Introduction: Flea-Scope™ USB Oscilloscope (18 Msps, $13 BoM, WebUSB)

About: I have a wife and 17yo daughter. I am grateful most of the time and Christian. I love anything outdoors or math/science related.

Flea-Scope™ is a very low-cost ($13 BoM in quantity) and easy-to-use 18 million sample-per-second (Msps) USB oscilloscope and mixed-signal logic analyzer with a built-in waveform generator, and so much more, based on the PIC32MK MCU! Flea-Scope can be controlled by any Chromium-based web browser that supports WebUSB API or Web Serial API running on a computer, tablet, or phone (!!!), with no need for further software install – just plug it in and open a web-page and you are up and running!

The Flea-Scope User's Guide (including some "how it works" internals) is here:

A preliminary video introduction is here.


Below is a bill of materials; alternately, you can get the bill of materials directly from using this link:

You can get all the parts from mouser, or you can get the MCUs a bit cheaper from Microchip Direct.

Step 1: Order the PCB

Below are all the files you will need to build the Flea-Scope printed circuit board (PCB). You can just upload a gerber zip file containing the below files to a place like and have them fabricate empty PCBs for you in a week or so.

Alternately, you can use my zip file from github here:

Step 2: Assemble the PCB

I usually build the boards with a solder paste stencil (also from using Chip Quik SMDLTLFP solder paste and a Kester 2331-ZX flux pen and Kester Pocket-Pak lead-free rosin-core solder for any rework; I clean boards after rework with isopropyl alcohol and a toothbrush followed by running water.

Below is an assembly drawing showing you where each component goes; the PCB silkscreen also locates each component value for easy hand-assembly (unlabeled caps are 0.1uF bypass). I find the PIC32MK MCU in its default QFN package (much!) easier to use than the QFP, but the board can also be modified in minutes to use a QFP instead of a QFN -- all traces are laid out for the larger part already.

I reflow my boards in a toaster oven that is controlled by another Flea-Scope (see link below -- I realize this is a chicken-and-egg problem -- you have to do the first board by hand -- just watch for the solder to melt).

Step 3: Solder the BNC Connector

The last assembly step, if desired, is to solder the BNC connector by hand on the board -- this is easier with a high-power soldering iron. I use an old Weller WES51 soldering iron.

Step 4: Program the MCU

"pic32.X.27.production.hex" contains the firmware to program the Flea-Scope PIC32MK MCU.  I use a Microchip PicKit 4 to program the MCU using the 6-pin ICSP header on the Flea-Scope board.

Step 5: Connect the PCB and Open the Graphical User Interface (GUI)

To use Flea-Scope, just connect it to a USB computer, tablet, or phone, and open the Flea-Scope GUI in Chrome or Edge and click "Connect".  (I Test on Windows, Mac, ChromeOS, and Android.)

The Flea-Scope GUI is here:

Step 6: See the User's Guide for More Info!

The Flea-Scope User's Guide (including some "how it works" internals) is here:

The github repository for the GUI is:

The github repository for the firmware is:

The instructions to build a Toaster Oven Temperature Profile Controller are here:

Step 7: Troubleshooting

If your assembled Flea-Scope does not work, typical troubleshooting includes:

  1. look for shorts/opens, especially on the QFN or QFP (shorts can be easily reworked with the Kester 2331-ZX flux pen; always clean and dry boards after rework; I use isopropyl alcohol and a toothbrush followed by running water)
  2. check power supply; measure 5V to ground, 3.3V to ground, -5V to ground
  3. check clocks; SY testpoint should be 117.2 kHz, UP testpoint should be 46.9 kHz
  4. check USB pull-ups; D- testpoint should be ~0V, D+ testpoint should be ~3V
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