Reed Switch- Normally Open

Magnet and Reed switch arrangement

Red LED blinks and indicates the activation of circuit. Fix the Reed switch on the door frame and Magnet on the door with exact positioning so that when door closes Reed switch make contact.

SCR 2P4M

This circuit gives a time delay of 1 minute before giving power to the TV. After this delay, a Green LED turns on and we can manually trigger the relay through the press switch S1. Relay activates and connects power to the TV. When power fails and resumes, Relay remains de-energized till S1 is pressed manually.

The circuit uses a voltage comparator built around IC1 (CA3140). Its Inverting input is connected to a potential divider R2, R3 that provides half supply voltage (4.5 volts) to the inverting input. The non inverting input is connected at the junction of R1 and C1. When power is switched on, output of IC1 will be low and capacitor C1 charges through R1. When it charges fully, the voltage at pin 3 increases above that of pin2 and the comparator gives a high output and Green LED turns on. Time delay depends on the value of C1 and with the given value; it will be around 1 minute. When S1 is pressed and released, SCR triggers and relay energizes to power the TV through the Common and NO contacts. SCR remains latched even after its gate current is removed by releasing S1. Red LED indicates the Load On status.

You can connect 12 volt batteries parallel to the set up.

A 12 Volt 150 mA solar panel provides sufficient current and voltage to charge the battery. Since the battery is under slow charge, it can be left unattended. To keep the battery in top condition, it is better to discharge to 50% once in a week using a 12 volt car bulb. 12 volt 150 mA Solar panel cost only Rs.300. If you have standby NiMH batteries, use a 6 volt 100 mA Solar panel for charging.Fix the solar panel in a place where direct sunlight is available.

About Solar Cell

These are photoelectric transducers generating electric current by accepting light energy. The photocell has many p-n junctions connected in series. One of these junctions is very narrow to allow the passage of light energy. When sunlight falls on the p-n junction, electron-hole pairs are formed. These charge carriers generate current proportional to the incident light energy. The sunlight incident on the semiconductor junction of solar cell collides with the valance electrons. This causes formation of charge carriers which cross the p-n junction in an opposing manner and creates a voltage across the p-n junction. Approximately 0.6 volt will be generated from each solar cell if the sunlight is strong.

About Lead Acid Battery

Battery cycle

One complete discharge and recharge forms a battery cycle. This cycle is usually a discharge from 100 % to 20 % charge followed by recharging from 20 % to 100 %. Life of the battery depends on the number of deep cycles per day. For example, if a battery is discharged 50 % per day and recharged to 100 %, its life increase to twice than a battery discharging and recharging occasionally. Therefore it is better to discharge and recharge emergency lamp battery and inverter battery daily to increase its life. It is also better to start vehicles daily even if it is not running. This prevents self discharge and increases the efficiency for cycling.

Self discharge

If the lead acid battery is not discharging through the load, self discharge takes place @ 4 % per week at 27 degree. For example, a 125 Ah battery shows self discharge @ 5 Amps current per week if it is not discharging through the Inverter.

Memory Effect

‘Memory effect’ causes the battery to ‘remember’ how much charge was released on previous discharge. So that the same amount of energy is released with every charge/discharge cycle. The battery then keeps the ‘memory’ of the primary platform and considers it as the end of discharge for the next cycle even though the battery can be discharged further. If a ‘memory effect’ develops, during the next discharge cycle, battery only remembers this. Memory effect is high in Lead Acid battery and low in NiCd battery. Memory effect is negligible in NiMH battery.

About NiMH battery

The NiMH battery is similar to NiCd cells in structure but it uses a hydrogen absorbing alloy as negative electrode instead of cadmium. The positive electrode is a nickel oxy hydroxide (NiOOH).Alkaline batteries have approximately 3000 mAh capacity with a 1000 mA load. Digital camera with LCD and flash light can draw over 1000 mA quickly and depleting the alkaline batteries after a few shots. NiMH batteries on the other hand can easily handle the high current levels and maintain their full capacity. AA type NiMH cells have a nominal capacity (C) ranging from 1000 mAh to 2700 mAh at 1.2 volts with a discharge rate of 0.2C / hour.

