I'm quite new to actual physical "engineering" and I am just getting started.

My current project is to build a light switch, which triggers my room light via wifi.

I have two cables in my wall (like this) which - when connected - trigger a relais in my flats fuse box which switches the light. The two wires run on ~16V, and when connected have a short spike of current of about 4-8mA. This spike lasts for about a second and drops to 0 afterwards.

So my plan is to use this SSR with an ESP-01 3.3V (which has a maximum current of 12mA per pin, so that should be enough), wire up the two cables and the esp-01 with the SSR and let the ssr switch the light.

So a few questions:

  1. Is there something obvious I missed? I'm still a beginner and trying to make sense of all these information, so there might be something I missed.
  2. If I read the datasheet right, I need 10mA@6V to trigger the SSR, is that right? How can I map this to 3.3V? And what does RL under conditions @ minimum trigger conditions mean? Is this a resistance I put before the Pin?
  3. Concerning the Pin-layout of the module: I guess the pins 1,3 & 4 are the ground pins for my ESP-01, a load on pin 2 triggers the optocoppler. I'm not quite sure about the pins on the AC side. What are the Pins T1, T2 and Gate for?

    Thanks in advance for your help!

  • \$\begingroup\$ What is the total load current and voltage and type of lights? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 6 '16 at 22:34
  • \$\begingroup\$ I don't switch the lights directly. The wires are connected to a relay in my fusebox, which turn the light on or off \$\endgroup\$ – mietzekotze Oct 6 '16 at 22:35
  • \$\begingroup\$ Depending on Light specs , you can replace relay with direct control from SSR or use a smaller solution like a reed relay to toggle your relay toggle power switch \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 6 '16 at 22:40
  • \$\begingroup\$ No no, its not a classic relay, but a fusebox like this. The wires coming out of the wall, are connected to the fusebox and trigger something in the fusebox with activates a standard 230V AC/16A circut which triggers the light. But I'll look into the reed relay, that looks interesting. \$\endgroup\$ – mietzekotze Oct 6 '16 at 22:45
  • \$\begingroup\$ You can drive this direct with CMOS 3V logic by adding reverse Sch. diode clamp to reed coil. rated for 500mA out 6ma digikey.com/product-detail/en/standex-meder-electronics/… \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 6 '16 at 22:53

It might work, but it's not designed to work at such a low voltage. The zero crossing inhibit is as much as 35V which means it could never trigger at all from a 16VAC source (22V peak). It is typically about 12V so it could just work badly.

I suggest using a MOSFET output SSR such as the Toshiba TLP2222A

enter image description here

The LED needs ~7.5mA at ~1.15V so a series resistor of about 240 ohms is probably about right- not sure what the voltage drop is of that chip so you might want to check the voltage across the resistor to make sure the current is high enough.


There's a schematic button on the editor toolbar. Schematics are better than words. Meanwhile ...

  1. Datasheet Electro-optical Characteristics says "Forward voltage @ 20 mA= 1.2 V". This is typical for an IR LED. You just need a series resistor to limit the current to 20 mA.

  2. The standard circuit on page 10 shows how to connect it up.

General notes:

  • 0.6 A is the max rating. Incandescent light bulbs have a current surge at switch-on of 5 to 10 times their steady state current as the filament is cold. This may blow your triac.
  • You need to design properly for mains isolation.

enter image description here

Figure 1. Good design practice. Note complete isolation between the sides of the opto-isolator and slot machined out of the PCB to ensure no creepage due to moisture, etc. Source: Vishay.


The problem with SSR's is they have a minimum load current to turn off reliably.

In your case the load current is actually less than the SSR trigger current.

In this case, one would review the LED requirements for AC or DC and the arduino power and any other supply voltages available. Since the load is quite small and noise may be a problem with a long line, one can solve this in many other ways.

Such a solution exists for small signals that fits this range is a DC optoisolator switch and small signal bridge rectifier if you have a 12Vac source.

But it also could be powered other ways .

I would suggest this driver reed relay for your 16Vac power relay coil. 6mA @3V , contact 500mA



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