# RoseOnRails – LEDs … It’s on !

Hi everyone,

This week I am in charge of answering all the questions we have about the LEDs we are going to put underneath the railway. Today, I answered some of them:

– How will we control the LEDs ?
After having discussed with Alexis, we found two solutions:
1. We can put independent LEDs underneath the railway and control them thank to PCBs ; each PCB would them be wired to one of the railway switches PCBs. This solution involves a lot of wires !
2. We can use ribbon of LEDs. Though the LEDs would we on a same line, each of them could be controlled independently thank to a ribbon controller. Each ribbon would then be linked to a railway switch PCB.
I personally prefer this solution, because it involves less wires than the first one …  Moreover, I have looked it up on the internet and have found numerous models of ribbons with different number of LEDs per meter, and different caracteristics. We will choose the LEDs ribbon according to how many LEDs we want, the length of the ribbons, the colours and the way they are controlled.

– How many LEDs ?
It would depend on the ribbons we can find, but approximately one for 5 centimeters.
I will measure the total length of the railway tomorrow.

– Will the LEDs be used to determine the position of the train ?
In our game, the only moment when we need to know the exact position of the train is when the train rolls over a LED ; so that it seems logical to determine the position of the trains thank to the LEDs. We will put an optical sensor underneath the train which will be able to determine when the train actually rolls over a LED.
However, we need to know which LED a locomotive rolls over. In order to do so we will modulate the light of each LED differently so that they send the accurate information to the central station and the good LED is shut down. (We now need to make sure the ribbon we will find will enable us to modulate the light of the LEDs).

– In which colors ?
If we use LEDs ribbons, we can easily use LEDs which can change colour.

Today, I answered a lot of questions regarding the LEDs ; but the answers have brought a lot more questions!
All those questions should be answered by Sunday.

By the way, I also managed to light the LEDs in my STM32 thank to the buttons! I think I have finally understood the events in ChibiOS!

Noémie Bristol-Courgeon

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