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chris

158 Lighting Improvements

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The Bachmann 158 is getting on a bit. Bachmann have recognised this and are currently producing a new version which will address problems such as the visible motor, DCC and the yellow head lights!

I can't do anything about the motor in my model, so I won't be adding internal lighting, but I can sort out the DCC (actually I did that 4 years ago) and the external lights.

This project is another step into new territory for me. This will be the first model I've added door warning lights to. It is also the first time I'm using twin colour LEDs which can shine white or red.

I've put off doing this project for 3 years, mainly because you have to break the model do it. The cab front is a separate piece of plastic, but it is glued in place and you just have to hope that they didn't go heavy on the glue as you snap it away :o

I've worked on the dummy car today and the cab front came away without incident 8-)

A bit of playing with resistors was required to get a matching brightness on the two red taillights. The twin colour LED isn't as bright as the red, so a smaller resistor was needed to get a similar look. This wasn't a problem with the white lights as they are headlight and marker light so matching wasn't necessary.

I'm an old hand at head and taillights these days, so that went smoothly enough, but I did nearly forget to wire the taillights for two functions. The two functions are needed if you want to be able to switch on the taillights at both ends, this happens when a train is parked in a platform. It's not a big feature, but I like to have it when I have a spare function on a DMU.

The door hazard lights are new to me, and something I've been wanting to add to my DMUs for a long time. On the 158 there's one amber light per side in the centre of each car. Surface mount "nano" lights are perfect for this job, albeit annoyingly fiddlely. So far I've carefully drilled out the holes for the two LEDs and fixed them in place with glue and glaze. I still need to wire them up to the decoder, but the quick test I did was impressive.

If all goes to plan I'll be adding the door warning lights to more of my DMUs.

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Ok. I'll try to remember to take a before and after when the dummy is complete and prior to working on the motor car.

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I've finished the dummy car and I'm very happy with the results.

I'll wait until tomorrows daylight before I try and take any photos. I may even try taking them outside, I did manage to give the track a quick once over with the track rubber today.

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Although it gets in the way most of the time, Colwick station lives in the conservatory between running sessions. It was a handy location for a photo shoot.

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The comparison is mainly between the original headlights and the new white headlight and marker lights.

The interesting lamp on this unit is the one on the right. It's a twin lamp shining white or red depending on direction.

My favourite improvement to this unit is door light on the sides. It's a tiny light, if anything it's under scale, but it really makes a difference.

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I'll have to see if I can program it to switch off when the train is moving, but then again, the point of the light is so platform staff and signalmen can see if the train is moving with the doors unlocked. And you thought they were for the benefit of passengers ;)

I wonder how long it will take Hornby or Bachmann to add these to a RTR DMU. The problem will be in DC mode, how would you operate them? One option would be to have them come on when the train stops, a small capacitor would do the job.

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Lovely stuff Chris. The whiter light makes a real difference to the frontal view. The small door light is a nice touch but I've commented elsewhere about how it's something I should avoid attempting myself. I'll not repeat it here.

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I'm one red LED short for the motor car of the 158, so I've put it to one side and switched to adding door warning lights to my 142 Pacer.

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I've added more pics of both to my gallery

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I managed to find a suitable red LED in the spares box and spent the day doing the lights upgrade on the motor car of the 158.

The only real difference to the dummy car was with the twin colour LED. Having two LEDS inside the same housing means that neither of the emitters are directly in line with the lens so the light looks a little off. I constructed I sleeve out of white plasticard (and aluminium foil) which does a good job of preventing light leakage and reflecting all the light so it comes out if the lens. The result is a much better and softer light for both the red and white colours.

The next train due a light upgrade is my Northern Rail 156 SuperSprinter, my Avatar pic. From memory the motor car only has a two function chip installed, but it's on a harness, so I should be able to get on with it and plug in a 4 function chip when I get one.

Onwards. 

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Turns out that the 156 has a 4 function decoder in it so it was all systems go.

However I wanted to squeeze 5 function in. I want these.

