Capacitive feedback

Google failed to help me with this one. Probably because this might be called something else.

A few months a I was at local gathering and someone who seemed to really know what he was talking about, explained to me that capacitance could work two ways. One way to sense obviously and another provide feedback through a very subtle shock or something. One of the guys demonstrated the effect with his macbook air plugged in and touch a specific spot on the uni-body.

Said it was used for silent triggers and things of the like.

I'm interested in using this type of feedback in place of pager motors for my project. Anybody know of any resources to get started?

I think he is yanking your chain. It would take a lot of voltage to make tingler like that.

You know after searching for this I want to say that he was yanking my chain. :slight_smile:

Typically I have pretty good sense for that type of joke though and the conversation was pretty serious. The idea was based on work with… well a company making devices that need to be absolutely silent when pulling the trigger, but the trigger puller still need to feel the sensation for legal reasons. Everything else was over my head at the time. Ok… this was probably more then a few months ago at this point. There was something said about the effect occurring with poorly grounded ac to dc inverters.

Really should have followed up with him. Failed realized if this was a joke or really something special.

You can look into TENS units. They provide a safe tingle. Any thing that puts current through a human body is going to have really high hurdles to jump through.

You can certainly get a shock from a charged capacitor. There's a classic electronics lab prank where someone charges-up a capacitor to a few-hundred volts and tosses it to someone, and they get a shock when they catch it. (The person throwing it holds it by the insulated body.) It's not something I'd recommend... It wouldn't be too funny if you trigger a heart attack.

You don't feel the voltage, you feel the current. And, since the human body has high resistance, it generally takes more than 50V before you feel anything, depending on how you are connected and the moisture of your skin, etc. You need more than about 50V before you can feel anything. Typically, things designed to shock someone have a few thousand volts (with no load connected) and current limiting (maybe just a high-value resistor) to keep them safe.

But a capacitor alone, won't generate high voltage from 5V or 12V. For that you need an inductor or transformer. And you really don't want to connect a human (or animal) to wall power! This kind of stuff is dangerous enough already!

All interesting input, thank you.

Hate to sound picky considering we are talking about potential magic, but I was told that this magic was painless.

Would a low current 50voltish alternating current possibly produce a painless sensation?

Think I need a guinea pig :)

I thought this was electric, turns out to be mechanical, still fun none-the-less.

You didn't look up TENS, did you? IT provides:

a strong but comfortable sensation

I found that 300uA was just perceptible on the thin flesh between my fingers. My fingertips were less sensitive, presumably because the thicker skin spreads out the current before it gets to where the nerves are. The skin on my arms is also less sensitive, presumably because there are fewer nerves.

1mA caused a definite sensation, not exactly painful, but not pleasant. 10mA is very uncomfortable. I never went beyond that, and kept the touch points about an inch apart.