Reasons to NOT use Grain of Wheat bulbs.?

[250BOB]

Hello again guys,

Just a small question on LED's...............I have a Micro Miniatures Point Position Indicator, and the instructions say you can use 3 to 4 LED's per outlet.

 

What are the rules regarding in series and in parallel with LED's.......and what happens if I overstep the mark and put in more LED's per outlet.

 

Thanks.................Bob.

[Suzie]

You can use three LEDs (each with its own resistor) in parallel from each output. Since the LED supply is 12V you could put up to three in series using a single smaller value resistor, and do this three times on each output for a total of nine LEDs and three resistors per output.

 

Since you are using DCC probably best sell it on to a DC person (who will find it quite handy) and stick with the methods described above, which are much more straightforward and give a more meaningful indication of point functioning rather than which button you pressed last. There will be a lot of wires if you are using the microminiatures unit versus just one wire to the frog for each point using the other methods.

[250BOB]

You can use three LEDs (each with its own resistor) in parallel from each output. Since the LED supply is 12V you could put up to three in series using a single smaller value resistor, and do this three times on each output for a total of nine LEDs and three resistors per output.

 

Since you are using DCC probably best sell it on to a DC person (who will find it quite handy) and stick with the methods described above, which are much more straightforward and give a more meaningful indication of point functioning rather than which button you pressed last. There will be a lot of wires if you are using the microminiatures unit versus just one wire to the frog for each point using the other methods.

 

Thanks Suzie,

Your information is really useful.

 

My real issue is with the double slip and the adjoining points on either side,

I cant use the slip frog polarity, as I use a hex frog juicer.

 

For all the other points 20 + of them, the above mentioned methods seem great.

 

Thanks.......Bob.

[Suzie]

In that case the micro miniatures unit might be useful. You can still wire bi-colour LEDs (the two legged ones) to it if you are going to use them for your other points.

[Nigelcliffe]

Bob - what are the indicators (LEDs) showing you ? Is it the turnout blade position, or is it the track polarity ? The reason for asking revolves around the Hex Juicer and the Micro Miniatures Indicator. I suspect you want to know the blade position (and thus route a wagon would take when pushed through the turnout), because if the track polarity is wrong, the Hex Juicer will auto-correct this. In the simple turnouts, the frog polarity provides the information of the blade position. Assuming your slip is controlled by two turnout motors, with cross-over control switches on the motors (unused because you have a Hex Juicer), then I'd wire up the cross-over switches, and use them to provide the LED information on the position of the blades.

 

The MicroMiniatures unit may reduce wiring runs from layout to panel, but adds another layer of complexity.

 

- Nigel

[silverlink]

 

 

Hi Ian,

I am indeed at Warley....thankyou for the invitation....I shall make myself known to you.

I seem to remember you did once before invite me to see your layout in Scarboro.....at the same time that I was maybe up there at the Gold Cup. Didnt get there this year I'm afriad.

Regards.......Bob

Remember it well Bob, just make yourself known to anyone on the layout & I will get you round to have a look at the panel. If you want you can even have a go!!!

 

Cheers

Ian

[250BOB]

]

Bob - what are the indicators (LEDs) showing you ? Is it the turnout blade position, or is it the track polarity ? The reason for asking revolves around the Hex Juicer and the Micro Miniatures Indicator. I suspect you want to know the blade position (and thus route a wagon would take when pushed through the turnout), because if the track polarity is wrong, the Hex Juicer will auto-correct this. In the simple turnouts, the frog polarity provides the information of the blade position. Assuming your slip is controlled by two turnout motors, with cross-over control switches on the motors (unused because you have a Hex Juicer), then I'd wire up the cross-over switches, and use them to provide the LED information on the position of the blades.

 

The MicroMiniatures unit may reduce wiring runs from layout to panel, but adds another layer of complexity.

 

- Nigel

 

Hi Nigel,

Thanks for your reply.

