22 November 2015

CCFL laptop inverter board for Nixie/valve testing - 2 - video

Want to see how a Nixie tube lights up when it is close to an HVAC source? Here you go:

The board is from an Acer laptop. Power supply is about 11 Vdc plus 3 Vdc for the control circuitry. Since there is no CCF Lamp connected the circuit shuts down after a couple of seconds, but that is enough to see the gas inside the Nixie so show its presence. Re-apply the 3 V control and HVAC appears again.

Remember: no light means broken Nixie.

21 November 2015

CCFL laptop inverter board for Nixie/valve testing - 1

A WORD OF CAUTION. This experiment involves dangerous high voltage AC. I take no responsibility for whatsoever damage may result in reproducing what is described below: if you don't know how to deal with HV, just read and learn.

Surfing around and reading about Nixie testing I came across a text that describes a way to check these tubes in a wireless fashion. With such a device, that is battery operated, it is possible to test Nixies found at flea markets so that you don't buy broken items.

The device produces high voltage AC through an antenna and when put close to the Nixie glass the gas inside lights up. There are commercial products starting from 12€, but a DIY solution is possible too.

The laptop CCFL (screen backlight) driver circuit fits this purpose. You need an older laptop with CCFL and not LED backlight. So all those laptops pre-2008 should do (do your homework first and check its specs before taking it apart).

The circuit usually sits in the lower part of the screen. How to get there probably will be covered in a future post. Hint: you don't need to take apart the whole laptop, just the screen. Otherwise you unscrew a lot for nothing.

Possibly do this job on a laptop you can power up, so that you can reverse engineer the connections. The driver has a least 4 inputs: broad range Vcc (like 8 to 20V), GND, enable and luminosity. The latter two signals usually take up to 3V, some are analog other digital, but in general if you pull both "high" you'll turn on the booster at max strength, that is what we need.

Here is the circuit powered with my own bench PSU and an extra battery for 3V lighting up the original CCFL:

The frequency counter can pick up the 56.1 kHz without any physical connection to the booster: radiated energy is enough! The yellow crocodile brings 3V DC to both Enable and Luminosity pins.

What happens if the CCFL is disconnected? This booster controller chip has a cut-off feature that stops HV if there is no current flow after few seconds. Anyway even without a wire going to the CCFL the frequency counter picks up the signal (at 80 kHz) and a good Nixie lights up too!

Next ... a video showing the effect on a B5092 Nixie.

17 November 2015

Simply dangerous sample?

I have not yet closed the Android radiation monitor case. Besides building a stand-alone circuit with parts that I have at home - sooner or later - I need to locate a source that does not require walking through security checks. One of the Chinese big online sellers has something that might come handy in the form of a self-luminescent keychain. Today I ordered one for about 12€.

Results in a couple of weeks, when the sample will arrive. Testing will be straightforward.

06 November 2015

biNixie clock - firmware complete

I have just tested the latest (and probably the last) firmware for my biNixie clock. It lacked a way to set hours/minutes, that has been implemented with two push buttons and the useful INPUT_PULLUP feature of AVR microcontrollers (the pin is set as input and an internal pull-up resistor is toggled in, so you save external components).

I am now able to understand how precise the RTC module is, so I will decide whether those buttons can be hidden into the case or they need an easier access.

Going happie (or nixpy?) to sleep.

19 October 2015

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!

15 October 2015

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!

19 September 2015

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.