03273 [alt-beam] BEAM servo driver

Alt-BEAM Archive

Message #03273

To: beam@corp.sgi.com
From: Ian Bernstein ian@beam-online.com
Date: Fri, 14 May 99 16:26:12 -0600
Subject: [alt-beam] BEAM servo driver

--Emailer_-1284367346
content-type: text/plain; charset="US-ASCII"

After seeing Wilf's version of a servo motor driver I decided to come up
with my own version (see attachment). It uses a bicore (not suspended) to
create the 2ms or so pulse required to move the servo. I bread boarded it
and tested it using a model FP-S148 hobby servo.

Circuit notes----
The cool thing that I found is that you can change the position of the
servo just by turning the 50K pot. The range of movement is 0K (servo is
all the way to the left) and 12K (servo is all the way to the right). The
chip is a standard 74HCT240 with the enables tied to ground.

Things you can do with the circuit----
You can make an effective motor driver by building two of them circuits.
Hooking the outputs of each circuit the the white wire of the servo. the hard part to explain - see bottom of message> Build each circuit
using it's own enable on the 240. Now what you have is two inputs (the
enables of the 240) which can then be hooked up to a bicore,
microcore.... (in effect it's just a motor driver just like the H-bridge,
245 driver....) but it can be tuned using the 50K pots to whatever
positions you want the motor to be in. Cool huh!

Bad explanation of a 74xxx240 and it's enables----
If someone else wants to elaborate on this please do! For a better
understanding of what I'm talking about goto my site and download the
data sheet for the 74HCT240 (do a search if you can't find it). OK,
inside a 240 there are 8 inverters and 2 enables. Each of the enables is
connected to 4 of the inverters (see data sheet to see which ones). Now,
think of the inverters as an inverting switch. When the enable in
connected to ground all the inverters that that enable is connected to
are open and are acting just like an inverter. But when the enable is
connected to positive it closes all the inverters that it's connected to
(so basically the switch is off). You can use the 240 as an effective
electronic switch.
So what I mean is that when you build the circuit that I've enclosed you
want to have both the inverters connected to the same enable.

I'm sure I'm going to get lots of questions about this one =)

I'll draw up a complete schematic and upload it to web site on my next
update.

*-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-*
Ian Bernstein "aka - Synet" The Master Builder

E-Mail - Ian@beam-online.com
BEAM Online - http://www.beam-online.com
Quote - I feel that if a person can't communicate, the very least
he can do is to shut up.
- Tom Lehrer

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--Emailer_-1284367346

Attachment: Servo1.jpg

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end

--Emailer_-1284367346--

3274 Fri, 14 May 99 16:55:39 -0600 [alt-beam] Re-tinning Solor cells "James Anderson" , "beam" Ian Bernstein >The blob of solar on one of my solarbotics cells has broke off a while ago; I
>got too greedy, and tried to trim the lead I'd connected to it to short and
>"POP!". It's likely a lost cause, as I can't even find any voltage with my
>multimeter, but if any of you know an ingenious way to savage the solar cell,
>I'd be very glad to hear about it.

The way I do it is to go to an auto supply store and get a "window
defroster repair kit". It includes a small bottle of a brown liquid, a
brush and a paper thing. The brown stuff is like a conductive glue so all
you need to do is apply a small amount of the stuff to the wire and pad
and glue it on. It takes awhile to dry so you'll need to let it sit over
night. In the morning check to see if your getting a voltage and if you
are cover the whole pad with hotglue or epoxy so it won't pull off (the
brown stuff isn't a very good glue).

BTW: Always cover the pads on your solar cell after you've soldered the
wire onto it with epoxy so they won't pull off.

*-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-*
Ian Bernstein "aka - Synet" The Master Builder

E-Mail - Ian@beam-online.com
BEAM Online - http://www.beam-online.com
Quote - A synonym is a word you use when you can't spell
the word you thought of first

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