I am having to use Peco surface mounted point motors...and cannot fit micro switches to them either....so I thought the Point Position Indicator is the answer. And yes, it is purely to tell me the position of the point blade.

You are right about complexity....but I'm slowly getting my head round this stuff, and LED's too.

Cheers..................Bob.

[250BOB]

In that case the micro miniatures unit might be useful. You can still wire bi-colour LEDs (the two legged ones) to it if you are going to use them for your other points.

 

How would that work Suzie.??

You may to start by telling me how a bicolour LED works first.?

Thanks..........Bob

[Suzie]

A bi-colour LED is two leds wired in inverse parallel, so when the current goes one way it lights green, and the other way it lights red.

 

You can connect one of these bi-colour LEDs between the output terminals of the Micro Miniatures unit, and connect the two current limit resistors between the common supply pin and each of the outputs.

[250BOB]

A bi-colour LED is two leds wired in inverse parallel, so when the current goes one way it lights green, and the other way it lights red.

 

You can connect one of these bi-colour LEDs between the output terminals of the Micro Miniatures unit, and connect the two current limit resistors between the common supply pin and each of the outputs.

 

Hi Suzie,

I appreciate your input on this topic.

Of the 16 LED outlets on the MM PPI unit....they work in pairs with a point switch......however, when one is on, the other outlet is dead. So how does the bicolour LED work.?

Apologies if the answer is obvious.....it isnt to me yet.?

Bob

[Suzie]

The answer is not obvious, but draw the diagram and you will see. In this case the current is supplied to the LED via the current limiting resistor connected to the output which is not on.

[250BOB]

The answer is not obvious, but draw the diagram and you will see. In this case the current is supplied to the LED via the current limiting resistor connected to the output which is not on.

 

Even better Suzie......I'm gonna make a trip to Maplins, get some, and try these things out.....I need to understand these things, even at my age.!!

Thanks.....Bob

[Suzie]

Bob

 

Maplin bi-colour 5mm LED is QY83E

[250BOB]

I have just been looking at some Tri colour LED's on the internet.

 

Maplins sell 3mm ones at what appears to be 99p each

http://www.maplin.co.uk/tri-colour-led-26361

 

On Ebay..."The Handsignalman" sells what appear to me to be the same item, 15 for £3.50, including the resistors.!!

http://www.ebay.co.uk/itm/LEDs-Red-Green-dual-colour-3mm-x-15-inc-res-/160839670990?pt=UK_Trains_Railway_Models&hash=item2572ca9cce

 

There is such a big difference in price, I thought there must be a difference.

 

Any advice...???

 

Bob

[Nigelcliffe]

Maplin are expensive. Some of the reason for the expense is the cost of operating shops and having customers wanting "1 LED".

 

Electronics specialist suppliers offer LEDs with three legs (tri-colour) from 16p, for ordering 1 at a time. Less if ordering lots. Similarly, resistors would be well under 1p each (eg. 1kohm is 63p per 100 resistors). But electronics suppliers usually have minimum order quantities which make them uneconomic for small purchases.

 

 

Note that a BiColour and a TriColour LED are different devices. The former has two legs, the latter three. I'm not quite sure how Suzie was proposing to use the BiColour.

 

 

- Nigel

[250BOB]

Maplin are expensive. Some of the reason for the expense is the cost of operating shops and having customers wanting "1 LED".

 

Electronics specialist suppliers offer LEDs with three legs (tri-colour) from 16p, for ordering 1 at a time. Less if ordering lots. Similarly, resistors would be well under 1p each (eg. 1kohm is 63p per 100 resistors). But electronics suppliers usually have minimum order quantities which make them uneconomic for small purchases.

 

 

Note that a BiColour and a TriColour LED are different devices. The former has two legs, the latter three. I'm not quite sure how Suzie was proposing to use the BiColour.

