biNixie Clock schematic diagram

For those interested in reproducing my biNixie Clock, here is the (most likely) schematic diagram:

I have realized I did not take notes while building it, probably because it is so straightforward (and a copy of other designs).

You need to pay attention to the current limiting resistor (one per Nixie tube), which depends on the tube model and your anode voltage ("HV" in the diagram).

Put everything on sockets so it can be easily replaced or reused.

At current prices (3/2016) the whole thing should cost less than 30 Euro if you use common Nixies like B5092/ZM1020.

The firmware for Arduino and compatible boards (ATmega368) is here https://github.com/jh1995/biNixieClock.

Please share pictures of your biNixie clock as well as firmware improvements!

Four digit display with HP 5082-7300

Arduino Nano counting...

My interest for old display technologies got a bit of satisfaction when I lighted up a bunch of HP 5082-7300 chips. These are 8 pin displays with an integrated BCD decoder (0-9, dash, blank) plus RHS decimal point that emulate a dot matrix configuration. The required power supply is 5 V and today they can be easily driven with the microcontroller of your choice. The integrated logic includes a latch, so you can connect more displays in parallel and multiplex data through the [Latch Enable] control.

One remark not clear from the datasheet: the decimal point is latched as well as ABCD inputs.

My first application is a simple 0000 to 9999 endless counter. It is a good way to test all dots work, measure current consumption and do other optimizations.

As expected, these little displays produce a good amount of heat. According to the datasheet, at 5 V the current drawn is well above 100 mA, so that's more than 0.5 W of heat to dissipate. To minimize the risk of failure due to heat I mounted my 5082-7300 on a "socket", so I can add a small fan on the side if I want to.

Then I tried to reduce the voltage supply, both to the Arduino and to the display string. The good news is that there is no change in dot luminosity down to 4.1 V and the average current goes down to 60-70 mA per display: that's about 0.25-0.3 W dissipation per display. Cool, isn't it?

Click to zoom and see the logic through the red plastic. Last digit was changing from 6 to 7.

Voltage supply can be further decreased but then pixel luminosity is not uniform anymore.

So, in the final application I can run the whole setup Arduino+HP 5082-7300 at 4.2 V or so. Given the amount of power needed by the display rack itself it makes no sense to optimize the firmware for a lower consumption or use a stand-alone microcontroller in place of an Arduino.

Now it is time to fill the perfboard with a Nano, an RTC and some form of alarm function. And write some code, of course.

I have some HP 5082-7300 spares in case you land on this post looking for this specific part.

Saba Compact Clock A - display sorted out

With the help of a DVM and the circuit diagram I sorted out few things on the Saba Compact Clock A.

One trace is hidden under the display support frame, and probably it even contains a diode. I cannot unplug the custom IC to look what is underneath it, so I must trust my DVM readings.

The IC does work, since it outputs voltages compatible with a blinking display (typical of "time not set" state), but there's something wrong on the path of the common cathode I couldn't sort out. On the positive side I could light up segments on the display and confirm they are plain red LEDs with a common cathode, so I can re-wire my own cock circuitry if I want to.

I also spotted a curious optimization: segments a-d-g of tens of hour digit are connected together. That makes sense since they always light up together in numbers 2 and 3, and don't display anything higher than 23 (hours) or 31 (day of the month).

Now I might try to replace a couple electrolytics badly corroded (externally) and then give up on fixing this device, for now.

Saba Compact Clock A - washed up - no joy

As announced, I washed with hot tap water the Saba Compact Clock A PCB covered with NiCd electrolyte spill.

I would say that 80% of the alien material has gone away and most tracks shine again. A ceramic capacitor was split in half and I had previously removed a trimmer that was badly damaged.

I reconnected the transformer and, unfortunately but expectedly, the clock does not power up at all. Not even a mildly reassuring sequence of "000".

Probing around with the DVM I spotted open diodes in the area closest to the was-backup-battery. And since I have no pinout of the microchip, let alone a datasheet, I have no idea which pin is not being fed correctly.

I might replace few 1N4148 here and there and fit a new 100k trimmer. If nothing happens I will leave a note to the future myself inside the device of what has been found and done, and the Saba Compact Clock A will join my collection of electronic items from 1980's.

It can be fixed. With patience and time. Do I really want to?


PS: the display is not a simple LED, and I need the microchip to work again so that I can measure voltage values!

PPS: according to the blogging platform, this is my 500th post!

Saba Compact Clock A clean-up from NiCd spill

During a ful immersion into my pile of electronic junk I noticed an alarm clock radio from early 80's: SABA Compact Clock A. Since it was not my target I skipped over it, just to come back the next day and pick it up for further analysis and putting it back into service.

The display is LED, not VFD. Nevermind. The whole thing powers up but radio and clock don't work, so a look inside was desperatly needed.

The battery still in place and visible leak.

Horror! The radio contained a NiCd backup battery that has leaked over 1/3rd of the PCB. It is all dry now, in small crystals. According to many online discussions the dry electrolyte (KOH) will come off easily with a brush and then some simple chemical solution.

I will try a first cleaning round without becoming obsessed about it. If it doesn't work out then I might fit into the case a custom alarm clock built with modern technology that reuses the AC transformer, the display and the loudspeaker.

Solder side. The green protective layer comes off.

One thing is sure: I must tidy up my desk because I have KOH crystals all over and it needs a thorough cleaning!

Six VFD tubes (IV-3) in a row

Work on old display technology continues. I spent few nights trying to align six VFD tubes on a piece of veroboard. The result looks neat but very hard to keep proper alignment when soldering 10 pins per tube.

So I dropped the idea of using veroboard and, given the very cheap prices for prototype PCBs, I will try to design one myself.

Originally I wanted to draw many single-tube boards, but I will probably go for a full board that includes driver transistor arrays (ULN2003).

A local OM will help me producing the files for the PCB factory, so hopefully I will save a little time on that step.

Compact power supplies for our circuits

While wondering around Aliexpress offers I stumbled upon a black box coded "HLK-PM01" that is said to be a 90-260Vac to 5Vdc at 600 mA output.

There is also an interesting 3.3V @1 A as HLK-PM03 and 12V @600 mA as HLK-PM12. The producer has even a website www.hlktech.net.

These blocks are the best solution so far I have encountered for DIY projects that need to run off an AC outlet, let alone the bulky "USB" chargers. And HLK-PM03 provides 3.3V that are needed for ESP8266-based projects.

I've ordered a couple of 3.3V modules, also because an positive review you can find on a .dk website (for HLK-PM01).

Veroboard at last!

When I was in primary school, at the age of 9 or 10, I received this book as a present:

Italian edition of "Science fun" by Usborne Publishing 1981

It shows simple electronics, chimics and physics experiments. All electronic circuits were supposed to be built on what I later found to be called "Veroboard": a multihole board with fully connected rows that could be easily interrupted with a drill bit or so. I searched all local shops to no avail. I resorted into building those circuits with componets sitcked in soft PVC food containers and showing them at school.

Now, more than 30 years later, in the local shop I tried asking for a "breadboard with connected rows", for the childish fun of asking, and ... what a surprise! They had it! Given the smell it was probably built long time ago. When I sat in the car after my shopping session I even though something was melting!

Now I have found out that I can shop online for "Veroboard" and get some more of it probably slightly cheaper than the local shop. Curiously most sellers are in UK and not in Far East. I had stopped looking for it too long ago.

Today I am using Veroboard in my VFD Clock transformation project, to simplify wiring between the four tubes that are connected in parallel next to each other.