Fan Regulator Circuit | Remote-Controlled Fan Regulator Circuit Diagram

Using this circuit, you can change the speed of the fan from your couch or bed. Infrared receiver module TSOP1738 is used to receive the infrared signal transmitted by remote control. The circuit is powered by regulated 9V. The AC mains is stepped down by transformer X1 to deliver a secondary output of 12V-0-12V. The transformer output is rectified by full-wave rectifier comprising diodes D1 and D2, filtered by capacitor C9 and regulated by 7809 regulator to provide 9V regulated output. Any button on the remote can be used for controlling the speed of the fan. Pulses from the IR receiver module are applied as a trigger signal to timer NE555 (IC1) via LED1 and resistor R4.

Security Lock | Door Security Electronic Key Combination Lock

This is a relatively simple circuit of electronic lock of safety with code of 7 digits. It should is given attention in the time that will be stepped the keys, that shape code and it does not exist it delays. With the right step of keys and if code is right then is activated exit Q7 for roughly 4 seconds, driving the transistor Q2, which with the line can drive one relay, for the opening of door, or any other circuit.

 

Triac based DC Motor Speed Controller Circuit

This Triac-based dc motor speed controller circuit is designed for controlling the speed of small household motors like drill machines. The speed of the motor can be controlled by changing the setting of P1. The setting of P1 determines the phase of the trigger pulse that fires the Triac. The circuit incorporates a self-stabilizing technique that maintains the speed of the motor even when it is loaded.

For example, when the motor of the drill machine is slowed down by the resistance of the drilled object, the counter-EMF of the motor also decreases. This results to a voltage increase in R2-P1 and C3 causing the Triac to be triggered earlier and the speed increases accordingly.

12V SCR controlled Battery Charger Circuit

Repairing /revamping a dead charger
What I started with was an inoperative 12amp battery charger. In hope of repairing it, I traced out the circuit, but did not like what I found-poor circuit design. So what I had to start with was an enclosure, ammeter, thermal overload interrupter, and center-tapped transformer all designed for battery charger application.
Since the maximum current delivered by the unit is a function of the transformer internal impedance, I recommend that the readers use the same type of transformer. If you are a good pack-rat (like me), you may already have a dead charger-or you can be on the lookout for one.

SCR (Thyristor) Rectifiers
First of all, the two SCRs (silicon controlled rectifiers or thyristors) are connected with their anodes (stud or tab) grounded—this makes for excellent thermal transfer because no insulating hardware is required (if it is permissible to connect the negative terminal of the charger directly to the steel enclosure). If you do not wish to ground this point, use insulating hardware to electrically isolate the SCRs. This makes the transformer center-tap the positive terminal. The reason for this circuit placement is the ease of driving the SCR gates via the positive battery voltage—it is very unconventional as I have never seen this trick done before.

SCRs are the ideal power device choice for a battery charger because they can both regulate battery charging voltage and prevent fault current when the battery is inadvertently connected reverse. I have actually connected mine reverse and thought that the charger was inoperative until I realized what I had done.

Adjustable Power supply | LM338, 4-30V 20A Adjustable Power supply Circuit

This is a regulated and adjustable power supply which can deliver up to 20A and adjustable voltage between 4 and 30V. It is easy to build and uses LM338 and 741 integrated circuits. VR1 it is used to adjust the output voltage.

Datasheet | LM338 IC

The LM138/LM238/LM338, LM350 are adjustable 3-terminal positive voltage regulators capable of supplying in excess of 5A over a 1.2V to 32V output range. They are exceptionally easy to use and require only 2 resistors to set the output voltage. Careful circuit design has resulted in outstanding load and line regulation comparable to many commercial power supplies. The LM138 family is supplied in a standard 3-lead transistor package.

Refrigerator Protector Circuit | Refrigerator Compressor Failure Protector

Gadgets involving compressors like AC and refrigerators are particularly prone to sudden and intermittent Mains voltage breaks, but ironically don’t carry any built-in protection system. A simple automatic refrigerator appliance compressor failure protector circuit presented here looks impressive.

However, modern electronic devices like TVs, music systems, computers mostly come with built in voltage regulators which are able to tackle voltage fluctuations quite reliably and very seldom do they fail. Moreover brief voltage failures and quick successive voltage interruptions don’t bother them too much.

Surge Protector | Whole-House Surge Protector Circuit

AC Mains Surge Voltage

An AC mains surge voltage may be defined as an instantaneous rise of voltage that may normally take place due to voltage fluctuations. Such voltage peaks may remain for a very short duration of time, but still can be fatally dangerous to household electrical and electronic equipment.

A rise of voltage according to Ohm’s law would force an appliance or the connected load to draw an equivalent excess amount of current beyond the tolerance range of the particular gadget. Thus, a spike generated due to a surge voltage may instantly and permanently damage valuable appliances.

Normally electronic gadgets, like TVs and music systems, etc., are typically prone to the dangers of such voltage surges. Even though they are mostly armed with built-in protection systems like an SMPS voltage stabilizer/regulator, fuses, etc.. a sudden jolt created by a spike arising due to a voltage surge may cause critical parts to burn. Also quite alarmingly, expensive electromechanical devices like refrigerators, air conditioners, water pumps etc. are even at a greater risk with such power abnormalities. These units may be quite vulnerable to voltage malfunctions and generally “dislike” sudden changes in the input voltages and currents. A voltage surge not only causes deterioration in the condition of machine components but at times may even instantly burn the windings of the motor involved. Moreover repairing such equipment are rather costly and one may even prefer buying a new one than repairing at the involved high costs. In short, the consequence can result in a lot of unnecessary wastage of money and time.
There may be a number of sophisticated mains surge protector units available in the market; however the above situation can be effectively handled even through a very simple concept.

Circuit Description

Voltage Stabilizer | High / Low Voltage Cutoff Circuit With Timer

This inexpensive high / low voltage cutoff circuit can be connected to an air-conditioner/fridge or to any other sophisticated electrical appliance for its protection. Generally, costly voltage stabilizers are used with such appliances for maintaining constant AC voltage. However, due to fluctuations in AC mains supply, a regular ‘click’ sound in the relays is heard. The frequent energization /DE-energization of the relays leads to electrical noise and shortening of the life of electrical appliances and the relay/stabilizer itself. The costly yet fault-prone stabilizer may be replaced by this inexpensive high-low cutout circuit with timer.

The circuit is so designed that relay RL1 gets energized when the mains voltage is above 270V. This causes resistor R8 to be inserted in series with the load and thereby dropping most of the voltage across it and limiting the current through the appliance to a very low value. If the input AC mains is less than 180 volts or so, the low-voltage cut-off circuit interrupts the supply to the electrical appliance due to energisation of relay RL2. After a preset time delay of one minute (adjustable), it automatically tries again. If the input AC mains supply is still low, the power to the appliance is again interrupted for another one minute, and so on, until the mains supply comes within limits (>180V AC).

Automobile Speed-Limit Alert Circuit Diagram

Wireless portable unit, Adaptable with most internal combustion engine vehicles

This circuit has been designed to alert the vehicle driver that he/she has reached the maximum fixed speed limit (i.e. in a motorway). It eliminates the necessity of looking at the tachometer and to be distracted from driving. There is a strict relation between engine's RPM and vehicle speed, so this device controls RPM, starting to beep and flashing a LED once per second, when maximum fixed speed is reached. Its outstanding feature lies in the fact that no connection is required from circuit to engine.