Andy's Solar-bugs

B.E.A.M.
BEAM is an acronym standing for :
Biology, Electronics, Aesthetics and Mechanics
last updated Aug. 8, 2002

White LED : powered by 9V battery

Parts list :

2 White leds

9v battery button

1 resistor : 75 ohms

3 items :-)

DIY Home-made 9V Flashlight or Torch :-) Aug. 8, 2002

	This is easy. I recycled the really old, used 9V battery. Broke it open to salvage the 9V button, and the bottom square plastic as cover. And you do have 6 AAAA battery cells (1.5V each) to play with :-)
	Using V=IR 9v-(23.6V)=A75 Ohms 1.8V=A*75 Ohms A=0.024Amp=24mA (This is good, Max A it can take is 30mA) so everything were soldered in series : +ve button ---75 Ohms resistor---first white led---second white led---ve button Test it to make sure it works and then crazy glue the whole thing together
	Don't even have the on/off switch :just unplug one of the button and it is off :-) Put one into your backpack and off you go
	Plug it back in and you have the instant MEGA-BRIGHT 9V Flashlight or Torch, depends on where you are.

Test drive the circuit on Breadboard June 24, 2002

2 : white leds and 1 : 75 ohm resistor : all in series
powered by 9V battery

see table 1

This is another one that works ( How well ? That is the question )

3 : white leds and 1 : 75 ohm resistor : all in series
powered by 9V battery

see table 2

Table 1

V across led	mV across resistor, 75 ohms	V of 9v battery, loaded	V of 9v battery, open	string of 2 leds	mA across resistor from calculation I=V/R
3.34	1510	8.46	8.77	1	20.13
3.23	1117	8.19	8.63	2	14.89
3.19	948	7.96	8.46	3	12.64
3.14	826	7.76	8.35	4	11.01

Table 2

V across led	mV across resistor, 75 ohms	V of 9v battery, loaded	V of 9v battery, open	string of 3 leds	mA across resistor from calculation I=V/R
2.87	258	8.92	9.02	1	3.44
2.86	246	8.86	9.01	2	3.28
2.84	206	8.84	8.99	3	2.75

There is something not quite correct about the calculation. But what is it ? Please help.