Reasons to NOT use Grain of Wheat bulbs.?

[SHMD]

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.

 

I like your attitude. Never give in AND keep on trying!

(And I get the impression that your happy about it too!)

 

At the very least, you could use your Tri-colour LEDs as “normal” LEDs. Choose which colour you want it to be – red or green - and then cut the other leg off!

(Pound to a penny that you end up with the “wrong” colour though!)

 

;)

 

Kev.

[250BOB]

I like your attitude. Never give in AND keep on trying!

(And I get the impression that your happy about it too!)

 

At the very least, you could use your Tri-colour LEDs as “normal” LEDs. Choose which colour you want it to be – red or green - and then cut the other leg off!

(Pound to a penny that you end up with the “wrong” colour though!)

 

;)

 

Kev.

 

Hi Kev,

I like to think I have the right attitude.......and this subject is fascinating. The more you learn, the more you want to find out. I've spent a few quid on various LED's etc., and some of it may never get used......but the fun I'm having setting up test rigs is amazing. The applications must be endless.

Can't wait to get my points all wired up and wired back to the control panel....my pals are gonna think me a right smartass.

Again....many thanks Kev, and everyone else on this thread who has helped. RMweb is a real treasure for all of us........how on earth I would have done what I have achieved in this hobby without the assistance from its membership. RMweb is now a permanent part of the hobby for me and many of us...long may it continue.

Bob

[Suzie]

There is no doubt that bipolar outputs would make driving the LEDs a lot easier. There is one further option to try that might save a few diodes if you are powering the circuit with DC:- Connect the tri-colour LED up as per the right diagram using the outer two legs, and connect the middle leg to the negative power supply terminal. It is a bit of a bodge and I would not do it that way (I would use the Bi-Colour LEDs), but since you have the tri-colour ones... It is possible that the LEDs might not extinguish properly this way, so you will need to experiment and if it does not work revert to the left diagram.

[Gordon H]

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!

Whilst push-pull capability would be the ideal, if source driving is sufficient there is a possibility of replacing the ULN2803A with a UDN2981A which is the equivalent source driver. Might need a bit of work around the pin 9 & 10 area to sort the supplies out, but otherwise the pinout is identical. If the existing chips are in sockets, so much the better.

[Grovenor]

Personally I would not use bi-colour or tri-colour LEDs to indicate point position, it is much better to show the position set by the position of the LED on the panel, ie one LED in each route and light up the relevant one, then all you need are simple yellow LEDs and the routes you have set are obvious from the line of lights on the panel. No need to remember which route is red and which route is green, and no confusion when you later use the tricolour LEDs to indicate the signal aspects. Always a good idea to copy what the real railway does.

 

On a slightly different topic, your DCC system is probably able to put out 3 to 5 amps and rather more into a short. You won't want to wire up your panel with thick wires to handle these currents, so its best to limit the current the panel may take from the DCC bus at the connection point, ie at the frog and at the two main connections to take the bus wires into the panel. All the panel wiring can then be in thin wire, eg 7/0.2mm. Attached sketch shows one way of doing this that I have tested out.

detector-schematic.pdf

Regards

Keith

[Suzie]

It is getting a bit technical now and possibly off topic, but the easy answer to getting bipolar drive is to remove the ULN2003 from the sockets and replace them with with wire jumpers from the input pins to the output pins, then all of the outputs would be bipolar at 5V with 25mA current limited drive from the PIC controller chip. Bi-colour LEDs would just need a lower value current limit resistor in series and could simply be connected between the output pins, and tricolour would just need lower value current limit resistors in series with the outer legs with the middle leg connected to a suitable 0V supply connection (looks like a 0V terminal could be obtained by putting a bolt through the unused hole in the regulator heatsink).

[250BOB]

It is getting a bit technical now and possibly off topic, but the easy answer to getting bipolar drive is to remove the ULN2003 from the sockets and replace them with with wire jumpers from the input pins to the output pins, then all of the outputs would be bipolar at 5V with 25mA current limited drive from the PIC controller chip. Bi-colour LEDs would just need a lower value current limit resistor in series and could simply be connected between the output pins, and tricolour would just need lower value current limit resistors in series with the outer legs with the middle leg connected to a suitable 0V supply connection (looks like a 0V terminal could be obtained by putting a bolt through the unused hole in the regulator heatsink).

 

 

Hi Keith

I am using a Point Position Indicator because I cannot use the frog polarity method with my slips......I appreciate that the other points can, and may well be done via the frog polarity method.

 

The PPI lights the LED's using a 12v DC source, and the points are operated by usual 16v AC, from which the point switches are connected to the opposite side of the PPI.

