Points Position Indicator Advice Please?

[amdaley]

9mb is less than one of my photos , the movies I upload to YouTube are typically 100mb +

 

Sorry Beast I thought you said 2 Mb not 2Gb He should have no problem so.

[Pete the Elaner]

Sorry Beast I thought you said 2 Mb not 2Gb He should have no problem so.

Maybe but I'm a former network admin so am over-concious about unnecesary large files because I was the poor sod always trying to fit the ever-growing backup into the available window.

 

Sod it. I've re-shot the file but the forum won't allow me to submit it. I'll have to create a YouTube account. Back to the bigger file then...

 

[Suzie]

Just to illustrate how simple it is to add a point position indicator on DCC with live frog points using nothing more than two LEDS and two resistors, here is a photo of the installation for one point:-

 

 

Red and black wires go to the running rails, green wire goes to the frog.

 

(pink wire supplies power for the point, Yellow and Orange wires from the push buttons go to the point motor normal and reverse coils respectively, but that is not required for the indicator)

 

You will need the LEDs and probably the resistors too in many of the alternative scenarios that have been mentioned and all of them will involve more wiring and not show you the actual position of the point. You can wire up additional indicators by either connecting additional LEDs in series or by paralleling the whole circuit on the red, black and green wires.

 

I have used AC LEDs here to keep it simple, but using standard LEDs is not that much more complicated. It is nice to be able to change the point by hand and see the indicator reflect the change in position just as if I had actuated it electrically.

 

 

 

 

 

[amdaley]

Just to illustrate how simple it is to add a point position indicator on DCC with live frog points using nothing more than two LEDS and two resistors, here is a photo of the installation for one point:-

 

 

Red and black wires go to the running rails, green wire goes to the frog.

 

(pink wire supplies power for the point, Yellow and Orange wires from the push buttons go to the point motor normal and reverse coils respectively, but that is not required for the indicator)

 

You will need the LEDs and probably the resistors too in many of the alternative scenarios that have been mentioned and all of them will involve more wiring and not show you the actual position of the point. You can wire up additional indicators by either connecting additional LEDs in series or by paralleling the whole circuit on the red, black and green wires.

 

I have used AC LEDs here to keep it simple, but using standard LEDs is not that much more complicated. It is nice to be able to change the point by hand and see the indicator reflect the change in position just as if I had actuated it electrically.

 

 

 

 

 

 

Hi Susie.

A picture really is better than a thousand words.Thanks.

If using standard Led's will not the constant switching on & off with the track AC not affect the led's life or is some form of bridge rectifier required. I know we can't see this on & off but what affect will it have on the led ?

I have a good stock of 3 legged bi-color led's,how can I use these in this type of setup ?

[Suzie]

Hi Susie.

A picture really is better than a thousand words.Thanks.

If using standard Led's will not the constant switching on & off with the track AC not affect the led's life or is some form of bridge rectifier required. I know we can't see this on & off but what affect will it have on the led ?

I have a good stock of 3 legged bi-color led's,how can I use these in this type of setup ?

 

If using the three legged LEDs (these are more generally referred to slightly misleadingly as tri-colour because they can typically display red, green and yellow in a steady state) you will need to connect the middle common leg directly to the frog (green wire in my picture), and put the resistors in series with the other legs which go to the track (red and black wires in my picture). The single LED will then display red or green depending on how the point is set. You will need to put an inverse parallel reverse protection diode (1N4148 or similar) between the central common leg of the LED and each of the outer legs to prevent excessive reverse voltage. The high speed switching will not upset the LEDs at all - gallium arsenide is used at the highest RF frequencies, 9KHz is nothing. 

 

 

You will probably solder better than me, my Nimrod portable iron I used for this has two temperature settings, thermic lance and thermic lance turbo!

 

 

 

 

 

[amdaley]

If using the three legged LEDs (these are more generally referred to slightly misleadingly as tri-colour because they can typically display red, green and yellow in a steady state) you will need to connect the middle common leg directly to the frog (green wire in my picture), and put the resistors in series with the other legs which go to the track (red and black wires in my picture). The single LED will then display red or green depending on how the point is set. You will need to put an inverse parallel reverse protection diode (1N4148 or similar) between the central common leg of the LED and each of the outer legs to prevent excessive reverse voltage. The high speed switching will not upset the LEDs at all - gallium arsenide is used at the highest RF frequencies, 9KHz is nothing.

 

 

You will probably solder better than me, my Nimrod portable iron I used for this has two temperature settings, thermic lance and thermic lance turbo!

 

 

 

 

 

 

Hi Susie.

Can you explain the highlighted piece please & in which direction do the diodes need to be fitted as I understand they work only in one direction ?

[Pete the Elaner]

Hi Susie.

Can you explain the highlighted piece please & in which direction do the diodes need to be fitted as I understand they work only in one direction ?

