempts to find the stored SSID while waiting on input) so it should never be needed. The dimmed screensaver will change to a clock, and a few other odd displays over time.
Cool/heat low/high:
These are the desired temperature ranges for cooling and heating, which are calculated based on outside temperature over the next 2 days.
Threshold:
The temperature offset to complete a cycle.
Pre-cycle fan time:
0 disables, 1 second to 5 minutes. This is the first phase of the cycle. When the temperature reaches the target, the fan is turned on to cycle air for the set time, which causes the thermostat to read a more overall temperature. If the threshold is reached before this ends, which it can and does, it will shut off. Otherwise it continues to the run phase, which runs for at least the cycleMin period to save wear on the compressor because this does shorten the run time considerably. A good value to use is the time it takes to lower the temperature after turning the fan on before it plateaus. Usually around 2 minutes.
Post-cycle fan time:
Runs fan after cycle completes. This is the third phase of the cycle, which continues to push air through the cold radiator and ductwork. 2 minutes is good, but you can use an IR thermometer on a vent to see how long the cold air continues.
Humidifier settings:
Off: Always off
Fan: Run when fan is on
Run: Run when thermostat is running a cycle
Auto1: Operate by humidistat during run cycles
Auto2: Humidistat runs indepentantly of thermostat (shares fan control)
Override:
Use to heat or cool by a selected offset temperature for a specified time.
Freshen:
Starts the fan with a timeout. This uses the post fan timer, so a normal cycle will cancel it.
Idle min, cycle min/max:
These are timers in seconds to control the thermstat operating limits. Idle min is the shortest time between cycles. Cycle min is the shortest time for a cycle, and max is the longest. Be careful with these settings. Running the compressor too short, too long or without the fan can cause damage. For example, the fanSwitch() function should always be used instead of direct I/O control.
Away time and temperature delta offset:
The away time is in hours:minutes unlike the rest of the timers, but uses the override timer. It can be turned on and off with the button, but will also turn off with the timer. There are 2 temp values. One for heat and one for cool, like the pre/post fan.
Like any setting, it can be automated with something like Tasker. To turn on would be http://ip:85?key=password&away=1
