SampleScope

A cheap, simple, and fun-to-build diy USB oscilloscope

Schematics based on http://jonw0224.tripod.com/ppmscope.html

• USB oscilloscope
• two channels
• almost all parts can be sampled directly from the manufacturer
• almost no parts needed anyhow, some capacitors and resistors
• pcb is really simple an can be done on perfboard
• input range +- 12V
• bandwidth about 200kHz, 1MSPS
• 1024 samples

Hardware

• PIC18F4455

• USB 2.0 Full Speed HID device

• simple analog part

• input limiting & buffering

• optional DC removal

• programmable gain amplifier (0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10 V/div)

• level shifter

• ADC

• no anti aliasing filter

• trigger system

• can trigger on both channel 1, channel 2, or free running

• can trigger on rising or falling edge

• time bases 'fastest' (~17u), 100u, 300u, 1m, 3m, 10m, 30m, 100m sec/div

• input selection

• sample single channel, two channel interleaved or two channel sequential

• uses dc-dc converter (xp power IQ0515) to supply analog circuitry

• everything is powered from USB - no external supply required

• IC List

• all parts can be sampled, at least as a student.

• MAX114 as ADC

• MAX532 as DAC: programmable gain amplifier and trigger voltage generation

• MAX942 as trigger comparator

• MAX4622 as AC/DC selector

• MAX6225, MAX6241, MAX6250 as voltage references

• TLE2082 as Op Amp

• PIC18F4455 as brain

• PCB

• as simple as it gets

• analog parts are simple to wire

• digital connections are "flying wires", verowire

Firmware

Very simple firmware based on the Microchip Application Library USB example, most parts written in C, sampling routines written in ASM.

Frontend

PC software written in C++ / Qt. OS independence by using libHIDAPI.

• Hardware emulation

• Plots

• Normal

• XY plot

• FFT

• autocorrelation

• Measurements

• frequency

• RMS and average voltage

• software emulation mode

• emulates hardware, allows testing without the actual device

• development

• uses HIDAPI https://github.com/signal11/hidapi

• libqt4

• libfftw3

• libqwt6

• libusb-1.0

To do

• build better PGA (the current one is the main bottleneck in bandwidth)
• put more effort into PCB layout
• i fixed some errors "on-line" without rerouting the pcb
• find cheaper DC-DC converter
• put some effort into graphical frontend
• more measurements
• more switches and customization
• clean calibration ui, calibration wizards
• cleanup code a little bit, get build environment better (link with HIDAPI)
• platform independence (HIDAPI, libusb)
• anti aliasing filter (!!!)

Probably I won't do any of those items. ;)

License

SampleScope
Copyright (C) 2012 mru

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.