 

However, I am listening to your thoughts of just using say lit yellow LED's to light up the set path....and save my tri colour red/green LED's for later signal indication. This might well be my direction once I have digested and thought about all the other incredibly useful information supplied in this thread.

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

[250BOB]

It is getting a bit technical now and possibly off topic, but the easy answer to getting bipolar drive is to remove the ULN2003 from the sockets and replace them with with wire jumpers from the input pins to the output pins, then all of the outputs would be bipolar at 5V with 25mA current limited drive from the PIC controller chip. Bi-colour LEDs would just need a lower value current limit resistor in series and could simply be connected between the output pins, and tricolour would just need lower value current limit resistors in series with the outer legs with the middle leg connected to a suitable 0V supply connection (looks like a 0V terminal could be obtained by putting a bolt through the unused hole in the regulator heatsink).

 

Hi Suzie,

Yes, this is getting a bit beyond my capabilities and understanding now, nevertheless, I am still fascinated by the whole subject, and equally fascinated by how much you guys know and understand this stuff. I really appreciate your input on this thread....it has all helped my understanding immensley.

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

[mezzoman253]

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.

 

OC milti-colour LED drive.gif

 

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).

Hi,

 

Sorry to resurrect this topic, but I'm going a similar way, but need both route LED's on at the same time. I was wondering if you could parallel 2 bi-colour LED's, like the RH diagram but two units, so that one would be showing GREEN whilst the other was showing RED at the same time. Then the switched route would all be GREEN's and the blocked route all RED's. Or is that too simplistic?

 

I'm considering the PP1's and already have lots of 2 legged bi-colour LED's. I'm using traditional point control.

 

Thank you, 

 

Rob

[Suzie]

Just put two 2-pin bi-colour LEDs in series, one round the other way. Paralleling will not work (only the red will light)

[mezzoman253]

Just put two 2-pin bi-colour LEDs in series, one round the other way. Paralleling will not work (only the red will light)

Hi Suzie,

 

Like this? Excuse the rough drawing.

 

 

thanks,

 

Rob

[Phil S]

Whilst you may already have plenty of bi-coour 2-legged LEDs in stock, buying conventional LEDs from Rapid, or Ebay, or other suppliers in 10's 20's ...100's is so cheap that its worth getting the approriate size and shape LED for your puropose .... you'll soon find another use for the bicolour types.

[mezzoman253]

Hi,

 

Normal LED's will do the job but not in the way I want.

 

I need a GREEN indication for the set route and a RED one for the unset route, BUT, at the same time. So when the point is thrown the colours swap over, the new set route going green and the unset red. Both LED's being lit together.

 

I'd need 4 conventional LED's per point for that, rather than 2 bi-colours. That would make the mimic panel rather cluttered having 20 sets for points to deal with.

 

Thanks,

 

Rob

[Phil S]

Then perhaps your best option are 'RGB' or RGB and White LEDS with 3 anodes and 1 cathode - no problems of reversed polarity - common location and toral freedom n colour choice.    The simpler scenario are the wider range of 2-colour, but common anode or common cathode LEDs - as opposed to the 2-legged bicolour which relies on current direction to change.  (Common cathode is 'standard', common anode are for 'dcc use' in function/loco decoders)

 

The drawing you included a couple of posts ago simply wastes 2 of the colour options - as it is shown +ve to the right ... unless this was in error, and the polarity of the power supply is supposed to change.

 

I suggest you browse through the LED section of Rapid Electonics or similar - just to see what is readily available, and at what prices!

[mezzoman253]

Hi,

 

The blocks on the left were supposed to illustrate the 2 terminals of the PPI1 points indicator, which is mentioned in the thread up a page or so. The polarity of these changes as the points change, so they are either on or off, but not both off or both on.

 

I've found some common anode 3 pin LED's on eBAy at reasonable price, but as I need 40+, I'd like to use what I have, which is 2 legged ones. But maybe it can't be done.

 

Regards,

 

Rob

[Suzie]

Here is how to do it, one LED in each leg of the route they will show green in one leg and red in the other, changing over when the route is changed.

 

 

The 2-pin LEDs are ideally suited for this application, the circuit is very straightforward.

[mezzoman253]

Here is how to do it, one LED in each leg of the route they will show green in one leg and red in the other, changing over when the route is changed.

 

OC milti-colour twin LED drive.gif

 

The 2-pin LEDs are ideally suited for this application, the circuit is very straightforward.

Hi Suzie,

 

Many thanks for the diagram, I knew it could be done somehow. 

 

Rob