Thermal Imaging of Fingerprints — How to get your PIN from a Number Pad

A few days ago I was able to get my fingers on, and under, an infrared camera. I had already heard before that the thermal signature of fingerprints is visible for quite some time — but what surprised me was that we were still able to see them for over a minute…


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Sharp PC ROM File Collection (with Hashes)

This short post is to document Sharp PC ROMs I’ve come across so far. I’ve used MD5 and SHA1 checksums to allow their comparison. It would be nice if you could notify me of any ROMs out there that do not match the ones documented here… In an earlier post I’ve described a simple way to dump the ROMs.

  • Sharp CE-150
    Serial 31015xxx
    Memory Area A000-BFFF (8 kB)
    MD5 eb9aa5156c6849890b137799efc50a4b
    SHA1 a3aa02a641a46c27c0d4c0dc025b0dbe9b5b79c8
  • Sharp PC-1500
    Serial 20007xxx
    Memory Area C000-FFFF (16 kB)
    MD5 fbc55a9a8743e619b7709721ff5bcbff
    SHA1 d706d2e69cabbbbbe24f708cb3bc921fa1a2b704
  • Sharp PC-1500 / Sharp PC-1500A
    Serial 20011xxx (Sharp PC-1500)
    Serial 31070xxx – 57012xxx (Sharp PC-1500A)
    Memory Area C000-FFFF (16kB)
    MD5 8ebec8b0ef358645df14807c31df7d06
    SHA1 51a9e37a670b6cf199f0814e96a7e4fda6f44b60

Feel free to contact me and provide me with ROM file I do not (yet) have in my collection. I will also try to make the ROM files available in the next weeks.

I made it: I switched from Eagle to KiCad to make my PCB designs…

Half a year ago I’ve started to use KiCad for new PCB designs I’m working on. I already wanted to try out KiCad for quite some time. Its release 4.0 and the latest changes in EagleCAD (annoying ads and recently being bought by Autodesk) were enough pressure to switch. And what should I say: after dealing with the rather unhandy library management and some cryptic error messages I really now enjoy KiCads workflow.

This post is about my experience with the transition to KiCad as my new PCB designer. It is based on the newest version 4.0 of KiCad and its daily builds via the respective Ubuntu PPAs. Continue reading “I made it: I switched from Eagle to KiCad to make my PCB designs…”

Backup your files and keep them in separate physical locations

I know I’m sounding like a moralizer and the suggestion should be a no-brainer. But the flood in Simbach a few days ago once again showed me how important backups are – and how even more important it is to keep them in separate physical locations. I’ve helped friends to remove mud from CD/DVD backups. I’ve extracted hard drives from computers and USB cases, removed mud and water as best as I could. The drives are currently drying at 40°C in an oven. Hopefully they will be readable again…

Oh, I nearly forgot: I’m also currently failing at making backups on a regular basis and even more: my backups are all in one place. 🙁

Jupiter Moon photo taken with a regular DSLR and Zoom lens

Yesterday evening I spontaneously made a photo of Jupiter with my Canon DSLR, a (300 mm) zoom lens, and a tripod. 🙂 I was really surprised that I was able to identify the four Galilean moons Europa, Io, Ganymed, and Callisto.DSLR Photo Jupiter Europa Io Ganymed Callisto

I did not expect much as I made the shot from my balcony with room and street lights on. Here in Munich we have a lot of light pollution. At first I thought the small spots were lens flares. Also chromatic aberration is pretty visible due to the manual focus, but I’m still proud of the photo because I did not expect anything special: I first had to compare it with the software-rendered constellation of the moons around the time the photo was taken (see below) to be sure.

Jupiter Moon Constellation 2016-05-28 2100

30th Anniversary of the Chernobyl Tragedy – or – Building a PIN Diode Geiger Counter

Exactly 30 years ago a great disaster struck the region of Chernobyl: a nuclear accident occurred that released a large quantity of radioactive particles into the atmosphere. And it is only five years ago that, with the Fukushima Daiichi nuclear disaster, a second similar catastrophic event has taken place.

These anniversaries did not directly let me build a PIN Photodiode based Geiger Counter, it is more or less a coincidence. The main drive to build such a device was my curiosity and (please forgive me) a fascinating green glow I’ve seen on various fluorescent Uranium minerals under UV light. But in this context it should not be forgotten that at present there still is a significant increase in background radiation in some regions and some agricultural products due to these events.

There are lots of descriptions of how to build such a device; even cheap commercial products (e.g. the Smart Geiger) use such a design. Especially two sites caught my attention: and Das Gammastrahlen-Mikrofon (German). The design I’ve chosen is based on these sources but I’ve begun to further modify it. In this post I’m showing the design I’ve started with. It mainly relies on two BPW34 (Vishay Datasheet) photodiodes connected in parallel, and two transistors to amplify the voltage fluctuations of beta and/or gamma rays striking the diodes. A 9 Volt battery was added to increase the pulse height.

