Introduction

A signal as referred to in electronics is a type of information carrier that “conveys data” about the behaviour or attributes of some phenomenon. Signals are time-varying i.e, with time it changes its value. Usually, the quantity that’s time-varying is usually voltage. Hence, when we talk about signals in this project, just think of them as a voltage that’s changing over time.

There are two type of signals:

  • Analog Signal
  • Digital Signal

You will learn what these are and how to visualize them in this project.

Components Required

Image Component Quantity Available in Kit
evive 1

Story

Step 1: What is Analog Signal?

Its’ easier to analyse a time-varying signal on a graph where time is plotted on the horizontal x-axis, and voltage on the vertical y-axis. Looking at a graph of a signal is usually the easiest way to identify if it’s analog or digital; a time-versus-voltage graph of an analog signal should be smooth and continuous (the image on the left). While these signals may be limited to a range of maximum and minimum values, there are still an infinite number of possible values within that range.

Example: Video and audio transmissions are often transferred or recorded using analog signals. Pure audio signals are also analog. The signal that comes out of a microphone is full of analog frequencies and harmonics (new thing, Google it), which combine together to produce melodious music. Sound is basically an analog signal that degrades over time etc..

evive Mini Oscilloscope Heat Beat Visualisation

Step 2: What is Digital Signal?

Digital signals must have a finite set of possible values. The number of values in the set can be anywhere between two or a very large number that’s not infinity. Most commonly digital signals have two values – like either 0V or 5V (the image on the right).

Step 3: Digital Signal: Logic levels

In digital electronics, there are only two states – ON (High or True) or OFF (Low or False). Using these two states, devices can encode, communicate, and control a great deal of data. Logic levels, in a general sense, describe any specific, discrete state that a signal can have. In digital electronics, we generally restrict our study to two logic states – Binary 1 and Binary 0. In simple words, signals can only have two values as far as digital electronics is concerned.

A logic level is a specific voltage or a state in which a signal can exist. We often refer to the two states in a digital circuit to be ON or OFF. Represented in binary, an ON translates to a binary 1, and an OFF translates to a binary 0. Sometimes, we also call these states HIGH or LOW, respectively.

Most of the signals are analog and most electronics (specially the one used to control things) is digital. Conversion from analog to digital and vice versa is not simple and vary for input and output. Usually, the analog signal is broken into three ranges: LOW, HIGH and floating (where the signal can be HIGH or LOW).

These are the ranges an analog signal for input:

  • 0V – 0.8V is LOW
  • 2V – 5V is HIGH
  • 0.8V – 2V is floating

For an output signal:

  • 0V – 0.5V is LOW
  • 2.4V – 5V is HIGH
  • 0.5V – 2.4V is floating

Step 4: Mini Oscilloscope

An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional plot of one or more signals as a function of time.

evive can be used as a mini oscilloscope to visualize voltage and current measurements.

 

Step 5: How to use Mini-Oscilloscope?

Before getting started make sure that you have evive firmware installed, otherwise you can download it and upload it in your evive from here.

The option for Mini -Oscilloscope appears on the main menu. The ports present at the bottom right of evive are used for connecting the evive with the circuit in order to use it as an oscilloscope. The three ports present are Channel 1, COM, and Channel 2 from left to right respectively. From channel 1 you can sense voltage between -30V and +30V.  From channel 2 you can either sense voltage from -5V to +5V or sense current from -3A to +3A by changing jumper (JP2). The signal from both these channels is plotted and displayed on the screen.

evive Jumper for Sensing

Navigation through the mini oscilloscope menu is done using the joystick. By moving it left or right and for selecting items and use the up and down movements for changing the value.

Step 6: Visualizing Analog Signals

We are going to visualize how voltage varies when we rotate the variable voltage knob (located towards bottom on right side of evive, marked as VAR Voltage). Connect the variable voltage supply (VVR) to channel 2 of oscilloscope as shown in the fritzing diagram.

Visualising Analog signal
Turn on evive, go to Mini Oscilloscope where you will see a yellow line which represents variable voltage output. Change the voltage by rotating knob and you can observe that the signal has infinite possible values.

Step 7: Visualizing Digital Signals

We will now visualize output of a tactile switch on the mini oscilloscope.

Switch is a device used to control the flow of current in a circuit. Switches are essentially binary devices: they are either completely ON (closed) or completely OFF (open). Therefore, it controls the open-ness or closed-ness of an electric circuit. When a switch is open, the circuit is broken and no current flows though the circuit, but when the switch is closed current flows through it.

Tactile Switch

VCC is a non-zero higher potential (+5V) and ground is at zero potential.
While using switches we measure the output from the switch. If there is nothing connected to the pin and you read the state of the pin, will it be high (pulled to VCC) or low (pulled to ground)? It is difficult to tell. This phenomenon is referred to as floating. To avoid this unknown state, a pull-up or a pull-down resistor ensures that the pin is in a known state- either high or low, while also using a low amount of current. While using switches you generally use pull-up or pull-down resistors.
With a pull-up resistor, the output will read a high state when the button is not pressed (since right now, it is connected to VCC). In other words, a small amount of current is flowing between VCC and the output pin (not to ground), thus the output pin reads close to VCC. When the button is pressed, it connects the input pin directly to ground. The current flows through the resistor to ground (remember, current chooses the path of minimum resistance), thus the input pin reads a low state.
Hence when the switch is not pressed, you get a HIGH reading on the digital pin and when the switch is pressed you get a LOW reading, when you are using pull-up resistor. Generally you use a resistor of 10k ohm. If you are using a pull-down configuration, the result is exactly opposite.
For pull-up resistor – “switch not pressed = HIGH”; “switch pressed = LOW’. The opposite is true for a pull-down resistor.
Given below is the circuit Diagram:
Digital Circuit Diagram
Let’s visualize it. Make the circuit on the top. If you press the switch, output will be 0V and if it is not pressed, output will be 5V.

Circuit Diagram

Analog Signal

Variable voltage output is connected to the mini-oscilloscope input channels.

Digital Signal

A switch circuit is build, with output connected to the mini-oscilloscope channel.

Code

evive Firmware
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