How Does Touch Switch Surface Area Affect Capacitance?

[Jso]

Hi,

I've taken apart a touch lamp and remodelled it with my own design. The problem is that now it only works with 50% of the people who use it.

The surface area of the switch is much larger than before. Is it a case of replacing a resistor or is there some fundamental problem to having the switching surface too large?

Thanks

 

[NoTime]

Does your unit connect to the AC mains circuits of your house?
If so, the changes you made could make this dangerous and kill somebody.

They do make touch switches that are designed to be connected to random metal objects.
I might suggest you buy one of these.

 

[Jso]

Hi,

Yes it is connected to the mains but the live wires are not remotely near the metal being touched.

I've looked for switches on their own but have had no luck. Searched Maplins and the net but the only things I've found are circuit diagrams. Do you know where I can find these switches on their own?

Thanks

 

[mgb_phys]

I don't know about touch switches, but if you are in the UK (you mentioned maplins) these guys are great for buying parts in hobby quantities and will send you a catalogue.
http://cpc.farnell.com/

 

[NoTime]

I'd do a leakage check on your plate to make sure that it is safe.
Systems are tested as a whole and changing one could inadvertently bypass some of the safety features built in.

You might find some touch switches in a home center.
They had a large rack of different kinds in the Home Depot (USA) I was in the other day.

 

[berkeman]

Hi,

I've taken apart a touch lamp and remodelled it with my own design. The problem is that now it only works with 50% of the people who use it.

The surface area of the switch is much larger than before. Is it a case of replacing a resistor or is there some fundamental problem to having the switching surface too large?

Thanks

Sounds like you made the plate area larger, which makes the percentage change in capacitance when touched smaller. The bigger the initial capacitance, the smaller the change in capacitance you will get when it is touched. Can you remodel it one more time, and use a smaller area touchpad? Maybe make it look visually big, but only the middle part of it is actually the capacitor area...