universal Zener Diode Tester project

Zener diodes available in the market are specified according to their breakdown voltage as well as tolerance. The tolerance may vary from 5 per cent to 20 per cent. The circuit of a versatile zener diode tester presented here enables you to verify the specified breakdown voltage and tolerance values. In addition, you can check the dynamic impedance of a zener diode. The dynamic impedance characteristics of a zener diode determine as to how well the zener diode regulates its own breakdown voltage. Thus this circuit can be used to compare the dynamic impedance characteristics of zener diodes from a lot and segregate/categorise them accordingly. For full-fledged zener diode testing you
will have to refer to the manufacturer’s datasheet to check zener diode parameters such as zener voltage, power, and current (maximum/nominal) ratings. In addition, temperature coefficient and dynamic impedance have also to be checked if zener diode is to be used for critical functions such as voltage reference for digital voltmeters, control systems, and precision power-supply circuits. However, for a common hobbyist it is not necessary to check zener diodes critically, and only
checking its dynamic impedance characteristic is sufficient. Dynamic impedance implies the degree of change in a zener diode’s voltage with the change in current. Expressed in ohms, it equals the small change in zener voltage divided by the corresponding change in zener current (centered around the test current figure prescribed in datasheets by manufacturers). From datasheets it is observed that test current value is high for low-voltage zener diodes and low for higher-voltage zener diodes. However, the dynamic impedance value will be low for low-voltage zener diodes and vice versa for higher-voltage zener diodes. To test 3.3V to 120V zener diodes by the practical dynamic impedance method, you need to have a variable voltage (0 to above 120V) and current (1 mA to 150mA) supply source. Designing this type of power supply is quite complicated and is prone to damage if excess current is drawn accidentally.

circuit diagram

The zener diode tester circuit presented here has been designed considering the above factors. It is capable of testing zener diodes of breakdown voltage ratings of upto 120V and wattage ratings of
250 mW, 400 mW, 500 mW, and 1W.

The circuit can be deployed in quicktest mode as also in quality-test mode of  you can
perform a rough check of zener diode’s breakdown voltage up to 47 volts. In quality-test mode, you can check dynamic impedance characteristic for zener diodes from 3.3V to 120V. Commonly available step-down transformers X1 and X2 (230V AC primary to 9V AC, 750 mA sec. each) are connected back-to-back as shown in the figure. A bridge rectifier followed by filter capacitor C1 converts the output from X2 transformer to DC. Neon lamp L1 indicates the presence of higher DC voltage (220V approximately) across capacitor C1, which is used to test various zener diode values from 3.3V to 120V.

An advantage of using this high-voltage circuit is that the current gets restricted to a low value. It delivers only 3mA (approx.) when testing zener diodes with higher breakdown values (e.g. 120V
zener diode), but while testing zener diodes of low breakdown values, such as 3.3V, it delivers a current slightly above 20 mA. Such power-supply characteristics suit our requirement, as stated earlier. Since a small current is used for testing of zener diodes, there is no danger of zener diodes getting damaged during testing using the dynamic impedance method. Before using the circuit, check DC voltage across test terminals A and B without connecting any zener diode and then flip toggle switch S2 to quick-test position. DC voltage available across terminals A and B will be around 200V DC. Now put toggle switch to quality-test position. DC voltage can now be adjusted from 6V DC to 200V DC (approx.) with the help of potentiometer VR1. After these preliminary checks, the circuit is ready for operation.
To test zener diode by quick-test method, connect zener diode across terminals A and B and flip switch S1 to ‘on’ position. Note down DC voltage in digital multimeter M2, which is the rough breakdown voltage. In quick-test method you can test zener diode values up to 47 volts safely. For higher-value zener diodes you will have to increase the value of resistor R3 suitably. If zener diode presents a short, digital multimeter M2 will read ‘0’volts To perform quality test on the same
zener diode, turn switch S1 ‘off’and remove zener diode from across terminals Aand B. Now turnswitch S1 ‘on’and adjust potentiometer VR1 to obtain DC voltage (on digital multimeter) across terminals A and B equal to the one found during quick test method. Now keep potentiometer VR2 in mid position and connect zener diode across terminals A and B.

(Note. Before testing zener diode, refer Table I and Table II for the minimum
test current (It min) and maximum test current (It max) required for various zener diode values, depending upon their wattage rating.)Test current is adjusted using potentiometer VR2 and measured using meter M1 (A 0-25mA analogue milliampere meter or a 0-20mA digital multimeter canbe used.)

 Now adjust potentiometer VR2 and note down changes in zener voltage during It min and It max conditions. If the required current is not available, increase DC voltage by adjusting potentiometer
VR1 suitably. While changing test current from It min to It max, the voltage variationacross zener diode should be less than 1 volt for lower-value zener diodes and a few volts for higher-value zener diodes. A voltage variation of more than this value ndicates that zener diode is not properly regulating. When comparing zener diodes of same values, the zeners showing less voltage deviation would regulate better

Lemon Battery - a simple elctrical project for school college students

Lemon Battery

The lemon battery is a simple type of electrical battery that is commonly made for school science projects because it illustrates a battery's main components. Typically, a piece of zinc metal and a piece of copper metal are inserted into a lemon. Everyday objects such as galvanized nails and copper pennies can be used for the zinc and for the copper. A single lemon is usually studied using an electrical meter. Several lemons can be wired together to form a more powerful battery that will power a light-emitting diode, a buzzer, or a digital clock.

