In a message on Sun, 06 Jun 2004 12:51:45 -0400, wrote :
"JS> Chris wrote:
"JS> > A few questions regarding Tortoise Switch Machines:
"JS> > 1. I have lost the spring wire for a Tortoise Switch machine. What would
"JS> > make a suitable replacement? Where can I find it?
"JS> "Music wire" is available at a good hobby shop. It is a very springy
"JS> steel wire. It should be possible to make a new spring wire from a
"JS> piece of music wire of the proper diameter.
"JS> > 2. I'm considering using Red/Green LED's or bicolor LEDs to indicate
"JS> > position on control panel. As an electrical newbie, what is a good LED
"JS> > to use for this purpose? (Manufacturer/Model number)? Thanks.
"JS> LED's are pretty much all the same. They differ only in color, physical
"JS> size, and maximum rated current. Used to be all LED's required 20
"JS> milliAmperes (mA) to light to full brilliance. Now a days a lot of LEDs
"JS> out there are "hi efficiency" types that only need 10 mA. All Light
"JS> Emitting Diodes are rectifiers. Biased forward (DC applied plus to
"JS> minus) they light up, and conduct like a closed switch. They have NO
"JS> internal resistance to limit the current thru them. You have to supply
"JS> an external resistor of the right value otherwise they blow out.
"JS> Instantaneously. Which converts them into Darkness Emitting Diodes
"JS> (DED). For 12 volts DC, 470 ohms is good for the 20 mA types, 1K is
"JS> about right for the 10 mA types.
"JS> Biased in reverse (minus to plus) LEDs are dark. If the reverse bias
"JS> exceeds 6 volts many LEDs blow out and become DEDs. So you want to be
"JS> careful to install the LED the right way round. This is easier said
"JS> than done because most LED's do not bear polarity markings. I use an
Commonly, one lead is a little longer than the other. Some LEDs may
also have one side 'flattened' to indicate polarity.
Have a look at this PDF file (a page out of the Mouser Catalog) for
details on LED polarity markings:
The Cathode gets wired to a "-" side of of the supply. The Cathode is
the shorter lead and the lead next to the flattened side of the LED
(some of the larger LEDs have a flattened side).
"JS> ohm meter to determine which polarity makes a LED conduct.
"JS> Bi colored LED's are actually two LEDs in the same package, wired in
"JS> opposite directions. Biased one way shows one color, reverse the bias
"JS> and you get the other color.
"JS> I haven't wired tortoises my self, but they have a permanent magnet
"JS> motor. Apply DC of one polarity and it turns one way, reverse the
"JS> polarity of the current and it runs the other way. The motor draws so
"JS> little current that the power is left on the motor all the time, it
"JS> doesn't mind being powered up even when the turnout has reached end of
"JS> travel and stalled.
"JS> There are several ways the wire the LED.
"JS> 1. You can put a bi colored LED in series with the tortoise motor IF
"JS> and ONLY IF the it draws less than 20 mA. I seem to remember they draw
"JS> 50 mA but I'd have to check a data sheet to be sure. This circuit has
"JS> the benefit of indicating good wire all the way out the the tortoise and
"JS> back. If the tortoise fails or the wire breaks, the LED doesn't light
"JS> in either direction. A useful trouble shooting aid.
"JS> 2. Put a bi colored LED with a current limiting resistor across the
"JS> tortoise motor.
"JS> This works, but the LED will stay lit even if there is a broken wire
"JS> running out to the tortoise.
"JS> > 3. Does Circuitron provide "application notes" as an addendum to their
"JS> > printed instructions? How does one go about attaining them? Just write
"JS> > to them and ask? Any payment/SASE required?
"JS> Try the circuitron web site. They must have one.
"JS> > 4. I'm new to wiring these but I think I know what to do. I see that the
"JS> > machine has 2 SPDT switches on it. I was going to use one set to power
"JS> > the frog. What sorts of applications do people use the other set for?
"JS> > Thanks in advance.
Robert Heller ||InterNet: firstname.lastname@example.org
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