Hestia

Node.js Raspberry Pi Pellet Stove Controller, named after the Greek virgin goddess of the hearth.

About

This project seeks to replace the OEM control panel on a Lennox Winslow PS40 pellet stove with a Raspberry Pi. I will be utilizing a Raspberry Pi Zero W, relays, and switches already installed on the pellet stove. I chose a Pi Zero W for its small form factor, the lack of pre-installed headers, its wireless connectivity, and familiarity with the platform. I had previously used an Arduino Nano for a much more rudimentary version of this project and found great difficulty in making adjustments to the code. Additionally the Raspberry Pi platform will allow for expansion in the future to include IoT controls and logging of usage utilizing networked databases. The project will be written using Node.js and the rpi-gpio Node module. I've chosen Node.js for its familiarity as well as ease of implementation of a web server for future expansion.

GPIO

Three GPIO pins are used along with a common ground to control three relays, supplying 120VAC power to the igniter and combustion blower when appropriate, and supplying power to the auger motor in pulses. Two more GPIO pins are used to detect open/closed status of a temperature-controlled snap switch and a vacuum switch. Another temperature-controlled snap switch is used to supply power to the convection motor when the pellet stove has reached a suitable temperature. A final temperature-controlled snap switch us used to interrupt the circuit for the auger motor to shut the stove off when an over-temperature condition is met. I will be utilizing a OneWire DS18B20 temperature sensor to detect the temperature of air exiting the stove vents.

Pi Pin	Function	Direction	Wire Color
7	Auger Relay	Out	Blue
13	Igniter Relay	Out	Blue/White
15	Combustion Blower Relay	Out	Orange
16	Proof of Fire Switch	In	Orange/White
18	OneWire Temp Sensor	In	Brown
22	Vacuum Switch	In	Brown/White
4	+5VDC for Switches	N/A	Green
6	GND for Relays	N/A	Green/White

Schematics

The Current Setup

The End Goal

Oddities

For ease of adaption, connection, and prototyping I've decided to use Cat 5 ethernet cabling and RJ45 connectors to connect the Raspberry Pi to the stove, and to a breadboard mockup of the sensors and switches for testing.

Environment Variables

• ONTIME - How long to turn the auger on, in milliseconds.
• OFFTIME - How long to wait between turning the auger on, in milliseconds.
• PAUSETIME - How long to pause when a pause file is detected, in milliseconds.
• DEBUG - Displays extra log information when set to true

Controls

• Run with node main.js > log.txt & to launch it in the background, piping output to a file log.txt which can be read from later.
• Pause the script by creating a file named pause in the root directory.
• Reload the environment variables by creating a file named reload in the root directory.
• Quit the script by creating a file named quit in the root directory.

Roadmap

• v0.1 - Get the pellet stove operating at a basic level. Only implements the auger relay and no safeties.
• v0.2 - Implement safety switches and put the igniter and combustion blowers on relays controlled by the Pi.
• v0.3 - Implement the HTTP module to allow controlling the stove from the LAN.
• v0.4 - Implement usage logging with a SQL database.

Testing Procedure

1. Launch app, check startup messages, check that it idles and pauses properly.
2. Provide ignite command, observe if the igniter, blower, and auger get turned on. Make sure the igniter turns off after the pre-set time.
3. Test that the following conditions cause a shutdown:
   • Proof of Fire Switch OPEN after igniter shutoff.
   • Vacuum Switch OPEN after igniter start.
4. Test manipulation of feed rates.
5. Test shutdown sequence.

SQLite Database Tables

status

Field	Type	Null	Key	Default	Extra
id	int(10)	No	PRI	NULL	auto_increment
key	varchar(100)	No
value	varchar(1000)	No

id	key	value
0	igniter	0
1	blower	0
2	auger	0
3	igniter_finished	false
4	shutdown_initiated	0
5	vacuum	0
6	proof_of_fire	0
7	shutdown_next_cycle	0

timestamps

Field	Type	Null	Key	Default	Extra
id	int(10)	No	PRI	NULL	auto_increment
key	varchar(100)	No
value	varchar(1000)	No

id	key	value
0	process_start	0
1	blower_on	0
2	blower_off	0
3	igniter_on	0
4	igniter_off	0

intervals

Field	Type	Null	Key	Default	Extra
id	int(10)	No	PRI	NULL	auto_increment
key	varchar(100)	No
value	varchar(1000)	No

id	key	value
0	auger_on	600
1	auger_off	1400
2	pause	5000
3	igniter_start	420000
4	blower_stop	600000