A year ago, electrical engineer Mark Omo unveiled his 1 Square Inch 20Msps Oscilloscope designed around a PIC32MZ EF, which used its internal ADCs in an interleaved mode to gain that 20Msps. It even had an integrated 1-inch X 1-inch OLED screen for the readouts. Now he’s back once again with another oscilloscope project, the Probe-Scope, a self-contained 60MHz 250Msps oscilloscope and probe in cable form factor — meaning all the acquisition hardware is contained along the cable.
According to Omo, “The Probe-Scope grows as you grow, giving you as many channels as you have USB ports, the probe scope is almost infinitely expandable to tens (or more!) of channels.” The Probe-Scope was designed in three sections — the input divider and buffer, programmable-gain amplifier (PGA), and the acquisition hardware.
The input/divider buffer passes the signal through a fixed 30X divider, which is then buffered through an op-amp that gives it a ±15V range/±150V in x10 mode. From there, the signal is piped over to a differential op-amp configured to sum the signal with an offset signal produced by a DAC, which is then passed along to the gain settings of the PGA.
An ADRF6518 PGA boosts (or attenuates) the signal and adds a dash of anti-aliasing before handing it off to an Analog Devices’ AD9481 ADC where the signal is conditioned and further handed off to a MachXO2–4000 FPGA, where it’s stored into 128Mb of HyperRAM and set for one trigger. A PIC32MZ EF microcontroller (connected to the FPGA) reads it off the HyperRAM and shoots it over USB to a connected PC.
Omo has uploaded a detailed walkthrough of his Probe-Scope project for those interested. He’s hoping to keep the cost of his build at the $100 mark, making it a competitor against Rigol’s DS1054Z digital oscilloscope, which goes for around a much steeper $350.
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Author: Cabe Atwell