Water Low Level Alarm
Same buzzer, the same power supply but with a little ingenuity this gives an alarm when the water falls below a certain level.This circuit as shown in Schematic 7, which can be used to indicate when the level falls low in overhead tank, a sump or even in a bore well.Now you will find a 100K resistance between the trigger terminal and positive supply which pulls the trigger terminal to the positive potential. As in the previous case both wires from trigger and ground are kept in the water. Even though pulled up, trigger will be at ground potential as long as there is water across the probes and hence the piezo buzzer can not go off. Once the water level goes down, the trigger terminal loses its ground potential and reaches the positive potential because of the pull up resistor and the buzzer will be on.
Digital Circuits
Incidentally in digital electronics parlance this is known as going high or pulling up. If the voltage at any terminal is close to the ground potential as dictated by system requirement, it is known as going low or pulling down. Conversely if the voltage at any terminal is close to the positive potential as dictated by system requirement, it is known as going high or pulling up. Digital circuits work usually with 0 andl. Obviously one is high level and zero is low level, which are known as logic states. Noise in the digital circuits can easily be eliminated. Follow the logic states depicted here.
Analogue Circuits
On the other hand analogue circuits process analogue signals which can output any value within a range of its power supply. Examples are audio, video amplifiers. Unlike digital circuits, noise here is difficult to control.Construction is similar to earlier project, except that the probes are now fixed at the required low level of water.
Popularity: 19% [?]
Water High level Alarm
This can be used as an alarm when filling overhead tanks. Quite some time ago, I used it as an indication when the municipal water used to start flowing to my pipeline. When I built this project, happiest one was my mother. Municipal water used to be pumped in the midnighl at unearthly hours and my mother used to wake up now and then to check if the water started pouring in.
With half wave power supply already built, connect the buzzer as shown in the schematic and fix the wires. As the water level rises to touch the wires, the buzzer gives out a loud alarm. I used to put these wires in a plastic bucket under the tap. When municipal water flows down, it indicates an alarm. It is one of those most useful and easiest projects I ever built.
You may use this as a rain alarm particularly if the lady of the house dries up clothes or grain in the open yard or even as bed wetting alarm for the baby ((Use only batter}/” power!!)).You can try this as a steady hand testing game. You may use this for a continuity tester but do not use this on live wires.
Bring two wires and keep them at the desired level in the tank with a little separating distance between them. You can use fairly long wires and run them along into the house. Needless to say scrap and expose the copper wires a little. Connect one of these wires to the trigger terminal (generally yellow) of the buzzer and the other to the positive terminal (red wire). Black wire goes to the negative.
If you want battery operation, use two battery cells (1.5V each). Use more cells for more sound. If you want to use mains supply, half wave circuit description is given above. Use a transformer with 12V or 6-0-6V at the secondary. Screw the secondary ends to the terminal strip; screw diode (Dl, IN 4003) CI is an electrolytic capacitor of 1000 mfd and 16V rating. Please follow the polarity marked on the can. Light emitting diode is optional. Use with resistor (Rl, IK). It gives an indication that the power supply is OK. You may use the mains plug mounted power supplies or eliminators and mount all the parts on it.
Popularity: 14% [?]
Three Terminal Adjustable Regulator
Three terminal regulators are just right when we need a single fixed voltage. But they will be cumbersome as a hobbyist works with different voltages at different times and it becomes unwieldy to keep power supplies with a number of three terminal regulators.
Wouldn’t it be better if we have an adjustable but regulated power supply, which can cater to all the voltages we need? And we have such a wonderful device where you can continually adjust your output DC voltage. Well! It is short circuit protected, has only three terminals and all other good things. LM317
LM317T is an adjustable 3 terminal positive voltage regulator capable of supplying around 1.5 amps over an output range of 1.25 to 37 volts. It also has built in current limiting and thermal shutdown features, which makes it virtually blowout proof. This is an excellent startup project with low ripple. With an easy adjustment of regulated voltage, it can be used as power source for most of the applications in the next chapters. Pin out is given in Figure 13.
Circuit :
Rectifier part is same as shown in the earlier schematic of bridge rectifier. Transformer is changed to 18 V to get a better range of regulated voltages. 9-0-9 Transformer is used as it is difficult to get an 18 V transformer. Please change transformer rating as per your requirement and the capacitor also for higher voltage rating. It is preferable to use 2200 mfd. caps as larger value makes good, low ripple output voltage.
Pulsating DC output from the bridge is now filtered by the 2200uF capacitor and fed to TN’-put terminal (1) of LM317 regulator. The output of this regulator is varied via the ‘Adj’ pin(3) and the 5K variable resistance or preset pot meter (Rl) connected to it. The regulator uses an internal Zener diode to provide a fixed reference voltage of 1.2 volt across the external resistor R2. Hence the lower end of output voltage is limited to 1.2 volts. C2 is 47uF decoupling capacitor to filter out the transient noise. Metal tab of LM317 is connected internally to the ‘Output’ pin (2). The circuit diagram is shown in Schematic 5.
