I'm sure everyone's had a good laugh over CShead-v3 but overlooking that it
only twitches when you shine a light in its eyes, it also requires less
power than most other head circuits. Just kidding, note the extra inverter
where the sun don't shine and much better now, thank you, in the attached
CShead3corrected.gif . But the silver lining is that the uncorrected version
had a big vacuum between PD1 and PD2 just waiting for a deadband diode: ergo
CSheadv4.gif - untested until tonight but it doesn't get much simpler! The
diode may be replaced with another PD, forward or backward biased, pointing
to the back of the head for more complex behavior.

wilf

-----Original Message-----
From: Wilf Rigter
Sent: Tuesday, November 06, 2001 12:35 AM
To: Wilf Rigter; ''R. Martin Keen ' '; ''beam@yahoogroups.com ' '
Cc: ''beam@yahoogroups.com ' '
Subject: RE: [beam] SC-head



Works great! Well only after fiddling with it. The 1M + 1M combination was
a dead wrong suggestion. But 1M in series and 4M in parallel with the
schmitt trigger and 1000 pf to ground works but is sesnitive to light
level. I tried your original design with 100pf in parallel with the schmitt
trigger and got a lot of oscillation. An easy test for efficiency of the
circuit is to measure current with no motor attached. With Vcc=5V and the
light balanced, if the current is more than 3mA then the circuit must be
oscillating. I measured 18mA with the parallel capacitor.

I have not tried many variations on your SC circuit nor have I build the
whole head assembly but the attached circuit seems to work well on a
protoboard with a pair of insensitive PDs and driving a small gear motor. I
replaced the series resistor with two parallel diodes to make the circuit
less sensitive to variations in light. If you add 10M resistors in parallel
with the PDs the circuit powers down to a few mA with very low light.

I will build the SC head circuit/assembly and test it as a unit.

wilf

-----Original Message-----
From: Wilf Rigter
To: 'R. Martin Keen '; 'beam@yahoogroups.com '
Cc: 'beam@yahoogroups.com '
Sent: 11/5/01 10:01 PM
Subject: RE: [beam] SC-head

Yes, "unusual" is a compliment. No luck, eh? Interesting! I'll play with
it and report back.

wilf

-----Original Message-----
From: R. Martin Keen
To: beam@yahoogroups.com
Cc: beam@yahoogroups.com
Sent: 11/5/01 9:08 PM
Subject: [beam] SC-head

Thank you, Wilf. I'll take 'unusual' as a compliment, after seeing your
NuRing circuit.

I bread boarded the new design, and it didn't really work. When a
photodiode is shorted out, it make a nice bistable flip flop. I tested
several different arrangements without luck. I hope someone else will
try.