The MegaPoints servo controller has three memories to provide for simple route setting. I have built a small switch panel to let me use this functionality.
Operation of the memories uses push buttons (to be provided by the modeller) with visual confirmation from an LED mounted on the servo controller. To my mind, any kind of reasonably ergonomic operation needs sight of the LED, so I modified the servo controller to drive a new LED beside the push buttons. This probably voids the warranty but I think the modification makes the project worthwhile.
The on-board LED is the one labelled MODE and it has a dedicated voltage-drop resistor marked 1001 meaning 10k ohm:
When this LED is lit, the voltage drop across its resistor measures 2.6 volts, suggesting a current of 2.6 mA. I cannot work out for certain what is driving this LED but it might be the CMOS octal register nearby - such a device could sink 4 mA on one of its outputs. It seems prudent to leave the current consumption much the same (or less) so I disconnected the on-board LED by lifting one end of its 10k resistor. This is easier than trying to lift the LED, and the resistor is still there if I ever want to put it back. I bought a high-efficiency LED and connected this (with a new 10k resistor) to the two 'via' holes beside the on-board LED:
I rather like these servo-style connectors. If you plug the mating connector in the wrong way round, you just swap it around to make the LED light up. I put the new resistor on my switch panel, beside the new LED.
My switch panel is a scrap of Veroboard with four pcb mounted switches. These are momentary action switches. When you push a switch, it connects the pair of pins on its left (always the common on my board) to the pair of pins on its right. The copper strips are running vertically in this photo, and the connections from the switches are fairly easy to understand:
For operation, you set up a route on the servo controller and then press and hold a 'route' button until the LED flashes three times and goes off. This response from the LED shows the route is stored in the memory. You can then proceed to operate the layout as normal, using the servos to set a different route. A short press on the same button recalls the memory, sets the servos to suit, and causes the LED to light constantly. A short press on the reset button extinguishes the LED and restores normal operation of the servo controller.
I am left-handed so I have indulged myself by putting the LED where I can see it when I press any button. I chose yellow for my LED because I prefer to keep red (as used for the on-board MODE LED) to show fault conditions.
I bought a 50 x 50 mm sample of acrylic sheet to make a small escutcheon / panel. This seems an economical approach, there is no waste and the functionality here doesn't lend itself to adding in beside a lever frame.
I trimmed the Veroboard and added some strip wood to hold the panel:
The finished panel looks like this:
I chose a matt acrylic colour called "Grey Ash". The LED is flush with the panel and the buttons are about 2 mm above it.
Eventually I made up a cable to connect the wanted pins on the panel to the servo controller. I ended up doing this about four times over but this is the final version:
I started with 7/0.2 wire and this left the terminals too fat to go into the housings. Trying with 7/0.1 wire I still made many many crimps wrong and I probably discarded thirty before I had 14 I was reasonably happy with.
My ribbon cable is about 0.9 m long. There is no specification for the maximum length of such wires in the MegaPoints documentation, but I had 1.5 m of ribbon cable and I wanted to leave myself with a usable offcut.
The nearest terminal labelled SC is free for use with the local point levers (switches) on S1 to S9. I am keeping S10 to S12 free for future use if I connect a fiddle yard directly onto the layout.