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Dummy load get’s a tune up and another test

Improvements and fine tuning

As mentioned in my last post on the dummy load, though I am very pleased with the results, there is always room for some fine tuning and improvement. Also, some parts needed to be bought. First off, here’s a revised version of the schematic:

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Nixie Clock Schematic Finished

After a lot of testing, it’s looking good!

My Nixie Clock Schematic

My Nixie Clock Schematic

So here is my more-or-less final schematic. Since I used bits ripped off from a bunch of places and cobbled them together, use it freely for your own clock project. Schematic posted here.

Please of course bear in mind that though I’ve made an effort not to make mistakes on the schematic, they are bound to be there so if you build this and hurt yourself because you didn’t check your work, well that’s your fault isn’t it? You’ve been warned. Some parts of this circuit have potential around 170Vdc which will zap you good!. I very much doubt the the circuit can kill, but I don’t want to see a test of that either. Enough, you get the point.

So I am quite pleased. Although I’ve been unable to breadboard up the entire thing at once, I’ve built it in pieces and it seems to work well. Quite low power also, I reckon the thing draws 150mA or less. I will have to wait a bit to give a measured reading on that as I accidentally melted one of the fuses in my multimeter and will seek a replacement for it.

Things put in, things left behind

There are many things I added to this circuit to give it some functionality and to make it usable. One can set the hours and minutes independently using push-button switches and in this sense works just like an alarm clock. There is also a seconds reset button which will zero out the seconds when whatever your setting it to reaches zero seconds to keep them close to in-sync. Holding down the button also acts as a seconds-hold so that’s quite useful. These three should be push-button momentaries, the type that have three terminals: a normally closed, input and normally open. The seconds reset needs to be double-pole double-throw momentary. All cheap and easy to find.

I’ve helpfully labelled the transistor pinouts as well. As it happens, I seem to have selected ones with every type of pinout combination possible. Infuriating really, why can’t they just stick to one standard one? Doesn’t matter what it is, just make it the same! All of the parts here, apart from the nixie tubes themselves, are cheap as chips and commonly available.

How it works

The circuit is divided into five basic sections. At the bottom left we have the 5V power supply (simple 7805 regulator) which powers all the CMOS chips as well as the crystal oscillator and the vanity LEDs. Moving right we have the 4521 frequency divider IC and the crystal oscillator. The resistors and caps start the crystal resonating and the 4521 divides its frequency down to the desired pulses we need for other parts of the circuit.

At the bottom right is the blue ultra-bright vanity LEDs which I plan to mound under the nixies to give them a nice nuclear blue glow that I’ve seen from other projects. Gotta have that! It pulsates once every four seconds and uses an RC timing circuit to fade it in and out. It should be noted that this circuit causes slight voltage fluctuations elsewhere in the circuit though these seem to not effect it’s function at all.

Above that we have our 12V Supply. I chose a 12V wall wort, since they are frequently over voltage anyway and as it happens it overcomes the 7812s dropout voltage to make a reasonable 11.90V. Moving right we have the small switch-mode supply that steps up the voltage for the nixies to about 170Vdc. This is quite a lovely circuit I lifted in its entirety from stuff posted around the net (see my previous posts for schematic). It is quite reliable and works well. As I mentioned in previous posts, it has a maximum output of 10mA. Since each nixie draws about 1.25mA, and each of the neons that make the separator colon draw about 1mA, we are only up to 7mA. Plenty of headroom. This saved me from having to step up un-isolated mains voltage and makes the whole circuit a damn lot safer.

The third row up from the bottom is where all the time calculation happens. Six 4017 counter ICs are used, one for each digit. Since the clock only has four nixies, the first two (the 1s seconds and the 10s seconds) are left with their outputs unconnected. Function couldn’t be easier: the 1s seconds accepts the 1Hz signal from the 4521, counts to ten then resets, passing a signal to the 10s seconds 4017 IC which counts to six and resets, passing it on to the minutes and so on. The function of the three switches is explained above and the hours in the previous post.

Finally, at the top we have the four nixie tubes and two neon lamps for our display. Each number of each digit (and the pair of neons) are driven by the MPSA42 high voltage transistor which accepts the input from the appropriate counter IC output via a 33k resistor. This works wonderfully. The two neons use the same transistor, but use the 1Hz signal from the 4521 as an input.