  1. Headlights
  2. Taillights
  3. Warning lights
  4. Parking lights
  5. Coach lights

The head and tail lights take 2 functions. The white wire is connected to the headlights and resistor in series to the blue wire (common positive) while the yellow goes to the tail lights, a resistor then blue.

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In the other car of a DMU the yellow and white wires would be reversed due to the fact it is facing backwards so you want the opposite lights on.

If you want the parking lights on you have a problem. How dow you switch on the red lights at both ends. Well if you have very fancy-dan decoders you can programme them to do this, but I don't have those decoders. In the 158 shown above I had to add another function wire to the taillights (green wire to both ends) to switch the red lights on. It works, but it does mean I can have the red and white lights on at the same time or that the lights are off for a second as I switch from driving lights to parking lights. And it wastes a function.

I needed a better solution.

Thinking about the lights from an logic point of view, I worked out when lights were on and when they were off. This changed the game. Put simply, the red lights are on all the time, unless the white lights are on, and then the red lights at the front of the train are off.

What I needed was a circuit where the white wire turned the white lights on and the red lights off.

It's been a long long time since my electronics degree and I didn't have a clue. So I did the sensible thing and asked a friend, Martin. He sent me a simple circuit, which i didn't understand. I designed my own. It didn't work. I took another look at Martins circuit, reminded myself how a transistor worked and decided that his circuit might actually to the job. And it did.

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The taillight is now connected to the purple wire and a transistor has been added. The base of a transistor works as a switch. While there is a voltage on the base then a current can flow through the transistor and the taillight is on. If there isn't a voltage at the base of the transistor then the taillight is off.

The purple wire switches the red light on and off as normal.

The white wire still switches the white light on and off as normal, but it also switches the red light off when it is on. This is because it takes the voltage on the base of the transistor to zero volts*

And it works. I installed this in my 156 DMU yesterday while adding the coach lights and it works as planned.

The really clever bit is that I can do all this with just the white wire. If the purple wire is replaced by a ground wire then the circuit still works, but the red lights can't be switched off by a function, they are always on (apart from when the headlights are on) but this is what happens on the modern railway anyway. This frees up another function in effect giving my 6 function on a 4 function chip (cab light?)

This will be the way I wire DMU lights from now on.

----------------------

*This is a lie. The voltage at the base is at 0.7v, because there is a diode between the ground and the base and there is a 0.7 volts drop over the diode. The diode is there to stop the purple wire turning on the headlights. The purple wire has a diode on it to give the same 0.7v at the emitter as at the base and thus there is Zero voltage difference between the base and the emitter, which is what is required. I do remember some of my degree course.

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chris said:

...It's been a long long time since my electronics degree ....

So THAT'S why I can never understand it! :)

It's great work Chris but there's no way on earth I could ever attempt anything like that with my knowledge and level of ability. I'd have one dead loco, or at least a frazzled chip, for sure. I've come to realise that my forte is in bricks and mortar - anything else and I'm out of my depth.

What I would like to do, and perhaps I'd give this one a go, is to use similar materials to add simple coach lighting to a standard coach. Now I know that's going to be relatively easy for most people but I'd probably end up having to buy the kit and hope it's got clear instructions!

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I've had this unit in pieces again. It sat down back on in the summer. At the time I lifted it off the track, put it to one side and then continued playing with other trains. At some point it moved from the side of the track into a storage box. Today, many months later it came out of the box and received the much needed attention.

It sat down due to a transmission failure. The axel of one of the cogs had worked loose. I spent more time removing a large amount of grease than I did fixing the actual issue. Not sure if it came greased up or I had foolishly applied the stuff. 

Once it was a runner I turned my attention to the lights. They had been miss performing for a while, an issue I'd ignored. With the body away form the chassis, today was the opportunity to get it sorted. It turned out that the DCC chip had developed a fault. The white wire was permanently on. This meant the headlight were always on. Also the red aspect of the two colour LED had failed. 

The solution was to replace both.

I didn't want to bin the chip so swapped it with a similar chip from another loco, which only required 3 working functions. Careful use of the soldering iron has resulted in a DMU which once again has a full set of working lights as well as being able to move under its own power. 
A successful evening.

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