CNC Controller Motion Schematics

Posted on Feb 4, 2014

The power supply is pretty mundane. The 110VAC comes in on connector N17 and is hooked in series with a power switch SW1, a fuse F1, and the primary coil of transformer T1. The secondary coil of T1 produces 24VAC at 12 Amps and is routed through the full wave bridge rectifier BR1 and onto the controller board at connector at pins 1 and 5 of N12. A

CNC Controller Motion Schematics
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large off-board filter capacitor of 10, 000 µF (C31) is connected to the controller board at pins 2 and 5 of N12. In addition, a 24VDC cooling fan is connected at pins 3 and 6 of N12. Resistor R12 and red LED D33 will bleed off the charge of C31 when power is turned off. As long as D33 is lit, there is charge on the capacitor and extra care should be taken. The 24V primary coil is rated in RMS (Root Mean Squared), so the actual peak voltage is 24V/. 707 or approximately 35 volts. The unregulated voltage is used by the stepper and selenoid drivers as VDC. The unregulated voltage is stepped down through VR1, VR2 and VR3 to produce the 5 volts needed by the digital circuitry. The reason for using 3 voltage regulators is because 1) the stepper motors and selenoid chopper circuits will be causing a fair amount of roughness on the unregulated voltage and 2) the amount of heat generated will be spread across 3 voltage regulators rather than just 1. While the schematic does not show it, there are test points for each of the voltage regulators on the PCB. Lastly, power on is indicated by the green LED D34 which is current limited by R36. LED D34 is mounted off board on the chasis. The I/O microcontroller U11 is only needed if the user intends to use either the RS-232 connector N9 or the USB (Universal Serial Bus) connector N10. The PIC16C745 is needed to support both USB and RS-232, whereas a simpler PIC16F876A is can be used if...

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