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I am trying to create a ping pong ball sized light-up ball that should light up when held in my hand, as in the 80's toy inspired by the movie/television series "Star man".

The circuit must be powered by a coin battery cell, preferable a 1.5 V LR44.

I have a ZXSC380FHTA LED driver and a 47 μH or 100 μH RF inductor.

The LED is a standard 5 mm white LED from a broken computer fan which lights up using only the LR44 button cell, LED driver, and inductor.

I have tried with a 2N2222A transistor to drive the touch (skin) switch and even tried to create a Darlington transistor by combining two of these, but no success.

So far I only tried on a breadboard to get a skin connection using two pins. Is the surface area to the skin insufficient, or is there something wrong with the electrical design?

Does have a suggestion?

When driven by 5 V from an Arduino it is no problem to light up the LED with just a transistor and using the skin to close the circuit between +5 V and transistor base, but when transitioning to 1.5 V I guess there is too little voltage to drive even an LED driver of the type mentioned above.

Also, should the load, i.e. the LED driver/inductor/LED be placed at the collector or emitter side of the transistor?

Update: When using 3 x 2n2222a in a darlington config, I can get the led to shine using a 3V coin cell. But only if the finger is licked a little before pushing the two pins I use to test this on the breadboard. I will try to use a bigger piece of metal as connector next and maybe order some triple darlington transistors to further test. Also when googling: "energy ball" seem to hit a simulcrum of what I want, the nowadays sold "energy balls" doesn't light up, but blink and make annoying noises. Which to some might seem like an improvement but to me seem like; "Oh why, for the love of a hot women (or man, if you are so inclined)."

Erik
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  • Some of them that I've used have two small metal contacts on the outside of the ball similar to a ping-pong ball. When both were in skin contact the ball would light up. I believe they used three BJTs, not two. I've since designed a circuit that can be used for similar purposes -- was designed to detect even slightly moist surfaces -- and I may be able to find the design (or recreate it) at some time later. – periblepsis Feb 01 '23 at 17:11
  • As in three BJT's in a darlington configuration? – Erik Feb 01 '23 at 18:05
  • Well, in my case not exactly. But in your current situation, assuming you are willing to have two contacts protrude the ball, I'd try that as a "next step." It might get you there. – periblepsis Feb 01 '23 at 18:10
  • you want a 3v cell (or two in series( and at least a darlington, maybe 2. basically, build a ghost detector and backoff the transistor count until you have to actually touch it to light. – dandavis Feb 01 '23 at 23:52

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I have made one of these in the past and they are certainly sensitive. You might need some kind of ESD protection but there are lots of interesting possibilities with this

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Dirk Bruere
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  • The 2n3819 might be better than a 2n2222a transistor for my project. But will it work as I described in my question, i e closing two metal points with the skin turn on the Drain-Source current flow? And if so should those metal points be between the gate and battery +? Will it work with a 1.5v battery and a led driver? – Erik Feb 01 '23 at 16:29
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    The pictured circuit constantly drains the battery – Phil Freedenberg Feb 01 '23 at 19:05