Tuesday, 16 February 2016

Cables

Next task is to make up some XLR cables.  I found a few metres of Gotham GAC-3 in my junk store and so set about an evening of soldering up some test leads:


A quick test on the SystemOne showed them to be as good as the internal "GENMON" loopback test.

On a related note, by setting the analyser input filter to 22Hz-22kHz it reads down to 0.00034% THD+N.  Awesome!

--Neil

Wednesday, 20 January 2016

Done (Mostly)

So there is one wrinkle in my System One interface card: the auto-detect doesn't work for some reason.  I'm pretty sure the logic is all there, and I've tested it with QBasic test programs.  I can start the AP software (S1.EXE) from the command line and specify the interface card address with the /I option and then everything is fine.  So at this moment in time I don't fancy digging in deeper to fix this minor issue.  It doesn't stop me using this amazing machine.

A side note: after setting the SystemOne to internal loopback I measure the THD+N as 0.0014% on both channels.  That's a decent 8dB better than the 8903B (about 0.0035%).

--Neil

Monday, 18 January 2016

Analyze This!

It works!  The damn thing works!!

Well, okay, there were a few bugs in the Verilog, but checking out each block soon ironed out those.

Ta daaa.... Start up screen:
Eagle-eyed readers will note the flat grey cable poking out the case - that's the ISP download cable for the Lattice CPLD.

A quick graph showing that scans are working (needed the external interrupt line wired up properly - took an evening to fix that little bug):
Note that the performance at the moment (THD+N @ 0.0033%) is about on par with the 8903B it currently sits on top of:
But that's with a less-than-ideal coax cable - I can shift the TND+N over 0.01% just by handling the cable.  I think I really need to look into replacing those BNCs with proper Neutrik XLRs.

The PC that I am using is an Advantech industrial control PC in a small case.  It has a 486 processor running DOS 5.00.

For now, this is just what I need.  Perfick!

--Neil

Friday, 11 December 2015

Stuffing for Christmas

So, yesterday's post showed the bare PCB.  Today we have the stuffed board ready for bring-up:
During bring-up I'll be adding each IC in turn, making sure it is doing what it should be doing.  The last one with be the CPLD - you can see the in-circuit programming header top-left of the board (a couple of the pins are also used to set the board address).

I've also checked the board fits into the PC. The next version of the PCB will be gold-plated.

--Neil

Wednesday, 9 December 2015

New project just in time for Christmas

I've started work on the next project.  Well, "started" in this case means getting the first prototype PCB back from the fab:
Took a while to get everything to fit, and the release version will be a little bit simpler.  As to what it does....I'm sure there are some folks out there who will be able to work out what this is for!
--Neil

Thursday, 18 June 2015

Ring....ring......

Latest project on the bench coming along nicely.  Prototype built and tested just in time for this year's synth-diy meeting in Cambridge.
Ring modulators are fun!
 

Wednesday, 21 May 2014

LEVIN is on the bench!

Finally, after some time to get things just right, the next CESYG module is almost ready for release.  LEVIN is an LED Voltage Indicator with a seemingly simple function: show an input voltage on a large LED bargraph.  I think it does it rather well.  Here's the first completed module after testing:


Note that in the above picture it looks like several LEDs are on at the same time, when in fact that is simply due to the LEDs sweeping upwards while the camera was capturing the image.  To keep the current consumption under control the display is always in dot mode.

All that remains to do is finish writing the manual, get it printed and bound, and then package up the first batch of modules ready for shipping.

--Neil