How to Convert PWM to PPM


Whereas pulse position modulation (PPM) is a digital and analog signaling technique that uses waveforms of equal height and width, pulse-width modulation (PWM) uses a series of waves that continuously succeed each other as a result of having varied waveforms. Converting PWM to PPM would require creating PWM signal and feeding it through a monostable multivibrator.

Things You'll Need

  • LM741 op amp, 8-pin dual-inline package
  • 22-gauge jumper wire
  • Breadboard
  • Operation amplifier integrated circuit
  • 10-volt bipolar DC power supply
  • Oscillators (2)
  • 2 Coaxial cables (with alligator clips on one end and BNC connectors on the other)
  • Pen & 3 Labels
  • Oscilloscope probe
  • Oscilloscope
  • 555 Timer Monostable Multivibrator

Insert the LM741 op amp integrated circuit to the breadboard. Ensure that you place the pins on each side of the breadboard’s horizontal channel.

Connect three wires of 12 inches each to the positive terminal of the power supply. Connect one wire end to pin 7 on your LM741 op amp, or operation amplifier, integrated circuit. Connect another wire to the power supply’s negative terminal. Connect the second wire end to pin 4 on the integrated circuit. Connect the third one to the power supply’s ground terminal. Leave the free end to stay unconnected in the meantime.

Connect your oscilloscope’s probe to its channel one input. Attach a coaxial cable to each of the oscillator with BNC connectors. Mark one of the cable “carrier” and the other “modulation” using your pen and labels.

Connect one 2-inch jump wire to pin 2. Insert another one to pin 3 and the third to pin 6.

Connect the “hot” alligator -- high signal -- clip located on the cable you marked “carrier” to the wire that runs to pin 2. Do the same to the one you labeled “modulation” to the wire that runs to pin 3. Also, connect the probe of your oscilloscope to the wire that runs to pin 6.

Connect the ground alligator clips -- low signal -- of the two cables to the power supply ground wire’s free end you had initially let to stay unconnected in step 2. Also, connect it to the ground clip of the probe of your oscilloscope.

Set the sweep rate of your oscilloscope to one millisecond per division and its triggering to channel one. Adjust the input sensitivity to volt one per division. Check the oscilloscope screen to notice a rectangular pulse waveform. Notice whether the width and height of the PWM signals slowly change in size. It will indicate PWM.

Feed the PWM output to trigger input of your monostable multivibrator (MMV). The vibrator will give PPM waves. The negative pulse applied at pin 2 will trigger a forward roll that will turn pin 7’s discharge transistor as well as bring pin 3, the output, level to “high” -- indicating PPM waves.

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