Hi all. I use a variety of occupancy detectors for my block signals but what they have in common is that they have a (-) negative output for both the clear and occupied signals with a common (+) positive. . For bipolar LED signals I need to reverse the polarity to change the signal from green to red. I can do it with relays but I'd rather do it electronically but I'm not sharp enough on electronics to figure it out. Any suggestions?
Thank,
bud
Welcome.
Nothing wrong with doing it using a relay. If you understand it, that will make it easier for you to troubleshoot if you ever have to.Some Bi-Polar LED's have three leads. You may be able to find some signals that use them. Just make sure that the common lead is for the Positive voltage.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
I have done this with two lead bipolar LED's using a TTL inverter chip some years ago. I use to take 74LS240 chips, eight inverters in a IC, out of surplus equipment, plus they were pretty cheap if you knew which surplus house sold the.
If you are not sharp enough with electronics. the relay may be the way for you to go.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
If it's easy enough to replace the LEDs, I'd look for three-lead, 2-color LEDs and use those. I have several of them on my layout and they work fine. They're quite inexpensive, less than the cost of a relay.
It takes an iron man to play with a toy iron horse.
Rich,
Thanks for your reply. I can get the chips you mentioned, could you tell me how I should hook these up to change the polirity to my signals. By the way th signals are two leed LED's.
Thanks,
Bud,
If you don't have many LEDs, switching them to 3 lead as mentioned above, could be a lot easier. Just a thought. Particularly in trouble shooting.
Richard
the reason I don't replace the LED's is that the manufacturer does such a nice job of making the signals look real as opposed to my rather crude attempts. I've used very thin 'electromagnet' wire but attaching that to the LED lead is my downfall so I've resorted to factory made but I bought a number of 2 lead signals on ebay without thinking it all the way through and now I'm determined to make them work!
thanks,
As determined as you are, it may be better to bite the bullet and resell them and get what you really need.
Hi Bud
I would use a very simple circuit:
the rectangles are resistors and needs to be matched to the voltage the signal board provides. Can you measure this? (Or do you know already?)
Note that this circuit works only if the (-) outputs are either - or off, open collector in other words, and not both - at the same time, and also requires that the signal board has no current limiting resistors of it's own.
cheers/jw
(jens)
My experience with bi-color LED's is the different LED intensity between colors. One was brighter than the other with the same value resistor but the LED specs told me that. I could have trimmed the resistors to make the color brightness the same but I am just not into counting all the rivets.
in that case make the R in my circuit (see above) different. The left one defines the current for the red and the right one for the green LED.
blrrfan Hi Bud I would use a very simple circuit: the rectangles are resistors and needs to be matched to the voltage the signal board provides. Can you measure this? (Or do you know already?) Note that this circuit works only if the (-) outputs are either - or off, open collector in other words, and not both - at the same time, and also requires that the signal board has no current limiting resistors of it's own.
Just a thought.
I'd be surprised if the green( -) and red (-) are left floating when not active low.
If they're pulled high when not driven low, use something like an LS125 to gate the signals.
Connect green- and red- to pins 1 and 4 respectively. Connect pins 2 and 5 to ground. Then connect pins 3 and 6 to Jen's diagram at "green -" and "red -" respectively.
Only unknown is what is board voltage (what value is Common +) along with green- and red- when not driven low.
Of course, you could avoid all of this buy getting some tri-lead LEDs. They're pretty cheap. Much cheaper than what it's probably going to cost you in putting together a circuit for the 2-leads.
Thank you for your help, one of those is bound to work! I'm going to give them a try tonight. Thanks again, Bud
not a chance! Too darn stubborn!
Hi all
here is a slightly more complicated version in case the signalboards red/green - outputs are not open collectors:
the two diodes prevent in that case the blowup of the dual LED
as for using TTL chips (74LS125A) those work with 5 Volts only.
How about the similar but for higher voltage range allowed CMOS chip 4041:
http://www.cmos4000.com/media/cmos/ic-cmos-4041.pdf
(img source: http://www.radiomuseum.org/images/tubesockel_klein/cd4041_s.gif)
PS: http://xkcd.com/730/