The common approach to protect the photodiodes from light is to use one layer of tin foil and connect it to ground. This should also protect the circuit against electromagnetic radiation. I’ve started with something different and dipped the diodes three times into liquid rubber (Plasti Dip). My hope was to at least allow some beta particles to reach the semiconductor material.

Photodiode with Liquid Rubber Coating

So far I’ve tested the basic design shown above and had mostly noise on my microphone input. I’d say that sporadic crackling has more to do with the 1 hour hacked together design than beta or gamma rays. The liquid rubber seems to block of light, but the simple design is sensitive to electromagnetic radiation. Waving your hand or even movements in about 1 m distance is visible in the sound profile. An additional tin foil shield connected to ground did not change the noise profile, although the EMR influence was reduced. I’ve tested it with two different sound cards (microphone inputs).

I’m currently redesigning the whole approach and expect better results. So stay tuned…

Sharp PC-1500/1600 ROM Dump Method 2: Desoldering the ROM Chips

To make it clear from the beginning: this is a (possibly) destructive method of reading ROM chips. The process of extracting and possibly a resoldering of the memory chip might fail. In my case I’ve tested it on two Sharp CE-150 PCBs I’ve declared to be spare parts. It is only a proof of concept as there are simpler non-destructive ways of ROM extraction on a Sharp PC. I was just curious and so I’m describing my experiences.

Well… At first I did not want to desolder the ROMs: I started with the intention to use a set of probes attached to the individual pins of the chip to read the content of the Sharp PC / CE ROM chips. This did not work due to the narrow leg distance of the QFP chips (0.8 mm).

Probe Connection Problem

Desoldering QFP chips can be done rather quickly with a hot air gun. At least that’s the most comfortable way I know of. I usually add some flux and in some cases larger quantities of leaded solder. The latter decreases the melting point and speeds up the process. I don’t care about solder joints as the chips and the pads can easily be cleaned after the removal. Excessive amounts of solder can be removed with flux and a clean soldering iron tip.
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Sharp PC Audio Output (CMT-OUT) Simulation in LTspice

This was a little test out of curiosity… I’m currently playing around with an amplifier circuit for the Sharp CE-150 audio output (CMT-OUT) and wanted to see if the signal I’m getting is already distorted when leaving my Sharp PC, or if my circuit and/or sound card is causing the distortions.

The CE-150 uses Frequency Shift Keying (FSK) to transfer binary data via audio signal (e.g. to a tape recorder). It sends four pulses of 1.27 kHz for a binary “0” and eight pulses of 2.54 kHz for a “1”.

Sharp CMT-OUT LTspice Schematic

To test the circuit I’ve taken the original design and simulated the circuit in LTspice (running under Linux with Wine). This tool allows the simulation of various analog (and digital) circuits – perfect for my test.

Sharp CMT-OUT LTspice Plot

Sharp CMT-OUT Audacity Plot

The result was – to be honest – pretty surprising for me. The upper screenshot shows the LTspice simulation of the output signal, the lower screenshot was taken from a WAV file in Audacity. I was not only able to simulate the circuit but also to use the resulting signals as a good approximation for my amplifier circuit (not shown). 🙂 One minor fix (also not shown) left was to adapt the transition time between a “0” and a “1” to better fit to the original curve.

Sharp PC-1500/1600 ROM Dump Method 1: Audio Transfer via CE-150 Extension

In this post I’m describing a method which is widely used to Dump RAM and ROM images on Sharp PC-1500 and PC-1600 systems. This method is non-destructive and can be used on most Sharp PC ROMs and extension cards. It only requires a Sharp CE-150 extension, an audio cable, and a computer with a microphone input (i.e. sound card).

Besides a plotter, the CE-150 Color Graphic Printer also provides two audio interfaces (line-in and microphone output). These were (and still are) used to transfer code or data between Sharp PCs and tape recorders. Today, such recorders are mostly outdated but the method works nonetheless with sound cards. Software tools are freely available (e.g. pocket-tools) that allow the transformation of recorded audio files into binary dumps and even further into BASIC code.

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Sharp PC 1500/1600 Schematics Collection

To facilitate the access to Sharp Pocket Computer schematics I’ve started to collect and mirror some of them on my web site. This should allow Sharp PC 1500/1600 enthusiasts to update, modify, and especially to repair their hardware.

The Sharp PC 1500/1600 series are obsolete hardware. Their schematics are already freely available on the internet and therefore considered to be in the public domain. Please inform me if you own a copyright on some of this material and do not want it to be available on my web site.