At this video we will learn how to slow down this tiny car. Well, the average speed decreased, but this solution is still very rough. Better, but still not optimal. That's the way it could be done. The average power of an electric motor can be reduced by turning the switch between the fly and load on and off at a fast pace. Those techniques is called pull-swipe modulation or pull-storation modulation. The motor is switched at a fixed frequency while the on compared to the off-period of the switch is right. The movement of the car gets smooth by using an electronic circuit with a switching frequency of approximately 1 kilohertz. One of the previous videos was about an electronic circuit reducing the power to just half of the total power. It's the R-stable multivibrator. The proportion of on time to the regular interval, which is called duty cycle, is 50% when using an R-stable multivibrator. By altering the circuit slightly, the duty cycle can be adjusted continuously. The resistor R3 has to be replaced by a potentiometer and two diodes have to be inserted. Now the charge current is running through diode number 1, while the discharge current is running through diode number 2. Depending on the adjustment of potentiometer 1, the resistance of the charging current running through the upper branch of the circuit is different from those of the discharge current running through the lower branch. At the oscillograph plot, you can see that the average gradient of the curve progression of the charging respectively discharging procedure is increasing or decreasing depending on the adjustment of the potentiometer. The duty cycle and so the power sent to the motor can be adjusted by turning the potentiometer. 100% duty cycle means fully on, while 0% means the motor is turned off. While a low switching frequency causes a visible violation of rotational speed during a single period, a too high frequency causes a warming of the power transistor. Like explained at the video about switches, there are losses at each switching operation and with increasing frequency, the number of switching operations per time interval is increasing too. While switching inductors, high voltages are generated whenever the power transistor is turned off abruptly and those distortions are also increasing with increasing switching frequency. The abrupt change in resistance of the power transistor and so the change in current through the circuit induces a proportional voltage which opposes the change in current across the inductor. Those voltage is added to the voltage drop across the transistor. The voltage peaks can be widely eliminated by a fly-back diode, which is switched with reverse polarity in parallel to the inductive load. When the transistor is turned off, the diode becomes forward biased relative to the voltage caused by the inductor. The current running through the diode causes an negligible voltage drop of just 0.6 volts. Like explained at the video about multivibrators, the switching frequency is affected by the resistance and the capacitance of the coupling RC network. While using a 1m2 and a capacitance of 0.33 microfarad, the resulting frequency of approximately 1 Hz is visible. By reducing the resistance or the capacitance of the RC loop, the frequency increases. When using a 1 nanofarad capacitor, the resulting switching frequency is approximately 340 Hz. The switching frequency can also be altered by varying the resistance of the coupling resistor network at the Schmidt trigger. When replacing R1 by 100 kOhm potentiometer, the frequency can be adjusted continuously. While turning the device, the upper and lower threshold of the Schmidt trigger is altered. Hence, the circuit kills to the positive, respectively negative, supply voltage at a lower, absolute voltage across the capacitor. The shorter the periodical time, the smoother the rotation of the electric motor becomes. At the simple circuit used here, both coupling networks are connected to the output of a single operational amplifier, hence there is a feedback between both loops. Whenever the duty cycle is altered, there is inevitably a slight variation in the switching frequency. To avoid this, a more complex circuit composed of three operational amplifiers can be used. The left device is forming a non-inverting Schmidt trigger, the middle one an integrator. The output signal of the middle operational amplifier is the input of the non-inverting Schmidt trigger to the left, while the output of the Schmidt trigger is connected to the inverting input of the integrator, via a resistor, respectively potentiometer, resulting in a triangular shape output voltage of both devices. Those signals is the input of the non-inverting Schmidt trigger formed by the right operational amplifier. The level of the triangular voltage can be adjusted by potentiometer number 1 and 2. Whenever the peaks of the triangular voltage are crossing the upper, respectively lower threshold of the Schmidt trigger, the output voltage kills to either the positive or negative supply voltage of the operational amplifier. Hence, the pulse width of the output signal is increasing with an increasing level of the triangular voltage. The frequency of the signal can be varied by a trusting potentiometer number 4. The lower the resistance value of the potentiometer, the faster the charging, respectively, destarching procedure of the capacitor, hence the higher the frequency of the triangular voltage, and so of the pulse-width signal. Frequency and duty cycle are generated by separate operational amplifiers, hence both parameters can be adjusted without affecting each other. The frequency of the output signal is more stable than before. A switching frequency of 1 kHz is sufficient to control our tiny electric vehicle very smoothly. The poor signal quality of the simple circuit is also appropriate to switch the low power of the electric motor. Besides electric motors, illuminants like LEDs or filament lamps can also be dimmed by pulse-width modulation. Whenever a high quality of the output signal at a wide frequency range is required, digital circuits are a good choice. Here an A-8A operates as the signal source of the circuit. The position of the potentiometer is read by an analog to digital converter, and the pulse-width signal is calculated by the microcontroller which is clocked at a frequency of 4 mHz. The switching frequency can be right precisely by software or by-champers, from a few hertz up to some 100,000 hertz. Servos are controlled by a specially-type of pulse-width signal. The frequency has to be adjusted to 50 hertz, while the duty cycle rises between 5 and 10%. In doing so, 3 wires between the sensor and the actuator are sufficient to control an element. In aviation, those type of steering is called fly-by-wire. Moreover, pulse-width modulation, including the dimensions of sample circuits, is written at the project page. Thanks for watching and I'll be back.