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For on-off switching my workbench light I am using Arduino modules CJMCU-0101 Touch-switch and IO25A01 Bistable relay. They are connected directly (without Arduino board) and powered by this 220V to DC 5V Transformer Power Supply Module. circuit diagram This combination works flawlessly until power loss. Always after power supply restore the light switches on. No matter which was relay state before power loss. The light always switches on. Same situation appears when I use Bistable-touch-switch and non-latching relay module. I understand that easiest way would be connect light to COM and NC pins of relay, but in this case the coil of relay remains be energized most of the time (when the light is switched off)

How prevent this "always switching on" situation without adding complex of electronic components (lack of space) or it is impossible ?

Current operation
            ___________________     ___________________
Power _____|                   |___|                   |____
              _   _       _                _    _
Touch _______| |_| |_____| |______________| |__| |_________
            ___     _______          _______      _____
Light _____|   |___|       |________|       |____|     |____

Figure 1. Timing diagram by @Transistor for OP to correct and copy / modify with desired operation.

Edit: added desired operation diagram enter image description here

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  • \$\begingroup\$ I can't find any good schematic on how the touch-switch works, is it always GND when not touched then goes to VCC when touched? \$\endgroup\$ – Ron Beyer Jun 28 at 20:03
  • \$\begingroup\$ @hirax: I've added a timing diagram of, I think, what you are describing. Please correct it if it is wrong and make a second one with your desired operation on it. \$\endgroup\$ – Transistor Jun 28 at 20:35
  • \$\begingroup\$ @Ron Beyer As far I know, yes, touch buttons signal output is 0V (GND) when not touching. \$\endgroup\$ – hirax Jun 28 at 21:06
  • \$\begingroup\$ I'm guessing that the "touch" floats when the switch isn't powered. When the power comes back on the switch goes to ground triggering the relay. \$\endgroup\$ – Ron Beyer Jun 28 at 21:17
  • \$\begingroup\$ I edited diagram again and now it must be ok \$\endgroup\$ – hirax Jun 28 at 21:19

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