Saturday, December 22, 2007

black magic

If you measure an optocoupler's output while driving its input directly from a 9-volt battery, you get a 2-leg transistor.

laugh! ha ha ha!*

You can still use it as a temperature sensor or maybe even as a radiation sensor.

"Merry fucking Christmas!"**

*) I HATE those movies where they insert laughter in the background whenever some idiotic underpaid actor recites some funny line. It's an insult to my sense of humor. Is it like, am I too stupid to figure out for myself when to laugh and when to go take a shit? Good comedies never insert that stupid laughter. Only mediocre ones that target mediocre people need to.
**) a famous quote by Mr. Garrison.

Thursday, December 20, 2007


As I said before in posts such as this, fuck environmental fanatism. People are part of the environment, they're part of nature, they're not above it. They can't objectively protect it or destroy it, they evolve with it, they go with it, they live and die within it. All toxic materials created by human industry come from the Earth (where the hell can they come from, outer space?), so they're part of the environment. Everything on this planet is part of the environment: stones, critters, humans and all the tools and crap and toxins they produce. We're not hurting the environment with anything, but we might be putting ourselves in a position of being evolved out of it a as species, I mean killed and re-integrated into it as dead molecules. Species go extinct all the time and that's a natural thing. So quit worrying about stupid panda bears that don't like to reproduce and small furry mice whose 20-head population count doesn't really influence anything, and start worrying about yourselves. This guy says it perfectly and I totally agree with him, with absolutely every word and sentence. And he's funny too.

Tuesday, December 18, 2007


This article claims that monkeys are just as good at math as college students. Well, 'mental math' at least. I saw a documentary once where chimps would remember a sequence of numbers at least two times better than an average human. Of course we like to claim we're the best and shit, but think about this: it's pretty normal for college students to be as dumb as monkeys, given the fact that certain 'big' and 'famous' colleges teach courses about... how iPods allow you to create a personal music library.

Friday, December 14, 2007


CMOS integrated circuits are almost exclusively used in modern computers and stuff because they're small and profitable. They also sometimes consume little power when doing nothing.
Digital circuits using bipolar junction transistors are usually TTL, and sometimes ECL, maybe even IIL.
But BJTs can also be arranged just like MOS devices. I mean, why not. So without further ado, here is a CBJTS inverter:
(Complementary Bipolar Junction Transistors with Schottky).
The Schottky diodes can of course be omitted, but they make the circuit faster.
I shoud really build some of these when I find some time, as simulations tell me it's interesting. Apparently it can switch in 20 nanoseconds, works with a 1 volt supply and draws between 1 and 2 milliamperes depending on temperature. I guess the supply voltage needs to raised a little bit above 1V if multiple-input logic functions such as NAND are to be implemented in the same way they're done in CMOS.
Anyway, it should be fun. Just try to pronounce "cbjts". It sounds and looks cool.

Wednesday, December 12, 2007


British religious leaders urge people to cut the crap regarding Xmas. They're not OK with people trying do de-Christianize and neutralize Xmas for the sake of "religious equality" and "political corectness". That's right. It's not called Winterval (idiots) it's called Christmas and many people celebrate it just because it's a nice holiday, eventhough they're not Christian. Now that's a good example of sensibility and reason versus fanatical idiotic political-corectness.
On the other hand, "biologist" guy sues employer for firing him for being an evolution-bashing, close-minded, bible fanatic. Good. I hope he loses. So this is the difference between religion as a positive element in human life, that gives hope and meaning and motivation, and misunderstood religion that dumbs people down, and misused religion that's used as a pretext for war by people that have no connection with moral and ethics whatsoever.
My comments on the second article:
Dude, you can see evolution in the test tube. Why do you think bacteria are getting stronger and stronger each year, while researchers are battling to come up with stronger and stronger antibiotics? Because bacteria evolve through natural and artificial selection. Wait, sorry, I forgot. Bacteria don't exist because God didn't create them in 6/7 days in the Bible. Sorry. Didn't mean to say that. Idiots.
Furthermore, humans have created artificial evolution using Machines. For example, Computers can be used to evolve all sorts of stuff in Virtual Reality. Such as antennas/ae for communications. All Hail Machines, Computers and Virtual Spaces. People have evolved electronic circuits on reconfigurable fabric, that outperform even the best human-designed circuits. They look tangled and mysterious. They seem to have parts that don't do anything, that are apparently separated from the main circuit. But take them out and the main part ceases to function, because they're connected in subtle ways that human engineers intentionally neglect, as those couplings are uncontrollable and weak. So the artificially evolved circuits almost look alive. They evolve to fit their environment perfectly and profit from all its resources. Their only downside is their fragility - change the environment a little bit, such as a few degrees of temperature, and they die. We're working on that.
Anyway, just as I can evolve circuits inside a machine artificially, life evolves "naturally" on Earth. So evolution really doesn't exclude God or other deities, it's just that most scientists are not interested in God because God is sometimes very hard to see or contact. There is no problem with that, the problem is with all the idiots and fanatics that interpret in a literal fashion some old texts that have no traceable super-human origin.