Typical NiMH battery is rated 1.2 volts/cell. This is the nominal voltage of the cell that is discharging at the rate of C/10 at 25 degree centigrade to an end voltage of 1 volt. The battery pack has three 1.2 volt cells making a total 3.6 volts. When a fully charged battery is used, the discharge voltage starts from 1.5 volts followed by a sharp drop to 1.3 volts. The voltage in the cell remains 1.3 volts to 1.2 volts until another voltage drop occurs during a deep discharge. The nominal voltage of the battery can be calculated by dividing the battery power by its capacity.

Fully charged battery loss it capacity when not in use for long time. The self discharge rate of NiMH battery is 5-10% on the first day. Self discharging property makes NiMH battery unsuitable for many light duty uses such as digital clocks, remote control devices etc where battery would normally be expected to last many months. Temperature at which the battery is stored is very important. Higher temperature above 55 degree increases self discharge rate.

If loud beep is required, use a driver transistor for the buzzer.

The timer circuit is built around the popular binary counter IC CD4060 which resets through C2 and R2 at power on and starts oscillating with the components C3 and R3. IC 4060 is an Oscillator cum binary counter cum frequency divider. Its inbuilt oscillator is based on three inverters. The basic frequency of the internal oscillator is determined by the value of the capacitor connected to its pin 9 and that of the resistor in its pin 10. Each output goes high after the completion of the timing cycle.

To get maximum time period output Q10 is omitted in the IC itself so that double time is available between Q9 and Q11. Inside the IC there is an oscillator and 14 series connected bistables (Ripple cascade arrangement). Internally the oscillator signal is applied to the first bistable which drives the second bistable and so on. Since each bistable divides its input signal by two, a total of fifteen signals are available, each of half the frequency of the previous one. Ten of these fifteen signals are available on the output pins Q3- Q13.


With 0.22 capacitor and 1M resistor, the time delay will be approximately:
Pin 3 Q3 4Sec
Pin5 Q4 8 Sec
Pin4 Q5 16 Sec
Pin6 Q6 32 Sec
Pin14 Q7 1 Minute
Pin13 Q8 2 Minute
Pin15 Q9 4 Minute
Pin1 Q11 18 Minute
Pin2 Q12 36 Minute
Pin3 Q13 72 Minute

In the circuit LED is connected to the first output Q3 so that it blinks at an interval of 4 seconds. After 30- 37 minutes (slightly affects if the input voltage drops) Pin 2 (Q12) turns high and buzzer beeps. Beep continues for 30 minutes so that ,we will get attention to switch off the load.

Enclose the circuit in a small plastic case and fix it inside the switch board. Power can be tapped from the Phase and Neutral contacts of the Plug to which the load is connected. So that when the plug switch is turned on, both the load and the beeper circuit gets power.

CD 4060 gives sufficient output voltage and current to drive LEDs and low volt buzzers. So the brightness of LED will be high and beeps from the buzzer will be loud.

33 K resistor will heat up slightly and if the heat is too high (check only after removing from AC lines) use 2 watt resistor. Since the circuit turns on only along with the load, it will not cause much problems.

Caution: The circuit is connected to the high volt AC directly and there is no galvanic isolation between the hot line and the circuit. So there is risk of Shock if handled carelessly. Do not touch or trouble shoot the circuit when it is connected to mains.

Role of GDT

GDT is the Gas Discharge Tube, a surge protection device similar to MOV (Metal Oxide Varistor). It diverts the extra current from the hot line to the ground using an inert gas as the conductor between the two lines. It can be incorporated between the Core (Central conductor) and the Shield (Copper clad aluminium braid shield conductor) of the coaxial  cable.

Gas Discharge Tube

GDT functions as an on/off switch with high impedance in the normal voltage conditions. Under surge condition, its internal gas ionizes to turn the device to a low impedance state called Arc mode or Short circuit. In this state the GDT conducts the high voltage transients from hot line to the ground. Once the transient passes to the ground, the GDT returns to its high impedance state.

