Subject:
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Re: power source
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 13 Feb 2002 12:11:24 GMT
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Original-From:
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Mathias Uhr <uhr@=spamcake=mathias.net>
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Reply-To:
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uhr@mathias.+NoMoreSpam+net
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Viewed:
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835 times
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hi!
> What you do is you connect the positive wire from your power supply to
> pin 1* of the 7809. Then connect the ground of the RCX and the power
> supply to pin 2. Connect pin 3 to the positive battery terminal on the
> RCX. I also put a diode in between pin 1 and the power supply.
> Also note that your supply voltage needs to be at least 1.2 volts above
> your output voltage. An unregulated 9v power supply should do fine,
> because they usually give a higher voltage.
if you use an unregulated supply, you need to add a big capacitator
in front of the ic (after rectifing of course)!
generally, they advice to use an electrolyt capacitator of sufficient
size (there are formulas for this) for filtering and a small tantalum
or ceramic one in parallel to smooth out fast peaks and avoid oscillation.
usually, you add such a pair of (smaller) capacitators behind the
regulator too.
see a circuit schematic here:
http://www.aaroncake.net/circuits/supply6.htm
you will probably come to the conlusion that it is easier and safer
to buy a power supply that is cleanly regulated to 9v dc...
please note that power from the batteries is not regulated inside the
rcx! (on the contrary to the power plug of rcx 1.0) if you connect a
power source to the battery clips, you need to make sure that it is
well rectified and regulated!
(for more details about the rcx's internal power regulation see one
of my earlier posts at http://news.lugnet.com/robotics/?n=16677
hope this helps, greetings
mat
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Message has 2 Replies:
 | | Re: power source
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| (...) What I meant when i said "unregulated" was a power supply without a 78xx in it. The power supply that I am using consists of a transformer, rectifier (4 diodes) and a 4700uf cap. This means that while it does give a clean voltage, that voltage (...) (23 years ago, 13-Feb-02, to lugnet.robotics)
| | | Re: power source
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| (...) Actually, it is regulated (speaking as one who has had to replace the fuse that comes before the regulator). Think about it. It has to be. The batteries provide 9V, the MCU requires 5V. If it wasn't regulated, you'd kill it. There is also a (...) (23 years ago, 14-Feb-02, to lugnet.robotics)
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Message is in Reply To:
| | Re: power source
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| You're right, I didn't realise it wasn't very clear. What you do is you connect the positive wire from your power supply to pin 1* of the 7809. Then connect the ground of the RCX and the power supply to pin 2. Connect pin 3 to the positive battery (...) (23 years ago, 13-Feb-02, to lugnet.robotics)
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