I like the circuit suggestion proposed by Kai. I would like to suggest two additional things.

First I would supply a relay, controlled by the microcontroller, that permits the +12V supply lead to opened up in the event there is ever a fault detected. There could be one relay per floor that switches the +12V to the 60 drivers on one circuit panel.

Secondly there could be an advantage to build the current sink circuit in an ever so slightly different way. Please see the snippett of Kai's circuit below:



The use of the BC817 type transistor, instead of the 2X LL4148 diodes, offers a closer bit of control over the setting of the threshold where the current limit kicks in. This advantage is offered due to the current gain in the transistor.


I particularly like the overall circuit solution becasue all of the parts are readily available and are also rather inexpensive. I can envision a packaging solution where the circuit board for 60/64 circuits is a long narrow board. It could be about 30 to 40 mm wide and about 350 mm long. It could be mounted on the inside flat of a length of aluminium angle stock. The row of the BD135's can be screwed along the inside edge on the 90 degree side of the angle bar. Using 5 mm center to center PC board mount screw terminal blocks would allow for two wires per lamp to be connected along the long side of the assembly. The +12 and GND wires can be connected on one end and run down the length of the PC board with huge wide traces even as much as 15 mm wide. Here is a crude drawing of the end view of such a construction.



Michael Karas