Monthly Archives: June 2017

Oscilloscope options – standalone or PC based?

I started redecorating the lab, so the EEG project is now relegated to an Autumn/winter project 😉 Which is a shame as I’d got close to replicating the Mind Mirror system in Open EEG and getting a hardware gizmo set up using a PIC. The best laid plans of mice and men…

Just before I cleared it down I tested a device I’d been given by Jason Wildlife Gadgetman when he was clearing his lab out getting ready to move. The DrDAQ is a bare-board device made by Pico Technology. which shows a lot of promise for the openEEG testing.

DR Daq from Pico Technology

It’s basically a single channel digital oscilloscope, but it works with Picotech’s Picoscope software, which has all sorts of features that are new to me, like software RS232 decoding, click to set trigger levels, and long persistence simulation.

I have a decent Tek 2245A analogue scope, which computes frequency and voltage levels from cursors on the traces,

This is now very old , from 1989. It does most of what I want/need, and most of my design career I worked with analogue ‘scopes, with the logic analyser as a separate piece of gear. However, despite its measly 100kHz bandwidth the Pico did show me some of the attraction of a more modern approach. Every so often I’ve toyed with the idea of getting a Chinese scope, something like Rigol 2000 series or similar. So far I haven’t cracked. There’s a lot to be said for a standalone scope, but I wonder if the combination of my regular analogue bench scope together with a Pico will be even better.

EEVblog did take the piss out of the cheap Chinese DSOQuad FPGA scope, and I’d agree with him. I got one of these DSO Quads  to be able to print out slow captures like the one in this project, and it works well enough at that

but it would be a terrible thing to do to give this to a beginner. I could only make this thing trigger properly because I’ve used analogue scopes for years and had some feel for what should happen – all too often on the FPGA scope if the vertical trigger wasn’t in range you simply don’t get to see anything useful at all, so you can’t see which way to shift the trigger point. And the user interface is revolting. Too much clickety-click of two separate left-centre-push-right buttons for my liking.

Picoscope is far better thought out although it still suffers from the problems of not enough control of input sensitivity and offset as a regular bench scope. But it, and the associated DC coupled arbitrary waveform generator will be a great tool for testing the OpenEEG filters at sub-audio frequencies. And unlike the typical fly-by-night USB scopes, the software supports legacy models back to when Pico started, because that is of course always the problem with any hardware that depends on a piece of software running on some other device – it easily becomes orphaned before its service life is over. See pretty much any hardware made by Apple that is more than three or four years old 😉

The DrDAQ does pretty much all that I want for the EEG work, but the AWG doesn’t support frequency sweep mode which is a shame. I’d need to go for something like the 2206B at £250 to get that. In that case I’ll probably do it the old way and set up the AWG to output a single frequency and step through the frequency range. What isn’t clear is the frequency resolution of the AWG.