Real world test of Radioactivity Counter app

As described in a previous post, a German team has developed an Android and iPhone app that detects ionizing radiation ("radioactivity") through the obscured camera sensor. But, how to test that your device actually works if - thanks God - you lack a radioactive source?

Airport security checks and alike is the answer.

I recently flew to Berlin, so for the sake of science and personal learning I gave it a try. I obscured the smartphone camera as described in the App manual. Please note that you need two layers of black cardboard to be effective even in full sunlight. I fired up the App, slipped the smartphone in a pocket  and waited for my turn. The jacket went into the usual box and through security scanning. I tried to stay calm when the operator at the screen asked for a second pass of the box containing my jacket. Got caught? No, I had simply piled up stuff and they couldn't see clearly everything. I grabbed my stuff with a nice smile since my counter disguised as a smartphone passed twice into the radioactive area!

This is the screenshot of both passes. The App log keeps track of hits per minute and probably the second pass was just across the minute change:

The two bars measure about 25k and 10k CPM.

Let us move forward. Upwards, actually, to the sky. When airborne we are exposed to higher doses of radioactivity because there is less air filter between us and the outer space. So, probably, the App could detect something during the flight too. Note 1: flying is perfectly safe with regards to radioactivity!! Note 2: the app ran for 21 minutes on each flight, but I kept the phone screen hidden under a paper or in my pocket.

First flight was before sunrise:

And the second flight after sunrise:

Not a big difference between the two airborne situations, but I can tell that I get fewer CPMs when on Earth.

Last but not least, I dared the security check experiment on the way back, thinking that it would have been fun to explain German security personnel what I was measuring and why. Well, I had plenty of time before boarding. I have no screenshot to show since during my stay in Berlin I needed my smartphone camera and I had no means to cover it back. So I simply fired up the app and threw it in the internal pocket of my Winter jacket: darkness in there is enough not to produce false hits.
The X-ray scan produced 17300 clicks, which is interesting.

Incidentally, the sum of both scans at my home airport is around 34k. Since the phone had gotten Xrayed twice, that makes an average of 17k CPM over those two minutes, which is very very similar to the third scan on the way back.

So. The Radioactivity Counter app does work. I do not claim it can produce calibrated uS/h readings, but it can detect ionizing radiation above normal/natural levels. Just let it self-calibrate, provide a good black screen (try it aiming the camera towards the Sun while the app is running, and look for 0 hits) and try it in a probably radiation free environment (your home, your basement) so that you know what is normal for your specific App/smartphone combination.

Good luck in not finding radioactive sources in your neighborhood!

A simple way to detect ionizing radiation (Geiger counter and alike)

One object I could not find last June in Friedrichshafen Ham Radio fair is a Geiger-Muller counter. What for? Mainly for curiosity of measuring if my home is radiation free given the amount of surplus around. And a Geiger counter can be re-sold easily afterwards. Failing my purchase, I started an online quest for an alternative.

First I came across a small dongle that plugs into a smartphone earphone/mike hole. It is made in Korea and costs about 30 EUR/USD, with an accuracy of ~30%. Few days of thinking later, I remembered an article on Hack A Day blog about an Android and iPhone app that acts as a Radioactivity Counter (that's the app name). It works by counting how many pixels of an obscured camera sensor turn white because of a high energy particle passing through (beta and gamma).

That's cool! Just need to cover the camera sensor area with thick black paper and let the app run. Fine. Almost no readings around home. It is a good sign, but I need a proof that it works when there is a radiation going on.

So, I have been looking for something that you would never want to find in your life: a beta/gamma radiation source. It is a paradox: you look for something and you hope to never find it! Granite, dangerous energetic jewels, ... all something that I would have to dispose properly afterwards. Then I came up with a different approach.

The most easy way to expose a smartphone to ionizing radiation is to get it X-rayed at some security checkpoint. I realized it when entering the Milan Expo 2015, but the lens was not covered (this "source" is even written on HaD post, right on top!). Too late. Next chance would be an airplane trip to Berlin.

Been there, done it.

Results in the next post!

Transforming 7-segment LED clock into IV-6 VFD clock

Take a cheap 4-digit 7-segment LED clock kit (like Bangood SKU142210, about 6.5 USD [red, without case]), design an adapter board and replace the display with four IV-6 VFD Russian tubes. That's what I have been working on during the last three weeks.

