did you manage to do anything with your 4031 ? ive just bought one thats in dire need of attention.. its got the same fails as yours + mine has a the switched mode part of the power supply thats blowing the power mosfet ive removed and tested almost every diode, cap and resistor but cant find a fault as of yet. regards the other faults it seems that every electrlitic cap needs changing on all the cards.


Pretty much all the SMT electrolytics in mine are leaking too, and it’s a fairly low priority since I don’t have an immediate need for it. When I bought it I was hoping it’d be something fairly trivial like a bad rail on the PSU, but it’s bad caps everywhere and until I get em replaced further analysis is probably going to be inconclusive.

I do however have a link to the service documents, which may be of use -

Hope that helps some, and if you’ve got any good ideas on how to get instrumentation to the test points on the boards inside the card cage I’d love to hear em; I’m thinking minigrabbers, but I may actually have to solder some leads on because it’s pretty tight.

Wargames Numerology

Reading through this trivia page and it notes that one of the launch codes is “JOB 9515 VNS”; this looks a bit like biblical chapter/verse notation, so I looked it up.

The book of Job chapter 9, verse 5-15 reads:

5 He moves mountains without their knowing it

    and overturns them in his anger.

6 He shakes the earth from its place

    and makes its pillars tremble.

7 He speaks to the sun and it does not shine;

    he seals off the light of the stars.

8 He alone stretches out the heavens

    and treads on the waves of the sea.

9 He is the Maker of the Bear and Orion,

    the Pleiades and the constellations of the south.

10 He performs wonders that cannot be fathomed,

    miracles that cannot be counted.

11 When he passes me, I cannot see him;

    when he goes by, I cannot perceive him.

12 If he snatches away, who can stop him?

    Who can say to him, ‘What are you doing?’

13 God does not restrain his anger;

    even the cohorts of Rahab cowered at his feet.

14 “How then can I dispute with him?

    How can I find words to argue with him?

15 Though I were innocent, I could not answer him;

If that wasn’t intentional on the part of the producers, it’s a pretty damn happy accident.

Jacob’s Ladder time exposures. I “painted” a tiny bit of aluminum powder on the electrodes to get the white sparks. The Al powder was recovered from a pyrotechnic mixture and is contaminated with a small amount of some oxidizer which made the arc much more blue. If it was NaClO4 the Sodium D line would be rather obvious, so I think it’s KClO4.

Lessig Blog, v2: A time for silence


A week ago today, Aaron gave up. And since I received the call late Friday night telling me that, like so many others who were close to him, I have not rested. Not slept, really. Not connected with my kids, at all. Not held my wife except to comfort her tears, or for her to comfort mine.


Cute weekend project. All relevant info here:


Hey could you explain how a circuit switches the numbers on a nixie tube? I can't find anywhere that gives a straightforward answer. I mean I know (well, think) it's changed by switching to the appropriate pin, but how does a circuit accomplish that switch and what kinda voltage and amps are required?

No problem!

Nixie tubes are basically neon lamps with a common anode(+) and multiple cathode(-) elements, one for each digit.

To turn on a digit, a switch of some sort connects the cathode pin of the desired digit to ground; assuming there’s sufficient anode voltage, the glow discharge illuminates the digit. If you replace the switch with a transistor or MOSFET, you can then use a signal to do the switching rather than physically flipping a switch.

In this example, the 1 and 2 digits are being controlled by SW1 and SW2. SW1 controls its element directly, but SW2 generates a 5v logic level signal that controls a MOSFET gate. In something like a clock, the gate control signal would be generated by a decoder chip or microcontroller rather than just a switch, but the principle is exactly the same.

As far as the voltage and current requirements, tubes vary but usually need an anode voltage of around +170v, around 1 milliamp of drive current, and have a “turn off” voltage of around 110v.

Once the tube turns on, it’ll attempt to conduct as much current as physically possible, so R1 is needed to limit it to a safe level.

When the Nixie is on, it drops voltage equivalent to the turn off voltage, so to calculate the required current limiting resistor value, subtract the turn off voltage from the anode voltage and use Ohm’s law to solve for the desired current:

Vcathode = 170v - 110v = 60v
Iwant = .001A (1ma)
Ranode = Vcathode / Iwant= 60k ohm

There’s quite a bit of latitude - if you use a 47k resistor as in my example schematic, the current will come out to 1.2ma, which is totally acceptable. It’s also good practice to ensure your current limiting resistor can handle the power dissipation, so multiply Vcathode by Iwant and make sure your resistor is rated for more watts than that. In the example this is .06W, so a typical 1/4W resistor is more than capable.

Since there’s the voltage drop from the tube, the transistor only needs to be able to handle Vcathode, in this case 60v. The BS108 in the schematic is good to around 200v, so there’s a huge margin for error in case the high voltage supply floats above 170v.

I used a Supertex driver array in my clock, but it’s just 32 n-channel MOSFETs and a shift register in a single package. The reasoning and calculations are the same as if I implemented it with 32 discrete MOSFETs. The chip’s drive outputs are all MOSFET drain terminals, and the source terminals are just internally tied to ground.

There are lots of ways to drive these things, including some vintage 74 series chips that are explicitly designed for driving Nixies. Much more info here and here.

8 pins so crazy

Looking forward to these, didn’t really expect ARM to ever show up in less than 24 pin packages.

Screw the penguins, go nuts with Acorns.

Screw the penguins, go nuts with Acorns.

Blowing holes in aluminum foil with capacitors, one of life’s simple pleasures.

2 x 390uF@400V

Nixie clock got some Hackaday love