Dancing Lights

Here is a simple dancing light circuit based on NE555 (IC1) & CD4017 (IC2) . The IC1 is wired as an astable multivariator to provide the clock pulses for the CD4017. For each clock pulse receiving at the clock input (pin14) of I.C. CD4017, the outputs Q0 to Q9 (refer pin diagram of CD 4017) becomes high one by one alternatively. The LEDs connected to these pins glow in the same fashion to give a dancing effect. The speed of the dancing LEDs depend on the frequency of the clock pulses generated by the IC1.

Note:-

1. The I.C. should be mounted on I.C. base
2. Using different color of LEDs would produce better visual effects
3. For testing use a breadboard.

555 Timer IC

One of the most versatile linear ICs is the 555 timer which was first introduced in early 1970 by Signetic Corporation giving the name as SE/NE 555 timer. This IC is a  monolithic timing circuit that can produce accurate and highly stable time delays or oscillation. Like other commonly used op-amps, this IC is also very much reliable, easy to use and cheaper in cost. It has a variety of applications including monostable and astable multivibrators, dc-dc converters, digital logic probes, waveform generators, analog frequency meters and tachometers, temperature measurement and control devices, voltage regulators etc. The timer basically operates in one of the two modes either as a monostable (one-shot) multivibrator or as an astable (free-running) multivibrator.The SE 555 is designed for the operating temperature range from – 55°C to 125° while the NE 555 operates over a temperature range of 0° to 70°C.

Important features of the 555 timer are :

1. It operates at a wide range from +5V to +18V Supply voltage
2. sinking or sourcing 200mA current.
3. high current output , can drive TTL

Pin Configration :

Pin 1: Ground Terminal. All the voltages are measured wrt this terminal.

Pin 2: Trigger Terminal: This pin is an inverting input to a comparator that is responsible for transition of flip-flop from set to reset. The output of the timer depends on the amplitude of the external trigger pulse applied to this pin.

Pin 3: Output Terminal: Output of the timer is avail­able at this pin. There are two ways in which a load can be connected to the output terminal either between pin 3 and ground pin (pin 1) or between pin 3 and supply pin (pin 8). The load connected between pin 3 and ground supply pin is called the normally on load and that connected between pin 3 and ground pin is called the normally off load.

Pin 4: Reset Terminal: To disable or reset the timer a negative pulse is applied to this pin due to which it is referred to as reset terminal. When this pin is not to be used for reset purpose, it should be connected to + VCC to avoid any possibility of false triggering.

Pin 5: Control Voltage Terminal: The function of this terminal is to control the threshold and trigger levels. Thus either the external voltage or a pot connected to this pin determines the pulse width of the output waveform. The external voltage applied to this pin can also be used to modulate the output waveform. When this pin is not used, it should be connected to ground through a 0.01 micro Farad to avoid any noise problem.

Pin 6: Threshold Terminal: This is the non-inverting input terminal of comparator 1, which compares the voltage applied to the terminal with a reference voltage of 2/3 VCC. The amplitude of voltage applied to this terminal is responsible for the set state of flip-flop.

Pin 7 : Discharge Terminal: This pin is connected internally to the collector of transistor and mostly a capacitor is connected between this terminal and ground. It is called discharge terminal because when transistor saturates, capacitor discharges through the transistor. When the transistor is cut-off, the capacitor charges at a rate determined by the external resistor and capacitor.

Pin 8: Supply Terminal: A supply voltage of + 5 V to + 18 V is applied to this terminal with respect to ground (pin 1).

Working Principle :

Comparator 1 has a threshold input (pin 6) and a control input (pin 5). In most applications, the control input is not used, so that the control voltage equals +2/3 VCC. Output of this comparator is applied to set (S) input of the flip-flop. Whenever the threshold voltage exceeds the control voltage, comparator 1 will set the flip-flop and its output is high. A high output from the flip-flop saturates the discharge transistor and discharge the capacitor connected externally to pin 7. The complementary signal out of the flip-flop goes to pin 3, the output. The output available at pin 3 is low. These conditions will prevail until comparator 2 triggers the flip-flop. Even if the voltage at the threshold input falls below 2/3 VCC, that is comparator 1 cannot cause the flip-flop to change again. It means that the comparator 1 can only force the flip-flop’s output high.

To change the output of flip-flop to low, the voltage at the trigger input must fall below + 1/3 Vcc. When this occurs, comparator 2 triggers the flip-flop, forcing its output low. The low output from the flip-flop turns the discharge transistor off and forces the power amplifier to output a high. These conditions will continue independent of the voltage on the trigger input. Comparator 2 can only cause the flip-flop to output low.

