The Little Tarheel screwdriver antenna is normally supplied with a manual rocker switch controlling motor drive direction with instructions not to exceed travel limit for more than ten seconds thus avoiding drive motor burn out. The third party controllers recommended by Tarheel the are very expensive so here is a limit alarm circuit that I obtained from K0BG.com's website; its really simple, just one transistor, one LED, two resistors and a fuse. An optional buzzer can also be added in parallel with LED if required. The manual switch is incorporated in the case as shown in photo and circuit diagram. When limit of travel is reached the high current is detected by the circuit and the LED illuminates,and optional buzzer will sound.
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