Universal Measurement Amplifier/Attenuator For laptop or PC
A computer is very suitable for making (audio) measurements thanks to the sound card that is usually built in. Unfortunately, the audio input on laptops is usually too sensitive to measure somewhat larger AC voltages. A small amplifier/attenuator circuit then comes in very handy.
By Michiel ter Burg (Netherlands)
If you build or repair audio equipment yourself, you don’t always need an oscilloscope. Any direct current or voltage can be measured with a multimeter. You can do a lot more if you happen to have a better model that can also measure (small) AC voltages. For more advanced measurements such as the frequency response or the
118
distortion it is very handy to use the soundcard in a computer combined with some software. A laptop or notebook can also function without an AC outlet, which means you’ll avoid earth loops and hum during measurements. However, a laptop often has just an oversensitive (microphone) input, so that you need to make a range of voltage dividers for your measurements.
This measurement amplifier has been designed especially for these situations. It has an adjustable input attenuation and an input impedance of 1 MΩ, so that standard scope probes with built-in attenuators can be used for even larger AC voltages. The input signal is first attenuated and then amplified to get the required
Elektor 7/8-2012