 

I believe I can answer that...

 

You understand correctly. When the voltage is forward, the LED's concucts so its resistance is low. Most (effectively all) of the circuit voltage is across another load.

When the voltage is reversed, the LED's resistance is high, so most (effectively all) of the circuit voltage is across the LED. It doesn't like this too much.

 

Connect a diode in parallel with the existing LED but in reverse so it conducts in the opposite direction. The circuit voltage will then be across the load instead of across the LED.

 

 

If that's as clear as mud, then I'll try to draw a couple of circuit diagrams. I'll be searcing for an electronics program for the next few minutes..........

[amdaley]

I believe I can answer that...

 

You understand correctly. When the voltage is forward, the LED's concucts so its resistance is low. Most (effectively all) of the circuit voltage is across another load.

When the voltage is reversed, the LED's resistance is high, so most (effectively all) of the circuit voltage is across the LED. It doesn't like this too much.

 

Connect a diode in parallel with the existing LED but in reverse so it conducts in the opposite direction. The circuit voltage will then be across the load instead of across the LED.

 

 

If that's as clear as mud, then I'll try to draw a couple of circuit diagrams. I'll be searcing for an electronics program for the next few minutes..........

 

Thank you for the answer. I understand the reasoning behind fittings of the diodes but I am unsure which direction they should be placed. Should the black band be at the center common connection facing out or the other way around ? This may seem like a simple question but my knowledge of electronics is limited.

[Suzie]

You need to identify whether your LED is common cathode or common anode. If it is common cathode the middle leg will be the cathode for both LEDS, therefore you will need to connect the anode (non-stripe end) of each of the inverse parallel diodes to the middle leg.

 

If it is common anode the reverse will be true and you will need to connect the stripe end of the inverse parallel diodes to the middle leg.

 

If you have a meter with diode check or continuity check, test the diode first to see which way round it is and not which probe is on the cathode (stripe) end, then test the LED and you can then identify the cathode and anode pin(s).

 

My little diagram in post no25 above on page 1 shows a common anode LED.

 

 

 

 

 

[amdaley]

You need to identify whether your LED is common cathode or common anode. If it is common cathode the middle leg will be the cathode for both LEDS, therefore you will need to connect the anode (non-stripe end) of each of the inverse parallel diodes to the middle leg.

 

If it is common anode the reverse will be true and you will need to connect the stripe end of the inverse parallel diodes to the middle leg.

 

If you have a meter with diode check or continuity check, test the diode first to see which way round it is and not which probe is on the cathode (stripe) end, then test the LED and you can then identify the cathode and anode pin(s).

 

My little diagram in post no25 above on page 1 shows a common anode LED.

 

 

 

 

 

 

Thanks Susie. I will go back & check it out.My leds are common anode as they require a resistor be connected to the center long leg (anode).

[Suzie]

Being common anode or common cathode makes no difference to where the resistor goes. The resistors have to be positioned with regard to the circuit, in this case on both of the outer legs with no resistor on the middle leg.

 

 

 

 

 

[amdaley]

Being common anode or common cathode makes no difference to where the resistor goes. The resistors have to be positioned with regard to the circuit, in this case on both of the outer legs with no resistor on the middle leg.

 

 

 

 

 

 

Hi Susie.

I understand what you are saying about this particular circuit. The led's I have are dual color with a center long leg which is common anode,the outer 2 legs being cathode. The instructional information that came with them tells me to connect the resistor to the center anode long leg of the led. This is what has confused me.

[amdaley]

I believe I can answer that...

 

You understand correctly. When the voltage is forward, the LED's concucts so its resistance is low. Most (effectively all) of the circuit voltage is across another load.

When the voltage is reversed, the LED's resistance is high, so most (effectively all) of the circuit voltage is across the LED. It doesn't like this too much.

 

Connect a diode in parallel with the existing LED but in reverse so it conducts in the opposite direction. The circuit voltage will then be across the load instead of across the LED.

 

 

If that's as clear as mud, then I'll try to draw a couple of circuit diagrams. I'll be searcing for an electronics program for the next few minutes..........

 

Mud is a good description. Now I know what confused.com means Is there a good article I could read which might explain led's etc in layman's terms. "Led's for Dummies"

[Suzie]

Hi Susie.

I understand what you are saying about this particular circuit. The LEDs I have are dual colour with a centre long leg which is common anode, the outer 2 legs being cathode. The instructional information that came with them tells me to connect the resistor to the centre anode long leg of the led. This is what has confused me.

They are not very good general instructions as you will often need to use different resistors for each of the colours, especially on lower voltages, and putting a resistor in the middle leg precludes you from using it to display yellow. It is also not suitable for when you want to use the LED on AC as is done in this example. as a rule of thumb always use a separate resistor for each LED, and in this case for each part of the LED and you cannot go wrong.

