DIY Solution to MegaPoints Mimic Panels

[ISW]

Apologies if this is posted in the wrong section, but a quick look through the forum titles seemed to indicate this was the best place to post. If it should be elsewhere let me know.

 

I'm building a layout (see signature) using MegaPoints Controllers and have reached the stage of building a mimic panel. In order to make it more 'plug n play', and to keep costs down , I'm thinking of using a DIY approach using off-the-shelf components and good old veroboard for each turnout / crossover. Each veroboard would be screwed to the back of the mimic panel, with holes drilled at appropriate locations for the LEDs & buttons. My current idea is as below:

 

 

All dimensions in fractions of an inch as veroboard is in 0.1" strips. The DPDT would actually be a single 'button' type (as used by MegaPoints themselves).

 

Each board would be connected to the MegaPoints processor with 2 simple fly-leads (3 leads for the crossover). With each turnout / crossover being 'standardised', drawing up the mimic track layout should be straight-forward and consistent.

 

Is this a good idea, or am I leading myself into problems that I'm not seeing?

 

[Brian]

I haven't any idea on what the Megapoints control board outputs for LEDs, but normally there would be series resistors in the LEDs.  Are these on the main Megapoints circuit board? 

[ISW]

Brian,

 

Yes, the MegaPoints Processor board conveniently includes a 1k resistor for each of the LED output connections. To quote from the manual:

 

"Flexible indication
You are free to hook up a single LED or pair of LEDs to each of the outputs depending on your needs. If a pair is used, one will always be on while the other is off, reversing when a button is pressed. This allows for route indication on turnouts etc. Our LED cable is available with a pair of LEDs attached.

If you choose to roll your own LED cable we’ve already installed the resistors for you. Just connect the LEDs to your cables."

 

At least that shouldn't be a problem. I'm still concerned there are 'other' problems I've missed  as I've not seen anyone else do what I'm proposing.

 

[Brian]

Excellent.. I didn't want you burning out any LEDs if there were no pre installed LED resistors.  

[ISW]

Brian,

 

It didn't burn out any LEDs, but they are are a lot brighter than I was expecting. The 'proper' MegaPoints LEDs are of a much lower intensity. I can only assume MegaPoints use 12v LEDs whereas the cheapo ones I used are the common 3v?

 

[meil]

8 minutes ago, ISW said:

Brian,

 

It didn't burn out any LEDs, but they are are a lot brighter than I was expecting. The 'proper' MegaPoints LEDs are of a much lower intensity. I can only assume MegaPoints use 12v LEDs whereas the cheapo ones I used are the common 3v?

 

There's no such thing as a 12v LED. All LEDs are 2v-3v. 12v LEDs are 2v LEDs with an in-built resistor.

 

For modern LEDs 1k is much too low - you should use 2k2 or even 3k3 in low light conditions.

Edited May 23, 2019 by meil

[sharris]

On 23/05/2019 at 20:13, ISW said:

Brian,

 

It didn't burn out any LEDs, but they are are a lot brighter than I was expecting. The 'proper' MegaPoints LEDs are of a much lower intensity. I can only assume MegaPoints use 12v LEDs whereas the cheapo ones I used are the common 3v?

  

 

You've probably just got high brightness LEDs - they can come in quite a range of brightnesses and efficiencies depending on which one you choose. A quick perusal of the Farnell catalogue indicates that green indicator LEDs have a typical forward voltage of 1.9V to 2.2V (depends on their chemistry) and forward currents from a few mA to about 20mA for different types. 

 

[ISW]

Sharris,

 

Thanks for the reply and your insight. I'll be a little more careful when ordering the next batch. I guess I just need to look for 'low brightness' LEDs.

 

[DCB]

Probably easier to add resistors to tone down the LEDs.Greens need different resistors to Reds for equal brightness. Also LEDs vary from batch to batch, buy a load at one hit for mimic panels where you want equal brightness, buy any old random tat for building lights which you want to vary in brightness and hue.

I would use DPDTs to operate the points with a separate operate push button myself. That way one side of the DPDT throws the point, when prodded the other lights the appropriate Mimic LED all the time . Saves a lot of wiring back from the point motors.

[ISW]

David,

 

2nd attempt at a reply. RMWEb went down as I was typing ... 

 

Probably easier to add resistors to tone down the LEDs. Greens need different resistors to Reds for equal brightness.

That was my thought, but fitting one in not exactly easy. If you look in my little Veroboards, there is no space to add a resistor (well, not elegantly anyway). Or is there? As you can see from the other photos, I use dupont type connectors / terminals for all the wiring. I'm wondering if there is an simple way to add a resistor into the cable??

 

Also LEDs vary from batch to batch, buy a load at one hit for mimic panels where you want equal brightness, buy any old random tat for building lights which you want to vary in brightness and hue.

