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<html><head><title>EXAMPLE 8: RADIO-CONTROLLED AIRPLANE SERVOMOTOR CONTROL</title><link rel="stylesheet" type="text/css" href="style.css"></head><body><a href="./ex07_sem.htm">[previous]</a><a href="./tutorial.htm#index">[index]</a><a href="./ex09_ledclock.htm">[next]</a><h1>Example 8: Radio-Controlled Airplane Servomotor Control</h1><p>This example demonstrates the control of a pair of radio-controlled (RC)airplane servomotors via the parallel port. The motors used are FutabaS3003 motors, but the protocol is standard and works with most RCservomotors.<ul><li>RC servomotors use pulse-width protocol, where the width of thepulse determines the angular position of the motor.<li>The pulses repeat every 20 milliseconds. A pulse width of 1millisecond signals mid-range position. Varying this between 0 and 2milliseconds sweeps the motor through its angular range.</ul><table><tr><td><img src="./futaba.jpg" width="200"></td><td><img src="./uln2003a.png" width="200"></td><td>Futaba S3003 RCServo with a 3-wire interface. The red wire is power, 4.8V to 6V; theblack wire is ground; and the white wire is the signal, 0- to 2millisecond pulses 20 milliseconds apart.<p>The parallel port can't drive this motor directly. Use a Darlingtonpair line-driver chip, e.g., ULN2003. Connections, parallel port (PPT)to ULN2003:<p>PPT pin 2 to ULN2003 pin 1, PPT pin 3 to ULN2003 pin 2<p>ULN2003 pin 8 to ground, pin 16 to 20 K-ohm to +5V, pin 15 to 20K-ohm to +5V<p>Futaba red wires to +5V, black to ground, first motor's white toULN2003 pin 16, second motor's white to ULN2003 pin 15</td></tr></table>Refer to the <ahref="../ex08_rcservo/rcservo_task.c">commented real-timesource code</a> and the <ahref="../ex08_rcservo/rcservo_app.c">commented applicationsource code</a> for the details.<h2>Principle of Operation</h2><ul><li>No new RT Linux concepts are introduced here. We're puttingtogether what we've learned in the previous examples.<li>Three tasks are run in one-shot mode. One task always runs at 20milliseconds and sets all pulses high.<li>That task also schedules the other tasks to run some time later,0- to 2 milliseconds depending on the commanded position. These othertasks set their pulse low.<li>The commanded position is set by a FIFO from a Linuxapplication. A handler on the FIFO sets global variables for the pulseperiods.</ul><h2>Running the Demo</h2>To run the demo, change to the 'ex08_rcservo' subdirectory of thetop-level tutorial directory, and run the 'run' script by typing<pre>./run</pre>Alternatively, change to the top-level tutorial directory and run the'runall' script there by typing<pre>./runall</pre>and selecting the "RC Servo Motors" button.<p>A small GUI will pop up, with sliders that let you change thepositions. <p><a href="../ex08_rcservo/rcservo_task.c">See the Real-Time Task Code</a><p><a href="../ex08_rcservo/rcservo_app.c">See the Linux Application Code</a><hr><a href="./ex09_ledclock.htm">Next: Example 9, LED Wand Clock</a><p><a href="./ex07_sem.htm">Back: Example 7, Semaphores</a></body></html>⌨️ 快捷键说明
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