That’s it really. Better explanations of how this works are out there written by others more eloquent than I.

If you are going to build this up, I would highly encourage you to examine the circuit closely and test as you build it up. For a beginner project (as that is what I am still) this has some quite excellent educational value.

So now, I just have to build it up. The last challenge is, of course, to select (or build) a suitably attractive case for it. I’m hoping to hunt through a few junk shops for a nice box I can use.

Zener diodes can be bloody useful

More problems… more solutions…

So, I was just going over the main power supply board, looking to solve something that on paper should work, but in reality is less than ideal. The output of my monster transformer is somewhere in the neighbourhood of 42.6V with no load. That’s a tad high considering the maximum voltage differential of the LM317 is 40V and the current output seriously suffers when it’s that high. I had tried breadboarding an earlier version of the circuit to get a total fail, the regulator refused to even bother to regulate. So, I figured an easy way to drop some voltage would be to use a bunch of series power diodes to drop 0.7V each, so I inline-soldered 6 of them to drop 4.2V (when under load) down to 38.4V. Looks nice and bodgy, i’ll post a photo at some point, looks laughable.

Though this approach sort of works, it is far from elegant, ugly, and I’m not entirely sure reliable. 38.4V vs. 42.6V is not that great a difference and still dangerously close to that maximum voltage differential. Not only would I like more padding for safety, but for more reliable operation that dissipates less heat.

The general calculation for linear regulators and power dissipation is given by: ( VIN – VOUT ) * IOUT. Even with passing most of my current via a pass transistor, the LM317 will dissipate an unacceptable amount of power. I read somewhere that the absolute maximum dissipation is on the order of 15W and at full load and minimum voltage, I calculate that it will dissipate 9.3W. Though this is under the limit, the wide differential voltage could potentially cause problems. Also, I just don’t like it. Yes, it’s my first power supply – but I want it to be a good one I will want to use for years.

Zeners to the rescue

A little googling around revealed that I could use a transistor, Zener diode and resistor to act as a voltage regulator. In this case it would be a pre-regulator and would drop the voltage down to about 30V which would solve the above issue. I found this circuit from Elliot Sound Products, a site I’ve been liking for several years now as most of his projects are for audio. The entire site is full of not only useful circuits but in-depth explanations, I highly recommend it. Turns out this technique is used all the time in audio amplifier applications for this exact purpose.

The mechanism of action is quite simple – use a zener to bias the transistor and the voltage drops by the zener voltage plus 0.6V. So a 12V zener would knock down my voltage to pretty much exactly 30V. Nice and tidy

I looked back at my schematic and didn’t like the idea that I would have to add yet another transistor pair and more circuitry. It then occurred to me that I’m already kind of doing the same thing with my current limiting darlington transistor which drops the voltage in response to hitting the set current limit. If I bias this transistor properly, I can essentially achieve the same effect without adding in another transistor and keep my circuit mostly as it was. Brilliant. Of course, I’ll need to simulate and then do a test build to make sure it won’t catch fire.

By my (inexperienced) reasoning, I believe I can combine both functions by using a 12V zener to bias the transistor from the positive rail, dropping it down to 30V by default, and keep my other transistor which will open to ground if the current limit is reached. Hopefully, this will still drop the base, when the current limit is exceeded, to 0V and thus zero current, shutting it down.

I have to point out here – I really have very little clue what the hell I’m doing, so if you try this I’m not in any way responsible for what may happen to you. Do your research and use caution. I’m learning out loud. If you have any comments on the above please post them, I can use all the help I can get. For myself, I’m not trying this until I simulate it first.

I’ll post schematics and simulation analysis when I have it.

Opamps and something I didn’t think of…

This process also brought to light something I completely forgot about. Using simulation, the opamps were omitting their power rails as is often done on schematics assuming rail to rail operation. In reality, these opamps would have a supply voltage, and the output of said opamps is limited by this. Under ideal conditions, the opamp would be rail to rail and be able to handle the full 80 odd volts (since I have to power them before all the regulation happens to ensure operation). I’ve never seen an opamp that can handle 80V rail to rail, though it wouldn’t surprise me if these exist … and are expensive as hell.

