Replacing 12v Signal circuit, or leading up to another MOD.

[Andromeda]

Hello All,

I've been busy again. I've managed to copy the inside circuit from a 12v signal 2 x 3 brick, onto strip board. I've got some thin 1.5mm black ABS plastic sheet lying around, so I'm probably going to butcher a black 2 x 3 brick at some point.

In the mean time here are a few pics of the circuit:

And working side by side:

Thanks for watching!

Edited April 19, 2016 by Andromeda

[alainneke]

Great stuff! Where did you get the sockets for the plugs (I think you also used these in your manual-to-motorized 12V switch conversion)?

[Andromeda]

I used 3mm brass tubing, funnily enough from a train hobby shop! It works well on the point switch Repairing 12v remote point switch because of the continuation, flanges and there being a solid plastic chassis to mount to.

I think I may 'split' the rings in my signal design to match the original, mainly because it is a tight fit, and the lack of mechanical strength by being only soldered to the board.

I did note the the 560R resistor got quite hot on both units whilst taking pics. A volt reading of the Transformers' side 'switch' connection showed 14+V, okay when running several lights, I think up to 800mA max draw.

Edited January 20, 2013 by Andromeda

[JopieK]

14V?! Should be 12V, so 14V is too much! 800mA is about 40 LED's so I'm puzzled how it can draw 800mA...

[Andromeda]

14V?! Should be 12V, so 14V is too much! 800mA is about 40 LED's so I'm puzzled how it can draw 800mA...

I did not insinuate that I was drawing 800mA, merely that 800mA was the Max.!

Read the bottom of the Transformer, Output II is listed as 12v @ Max. 0.8A(800mA). When measured under NO load it is 14+V.

I only had two LED's running at one time, both through 560R resistors that got hot, ow(bloody ow) hot...!

Edit:

Measured voltage with nothing attached (side power)14.49V but signal switch(pass through), with both signal lights(originalx2 and orig + mine) is 13.42V.

Side power with nothing at all connected is 14.49V. Normally Transformers read higher than stated voltage under no load.

Edited January 20, 2013 by Andromeda

[alainneke]

When hooking up my 7866 to a Esu SwitchPilot (DCC accessory decoder), I also noticed that the power from one of my 12V transformers (not LEGO) was not enough to lift the booms. Raising the voltage to 14V solved this.

Are the brass tubings if fact bushings, used for train wheels?

[bricks n bolts]

Great job! Can't wait to see finished product.

Also curious about the item description for the brass tubing you've used.

[Andromeda]

When hooking up my 7866 to a Esu SwitchPilot (DCC accessory decoder), I also noticed that the power from one of my 12V transformers (not LEGO) was not enough to lift the booms. Raising the voltage to 14V solved this.

Are the brass tubings if fact bushings, used for train wheels?

I found the same when testing remote switch motors, I plugged one into the train controller output and got nothing - even on full tilt. Shat meself then tried the end connection and phew!!

The tubing was bought from www.hobbyholidays.co.uk. The sizes were 3.0 and 3.5mm, which fit inside each other nicely. I used both sizes on the remote switch point, see link above, and only used the 3mm for this project!

Oh and if you are wondering about the flanges on the tubing, they were done by hand.

Edited January 21, 2013 by Andromeda

[Brickthus]

The voltage I measured from a 12V transformer was 14.7V.

An LED needs 2V at 20mA.

The resistor has to drop 12.7V at 20mA, which gives an ideal value of 635 ohms.

A 560 ohm resistor was chosen. This will drop 11.2V at 20mA allowing a mean loaded transformer voltage as low as 13.2V whilst maintaining 20mA.

Bear in mind that the switch panel is supplied from a separate winding from the train power ones and the switch devices are mostly off, being on only when switching (points, level crossing, decoupler). Only the signal LEDs will be on all the time, so the voltage is likely to be high end of the 12V to 14.7V range.

The maximum power dissipated by the resistor is 12.7V x 20mA = 0.254W.

You have used 1/4 Watt resistors, which is why thery get hot.

This application needs at least 0.5 Watt resistors. I think there are some 0.6W ones that are as small as 1/4W ones used to be.

The design needs to shed the heat too, so holes in your housing would be advisable, and don't set the resistor too close to the case or it might melt the plastic.

Well done for reviving the 2x3 brick signal idea.