 

 

- Nigel

 

Hi Nigel,

many thanks......I have just placed an order for tri colour LED's with the Handsignalman on ebay....I have bought 45 for about £8 inc postage and resistors. I view this outlay as on the tri colour leds as a small amount to enjoy some experimenting/playing around with.

 

I'm looking forward to it.

 

With my limited knowledge on this subject...I can see how these would work on the Micro Miniatures PPI unit.....I'm struggling to understand how the Bi colour LED's would work with the unit though.

 

My control panel is under construction.....here is a picture, still a couple of crossovers to add, but the 2 double slips are seen....not sure yet if I will use toggle switches or push buttons. With the toggle switches it leaves me more room for the LED's.

 

Thanks for your help again.

 

Bob

 

[Suzie]

Bob

 

Here are the diagrams of how to wire up multi-colour LEDs to the Micro Miniatures. These diagrams work for any device that has open collector outputs such as most DCC decoders.

 

 

You can see that the wiring is a little easier for the 2-legged bi-colour LED than for the 3-legged common cathode tri-colour LED. Common anode LEDs are very rare (DCC concepts have some if you really need one).

[250BOB]

I cant get the tri colour LED's to work with the Micro Miniatures PPI unit.

 

If I put the two outer wires of the LED into the two terminals on the PPI, the ones which go on and off as the point is switched, then connect through a resistor the centre wire to the common return......the LED is dead.

 

However, if I put the centre common LED wire into the live PPI terminal, then touch the common return wire from the PPI, alternately to the two outer wires on the LED, it all works fine.

 

I wondered if I connect the 12v DC supply to the PPI the opposite way round to get it to work....but then unit is just dead, it only works one wired one way.

 

I am looking hard at Suzies diagram in the last post.....and with my very limited knowledge of electronics(none).....I think I am seeing that the tri colour diagram is sending the current into the opposite(correct) end of the LEDs....????

 

Any thoughts.? PPI wiring diagram here if it helps.

 

Bob

 

[Suzie]

The Micro miniatures unit is designed to work with common anode LEDs which are about as common as rocking horse manure, and what you have is the normal common cathode type, hence the diagram on the left with the routing diodes to generate a common cathode supply where none exists.

 

You have two options:-

1. Get some 1N4148 diodes which are very cheap (or 39p each from Maplin, QL80B) and use the left diagram.

2. Get some bi-colour (two legged) LEDs that match your tri-colour ones (Maplin UF96E) and use the right diagram.

 

There is a third option of find some common anode 3mm tri-colour LEDs, but I cannot find any so that is probably not a realistic option, and will probably be the most expensive (the DCCConcepts LEDs are $10 each!).

 

Since you will be needing two protection diodes for each of the other LEDs which will be connected to the frogs anyway, you might as well see if you can get a bulk lot of 100 1N4148 from somewhere, I never pay more than a penny each for them.

[250BOB]

The Micro miniatures unit is designed to work with common anode LEDs which are about as common as rocking horse manure, and what you have is the normal common cathode type, hence the diagram on the left with the routing diodes to generate a common cathode supply where none exists.

 

You have two options:-

1. Get some 1N4148 diodes which are very cheap (or 39p each from Maplin, QL80B) and use the left diagram.

2. Get some bi-colour (two legged) LEDs that match your tri-colour ones (Maplin UF96E) and use the right diagram.

 

There is a third option of find some common anode 3mm tri-colour LEDs, but I cannot find any so that is probably not a realistic option, and will probably be the most expensive (the DCCConcepts LEDs are $10 each!).

 

Since you will be needing two protection diodes for each of the other LEDs which will be connected to the frogs anyway, you might as well see if you can get a bulk lot of 100 1N4148 from somewhere, I never pay more than a penny each for them.

 

Hi Suzie,

Its all coming together thanks to your explanations. I am now beginning to understand how these things work, having never even handled an LED a week ago.

 

As you say, option 3 is not what I shall do........but I shall get some bi colour LEDs and also some diodes to have a go at the other options.....this is all so interesting.

