Hi everyone,
I want to use copper tape to connect two pennies to a 3v coin battery and an let light. Then each of the two kids touches a penny and they touch each other, thus closing the circuit and lighting the bulb. All of this would be in a simple valentines card. Does this sound workable?
Thanks in advance!!
Rebecca
Yes. I’ve seen similar LED lights done w/a coin cell, an LED and thin wires. The resistance of the wires and the internal resistance of the coin cell were enough to limit the current through the LED … so that it wouldn’t burn out.
The problem I forsee is the connection between coppertape and the pennies. Is there a conductive path between them or is the sticky side of the tape (or whatever used to fix them together) perhaps isolating?
Not sure that what you describe is what people are interpreting.
Are you saying that each kid touches a penny with one hand and also hold each others’ hand to complete the circuit? If so, no, that won’t work.
The idea could work very nicely but you or someone will need to construct a circuit for it to work effectively. Use one of those quarter size flat 3 volt batteries. It is only ON when the pennies are touched, no need for a switch.0987:
I want to use copper tape to connect two pennies to a 3v coin battery and an let light. Then each of the two kids touches a penny and they touch each other, thus closing the circuit and lighting the bulb. All of this would be in a simple valentines card. Does this sound workable?
http://www.oldtemecula.com/sparkfun/penny-switch.gif
That’s my two cents! :snooty:
Christopher
Upon rereading it, I think you're right. Let's see if the OP can clear up what it is that he wants.lyndon:
Not sure that what you describe is what people are interpreting.Are you saying that each kid touches a penny with one hand and also hold each others’ hand to complete the circuit? If so, no, that won’t work.
that’s the idea. I got it from the “Friendship Box” in Mark Frauenfelder’s Maker Dad book.
Are the resistors and capacitors necessary with the coin battery?
R1 isn't given the resistance of the path between the coins. R2 is a good idea so as to not stress the battery. There's no caps in that circuit.0987:
Are the resistors and capacitors necessary with the coin battery?
Hello Rebecca and Master Makers,
I did a little experiment just now. Using 3 volts directly with a LED that had a 1.2 forward voltage, it would not light up with the pennies placed on both sides of my tongue which was the most conductive part of myself available. :o
With spit on my fingertips on opposite hands my body resistance is 500K.
The 1.2v LED @ 3v only showed useful brightness if the resistance was less than 3000 ohms while 1000 ohms was ideal.
The Darlington pair drops about 1 volt while the LED drops ~1.2 volts. That leaves ~.8v / 100R = 8 ma through the LED. R1 protects against the pennies being touched together.
It is important to use an LED with the lowest forward voltage rating, 1.2 volts is ideal.
That’s my Saint Valentine Day Massacre 
Christopher
