Have an UFH controller which can open a 24v 2w actuator for the required zone.
Looking to find the most efficient way to register in Arduino when an Actuator is open or closed.
Thinking along the lines of measuring when voltage is sent to actuator, but as I have 8 separate actuators to monitor I'm looking for some guidance.
Plan is to measure what %age of the time the actuator is active.
Under floor heating?
I think perhaps opto-isolators would be a safe and sensible way to detect if the voltage is present at each actuator. That way you don't need to worry about having a common ground between the actuator controller and the Arduino.
For example K844P has 4 channels so you would need 2 of these chips. You would need a series resistor for each channel's input, e.g. 4K7. In this case they will work with AC or DC input voltages, so you don't need to worry about the correct polarity. For the outputs, the collectors can be connected direct to an Arduino input and the emitters to the Arduino ground. Use pinMode(pin, INPUT_PULLUP) to prevent the Arduino inputs from floating when there is no voltage on the channel (they will read HIGH in that case).
Hello rincewindy
Take some time and describe the desired function of the sketch in simple words and this very simple and short form.
Have a nice day and enjoy coding in C++.
Дайте миру шанс!
Most such control stuff in a home is AC operated. Why not tell us, so we can know?
There are (at least) 3 possibilities.
If it's DC and it's regulated or reliable you can use a voltage divider (2 resistors). Typically the resistors should sum-up to about 10K but it's the resistance ratio that's important.
If the 24V varies you can use an over-voltage protection circuit (a resistor and one or two diodes).
If it's AC the 2nd diode can be a rectifier or a diode wired to protect against negative voltages.
It's also possible to add "protection diode" to a voltage divider. In this case you'd calculate the voltage divider for a little-extra voltage, and let the diode take it from there.
An opto-isolator is usually "foolproof" because there is no electrical connection and a common ground is optional so it can be completely isolated.
If you can't have a common ground optical isolation is your only option (for DC). The other methods require a common ground.
And if it's AC, the Arduino can be damaged by negative voltages so you'll have to rectify, or add negative-voltage protection. If you use regular half-wave or full-wave rectification, you'll probably want to add a capacitor filter so you don't read "no voltage" during the negative half-cycle and during the low-voltage part of the cycle.
With AC an opto-isolator will also usually need a reversed diode across the internal LED to protect it from reverse (negative) voltage. Most are not rated for 24V reverse voltage, and with 24VAC RMS the positive & negative peaks are about 33V.
The wattage (or amperage) isn't important. Only a tiny amount of current will flow into the Arduino circuit (unless it's over-voltaged. 
)
That sounds just the job thank you @PaulRB. I'll give that a go. Do you think a PC817 8 channel module would be suitable?
Please post a link to the module you are considering.
@DVDdoug please check out the component I suggested in post #2 above and advise. In my mind, the external reverse diode would not be needed because there are two internal diodes, back-to-back, so the reverse voltage would always be no higher than the forward voltage. The external 4K7 resistor would keep the current in a safe range.
This is the module I was looking at:
With that module, the problems mentioned by @DVDdoug would be valid, those opto-isolators are designed for DC only and would need extra protection for use with AC. The opto-isolators I suggested should be ok for either AC or DC. Do you know which the actuator voltage is?
This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.