Digital signal processing experiment

Equipment Required:

  • U-2970A Data source.
  • U-2970H Data receiver.
  • U-2970K Audio module.
  • U-2970M power supply.
  • U-2970N Set of connecting leads.
  • Function Generator.
  • Two-channel oscilloscope.


  1. To show how data represented by data words can be sent as a digit stream, one bit at a time & reconstructed at a distant receiver.
  2. To show that analog signals can be converted to data words & sent by this process.
  3. To show that communication (i.e.: between telephones) can be done in this way.


In order to learn what do we mean by a digit stream & many of the words associated with it, we shall build up a digital system, part by part. At each stage we shall study it using some very simple signals.

When it is all working, we shall see that the system can transmit audio signals.


1. Establishing the Data Source

Connect the Data Source Module “U2970A” into a power supply unit “U-2970M” and see that the power is on.power supply

Make the connections and the two switch settings.

Now we adjust CH1, CH2, & Time base as in the previous oscilloscope diagram.

 The oscilloscope should produce a display as indicated below the upper trace shows bit clock which determines the rate at which bit signals will be generated; the lower trace shows a clock which re-cycles after 8-bit times. It is called the “WORD CLOCK” and mark the start of a group of 8-bits called a "WORD".

Move the CH2 connection down to the “NRZ data” socket, here the CH2 trace simply shows a straight line at this stage

Now since there is a set of 8-push buttons on the previous module, & each one of them controls one “bit” of the signal, which will be sent.
A bit, or binary digit is a signal which may be in either of two states, conventionally labeled 0 & 1 pressing a button will change the state of its bits, indicated by a small lamp being lit for a “1” and dark for a “0”.
Now we note that if we set any 8-bit binary digit on the push buttons we will get a corresponding pulsating waveform on the display as follows:
We conclude that the word set up on the buttons presents all 8-bits of the word at a once, “in parallel”, they are applied to a “parallel to serial converter”.

2. Sending an Analog Signal Digitally:

In order to send an analog signal it must first be converted into digital form. The data source module has an analog-to-digital converter (ADC) in it. Select the ADC using the switch near the lower left corner, as follows:

Next we will connect a function generator (fig 2-4) to provide an analog signal (setting it at triangular waveform,4-v p-p, 0.1Hz)
Connect the function generator to the “analog input” and earth terminals

3. Receiving a Digital Words:

Add the data receiver module, U-2970H, by placing it to the right of the data source connecting the two together, and setting the two switches on the data receiver. Now if every thing is connected in a correct manner we will conclude that the received digital bits are identical to the sending ones; so the receiver is completing its work we will see the same lightning and darkling on both the sender unit and the receiver unit that we connect in the upper diagram.

4. Obtaining an Analog Output:

If (as is usual) the output to be presented to an analog device; the received word is processed by a digital to analog converter (DAC).
The DAC on the U-2970H receiver module is permanently connected.
Move the oscilloscope connections:

  • Ch1 to analog input of Data Source.
  • Ch2 to analog output of Data receiver.
  • Trigger to function generator.
  • The time base will need adjustment to match the frequency of the function generator.

We conclude that now we really have a simple digital communication system which will accept an analog input then after some internal digital-to-analog and vise versa conversion we get an analog output is a good copy of the base input analog signal: for example;

5. Operating the Audio Module U-2970K:

The audio module U-2970K can work either as a microphone or as a speaker; now by connecting the input terminals of the audio module to the function generator and set its switches to the speaker; and by raising the frequency of the function generator to about 600 Hz and adjust the “level” control on the module; A tone should now be clearly audible.

6. Completing a Digital Audio Channel:

The generator was linked to the speaker by a pair of wires whose function was to impress on the “speaker input” terminals the voltage present at the generator output terminals. But this function could also be done by the digital system made up of the data source and data receiver modules.
Now without disturbing the connections between the data source and data receiver modules, disconnect the direct link to the speaker and substitute the digital data link as shown in figure 2-7. If this is done correctly, the speaker’s behavior should be much as before.

We conclude that an audio signal can be sent through the data source and data receiver modules. But why bother, we may ask, when a simple pair of wires will do the same? This is not our concern here#
Now try the effect of the digital channel on the sound and the waveform of the received signal as the frequency is increased. It will be found that, as the frequency goes above 5KHz (half the word clock frequency), different frequencies, called al.ias frequencies are generated. This is not directly because the system is digital, but is due to the fact that the analog signal is sampled at the word clock rate.

7. Testing a Simple Telephone:

If a second Audio Module is available, it can be set up as a microphone and replace the function generator, thus making a “one way” telephone.
Set the oscilloscope on the following settings:

  • Ch1 0.2V/div.
  • Time base 1ms/div; free running.

We note that if the level control on the left hand “microphone” module is turned clockwise, the oscilloscope should now show a signal in response to any noise entering the module.
If a howling noise results, turn the “level” control on the right-hand “speaker” module down (anti-clockwise) until the howl just stops. If we then listen closely to the “speaker” we will be able to hear any sound entering the “microphone”.


  • The analog information can be converted to digital ones using A/D converter.
  • The highest frequency which can be sent is related to the sampling rate.
  • Bit and word are necessary to govern the serializing and de-serializing processes, which are also effectively sampling processes.
  • We note that data can be represented as groups of binary digits (bits); which then called “Word”, we send them serially then received as sent but displayed in parallel as in the first appearance at the sender unit.

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