CRT Clock Build

While it’s not particularly new or novel, I’ve long been interested in setting up an Oscilloscope Clock with one of the various kits that have been available for some time. Over the holidays one of the gifts from my family was based on this, and encouraged me to go further to build a clock around a raw CRT tube, rather than just something that interfaces with an existing oscilloscope.

Soon enough I had found a real gem of a tube with a helical PDA, which I thought was just gorgeous.

The tube is a 3BFP1, which is a 3 inch, flat face, with a standard green phosphor like you’d see on an oscilloscope.

Next I needed a setup to drive the tube, which needs a number of various high voltage sources to drive it. I didn’t particularly feel like jumping into designing those circuits myself at the moment, so I found a kit from a fellow in the UK which handled the various power supply needs, and included a very smooth clock display board as well at

Soon enough the kit was in hand, and thus began a few evenings of soldering the kit together.

At this point I’ve got power to the tube, and first light. It’s still not well focused, but good progress. Next I move onto building the clock and signal amplifier boards, which will let me actually try displaying something on the tube.

Finally some more work on getting the voltages tweaked to improve brightness and focus, and I had a display I was happy with.

Not perfect, but there may also still be a little room for improvement when it all gets built into an enclosure when I add magnetic shielding. Next I started working on a prototype layout for all the components before I commit to things.

This is how it stands today. I think I’m happy with this layout, so now as I have the time, I’ll make a base out of some wood that’s a bit nicer than plywood, and work on an acrylic enclosure to keep fingers out of the high voltage bits, but still allow the tube to be on display.

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Black Rock 2018

After having to cancel the trip last year due to poor weather conditions, we were able to make the trip down again this year to the Black Rock desert in the northwest corner of Nevada.

We had a bit of a smaller group than usual due to having to schedule the trip later than typical, but still a number of good launches, as well as an afternoon visit up to the Soldier Meadows hot springs north of the playa.

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Cellular Webcam

A bit ago I posted about setting up an RPi with cellular connectivity which could be used for any number of ideas. One I mentioned was a remote webcam.

I took the basic setup I had shown before, and attached a small solar panel, sealed it in a watertight enclosure, and placed it on some national forest land adjoining a nearby mountain pass.

I used a small arduino board and a mosfet to control power to the RPi. It woke up once an hour to take a photo and upload some telemetry and a thumbnail to my server over the cell connection. If there was a thumbnail I wanted a better look at, or to establish a ssh connection for admin, there were command files I could leave in place on the server that would instruct the RPi to perform additional actions before going back to sleep.

Every so often as the SD card got full, I would drive up and park nearby, and download the full size files over wifi connected directly to the RPi.

Unfortunately, in summer the unit stopped responding and had to be retrieved. Once I was able to get it home and look at it, I found the RPi’s SD card had died, so it couldn’t boot up to do anything. I’m usually careful to buy quality name brand SD cards, but it appears this time one slipped through and lead to the failure.

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New RNG Revision

Speaking with a few folks I chat with regularly there ended up being some renewed demand for the Random Number Generator USB Sticks I had made a few years ago.

I didn’t have any of the original ones remaining, so I did a minor board revision to make them a little bit easier to assemble.

Once the new boards were assembled, I grabbed a bunch of them to start gathering data to test the quality, and tune the stick firmware, as well as the daemon software to get the fastest speed, and the best whitening possible.

It was nice to revisit this older project and give it some new life, as well as get a nice handful of them out to other folks who can get good use out of them. As always you can get a taste of their entropy for yourself via my Entropy Service.

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Cellular IoT Connectivity

With the recent interest in “Internet of Things” devices, most of the major cellular carriers have started offering very affordable plans targeted at this market.

  • AT&T is offering prepaid data, and $1/month/sim card at
  • T-Mobile is offering unlimited data (speed restricted) with a minimum of 2 SIMs at $5/month each, plus $25/yr for the plan. Assuming you can even get started. Unlike AT&T, they require you to speak with a sales rep, and I haven’t been able to get them to respond to me more than once. A friend has had a similar experience trying to get started.
  • Verizon seems to be the laggard of the bunch, with very expensive plans. Their model may work alright if you had a large number of devices to use on the pool, but for one or two, the price difference is massive.

I was interested in setting up a Raspberry Pi with some cellular connectivity for use in a number of potential projects. Some quick ideas might be:

  • An OOB (Out Of Band) connection to your servers if your main internet link dies, you can still manage them.
  • A portable iGate for mobile packet operations. This could be useful for example with the high altitude balloon flights I participate in, to have a ground station set up with connectivity.
  • Add a solar panel, some power management, and a camera for a wilderness webcam. Find a forest/mountain/beach/whatever with a bit of cell service, and set up a webcam.

I was looking around at various options for the modem itself, and happened upon a module set up for use with embedded systems from Adafruit ( and decided to give it a try paired with a Raspberry Pi Zero W.

This module, which supports 3G and 2G networks, I decided to pair with AT&T’s IoT plans, one because AT&T has a 3G network whereas T-Mobile’s network is 2G, and because I couldn’t get T-Mobile’s sales staff to respond in a timely manner.

The setup is pretty straightforward, and Adafruit has put together a nice tutorial on how to hook up the module to the Raspberry Pi’s GPIO pins.

Note that their tutorial is based around their older modules that don’t support 3G connectivity, so they make some warnings about carrier selection, but if you chose the 3G capable module I listed above, the instructions are just the same. You’ll wire the module to the Pi’s serial GPIO pins, ground, and 3.3V power to set the voltage levels.

At this point, it’s just configuring the software as described in the tutorial. I’ll add a note of caution here, the serial device naming scheme on the Pis has changed in the Pi3 and PiZero families versus the older Pis. On the newer Pis, /dev/ttyAMA0 is not the hardware UART by default, and instead you should be using /dev/serial0. So in the PPP peers file you create, make sure to update it appropriately for the right serial device.

Add a little script to startup a reverse SSH tunnel to a device you control when the Pi boots up, and now you’ve got a device you can drop anywhere with cell service, and remotely manage it.

Here’s a quick shot of my setup in development. Bottom row from left to right is some batteries, the FONA cell module, a Arduino Pro Mini, and a small boost regulator to power the Pi. The top row is the Pi Zero W with attached camera, and a proto board to control power on/off to the Pi and handle voltage translation between the Pi and the Arduino Pro Mini.

The arduino controls power to the Pi, so we can shut down the pi and the cell module for a very low draw sleep, wake up occasionally to take a picture or perform some other task, then go back to sleep again. I plan to add some solar charging to the current setup, and it should be about done at that point.

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