When the voltage through the cable is at a certain level, GDT will not conduct. When the voltage increases above this normal level due to a surge, the electrical power is strong enough to ionize the gas inside the GDT which act as a conductor to pass the high current to the ground until the voltage returns to the normal level. Again the GDT becomes a poor conductor.
The GDT used in the circuit is 2035-30, make 300 V 2 pole Arrester.

GDT DATASHEET

Role of Safety capacitor

A high voltage capacitor is also included in the circuit to withstand high impulse voltage during surge. The capacitor will shunt the energy from the impulse to ground. Safety capacitors are available in ceramic disc and metalized film or paper. The film type are made of self-healing metalized polyester, polypropylene or paper and usually come in a “box” style casing as the capacitor is encased is a flame retardant or flame-proof case. The safety capacitor used in the circuit is 105 K 400 Volt DC.

Safety Cap

TV Guard circuit

Coaxial cable

The components can be soldered lead-to-lead without a pcb. Enclose in a small plastic case and connect the circuit between the cable core and shield as shown in the diagram.

A similar circuit is used in Telephone connector Box

Filed under: Circuit, Components, Design, Electronics, Energy, Hobby Circuits, Home, Internet, Techniques, Television Tagged: Cable TV protector, Coaxial cable, copper clad aluminium, Gas Discharge Tube, GDS, high voltage capacitor, lightning protector, metal oxide varistor, Modem protector, safety capacitor, Set top Box, Spike Arrestor, Spike guard, Spike protector, surge protection device, Surge protector, Transient protector, Transients, TV Guard, voltage spikes, Voltage transients ]]> http://dmohankumar.wordpress.com/2012/01/26/trick-to-protect-tv/feed/ 2 dmohankumar GDS GDS 2735 105K 400V TV-GUARD CABLE TELEPHONE-GUARD http://dmohankumar.wordpress.com/2012/01/25/heat-sensor-2/ http://dmohankumar.wordpress.com/2012/01/25/heat-sensor-2/#comments Wed, 25 Jan 2012 13:56:36 +0000 D.Mohankumar http://dmohankumar.wordpress.com/?p=6416 Continue reading →]]> This simple circuit can monitor the heat generating devices like Amplifier, CD player, Inverter etc. The LED in the circuit blinks when the heat inside the device increases above the preset value. To give more visual attraction, a seven segment display is also included which shows a digital display as the temperature increases.

The circuit uses an NTC (Negative Temperature Coefficient) Thermister as the heat sensing element. Its resistance is 4.7K at normal temperature which changes to a low value depending on the heat. Preset VR1 and Thermister forms a potential divider to control the voltage at the reset pin 12 of IC1. IC1 oscillates only if its reset pin 12 is grounded. When the temperature increases, resistance of thermister decreases and the reset pin 12  of IC1 will be grounded. CD 4060 is the 14 stage ripple free binary counter IC that oscillates with the components C1 and R1. To give fast blinking rate of LED, a low value resistor is used as R1. Two outputs of IC1 are used. Pin 7 is used to connect the LED through the current limiting resistor R3. CD 4060 gives sufficient output current to drive LEDs (see image) and most of the LEDs now available are high bright low current types.

Output pulses from pin 5 of IC1 are used to give input pulses to the seven segment display driver IC CD4033. When its input pin 1 gets pulses from IC1, its outputs drive the common cathode 7 segment display to show digits 0 to 9. This digital display is not related to the temperature level, but only as a moving display to show the rise in temperature. This part can be omitted if not needed. Only CD 4060 is sufficient to make the heat sensor. Its pin5 can be used to drive a piezo buzzer.

Normal heat. LED off and Display shows any digit

Heat increased. LED blinks and display changes from 0 to 9 and repeats

Fix the Thermister near the heat generating part of the device like heat sink. Connect the Thermister to the circuit using thin wires. Power to the circuit can be obtained from the device itself , if its power supply is 6-12 volt DC. If the power supply of the device is above 12 Volts, use a 9 V regulator IC to reduce the voltage.
After fixing the Thermister, switch on the device and wait for 10 minutes to increase the temperature inside the device. Then slowly adjust VR1 till LED blinks. Then turn back the preset till LED stops blinking. When the temperature increases above this preset value, LED starts to blink.