The lemon battery is similar to the first electrical battery invented in 1800 by Alessandro Volta in Italy. Volta used brine (salt water) instead of lemon juice. The lemon battery is described in some textbooks in order to illustrate the chemical reactions that occur in batteries. The zinc and copper are called the electrodes of the battery, and the juice inside the lemon is called the electrolyte. There are many variations of the lemon battery that use different fruits (or liquids) as electrolytes and metals other than zinc and copper as electrodes.

This article contains instructions for making a lemon battery and using it to power a light-emitting diode. If you want to know more about the science and history of the lemon battery, you can get started  Wikipedia.

Materials and equipment required:

• Light emitting diode. These look like plastic pieces with 2 wires stuck into them. They are usually just called LEDs, which comes from the first letters of the three words Light Emitting Diode. When the right battery is hooked up, the LED will glow. A red one is good for the lemon battery experiment; there is another section of this article that discusses how to find an LED. While LEDs are a good choice for this experiment, some other ideas are given below in the section "Alternative devices".
• Lemons. You'll need 3 or 4. Any citrus fruit, like limes, grapefruits, or oranges, or even a potato will work.
• Zinc electrodes. You'll need 3 or 4. Most likely you'll use a piece of metal that's been coated with zinc. This is what the word "galvanized" means. A galvanized metal washer that's about one inch (2 – 3 cm) in diameter will work well. Galvanized roofing nails, galvanized screws and bolts, and even paper clips can also work. If you can find some zinc sheet, and some shears or tough scissors to cut it, that will work very well. Be careful if you do this; the edges of sheared metal sheets are sharp. If you can, file the edges to make them less sharp.
• Copper electrodes. You'll need 3 or 4. Copper or copper-coated pennies work well. You may find some good copper fittings in the plumbing section of a hardware store. Again, if you can find some copper sheet, and some shears or scissors to cut it, that will work. Again, be careful about sharp edges.
• Leads. You'll need 5 or 6. The easiest thing is to get hold of a packet of insulated lead wires with "alligator clips" on each end.
• Multimeter (optional). If you know how to use an electrical multimeter, it can be helpful in getting your battery to work.

Making a single lemon cell

Make the first lemon cell. Your battery is going to have at least 3 lemon cells, but each cell is made the same way.

1. Clean your electrodes carefully. Your goal is to get any dirt or grease off of them, and also to scrub away the thin "oxide" coatings on them. It should work fine if you clean them in the same way that you'd clean a pan in the kitchen to make it clean and shiny. Scrubbing with steel wool or with an abrasive sponge will work fine; if you are using a galvanized electrode, be careful not to rub off the zinc coating completely.
2. Stick one zinc electrode into the lemon (or other fruit). You may need to use a small knife to cut a slit into the lemon. You want the electrode to go into the lemon as deeply as possible, but you'll need a little bit of the electrode to stick out of the fruit so you can attach a lead wire to it. Wiggle the electrode around a little to smash the membranes inside the fruit.
3. Next, stick the copper electrode into the same lemon. You want this electrode to be close to the zinc electrode, but it must not touch the zinc inside the lemon. If they do touch, your cell will not work. As for the zinc electrode, you want to stick the copper electrode into the fruit as far as you can, and you want to wiggle it a bit to make sure the membranes near the electrode are broken.(Optional) If you are using a multimeter, you can do the following tests to make sure your lemon cell is working.
4. Hook up two alligator clips from your leads to the two electrodes. Connect the two clips to the leads of the multimeter.
5. Measure the voltage from your lemon cell. It should read about 0.9 - 1.0 volts.
6. Measure the current from your cell. You should read a few tenths of a milliampere. Some multimeters are not sensitive enough to measure currents less than one milliampere, in which case you'll just see 0.0 as the reading.

Making the lemon battery

When several lemon cells are wired together, the collection is called a battery. We usually call a single lemon cell a battery also. Most batteries that you may purchase to use in toys and electronics have just one cell inside.

1. You need to make 3 lemon cells. If you're using a multimeter, make sure that each cell generates the correct voltage and the correct current.
2. Using two lead wires, connect the three cells together. Connect the zinc electrode on the first cell to the copper electrode on the second. Connect the zinc electrode on the second cell to the copper electrode on the third lemon. This is called a "series" connection; the three cells make up the lemon battery.

Connecting the LED

Connect a lead wire from the copper electrode of the first lemon cell to the longer lead wire from the LED. Connect a lead wire from the zinc electrode of the third cell to the shorter wire of the LED. You may need to gently pull the lead wires that come from the LED apart; the alligator clips on the ends of the two lead wires that connect your battery to the LED must not touch each other.
The LED will glow now enjoy your diy project.

Any questions please leave a comment below: