Smallest way to switch 1-10v 20ma with 240v

[Scarr]

Hi All,

What the smallest relay with 240vac a coil that you know? or is there a solid state way of switching that is small keeping in mind the 5v is monitored by a MCU and so needs to be a constant ON / OFF switch

Thx

Scarr

 

[MikeMl]

Something utilizing an opto-isolator. However, by the time you add the high-voltage capacitor, diode, current limiting resistor on the input side, it will not be very small...

Here are some relays.

 

[Nigel Goodwin]

Hi All,

What the smallest relay with 240vac a coil that you know? or is there a solid state way of switching that is small keeping in mind the 5v is monitored by a MCU and so needs to be a constant ON / OFF switch

You need to give far more details of what you're trying to do?, however a relay sounds a very poor choice whatever you're trying to do.

 

[dr pepper]

You can get ac opto isolators, just an opto with 2 back to back led's, you could drive the leds from ac via a capacitor and resistor.

 

[MikeMl]

Here is about the simplest opto-coupler circuit that won't burn up or kill you... and doesn't use huge capacitors. C2 can be a small disc ceramic.

It detects the turn-on of the AC almost immediately, but it takes it a while to realize that the AC turned-off. R3 could be the "weak-pull-up" inside the PIC. Note that the input resistors are half Watt. It is active-low at the PIC input.

 

[spec]

Here is a circuit that relies on the electromagnetic coupling to a wire placed near the mains cable required to me monitored.

spec

 

[tcmtech]

A submini neon bulb and a photodiode in a black plastic tube would work. ~1/4" round by 1/2" long.