According to the schematic, the original clock uses common anode displays and multiplexes all four digits: IV-6 VFD satisfy this requisite, even though I have no idea how fast the multiplex is and whether tubes can react that fast.

IV-6 on veroboard, note the 3rd tube leads.

These VFDs require a grid and anode drive of 12-30 V or more, while LED displays and the clock run at 5 V. After few tests I opted to keep the 5 V input voltage (ubiquitous USB...) and insert a step-up module to obtain 12 to 35 V, which also controls luminosity.

The clock microprocessor outputs a low logic level to turn on segments, while VFD requires a high "logic" level, so the adapter board must both adapt voltage levels and invert the signal. Well, the ULN2003 darlington transistor array is fit for this purpose. Since I need to control 7 (segments) + 1 (digital point) + 4 (tubes) I need 12 lines, two ULN2003 chips (total of 7 + 7 = 14 transistors).

For the sake of simplicity I opted for wiring in series the four VFD filaments that operate at 1 Vmax and add a voltage-drop/current-limting resistor on the cold end: this ensures that the anode voltage is below the grid potential, so the segment turns completely off (otherwise it could still be visible in complete darkness).

Wiring up the boards requires a lot of concentration.

In order to limit the current through ULN2003 transistors when they are "ON", meaning a segment is "OFF", I needed to choose a suitable pull-up resistor value: too high and the current will not be enough to switch off, too low and the overall current consumption increases as well as unnecessary heat dissipation. 3k3 ohm is fine but pretty low, 9 mA apparently not worry much, but they mean 270 mW if I run anodes and grids at 30 V, on a single resistor. 51 kohm with their 51 mW (@ 30V) are too much and Darlingtons don't turn off properly. At least at a first test, but I want to add decoupling capacitors on the high-voltage side because moving wires around seem to fix the problem.

QYT KT8900 - digital noise on audio

One of the most noticeable defects of QYT KT8900 is a digital buzz that can be heard when the stock microphone is plugged in. This problem has been tracked down to the digital logic on the microphone communicating with the main radio board.

The picture shows how the loudspeaker signal looks like on an oscilloscope:

 

Spikes are about 25 mV peak, one every 3.5 ms or so. I couldn't get a stable trigger on the signal and the picture shows my best capture (100 MHz analog Tek, 100 MHz probe at 1x).

Any idea for a simple fix?

AA to C cell adapter

[In Italian: "Adattatore da stilo a mezza torcia"]

So, your kid just received a new toys that requires batteries. Not plain simple AA cells, but C size. "Batteries not included" the box says. After the fist moments of unspoken words, this is a good chance to prove your audience your homebrew ability with a macgyverism!

Grab two ubiquitous AA cells and wrap them with cardboard until their diameter fits comfortably into the battery compartment. Fix the wrapping with a bit of adhesive tape. That's it!

AA on the left was partially extracted from the adapter.

How is it possible? AA and C cells share the same height. A C cell is an AA put on steroids. Theoretically it holds 2-3 times the capacity, but some people reported fake C batteries that were wrapped up AA's.

Have fun with the new toy!

QYT KT8900 current consumption

Is it me, or the QYT KT8900 manual does not specify the current consumption? I measured it. The unit I got my hands on, performs as follows:

RX: 0.27 A (backlight on, stand-by)

VHF TX LOW: 2.7 A
VHF TX HIGH: 3 A
UHF TX LOW: 2.5 A
UHF TX HIGH: 3.3 A

Readings taken at 12.5 V out from the PSU.

I have no idea what the RF power output is. But I noticed that it will not transmit below 10 Vdc, while the current drain is constant between 10 and 13 Vdc supply.

QYT KT8900 arrived

The parcel containing a QYT KT8900 has arrived today. It took less than 20 days and it was shipped through Germany to Italy. I haven't opened it yet...

QYT KT8900 transceiver

Online reviews do not rate it at the top of the category, but QYT KT8900 VHF/UHF mobile transceiver has worthy features for less than 100 USD. And it is small, very small.

I have ordered one, that will come once it completes its long journey from CN/SG/HK. I am looking for two info that current reviews do not cover:

• spectral purity of the transmitter
• microphone sensitivity

My own tests will tell me how it performs. The challenge will be to build a probe that turns 25W RF into something acceptable by the spectrum analyzer...