CO-2

LED types:

LEDs are categorized based on their frequency of emission.

“The intensity of light depends on the current flow”

“The color of emission depends up on the combination of materials used to fabricate it”

LED lamps have long lasting than CFL or incandescent.

They are meant to represent/display/specify something to people in their daily life.

This LED indicates power

These LEDs indicates 3 LAN cables have been connected to router

(LED Board at Ireland station)

LEDs like all electronic components have a maximum limit of current flow through them as specified in the datasheet.

Without the current limiting resistor, an LED gets a flow exceeding its peak forward current which damages it in the span of seconds.

Say, 3V is the supply & an LED has to glow at its full intensity (28.5cd), which requires a peak forward flow of 50mA & forward voltage of 2.8V.

3 - 2.8/R = 50mA = > R = 4Ω

Common anode & cathode:

If anodes (+) of all LEDs make a common node, it can be referred as common anode configuration. Similarly, common cathode. These configurations are used where a pattern/sequence has to be displayed to people in their daily life.

(8 * 8 dot matrix LED) (5 * 7 dot matrix LED)

These common anode/cathode LED configurations are commercially referred as dot matrix LEDs and they are used in elevators, railways, airports, gas stations & even in hotels.

(A dot matrix LED in an elevator) (A dot matrix LED board at some railway station)

(7 segment LED matrix board at a gas station) (LED Dot matrix board at a gas station)

For displaying some info in a fancy format (multicolor), again common anode/cathode LEDs come in to picture.

(Multicolor LED)

Except the longer one which is anode, rest of the terminals are cathodes & each one is meant for a particular color.

1 (common anode) + 1 (cathode->red) + 1 (cathode->green) + 1 (cathode->blue) = 4 terminals

LCDs:

LCD modules are seen in daily life at grocery stores (for price display to the customer & weight of supplies) and body weighing scales.

LCDs meant for info has to be controlled by some IC & it contains pins for data, read/write control & for enabling as well.

LCDs are most widely used displays for serving as info display to people in their day-to-day life.

Like LEDs, LCDs are of dot type & segment type as well.

Even Multimeter, calculator, watches are equipped with LCDs

(commercially available 16 * 2, 5 * 7 dot matrix type LCD) (commercially available segment type LCD)

(commercially available calculator with segment type LCD)

LCDs are integrated with a controller/driver unlike LEDs. Moreover LCDs contain commands to use them. An LED can be used even with BJTs, but LCDs require microcontrollers/microprocessors to use them.

(sample of commans for a 16 * 2, 5 * 7 dot matrix type LCD)

Relay & types:

Relay purpose is to reroute a contact as long as it gets its input. EMRs are mostly used in elevators and can be used in more rugged environments & hence it is preferable than SSR for most of the applications.

(a control panel with EMRs)

Applying some voltage across the i/p terminals/contacts makes the coil to get magnetized which in turn makes the common contact to get connected to the other contact which has been open.

So, any source/device that got connected to output terminals of relay gets a closed loop.

Control terminals (i/p) Output terminals

Temperature sensor & calibration:

In day-to-day life, digital wall clocks display temperature of a room/environment as they are equipped with temperature sensor.

(commercial digital wall clock) (i7 processor temperature monitor window)

Even a mother board of a computer is equipped with temperature sensor

for processor.

Temperature estimation of LM35 (analog sensor) when interfaced to ADC 0804:

ADC 0804 is 8-bit. Resolution = VRef/2n -1 = 5/255 = .0196 (20mV)

LM35 rises its output voltage by 10mV for a change of 1°C

A change in a bit of ADC indicates there is a change of 20mV in its analog input, which in turn indicates the temperature has been altered by 2°C.

Microphone as a sensor:

A combination of some permanent magnets and a coil bonded to a diaphragm makes a MIC (short for microphone). Working of a loudspeaker works exactly opposite to that of microphone. In that, based on the current flow (frequency), the coil behaves as an electromagnet and its to-and-fro makes the diaphragm move making the sound audible .

Whatever the type (dynamic, condenser, piezo) may be, the operation principle is the same.

(dynamic) (condenser) (piezo)

In real world when something is supposed to be done on occurrence of some sound, then a miniaturized MIC is used as a sensor.

(an audio sensor) a MIC with a HD camera

Gas sensor:

Gas sensor finds its application in home safety sensors equipped in kitchen for CO & LPG, and more commercially in refrigerators for monitoring methane (CH4) leakage & Freon detection.

(MQ139 Gas sensor)

(Freon detector)