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

47K 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. Not bad at all.
If you use battery to replace solar-panel and capacitor, that will be 5 items all together !!

Tutorial   May 13, 2002
Test drive the circuit on Breadboard   Feb. 8, 2002

3J connected to +ve with jumper wire 
6J connected to -ve with jumper wire 

I'll explain it later 


spread the legs of the 2N3904 a bit so it will fit into the sockets of the breadboard

6F : E of 2N3904 
5F : B of 2N3904 
4F : C of 2N3904

6G : E of photo-transistor (longer leg) 
5G : C of photo-transistor (shorter leg)

4G : Cathode of fled (shorter leg) 
3G : Anode of fled (longer leg)

3H : 1 leg of 100K ohms resistor 
5H : the other leg of 100K ohms resistor 

To turn on the fled at "Complete Darkness", use 100K ohms resistor 
lower the value of the resistor to adjust the sensitivity, ie, 47K, 33K, 22K

Hook up the battery : +ve to +ve, and -ve to -ve. 
When I cast a shadow onto the photo-trnasistor, the red fled is on !!

Mega-easy, eh :-)

Tutorial   May 13, 2002
Here's the pics :-)       26 Nov., 2001

General layout of the 'dark" detector. I'm going to put it close to my window, so the photo-transistor should point to the outside and the fled should point toward me.

cast a shadow onto the photo-transistor, 
the fled starts to blink

darker the shadow, brighter the blinker :-)

Tutorial   May 13, 2002

Basic concept :

The  common use of photo-transistor is light trigger, ie, light shined onto the photo-transistor will activate the circuit. Thus, the "Light" detector.

What if we want to turn on a fled when light is out ? A nocturnal circuit.

Basic circuit used here is to have the Vo "low" when light is shined onto the photo-transistor.  :-)

The "load" can be fled, flag spinning motor or anything you can think of.


Simple enough to do it yourself :-)

Parts I used instead:

solar-panel : Panasonic  2433 panel

capacitor :  NEC 0.047F, 5.5V Gold caps

photo-transistor : 5mm p-transistor with deep blue casing (daylight filter)

resistor : 100K resistor 

transistor : NPN 2N3904 transistor

load : red fled

More pics are coming. Not today, need more time to rest :-(

Nov. 18, 2001, Nov. 23, 2001, Nov. 26, 2001

Circuits quoted from :

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Robot kits & parts

Tutorials : DIY

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