Really, I have no need of such precision and such a wide voltage swing in my outputs. The opamps are used to manage the set voltages for the current limit and voltage regulation. Using the idea from Dave Jone’s excellent power supply videos, I use a 1Ω current shunt, and a bunch of opamps to compare a measured current to a set voltage and keep the two in line allowing me to set the maximum current allowable. For the voltage setting, the opamps are used to buffer, split and invert the signal so that one voltage setting can be used for both the positive and negative regulators so they track each other and avoid the messy issue of using dual-gang pots (also, I’ve never seen a 10-turn dual gang, again, wouldn’t surprise me if they exist but man that would be expensive).

Last night, before I slept, I chewed it over a little and figured out how I can solve this supply voltage issue. The requirements are that I need to have a 3V voltage swing for the current limiters and a 24V voltage swing for the voltage setting. The former is quite easy – I can use just a couple of standard LM3900 quad opamps since they can easy output a 5V swing. If I supply them using say ±5-12V that would provide an adequate swing for both positive and negative current limiting (whose desired values are 0-3V for the positive, -3-0V for the negative) and prevent going anywhere near either rail since these are not rail-rail opamps. I can use two LM3900s (one for positive, one for negative) and supply them both with at least ±5V using zener diodes. Lovely solution!

The voltage setting is a bit more difficult. In shopping about I had a hard time finding opamps with a supply voltage greater than 44V rail-rail, which is just shy of the 48V r-r I would need to set the voltages from 0-24V (and invert to negative for the negative regulator). Of course, they beauty of op-amps is that they are analog calculation machines, in essence.

The circuit as I have it uses 4 opamps which act as buffers and one inverting amplifier. It would be a simple matter to power the positive ones from 0-24V (the LM3900 has, I believe a ±16V supply limit, giving me 36V if I were to single-supply power them) and the negative ones from -24-0V. The one inverting amplifier would, according to my reasoning, have to straddle the negative and positive voltage rails in order to invert the signal. Here’s the neat bit: to overcome having to convert a maximum of 24V to -24V (and use the associated > 48V power supply) I can simply convert the buffers leading to the inverter into variable gain amplifiers to divide the voltage in half, then invert it, then multiply it by two. This way the inverting amplifier can run on half it’s supply voltage (24V, -12V – +12V) and stay well within it’s limits. I’m not sure how much precision I would lose in this conversion but it would afford me greater control of the symmetry between the rails as well if I add in a couple of trim pots on the gain of the divide-by-2 and multiply-by-2 amps. The supply voltage for the all the amps can be easily accomplished using zener diodes in various configurations.

I know some of you are screaming at my already to use a bloody microcontroller and stop fiddling about with messy opamps. Really – I want to do it this way. I feel that in my self-education, I want to use opamps effectively and get a good understanding of analog electronics before pushing on to digital. This is why I am trying to keep the power supply entirely analog, which I have done so far apart from the meters.

Edge Animate

I always try to follow up a negative, ball-slicing rant with something positive. Both for my own mental health and those mysterious ghost readers of my blog (which I probably don’t have anyway).

Adobe is usually one of my favourite companies to take a crap on. Sure, they often deserve it. Being so big and bloaty and annoyingly necessary. This time though, they’ve really done it.

I’m talking about Edge Animate.

Stop the world, you’ve finally done something GOOD and USEFUL. I’m surprised I’m saying that. Just saw a talk this morning at FITC  from Sarah Hunt from Adobe. Quite frankly, i’m impressed.

Get this – what if you could have flash-like animations without flash? What if you could animate something pretty damn cool without having to hand code every transition? What if there was a visual tool that marries javascript and css to produce these lovely animations?

There is: Adobe’s Edge Animate.

If you are familiar with Flash or After Effects, this will be a breeze. Hell, its better than dealing with Flash and its annoying tweening system. Make your vector animations using their keyframe editor, handily making automatic keyframes and transitions (formerly known as tweens for the former flash heads) . Then, you get to spit them out as a bunch of css and js files. That simple.

About time. Though I feel bile rising in my throat in grudging, I have to say: “thank you, Adobe”.

Fax machines must die

A client recently offered to ‘fax’ something to me. Yikes. In his defence, he’s old school and wanted to send me the latest batch of changes to a visual product we are producing. We settled on the scan-and-email solution, which I prefer and has been the only proper way to do it since the year 2000.

