Controlling LED brightness using PWM

   
Pulse Width Modulation or PWM is a term you hear a lot if you are interested in controlling power output using a microcontroller. It has many applications, although one of the most popular amongst hobbyists is controlling the brightness of LEDs. In this tutorial we will cover the basic principles behind PWM and how it can be used for LED brightness control including fading out LEDs rather than just turning them on and off.

This article will focus on some of the more specific details of the PIC18F range of microcontrollers; however the techniques and principles are the same for all other microcontroller products. Some microcontrollers include PWM modules which perform all of the hard work for you; however this article focuses on the more universal (and scalable) technique of using interrupts. 

InfraRed Proximity Detector

This proximity detector using an infrared detector (Fig. 1) can be used in various equipment like automatic door openers and burglar alarms. The circuit primarily consists of an infrared transmitter and an infrared receiver. The transmitter section consists of a 555 timer IC functioning in astable mode. It is wired as shown in the figure. The output from astable is fed to an infrared LED via resistor R4, which limits its operating current. This circuit provides a frequency output of 38 kHz at 50 per cent duty cycle, which is required for the infrared detector/receiver module. Siemens SFH5110-38 is a much better choice than SFH506-38. Siemens SFH5110-38 is turned on by a continuous frequency of 38 kHz with 50 per cent duty cycle, whereas SFH506 requires a burst frequency of 38k to sense. Hence, SFH5110-38 is used.

The receiver section comprises an infrared receiver module, a 555 monostable multi vibrator, and an LED indicator. Upon reception of infrared signals, 555 timer (mono) turns on and remains on as long as infrared signals are received. When the signals are interrupted, the mono goes off after a few seconds (period=1.1 R7xC6) depending upon the value of R7-C6 combination. Thus if R7=470 kilo-ohms and C6=4.7μF, the mono period will be around 2.5 seconds.
Both the transmitter and the receiver parts can be mounted on a single breadboard or PCB. The infrared receiver must be placed behind the infrared LED to avoid false indication due to infrared leakage. An object moving nearby actually reflects the infrared rays emitted by the infrared LED. The infrared receiver has sensitivity angle (lobe) of 0-60 degrees, hence when the reflected IR ray is sensed, the mono in the receiver part is triggered. The output from the mono may be used in any desired fashion. For example, it can be used to turn on a light when a person comes nearby by energizing a relay. The light would automatically turn off after some time as the person moves away and the mono pulse period is over.
The sensitivity of the detector depends on current-limiting resistor R4 in series with the infrared LED. Range is approximately 40 cm. For 20-ohm value of R4 the object at 25 cm can be sensed, while for 30-ohm value of R4 the sensing range reduces by 22.5 cm.

RESISTOR COLOR CODE

A resistor is a two-terminal electrical component used in electronic circuits to oppose the flow of an electric current. If an object inserted in a circuit displays a current flow which is proportional to the voltage across it, the ratio of voltage V divided by current I will be constant. This constant ratio is called resistance R=V/I. It can be measured by a device called ohmmeter. In an ideal resistor R does not depend on the current. The Ohm's law states that I=V/R.

Parrot Sounding AC door Bell

Here is a mains-operated doorbell that produces parrot-likesweet voice without requiring any musical IC. The circuit is cheap and easy to construct. The AC mains is fed to the circuit without using any step-down transformer.

STK4050V 200 watt amp

This 200 watt amp schematic circuit is based  on STK4050V high power audio amplifier IC and is designed do deliver up to 200 watts audio power on a single channel .
STK4050V 200 watt amp audio amplifier IC is pin compatibility with other STK amplifiers series .
Because of current mirror circuit application the distortions are reduced to 0.08 % .
STK4050V supports addition of electronic circuits for thermal shutdown and load-short protection circuit as well as pop noise muting which occurs when the power supply switch is turned on and off.
The maximum output power of STK4050V audio amplifier is around 200 watts on 8 ohms load impedance with a 66 volts split power supply .
If you want to make this power amplifier you need to make a separate thermal protection and load short protection circuit because the IC don’t offer these kind of protection and you can destroy the chip and the speaker box .

Musical light chaser circuit

                                                          Circuit Diagram





Description

Here is a simple state of the art musical chaser circuit that can be used in discotheques or even at home if you are a little music crazy .The working of the circuit is straight forward ,the condenser mic pickup the sound and Q1amplifies it.This signal is fed to clock input of IC1 ,CD 4016.The IC is wired in divide by ten mode.The out put of IC1 is given to clock input of IC2, CD4016.The out puts of IC 2 shown in the right side of IC2 in circuit diagram will run run according to the frequency of the input.Result ,we get 10 lights dancing in the according frequency of the sound available.If no sound is there the first light will glow steady.For saving space only arrangement for connecting only one lamp is shown in the diagram.Make 9 lamp arrangements like the one shown in figure and connect each if them to the each outputs of IC2 with the other ends connected to the circuit as that of one shown in circuit.

The power supply for the circuit is directly derived from the mains itself using D2 , R9,C4,C3 and D3, which adds an extra bonus of avoiding the bulky transformer to make the circuit compact.

Notes

• If the output doesn't respond to the music and only the first light remains glowing, adjust the level of input signal to IC1 by adjusting R1 since the cause of problem is the low voltage level of input to IC1.Problem is solved.
• Some parts of the circuit are live with potential shock hazard.So be careful.

Sound Level Meter

                                                                  Circuit Diagram
 
 

Description

This is a one chip sound level meter that can be use for displaying sound level of an amplifier or simply the sound level from a microphone.The heart of the circuit is IC LM 3915 Audio level IC.Even though it is a stand alone IC , a peak detector based on Transistor BC 558 and diode 1N4001 is also included for better performance.

Tips

Supply voltage can be from 3V to 20V.The input is set for audio line voltage (1V peak to peak) and has a max input voltage of 1.3V. To make the circuit use a moving dot display instead of bar graph display,Pin 9 can be should be disconnected from +V.

Parts List.
C1 2.2uF 25V Electrolytic Capacitor
C2, C3 0.1uF Ceramic Disc Capacitor
R1, R3 1K 1/4W Resistor
R2 10K 1/4W Resistor
R4 100K 1/4W Resistor
R5 1M 1/4W Resistor
D1 1N4001 Silicon Diode
Q1 BC 558 PNP Transistor
LED1-LED10 Standard LED or LED Array
U1 LM3915 Audio Level IC
MISC Board, Wire, Socket For U1

Ultra Bright LED Lamp

This ultra-bright white LED lamp works on 230V AC with minimal power consumption. It can be used to illuminate VU meters, SWR meters, etc. Ultra-bright LEDs available in the market cost Rs 8 to 15. These LEDs emit a 1000-6000mCd bright white light like welding arc and work on 3 volts, 10 mA. Their maximum voltage is 3.6 volts and the current is 25 mA. Anti-static precautions should be taken when handling the LEDs.