29 July 2016

How I rescued the Bareconductive lab at Torino Mini Maker Faire 2016

Kids activity at Torino MMF 2016
I couldn't miss the chance to attend a Maker Faire in my home towm. So off we went at the Officine Arduino venue on a sunny Saturday afternoon in May 2016. In order to let my daughters enjoy the event I registered them to the Bareconductive lab, where they where supposed to draw a circuit with conductive ink.
I had booked a total of 4 seats together with two more children, but when we came (a bit late I must admit), the lab volunteers could take only one child because they had run out of CR2032 battery holders. Too bad, because the two boy-friends were willing to try! On the other hand the staff had conductive ink to spare.
My quick and dirty button cell holder.
I took along with me a simple TIL305 name badge powered with a CR2032 button cell, and since I had no suitable holder at home I used a small but powerful clothes peg with adhesive copper tape as a suitable replacement. Idea! Emulate the clothes peg using the conductive ink and folded paper!
I asked one guy if they had more LEDs. Since they had, I showed them my "battery holder" and explained my idea of replicating it on paper. They engineered a path for the conductive ink and could let many more children light their LED.

Original (top) and hacked (bottom) versions.

16 July 2016

Higher voltage from the lumos.sk HV PSU

I bought a second Nixie HV PSU from the great Lumos.sk website. The stock device outputs 110 to ~190 Vdc, which may be not enough for lightly depleted Nixies. For example, my B5094 requires about 205 V to light up.

Before assembling it I checked the diagram and the MC34063 datasheet for a way to change the output swing. Why? Because I want to build a bench PSU with a higher output, just in case. And currently I don't need voltages in the lower range. Basically I need to recalculate the feedback network and after a few typings on a spreadsheet I decided to decrease R3 from 3k9 to 3k3: this should result in a 130-230 V swing.

One constraint: output cannot be more than 250V unless the output capacitor is replaced with an equivalent with a higher operating voltage. The supplied electrolytic cap is rated at 250V.

Another good mod is replacing the small resistive trimmer with a potentiometer to bring the control over to the front panel. I forgot to do it this time. Well, I will keep this variation for my next build of this useful piece of gear.

12 July 2016

Raytheon 2051 Thyratron

One of my FN2016 purchases was a Raytheon 2051 valve probably from end of 1950's. I bought it just because it looked nice, not for real use.

I should have bought a socket for it, so it would be easier to keep it standing out of a box.

I was thinking that maybe the filament will glow, but it doesn't. Not because it is broken since it draws the stated current, but probably because it is not meant to glow.

I will read a bit about thyratron so that I can explain it to whoever will see it.

03 July 2016

Success with the Philips PM2421 U4 board!

At Friedrichshafen 2016 I bought a board with 5 Nixie tubes (ZM1000 and ZM1001). It is a U4 board from a well documented Philips PM2421 instrument. Even if a 1974 circuit is easy to follow and understand, having access to the schematic diagram saves a lot of time!

Before buying the board just for the tubes and their sockets, I tested them in case they were outgassed with my HVAC circuit (see my posts about CCFL laptop inverter in end-2015), and they all happily glew.

The board on a printout of the schematic diagram for U4 board.

Looking at the schematic diagram I realised that the symbol Nixie will display only plus, minus or tilde (AC) and that the thousands tube is wired only for 0 or 1: out of the box I cannot make a 9'999 counter, or a 24h clock with it. On the other hand a 12h clock will fit.

Nevermind, I have to light it up first.

Everything on the board is clearly marked, and it matches what is drawn on the diagram I found.

The digital logic needs a +5 Vdc while Nixies call for +180 Vdc. 5V/GND are clearly marked on the board, while HVDC can be reverse engineered to be fed at pin #20. If I was to use the analog part I would have to provide more voltages, like +/- 12 Vdc, but I am not going down that route.

So, 5V is easy. 180V were picked up from my biNixie clock PSU. Fire both and ... there you are!

The board greeting me with a reassuring quadruple 0 AC :)

Then I grounded one of the AC/DC selector pins and a minus sign appeared:

DC configuration without input signals.

According to the shematic, points P and /P are where a counting signal is supposed to be, the output of the ADC process. I will throw in a square wave and see what happens.

01 July 2016

Bad IV-27M VFD

IV-27M on its datasheet.
I bought this IV-27M NOS VFD display at Ham Radio Friedrichshafen 2016 flea market for 5€. The seller had three pieces and I took one. Its date code is 91XX.
When I came home I dug a datasheet looking mainly for the filament pins, so that I could test the display for good. Then with the DVM I kept looking for continuity (a low resistance value, few tens of ohms) but nothing was found.
I spent the next ten minutes looking into through the glass, trying to see the thin filament and where it should go to pins 1&2, just to discover that the connection between pins and filament is missing. Now I am the unhappy owner of a cold-war era leftover.

Lesson learned: do bring a DVM and do use it!

This display does not have a thoriated tungsten filament, it does not emit weak radiations, so that it cannot be reused as a test source. It will remain a warning reminder with a 5€ price tag.

Can you spot the filament ends in there?
The same seller had both new (5€/pc) and used (3€/pc) red-coated Nixies I forgot the model, that I haven't bought because I don't like red ones. Now I am thinking that used tubes (you can tell if they were cut out from PCB) might even be more reliable than new ones, that could have been once discarded but then followed a different route than the trashbin.