I would consider driving some of these signals from Power Functions pole reverser switches on a 9V supply. It might be cheaper than PF light bricks with color filters, depending on convenience of location. It means I could use the PF light bricks for semaphore signals (1 white light with moving filters) and LEDs for colour light signals, either discrete ones back to back or a bi- or tri-colour LED for a searchlight signal.

Assuming the same LEDs (2V, 20mA) and a better-regulated supply (or batteries), the maximum PF voltage with fresh batteries would be 9.15V

The resistor would have to drop 7.15V at 20mA, so the ideal value is 357.5 ohms.

A 330 ohm resistor is common and allows for a supply value as low as 8.6V whilst maintaining 20mA.

The resistor will need to dissipate up to 0.143W so 1/4W resistor would do in a domestic application, but I might go for 0.5W or 0.6W if the size fits because of the long term operation - 8 hours at a time for a railway show.

I would probably cut a PF lead in half and solder the wires into the veroboard or PCB.

Mark

[LEGO Train 12 Volts]

Great work and usefull pictures ...thanks for sharing!

[Andromeda]

@Mark Bellis

Ohms law... Ah I remember it well! Indeed you are correct about the sizing, and perhaps ogeL used 6W. Both mine and the original get equally hot, but then again it is a test environment i.e. they are the only devices connected! OgeL also omitted to put any cooling holes into the unit so I'm going to run with it for now.

I visited your 'Brickshelf' today. I was impressed with your reverse engineering of the level crossing flasher unit. I may implement that into another future 12V train MOD, kudos !

Moving onto the main reason for replying....

I have, to some success, managed to house my above copy of the signal cct. I did, however, use a very old 2 x 3 black brick(so old it had 'Pat Pend' written inside!), primarily because it's walls are 1.5mm - not the modern 1mm. And because of this, there are no strengthening 'bridges' between the outer sides and the two tubular risers in the brick - in short easier to clear out the unwanted material!

Without access to a milling machine I was unable to fathom how to remove 1.5mm from the entire bottom of the brick, to match the original. So I decided that a brick that ends up 1.5mm fatter was no big deal!

The unwanted brick material was removed with a 10mm drill, drilled carfully close to the top of the brick, then chiseled out. The front was made from, not too shiny, black ABS plastic sheet. The cowling over the LEDs was four layers of heat-shrink tubing, shrunk to a 5mm drill bit, then cut to fit.

Edit:

I cannot find any sources for 7.5mm O.D./5mm I.D. black ABS tubing, anyone who knows of any, please let me know?

Edit: My MOD appears on the LHS in each pic.

Edited April 19, 2016 by Andromeda

[bricks n bolts]

Wow, amazing work Andromeda!

I cannot find any sources for 7.5mm O.D./5mm I.D. black ABS tubing, anyone who knows of any, please let me know?

Can you cut to shape a black "Brick, 1x1 Round"? Certainly seem the right outer diameter, not sure about inner diameter (http://www.bricklink.com/catalogItem.asp?P=3062b) but the walls are likely thinner than on the old ones (http://www.bricklink.com/catalogItem.asp?P=3062old).

[alainneke]

Nice work!

I cannot find any sources for 7.5mm O.D./5mm I.D. black ABS tubing, anyone who knows of any, please let me know?

Not that I know of, but I can turn some black Delrin to these dimensions (maybe with a little flange at the back, so that they are easier to glue?)...

[Andromeda]

Wow, amazing work Andromeda! Can you cut to shape a black "Brick, 1x1 Round"? Certainly seem the right outer diameter, not sure about inner diameter (http://www.bricklink...tem.asp?P=3062b) but the walls are likely thinner than on the old ones (http://www.bricklink...m.asp?P=3062old).

Thanks! I'll have dig through my ogeL and see what I find in the way of 3062's...

Nice work! Not that I know of, but I can turn some black Delrin to these dimensions (maybe with a little flange at the back, so that they are easier to glue?)...

Thanks again! You have a lathe, I'm jealous! I know that MEK won't bond delrin but neither does it bond the heat-shrink I used. If the MEK has some black ABS plastic dissolved into it, it does 'hold' the heat shrink in place, so it should work. If you try it, let us know how you get on?

[Andromeda]

It's funny what you find along the way!

http://www.ebay.de/itm/Lego-12V-Eisenbahn-Signale-7860-/271157349645?pt=DE_Allesf%C3%BCrdKind_Spielzeug_Lego&hash=item3f223ccd0d