Friday, December 7, 2007


A Santa was fired because he said "ho ho ho" and sang "Jingle Bells", two classic Western Xmas emblems. This happened because the word "ho" is supposedly insulting due to its "American slang" meaning of whore.
First of all, it's not strictly American slang, it's American ghetto contraction.
Second, it's American "slang", not Australian slang, and the stuff happens in Austrialia. So I don't get it.
Third, a lot of words can have very different meanings, and unintentional double entrende happens all the time without anyone in their right mind getting offended.
Fourth, a woman that would get offended by a Santa chanting the well-known festive "ho ho ho" may very well have a good chance of either being itself a whore, or terribly sexually frustrated.
Fifth, a man that would ban Santas from ho-ho-hoing is itself an idiot that has nothing better to do to and chooses to take such radical and unwarranted actions in order to justify its salary.
Sixth, Xmas is almost as bad as Valentine's Pay.
Seventh, it's not 'the word "ho," which is', it's 'the word "ho", which is'. The comma inside the quotes is illogical, and due to very old, outdated reasons having to do with the mechanics of typesetting.
Eighth, it's probably correct to write "ho' ", but who cares anyway.
Ninth, "They're trying to kill the spirit of Xmas", said the man who was fired. Notice the logically-correct use of punctuation in my case versus the original article, but what spirit of x-mas?
In some unrelated news, some Indian court decides women are allowed to serve drinks in Delhi. What an impressive sign of progress. Maybe in 10 years they'll be able to be kissed by men on their cheeks. Maybe in 100 years they could actually marry whoever the hell they feel like marrying. Make that 300 years. Maybe in 600 years they'll be able to tell between actually wanting something and being educated to want something. It's interesting to see how in a country plagued by poverty and overpopulation, people choose to worry about stuff like this instead of increasing the standard of living or something. They deserve their fate. Everybody does.

Monday, December 3, 2007


I've been feeling horrible lately and yesterday's night out didn't help much. So I decided I had to pop something off the project queue and just do it. A night of testing capacitors revealed some interesting results. Here is the story:


Whenever you need to power electronic stuff you need a constant voltage source. Circuits are specified to work for certain supply voltages, for example 5 volts plus or minus 10%. Circuits also like to draw different amounts of current depending on what they're doing, and that's bad for the power supply, who must struggle to keep a constant voltage output as the current demand from its load varies in time. So what happens if the power supply is suddenly required to provide more current for, let's say, a processor that's waking up from sleep and starting to do some work. Or a light or motor or something. It's bad. It can't keep the voltage constant. The voltage will drop for a very short time until the supply can sense that through its feedback loop and stabilize it. If it drops more than 10% or whatever the design margin is, the circuits might malfunction. When the circuit is done working and reduces its current demand, the opposite thing can happen and the supply voltage overshoots for a short amount of time. It it overshoots too high, the load circuit is fried.
So how can we fix this? Well, it's very simple in theory. Don't change the load current abruptly, so the supply has time to follow it and compensate for its change and mantain constant voltage output. The simplest way to do that is to throw a capacitor across the load. If the supply is slow to respond, the difference in current will come out of the capacitor instead of the supply, and the voltage variation will be much lower and everyone's happy.
Because the supply voltage is now constant, it means that various modules can't talk to each other through the supply wires (which would be bad), so they're being decoupled. That's why they're called (supply) decoupling capacitors.

