Subject:
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RE: 5VDC Voltage Regulation
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 27 Sep 1999 16:04:20 GMT
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Viewed:
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628 times
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> I'm in over my head with a project and need some help. I'm
> trying to use an RCX
> output port to control a 5VDC SPDT Relay from Radio Shack (part
> #275-240A). I
> need to limit the voltage of the port to 5 volts. How can I
> accomplish this?
> Is a voltage regulator IC correct? Alternatively, does anyone
> know if putting
> excessive voltage across this relay (max. VDC is listed as 6.5)
> for long periods
> of time will damage it? I have put as much as 8.3VDC across the
> coil for a few
> seconds without damage.
The RCX puts out a variety of waveforms depending on the power level.
If you have acecss to an oscilloscope, you can see that the higher
power levels give you more "on time" that lower levels.
The DC level at full on is about a diode drop below the battery
voltage. If you were to set the power level to, say 4, there should
be enough DC level at the rate the PWM changes that the relay
will not chatter.
Another solution is that the relay will take MUCH less current than
the motor ever will. You could drop the voltage using a zener diode
in series with a dropping resistor. You could also put a couple
of diodes in series with the relay coil to drop the voltage. The
RCX won't work with low batteries anyways.
If this is too complex, you'll want to look at some basic electronics
texts, the Forest Mims volumes from Radio Shack are pretty decent...
Hope this helps
Cheers,
Ralph Hempel - P.Eng
--------------------------------------------------------
Check out pbFORTH for LEGO Mindstorms at:
<http://www.hempeldesigngroup.com/lego/pbFORTH>
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Reply to: rhempel at bmts dot com
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Message has 1 Reply:
 | | Re: 5VDC Voltage Regulation
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| Ralph Hempel <rhempel@bmts.com> wrote in message news:000001bf0901$f5...@pro150... (...) I would just put a 33Ohm 1/2W resistor in series with the relay coil. According to the spec for the relay, the coil wants 5V at 90ma. The RCX outputs about 8V (...) (25 years ago, 27-Sep-99, to lugnet.robotics)
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Message is in Reply To:
| | 5VDC Voltage Regulation
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| I'm in over my head with a project and need some help. I'm trying to use an RCX output port to control a 5VDC SPDT Relay from Radio Shack (part #275-240A). I need to limit the voltage of the port to 5 volts. How can I accomplish this? Is a voltage (...) (25 years ago, 27-Sep-99, to lugnet.robotics)
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