Microcontroller Drives DSEC Motors

DSEC (digital-satellite-equipment-control) motors find wide use in TV-satellite reception; thus, they are readily available. Eutelsat defined the DSEC control protocol, which has been in existence since 1998. DSEC motors offer a resolution angle as high as 0.1°. Thus, you can use them as low-cost alternatives to stepper motors.

The circuit in Figure 1 is a simple design to drive protocol Version 1.2 of DSEC motors using a PIC10F200 microcontroller from Microchip. Version 4.2 fully describes the bus-functional method of data-bit signaling (Reference 1). You derive the 22-kHz-frequency tone from the internal 4MHz ±1 percent clock. Positioner commands from the protocol specification suit one-way communication. This application requires no receive responses or data messages from the remote motor unit. The long-term recommendation for the dc supply is 12V±1V, and the maximum current is 400mA.


Figure 1


The circuit uses just one pushbutton switch, S1, and two LEDs to control the state of the motor. At power-on, LED1 remains continuously on. One 1s-long push on S1 blinks LED1 for 0.25s and drives the motor one step. A 1s to 2s push on S1 changes the state of direction. LED1 turns off, and LED2 turns on. Pressing S1 for more than 3s causes one LED to blink during the time necessary to drive the motor back to 0°.

This design uses a motor with a resolution angle of 0.3° and maximum angles of 75° east and 75° west. So this circuit has only 250 pulses for each direction. Once it reaches that value, the active LED continues to blink.

You can download fully commented, three-file assembler source code here. You can adapt this code to any other baseline family of Microchip microcontrollers that use 12-bit instruction code.

Reference
Digital Satellite Equipment Control Specification 4.2, European Telecommunications Satellite Organization