Transistor touch switch with relay. Will this work?


So, I'm new to electronics, but I'm really interested to learn. As you will see from the diagram below, i still have a lot to learn.

Basically what i need to know is, will the diagram below work in practice. I tried it out without the relay and with a led and it works i.e. pos to one side of the transistor, relay to the middle of the transistor and led to the other side of the transistor with the other end of the led to neg.

I'n the diagram, i tried to add a relay and replace the led with a solenoid. Will this circuit work?

Picture of Transistor touch switch with relay. Will this work?
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rickharris6 months ago

A darlington pair will give you much more gain and a better result.

Google has lots of options. Where a relay isn't shown it will be the load driven by the transistor.

GhengisKhan1981 (author)  rickharris6 months ago

Thank you! In other words, i will not need a relay if i do it this way?

It depends on what you want to control. If it is more than an LED or toy motor then yes you still need the relay - The relay is the load for the transistor.

GhengisKhan1981 (author)  rickharris6 months ago

Thank you very much for your time :)

Back to the shed to tinker some more......

GhengisKhan1981 (author)  GhengisKhan19816 months ago

Would i be able to apply the same principle to this :

Your touch plate will activate the switch wherever you touch it. not in one specific place. There is no real electronic way to do that that would be easy for a beginner. unless you make a light operated switch and drill small holes all over the plate.

iceng6 months ago

Probably not, because the NPN needs to draw a current through the relay coil to ground => "neg-".

The 12v "pos+" needs to to also go to the other side of the relay coil.

iceng iceng6 months ago

Redrawn might work once a lot depends on the NPN gain and the needed relay coil current.

Then there is an issue with inductive kick-back from both the relay and solenoid which may destroy the transistor when the coil gets turned OFF.

To avoid this always put an inverse diode across each coil..

GhengisKhan1981 (author)  iceng6 months ago

Thank you! Seems from your drawing that i was not too far off or maybe just a million miles :P

I will try both your suggestions. As i's easy just to go and buy something that works, but that defeats the point. I want to learn more about the interesting and VERY exciting world of electronics.

Probably silly, but you've never seen a grown man get this excited about getting an led to shine with a touch switch.

You guys and this site is AWESOME. Thank you!