Servo Driver

Posted on Feb 7, 2014

This circuit can be used to check the operation of your servos, check for full travel, binding and `drag` or rubbing when the servos are installed in your model, or even be used as a control circuit in a robotics project. PARTS LIST: IC1 = LM555 Timer (or equiv. ) R1 = 18K (Brown-Gray-Orange; 183) C1 = 0. 033uF (33nF; 333) R2 = 680K (Blue-Gray-Yello

Servo Driver
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w; 684) C2 = 0. 1uF (100nF; 104) D1 = 1N4148 or other small P1 = 50K Linear Potentiometer silicon signal diode The simple, inexpensive circuit above can vary the control pulses from about 0. 6 to 2. 4 mSec, and handle control signal currents up to 200 mA. (If your servo`s control input needs this much current, something is wrong!) This should be sufficient to achieve standard or greater control horn deflection with all servos. At Vin = 4. 8 volts, positive pulse amplitude is about 4 volts at a frame rate of about 50 Hz (20 mSec). For more info on how servos work, see my Servo. txt file. Warning: this circuit can produce pulses which exceed the nominal limits of 1. 0 to 2. 0 mSec, which can cause servos to attempt to overtravel or behave strangely in the regions near the travel limits. A side effect of this is that servos will have MORE travel (or "throw") when using this ciruit than they will when using most R/C radio setups. If you wish to change the travel provided by this circuit, decreasing R1 will shift both endpoints in one direction. Increasing R1 will shift both endpoints in the opposite direction. Adding a resistor between pin 7 of the 555 and +V will shift both endpoints in the same direction as increasing R1, but will also reduce the total travel - try 680K to start, reduce this to reduce travel further. If you want a high degree of adjustability in the circuit, replace R1 with a 50K trim rheostat, and put a 1Meg...

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