stmartins Posted November 27, 2016 Share Posted November 27, 2016 I have just purchased a range of 5 aspect traffic lights, ( red amber green & red & green) Trying to keep wiring to a minimum I have installed 5 way rotor switches to feed the lights. Having worked out the combinations i.e. main line green & branch line red I thought I was being clever but I now realise the "loop" wires are feeding the other lights so I was wondering if anyone is aware of any resistor or diode that will allow the current to run just one way and stop "feedback to the other lights. Any advise appreciated Link to post Share on other sites More sharing options...
RMweb Premium Ray H Posted November 27, 2016 RMweb Premium Share Posted November 27, 2016 All diodes only allow current to flow one way. This is what makes them so suitable for a diode matrix for operating points and signals in various combinations. Link to post Share on other sites More sharing options...
Grovenor Posted November 27, 2016 Share Posted November 27, 2016 I have just purchased a range of 5 aspect traffic lights, ( red amber green & red & green) Trying to keep wiring to a minimum I have installed 5 way rotor switches to feed the lights. Having worked out the combinations i.e. main line green & branch line red I thought I was being clever but I now realise the "loop" wires are feeding the other lights so I was wondering if anyone is aware of any resistor or diode that will allow the current to run just one way and stop "feedback to the other lights. Any advise appreciated Just by the way, but traffic lights are for roads, on the railways we have signals. For railway signals the colours are red, yellow and green, not red, amber and green. Regards Link to post Share on other sites More sharing options...
RMweb Premium dhjgreen Posted November 27, 2016 RMweb Premium Share Posted November 27, 2016 I have just purchased a range of 5 aspect traffic lights, ( red amber green & red & green) Trying to keep wiring to a minimum I have installed 5 way rotor switches to feed the lights. Having worked out the combinations i.e. main line green & branch line red I thought I was being clever but I now realise the "loop" wires are feeding the other lights so I was wondering if anyone is aware of any resistor or diode that will allow the current to run just one way and stop "feedback to the other lights. Any advise appreciated I will make a couple of assumptions here. I presume you are using LED signals and that you are switching the positive + leg. If these assumptions are correct and your signal aspects are: main line green,then yellow, then red (all with branch red); then main red with branch green. I make that 4 options BTW, then a 1N4001 (pennies each) in each of the first 3 aspects to the branch red should be all you need. The band on the diode should go towards the LED. A diagram would help if this sounds like gibberish. Link to post Share on other sites More sharing options...
RMweb Premium dhjgreen Posted November 27, 2016 RMweb Premium Share Posted November 27, 2016 All diodes only allow current to flow one way. This is what makes them so suitable for a diode matrix for operating points and signals in various combinations. Let me be the first to say, not all types of diode, of which there are many. Link to post Share on other sites More sharing options...
Butler Henderson Posted November 27, 2016 Share Posted November 27, 2016 As far as most model railway use goes the diodes needed are either the 1N400x series (1 Amp) or the 1N540x series (3 amp). The last digit indicates the max voltage and given that the lowest is 50v then any can be used provided you have got the amperage current - the 50v ones being the 1N4001 and the 1N5400. A diode will cause a voltage drop of around 0.8v. Maplin at times have bargain packs of them typically full of very high voltage ones but they work fine on 12v / 16v etc. Link to post Share on other sites More sharing options...
Tricky Dicky Posted November 27, 2016 Share Posted November 27, 2016 LEDs are diodes after all and it is quite straight forward by reverse biasing some and reversing polarity to get some to emit light whilst others are off. Adding further diodes could result in the LEDs dimming owing to the 0.7V hreshold voltage for each diode. Richard Link to post Share on other sites More sharing options...
Junctionmad Posted November 27, 2016 Share Posted November 27, 2016 LEDs,of course are normally forward biased and of course have quite low reverse voltage , making them very bad diodes in general !! You can add as many ordinary diodes as you like once the Vf operating conditions are met , the current and hence illumination levels are set by the appropriate current limiting device , typically, though not always , a series resistor Link to post Share on other sites More sharing options...
Tricky Dicky Posted November 27, 2016 Share Posted November 27, 2016 LEDs,of course are normally forward biased and of course have quite low reverse voltage , making them very bad diodes in general !! Vr is generally higher than Vf it is Ir that is usually considerably lower than If. Reverse biasing one LED with another with the correct current limiting resistor should pose no problem after all bi-colour 2 pin LEDs are nothing more than two LEDs reverse biased to each other in one case. Richard Link to post Share on other sites More sharing options...
cliff park Posted November 27, 2016 Share Posted November 27, 2016 Guys, look carefully at the op. This is a question from somebody who does not know the difference between a diode and a resistor (no disrespect, of course, we all have our own areas of knowledge) and here you are arguing about Vf, If, Vr and the viability of reverse biassing multiple LEDs. Not helpful Link to post Share on other sites More sharing options...
