BEAM is an acronym standing for :
Biology, Electronics, Aesthetics and Mechanics
last updated Mar 27, 2007

DIY : "Dark" Detector

Parts list :

solar-panel : Panasonic 2433

NEC 0.047F, 5.5V Gold caps

red fled

100K resistor *

NPN 2N3904 transistor

5mm photo-transistor 

Optional Powerstor 1.5F supercaps



* ( 22K, 33K, 47K and 100K Ohms resistors are included in Kit#7 to play with sensitivity)

6 items for a "Dark" detector. Wanna give it a try.........  :-)

1a. Small wires are soldered onto the pads first.

1b. epoxy is used here to fix the wires position

2a. bend the legs of 2N3904 as above

2b. soldering the "brain" 
Phototransistor Emitter (longer leg) with 3904E 
P-trans collector (shorter leg) with 3904B, then add the 100K Ohms resistor to the 3904B as above

3a. this is the "brain" of the "Dark" detector

3b. 100K ohm resistor goto +ve of solar-panel 
3904E goto -ve of solar-panel

4a. don't forget to bend the panel wires upward for the capacitor later

4b. make sure the "brain" is located closee to the center 
I'll bend the P-trans later so leave room for that


5a. fled anode (longer leg) goto 100K ohms resistor 
fled cathode (shorter leg) goto 3904C

5b. marking on the 0.047F capacitor is -ve (longer leg), should goto -ve wire of solar-panel 
0.047F caps +ve (shorter leg) goto +ve wire of solar-panel 
make sure the 3904C is NOT shorting the circuit :-)

6a. bend the legs like that

6b. flip it over to let it sit on my desk, with the P-trans facing the window. The red fled will start blinking when the sun is down !!

Viola, 30 mins later, you got yourself a "Dark" detector :-)

last updated    Mar. 20, 2002

Roll of 40 pins IC round legs socket in 2 rolls, that gives you total of 80 pins :-) Just use your nippers to cut into the plastic case.

solder 2N3904B with 1 pin, and then the +ve solar-panel with the other pin. Crazy glue the pins onto the panel. Let it set for overnight (I used 5 min crazy glue)

You can now plug in the diff. value of resistor to play with the light sensitivity. Have fun :-)

100K ohms resistors will turn on the "Dark" detector when it is "completely" dark. 

47K ohms  resistors will turn on the "Dark" detector when you cast a shadow on it. 

33K ohms  resistors will turn on the "Dark" detector when you cast a "slight" shadow on it.


Hook up the 1.5F Supercaps and the fled will blink for hours :-)

Back to more pics on "Dark" detector

Basic concept :
Circuits quoted from :

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