voltage stepper

In conventional voltage multiplier circuits, AC is used to charge the capacitors network via diodes in one cycle and discharge in the other cycle in a particular combination, which thereby produces multiples of the peak voltage. However, this circuit works on a different principle, and it is DC which is doubled. It can be used to power low current circuits.

IC555 is configured as an astable multivibrator producing rectangular pulses of about 10kHz frequency. Its output is made to drive the transistor pair T₁ and T₂. Transistor T₂ being a pnp type, conduct when its base is negative, i.e. when the output of the IC produces a “low”. This charge C₄ via diode D₁ and ground (collector of T₂ is grounded).

For the next pulse, i.e. when the output of IC is high, T₁ conducts but T₂ is cut-off, C₄ cannot discharge because of diode D₁. So the voltage across C₄ and input voltage adds up and charge C₅ via D₂. Voltage across C₅ will equal Vcc pulse voltage across capacitor C₄ and Diode D₁. Hence the operation.

However, it was found that if current greater then 50 mA and drawn, output voltage, hence regulation, is lost. Any DC voltage between 5V and 18V can be boosted (both voltage being the minimum and maximum range of the IC).

For better results, increase the value of C₄ and C₅ to 47 µF/40V.

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R₁ = 220 Ω

R₂ = 6.8 KΩ

..Read more https://electronicsproject.org/voltage-stepper/

Rain Alarm

Rain Alarm

The following rain circuit is used to give an alert when it’s going to rain. This circuit is used in homes to guard their washed clothes and other things that are vulnerable to rain when they stay in the home most of the time for their work. The required components to build this circuit are probes. 10K and 330K resistors, BC548 and BC 558 transistors, 3V battery, 01mf capacitor and speaker.

Rain Alarm

Whenever the rainwater comes in contact with the probe in the above circuit, then the current flows through the circuit to enable the Q1 (NPN) transistor and also Q1 transistor makes Q2 transistor (PNP) to become active. Thus the Q2 transistor conducts and then the flow of current through the speaker generates a buzzer sound. Until the probe is in touch with the water, this procedure replicates again and again. The oscillation circuit built in the above circuit that changes the frequency of the tone, and thus tone can be changed.

Invisible Burglar Alarm

Invisible Burglar Alarm

The circuit of the invisible burglar alarm is built with a photo transistor and an IR LED. When there is no obstacle in the path of infrared rays, an alarm will not generate buzzer sound. When somebody crosses the Infrared beam, then an alarm generated buzzer sound. If the photo transistor and the infrared LED are enclosed in black tubes and connected perfectly, the circuit range is 1 meter.

Invisible Burglar Alarm

When the infrared beam falls on the L14F1 photo transistor, it performs to keep the BC557 (PNP) out of conduction and the buzzer will not generate the sound in this condition. When the infrared beam breaks, then the photo transistor turns OFF, permitting the PNP transistor to perform and the buzzer sounds. Fix the photo transistor and infrared LED on the reverse sides with correct position to make the buzzer silent. Adjust the variable resistor to set the biasing of the PNP transistor.Here other kinds of photo transistors can also be used instead of LI4F1, but L14F1 is more sensitive.

Parallel Telephone With Secrecy And Call Prevention

This circuit provides secrecy when two or more telephones are connected in parallel to a telephone line. The circuit also prevents incoming calls to as well as outgoing calls from other telephones connected in parallel, except from the one lifted first.

When someone picks up the handset of the telephone connected in parallel to the original (master) phone for making an outgoing call, no dial tone is heard and the phone appears to be dead. But when a call comes, the ring signal switches the SCRs ‘on’ and conversation can be carried out. As soon as the handset is kept on the hook, the SCR goes off and the telephone can again only receive incoming calls.

When a call comes, conversation can be made only from the telephone which is lifted up first. To carry out conversation from the other telephone, the handset of the telephone that was lifted up first has to be placed on the hook and then the push-to-on switch of the associated circuit of the other telephone has to be pressed after lifting up its handset. Thus the circuit ensures privacy because both the telephones cannot be active at the same time.

