TopBox Technical Manual

Electronics Design

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  • AC Power and Chassis Ground

    Fig. 1 below shows the AC power connections from the power entry module PEM to the hot (black) and neutral (yellow) terminal blocks TBH and TBN, where separate lines split off to power the two 24VDC power supplies, the motor controllers, the focuser, and the time delay relay. The ground wires (green) connect each component to the aluminum mounting subpanel, which serves as the "protective earth" (PE) chassis ground. The neutral wires, color coded yellow in the illustration, are actually white. Fig. 2 shows the power entry module (PEM) wiring in detail. Any power cord used to supply AC power to the electronics box should be checked to verify that its wiring agrees with Fig. 2.

    A power strip is mounted with adhesive Velcro tape on the S panel of the electronics box so the TopBox power can be switched remotely together with the camera on a single outlet.

    Fig. 1. AC power and chassis ground wiring connections.

  • Fig. 2. Power Entry Module (PEM) wiring connections.

  • DC Linear Power Supplies (PS1, PS2)

    As shown in Fig. 3 below, the AC neutral input N of each 24VDC linear power supply PS1, PS2 is connected to transformer input 4, and the AC hot input H is connected to transformer input 1 (after passing through fuse F1, F2 as shown in Fig. 1). The "remote sense" feature of the power supplies is not used, so the output terminal jumpers are left as shipped from the factory. The output terminals used for +24VDC and GND are also marked in Fig. 3.

    PS1 is used to supply +24VDC to the serial interfaces, line driver pulse outputs, and general I/O signals for each of the motor controllers through connections to the three I/O Terminal Blocks and Serial Terminal Blocks. PS2 is used to supply +24VDC to the electromagnetic brake circuit of the autoguider linear positioner.

    Fig. 3. DC power supply wiring connections.

  • Motor Controller Wiring

    The pinouts and signal functions for the motor controller terminal blocks are shown in Figs. 4–7 below. Since the Oriental Motors manual refers to the 36-pin I/O Terminal Block as CN4 and the 20-in Serial Terminal Block as CN5 according to their cable connector ports on the motor controllers, the identifier labels "I/OTB(1,2,3)" and "STB(1,2,3)" in the "Electronics Parts" illustration of the previous section correspond to "CN4(1,2,3)" and "CN5(1,2,3)" in the manufacturer's terminology.

    Fig. 4. Motor driver connection diagram from the Orientalmotor Alpha Step Brochure. The driver terminal numbers correspond to the terminal numbers on that driver's 36-line I/O Terminal Block (CN4). The TopBox is wired according to the "Current Source Input and Current Sink Output" option as shown in this diagram.

    Fig. 5. Motor driver pinout and signal table from the Orientalmotor Alpha Step Brochure. The driver terminal numbers correspond to the terminal numbers on that driver's 36-pin I/O Terminal Block (CN4).

    Fig. 6. Motor driver pinout and signal table from the Orientalmotor Alpha Step Brochure. The driver terminal numbers correspond to the terminal numbers on that driver's 20-pin I/O Terminal Block (CN5).

    Fig. 7. Motor driver RS-232C daisy-chain connection diagram from the Orientalmotor Alpha Step Brochure. The driver terminal numbers correspond to the terminal numbers on that driver's 20-pin I/O Terminal Block (CN5).

    • PS1 Connections

      • 24VDC
        PS1+24VDC → CN4(1,2,3)#1
        PS1GND → CN4(1,2,3)#4
        CN4(1)#1 → CN4(1)#17
        CN4(1)#17 → CN4(2)#17
        CN4(2)#17 → CN4(3)#17

        As shown in Fig. 4 above, the +24VDC power supply connection from CN4#17 to CN5 is internal for each individual controller (COM1), so no external connection is required to power CN5.

