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2018 July 9

Analog Discovery breadboard adapter

Filed under: Circuits course,Data acquisition — gasstationwithoutpumps @ 11:16
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As I mentioned in Analog Discovery Impedance Analyzer, I recently bought two new attachments for my Analog Discovery 2.  I reviewed the Impedance Analyzer in the earlier post, so in this one I’ll review the breadboard breakout.

The breadboard breakout provides a simple way to attach the Analog Discovery 2 to a breadboard, without using the female headers that come with the device.

Here is the breadboard adapter, plugged into the end of a breadboard.

The Analog Discovery 2 can plug into the breadboard vertically, which is compact, but requires disassembly to put the test setup back in its box for carrying.  Here it is shown plugged into the last 15 rows of the breadboard, but I had to move it in two rows to keep the weight of the AD2 from tipping the breadboard.

I tried doing a little work with the breadboard adapter and found it to be a mixed blessing. I used it for testing a circuit where I needed both oscilloscope channels, one power supply, and one waveform generator, which would normally use 7 of the 30 wires on the AD2.  Some of the wires (the power, ground, and oscilloscope 1- and 2- wires) could be quite short, as they connected to the power busses on the breadboard, but the other wires had to be fairly long, as they had to skip past all the trigger and logic-analyzer inputs that I wasn’t using.  I could have plugged the adapter into the breadboard the other way around, but then the AD2 itself would interfere with convenient wiring.  It would have been nice to have the most frequently used connections at the tip of the adapter, instead of the base of the adapter.

For a fixed setup, where the oscilloscope channels are always looking at the same signals, the breadboard adapter is more convenient that the standard flywire connections, which have a tendency to slip off the double-ended male headers that I use for connecting them to the breadboard.  The female headers of the flywires are not designed for many cycles of attaching and detaching, and end up getting too loose after a while.

But for debugging, when the oscilloscope channels have to be moved rapidly from node to node, the breadboard adapter is less convenient than having the separate flywires—unless much longer wires are used (with the attendant problems of extra inductance and capacitive pickup of 60Hz interference). Losing 17 rows of the breadboard to the adapter is also a problem, as it leaves only 47 rows of a standard 64-row breadboard, or 15 rows of half-length breadboard for building the test circuit.

I think that I will use the adapter for lecture demos, where I have fixed wiring to carry around, as I can spend less time setting up the demo just before class, at the cost of slightly more time the night before. My standard lecture setup will use a full-length breadboard with the adapter in one end and a Teensy LC in the other end (for PteroDAQ demos) using up 31 of the 64 rows, leaving me with the equivalent of about a half-length breadboard in the center for the circuitry being demonstrated.

I don’t know yet whether I’ll find the adapter useful for regular debugging—probably not much.

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2018 June 27

Three boxes this morning!

Filed under: Uncategorized — gasstationwithoutpumps @ 21:30
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I got three boxes this morning: two via FedEx and one via an unmarked van.

One of the FedEd boxes was from Digilent—I ordered the new Impedance Analyzer attachment for the Analog Discovery 2.  I plan to check it out later this week with some precision resistors.  The design looks a little strange to me (using latching relays with 100mΩ contact resistance rather than lower impedance FETs), and there is no mention of using precision resistors for the reference impedances, so I suspect that it is not quite as good as it should be.  I also ordered the Breadboard Breakout for the Analog Discovery 2, as the female headers on the flywires that it comes with are getting a little loose.  I’ll probably test that out in the next week or two also.

Another FedEx box was from eBay for a new toaster oven (the Breville BOV845SS).  Our old one still works, but the buttons on it are getting a bit unreliable, and I was unable to take the box apart to clean the contacts (one of the screws I needed to remove had its head stripped without my being able to get it out).  The new one does a better job of producing uniform toast, so I like it better already. (I had toast for lunch today, so that I could test the toaster oven.)

The third box was the most fun: a Monoprice Delta Mini 3D printer. I spent a chunk of the day trying to get it to work. The gcode file included on the micro SD card printed ok for about 20 minutes, then retracted the filament a long way and continued “printing” without laying down any more plastic. I tried it twice and it failed at about the same point each time, so I suspect a corrupted gcode file, but I don’t currently have any way to read the micro SD card to see. (I have an SD reader, but it is old enough that it doesn’t include a micro SD slot.)

I then downloaded Cura and Printrun-Mac-18Nov2017 to try driving the printer directly from my Macintosh. I downloaded the Make Magazine test files from Thingiverse and Cura profiles from https://www.mpminidelta.com/slicers/cura.  The profile files on that wiki only work with Cura 3.2 and 3.2.1, so I had to download version 3.2.1 of Cura also.

