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[DPRG] Line Following

Subject: [DPRG] Line Following
From: Dale Wheat dale at dalewheat.com
Date: Sun Aug 31 09:53:01 CDT 2003


But a relay is a switch, just like a transistor is a switch.

A truly simpler line follower would use the large, 1W CdS photocells from
American Science & Surplus:

http://www.sciplus.com part number 32155 3/$2.25

... with two small (<1W) motors and a bright incandescent light bulb (and a
battery and some wire...).  Each photocell would be used to directly govern
the current going to each motor.  On our course (white line on black
background), you would need to swap the left and right sensors, so that as
the left sensor registered less light (straying into the lefthand black),
less current would flow through the right motor, inducing a right turn.
Note that this is how the human body works (left side nerves connected to
right side of brain, etc.).

This model uses no "switches" at all.


Dale Wheat
(972) 486-1317
(800) 330-1915, access code 00

----- Original Message ----- 
>From: "Earl Bollinger" <earlwbollinger at comcast.net>
To: "'Randy M. Dumse'" <rmd at newmicros.com>; "'DPRG'" <dprglist at dprg.org>
Sent: Saturday, August 30, 2003 9:01 PM
Subject: RE: [DPRG] Line Following

> No transistor line following robot.
> I believe it's possible to build a zero transistor line follower robot.
> You use two small motors, and a small low power relay, with a solar cell
> or cadmium sulfide photocell in series with the coil. One motor runs at
> 1/4 to 1/2 speed, the other at full speed through the relay. The relay
> coil is controlled by the photocell being on or off. The trick is you
> run a potentiometer in parallel with the photocell, and adjust it so
> that the relay is almost on, but not quite. This is the ancient
> technique they used with vacuum tubes in old computers to improve their
> clock speed.
> Thus there is no transistors involved.
> You can even run a second "latching" relay with a similar setup too.
> Except when you trip the relay it opens the motor power circuit and the
> robot stops when it reaches the end.
> The real trick is starting it without touching it. You guessed it a
> "second" latching relay with a photocell that you trigger using a
> flashlite to trigger it on. I'd probably use a shield tube to protect
> the start photocell from the daylight and other stray light sources.
> I know I'll have to find some time to build one.
> Anyway, I see no reason why one couldn't get a no transistor line
> following robot to work, except maybe the relay(s) would get stuck.
> Speed might be critical as it can't go too fast or the relays couldn't
> keep up.
> On a further note, after my experiments with multi sensor line following
> sensors, I am able to get my little Crystal robot to run the course very
> smoothly, but at a speed price. I think we need to have the robot be
> able to "anticipate" the upcoming direction changes so it can start the
> turn appropriately at speed.
> This is the same thing people do, they see a turn coming up so then they
> start taking the appropriate action to negotiate it. Thus the robot
> needs to know what it's doing now on the line versus what the line is
> like up ahead a short distance.
> Before anyone goes crazy on that one, remember that a UPS
> (uninterruptible power supply) can actually anticipate the impending
> power failure to start up the high voltage switcher, in order to give it
> time to ramp up the power before it switches over to battery power from
> the mains. A UPS can do this before the AC mains power actually fails.
> Now that's a pretty good trick.
> I've always been fascinated by that one.

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