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Topic: HVAC Utility Monitor (Read 493 times) previous topic - next topic


I am working on a new project. it is the newest one since i made my snake controller here

i am going to be making a monitor/logger for my HVAC/Utility room.

  • update status live to central web server running locally in the house. this will allow me to see what is currently running which can include the following:
    • Low Cool
    • High Cool
    • Low Heat
    • High Heat
    • Fan
    • Whole House Humidifier
    • Whoile House Dehumidifier

  • record duration the monitored item was operating. This will allow for logs to be generated knowing how hard the HVAC system is operating
  • Monitor NO/NC contacts on water heater leak break detector. if leak is detected, E-mail me (already made and works perfectly)

the leak break detector on my water heater is the following:

of course the issue is that my HVAC equipment operates on 24VAC. to interface the arduino MEGA i plan to use with the 24 VAC, i will be using seven HCPL-3700 IC's.

these have integrated full-wave bridge rectifiers, and built in opto-isolator and variable level voltage trigger output. the heat, cool, and fan are powered off the internal 24 VAC transformer of my furnace so those will share a common 24 VAC neutral line. the HOT lines will be pulled off my thermostat connections.  The Humidifier and Dehumidifier each have their own separate 24 VAC transformer supplies so they will need their own dedicated 24 VAC neutral from their respective supplies. attached is a layout of my existing thermostat/HVAC wiring to my Honeywell YTHX9421R5101WW/U Prestige IAQ.

i have also attached the basic circuit i am going to use.

on the web server end, i will have a SQL data base to store the live real time status of the HVAC equipment but to save the cycle duration information. i will then code in PHP a web page to display the following:

Daily Breakdown (last 30 days prior):
•   Total number cycles per each day
•   cycle start / end time for every cycle
•   cycle duration for every cycle

weekly breakdown (last 52 weeks)
•   average cycles per week
•   average cycle duration per week

monthly breakdown (last 12 months)
•   average cycles per month
•   average cycle duration per month

yearly breakdown (last 5 years)
•   average cycles per year
•   average cycle duration per year

my hardware is on order and i will begin building within a week or so. will post code soon too.


Feb 26, 2019, 02:08 pm Last Edit: Feb 26, 2019, 06:59 pm by wallaceb
i have tested by circuit attached in the first post and no issues were found. i have written all of my arduino code, and the server backend code to log everything into the SQL data base. i will post the code likely tonight.

i have designed a small PCB to allow me to build 9x copies of the circuit to monitor 9x inputs from my HVAC system. attached is a layout and how everything interfaces with my HVAC equipment. the circuit is configured to trigger the IC chip output around 15 VAC. that is controlled by the resistor in series with pin 1 (AC in)

the custom PCB should be here in around a week or so. i have the arduino hardware and an enclosure so i will at least begin construction of my monitor.

the enclosure i am using is from mouser: 616-63274-510-039
the 47 uF caps between +DC and -DC pins on the IC chip is from mouser: 80-ESK476M050AE3AA
the 3700 IC chip is from digikey: HCPL3700-ND
i am using DIP sockets for the chips from digikey: AE9986-ND
the 0.1uF caps between VCC and GND for each IC chip is from digikey: 399-5453-1-ND
the LEDs have integrated 5V current limit resistors, they are from digikey: 754-1724-ND

the power supply i am using for the monitor is the same power supply i have been using 24x7x365 for 7 years with zero issues is from amazon: B000Z31G3M


everything works 100%

i even added a Adafruit_AM2315 temperature and humidity sensor.

attached is the code for the arduino.

also attached are screen shots of the PHP server code i made to display the data

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