Hackaday Prize Entry: A Better DIY CT Scanner

If you’re entering something in The Hackaday Prize this year, [Peter Jansen] is a guy you need to watch out for. Last year, he won 4th place with the Open Source Science Tricorder, and this year he’s entering a homebrew MRI machine. Both are incredible examples of what can be built with just enough tools to fit on a workbench, but even these builds don’t cover everything [Peter] has built. A few years ago, [Peter] built a desktop CT scanner. The CT scanner worked, but not very well; the machine takes nine hours to acquire a single slice of a bell pepper. At that rate, any vegetable or fruit would begin to decompose before a full scan could be completed.

This didn’t stop a deluge of emails from radiology professors and biomedical folk from hitting [Peter]’s inbox. There are a lot of people who are waiting for back alley CT scans, but the CT scanner, right now, just isn’t up to the task. The solution is iteration, and in the radiology department of hackaday.io, [Peter] is starting a new project: an improved desktop CT scanner.

The previous version of this CT scanner used a barium check source – the hottest radioisotope source that’s available without a license – and a photodiode detector found in the Radiation Watch to scan small objects. This source is not matched to the detector, there’s surely data buried below the noise floor, but somehow it works.

For this revision of a desktop CT scanner, [Peter] is looking at his options to improve scanning speed. He’s come up with three techniques that should allow him to take faster, higher resolution scans. The first is decreasing the scanning volume: the closer a detector is to the source, the higher the number of counts. The second is multiple detectors, followed up by better detectors than what’s found in the Radiation Watch.

The solution [Peter] came up with still uses the barium check source, but replaces the large photodiode with multiple PIN photodiodes. There will be a dozen or so sensors in the CT scanner, all based on a Maxim app note, and the mechanical design of this CT scanner greatly simplifies the build.

Compared to the Stargate-like confabulation of [Peter]’s first CT scanner, the new one is dead simple, and should be much faster, too. Whether those radiology professors and biomed folk will be heading out to [Dr. Jansen]’s back alley CT scan shop is another question entirely, but it’s still an amazing example of what can be done with a laser cutter and an order from Mouser.

The 2015 Hackaday Prize is sponsored by:

Use a Cheap PIN Diode as a Geiger Counter

After the Fukushima nuclear power plant disaster, radiation measurement became newly relevant for a lot of people. Geiger-Müller tubes, previously a curiosity, became simultaneously important and scarce.

Opengeiger.de (English-language version here) has complete instructions for making a Geiger counter without a Geiger-Müller tube. Instead, this counter uses a PIN photodiode and some carefully chosen operational amplifiers. The total cost of such a device is significantly cheaper than the alternative: under $1 for the diode and around $5 for the rest. And since the PIN photodiode in question is used in many other devices, it’s not a niche component like a Geiger tube is.

The secret sauce is in component selection and tuning. Opengeiger uses the BPW34 diode because it is relatively common and has a large surface area, but also because it has a very low capacitance when reverse-biased. The first-stage opamp choice is also fairly critical. Considering that an average gamma radiation event produces only around 10 nanoamps for about 50 microseconds, a lot of amplification (100,000x), low noise, and high bandwidth are a must.

If you want to get started with this project, you could first browse through the explanation (PDF) to get an overview of the project’s goals, read up on all the technical considerations (PDF) or just head straight for the DIY instructions for the “Stuttgarter Geigerle” (PDF, schematic is on the last page). All of the documentation is chock-full of relevant references and totally worth the read.

THP Quarterfinalist: Low-Cost Solid State Cosmic Ray Observatory

There are a number of crowdsourced projects to put data from around the world onto the Internet, tracking everything from lightning to aircraft transponders. [aelias36]’s entry for The Hackaday Prize is a little different. He’s tracking cosmic rays, and hopes to turn his low-cost hardware into the largest observatory in the world.

Cosmic rays are protons and other atomic nuclei originating far outside the solar system. They hit the very top of Earth’s atmosphere at a significant fraction of the speed of light, and the surface of the Earth is frequently sprayed with particles resulting from cosmic rays. Detecting this particle spray is the basis for all Earth-based cosmic ray observatories, and [aelias] has figured out a cheap way to put detectors in every corner of the globe.

The solution is a simple PIN diode. An op-amp amplifies the tiny signal created in the diode into something a microcontroller can use. Adding a GPS module and an Ethernet connection, this simple detector can send time, position, and particle counts to a server, creating a huge observatory with crowdsourced data.

The detectors [aelias] is working on isn’t great as far as cosmic ray detectors go; the focus here is getting a lot of them out into the field and turning a huge quantity of data into quality data. It’s an interesting project, and the only one with this scale of crowdsourcing we’ve seen for The Hackaday Prize.

You can check out [aelias]’ entry video below.

SpaceWrencherThe project featured in this post is a semifinalist in The Hackaday Prize.

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