If you think a portable oscilloscope is difficult to carry around, then we're in for a surprise. This oscilloscope, built by [Mark Omo], is only one square inch (6.4516 square centimeters) in size, with most of the space taken up by the OLED display.
It folds up so it's much easier for the user to hold, and of course it requires external inputs, so it's not exactly a standalone tool. The oscilloscope runs on a PIC32MZ EF processor, achieving 20Msps and 1MHz bandwidth.
For the analog front end, the signals first enter a 1M ohm terminal that divides the signals by 10x to measure them “off the rails”. They then pass through a “diode pair” connected to the “rails”, clamping the voltage to prevent damage. The divider concentrates the incoming AC signal around 1.65V, halfway between AGND and +3.3V. As a further safety feature, a large 909k Ohm resistor is placed between the signals and the diodes to prevent high voltage current from passing through and causing a problem in the system.
For the subsystem, a switch are used to provide a power bandwidth around the system response causing concerns. In particular, the resistance of the switch is non-negligible, possibly varying with voltage. Fortunately, the display used in the oscilloscope requires 12V, so supplying 12V to the mux results in a lower voltage and therefore a flatter response.
The ADC module, PIC32MZ1024EFH064, is a 12-bit sequential ADC approach. An advantage of the ADC is that the additional bits of analysis only take constant time, so speed and accuracy can be traded off. The conversion begins with a sample and hold sequence, using the stored voltage on the capacitor to calculate the voltage.
Multiple ADCs are used simultaneously with the sample, resulting in dispersion in the improvement of the sampling. Since there are 120 Megabits per second of data coming from the ADC module, the PIC32MZ's direct memory access (DMA) peripheral allows the data directly to the microcontroller's memory without processor involvement.