      • MBC (Linear Actuator Motor Brake Control Signal)
        CN4(3)#1 → SSR#A1
        CN4(3)#3 → SSR#A2
        CN4(3)#4 → CN4(3)#2

        See the discussion of Linear Actuator Motor Brake Current below for further explanation.

      • HOMELS (3 × Home Limit Sensor Signals)
        CN5(1,2,3)#15 → 3 × Switch NO (red wires)
        CN4(1)#4 → 3 × Switch GND (COM) (black wires)

        To connect to the TopBox, these 6 wires are attached to the inside of the RJ25 keystone panel jack HS mounted on the electronics box in the following order from left to right, looking at the jack from the outside with the clip at the top:

        Linear Positioner:
        CN4(1)#4(Switch GND)
        CN5(3)#15(Switch NO)
        Motor 2:
        CN4(1)#4(Switch GND)
        CN5(2)#15(Switch NO)
        Motor 1:
        CN4(1)#4(Switch GND)
        CN5(1)#15(Switch NO)

        A 6-wire flat telephone cable with RJ25 crimp connectors on both ends is used to connect from this panel jack to a matching panel jack on the TopBox which is wired to the home switches inside. See Electronics Parts, Fig. 2 for photos of the switch wiring inside the TopBox.

      • ALM Output, START Input
        (Home Motor Controllers on Power-Up with Time Delay)

        CN4(1,2,3)#27(ALM Output) → CN4(1,2,3)#15(START Input)
        CN4(1,2,3)#28(ALM Output Complement) → TDR#3
        CN4(3)#2(GND) → TDR#1
        AC Neutral → TDR#2
        AC Hot → TDR#7

        A homing program named "STARTUP" is stored in each controller. If it exists, a program with this name will be executed by the controller on the OFF → ON edge of the START input signal. As shown in Fig. 8 below, a START signal is only valid after a delay of 0.1s or more from the OFF → ON edge of the ALARM output signal, which occurs 0.5s or less after the power is turned ON. To generate a START input signal with valid timing, the START input (current source) of each controller is enabled by connecting it to the ALM output (current sink) with a time-delay relay on the drain line from the ALM output complement to GND. The adjustable time delay is set for approximately 0.9s.

        Fig. 8. Power-on timing chart from the Orientalmotor Alpha Step Built-In Controller Operating Manual.

    • PS2 Connections

      • Linear Actuator Motor Brake Current
        PS2+24VDC → SSR#13
        PS2GND → Motor Brake Negative Lead (gray)

        Terminal connections for +24VDC from PS2 to the autoguider linear positioner electromagnetic brake circuit follow the sample wiring diagram for the Solid State Relay (SSR) in Fig. 9 below. The two free wires from the autoguider linear positioner cable connected to Motor Controller 3 has two free wires to power the brake circuit. The gray wire (negative) is connected directly to PS2GND. The orange wire (positive) is connected to terminal 14 of the SSR (SSR#14) and the +24VDC output of PS2 is connected to SSR#13. The switching of the SSR is triggered by connections to the MBC output signal on CN4(3), which must be programmed to appear on one of the eight general output pairs Y0–Y7. We choose Y0 = CN4(3)#3,4. According to the "Current Sink Output" configuration of the controller wiring, the Y0 signal terminal CN4(3)#3 is connected to SSR#A2, while SSR#A1 is connected to the current source PS1+24VDC at CN4(3)#1 and the Y0 complement terminal CN4(3)#4 is grounded to PS1GND at CN4(3)#2.

        According to the AlphaStep controller manual, "the MBC output turns OFF when the motor loses holding torque due to a current cutoff or alarm. The customer's host controller should be set so that it detects an MBC OFF and turns OFF the power the the electromagnetic brake, thereby activating it." The manual also states, "Do not attempt to use it as a safety brake," so the brake is intended to be operated automatically by the controller after the MBC signal is set to a wired output, and the user is not intended to operate it directly.

