Subject:
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Re: Use RCX motor output to switch devices
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 30 Aug 2002 16:11:55 GMT
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Viewed:
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986 times
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"Da Byte" <dabyte@hotmail.com> wrote in message
news:H1nuMp.CMK@lugnet.com...
> I live in The Netherlands, so instead of Radio Shack I buy at Conrad. Is
> there a universal transistor description in this case?
Try looking for 2N2222A. 2N4401 should also work.
They're both fairly common.
> > it's important to keep the transistor in saturation to avoid it • overheating.
>
> What does "in saturation" mean exactly?
Sorry... basicly, it means "fully on". When the transistor is
fully on the voltage between the collector and emitter is about
0.3V or so. This means most of the voltage drop occurs
across the load (~11.7V) and that is where most of the
power is dissipated. If you start reducing the current
supplied to the transistor base, the collector-emitter
voltage will eventually start increasing and more power
(i.e. heat) is dissipated by the transistor. Eventually,
the power dissipated exceeds the transistor's rating and
you get that lovely "fried electronics" smell.
> > Also, don't try to hook up more than one switched device to the RCX in • this fashion.
>
> The transitor will blow up (overheat), because of the large current (I)
> through it?
No, just that because the motor outputs can reverse
polarity and you're dealing with more than one output,
you can easily end up with a short circuit if you don't take
care to keep track of what is "ground". It can be done,
I was just trying to caution that you should fully understand
the circuit if you're going try anything more complicated.
> > To be safe try the circuit first by connecting it to a 9v
> > battery box (try both polarities).
>
> I was planning on doing that. I have a 9.6V, 300mA powersupply, I suppose
> that works just as well for testing purposes.
Perhaps. But again you have to be careful about ground
issues. If it's an electrically isolated supply then it's ok.
Otherwise, if you connect the negatives of both supplies
to circuit ground, they could fight one another. Just a
plain 9V battery will work for testing purposes.
Mark
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Message is in Reply To:
 | | Re: Use RCX motor output to switch devices
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| Thanks for the help, Mark! I have a few questions still (I'm a novice at electronics). (...) I live in The Netherlands, so instead of Radio Shack I buy at Conrad. Is there a universal transistor description in this case? (...) What does "in (...) (22 years ago, 30-Aug-02, to lugnet.robotics)
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