Electric Kiln/Installation/Hardware Assembly
As you could see in hardware description and BOM, you are free to choose what components are you going to install and use. There are some recommended configurations - but this are just more guidances then the rules.
I would recommend to build your PIDKiln first on breadboard, and then transfer it to some other kind of permanent solution. PIDKiln of breadboard
GPIO/PINs connection
LCD
Connected to one of three SPI on ESP32 - called VSPI (MOSI-23, MISO-19, CLK-18, CS-5)
| ESP32 | LCD |
|---|---|
| +3.3V | BLA (this can be also +5V if you wish) |
| GND | BLK |
| 4 | RST |
| GND | PSB |
| +5V | VCC (This should be - for ESP sake - 3,3V, but my LCD doesn’t work with lower voltage. Try first with 3,3V) |
| GND | GND |
| 5 | RS |
| 18 | E |
| 23 | R/W |
Encoder
| ESP32 | Encoder |
|---|---|
| +3.3V | 5V/VCC |
| GND | GND |
| 32 | Key |
| 34 | S2 |
| 35 | S1 |
MAX31855
Connected to one of three SPI on ESP32 - called HSPI (MOSI-13, MISO-12, CLK-14) CS-15/27
| EPS32 | MAX31855 A |
|---|---|
| +3.3V | VCC |
| GND | GND |
| 12 | SO/DO (slave output/data output) |
| 14 | SCK (clock) |
| 27 | CS (chip select) |
| EPS32 | MAX31855 B |
|---|---|
| +3.3V | VCC |
| GND | GND |
| 12 | SO/DO (slave output/data output) |
| 14 | SCK (clock) |
| 15 | CS (chip select) |
Relays
| ESP32 | SSR |
|---|---|
| GND | GND |
| 19** | IN |
| ESP32 | EMR (SLA-05VDC-SL-C) |
|---|---|
| GND | GND |
| 21 | IN |
| 5-48V* | VCC |
(*) Do not connect 5V from ESP - use external source. This can be any 5V-48V power supply with around 1W power.
(**) For additional SSR relay (works simultaneously with first one) use PIN 22 - see documentation for explanation
Power meter
See the documentation for detailed instruction.
| ESP | 30A/1V |
|---|---|
| 3,3V | 3,3V |
| GND | GND |
| 33 | most outside mini jack connector |
Alarm
This ALARM_PIN goes HIGH when program ABORT is called (somethings wrong, or user triggered). You can connect this pin to buzzer or small relay to trigger some other action on failure.
| ESP | Relay/Buzzer |
|---|---|
| GND | GND |
| 26 | +3,3V |
Minimal configuration of PIDKiln
This is minimal, but fully functional configuration that is able to control heating device. You can easily extend it later with additional components.
Standard configuration of PIDKiln
Full configuration with all possible bells and whistles.
Power meter
As an option, you can install additional power meter, to measure energy usage and to know if heating element(s) is actually working.
If you have meter with voltage output, you are only require to have two additional 10kOhm resistors and 10uF capacitor. You need to connect first and third “pin” from micro jack.
This additional hardware is required to change output voltage from meter. Since it’s AC voltage -1V to +1V and ESP32 can only measure 0V to +3,3V we need to “shift” it up. So we create simple voltage divider with resistors and we should have 3,3V/2 = 1,65V in the middle of it. When combined with power meter voltage we should have 0,65V to 2,65V voltage range to measure. This is something that ESP32 can handle. Capacitor is only to provide some kind of hysteresis.
Power supply
Preferably you should power your PIDKiln device with regulated +5V power supply. This way you can power ESP32 board through VIN (do not use VIN and USB at once!) pin and use 5V to directly power EMR relay (around 185mA) and LCD backlight (current depends of brightness).
You could power board with just USB, but 5V output from my board (ESP32-Wrover TTGO with microsd) is too weak to handle EMR and LCD and most of other boards even do not have 5V out. You could also use VIN as 5V vout (this pin should be connected directly to USB 5V output) - but then you are limited by USB output and how much board traces can handle.
If you plan to do remote relay box (as I did) you have to take into account voltage drop on cable. Mine (cable) was 1,5m long with 0,35mm2 wires - and 3,3V dropped on the end to 2,75V. Luckily my SSR relay is quite forgiving and despite it’s rated 3-32V it will trigger “high” even with 2V (this was the limit I’ve tested). Still it’s not wise to go with voltage so low for reliability reason.