This is a repair of Bose L1 tower PA system. These skinny tower speakers are somewhat of a marvel because they are designed to stand behind the musician (aimed RIGHT AT the microphone) and don’t generate feedback. Ah, the miracles of DSP.
It turns out these PA’s have a frequent failure in their power supply. Read on for details.
I recently got a Tormach PCNC 770 CNC milling machine. So far, I’m very happy with it (but have not cut much yet). I figured that since I wouldn’t be using flood cooling, that I could get away without a full enclosure. But even with mist rather than flood, chips were shot everywhere, so I decided to roll my own enclosure using 80/20 parts https://www.8020.net/
This is a outstanding machine DRO for hobbyists, not just an outstanding DIY project, but a super DRO even compared to high-end pro setups. The beauty of TouchDRO is that it uses a (cheap) Android tablet for the display and control (I used a 1st-generation Nexus tablet – $50 on eBay) and then the scales connect to a small box that wirelessly sends data to the tablet via Bluetooth.
More info and pics to follow. Below are a schematic and a link to the TouchDRO website.
This particular circuit is designed for quadrature-output scales only. It will not work with the cheaper Chinese “caliper” or other similar scales. Examples of quadrature output scales are optical scales and some magnetic scales. In my particular case, I used magnetic read heads made by Renishaw and linear magnetic tape that I purchased used on eBay.
Below are links to Eagle files for the above circuit. Note that you can get an MSP430 Launchpad board for less than building the above board, but I wanted a specific size with particular connectors for my read heads, so I made my own board and got PCBs made at OSH Park.
This is bender specifically made to put a very tight radius bend in 5/32″ brass rod for banjo hooks. The original design was modified from this: http://www.micromark.com/universal-bender,8229.html but required a few revisions to get the desired result. Finally, when I was able to force the rod into a tight radius bend, some would crack. I learned that they needed to be heated with a torch before bending, but don’t have to be bent while hot.
The key difference between this and the little universal bender (besides less “slop” and tighter-tolerance fittings) is the movable round die is a “cam” that can be pivoted (with a 3/4″ wrench) and forced tightly against the stationary die while the bend is being made.
This was also my first exercise with hardening O1 tool steel. There are tons of guides on line covering this topic so I won’t go into detail here. Having the working surfaces hardened may not be necessary for bending brass but I wanted to play with O1 steel and this was pretty forgiving applications for a first try. It went quite well.
I found two heavily trashed Ainsworth antique balance scales at the flea market. $40 later, they followed me home. Between the two carcasses, I was able to get parts to assemble one complete unit.Continue reading →