Alt-BEAM Archive
Message #00044
To: BEAM List beam@corp.sgi.com
From: Victor Snesarev vsn@eel.ufl.edu
Date: Sat, 30 Jan 1999 22:02:37 -0500
Subject: [alt-beam] New (feasible) photovore circuit?
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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