Every amateur in his home lab should have a device like an oscilloscope. It is required for the repair and commissioning of electronic circuits. In addition, the aforementioned device is indispensable in the study of new circuits and their properties. However, the cost of a digital or analog oscilloscope is quite high. You can try to find a used device, but not everyone can afford such devices. This article is about how to make an oscilloscope from a sound card. The price of such an alteration is insignificant, because the mentioned PC part is taken as the basis of the device. Special software is used to display the waveform.
Oscilloscope on a sound card: advantages and disadvantages
The advantages of this device include low cost, of course, except for the computer itself. Now about the shortcomings. We’ll make a reservation right away: there will be more of them than advantages. The main disadvantage that characterizes the oscilloscope from the sound card is its very high sensitivity. It even responds to radio interference, as a result of which the waveforms may have errors. The second drawback is the fact that the input interface of the sound card is able to withstand a signal amplitude not exceeding 2 V. This means that the card can easily fail. This disadvantage must be taken into account when manufacturing the adapter. The sound card oscilloscope is not able to measure a constant voltage.
How to make an adapter
First of all, it is necessary to take into account the input level of the sound card, most often it does not exceed two volts, and in some boards - no more than one volt. Naturally, such an amplitude will not be enough for measurements. This requires an adapter that allows you to increase the limits of the signal amplitude. The software — the oscilloscope — has two valid measurement levels: 12.5 V and 250 V. The circuit diagram of such a device contains only six elements - resistors. R1 and R2 have a nominal resistance of 1.5 MΩ, R3 and R4 - 75 kΩ, R5 and R6 - 1.5 kΩ. The dissipation power of the resistors should not be less than 0.5 watts. The circuit has 5 contacts at the input (two from the signal source 250 V, two from 12.5 V and the fifth common wire) and three outputs connected to the line input of the sound card (left and right channels and common).
We proceed to the description of the circuit diagram of the adapter. The first pair of inputs - “250 V signal source” - is connected to resistors R1 and R2, then to R3 and R4; to the output connector, respectively, the left and right channels of the line input. The second pair “12.5 V signal source” is connected “into the gap” between the resistors, that is, one output is between R1 and R3, and the second is between R2 and R4. And finally, the last, general output goes to the line- in connector of the sound card. It is connected to the right and left channels through resistors R5 and R6, connected after a pair of resistors R3 and R4. In order to reduce the influence of interference on the device, it is necessary to place the adapter board in a metal case. Here, in fact, is the entire oscilloscope. A sound card receives incoming signals, and the software displays waveforms on a computer monitor.
Program setting
To adjust the oscilloscope from the sound card, you need to go into the mixers of the personal computer and turn off the gain on the microphone, set the volume level below average. The resulting measuring device is able to quite clearly draw a low-frequency waveform , as well as determine the frequency of the signal.