I recently picked up an old HP 6632B power supply to add to my electronics bench. It’s overall a nice supply, and is capable of two-quadrant operation so it’s useful for discharge testing batteries as well.
Unfortunately, the unit I got didn’t have front binding posts, and dealing with the leads coming out of the back of the unit is more of a hassle for my use case. Luckily a friend pointed me to another electronics hobbyist’s blog post talking about adding binding posts to the front of his unit as well. He was also kind enough to share the schematic for the version of the interface board he designed.
He’s got much better pictures than I bothered to take, so go check his post out if this is a mod you end up wanting to do yourself. I’m real happy I did.
I keep my servers and networking gear in an enclosed, sound insulated rack in my garage. It keeps the noise down, makes it easy to duct the heat outside in the summer-time, and is a setup I’ve been quite happy with over the last number of years.
Unfortunately it seems the old sound foam has gotten to the point in its lifecycle where it starts falling apart if you look at it sideways, so it’s time for a refresh.
I found some inexpensive sound panels through the usual megastore, and after finishing clearing out the old foam, and giving up on getting all the old adhesive off, set to work cutting and fitting the new panels into place, and adhering them with double-sided foam tape.
Subjectively, they seem as quiet as before, but I don’t have any quantitative data. I think they look a lot nicer, and hopefully they hold up well for the next $X number of years.
After watching a recent Technology Connections video about Numitron tubes, I was inspired to pick some up to add to my dragon’s hoard of junk. A quick visit to eBay later, and a few less dollars in my bank account, and I had some new-old-stock tubes in hand.
At first I wasn’t sure what I wanted to use them for, so the obvious answer is a clock. I did decide, that if I was going to make *yet another* clock, it was going to be a very nice one.
Starting with the electronics, I put together a board using an ESP32, some shift registers and driver transistors, and a Real-Time Clock chip with battery backup to keep time even when the clock is unplugged.
A little bit of bad Arduino code later, and we have a functional clock, with 12/24hr modes, three brightness levels (done with PWM), and calibration methods so I can calibrate the cheap quartz crystal on the board against something better, like a GPSDO or my Rubidium standard. It won’t really be that accurate over the long term, but I can calibrate out enough error that you’ll never notice the clock being wrong before you have to re-set it again anyway next time daylight savings rolls around to give everyone the big middle finger.
Next was to figure out a case for it. Obviously 3D printing would be an option, I thought about laser cut acrylic as well, but I didn’t think it really made for a polished enough end product, and the overall look seemed off to me. So I get to pretend like I’m a woodworker, and ordered some small blocks of maple and redwood (from already fallen trees) from a specialty wood supplier.
And just like a TV cooking show, through the magic of a million hours of cutting, sanding, chiseling, gluing, finishing, and self-loathing that we’re not going to show you, it’s done!
I’m really happy with both of them. The redwood and the maple both have some really appealing characteristics. I ended up keeping the maple one for myself, and giving the redwood one to my dad for the holidays. He displays his with a quartz crystal he was also gifted this year.
A few years ago I posted about a homebrew box I made containing a cell modem, a GPS receiver, and a couple of Raspberry Pi SBCs to handle Out-of-Band access to my gear at the datacenter where I only have one transit connection, and provide Stratum 1 NTP for my gear.
I’ve recently been working on cleaning up/modernizing some of my infrastructure here at home as well, and decided to build another unit, tweaked to the needs here at the house.
I don’t have redundant power feeds here at the house, so there’s only one power connection, and I have a number of other GPS-fed devices, so I put in one of my GPS antenna distribution amps, which makes it very easy to feed multiple receivers from the same antenna.
A little cheap OLED for displaying stats, and shove it all into a spare 1U box I had sitting around, and we’ve got a nice compact little setup.
FlipDots are a very cool electromechanical display mechanism, and can offer significant power advantages, as they only consume power when changing state. These have been commonly used in roadside construction signs because they’re reliable, and can be easily powered from battery for an extended time next to the road.
I found a panel (which I believe came from a display on a transit bus) on eBay, for a reasonable price, and wasn’t immediately sure what project I wanted to use it for, but needed to grab it.
One disadvantage of these, is that they’re a bit more complex to drive electrically. To flip a dot, a couple millisecond pulse needs to be applied in either positive or negative polarity. Additionally, though short, we need to ensure the pulse can be of reasonably high current. This is much like driving a DC motor with an H-bridge driver, but we have hundreds of dots. Adding an H-bridge for every dot would be extremely impractical.
With the use of diodes, we can arrange the control lines into groups of rows and columns, so we reduce the need for drivers down to a driver for each row, and for each column. For the full panel this reduces the number from 294 drivers for each dot, to 35 to cover each row and column.
I found some high current shift registers, one part is a high current source and the other a sink, so they’ll need to work in pairs. However we need to ensure that both are never on at the same time or you’ll end up in a ‘shoot-through’ condition where one driver is just feeding straight into the other and deliver potentially damaging current. Using some NAND logic, we can ensure that the enable control lines on the shift registers are never on at the same time.
To test all this, I put together a small board to test a single row of dots.
After a successful test platform, it was time to work on building up the full control board. Using the same building blocks we tested, with the high current shift registers, and the NAND protection logic, we set up the row and column groups.
Finally, we can mount everything on a nice wooden base, and program up a classic nokia-style snake game. I might also work on adding game modes for Pong, or Breakout.