 

Many many thanks for all your help Suzie, your diagrams and explanations have been extremely helpful to me. Thanks for taking the time to post them for me.

 

Bob

[SHMD]

I cant get the tri colour LED's to work with the Micro Miniatures PPI unit.

 

If I put the two outer wires of the LED into the two terminals on the PPI, the ones which go on and off as the point is switched, then connect through a resistor the centre wire to the common return......the LED is dead.

 

However, if I put the centre common LED wire into the live PPI terminal, then touch the common return wire from the PPI, alternately to the two outer wires on the LED, it all works fine.

 

I wondered if I connect the 12v DC supply to the PPI the opposite way round to get it to work....but then unit is just dead, it only works one wired one way.

 

I am looking hard at Suzies diagram in the last post.....and with my very limited knowledge of electronics(none).....I think I am seeing that the tri colour diagram is sending the current into the opposite(correct) end of the LEDs....????

 

Any thoughts.? PPI wiring diagram here if it helps.

 

Bob

 

 

Hi Bob,

 

Can you give me the details of the two chips nearest the LED outputs?

Just give me all the writing that is on the top of one of them. (The other chips, on the PCB, I could identify from Photos off the “Net” but the LED driver ICs were not clear!)

 

With these details I will be able to check the circuit.

There is a small chance that the Tri-colour LEDs could be driven a different way. But that depends on the LED driver ICs being push-pull outputs and not open-collector outputs.

 

(Do NOT swap the +ve and -ve supplies to the circuit!!!)

 

 

Kev.

[Suzie]

Kev

 

They look to me like ULN2803 or similar, but it would be nice to get confirmation.

[250BOB]

Kev

 

They look to me like ULN2803 or similar, but it would be nice to get confirmation.

 

Hi Suzie Hi Kev,

 

Yes, they have ULN2803A printed on them.........it might as well be a foreign language to me...but you obviously know these items.

 

I'm curious as to what you are thinking.?

 

Bob

[SHMD]

I'm afraid that ULN2803A is bad news. (If you want to use tri-colour LEDs that is.)

 

I was hoping that they had used something, other than the 2000 series Darlington Driver ICs. Something with open collector outputs that could, (and this IS relative), be easily swapped for something with push-pull outputs.

 

No chance of that happening, though, as the 2803 has none standard pin assignments when compared to the vast majority of logic (TTL) ICs.

Don't get me wrong, the 2803 is an extremely good choice, and I have used it myself in designs many times, but it “sinks” current (robustly) and can not source any at all!

 

That micro-miniatures point indicator board is simple and robust but can only switch LEDs, on or off, by connecting them, (digitally), to 0v – hence the LED anodes need to be connected to +ve (common!!!) rail.

(Sure is a good price though!)

 

Kev.

[250BOB]

I'm afraid that ULN2803A is bad news. (If you want to use tri-colour LEDs that is.)

 

I was hoping that they had used something, other than the 2000 series Darlington Driver ICs. Something with open collector outputs that could, (and this IS relative), be easily swapped for something with push-pull outputs.

 

No chance of that happening, though, as the 2803 has none standard pin assignments when compared to the vast majority of logic (TTL) ICs.

Don't get me wrong, the 2803 is an extremely good choice, and I have used it myself in designs many times, but it “sinks” current (robustly) and can not source any at all!

 

That micro-miniatures point indicator board is simple and robust but can only switch LEDs, on or off, by connecting them, (digitally), to 0v – hence the LED anodes need to be connected to +ve (common!!!) rail.

(Sure is a good price though!)

 

Kev.

 

Thanks Kev,

 

I am far more knowledgeable about LED's than I was a week ago, thanks again in principal to RMweb and its membership.

 

Having now understood some of the complexities and do's and dont's.....I now need to reflect on the best way forward for what I want to achieve. I can think of other uses for the Tri Colour LED's I bought now that I understand how they work.

 

Thanks again.............................Bob.