The first fax machine, as we know it today, was made by Xerox in 1966 and could send a letter-sized document in blistering six minutes! Wikipedia has the whole sordid tale if you’re bored. Anyway, to the particularly beaurocratically obsessed office workers of that time, it must have seemed like a tech-filled wonderland future-world would soon blossom, where you still had to write your friggin letter out with a pen in handwriting no one can read especially after the mojo-wire mangles it and sends it to the recipient by sometime next month.

Or it could just have been the harbinger of a dystopian nightmare future played out in office scenarios around the globe featuring normally level-headed corporate drones who suddenly lose their cool and become violent animals when the damned thing malfunctions. We all saw that scene in Office Space so don’t tell me its not true.

Did you know a certain precursor to the fax machine was a German invention aptly named ein “Hellschreiber“? Serious, here it is:

The dreaded “Hellschreiber”

Fast forward to a few nights ago. I’m sleeping. For those who know me, I’m a light sleeper and really resent anything (or anyone) who disturbs my precious slumbers. So you can probably guess about how I feel about my cellphone going off at 3:19am. Of course I ignore it, and check the voicemail next day amid mumbled promises to break the legs of whomever called me. Great. I hear the tell-tale “beep….beep” of some douche trying to fax me.

That’s the worst. If some poor person calls me at three in the morning and merely has the wrong number, he’s going to feel bad about it. Especially after the hot dish of burning fuck I’m going to inject in his ear for doing so.

With a fax machine, there’s no human to beat up. Especially one coming from a blocked number. WTF. Isn’t that illegal or something? Why is someone trying to send a mysterious fax to my cellphone? If they had the caller ID programmed, I could call them back on their voice line and deliver the aforementioned burning dish.

The hell does not stop there. Pop quiz: what does a fax machine do if it cannot connect to another fax machine on the number its trying to dial? It calls back. THREE FUCKING TIMES.

So lets take this in stages for the unbelievably dim-witted. Here’s ten good reasons not to use fax machines. I’m not one to limit myself, so if you know of any I have forgotten, please feel free to add in the comments.

  1. They waste paper, a shit-ton. Especially in printing out those useless tx/rx reports that no one ever reads.
  2. They make annoying noises — beeps squaks and squeals, both when you are standing beside one, within earshot and trying to concentrate on something, and shouting at one through the phone to stop calling and hoping the douche who’s sending it can hear you through the crappy little speaker.
  3. The fax machine has no way of knowing its a voice line or a cell phone, and yes you are bloody well disturbing someone.
  4. No one ever cared about fax marketing. It moved to email once the Nigerian princes of the word caught up to 1995. People used to care about it back in the day though, for the exact amount of time it takes to curse it for wasting paper.
  5. It eats more documents than it sends or receives. Serious, why do they have the crappiest sheet feeders?
  6. Its always out of paper anyway (pilfered for the actually-useful laser printer doubtless) and probably has something like 12kb of memory — which doesn’t hold dick.
  7. It ties up an expensive phone line, sometimes helpfully answering it for you. When it does, the potentially large client on the other other end is greeted with “beep” instead of hello. He then hangs up the phone and NEVER calls you back
  8. A cheap piece of crap scanner you can buy from anywhere can scan your document at much higher resolution, in full colour, and in a tenth the time
  9. There is not a single place on this earth you cannot get to the internet somehow (there are satellites) unless you are at the Earth’s core or something, then you have other problems
  10. Scanner + email = something that not only completely replaces the fax machine, but is superior to it in every way imaginable (and is constantly improving, which the fax machine has not done in decades)

So you can see, any argument you could possibly have is completely invalid. You may try and post them in the comments below if you dare. I will use them (and you) for my amusement.

Don’t you dare give me that crap that starts “I’m a lawyer…” or realtor or government worker. The only reason you use the damn things is because there are a thousand other neanderthals out there who use insist on using it. It’s like crack or Microsoft Word — all pain and peer pressure. If everyone insisted on using scan-and-emailed document, no one would have any reservation about consigning the fax to whatever hell it came from.

World, stop using fax machines and let me have an uninterrupted nights sleep. Now, some catharsis:

Blog under development, please excuse the eyesore.

I’m currently messing with my stylesheet, so if it looks like hell, that’s the reason. Come back another time to see if i’ve sorted it.


Hello world!

oops! forgot to #include stdio.h, dang.

well, its here! Now to start messing with it and do something useful