Decibel Level Detector
The objective for this project is to produce a decibel level detector with a range of 0-50 decibels. The main component of this project is the LM3915 integrated chip which drives a series of ten groups of LEDs with a range of 30 decibels with each step being three decibels.
The circuit consists of three basic parts with a simple omnidirectional electret microphone serving as the input. This is then passed through two amplifiers with the first amplifying the signal and the second serving as a rectifier driver. The Q2 transistor charges capacitor C8 and then discharges it across R13 to make a peak detector. The Q3 transistor changes the sensitivity of the LM3915 chip giving the system an extra 20db of range. The main component of the system is the LM3915 itself which controls the currents through the LEDs while also measuring the input voltage line SIG logarithmically with a range of 0-50db
After completing this project I have a fully functioning sound level reader with a range between 0-50db with steps of roughly 5db between each LED. I have learned more about audio projects through this project including the necessity of amplifiers. Overall I am happy with what I achieved with this project although if I could go back and change one thing I would have added an extra LM3915 chip to double my sound range as 0-50db is a little on the low end of the sound level scale.
Downloads
- Presentation (PDF)
- BOM (PDF)
- Schematic (PDF)