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Reply-To: "Dave M"
From: "Dave M"
Subject: Re: Circuit Design Question for RF Remote
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Date: Sun, 05 Jan 2003 23:01:34 GMT
NNTP-Posting-Date: Sun, 05 Jan 2003 23:01:34 GMT
Organization: AT&T Worldnet
"skips" wrote in message
> It's been 17 years since I took circuit analysis in school and I have
> what I hope is a simple design question. Any help is greatly
> appreciated. I am trying to remotely light some LED's powered by a 3
> volt battery. Using a transistor as a switch - when the transister
> receives a small control signal - it completes the basic circuit and
> lights the LED's. The transistor receives it's control signal from a
> small R/F receiver (an RXM-433). My question is in this area.I would
> like to power the "receiver-on" circuit with the same battery that
> will power the LED's. In other words, the 3-volt always-on circuit to
> the R/F receiver will send a control signal (when a transmit is
> received) to the transistor acting as a switch for a simple circuit
> that uses the same 3 volt power supply. I hope I'm making sense here.
> I have posted a diagram of this circuit and this site,
> (http://www.pan-view.com/led/circuit.jpg). I would appreciate it if
> someone could look at this and tell me what's wrong or right with it.
> Or perhaps provide another alternative? Thanks for your help.
The LED is in the wrong place. Put it between the transistor's collector
and battery (+). Also, put a resistor of about 4.7K between the
transistor's base and the receiver's control line and a resistor of 100K
from base to emitter. Also, you might think about putting a small resistor
(around 56 - 62 ohms) in series with the LED to limit current through it.
Otherwise, you're depending on the transistor to limit the current through
the LED, which you can't predict. That will save the battery also.
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