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

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

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

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

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