        This means that once the brake circuit is wired as described above, its emergency function is fully enabled simply by setting OUTMBC=0 in software, which assigns the MBC signal to the Y0 output pair. Then the MBC output signal is ON for normal operation, which keeps the brake current switched on through the SSR so that it is deactivated, and allows the brake current to be switched off when the controller detects of a loss of holding torque and turns the MBC output OFF, activating the brake. Each program which operates the linear positioner must begin with the OUTMBC=0 command because starting a program resets all programmable output signal assignments.

        Fig. 9. Sample motor brake wiring diagram from the Weidmuller Solid State Relay Datasheet.

    • RS-232 Serial Port Daisy Chain Control Wiring

      The three TopBox motor controllers are connected to an RS-232 serial port of the Control PC on a daisy chain as shown schematically in Fig. 7 above.

      PC GND → CN5(1)#10(GND)
      CN5(1)#10(GND) → CN5(2)#10(GND)
      CN5(2)#10(GND) → CN5(3)#10(GND)
      CN5(3)#10(GND) → PC GND
      PC TX → CN5(1)#7(RX)
      CN5(1)#5(TX) → CN5(2)#7(RX)
      CN5(2)#5(TX) → CN5(3)#7(RX)
      CN5(3)#5(TX) → PC RX

      Starting at the Control PC, the motor control line is on a USB-to-Serial adapter leading from a USB port to a DB9 RS-232 connector which is coupled to a 4-wire flat telephone cable by a DB9-RJ25 adapter using only 3 wires: PC- DB9-2(RX), PC-DB9-3(TX), and PC-DB9-5(GND). The cable passes through conduits to the telescope pier and plugs into the RJ25 6-conductor keystone panel jack PCM on the electronics box. To use the P232R serial port surge protector, the inside connection from this panel jack to the surge protector (which is an 8-conductor device with RJ45 input and output jacks) is made with flat 6-conductor cable crimped onto the middle 6 conductors of an RJ45 plug. A matching surge protector output cable then has 3 leads which connect the original 3 conductors to the daisy chain as shown above.

  • Focuser Wiring

    Since the JMI SmartFocus controller is designed to connect to a PC with a straight-through serial cable and the PC transmits on 3=TX and receives on 2=RX, the controller must receive on 3 and transmit on 2. Starting at the Control PC, a straight-through DB9 RS-232 serial cable is connected to a 4-wire flat telephone cable by a DB9-RJ25 adapter using only 3 wires: PC-DB9-2(RX), PC-DB9-3(TX), and PC-DB9-5(GND). The cable passes through conduits to the telescope pier and plugs into the RJ25 6-conductor keystone panel jack PCF on the electronics box. To use the P232R serial port surge protector, the inside connection from this panel jack to the surge protector (which is an 8-conductor device with RJ45 input and output jacks) is made with flat 6-conductor cable crimped onto the middle 6 pins of an RJ45 connector. A matching surge protector output cable is wired to a male DB9 RS-232 connector to complete the straight-through connection of RS-232 pins 2, 3, and 5 to the focus controller input.

    A 6-wire flat telephone cable connects the focus controller to the inside jack of the RJ45 keystone data coupler panel jack FC on the electronics box. Another 6-wire flat telephone cable with RJ25 crimp connectors on both ends is used to connect from this panel jack to a matching panel jack on the TopBox which is wired to the focuser inside. The wiring from the controller to the focuser is non-standard in that the wiring sequence is the same at both ends, while the ends of standard telephone cable runs are wired oppositely.

  • Serial Port Surge Protector

    The SPSP chassis is mounted on edge with one side clamped to the DIN rail as shown in Fig. 10 below. It contains two plugin modules to protect the serial lines from the Control PC to the motor controllers (MC) and the focus controller (FC):

    MC IN: from panel jack
    MC OUT: to motor controller daisy chain

    FC IN: from panel jack
    FC OUT: to focus controller

    Fig. 10. Serial port surge protector connections.


Last modified: Nov 15, 2012
David McDavid

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