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This nifty sound level meter is a perfect one chip replacement for the standard analog meters. It is completely solid state and will never wear out. The whole circuit is based on the LM3915 audio level IC and uses only a few external components. This circuit can also be integrated into audio amp projects.  Circuit Schematic Part Total Qty. Description Substitutions C1 1 2.2uF 25V Electrolytic Capacitor C2, C3 1 0.1uF Ceramic Disc Capacitor R1, R3 2 1K 1/4W Resistor R2 1 10K 1/4W Resistor R4 1 100K 1/4W Resistor R5 1 1M 1/4W Resistor D1 1 1N914 Silicon Diode Q1 1 2N3906 PNP Transistor LED1-LED10 10 Standard LED or LED Array U1 1 LM3915 Audio Level IC MISC 1 Board, Wire, Socket For U1 Notes V+ can be anywhere from 3V to 20V. The input is designed for standard audio line voltage (1V P-P) and has a maximum input voltage of 1.3V. Pin 9 can be disconnected from +V to make the circuit use a moving dot display instead of a bar graph display. Thanks to help from the forum, this circuit has ...

The main source of power in a telecommunications system is -48 V. This source’s negative polarity and its large magnitude with respect to ground pose a challenge when designers want to use low-power ICs in the telecom system’s application circuits. Fortunately, the emergence of high-voltage ICs with operating voltages of 75 V and higher has enabled the use of simple biasing techniques in designing circuits for -48-V systems. The technique described here provides a dimming control for an LED. The circuit uses a 65-V hysteretically controlled LED driver (MAX16822A) with its ground pin connected to -48 V and its power input connected to the system ground (Fig. 1). For proper dimming, therefore, the circuit’s logic-level control signal (at Control) must be level-shifted down to –48 V and applied to the DIM input. The high-voltage pnp transistor (CMPT5551) (80 V/500 mA) enables a simple solution to that problem. Logic-Level Signals Dim -48V LED Driver Circuit Diagram The transistor circuit ...

Battery Level Monitor Circuit This simple circuit can monitor the charging process in 12 Volt Lead Acid battery or Tubular battery. The status of LED indicates whether the battery is accepting charge or not. It also indicates the full charge condition. Battery Level Monitor Circuit Diagram The circuit can be incorporated in any battery charger like 6 volt, 9 volt, 12 volt etc. The only change needed is replacement of the Zener ZD with appropriate value. That is for 6 volt charger , use 6.1 volt Zener and for 9 volt charger it should be 9.1 volt Zener. The circuit is based on the switching of two NPN transistors (BC547) to drive the corresponding LED. Zener diode ZD is connected to the base of T1 so as to switch on T1 when the Zener conducts. This happens only when the battery voltage is above 12 volts. Green LED lights when the battery voltage is normal or battery attains full charge. Resistor R1 and Preset VR adjust the base bias of T1 for smooth switching. When T1 conducts, base of T...

This circuit will emit an intermittent beep (or will flash a LED) when the water contained into a recipient has reached the desired level. It should be mounted on top of the recipient (e.g. a plastic tank) by means of two crocodile clips, acting also as probes. If a deeper sensing level is needed, the clips can be extended by means of two pieces of stiff wire (see pictures). Circuit operation: IC1, a 555 CMos timer chip, is wired as an astable multivibrator whose operating frequency is set by C1, R1 and R2, plus the resistance presented by water across the probes. If the resistance across the probes is zero (i.e. probes shorted), the output frequency will be about 3Hz and the sounder will beep (or the LED will flash) about three times per second. As water usually presents a certain amount of resistance, the actual oscillation frequency will be lower: less than one beep/flash per second. As probes will be increasingly immersed in water, the resistance across them will decrease and the o...

This is a simple project of Logic-Level Signals Dim -48V LED Driver Circuit Diagram. The main source of power in a telecommunications system is -48 V. This source’s negative polarity and its large magnitude with respect to ground pose a challenge when designers want to use low-power ICs in the telecom system’s application circuits. Fortunately, the emergence of high-voltage ICs with operating voltages of 75 V and higher has enabled the use of simple biasing techniques in designing circuits for -48-V systems. The technique described here provides a dimming control for an LED. The circuit uses a 65-V hysteretically controlled LED driver (MAX16822A) with its ground pin connected to -48 V and its power input connected to the system ground (Fig. 1). For proper dimming, therefore, the circuit’s logic-level control signal (at Control) must be level-shifted down to –48 V and applied to the DIM input. The high-voltage pnp transistor (CMPT5551) (80 V/500 mA) enables a simple solution to that pro...