1. Slow wave sleep: This is characterised by very strong brain waves with very low frequency. Slow wave sleep occurs during the first hour of sleep and is restful with decreased peripheral vascular tone. Ten to thirty percent decrease in BP, respiratory rate, basal metabolism etc occurs in slow wave sleep. Generally slow wave sleep is considered as” dreamless sleep” but occasionally dreams appears without less bodily activities so that these dreams will not be remembered.

2.REM (Rapid Eye Movement) sleep: During this stage of sleep the eye balls move rapidly, even though the person is in full sleep. REM sleep is referred to as Paradoxical sleep or Desynchronized sleep. During the entire sleep time, bouts of REM sleep occur five to thirty times at an interval of 90 minutes. REM is sleep is considered as” Dream sleep” and the dream can be remembered since it involves bodily activities. The important characters of REM sleep are

a. Active muscle movements and dreaming
b. Sensory stimuli will be absent so that it is difficult to arouse through touch, sound or light stimuli.
c. The spinal muscle control area will be inhibited so that the person shows depressed muscle tone.
d. Heart rate and respiratory rate diminishes or irregular.
e. In addition to rapid eye movements, irregular muscle movements also occur.
f. Bain metabolism increases to 20 percent and brain becomes highly active. Due to the increased activity of brain during the sleep, REM sleep is called paradoxical sleep because it is a paradox.

How do we sleep?

There are theories regarding the mechanism of sleep. According to the passive theory of sleep, the reticular activating system of the upper brain is fatigued due to the activities in the wakeful state. But according to the current view, sleep is induced by the active inhibitory centre located below the mid pondile level of the brain stem.

Sleep inducing factors
Several specific areas of brain are involved in inducing sleep. One important area is the Raphe nuclei in the pons and medulla.

Brain stem

Role of Raphe nucleus

The Raphe nuclei are aggregates of special nerve cells and the nerve fibres from the Raphe nuclei pass into the thalamus, hypothalamus, brain stem and most areas of the limbic system. Nerve fibres from the Raphe nuclei also spread into the cerebrum and to the spinal cord where they inhibit the incoming sensory stimuli including pain. The nerve ending of these fibres secrete Serotonin, the sleep inducing neurotransmitter.

Nucleus of Tractus solitarius

This is the termination in the pons and medulla for visceral sensory signals entering through vagus and glosso pharyngeal nerves. Stimulation of the Nucleus of Tractus solitarius induces sleep.

Diencephalon

Several regions of diencephalon such as rostral part of hypothalamus, occasional area in the diffuse nuclei of thalamus are involved in the process of sleep.

Electrical activity during sleep

Several changes in the electrical activities take place during the different stages of sleep as experimented in human volunteers using EEG(ElectroEncephaloGram),EMG(ElectroMyoGram) and EOG ( ElectroOculoGram).These studies revealed that the brain waveform changes dramatically during the different stages of sleep. When a person is fully in the awake stage, his brain produces beta waves characterized by high frequency of 14-30 cycles with low voltage. When the person enters into the rest stage before the sleep, the beta waves will be replaced with alpha waves. The alpha waves have lower frequency of 8-12 Hz but have higher voltage level or amplitude.

Brain waves

Sleep stages and brain waves

Stage 1.

This is the initial stage of sleep. It is characterized by the appearance of theta waves of 3.5-7.5 Hz. Stage 1 of sleep is the border line between the wakefulness and sleep.

Stage 2

The second stage of sleep generally occurs after 10 or 15 minutes if the person is in stage 1. Stage 2 is marked by the occurrence of Sleep spindles and K-Complexes. Sleep spindles are short bursts of waves of 12-14Hz that occurs 2 to 5 times per minute. The Sleep spindles show the activity through which the brain’s sensitivity to sensory inputs is inhibited. K-Complexes on the other hand are sudden sharp waveforms one per minute.  It consists of a brief high-voltage peak, usually greater than 100 µV, and lasts for longer than 0.5 seconds. K-complexes occur randomly throughout the stage 2 sleep, but may also occur in response to auditory stimuli.

