Electronics Last update: 2019-07-25
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
We use a +24V power supply for the motor drives an the cover
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.