Construction
Use a small Vero board to fix all the components, cut the tracks where not required and solder the pins. Mount the LM317 regulator on a heat sink. However it can be screwed to the metal case of the enclosure box with the mica insulator and the nylon washer with the mounting screw as shown in Figure 12.
Use a little of heat sink compound on the metal tab and mica insulator as it helps to transfer heat between LM317 and case or heat sink.Use a metal box of suitable size and fix the veroboard and transformer. Mains wire is connected to the primary side of the transformer and taken out. Carefully insulate the mains joints. Mains switch is not shown in the schematic. You may add one if it is required. 5k linear potentiometer is fixed at the casing. Measure the voltages and mark them suitably on a dial fixed on the face of the casing with appropriate indication of the voltage. LED is also fixed on the casing to indicate the power supply.
Use a little of heat sink compound on the metal tab and mica insulator as it helps to transfer heat between LM317 and case or heat sink.
Use a metal box of suitable size and fix the veroboard and transformer. Mains wire is connected to the primary side of the transformer and taken out. Carefully insulate the mains joints. Mains switch is not shown in the schematic. You may add one if it is required. 5k linear potentiometer is fixed at the casing. Measure the voltages and mark them suitably on a dial fixed on the face of the casing with appropriate indication of the voltage. LED is also fixed on the casing to indicate the power supply.
Popularity: 12% [?]
Three Terminal Regulators- Unadjustable
These are simple, effective and interesting integrated circuits. They are short circuit protected, can stand up to 32V, have thermal protection and they can easily deliver regulated voltage with 1 amp of current. In these ICs, the last two digits give you the regulated voltage they deliver, 7806 gives you 6 volts and 7812 gives you 12 volts and so on. These are available from most of the manufacturers and are cheap. They are connected after the conventional power supply. There should be 3V more than the required voltage at the input for proper regulation. You need 9V for a 7806 regulator. Use this circuit whenever single regulated voltage is required. Pinout and heat sink mounting procedure are given in figure 11 and Figure 12 respectively.
solder the three terminal regulator after the bridge. Connect the input pin (1) after the bridge and capacitor. Connect the common terminal (2) to the negative rail and you have the regulated voltage at the output (3). 47 uF capacitor (C2) is required if the regulator is placed faraway from the main power supply.
Metal bodies of these ICs are connected to the ground (common) terminal. Follow the mounting procedure as given below and fix a small aluminum plate to remove the heat and to improve its current capability. (This is a standard practice to mount heat sinks on ICs, transistors, SCRs, and triacs, etc.) By now you must have caught up with the art of soldering and the IC should be soldered well and fast.
Schematic 4 shows a 9V regulator appended to 12V power supply of the earlier bridge power supply of 12V DC.
Popularity: 7% [?]
Regulated Power Supplies
Unfortunately our hobby circuits work on different voltages and a power supply with single voltage will not be sufficient. Simplest way would be to buy a multi-tapped transformer and connect the voltage taps with a suitable switch. These transformers are available with taps of 1.5,3,4.5,6,9,12V. We need a single multi throw switch (as many throws as there are taps). With 9-6-0-6-9 transformer and with a double pole double throw switch, you can get 6 and 9V DC. With the same transformer, and with a double pole six throw switch, it is possible to get 3, 6, 9, 12, 15, 18 V. Switches and multi-tapped transformers are difficult to procure; cumbersome and even unavailable at some places.
Such schematics are not shown here as there are better ways to build circuits to get variable voltages. Also these power supplies suffer from a major draw back; poor voltage regulation, the voltage falls as more and more current is drawn and voltage also changes with mains voltage fluctuations.
A 12 V power supply shown in Schematic 3 may show as much as 16.8 V without load and it may go down to less than 12 V as the load current is increased. This still can be and is safely used for most of the non-critical circuits, but it is an unstabilised supply.
Why not build a regulated power supply, which doesn’t cost an earth but still gives very good results. Now for the time being, without going into details and complications of integrated circuits, we will use them for the pleasure and ease of using them and build a regulated power supply as a starter.
Popularity: 8% [?]
Batteries
Presently we have a variety of cells or batteries to choose from; lead acid, zinc carbon, Nickel cadmium and Nickel metal hydride, lithium, silver oxide and what not!Cell is a storage form of electrical energy. When more cells are used, it is known as battery, but these words are used interchangeably. These are used where portability of the equipment is needed and some times as a back up for the mains voltage. Each these cells have their own characteristics, like cell voltage, current capability, storage capacity and rechargeability.
Good old Zinc carbon cells have 1.5 volts and if two cells are fixed in series, they show 3V. These are the most common cells powering most of the portable devices and are available in various sizes known variously as AAA, AA, BB, CC etc. This nomenclature denotes the capacity and dimensions of each cell but all these cells show a voltage of 1.5 volts. These are not normally rechargeable. Alkaline batteries last longer.
