purpleAirRelayControl

Control an ERV/HRV and/or damper based on PurpleAir to limit wildfire smoke exposure.

Arduino requirements

• Arduino MKR 1010 (https://store-usa.arduino.cc/products/arduino-mkr-wifi-1010)
• MKR Proto Relay board (https://store-usa.arduino.cc/products/arduino-mkr-relay-proto-shield)
• Three way on-off-on DPDT switch (example: https://www.amazon.com/B07VJ4DXMF)
  • this allows us to select between on/purpleAir/off states without any external resistors
  • this particular example uses screw terminals so no soldering is required
• 3D printed case
  • todo

Instructions

Arduino

• Install the following libraries from in your Arduino IDE (Tools > Manage Libraries)
  • WifiNINA
  • ArduinoHttpClient
  • Arduino_JSON
• Stop git from tracking your secrets file
  • git update-index --skip-worktree arduino_secrets.h
• Edit arduino_secrets.h to include your personal and private info
  • wifi network ssid
  • wifi password
  • PurpleAir id (e.g. 12345)
• Flash Arduino
  • connect Arduino to your PC, compile and upload code

Case

The case is optional if you have another mounting method.

• Generate STLs
  • install OpenSCAD if necessary
  • run exportSTLs.bat
• Print box and shelf
  • print external perimeters first for dimensional accuracy
  • recommended settings: 0.3 mm layer height, 15% infill, slow enough perimeters to avoid overextruded corners

Installation

• Fill box
  • attach arduino to the case with M3x4 screws (or longer if you have washers available)
    • the fasteners should self tap the holes if your printer is accurate
    • don't overtighten or you will strip the plastic
  • attach the switch to the case using included screws/washers
  • wire the switch to the board (see below)
  • wire the relay outputs to whatever you are controlling
• Attach wall mount
  • install the wall mount (holds box) to a nearby wall using your preferred method (drywall fasteners, adhesive, etc)
• Wiring
  • run wires from your HVAC equipment to the Arduino mounting location
  • i'd recommend using a quick disconnect (e.g. Wago) between the HVAC equipment and the Arduino to allow for easy box removal
  • connect a powered micro usb cable to the Arduino
• Test
  • confirm that your HVAC equipment is controlled appropriately with the switch in the on/off/purpleair positions

Electronics

Switching hardware:

• ERV
  • Any HRV/ERV with dry contact controls (tested on Lifebreath 170 ERVD)
• Damper
  • Any 24VAC damper
    • Suncourt Adjustable Motorized Damper, Closed, 6" (includes 24 VAC transformer)
    • Honeywell EARD6TZ Round Fresh Air Damper, 6"
  • 24 VAC transformer to provider power
• Wiring
  • Relay1
    • COM = ERV contact 1 (e.g. Lifebreath ON)
    • NO = ERV contact 2 (e.g. Lifebreath LO or HI)
    • Open -> do nothing
    • Closed -> connect two ERV contacts
    • Ensure that ERV is in standby mode (e.g. Lifebreath set to fan speed 0 or short the RED/ON contacts, see manual)
  • Relay2
    • COM = Damper contact 1
    • NO = 24 VAC transformer
    • Connect the other transformer lead to damper contact 2
    • Open -> do nothing
    • Closed -> close circuit to provide 24 VAC to damper
  • Switch
    • ABC / DEF on each side from top to bottom
    • A = GND
    • B = pin 3
    • C = NC (no connection)
    • D = NC
    • E = pin 4
    • F = GND
    • switch up (force on)
      • B = GND
      • E = NC (pulled high)
    • switch middle (purple air)
      • B = NC (pulled high)
      • E = NC (pulled high)
    • switch low (off)
      • B = NC (pulled high)
      • E = grounded