Servo-Checker JR / Futaba

The first timer IC555 creates a negative trigger signal of approximately 45Hz (a trigger impulse every 22ms, DO NOT exceed 50Hz for proper servo function). The second timer IC555 modulates a positive square signal from 0. 9ms to 2. 1ms every 22ms, a method commonly known as pulse width modulation (PWM). The modulated pulse width provides the full in
Servo-Checker JR / Futaba - schematic

formation for the exact servo position, and allows a total swing of 140-160degrees of the servo head (see pictures below). M is a trimmer to adjust the middle-position (the default pulse width of 1. 5ms), the main input for the servo control is the potentiometer P, which modulates the pulse width from 1. 0ms to 2. 0ms. Note: Since the servo draws quite some instantaneous current (what might cause some power supply droops), ensure that there are sufficient capacitors to support the supply voltage (at least 100nF & 10uF). Otherwise the power supply droops slightly affect the timer circuitry: the pulse width may temporarily vary slightly, resulting in temporarily jerky servo movements. The two markers are 22. 5ms apart (T2-T1), the first pulse on the screen has a width of approximately 1. 0ms, the second one a width of approximately 2. 0ms.

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