I had no problem getting Cura to load and slice the stl files, but I could not get my Mac to talk to the printer (it saw the USB device  as

Malyan 3D Printer:

Product ID: 0x0300
Vendor ID: 0x2e26
Version: 2.00
Speed: Up to 12 Mb/sec
Manufacturer: Malyan System

but did not create a serial port for it).

Several online sources also concluded that Mac OS X cannot talk to the printer via USB. This is generally believed to be a firmware bug in the printer.  The printer is running version 44.160.3 of the firmware, which seems to be a very recent version, so Malyan System has not fixed the USB bug yet.

I have one very low-speed HP laptop that runs Windows (which we refer to as the “Barbie” laptop, because of its bright color and toy-like capabilities), which was originally purchased (used @ $75) for testing PteroDAQ on Windows.

The Barbie laptop had no trouble talking with the printer using Printrun, and I tried printing the Make magazine 4_DimmensionalAccuracy.stl file (note: the double “m” in “dimension” is Make’s spelling error, not mine).  Cura estimated a 45-minute print time, but Printrun estimated 67 minutes, which was fairly accurate—there must be some speed setting in Cura that is wrong about what full speed is for the printer.

Make’s preview of 4_DimmensionalAccuracy (from their Thingiverse folder).

The MDM_4_DimmensionalAccuracy.gcode file printed ok, but I had trouble getting it off the build plate. A wrench to twist it off worked best (after putting a small gouge in the plate trying a technique with a screwdriver and mallet). The nominal 20mm dimension of the object turned out to be 19.35mm, which is rather smaller than desirable. The layers were 24.35 by 24.30mm, 19.35×19.35mm, 14.50×14.55mm, 9.70×9.75mm, which is fairly consistently 3% smaller than they are supposed to be.

Make’s 2_XY-test preview file, from their Thingiverse folder.

My second test was with Make’s 2_XY-test.stl file, which I sliced with 0.2mm layers, 10% infill, and a Cura-generated raft (“build plate adhesion” checkbox). The raft did seem to make popping the print off the build plate easy (though not having much area in contact with the plate probably helped also).  Removing the raft did delaminate a little of the bottom layer in one place.  The texture of the vertical walls changes rather abruptly each time there is a hole in one wall, probably due to a change in the way the head moves when a continuous circuit is possible and when it has to either reverse or skip the hole. (Sorry, no photos—it is now too dark out for natural-light photos, and I’ve never had much luck with flash on macrophotography.)

I’m now convinced that I can get the printer to work, so I need to pick a tool for building models in STL format and pick some project(s) to work on.  My son thinks that I should use OpenSCAD, which is a “programmer’s CAD tool”, providing easy ways to create shapes using programming language and view the results, but not edit them interactively.  Given how very frustrating I found the SolidWorks GUI last fall, I think he may be right—I’ll look into OpenSCAD.

One of the first things I’ll print, though, is a design by someone else—extension legs to raise the printer and improve the air flow underneath.  Lengthening the legs by just 1cm will greatly reduce the noise the printer makes.

2016 August 5

Digilent Analog Discovery 2 USB Oscilloscope

Filed under: Circuits course — gasstationwithoutpumps @ 14:12
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I have recently learned about a new USB oscilloscope, Digilent’s Analog Discovery 2, which seems to be a step up from the BitScope BS10 USB oscilloscope that I currently own. Digilent’s offering has differential inputs, 14-bit ADC (instead of 8), 100MS/s (instead of 40MS/s), and much nicer-looking user interfaces (no more black background!).  It costs a little more ($279 vs. $245, both costing more to get BNC connectors for higher-speed oscilloscope probes), but Digilent has an academic program that reduces the cost to only $179, so that even with an extra $20 for the BNC adapter and $20 for scope probes, the price is still lower than the BitScope.

I’m considering getting the Analog Discovery 2 scope (if I qualify for the academic discount), but I’ll probably wait until I replace my laptop.  The free Waveforms 2015 software runs on a wide range of Windows versions, but only 10.9 or newer on Mac OS.  (It also runs under some versions of Linux).  I’m still running Mac OS 10.6.8 on my laptop, and I don’t want to “upgrade” to a newer OS on the old hardware—I’m planning to replace the laptop this year, but I’m waiting to see whether Apple comes out with a usable MacBook Pro in 2016, or whether they’ve gone all in for connector-less laptops, in which case I’ll probably have to switch to a cheaper, but clunkier Linux laptop.

One of the things I like about Digilent’s marketing is that they have a very thorough reference manual online, which goes through the design of the hardware, explaining the schematics and some of the design choices for what chips they used. The online reference manual for Waveforms 2015 seems decent, but not as thorough as the hardware manual.

I’m curious whether any of my readers have tried the Digilent USB oscilloscopes.

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