 

 

I would recommend that you put a 560R resistor in series with the green part of the LED, and a 680R in series with the red part. You will be able to use 1K resistors OK and probably not notice any significant difference.

 

 

 

 

 

 

 

 

 

 

 

[amdaley]

They are not very good general instructions as you will often need to use different resistors for each of the colours, especially on lower voltages, and putting a resistor in the middle leg precludes you from using it to display yellow. It is also not suitable for when you want to use the LED on AC as is done in this example. as a rule of thumb always use a separate resistor for each LED, and in this case for each part of the LED and you cannot go wrong.

 

 

I would recommend that you put a 560R resistor in series with the green part of the LED, and a 680R in series with the red part. You will be able to use 1K resistors OK and probably not notice any significant difference.

 

 

 

 

 

 

 

 

 

 

 

 

Cheers for that Suzie.Much appreciated.

[Dagworth]

Mud is a good description. Now I know what confused.com means Is there a good article I could read which might explain led's etc in layman's terms. "Led's for Dummies"

 

This one?

 

Andi

[amdaley]

This one?

 

Andi

 

Thanks Andi.

[amdaley]

You need to identify whether your LED is common cathode or common anode. If it is common cathode the middle leg will be the cathode for both LEDS, therefore you will need to connect the anode (non-stripe end) of each of the inverse parallel diodes to the middle leg.

 

If it is common anode the reverse will be true and you will need to connect the stripe end of the inverse parallel diodes to the middle leg.

 

If you have a meter with diode check or continuity check, test the diode first to see which way round it is and not which probe is on the cathode (stripe) end, then test the LED and you can then identify the cathode and anode pin(s).

 

My little diagram in post no25 above on page 1 shows a common anode LED.

 

 

 

 

 

 

Hi Suzie.

A few further questions if I may.

 

(1) What happens if you connect the diodes the wrong way around ?

The reason I ask is because I connected the diodes the way I thought I should & the circuit didn't work.The diodes seem to blow as when I tested them with a continuity tester they seem to conduct in both directions. I connected two more diodes in the opposite direction & the circuit worked fine.

 

(2) What would happen if no diodes were fitted to the circuit using it on DCC ?

 

(3) What would inverse voltage do to the circuit & what would cause inverse voltage.

 

Thanks for your help.

[Suzie]

Hi Suzie.

A few further questions if I may.

 

 

 

 

(1) What happens if you connect the diodes the wrong way around ?

The reason I ask is because I connected the diodes the way I thought I should & the circuit didn't work.The diodes seem to blow as when I tested them with a continuity tester they seem to conduct in both directions. I connected two more diodes in the opposite direction & the circuit worked fine.

 

If you get the diodes the wrong way round the LEDs will not light and the LEDs will not be protected from the high reverse voltage.

 

 

 

(2) What would happen if no diodes were fitted to the circuit using it on DCC ?

 

Again the LEDs would not be protected from the high reverse voltage. Degradation of the LEDs will probably be slow so you will not notice anything at first.

 

 

 

(3) What would inverse voltage do to the circuit & what would cause inverse voltage.

 

 

The circuit is designed for AC so there is no possibility of inverse voltage. The LEDs will light when the voltage is one way, and then be extinguished and protected by the inverse parallel diodes when the voltage is the other way. The polarity changes on DCC between 4KHz and 9KHz - very fast and a lot.

[amdaley]

The circuit is designed for AC so there is no possibility of inverse voltage. The LEDs will light when the voltage is one way, and then be extinguished and protected by the inverse parallel diodes when the voltage is the other way. The polarity changes on DCC between 4KHz and 9KHz - very fast and a lot.

 

Sorry Suzie but I got this part of my question wrong. What I meant to ask was "What would reverse voltage do to the circuit & what would cause reverse voltage.Would the effect be immediate ? I used the word inverse instead .Sorry.

[Suzie]

Sorry, I am not really understanding your question now.

 

The circuit is protected against reverse voltage by the inverse parallel protection diodes. Reverse voltage occurs on the LED when the frog is at a negative potential with respect to the other rail (common anode LED). The diode limits the reverse voltage to around 0.6V, well below the safe level. The excess voltage is absorbed in the series resistor. 

 

 

 

 

 

[amdaley]

Sorry, I am not really understanding your question now.

 

The circuit is protected against reverse voltage by the inverse parallel protection diodes. Reverse voltage occurs on the LED when the frog is at a negative potential with respect to the other rail (common anode LED). The diode limits the reverse voltage to around 0.6V, well below the safe level. The excess voltage is absorbed in the series resistor.

 

 

 

 

 

 

Sorry about my questions Suzie,just trying to get my head around what happens in this circuit. Just wanted to make sure that I had it wired correctly. It works so I must have it right.

[Suzie]

Excellent. :-)