Grid Frequency Measurement

Posted on 2024-07-16 by Nigel VH

Some recent conversations with a friend regarding instability of the power grid, and particularly the issues they are facing regularly down in California, got me interested in setting up some logging of the local grid frequency.

Of course, there are wonderful resources already available, like FNET/GridEye at the University of Tennessee, but I tend to be inclined to want to make my own projects for the fun of it.

In contrast to many of my projects, which are cleanly built on custom circuit boards, this one is an example of classic throwing it together with the parts I had on-hand.

It’s an AC-AC wall wart transformer, feeding into a full bridge rectifier. Then it splits with a forward diode to a large capacitor and a 7805 linear regulator to power the ESP32 dev board. The second path goes to a basic op-amp zero-crossing detector.

The ESP32 timestamps the zero-crossing pulses, averages them over a few different time windows, and outputs frequency measurements. The measurements get uploaded over wifi to my central data-collection system and I generate graphs of the data.

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Pacific Northwest Aurora

Posted on 2024-05-11 by Nigel VH

With the anticipated Aurora being visible, I decided to head out to a dark area on Camano Island to try and get a better view. On initial arrival, I really couldn’t see much, but over the course of the evening, we ended up getting quite a good show. Here’s some photos I took just on my phone.

I also took the footage from a camera on one of HamWAN’s mountain-top radio sites, and made a timelapse of the evening. Some really incredible action about 2 minutes in.

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HP 3478A Repair

Posted on 2024-04-26 by Nigel VH

I’ll start with noting that these repairs on the HP 3478A (and many other older HP instruments) are well documented amongst the community. I mostly referenced the excellent write-up here by Tom.

I mostly followed the procedure described, I backed up the SRAM via querying the contents over GPIB, wired in a pair of AA batteries to keep the SRAM active, and replaced the lithium cell. After which, followed it up with replacing the old RIFA caps, which are infamous, and as expected, had cracked in my instrument.

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Switch / Router Learning Platform

Posted on 2024-03-19 by Nigel VH

I’ve been interested for a while in playing with ethernet switching on a hardware level, and decided to put together a platform to play with routing and switching hardware with a Raspberry Pi compute module, and an ‘off the shelf’ switching chip available commercially.

The switch chip I ended up choosing is the KSZ9477 from Microchip, with seven gigabit interfaces, including an SGMII interface for an SFP cage. While this device can’t hold a candle to the big-boy chips from Broadcom that a lot of the big network vendors use, I can’t source those, and the fundamentals should be reasonably accessible with the Microchip device.

The device is configured using Python scripts on the Pi talking SPI to the switch chip to configure ports, vlans, and read out things like the interface counters. The Pi can be configured with multiple VLAN interfaces to handle routing functions.

The hardware design files, and if I ever get around to it some of the software scripts, are available on GitHub.

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UPS Expansion Butchery

Posted on 2024-02-20 by Nigel VH

I picked up a used Emerson Liebert Vertiv GXT4 Double-Conversion UPS a little while back to better handle the dirty power coming from my portable generator, while feeding my server cabinet at the house. The internal batteries work fine, but I wanted to wire in some additional batteries for extra runtime before the generator would actually be needed. Unfortunately, it seems the external battery pack cable is exceedingly hard to find.

As my UPS is a 48V battery pack model, I believe the right cable for mine would be model number GXT3CABLE48V1, unfortunately, that proved to be effectively impossible to reasonably source. I did find some GXT3CABLE144V1 model cables that in the pictures looked essentially identical, so I took a gamble and ordered one.

I’ve found that the cables are effectively the same, but the plugs are keyed differently. So, all I needed to do was shave off the keying on the cable, and it worked fine in my UPS. Below is a photo of the shaved version above, and the stock version below. Hopefully someone else finds that helpful as well.

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