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Download Circuits for pulse shortening
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Circuits for pulse shortening. Assignment: 1. Create circuit connections (Figures 1, 2 and 3) to shortening the pulse and determine the length of this impulse. 2. Make a report from these measuring. Theory: Monostable flip-flops These circuits have only one stable state, which is break by trigger pulse. Trigger pulse may be longer or shorter than the output pulse. According to the type of connection is the output pulse more or less steep, and therefore needs to consider the connection. Otherwise it can be use to achieve the desired shape e.g., Schmitt flip-flop circuit. Most common monostable flip flops are 74123 or 555 timer circuit. Involvement of flip-flops with these circuits can be found in catalogs. Basic connection for pulse shortening. Basic connection, which uses the hazard states (variable length of pulse) of logical circuits, is seen below. & & & Input & Output Fig. 1 The output of this circuit gives steep pulses, suitable as an exciter of clock, reset and write inputs at flip-flop. Length of pulse depends on the number of gates and theirs delays. To get more dynamic, we can use RC element to the gate. These connections have worse rising edge of output pulse. Connection is ideal for pulses to a length of 10 micro seconds. We must also consider the time to charge the capacitor (regeneration time). Another possible connection is on the right. Circuit reaches longer times for the same values of C. & R C Fig. 2 C R Fig. 3 D Flickering of button Button contact is never perfect. If operator presses a button, the contacts are first connected and then disconnected several times and then combined before the contact stopped and the button is connected firmly. Wiring diagram, which eliminates the flicker of mechanical contact button shown in the picture below. The original button is accompanied by a low pass filter and closes the entry gate equipped by the Schmitt flip flop circuit. Off frequency of lowpass filter is realized by a resistor and capacitor is determined by: 1 R1 R2 .C Typically it can be assumed that the operator is unable to press the button for more than 10 times per second. So we get frequency 10 Hz. We choose the filter off frequency of about 5 times to 10 times higher. So f0 = 50 to 100 Hz. f0 Schematic diagram of non-flickering buttons using Schmitt flip-flop at input. Schematic diagram of non-flickering buttons using reset-set circuit. Datasheet: 7414 7400 74LS74