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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Wed, 4 Sep 2002 12:35:16 GMT
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Viewed:
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1296 times
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In lugnet.robotics, Mark Riley writes:
> > > ...
> > > 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.
Can't I secure my circuit against this 'switch', or even use it to achieve
the same with output in both directions: by using diodes for example?
I have tried to model something like that in software called "Crococlips"
(screenshot: http://dabyte.dynu.com:7070/html/crocclips.gif).
> > > 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.
And how exactly do you 'make' a ground in your circuit? Connect it to the
ground wire of a wallsocket or powersupply?
> > > > ...
> > > > The transistor is easy to find (Radio Shack in the U.S. carries it).
> >
> > > I live in The Netherlands, so instead of Radio Shack I buy at Conrad. Is
> > > there a universal transistor description in this case?
> >
> > BC557
>
> This appears to be a PNP transistor according to this datasheet:
>
> http://www.semiconductors.philips.com/pip/bc557
>
> The transistor in the circuit diagram I provided is NPN. Also, the
> maximum current the BC557 can handle is only 100ma (I think
> you needed 250ma or so). In other words, this won't be a
> good substitute for the MPS2222A.
Yes, I know I need an NPN type. Conrad also displays the BC557 as being an
PNP type.
> BTW, I went to the Conrad (International) website and I couldn't
> find any semiconductors listed, so you might need to find another
> supplier.
Yes, they do have it (on the dutch mirror) You can find the table of
transistors I use at
http://www.conrad.nl/cgi-bin/conshop/ConShop.pl?TK_PAR[USER_ID]=0101090520997101431&TK_EV[SHOWPAGE]=&TK_PAR[PAGEID]=92634&TK_PAR[MEDIUM]=
N.B. cut 'n' paste the URL (you also may have to scroll down quite a bit for
the table).
Thanks very much again, Mark!
Grtz.,
Remko
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Message has 2 Replies:
 | | Re: Use RCX motor output to switch devices
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| In response to the following, Ran Talbot e-mailed me. (...) "A "full-wave bridge rectifier" (as used in AC-to-DC power supplies) will do that nicely. I believe some of the Lego "active" sensors do this. I don't know if anyone makes an AC (...) (22 years ago, 8-Sep-02, to lugnet.robotics)
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Message is in Reply To:
| | Re: Use RCX motor output to switch devices
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| (...) This appears to be a PNP transistor according to this datasheet: (URL) transistor in the circuit diagram I provided is NPN. Also, the maximum current the BC557 can handle is only 100ma (I think you needed 250ma or so). In other words, this (...) (22 years ago, 3-Sep-02, to lugnet.robotics)
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