Invisible Tester. Simple Design 8

IR-DIODE-TESTER-CIRCUIT-2Title of the circuit is deliberately given because it is used for testing the Photo diodes, Infrared LEDs, Photo transistors etc working in “Silent Mode”. How can we confirm an Infrared LED is working or not. It gives No visible indication. It is working and emitting Infrared rays but the IR rays are beyond our spectral response and we can’t see it. So this simple tester will help you to check whether such devices are good or bad before using in a circuit or even during trouble shooting. Not only one function the tester doing . It can test, all diodes, Capacitors, LEDs etc. Its cost is just Rs.10 but it is a worth tool.
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Two Heat Soldering Iron. Simple Design 7

3Soldering may sometimes make nuisance because the Iron will be either too hot or cold. If it is switched on continuously, it becomes too hot, wasting power and the bit gradually erodes. If it is switched off during a work, it takes time to become hot. So what is the solution to solve this problem? Do it, your Soldering Iron will always be ready in its two heat conditions. Simple, see how the trick works.
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USB Light. Simple Design 6


You can make a simple LED light to read and type in Computer or Laptop during night without disturbing other’s sleep. It is also useful as a mini Emergency light in the event of a power failure. It is too simple and powered from the USB port. USB lights are available in the market, but costs around Rs.150. You can make this USB light at the cost of just Rs.5.
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Battery Charge Indicator. Simple Design 5

BATTERY-CHARGE-INDICATOR-2This is one simple but highly useful circuit for you. Most of us use different types of Rechargeable batteries in Portable devices, Inverter, Emergency lamp etc. If the battery is deeply discharged, sometimes it will not get fully charged later. This is the most common reason for the failure of Emergency lamp. So we need an indicator to show the safe level of battery voltage. It is too simple to make it and needs only three components. Just hook up it in the battery and it will remind you when it needs charge.
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Ohms Law and Zener Resistor. Simple Design 4

Zener is a kind of Diode widely used in Voltage regulation and Switching applications. Zener is similar to other signal diodes but it conducts only if a specific voltage is provided to it based on its voltage rate. For example, a 5 volt Zener conducts only if it gets more than 5 volts. When the voltage to the zener rises above its value, its p-n junction undergoes breakdown and conducts. This breakdown point is known as Avalanche point. Unlike other diodes, current through the zener must be controlled, otherwise it will fail. So a series resistor must be connected to control the current through it. Here comes the importance of Ohms law .
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Ohms Law and Voltage Drop. Simple Design 3

As you know, when a resistor is connected across the positive and negative rails of a power supply, some voltage will be dropped through the resistor. This is due to the resistance offered by the resistor. Let us see one example.
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Ohms Law and Voltage through Resistor. Simple Design 2


In a circuit diagram, we can see a number of Resistors connected in series or parallel between the positive and negative rails. These resistors are controlling the voltage and current to the particular sections of the circuit. When we design a circuit, we should have an idea about the voltage and current requirements for each section of the circuit. Then only we can select the proper values of resistors. If you know this, you can easily answer the questions in Project Viva regarding the selection of resistors.
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