Simple Power-On-Rail Indicator

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D

Dougget

Member
I finally got a chance to do some experimenting. My goal was to have some type of indication when I had power on a given section of rail, siding, spur, etc. Here's what I came up with.

PowerOnRail.png


What do you think?
Doug
 
Hi Doug, Is this circuit for DCC? If it's for DC have you done some calculations for when let's say a loco is going slow?

Cheers Willis
 
Regular DC setup. No I have not done the calc for a slow train (lower voltage). I did experiment with my powerpack, and the LED lights at a lower voltage setting, but not very bright.

Tough to deal with variable voltage, I've been looking for a circuit to do this, but I've had no luck. I'll keep at it until I find a solution that works for me.

I'd rather have a dim light then magic LED smoke :)
Doug
 


How about using a double pole, single throw switch, and a seperate power supply for the indicator LED? That would eliminate the issue with the variable track voltage.

I tried to draw a schematic in Paint, but it didn't turn out too well.

You could even use the seperate power supply to power other accessories on the layout.

Rotor
 
Last edited by a moderator:
Rotorranch said:
How about using a double pole, single throw switch, and a seperate power supply for the indicator LED? That would eliminate the issue with the variable track voltage.

I tried to draw a schematic in Paint, but it didn't turn out too well.

You could even use the seperate power supply to power other accessories on the layout.

Rotor
Click to expand...

Absolutely right, and only one LED would be necessary as the polarity wouldn't change on the separate power supply. If you had a whole lot of these, they can be all run off one power supply set to supply the right voltage, and no resistors would be needed.
 
I'll keep at it until I find a solution that works for me.
Click to expand...

Ok here's a start for you. Forget the AC tag (it'll work for both polarities of DC also) now as long as you have 5 volts of power on the track you'll have plenty of output. Do a little calculation and add your circuit to it.

PowerSupply.png


Cheers Willis
 
Willis read my mind, I was going to suggest a circuit exactly like that. :)

Only change I'd make is go with a 3.3V regulator - that way the LED will come on quicker.

Mark
 
I'd make is go with a 3.3V regulator
Click to expand...
Yep good idea, the cct drawing is one I had on Photobucket, was hoping some more would jump in with more ideas. I think I'd try reducing the capacitor to 50 uf or 25 mf for a quicker on/off action on the leds

Willis
 


Doesn't that circuit need a resistor to give the output voltage, as with an LM317? Just a query, I have only ever used the 317's for output voltage
 
Doesn't that circuit need a resistor to give the output voltage,
Click to expand...
Well yes, but the idea was to add Dougget's circuit to the output and that would be the load. Again the resistor would have to be recalculated to drop from 5V or 3.3V as the case might be for the 2.2V and 25 ma LED current.

Cheers Willis
 
Shortliner2001 said:
Doesn't that circuit need a resistor to give the output voltage, as with an LM317? Just a query, I have only ever used the 317's for output voltage
Click to expand...

Are you referring to the programming resistor to set the voltage? If so the answer is no - that 7805 IC is a fixed voltage regulator. But you would still need a small current limiter resistor in series on the LED to drop the voltage down a little.

You mention the 317 - one cool thing about the 7805 and the 2950 (3.3 volt regulator) is they lock voltage with as little as about .5 volts over their rating - in other words, when the input voltage gets to about 5.5 volts, the 7805 locks at 5v on the output. With the 317, it requires at least 2 volts higher than its programmed output. So to achieve 5v, it needs at least 7v in. (Just a bit of useless trivia to get you through your day. :) )

Mark
 
Alright, there's been some good suggestions, bi-color LEDs, IC's etc... Can someone draw up this circuit for me? (Part numbers would be very helpful too.)
Thanks,
Doug
 
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