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So the balancing is an interesting feature of mechanical switches, and it may cause some problems when

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we connect the mechanical switch, such as push buttons or light switches to digital circuits.

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This lecture will define this phenomenon and you'll explain how to solve that.

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A mechanical switch such as a slight switch and a push button that we have on the basis three more toggles,

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two metal plates touch each other to create an electrical circuit.

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However, this touching process does not happen instantly.

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The metal plates touch each other several times before the final stable connection is made.

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Although this bouncing phenomenon can last milliseconds, a high logic circuit can detect all the bouncing

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values.

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To cope with this issue, we should balance the switch.

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There are several techniques to implement a switch demands.

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Electrical solution, digital solution, software solution.

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The goal is describing a digital circuit, then necklace that converts the switch bounces signal outward

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into a pulse with clear edges, let's assume the circuit clock and the switch bounces signal.

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One of the simple ideas is using a delay after detecting an edge on the switch out.

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For this purpose, the circuit samples the switch output on the rising edge of the clock when an age

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is detected, it stops sampling for a period of time and then starts sampling again.

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If the sampling polls delay is greater than the bouncing period, then the circuit can generate the

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desired output.

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Note that there are more robust solutions for the Swiftie bounce or circuit.

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However, a study, all of these solutions is not the goal of this course.

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Kurita White Essentialists project with the name of the bouncer Dasch White Essentialists.

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Choose the basis to bought as a target FPGA platform.

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Create a new design, Sourcefire and the New Testament, Sourcefire.

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Open the design, Sourcefire.

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Let's define the delay under escort counter macro for defining a five millisecond delay.

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Our demands are circuit has to states transfer and delay in the transfer of state, it connects the

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input signal to the output.

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The circuit keeps the output unchanged in the delay state and waits for bounces on the input to expire.

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The design top function has two arguments, an input and an output.

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Let's define two static variables, one for the circuit, the state and another for saving the delay

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counter.

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We also need another static variable to keep the previous value on the input signal to detect an edge

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on the.

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Please know that these are static variables will be synthesized into registers in hardware.

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Now let's define the temporary variables corresponding to two estate and countless static variables.

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As we won't change the content of the previous underscore S.W. static variable in our Suchiate statement,

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we don't need a temporary variable for that.

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We also need a temporary variable corresponding to the output signal.

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Now, let's define our state machine between states.

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For this purpose, we use a switch case statement.

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When the circuit is in the transfer state, it goes to the delay state.

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If the current and previous values on this stability input are different, which means there is an edge

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on this subject, otherwise it stays in the transfer state and the instability input is connected to

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the output.

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Also next, kountouris delay underscore counter macro.

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In the DeLay state, the circuit recommends the counter on each clock, and when the counter gets to

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zero, the state machine goes to transfer state.

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In the delay state, the output signal keeps its previous value.

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Finally, we should update the static variables and function output signal.

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Now, let's try the test code, simulating the code for five hundred thousand clock cycles is not comfortable.

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Let's reduce a delay only for simulation purposes and define the delay.

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Underscore counter macro again for only 500 clock cycles.

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Please open the test page Sourcefire include the iList three, Mahadev five and the design top function

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prototype.

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Now let's define the main function.

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As usual, we should define the status valuable that returns the design correctness a status we need

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to variables representing the design, input and output arguments.

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Now, let's call the design for 5000 times while to establish an input signal, Izell.

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And use a for loop with 250 iterations to generate a synthetic bouncing on this.

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Then keep the S.W. input stable on the high logic level, using a 5000 iteration for now, let's insert

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the artificial bouncer's on the input switch again.

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Finally, keep the input signal stable on the low logic level.

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Let's do the simulation to find possible syntax on some hunting arrows.

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Here, I haven't printed any signal values on the screen that is not so readable, but you can do so

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if you are interested now perform the synthesis and artillery simulation after that.

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Don't forget to dump all signal values for inspecting their signal waveforms.

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Now, let's click on the waveform viewer I come all the way from viewer will be opened shot design and

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put an end to the signals and inspect the output signal, which is a clear pulse, even though there

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are lots of bounces on the.

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How can we design a digital counter in the next lecture will cope with this question.

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These are our takeaway messages.

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Mechanical switches suffer from bouncing phenomena.

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If we are going to use the output of a mechanical switch as an input to a digital circuit, we should

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utilize it.

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The balancing mechanism.

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There are several developing mechanisms available categorized into hardware and software solutions.

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As the sweet bouncing is a low level physical phenomenon, low level solutions are usually more efficient

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than high level software based solutions.

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Now, the quiz question, calculate the delay in the code in terms of millisecond when DeLay underscore

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Kountouris 500 and 500000.