利用单片机加控制直流电机，利用P1口，编制程序输出一串脉冲，经放大后驱动小电机，改变输出脉冲的电平及持续时间，达到使电机正转、反转、加速、减速。停转之目的。
可以通过74LS244输入开关量数据来控制小直流电机的转动，实现正转四种转速，反转四种转速及停转。
-The use of SCM in controlling the DC motor
SHOW FULL COLUMNS FROM `jrk_downrecords` [ RunTime:0.001301s ]
SELECT `a`.`aid`,`a`.`title`,`a`.`create_time`,`m`.`username` FROM `jrk_downrecords` `a` INNER JOIN `jrk_member` `m` ON `a`.`uid`=`m`.`id` WHERE `a`.`status` = 1 GROUP BY `a`.`aid` ORDER BY `a`.`create_time` DESC LIMIT 10 [ RunTime:0.093263s ]
SHOW FULL COLUMNS FROM `jrk_tagrecords` [ RunTime:0.001270s ]
SELECT * FROM `jrk_tagrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 20 [ RunTime:0.001975s ]
SHOW FULL COLUMNS FROM `jrk_member` [ RunTime:0.001312s ]
SELECT `id`,`username`,`userhead`,`usertime` FROM `jrk_member` WHERE `status` = 1 ORDER BY `usertime` DESC LIMIT 10 [ RunTime:0.003695s ]
SHOW FULL COLUMNS FROM `jrk_searchrecords` [ RunTime:0.001086s ]
SELECT * FROM `jrk_searchrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 5 [ RunTime:0.003422s ]
SELECT aid,title,count(aid) as c FROM `jrk_downrecords` GROUP BY `aid` ORDER BY `c` DESC LIMIT 10 [ RunTime:0.017308s ]
SHOW FULL COLUMNS FROM `jrk_articles` [ RunTime:0.001922s ]
UPDATE `jrk_articles` SET `hits` = 1 WHERE `id` = 183016 [ RunTime:0.001431s ]