Stage 3

This is marked by the appearance of Delta waves. The delta waves have high amplitude and show less than 3.5Hz frequency.

Stage 4

The delta activity progresses as the person enters into the stage 4 of sleep. In stage 3 around 20 percent delta activities occur while in stage 4, it increases to 50 present. After 90 minutes of delta activity, the person enters into the REM sleep. During REM sleep, the brain’s activity increases rapidly and the brain is almost like in the wakeful state. The delta waves disappear and fast low voltage waves appear. The most important aspect of REM sleep is the fast eye movements. Muscular movements also occur but the person is unaware of the surroundings, since the sensory inputs are blocked. Dreams may also develop during the REM sleep. During the rest period, REM sleep continues and alternate with other stages till morning.

When IC1 gives high output, IC3 also gets power and it starts to oscillate. CD4060 is the 14 stage ripple free binary counter which oscillates with the components C3 and R4. These oscillations are available from the outputs of IC3. Out of the 10 outputs, the first output is used to drive the seven segment display.




A common cathode seven segment display is used here. Its pins 3 and 8 are Cathode (ground) pins and the remaining pins are anode pins. Its anode pins are connected together to get “ I” for IN and “ O” for OUT. When the toggle switch (2 pin type) is in the Off position, only pins 1 and 9 gets power supply so that it displays I to indicate IN. When the toggle switch is in the ON position, pins 6,7 and 2,4 gets power along with 1 and 9. This shows the O display to indicate OUT. Display blinks for 2 minutes and turns off along with the bell.
Use a small 8 ohms speaker. Power source can be a 9 volt PP3 battery or 9-12 volt power supply.

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To compare the current through the meter, a Differential Amplifier built around IC1 is used. Since the current flowing through the meter is too low, the voltage developed will also be very low. The differential amplifier amplifies this minute voltage to give a high output around 2 volts (as set by VR1).This is used to control the Schmitt trigger built around IC2. When the voltage level in the Trigger input of IC2 (Pin 2) is less than 3 volts (as set by VR2), output of IC1 remains high which lights the Green LED and inhibits the buzzer and Red LED. This indicates that the Inverter load is not high. When the load increases, the current flowing through the meter also increases and the output of IC1 gives more than 3 volts which changes the output of IC2 to low.Red LED turns on along with beeps from the buzzer. This indicates that the inverter is overloaded.
How to use it to measure inverter capacity?
In order to assess the inverter capacity, it is necessary to calibrate the circuit with a known load. No inverter will handle the load power as specified in its VA. Volt Ampere is used to indicates the maximum load capacity of the inverter. VA = W x Inverter loss. Inverter loss is typical around 1.15. If the total load connected to the inverter is 400 watts then the minimum inverter size should be 400 x 1.15. That is 460 VA. A 500 VA is suitable for the load.

We can use 100 watts bulbs as load to calibrate the circuit. Connect points A and B to the 12 volt battery using Crocodile clips. Connect points C and D to the inverter using crocodile clips. Always observe polarity while connecting. Then connect four 100 watts bulbs (for a 500 VA inverter) to the inverter out and switch on the inverter. So the load is 400 watts. Slowly adjust VR2 till buzzer stops beeping and Red LED turns off. At this time, Green LED should turn on. This indicates that the load is within the limit. Mark the Wiper position of VR2. Then connect one more 100 watt bulb. At this time Buzzer should beep. If not, adjust VR1 and VR2 till buzzer beeps. Mark that position also. This indicates that the inverter is handling 500 watts which is an overloaded condition of the 500 VA inverter.
How it measures load capacity.
The circuit is now calibrated for the maximum load capacity. In VR2, now there are two makings. One for 400 watts and another for 500 watts. Turn the POT VR2 to the 400 W position and connect it to the 500 VA inverter with 400 W load. If the buzzer beeps, it indicates that the 500 VA inverter is capable of handling only less than 400 watts. The same procedure can be used to calibrate the circuit for 800 VA inverter with Seven 100 watts bulbs. Use a preset for VR1 and 10K Lin POT for VR2.