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The post explains a 10 km long range transmitter circuit using ordinary components .PCB fabrication also explained. With the increased activity on 2 metres, some who may have contemplated working this band, have possibly been deterred by the cost of a " black box " and the uncertainty of modifying commercial equipment. With this situation in mind, the Author has , designed a simple , easily-built 2m f.m. transmitter, that can be assembled by anyone who can use a soldering iron and small tools whilst possessing a reasonable amount of patience. The completed unit will perform well, being as versatile as the constructor ultimately wishes to make it. An r.f. output of around 1 watts can be expected if the unit is constructed as described but power far in excess of this may be, achieved if the design is regarded as a working basis and the p.a. stage is developed. Construction Procedures for the proposed long range transmitter circuit A simple printed circuit technique is employed...

Description The circuit below responds to sound pressure levels from about 60 to 70 dB. The sound is picked up by an 8 ohm speaker, amplified by a transistor stage and one LM324 op-amp section. You can also use a dynamic microphone but I found the speaker was more sensitive. The remaining 3 sections of the LM324 quad op-amp are used as voltage comparators and drive 3 indicator LEDs or incandescents which are spaced about 3dB apart. An additional transistor is needed for incandescent lights as shown with the lower lamp. I used 12 volt, 50mA lamps. Each light represents about a 3dB change in sound level so that when all 3 lights are on, the sound level is about 4 times greater than the level needed to light one lamp. The sensitivity can be adjusted with the 500K pot so that one lamp comes on with a reference sound level. The other two lamps will then indicate about a 2X and 4X increase in volume. In operation, with no input, the DC voltage at pins 1,2 and 3 of the op-amp will be about 4 ...

Build a 10 LED Bar Dot VU meter circuit based LM3915 . It differs in many respects from other applications on the same chip. The circuit is intended for those who want a VU meter that is connected directly to the output of an power amplifier.  10 LED Bar Dot VU Meter Circuit based LM3915 Circuit Diagram It’s possible to adjust the sensitivity to work with amplifiers that have different output power, you just need to change the value of R1 according to Table 1. In case you did’n find the exact resistor value, then choose the next standard value (for example if you cannot find 33K ohm, then find the 36K ohm), or if you want maximum accuracy you need to put resistors in series or in parallel to achieve the correct value.   You can use various types of LEDs (round or square) to get the visual and aesthetic result you want. The switch S1 will allow you to choose whether VU meter will work as a bar or one by one (dot). In position ON [closed switch], the LED operation is Bar, while ...

This is the Simple LED Volt meter to Monitor the charge level in Lead Acid Battery or Tubular battery. The terminal voltage of the battery is indicated through a four level LED indicators. The nominal terminal voltage of a Lead Acid battery is 13.8 volts and that of a Tubular battery is 14.8 volts when fully charged. The LED voltmeter uses four Zener diodes to light the LEDs at the precise breakdown voltage of the Zener diodes. Usually the Zener diode requires 1.6 volts in excess than its prescribed value to reach the breakdown threshold level. When the battery holds 13.6 volts or more, all the Zener breakdown and all LEDs light up. When the battery is discharged below 10.6 volts, all the LEDs remain dark. So depending on the terminal voltage of the battery, LEDs light up one by one or turns off. LED Volt Meter Circuit Diagram      LED Volt Meter Circuit Diagram Author: D. Mohan Kumar Copyright: electroschematics.com

Volt meters & ampere meter with PIC can be used to measure voltage and current simultaneously. The series of volt meters & ampere meter with PIC16F876A PIC is used as a data processor voltage and current are measured.  This circuit uses the viewer in the form of 16 × 2 LCD used for the data display voltage and current measurements. In the article volt meter and ampere meter with PIC are discussed kerannya limited to devices only. More detail can be seen from the image sequence volt meter and ampere meter with PIC below.  The images of Volt Meter & Ampere Meter With PIC Circuit Volt meters & ampere meter with PIC