Lead acid cells are most widely used for high power applications such as in automobiles, UPS systems, emergency lighting systems where weight of the battery is no concern but the capacity required is high. Sealed lead acid batteries or maintenance free batteries are another form of the same where the electrolyte is within the moistened separators. Lead acid batteries can deliver high currents and recharge cycles are high. Each cell voltage is 2 volts and in a typical car battery, six of such cells are connected in series in a single container to give 12 V.
Nickel cadmium cells (Ni. Cad) show a voltage of 1.2 volts, which means that two cells in series show a voltage of 2.4 volts. These are rechargeable. They suffer from a memory effect. If they are recharged after only partially discharged, they tend to recharge only to that partial extent rather than to their full capacity.
Nickel metal hydride cells (Ni. Mh) also show a voltage of 1.2 volts and are rechargeable. They show certain better characteristics than nickel cadmium cells. They are environmentally friendly and do not show the memory effect ofNi-Cad cells.
Lithium ion cells are the fast emerging technologies. These have higher energy density and most of the present day cell phones, laptops; handy-cams are powered by these cells. They should be always used with protection circuit. Charge them only with specified charger. They have a cell voltage of’3.6 volts
Popularity: 7% [?]
Resistors
Resistors are measured in ohms, and have a wattage rating. Resistance value is marked on the resistor in an internationally accepted color code. Normally quarter-watt resistors are used in the following circuits unless otherwise specified. Carbon film and metal film resistors are generally used. Wire wound resistors are used for higher wattage resistors.
Popularity: 15% [?]
capacitors
Capacitors store a bit of electrical energy and come in many types and varieties. Capacity is measured in terms of Farads named after the great scientist Michael Faraday. As farad is too large a value for most general applications, microfarads (mfd) and nanofarads (nf) are normally used in hobby and consumer applications.
Ceramic, polyester, paper, mica, and electrolytic capacitors are some of the types. A detailed discussion is left out here. Each type has distinctive features and qualities and capacities. Capacitors are marked with voltages at the maximum voltage they can operate. It is a good practice to use a capacitor rated at twice the operating the voltage. Capacitors above the range ofl mfd generally are electrolytics and are used such in these circuits. Electrolytic capacitors are polarized and marked on the can. They should be connected as per the polarity. Electrolytic capacitors of 25 V rating are used in the following circuits unless otherwise specified. Capacitors rated at higher voltages can be used in any of the circuits. Capacitors with higher capacity should not be used unless the implications are understood. Other capacitors normally rated at 30V are used in the following circuits unless otherwise specified.
Popularity: 23% [?]
Full Wave Power Supply
Make a full wave rectifier, as it is cheaper and better than a half wave one and has less AC ripple. Full wave rectification can be accomplished by two ways, either by a center-tapped transformer using two diodes, or by a bridge circuit, which uses four diodes.
We need center tapped transformer as used in the earlier circuit. .As already described, in this transformer, you have three wires on the secondary side. Simply speaking in this transformer center wire is taken as zero reference; two outside wires give you equal voltages. Say for a 6-0-6 transformer, center wire gives 0 volts while both ends give 6 volts each. The circuit is shown in Schematic 2.
Connect diodes, capacitor and resistor and LED just as in earlier project but follow the circuit is shown in the Figure below. Now if you wish to use the same 6-0-6 transformer, you will get 6V DC. If you wish to have 12 V DC by this method, you should get a 12 – 0 -12 transformer.
Solder lOOOuf / 25Vcapacitor after carefully noting the polarity. Negative side of the pin is marked on the can. A light emitting diode along with lK-x/4 watt resistor in series with it is idded to indicate that the power supply is on.
Popularity: 18% [?]
Half Wave Power Supply
Half wave rectification is simplest, as it requires only one transformer, one diode and one capacitor, but we have added a LED to give power supply indication. A simple half wave rectifier for 12V is shown below
500mA transformers are generally used for these circuits. Connect the primary wires to the mains chord after carefully insulating the joints. This transformer has three wires on the secondary side. AC voltage across both end wires is 12 and voltage across any one end wire and center wire is 6. So if both end wires are connected as shown in the present schematic the output DC voltage will be 12 and if any one of the end wires and center tap are connected the voltage will be 6.
Take a Veroboard and solder all components on it except mains power supply. Solder IN4003 diode to one end of secondary winding making note of the cathode. Solder lOOOuf /25V capacitor. Please note the capacitor is polarized, which means that you should connect it one way only. Negative side of the pin is marked on the can. Add a light emitting diode to know that the power supply is on. Now use a 1K-1A watt resistor in series with it.
LEDs are also polarized and marked. LEDs will not light up if they are connected in reverse. Take two pen light cells and connect the ends of a Red LED to positive and negative and then turn the leads over and try. (Forget the cathodes and anodes for the time being.) You will know that it works only one way. That also explains how a diode works. Do not connect them directly to 12 V LEDs cannot work beyond 5 V and their current capability is extremely limited. Although they are very rugged devices, they must always be used with a current limiting resistor.
Popularity: 9% [?]