Synthetos

Headless VirtualBox

I’m currently laying out a DSP/FPGA board to interface to the MUSAMP board below for real-time signal processing. I’m laying out the schematics and PCB layout using gEDA (GPL Electronic Design Automation) tools. I originally started working on gEDA through a SuSE VirtualBox virtual machine on a Mac OSX host.

The Mac OSX host is on a Macbook Pro, which is naturally somewhat limited in resources compared to desktops. In addition, I tend to have my spec sheets open through spaces. Zooming in and out in gschem and flipping between spec sheets wasn’t as responsive as I hoped.

After some trouble migrating the VirtualBox ‘Appliance’ to my Windows 7 desktop (required an NTFS partition), I started using ‘Headless’ mode in VirtualBox. ‘Headless’ starts the virtual machine in the background, which can then be accessed using Windows’ RDP protocol (the standard windows remote desktop software).

A few things of note, Windows 7 uses port 3389 for remote desktop, which is the same as the default port in VirtualBox. Change the port, and make sure your firewall lets the chosen port (in TCP) through.

Execute in command prompt

%VirtualBox Installation%/VBoxHeadless –startvm “VirtualMachineNameHere” –vrdp=config

Choose a remote desktop client for your remote computer (TSclientX is the only Mac OSX client that worked with VirtualBox, CoRD worked only for getting to Windows 7).

If it works, make a shortcut to the above command with cmd.exe as a prefix.

 

EDIT #1: make sure to install VBoxGuestAdditions. You can then change the resolution from your RDP client by

$ sudo /opt/VBoxGuestAdditions-3.x.x/bin/VBoxControl guestproperty set /VirtualBox/GuestAdd/Vbgl/Video/SavedMode 848x480x32

MUSAMP

I was browsing G Randy Slone’s High-Power Audio Amplifier Construction Manual (great resource!) when I noticed he had some sample PCB layouts in the back of the book. Although he mentions that the layouts are dual sided, they’re really single sided, with components on the other side. The PCB layout sheets are a bit confusing because of this. He has a negative of the ‘top’, ‘bottom’ and combined top and bottom which is really the see through of the two layers.

I picked the ~250w amplifier for musical instruments (short circuit protection, etc) which is not the best performing of the bunch but is a good compromise between complexity and performance.

 

Armed with some copper clad and spray paint, I went over to the Synthetos Laboratory for some rapid prototyping of this 0.05% THD amplifier. Step one is to paint the copper clad with spray paint primer. Step two is to import the layout (scanned at 1200 dpi-native res for the lazor etcher), cleaned it up a bit in Photoshop then presented it as a print out to the Laser Etcher.

As you can see, the laser etcher prints on the copper clad by removing the spray paint primer, which exposes the copper. Next up, is the traditional Ferric Chloride solution which removes the copper from the clad material.

After etching, the exposed copper dissolves in to the Ferric Chloride solution (oxidation/reduction?) and what is left is the covered copper (with spray paint primer) and the see through clad material. At this step, I tried to use Paint thinner to remove the spray paint.

The sponge brush that I got from the paint section at Home Depot is a great tool. Along with a plastic/rubber paint tray, I was able to use only a small amount of Ferric Chloride to remove the copper. Basically I poured a small amount in to the plastic tray, and brushed the copper clad continuously until the copper came off in about 15 mins. No heating was required, and compared to the amount of Ferric Chloride saved (vs using complete submersion), this was well the effort.

Unfortunately, the paint thinner didn’t quite work, or maybe I didn’t rub it hard enough. I then used some nail polish remover (Fisher Scientific acetone passed away) and some #0000 steel wool to remove the paint. Below is whats left.

A nice feature of the laser etcher is that it works on so many different materials for just as many uses. Below is the ‘top’ side print of the components.

The beauty of this is that all of this was done, in one evening!

 

And now, I’m off for some classical music!! Ciao.

 

Hello World!

A small note of thanks for the generosity of the people of the Synthetos Lab, who welcome the mischevious among us, and aid us in realizing the power of E=mc^2.

 

 

Omer Osman
DSP/Analog ckts