The Monostable 555 Timer

The operation and output of the 555 Monostable is exactly the same as that for the transistorised one we look at previously in the Monostable Multivibrators tutorial. The difference this time is that the two transistors have been replaced by the 555 timer device. Consider the 555 Monostable circuit below.

LM3915/LM3916 VU Meter

Features

Fast responding electronic VU meter

Drivers LEDs, LCDs, or vacuum fluorescents

Bar or dot display mode externally selectable by user

Expandable to displays of 70 dB

Internal voltage reference from 1.2V to 12V

Operates with single supply of 3V to 25V

Inputs operate down to ground

Output current programmable from 1 mA to 30 mA

Input withstands ±35V without damage or false outputs

Outputs are current regulated, open collectors

Directly drives TTL or CMOS

The internal 10-step divider is floating and can be referenced to a wide range of voltages The LM3916 is rated for operation from 0°C to +70°C. The LM3916N-1 is available in an 18-lead molded DIP package.

Description
The LM3916 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs, LCDs or vacuum fluorescent displays, providing an electronic version of the popular VU meter. One pin changes the display from a bar graph to a moving dot display. LED current drive is regulated and programmable, eliminating the need for current limiting resistors. The whole display system can operate from a single supply as low as 3V or as high as 25V.
The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further, it needs no protection against inputs of ±35V. The input buffer drives 10 individual comparators referenced to the precision divider. Accuracy is typically better than 0.2 dB.
Audio applications include average or peak level indicators, and power meters. Replacing conventional meters with an LED bar graph results in a faster responding, more rugged display with high visibility that retains the ease of interpretation of an analog display.
The LM3916 is extremely easy to apply. A 1.2V full-scale meter requires only one resistor in addition to the ten LEDs. One more resistor programs the full-scale anywhere from 1.2V to 12V independent of supply voltage. LED brightness is easily controlled with a single pot.

Stereo FM/AM Receiver CXA1538

Description Of Stereo FM/AM Receiver CXA1538

The CXA1538M/N/S is high performance one-chip bipolar ICs designed for FM stereo/AM radios. These include an FM/AM front end, FM/AM IF amplifier, FM/AM detection output and FM stereo demodulator output. Pin 4 is the stereo indicator and VCO check pin. Therefore, in stereo mode (when stereo indicator drive Tr Q2 is switched on), pin 4 voltage lowers down, Q1 is cut off and VCO oscillation waveform can not be seen. In AM mode as well, the oscillation waveform can not be seen as VCO turns off. 


Adjust the free run frequency at 76 kHz ±50 Hz. This IC has a built-in auto blend circuit and a MONO switch is not required as a rule. This circuit controls the separation in proportion to the signal level and reduces noise automatically for stereo reception below the mid electric field when the electric field strength reaches lower than about 40 dBμ. When the electric field strength turns below 10 to 15 dBμ, MONO operation is automatically activated. To switch MONO mode on externally, ground pin 3 with 33 Kohm. This IC has a built-in soft muting circuit. As shown in the following I/O characteristics diagram, 23 dB (Typ.) muting is applied and noise level reduced during weak electric field and out of tune instances.

Features Of Stereo FM/AM Receiver CXA1538

• Low current consumption (In FM mode ID=11.0 mA, in AM mode 8.5 mA, VCC=6.0 V)
• Built-in LED drive circuit for tuning
• Built-in LED drive circuit for stereo indicator
• Built-in muting circuit for the FM band
• Few external parts