Alt-BEAM Archive

Message #01103



To: "'Les Davis'" upnrunin@bc-alter.net,
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Mon, 1 Mar 1999 00:34:27 -0800
Subject: [alt-beam] New photovore circuit



content-type: text/plain


Thanks for that Les (RC Pitstop's just down the road from me)! In the
spirit of a little local group support thing, here's my new photovore
circuit. I have a version which is suitable for solar power but got to do
some more tests. Note the (I think) unique photodiode "discriminator". It
detects the difference between photo diode leakage rates ie light level and
flips the output. Somewhat similar to a BiCore in behaviour but fewer parts
and only oscillates when the photo diodes are in balance. I use green LEDs
for photo diodes and they work fine. The complementary outputs of the
discriminator circuit are buffered with double 240 gates to drive one side
of each motor. The thing waggles towards the light as each motor is
alternately driven. The 1000pf feedback cap can be varied to
increase/decrease the left/right motor on times. These on times are also
dependent on light level. It makes for a interesting (ie complicated)
response to light conditions. The reverser is also kind of different : it
references the motor commons to +V or 0V and thereby reverses direction for
5 or 6 seconds when the feeler is closed. Pretty compact circuit design with
few components, suitable for small motors. The design was tested on a
breadboard with little camcorder gear motors. I will try a mobile platform
next. Feed(back) me!
<> Wilf Rigter
mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411

> -----Original Message-----
> From: Les Davis [SMTP:upnrunin@bc-alter.net]
> Sent: Sunday, February 28, 1999 11:02 PM
> To: Chiu-Yuan Fang; Keagan Schpfer
> Cc: beam@corp.sgi.com
> Subject: Re: Finding Motors??
>
> On Scott Road at 103-8386 120th. (Surrey/Delta) a store called RC Pit Stop
> handles some reasonably priced (for Canada anyway) servo motors ($17.00
> ea.). They get them from a place called R/CHMOND RC Supply Ltd., in
> Delta,
> BC. They're labled RRC-31303 HITEC HS-303 standard sport OEM Servo. The
> reason I bring these up is, I've used them on several walkers and have
> been
> driving them with a 74HCT245 each.
>
> PS..... Chiu, I would still like you to come out and speak to my
> robotics
> group someday.
>
>
> Les Davis
> -----Original Message-----
> From: Chiu-Yuan Fang
> To: Keagan Schpfer
> Cc: beam@corp.sgi.com
> Date: Sunday, February 28, 1999 1:29 PM
> Subject: Re: Finding Motors??
>
>
> >Probably not, although it really depends on the quality of the motor
> inside
> the
> >servo.
> >
> >Chiu
> >
> >Keagan Schpfer wrote:
> >>
> >> >
> >> >Hobby servos for the Radio Control types are the only steady source
> for
> >> gear
> >> >motors. Most need an h-bridge to drive them though.
> >> >
> >> >http://www.towerhobbies.com/
> >> >
> >> >Chiu
> >>
> >> Con't you drive them with 74HCT245's?
> >>
> >> ______________________________________________________
> >>
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Attachment: photovor1.gif

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