B.E.A.M.
BEAM is an acronym standing for :
Biology, Electronics, Aesthetics and Mechanics
Andy's Light-Tracking Head
DIY : "Bicore" Head
Parts list : updated Apr.2, 2002 (using photo-transistors)
1 bicore chip : 74HCT240 1 Copal gearmotor 1 voltage regulator 78L05 (5V)
2 green leds * 2 3.3K Ohms resistors 2 0.22 uF monolithic capacitors (224)
2 photo-transistors (or IR leds* donated from my PC mouse :-) ) 1 " Bright " resistor 1.0M Ohms 1 " Dark " resistor 2.2M Ohms
9V battery * 1 small terminal block * not included in kit #006
It's only 11 items, ready.....ready.......go !!!
Looking for schematics ? 
Here's the original idea coming from :-)
Lee Golden 
Light Tracking Bicore Head

My version on How to freeform it (without PCB) : Light tracking bicore head

1.  make sure you know the orientation of this chip : 74HCT240
pin 20 is anode +ve, ( Vcc ), pin 10 is cathode -ve, ( ground )
2.  using the brand-new resistor lead, lay down the track as shown
solder the pin 1, 19 and 10 this is all connected together as cathode -ve.
3a. solder pin 11,13, 15 and 18 together. 3b. You may need to bend the pin outward, not too much though.
4a. solder pin 3, 4, 6 and 8 together. 4b. You may need to bend the pin outward, not too much though.
5a. solder pin 5, 7 and 9 together, this is the motor lead. 5b. motor lead is 25mm, with 15mm extended from pin 9. (long!!)
6a. solder pin 12, 14 and 16 together, this is the other motor lead. 6b. motor lead is 25mm, with 15mm extended from pin 12. (long!!)
Now the mono caps & led eyes
7a.  solder pin 17 and 18 with the leads of 0.22uF monolithic capacitor 7b.  watch out area : don't short-circuit it :-)
8a. solder pin 2 and 3 with another 0.22uF mono caps 8b. bend the leads as shown, and view from the back
9a. top view : leds and 3.3K resistors 9b. led leads go to pin 3 and 18, resistor leads go to pin 20 (+ve)
10a. right led goto pin 3, watch out and don't short circuit it 10b. left led goto pin 18, resistor leads goto pin 20
and now, the IR leds donated from my PC mouse, or
To use photo-transistors
11a. with the IR led bubble facing you, the +ve lead goto pin 2 & pin 17 11b. the -ve leads of IR leds joint together
and finally, the 5V voltage regulator 78L05
12a. layout of 78L05 facing you :1,2,3 as output,Gnd & input 12b. output goto pin 20, Gnd goto pin 1(-ve 9V), & input hocks up with +ve 9V
13a. That's it. 1 hr of soldering !! 13b. hock up battery and motor leads (bottom), and ready to track light :-)
Further upgraded : light/dark bias resistors (1M & 2.2M resistors)
"Dark" resistor (2.2M Ohms red, red, green) was soldered in parallel (pin 2 & pin 17) with the IR leds to provide a max. resistance so the Bicore-Head doesn't just spin endlessly in one direction in very low light conditions (indoor, under my desk-lamp) "Bright" resistor (1.0M Ohms brown, black, green) was soldered in series (pin 2 & +ve lead of IR led) with the IR leds to provide at least some min. resistance when the Bicore-Head is in extremely bright light (outdoor, under the sun)
Lee took his time to explain it clearly to me :

" The purpose of the bright resistor, if I remember correctly, is to guarantee that there is at least *some* minimum resistance in the light bridge (for example in full sun).  With sun shining on the photodiodes, there is almost no resistance in the circuit from the photodiodes at all.  This is when the head locks on and just sits there vibrating (and sucking up current like crazy).  With a suitable light resistor in place, the head should still move back and forth a bit even in full bright light.  As I said, I wasn't worried too much about this, so I just left them out of my circuit... "

If you are using the photo-transistors that come with the kit :
I just bend the photo-transistors legs 45 degree. After the soldering, they form the " eyes " and they are not parallel to each other. This is a closer view on the photo-transistors : pointing away and not exactly facing the front.
Right eye : Pin 2-resistor(1M)-collector of photo-transistor (shorter leg). Solder the emitters (longer legs) of both photo-transistors together. Left eye : Pin 17- collector of photo-transistor (shorter leg) Solder the emitters (longer legs) of both photo-transistors together.
Motor leg (pin 5,7 and 9) goto red lead of the motor; and the other motor leg (pin 12, 14 and 16) goto the black lead of the motor to make it phototropic(facing the light source). If you plug it in the other way, it will become photophobic(turn away from the light source). Isn't it fun :-) A closer view on the arrangement of photo-transistors. If you so desire, you can solder the photo-transistors behind the Bicore chip (74HCT240). 
But most of all, enjoy the BEAMing.

Tutorial on how to make solar-bug (Ben Hitchcock's Fred : light-seeking robot)
 
 

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