Butler Henderson Posted November 27, 2016 Share Posted November 27, 2016 May help - at school I had them explained as a diode being a waterfall and a resistor a narrow channel in a watercourse; one can only flows one way, the other limits the flow Link to post Share on other sites More sharing options...
RMweb Premium dhjgreen Posted November 28, 2016 RMweb Premium Share Posted November 28, 2016 I will make a couple of assumptions here. I presume you are using LED signals and that you are switching the positive + leg. If these assumptions are correct and your signal aspects are: main line green,then yellow, then red (all with branch red); then main red with branch green. I make that 4 options BTW, then a 1N4001 (pennies each) in each of the first 3 aspects to the branch red should be all you need. The band on the diode should go towards the LED. A diagram would help if this sounds like gibberish. Edit to say you also need a diode in the main line red for when the branch is showing green. Much of this between my reply above and now is not really helpful, I hope you (OP) are back soon before you are thoroughly confused. Link to post Share on other sites More sharing options...
Crosland Posted November 28, 2016 Share Posted November 28, 2016 May help - at school I had them explained as a diode being a waterfall and a resistor a narrow channel in a watercourse; one can only flows one way, the other limits the flow There are a whole host of analogies between plumbing and electrics which can be useful to visualise. I've even used a toilet cistern as an analag of a CDU - fill the cistern slowly (charge the capacitor) then flush the toilet to empty the cistern quickly and move the t***s (discharge the capacitor quickly to give a good jolt to the point motor) Link to post Share on other sites More sharing options...
Dazzler Fan Posted November 28, 2016 Share Posted November 28, 2016 +Does it matter which side of the LED has the resistor?Also - PECO Booklet showing pictorial of Diode Matrix, although an excellent explanation, was discontinued because of the load capabilities of Veroboard PCB lines when using CDU's - somewhere there was discussion that left the question open.Has anyone come up with an alternative former to assemble a diode matrix that will take the current.? Noel Link to post Share on other sites More sharing options...
Butler Henderson Posted November 28, 2016 Share Posted November 28, 2016 + Does it matter which side of the LED has the resistor? Also - PECO Booklet showing pictorial of Diode Matrix, although an excellent explanation, was discontinued because of the load capabilities of Veroboard PCB lines when using CDU's - somewhere there was discussion that left the question open. Has anyone come up with an alternative former to assemble a diode matrix that will take the current.? Noel Robert Penfolds books always seem to show the resistors on the negative side of LEDs. Re diode matrix - solder and tag strips. Link to post Share on other sites More sharing options...
RMweb Premium dhjgreen Posted November 28, 2016 RMweb Premium Share Posted November 28, 2016 + Does it matter which side of the LED has the resistor? Also - PECO Booklet showing pictorial of Diode Matrix, although an excellent explanation, was discontinued because of the load capabilities of Veroboard PCB lines when using CDU's - somewhere there was discussion that left the question open. Has anyone come up with an alternative former to assemble a diode matrix that will take the current.? Noel When the components form a ring from + to - (called series) the position of each component makes no difference. Sometimes there is a convention, sometimes you fit the part for convenience. Link to post Share on other sites More sharing options...
RMweb Premium dhjgreen Posted November 28, 2016 RMweb Premium Share Posted November 28, 2016 Robert Penfolds books always seem to show the resistors on the negative side of LEDs. This would be a good idea if you were switching the positive to several LEDs (as on this thread) and sharing a resistor. Link to post Share on other sites More sharing options...
Dazzler Fan Posted November 28, 2016 Share Posted November 28, 2016 + Veroboard represents a nice clean layout because there are edge connectors available for easy servicing. Initial prototyping, I have beefed-up the 8 supply lines with wire, where current on a route might be carried for up to 4 solenoids in a single switching. Some instances may be redundant but included as a belt & bracers fail safe. To help, each board can be removed from the layout and the wiring either side of it. I have made a test rack on an spare edge connector with LEDs to check against the matrix table, and any solder shorts between tracks. I will report back on smells of any burn-outs. Noel Link to post Share on other sites More sharing options...
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