AC 220V MCU TTL Level 8 Ch Optocoupler Isolation Test Board

[Rincewind]

Hi,
I am trying to add a sensor to my 8 underfloor heating actuators (24V) so I can monitor when they are 'On'. I thought this would do the job, although I'm only sensing 24V DC.
Input goes through MB6M bridge rectifier, then PC817 optocoupler. From the output TTL pin I'm always getting high reading though.
I understand DC into bridge rectifier also outputs DC.
Would this be due the the input voltage being too low so its not suitable for my project?

Specs from AliExpress:
Feature:
Functuon: Test whether AC 220V is existed
Ouput TTL Level: can use MCU to test,voltage is 3-5V
Output can connect PLC 24V

Wiring:
When connecting the PLC input, the PLC's COM terminal is connected to the 24V power supply, the input is connected to signal outputs S1-S8 of the board, optocoupler GND is connected to the power supply negative.
Blue 5.0 terminal is connected to 220V voltage, yellow pin signal output.
When the 220V voltage is normal, it output low level; when 220V is powered off, it output high level.

 

[Rincewind]

Bumped the input up to 30V and the TTL output went low.
Any suggestions on which components I should switch out to convert board to a 24V sensor?!

Existing:

220V input
Resistor - 150k ohm
Bridge Rectifier - MB6M
Diode
Capacitor - 100uF 25V
LED
PC817
Output pins

 

[danadak]

Schematic ? Even hand drawn OK.....

Regards, Dana.