Problem 2.If you\'re wiring an LED to be controlled by your LaunchPad (as shown

Question

Problem 2.If you're wiring an LED to be controlled by your LaunchPad (as shown below) MSP430F5529 Pin-X GND R1 Node-1 L1 A simplified schematic diagram of the LED connected to the MSP430F5529 Launchpad (a) What are the typical voltages at Pin-X for HIGH and LOW? (b) If the HIGH voltage at Pin-X is Vhigh when the LED is ON, and the diode's forward built-in voltage is VLED, what should you check in your LED and/or MSP's datasheets to determine the value required for R1 and how do you calculate R1? Should you choose a resistor "less than or equal to" or "greater than or equal to" the calculated value? (c) Is it possible to light up an LED using LOW at Pin-X? If so, what changes do you need to make in your configuration and your sketch? (d) With R1 unchanged, if you connect a second identical LED parallel to L1 (between Node-1 and the ground), how does that affect L1?

Explanation / Answer

A)

For high and low we must keep in mind diode can be consider as 0.7 V equivalent cell in the circuit.

Hence , Now for high the Pin X must have Voltage greater than 0.7 V

For low V<0.7 V hence diode will not let current pass which will make it off.

B)

For calculating R1

Let us say the diode is On

Hence , V(pinX)=Vx >0.7V

So now Using , Kirchoffs Voltage Law

(Vx -0.7) /I1 =R1

Since diode current is in mA

Henfe , R1 >1K ohms

C)

Yes it is possible to make On state using Vx low

Reverse the direction of diode in the circuit .

D)

It will make current value reduced across LED1

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