Alt-BEAM Archive

Message #00319



To: Evan Dudzik evandude@yahoo.com
From: Bob Shannon bshannon@tiac.net
Date: Wed, 10 Feb 1999 21:52:36 -0800
Subject: [alt-beam] Re: VORE N MORE... help me.


Evan Dudzik wrote:
>
> Help me... I came up with a sort-of schematic for VORE N MORE but i
> cant seem to figure out how to integrate the the light sensor so it
> knows when the light is too low to go on and starts using the power
> from the large cap to run really fast towards a new light.
> can anyone help me? i have the cap and everthing, all i need is the
> light sensor that actually lets the cap discharge to the rest of the
> circuit.

Wow, this is the second request for Vore-n-More info is less than 20
minutes.

And my bots are not even on the BEAM web ring!

Vore-n-more uses a Radio Shack NPN phototransistor. It looks like a
large, clear LED with two leads.

I call this circuit the Smart Capacitor, as it will slow or stop the
photovore (which should be near light, right?) to recharge the
supercapacitor energy reserve. Then, when it gets dark, this stored
energy reserve is fed into the photovores main drive capactiors for a
burst of high speed movement towards another source of light.

It really works quite well, and I have had several requests for the
circuit. Here it is:

Start with a normal photopopper photovore. It should have a largish
solar cell, like a 3733, or a pair of 2224 cells from Solarbotics.

You will need to add (to plan ahead for this):

A 'floater' solar cell(s), another 2224, or a pair of Sanyo AM-1437
cells (as in the original Vore-N-More) wired in PARALLEL.

A 1N5817 Schottkey diode (do not substitue non-shottkeys here).

A Panasonic Gold Series super capacitor, I used 1.5 Farads, a larger cap
will cause a hungery Vore-n-more to sleep longer in the sun, and run
longer in the dark. Smaller values will give shorter sleep and burst
mode times of course.

A NPN phototransistor (like the Radio Shack part I used). This should
be a two lead type, or cut off the base lead from a three lead device,
just so electrostatic charges dont cause odd behaviors.

A 5.1 K resistor. I used 1/16 watt devices to 'hide' them in the main
drive capacitor banks wiring. This value sets the darkness detection
threshold, and may vary if you use a different phototransistor.

A PNP switch transistor, like a 2N3906

A discharge rate control capacitor. I used 75 ohms. This will set the
burst mode discharge rate, how fast your Vore-n-more will move when its
running from the super capacitor.

If this value is too low, your Vore-n-more will lock up, and spin in
circles when the lights go out. (maybe you like this?) If its too high,
your photovores SE's may never fire.

(Random Tip - For the photovore's drive capacitor, I often like to use
an array of smaller capactiors wired in parallel rather than a single,
larger value cap. This way all their series resistances are in parallel,
making a 'more efficient' main drive capacitor. Its also possible to
arange the main drive capacitor around the rest of the photovore, rather
than the other way around, see the Eat at Joe's photovore to see this
trick in a different form.)

How does it get hooked together?

Its so simple, you'll kick yourself once you get it.

Run a wire from the positive side of your solar cell, to the negative
lead of your 'floater' cell(s). This puts your floater cell in series
with the main solar cell.

But your not supposed to connect solar cells in series, right?

Well, sometimes. I'll get to that later...

Connect the positive side of the floater cell(s) to the anode of the
schottkey diode. The cathode of the diode connects to the positive side
of the super capacitor. The negative side of the super capacitor is
connected to the photovores ground connection.

Next, we make a voltage divider circuit with the phototransistor and
5.1K bias resistor. The collector of the NPN phototransistor is
connected to the positive side of the super capacitor. The emitter goes
to the 5.1K resistor. The remaining lead of the 5.1K resistor goes to
the main photovore ground (negative side of the main drive caps).

Next, we add the PNP switch transistor. The PNP's emitter goes to the
collector of the phototransistor. The base of hte PNP connects to the
emitter of the NPN phototransistor.

(I mounted this transistor right onto the NPN phototransistor by
notching out the clear plastic and gluing the PNP transistor into the
notch. You can sorta see thin in the guts view photos.)

The collector lead is the output of the smart capacitor circuit.
You can connect this to any small device you wish to operate, like a
LM3909 LED flasher.

To drive the photovore with the output, we connect a 75 ohm resistor
from the collector of the PNP switch to the positive side of the
photovore's main drive capacitor. You may want slower bursts, and may
get away with faster ones as well, by experimenting with the value of
this resistor.

So how does it work?

First, lets assume that Vore-n-more has zero power. Its dark, so
nothing happens, and we are asleep.

When the sun rises, the super capacitor acts like a dead short, and
prevents the photovore from moving. We are now in feeding mode.
The super capacitor voltage slowly begins to rise.

Once the super capacitor voltage rises above 2.5 volts or so, the
photovore begins to wake up, and seek light normally. We are awake.

The voltage from the photovores main solar array is now changing,
charging up for each step. The floater solar cell takes this changing
voltage, and adds to that, so we are using a peak charging voltage that
is higher than the trigger voltage of the solar engines.

The schottkey diode prevents the super cap from discharging through the
solar cells in the dark. We must use a schottkey to keep the voltage
drop across the diode very low.

This is critical, we must charge the supercapacitor to a voltage higher
than the SE's trigger point. For 1381-J triggers, a good 'fully
charged' voltage would be around 3 volts. Once we reach this point, we
are ready for burst mode behavior.

Light falling on the NPN phototransistor holds the transistor in a state
where is starves the PNP switch transistor off. As the light level
falls, the phototransistor will switch off (at a point set by the 5.1K
bias resistor). This in turn switches the PNP transistor on.

Now we are in burst mode. The light level has fallen, and the switch is
on. The super capacitor begins to discharge through the switch
transistor and the 75 ohm discharge rate resistor. The power is used to
drive the photovore. With 75 ohms, it will move FAST, and still be
highly phototropic. The photovore will lock onto a dim, distant light
source in another room, and track it perfectly.

Your Vore-n-more will also move for quite a distance in a burst. With a
1.5 farad cap, you will get several dozen of steps per charge.

This circuit can be used to drive a photovore, or even a Turbot (right
Dave?), perhaps even a solarized walker as well. It can drive SE's,
microcores, and bicores.

I've even used it to power up a PIC when it gets dark.

On my beam robot site, you will also see a Symet (Triluminary) that
carries around a smart capacitor circuit and a LM 3909 LED flasher, so
it blinks away (for about half an hour on a 1.5 farad cap) when it gets
dark and stops moving. In this robot, the solar cell that charges the
super capacitor is not connected to the drive capacitors in any way, yet
the two system still interact perfectly.

One list reader has already made a .GIF (or .JPG ?) file that shows the
basic circuit. The interconnection of the basic smart capacitor curcuit
and the photopopper should be fairly clear in the description above.

I'll try to get a full diagram onto the web site soon.

I hope this gets some people playing with the circuit. There are
several variations you can try:

Replace the PNP switch with a PNP darlington.

Replace the NPN phototransistor with a photodarlington.

Replace the floater cell and schottkey diode with a coin cell and series
resistor. This is the 'smart socket' varient. You can see this circuit
in the Symet Zaraam on the web site, where it flashes a LED just like in
Triluminary.

Enjoy, and let me have any questions if I've left out any important
details.

------------------------------------------------------------------------
eGroup home: http://www.eGroups.com/list/alt-beam
Free Web-based e-mail groups by eGroups.com

Home