Difference between revisions of "Simple USB Oscilloscope"
From Francois Louw
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==A Simple USB Oscilloscope== | ==A Simple USB Oscilloscope== | ||
I have at many times wished that I had an oscilloscope. Given the prices, and shipping costs they are a bit too expensive for just hobbyist jobs. I have looked at USB oscilloscopes that are currently available, but starting at around $50 for one, that has a bit too high claims of sensing speed and accuracy, I realised that it will be a good weekend project to create one myself. | I have at many times wished that I had an oscilloscope. Given the prices, and shipping costs they are a bit too expensive for just hobbyist jobs. I have looked at USB oscilloscopes that are currently available, but starting at around $50 for one, that has a bit too high claims of sensing speed and accuracy, I realised that it will be a good weekend project to create one myself. | ||
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When running the Qt Interface application there are two calibration values. The first value is the offset, and the second is the full range divider. To calculate these values, connect the input signal to the ground wire and adjust Cal1 until the graph displays 0. Then connect the input signal to the 3.3V regulated voltage of the PIC. Adjust the Cal2 value unitl it shows 3.3V. '''Do not use the USB 5V as a reference. The USB voltage is 5.1-5.2V most of the time and not precise 5V.''' Remember this device uses 5% or 10% resistors, meaning that the calibration is not perfect. Some nonlinear effects may be observed. | When running the Qt Interface application there are two calibration values. The first value is the offset, and the second is the full range divider. To calculate these values, connect the input signal to the ground wire and adjust Cal1 until the graph displays 0. Then connect the input signal to the 3.3V regulated voltage of the PIC. Adjust the Cal2 value unitl it shows 3.3V. '''Do not use the USB 5V as a reference. The USB voltage is 5.1-5.2V most of the time and not precise 5V.''' Remember this device uses 5% or 10% resistors, meaning that the calibration is not perfect. Some nonlinear effects may be observed. | ||
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The Windows application sets up the display, and then generates a thread to read the USB. This separate thread is necessary because the QWT display routines are blocking and slow. Without the separate thread the USB reading is too slow. | The Windows application sets up the display, and then generates a thread to read the USB. This separate thread is necessary because the QWT display routines are blocking and slow. Without the separate thread the USB reading is too slow. | ||