Those who are don’t need parallel telephones can rig up the associated circuit of a single telephone to work as an outgoing call preventer. An outgoing call can be made only when one lifts up the handset and presses the push-to-on switch of its associated circuit.

The polarity of the telephone line can be determined by a multimeter. To avoid confusion, a bridge rectifier can be used at the input of the circuit.

This circuit costs around Rs 80.

PROTECTION FOR YOUR ELECTRICAL APPLIANCES

Here is a very low-cost circuit to save your electrically operated appliances, such as TV, tape recorder, refrigerator, and other instruments during sudden tripping and resumption of mains supply. Appliances like refrigerators and air-conditioners are more prone to damage due to suchconditions.

The simple circuit given here switches off the mains supply to the load as soon as the power trips. The supply can be resumed only by manual intervention. Thus, the supply may be switched on only after it has stabilised.

The circuit comprises a step-down transformer followed by a full-wave rectifier and smoothing capacitor C1 which acts as a supply source for relay RL1. Initially, when the circuit is switched on, the power supply path to the stepdown transformer X1 as well as the load is incomplete, as the relay is in de-energised state. To energise the relay, press switch S1 for a short duration. This completes the path for the supply to transformer X1 as also the load via closed contacts of switch S1. Meanwhile, the supply to relay becomes available and it gets energised to provide a parallel path for the supply to the transformer as well as the load.

If there is any interruption in the power supply, the supply to the transformer is not available and the relay de-energises. Thus, once the supply is interrupted even for a brief period, the relay is de-energised and you have to press switch S1 momentarily (when the supply resumes) to make it available to the load.

Very-short-duration (say, 1 to 5 milliseconds) interruptions or fluctuations will  not affect the circuit because of presence of largevalue capacitor which has to discharge via therelay coil. Thus the circuit provides suitable safety against erratic power supply conditions.

OVER- / UNDER-VOLTAGE PROTECTION OF ELECTRICAL APPLIANCES

This circuit protects refrigerators as well as other appliances from over and under-voltage. Operational amplifier IC LM324 (IC2) is used here as a comparator. IC LM324 consists of four operational amplifiers, of which only two operational amplifiers (N1 and N2) are used in the circuit.

The unregulated power supply is connected to the series combination of resistors R1 and R2 and potmeter VR1. The same supply is also connected to a 6.8V zener diode (ZD1) through resistor R3.Preset VR1 is adjusted such that for the normal supply of 180V to 240V, the voltage at the non-inverting terminal (pin 3) of operational amplifier N1 is less than 6.8V. Hence the output of the operational amplifier is zero and transistor T1 remains off. The relay, which is connected to the collector of transistor T1, also remains de energised. As the AC supply to the electrical appliances is given through the normally closed (N/C) terminal of the relay, the supply is not disconnected during normal operation.

When the AC voltage increases beyond  240V, the voltage at the non-inverting terminal (pin 3) of operational amplifier N1 increases. The voltage at the inverting terminal is still 6.8V because of the zener diode. Thus now if the voltage at pin 3 of the operational amplifier is higher than 6.8V, the output of the operational amplifier goes high to drive transistor T1 and hence energise relay RL. Consequently, the AC supply is disconnected and electrical appliances turn off. Thus the appliances are protected against over-voltage. Thus the appliances are protected against over-voltage.

Now let’s consider the under-voltage condition. When the line voltage is below 180V, the voltage at the inverting terminal (pin 6) of operational amplifier N2 is less than the voltage at the non-inverting terminal (6V). Thus the output of operational amplifier N2 goes high and it energises the relay through transistor T1. The AC supply is disconnected and electrical appliances turn off. Thus the appliances are protected against under-voltage. IC1 is wired for a regulated 12V supply.
Thus the relay energises in two conditions: first, if the voltage at pin 3 of IC2 is above 6.8V, and second, if the voltage at pin 6 of IC2 is below 6V. Over-voltage and under-voltage levels can be adjusted using presets VR1 and VR2, respectively.