Light detect alarm

This circuit is actually a light detector. when light falls on the LDR it trigger an alarm sound. its a school project .this circuit attached with a model remote car .every time the car passes under a model tunnel it make alarm.

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How to read value of a Capacitor ?

Capacitance is the ability to store electrons and is measured in Farads.One Farad is a very large value! So most capacitors used in electronic circuits are measured in MicroFarads (uF) or even Picofarads (pF). Capacitance = Q / V Where Q is the charge and V is the voltage. Thus the capacitance is the charge divided by voltage. The important parameters of the capacitor are 1. Value -Value is marked on the capacitor directly or in colour codes 2. Tolerance -It indicates how much more or less the actual capacitance of the capacitor 3. Working voltage -It is the maximum voltage a capacitor can withstand before the dielectric breakdown 4. Leakage current .There is always small leakage current in all capacitors. Ideally this should be zero. But no capacitor is perfect without leakage current. Tantalum capacitor is comparatively better with minimum leakage current Value 1pf (Pico Farad) = 0.001nf (Nano Farad) 1nf (Nano Farad) = 0.001μf (Micro Farad) 1μf (Micro farad) =

Ring tester

In my Electronic repair job I found normal multimeter is somewhat limited in certain area. so special tools are needed for saving a lot of time Ring tester is one of this kind .helping me to check small hi Q inductors SMPS transformer, TV Deflection coils ,LOT ,line driver transformer and almost any inductor working on hi frequency.Normal multimeter can only identify a open coil ,but not a shorted windings. I found some commercial available ring tester. but it is not available in local shops of my area.also it seems priced high. So I decided to make a ring tester of my own. Below is the one I successfully made from the junk box components. I found it very useful. and now it is one of my best test tool collection. Two Ic's, few LED's ,one plastic container and few resistors made this wonderful tool. If we test it with primary of SMPS transformer or LOT windings of a good one shows all its LEDs will light. depending on the inductive reactantce the number of LED 's

Transistor numbers and codes

Most transistor markings follow one of these codes: JEDEC, JIS or Pro-Electron. For ICs, look for known numbers (e.g. 741, 4001, 7400) between the prefix and the suffix. Don't confuse it with the date code. ICs typically have two numbers: The part number and the date code. 1. Joint Electron Device Engineering Council (JEDEC) These part numbers take the form: digit, letter, sequential number, [suffix] The letter is always 'N', and the first digit is 1 for diodes, 2 for transistors, 3 for four-leaded devices, and so forth. But 4N and 5N are reserved for opto-couplers. The sequential numbers run from 100 to 9999 and indicate the approximate time the device was first made. If present, a suffix could indicate various things. For example, a 2N2222A is an enhanced version of a 2N2222. It has higher gain, frequency, and voltage ratings. Always check the data sheet. Examples: 1N914 (diode), 2N2222, 2N2222A, 2N904 (transistors). NOTE: When a metal-can version of a JEDEC tra

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