From the above discussion it is concluded that for the having low output from the timer 555, the voltage on the threshold input must exceed the control voltage or + 2/3 VCC. They also turn the discharge transistor on. To force the output from the timer high, the voltage on the trigger input must drop below +1/3 VCC. This also turns the discharge transistor off.

A voltage may be applied to the control input to change the levels at which the switching occurs. When not in use, a 0.01 nano Farad capacitor should be connected between pin 5 and ground to prevent noise coupled onto this pin from causing false triggering.

Connecting the reset (pin 4) to a logic low will place a high on the output of flip-flop. The discharge transistor will go on and the power amplifier will output a low. This condition will continue until reset is taken high. This allows synchronization or resetting of the circuit’s operation. When not in use, reset should be tied to +VCC.

16 X 2 LCD

LCD (Liquid Crystal Display) screen is an electronic display module and find a wide range of applications. A 16x2 LCD display is very basic module and is very commonly used in various devices and circuits. These modules are preferred over seven segments and other multi segment LEDs. The reasons being: LCDs are economical; easily programmable; have no limitation of displaying special & even custom characters (unlike in seven segments), animations and so on.

A 16x2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in 5x7 pixel matrix. This LCD has two registers, namely, Command and Data.

The command register stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing it, clearing its screen, setting the cursor position, controlling display etc. The data register stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD.

Pin Diagram :-

Pin Description: 

Pin No	Function	Name
1	Ground (0V)	Ground
2	Supply voltage; 5V (4.7V – 5.3V)	Vcc
3	Contrast adjustment; through a variable resistor	VEE
4	Selects command register when low; and data register when high	Register Select
5	Low to write to the register; High to read from the register	Read/write
6	Sends data to data pins when a high to low pulse is given	Enable
7	8-bit data pins	DB0
8		DB1
9		DB2
10		DB3
11		DB4
12		DB5
13		DB6
14		DB7
15	Backlight VCC (5V)	Led+
16	Backlight Ground (0V)	Led-

Simple Proximity Detector

Description

This is a simple proximity detector using IC CS209. The CS209A is a bipolar monolithic integrated circuit for use in metal detection/proximity sensing applications.The CS209A contains an oscillator set up by an external parallel resonant tank and a feedback resistor connected between pin 2 & 3 .The internal oscillator operates close to the resonant frequency of the tank circuit.As a metal object is brought close to the inductor, the amplitude of the voltage across the tank gradually begins to drop. When the envelope of the oscillation reaches a certain level, the IC causes the outputs to toggle states.potentiometer connected between pin 1 & 8 is adjusted to achieve a certain detection distance range. The larger the resistance the greater the trip-point distance.Detection range can be increased by using a high Q coil.Maximum possible range is 1 inch with a  well tuned  circuit.Only difficulty in making this  circuit is the tuning up the circuit to a particular range.For making it easy place a metal piece at the desired distance from coil (with in 1 inch) and adjust resistance Rf to make one of the outputs (  pin4 or 5) to change state.

Automatic Night Light

Description.

A cheap and simple automatic night light using few transistors and NE555 timer is shown here. The circuit will automatically switch on the AC lamp when night falls and the lamp will be automatically switched off after a preset time.

The working of this night light circuit very simple. An LDR is used as the sensor here. At day time the resistance of the LDR will be low and so do the voltage drop across it, the transistor Q1 will be in the conducting mode. When darkness falls the resistance of LDR increases and so do the voltage across it. This makes the transistor Q1 OFF. Base of Q2 is connected to the emitter of Q1 and so Q2 is biased on which in turn powers the IC1. NE555 is wired as monostable multivibrator that is automatically triggered at power ON. This automatic triggering is achieved with the help of capacitor C2. The output of IC1 remains high for a time determined by resistor R5 and capacitor C4. When output of IC1 goes high transistor Q3 is switched ON which triggers triac T1 and the lamp glows. A 9V battery is included in the circuit in order to power the timer circuit during power failures. Resistor R1, diode D1, capacitor C1 and Zener D3 forms the power supply section of the circuit. R7 and R8 are current limiting resistors.

Notes :-

1. R2 Can be used to adjust the sensitivity
2. R5 @ 4.7M can be used to adjust the on time of the lamp
3. heat sink should be used for  BT136
4. The wattage of L1 should not exceed 200W