All my LEDs came from the same supplier in the same batch and are the same, green, colour. I only have one that is brighter than the others. Yes, there are all too bright, but one manages to be even brighter. I did change the LED, but it made no difference. I can only assume that one of the resistors on the MegaPoints Controller is slightly out-of-spec. 

 

I would use DPDTs to operate the points with a separate operate push button myself. That way one side of the DPDT throws the point, when prodded the other lights the appropriate Mimic LED all the time . Saves a lot of wiring back from the point motors.

With the MegaPoints controller boards there is very little cabling to/from the mimic board. Just 2-wires for power and 3-wires for the network.  See photo below. That's all. One of the main reasons I went with MegaPoints Controller, simple wiring and plug-n-play (ish) simplicity.

 

As for the buttons, these can only be Momentary type as that is what the MegaPoints Controller board is compatible with. Cheap as well at less than 10p each. 

 

[Nigelcliffe]

2 hours ago, ISW said:

David,

 

2nd attempt at a reply. RMWEb went down as I was typing ... 

 

Probably easier to add resistors to tone down the LEDs. Greens need different resistors to Reds for equal brightness.

That was my thought, but fitting one in not exactly easy. If you look in my little Veroboards, there is no space to add a resistor (well, not elegantly anyway). Or is there? As you can see from the other photos, I use dupont type connectors / terminals for all the wiring. I'm wondering if there is an simple way to add a resistor into the cable??

 

 

There looks to be plenty of space for resistors in the veroboard circuit illustrated.   Unless there is something meaning you can't put components on the other side of the veroboard.

 

From the left, track 1 - make a break in the track, put resistor over the break (resistor on rear of veroboard, like the pins).

 

Track 3 - a bit more tricky, but looks to be space for one break, leaving a hole clear.  One leg of resistor in that hole, then resistor goes towards far end of track to feed into leg of LED.

 

 

- Nigel

[ISW]

1 hour ago, Nigelcliffe said:

 

There looks to be plenty of space for resistors in the veroboard circuit illustrated.   Unless there is something meaning you can't put components on the other side of the veroboard.

 

From the left, track 1 - make a break in the track, put resistor over the break (resistor on rear of veroboard, like the pins).

 

Track 3 - a bit more tricky, but looks to be space for one break, leaving a hole clear.  One leg of resistor in that hole, then resistor goes towards far end of track to feed into leg of LED.

 

 

- Nigel

Nigel,

 

Thanks you for the idea(s) and the prompt . Actually, Track 2 is 'common' to both LEDs so that's the better / simpler place to locate a single resistor. I like your idea for Track 3, so I'm thinking of applying that to just Track 2 as follows:

 

 

The only problem then is that I have to do this 33-times

.

[sharris]

... or if your hands are steady enough  - cut the copper track and solder a surface mount resistor across the cut. 

 

 

Incidentally, if track 2 is common, is one of the LEDs facing the wrong way? One has its flat facing towards the common, the other away from it, and unless my eyes deceive me, they are opposite ways round on the two boards you've photographed. 

 

 

Edited June 4, 2019 by sharris

[spikey]

3 hours ago, ISW said:

 ... If you look in my little Veroboards, there is no space to add a resistor (well, not elegantly anyway). Or is there?

 

At the risk of stating the obvious, don't forget that resistors always need much less space when installed vertically, with the "top" lead bent back along the body ...

[ISW]

14 minutes ago, sharris said:

... or if your hands are steady enough  - cut the copper track and solder a surface mount resistor across the cut. 

 

 

Incidentally, if track 2 is common, is one of the LEDs facing the wrong way? One has its flat facing towards the common, the other away from it, and unless my eyes deceive me, they are opposite ways round on the two boards you've photographed. 

 

 

Hmmm, surface mount resistors . Not sure about that. I did solder some 0805 LEDs previously and that was hard enough. If I can get physically 'larger' surface mount resistors I might be tempted. Although I would use normal resistors for all 'testing' to get the right value / brightness.

 

The LEDs are both facing the same way round for the turnouts they applied to, as I have to be careful on that front . The actual 'direction' is a bit hit-n-miss, as left / right get mixed up on the MegaPoints Controller depending on LH / RH turnouts as I always set the 'normal' position to straight (leaving the frog polarity microswitch 'open' and not in contact with the servo actuator arm). That's one reason I used sockets for the LEDs - easy to turn them round . And the sockets also raised the LEDs to the same height as the momentary switch for panel mounting.

 

[ISW]

23 minutes ago, spikey said:

 

At the risk of stating the obvious, don't forget that resistors always need much less space when installed vertically, with the "top" lead bent back along the body ...

Very true, but in my case I'm limited in the vertical axis as the veroboards are mounted on a panel with holes cut for the LEDs and momentary button switch.

 

Yes, I could mount them on the 'underside' but I can't see where I could get the 2 wires through.

 

I think my solution (in the marked up photos) or the surface-mount method are the ways to go.