Electronics                                                                                                                               Last update: 2019-07-25

Power Distribution
The whole machine runs from 1 mains power entry combined with the Mains Power Switch and a fuse.
We use a PC Power supply for +5 Volt for SFB, SMB, etc. and +12V for the video schreen and some ledstrips in the laser area and in the cover.
We use a +24V power supply for the motor drives an the cover winch.

Mains Power Present Detection
For certain logging purposes it is required that the Pi knows that mains power is going down in a while.
We placed an opto-coupler in series with the Neon bulb wich signals “Swiched On” on the cpnsole. This Opto gives us a 100 Hz interrupt on the SFB Arduino. When this interrupt is missing for 14 msec the message “Power Is Going Down” is given to the Pi.

Drive Power circuit
To allow safe start-up and secure emergency stop we implemented a “Drive Power” switching circuit.
A special relay switches power to a.o. the Motor drives and the HVPSU. This power can only be manually switched on when the Pi is running and the communication with the SFB is established. When this communication fails the Drive Power is switched off by the SFB. The circuit is such that the software/firmware can switch off DP or prevent it being switched on, but is not able to switch it on by itself. Always a manual action is required to switch DP on.Motor Drives For reasons of required torque we do not use the Polulu type motor drives on the SMB. Instead the Dir and Step signals from the SMB are routed to 3 stepper drives of type MSD415, allowing motor currents up to 1.5 A. These signals are bufferd by a ULN2003 IC because the SMB runs on 3.3V which is insufficient to steer the motordrives.