A Programmable Current Source

The usual engineering minutia takes up much of my week… Paperwork, documentation, purchase orders, meetings, etc. There are the occasional chances to just have a little electronic fun. Thus I greeted a request from a couple of our support astronomers with some enthusiasm. They needed a variable intensity light source for calibration of the OSIRIS spectrograph. This source sits inside an integrating sphere on the AO bench along with four spectral sources, small tubes of neon, argon, xenon and krypton.

One Amp Current Controller
The remote current controller PCB and case prior to final assembly
There was already a white light source in the calibration sphere, but control was limited to simply on or off. The spectrograph uses various filters that each let through differing amounts of light from the calibration source. This created problems during calibration, some sort of variable intensity source was needed. It also needed to be quite precise, with a well regulated output that would not vary during the hours a calibration script could run.

I set aside a bit of time each day to design and build the source. The last couple hours of the afternoon are best, at this point I have had quite enough paperwork. A chance to practice my trade sketching out the circuit, or simply sitting at the bench and soldering… Perfect.

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A Dive That Went Wrong

Five days, a quick island hop to Oahu, our first time exploring the island. A major feature of the plan was a bit of diving. Oahu features a number of unique dives we can not experience on the Big Island, particularly the wrecks. Based on conversations on ScubaBoard I chose to book with Gabe and Kaimana Divers. The reviews and comments of this dive op have been uniformly positive. After some experience I can second that opinion.

Along with a few changes of clothes and the cameras, we packed two full sets of dive gear. There would be five full days, including two days of diving. The basic plan each day was a two tank morning dive trip, a deeper wreck dive, followed by a shallower reef dive. The YO-257, the Corsair, there are several sites to choose from. On the Big Island we do have the SS Kauai at Mahukona, but scattered bits and pieces are not the same as a large intact ship.

Walking across the posh lobby of a luxury hotel with full dive gear over your shoulder is fun. Everyone looks in your direction, you can only guess at what they are thinking. It was 7am, meeting our ride to the marina. We were looking for our ride from Kaimana Divers in a big black pickup truck. Already in the truck were a couple from Texas and another fellow, five divers total, a nice small group.

We met Drew, our divemaster for the day. Like all divers we introduced ourselves, Jeannie and Charles lived near the gulf coast, but traveled regularly to dive under better conditions than local waters offered. Our fifth diver was somewhat less experienced, with a dozen dives behind him. We were all looking forward to this dive.

Surf to Diamond Head
Surf and Surfers along the famous Waikiki breaks with Diamond Head in the background
Heading of of the marina we saw the first sign that perhaps not all was well… The surfers were out.

Dramatic breakers rolled across the famous Waikiki reefs, stretching from the marina to Diamond Head. There is an adage in the local dive community, if the surfers are happy, the divers are not.

Arriving over the wreck for the YO-257 there was a notable swell, while it was going to be a problem, it was diveable. Drew hopped in to secure the mooring line. Upon returning to the boat he reported a moderate current. We geared up and readied for the water.

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