Posted on Feb 6, 2014

The modifications involve direct access to the stepper motor controls of your mount. Any `mis-control` or `mis-command` / `invalid parameter` or `garbage` data sent to the mount could accidentally activate the stepper motors and allow it to rotate `freely` damaging any equipment connected to your mount. It is also possible that any garbage or

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invalid data sent to the mount could cause its firmware to generate mis-steps pulse sequences to the motors causing it to overheat. Make sure that you perform the modifications and testing while there is no physical "load" or dangling wires on your mount. Be sure to disconnect the power once this event happens or if you notice any unusual sound coming from the motor assembly. The modification allows the user to control the mount`s stepper motor board via the PC`s serial connector. The mod is implemented on the handcontroller utilizing the existing RJ11 PC serial interface connector and its built-in RS232C to TTL level converter. This will avoid any external circuit required to connect the mount`s DB9 TTL level connector to the PC`s serial port. The mod circuit utilizes a Quad 2-1 Multipexer 74HC157 (Figure 2) that switches serial signals between the PIC controller of the paddle and the mount and PC. The mode of operation is set through an external SPST toggle switch; Below is a diagram of the modification (Figure 3). It shows the connections of the individual multiplexer component of the 74HC157 chip to the respective pinouts and tap markings of the handcontroller board. Also, pinout labels of the actual chip with respect to the circuit diagram is also shown. Use this as a reference in connecting the wires to the board. The tap points image (Figure 4) shows were to solder the wires as labeled in the circuit diagram. It...

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