11a. with the IR led bubble facing you, the +ve lead goto pin 2 &
11b. the -ve leads of IR leds joint together
and finally, the 5V voltage
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... "
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
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.