Hi,

I was just checking the BEAM list as I do from time to time, and
found the discussion about Fred Heads. Wow! I also watched
fred_3.mpg, and there was a little fred sauntering around, obviously
very well cared for, and happy with his surroundings :-)

I would just like to thank the BEAM community for taking this idea
and making it go further, especially to Steve for making the kit
(yes, he has gotten in contact with me and we settled on a very
generous offer so that he could use the circuit in kit form), Andy
Pang and Dave Simmonds for being such vociferous Fred advocates,
Wilf, for being his inimitable self, and all the people who have
written to me asking for help and/or sending pictures of their Freds.
I might get a bit crabby some of the time, but be assured that I
appreciate every one of those emails!

Dave wrote:
> even though I didn't see so much as a copyright
> notice on Ben's pages.

I don't go much for copyright, I prefer to give people the benefit of
the doubt. The only stipulation I put on using any of my schematics
is that you must put a link to my site next to the schematic. Apart
from that, it's free to do with as you please!

Now for wilf's post:
--
However I am not happy with the FRED trigger mechanism now that I
understand
it's behaviour better. It does not seem very directional and draws a
fair
bit of current prior to triggering. It probably needs fine tuning of
the
component values for a given motor. It certainly is not as
predictable as a
1381 trigger but a bit of randomness can make life more interesting
especially for roving photovores.
--

I had the same problem, when I originally connected the 33k resistor
(as you have done) to the positive supply rail. When I moved the
resistor to the negative terminal on the motor, the Fred mechanism
latched really well. I can see from your schematic that doing this
will be very difficult, unless you can somehow trickle some current
through the base of the top driver transistors and then feed the 33k
from the collector of those transistors perhaps? Very tricky, I
can't see an elegant solution to the problem. I've tried to make a
Fred Head before, and haven't been happy enough with the results to
publish them. Good luck, it looks like you're on the right track :-)



Now, for all you newbies having trouble with your Freds, here's a
handy trick I use when debugging someone's Fred via email:

A) If you can see Fred's eyes flashing (no motor movement), then:
1) Grab a piece of wire, and connect one end to the negative
terminal on the capacitor. Put your Fred under a lamp, or put him in
sunlight, until the eyes start to flash.
2) Touch the wire to the base of the PNP transistor.
3i) If the motor moved, then the problem is with the 33k resistor,
the 3.3k resistor, the 0.22 uF capacitor, or the FLED connections.
3ii) If the motor didn't move, then the problem is with the
transistor connections.

B) If Freds eyes never flash (no motor movement):
1) Check the solar panel and capacitor connections.
2) Short out the capacitor, and then watch the FLEDs closely. If
one flashes faintly, then stops and doesn't flash again, then you may
have a bad motor connection.
3) If this doesn't happen, then go over the whole robot component by
component.

C) If the motor makes funny noises but doesn't fire:
1) Try putting a 1 uF cap across the motor terminals.
2) Try using a physically bigger storage cap (like a 2200 uF 16V).


D) If the motor fires strongly once when you put it in light, but
then is either weakly on all the time or stops and doesn't pop again:

1i) Your solar panel is too big. Put some tape across it or put it
inside, to lower the amount of current it can produce.
1ii) Your motors are too efficient. Put a 100 ohm resistor across
your motor terminals.
2) Send me some of your motors or solar panels, because you are
obviously too rich, and need to scavenge more (lower quality) parts.


Those are some of the more common problems, but I have had some
doozies that took a while to figure out what's happening!

Anyway, just thought I'd drop in and say "Hi", and once again thanks
to everyone for being so helpful and polite!

Cheers,
Ben
--
www.wollongong.apana.org.au/~ben