Alt-BEAM Archive
Message #00047
To: Victor Snesarev vsn@eel.ufl.edu, BEAM List beam@corp.sgi.com
From: "Ben Hitchcock" beh01@uow.edu.au
Date: Sun, 31 Jan 1999 17:30:09 +0000
Subject: [alt-beam] Re: New (feasible) photovore circuit?
I have done something very similar. Check out
http://wollongong.apana.org.au/~ben/alf/schematic.html
And guess what? Your idea does work, and work very well.
Ben
----------
>From: Victor Snesarev
>To: BEAM List
>Subject: New (feasible) photovore circuit?
>Date: Sun, Jan 31, 1999, 3:02
>
>Below is a circuit and a description of possible photovore. Since I have
>not built this circuit yet, I cannot be sure that it works, but the
>theory seems ok to me. I would appreciate any comments or suggestions
>that you might have.
>
>Also, I sending this message as text, and if viewed with fixed width
>font the schematic below should have correct proportions. I also put the
>schematic in graphics on my WWW site
>(http://www.eel.ufl.edu/~vsn/photovore_circuit.html).
>
>
> (+) (+)
> | |
> | ----[MR]----
> | |
> - /C
> RR ----[R1]----| B Q1
> - | \E
> | | |
> | N1 | (gnd)
> |-------[>o-----|
> | | (+)
> | | |
> - | /E
> RL ----[R2]----| B Q2
> - \C
> | |
> | ----[ML]----
> | |
> (gnd) (gnd)
>
>RR & RL = Photoresistors (CdS) right and left
>N1 = 74HC14 (Inverter with Schmitt-trigger input)
>R1 & R2 = 1k transistor bias resistors
>Q1 = NPN transistor (2N2222 for example)
>Q2 = PNP transistor (2N3906 for example)
>MR & ML = motors
>
>Circuit operation (at least how I expect it to work):
>
>Photoresistors (devices that change resistance in proportion to light
>intensity. More light = less resistance.) form a voltage divider. The
>voltage is "sensed" by the schmitt-triggered inverter which, depending
>on the difference between the voltage dropped by RR & RL, would output
>either a 1(+) or a 0(gnd).
>
>When the light source is left of the direction faced by the bot RL is
>lower than RR, so the voltage at the input of the inverter drops. The
>inverter output goes high. Q1 turns on. MR runs (ML doesn't run), and
>the bot turns left around the left motor.
>
>Opposite happens if the light source is to the right of the bot.
>
>If the light source is straight in front of the bot, and both CdS get
>the same amount of light, due to hesterisis (schmitt-trigger) the bot
>will turn in whatever direction it was turning before it was facing the
>light source (before entering the threshold region of the trigger). Once
>it turns far enough to cause the inverter input voltage to go above or
>below the schmitt-trigger threshold, it will turn in the other
>direction.
>
>I am not sure what to call the forward movement of such a creature, but
>it's almost like a walking gate (or is it just wishful thinking on my
>part?). A wide wheel base would be advantageous in this design.
>
>I should also say, that I realize that the design is not very efficient.
>The inverter would keep switching, and doesn't CMOS need more current
>for switching then driving a constant voltage? Also, below 2V (lowest
>operational voltage of CMOS) the inverter would not work.
>
>Anyway, please let me know if you think this might work and include any
>other comments.
>
>Victor
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