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The headphone amplifier is based on National Semiconductor's LM4880 headphone amplifier chip. It reduces the size of the headphone amp used.
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Description:
This circuit uses a synthesized sound chip from Holtek, the HT-2811. This reproduces the sound of a "ding-dong" chiming doorbell. Additionally, the circuit includes a CMOS 4026 counter display driver IC to count your visitors.
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Description:
- Automatic switch on on rear gear
- Led-bargraph display
- Audible bleep on last led
- "Good old" design style, no microcontrollers!
This is an ultrasonic parking sonar based on an ultrasonic amplifier from an article seen on a 1982 magazine, it was once installed on the rear bumper of my Volvo Station Wagon. It served very well for many years. Connecting it to the reverse gear lights, it switches on automatically and shows you the distance to the nearest obstacle (according to his beam) on a led scale. When the last led lights, a buzzer is also activated telling you to stop immediately...
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Description:
One LED Indicates 50dB,70dB and 85dB. Useful to detect too noisy environments
This circuit is intended to signal, through a flashing LED, the exceeding of a fixed threshold in room noise, chosen from three fixed levels, namely 50, 70 & 85 dB. Two Op-amps provide the necessary circuit gain for sounds picked-up by a miniature electret microphone to drive a LED. With SW1 in the first position the circuit is off. Second, third and fourth positions power the circuit and set the input sensitivity threshold to 85, 70 & 50 dB respectively...
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