Today I managed to get the soldering station working again. I took the soldering iron apart (to see what is inside) and put it back together again. When I switched it on it became quite hot very quickly. I soldered a couple of white leds with a 470 ohm resistor together and connected a 5 volts power supply. The picture on the left shows the result.
After that I soldered three leds together and put them in the prototype. For both pictures goes that the leds are just put in without putting them in the right place. As soon as I have figured out how many leds are going to be used I will make a piece of polystyreen to size underneath which the leds will be mounted.
Three leds are prefarable. For this test I used a resistor of 470 ohm (just to be sure). After I made the calculations it appeared that I only needed a resistor of 90 ohm (100 ohm) for these leds. This will make the leds shine brighter as you can see in the picture on the left.