My Problem.

People have always recommended using many small ceramic capacitor near integrated circuits and a few big electrolytic capacitors. The idea is that ceramics take care of the higher frequencies (rapid current variations), while the electrolytics deal with the lower ones. For a long time I've been wanting to actually test the effect of different kinds of capacitors on a power supply that's required to quickly switch between two values of current. Now I decided it was finally time to do that.
So I took a piece of copper-clad board and cut some trenches in the copper, isolating two big islands for the power and ground nodes where the action takes place, and some small islands for the other voltages. I soldered a good-old 7805 voltage regulator with capacitors on the input but not on the output, and a genric transistor that would suck a little bit less than 100mA when turned on by a signal generator. Some ports for the control signal, oscilloscope and raw power input, some very tight construction to avoid "parasitic inductance and capacitance", and it was ready. So here's the schematic:
Notice the Schottky diode connected from base to collector รก la 74LSxx. It diverts control current from the base to the collector whenever the collector voltage drops too low, preventing the transistor from saturating. That ensures fast switching.
So here is how the regulated voltage (that's supposed to be constant) looks like when current is switched on and off.
First, with no capacitor at all:
Notice the almost 2V undershoot and 0.5V overshoot. That's... quite bad.
Here you can see a zoom-in on the negative spike:
The oscilloscope samples at 100MHz, so that's 10ns between samples. The spike is just 3 samples. So it takes a bit of luck for its peak to coincide with the moment the sample is taken. Most of the time the peak falls before or after the sample, and the drop in voltage appears smaller than it actually is. You can see that in the first picture, where the drop is only around 1.7V, while in the second one I waited for a lucky sample and you can see the full 2V. Even after the spike is quickly dealt with, it takes a lot of time to compensate for the remaining half a volt. The same can be said about the 0.5V overshoot. I mean, 2 microseconds is a lot of time.
So I soldered in a 4.7 uF (microfarad) electrolytic capacitor, rated for 63V, and here is what I got:
The red trace is the control signal. The current is drawn when the control signal is high. You can see an enormous improvement: the spike is gone, the drop is now only 100 mV (20 times less) and the overshoot is only 50 mV (10 times less). But it still takes about the same amount of time to stabilize. Anyway, while the first case would almost surely upset 74xx logic circuits, in this case they'd function allright. With no ceramic capacitors, mind you.
Then I did something horrible. I desoldered the capacitor, which was soldered close to the board, and put in a new one, holding it with my fingers. Its leads were about 1 inch long, which is supposed to be a big no-no: long leads means inductance, which slows down "reaction time" and prevents the capacitor from absorbing rapid current variations, leading to the voltage spike you saw in the first picture. But it was not the case:
The 1 inch of wire did nothing noticeable, and that's in agreement with what the theory says. The oscilloscope samples at 100MHz and it's supposed to record signals at least as fast as 60MHz. How can you record a 60MHz signal on a 100MHz oscilloscope whose Nyquist frequency is only 50MHz? Figure it out, you most certainly can. So if, per Google, light travels 30cm in one nanosecond, it travels 3 meters in 10ns (that's 100MHz), which is much more than the 3 cm of the capacitor's leads. So they shouldn't matter that much.
Next I connected a 10uF, 16V tantalum capacitor. That's supposed to have a better frequency response than the usual electrolytics, as well as lower ESR (effective series resistance) - the stuff that limits how well it can filter spikes (think voltage drop over the ESR caused by the current you draw from the capacitor). It looks a little better:
It's got a weird shape now. Oh well.
Here's a 22uF, 25V electrolytic with short leads (it's 20mV/div as before):
Worse than the tantalum.
On all the pictures you can see the command signal feedthrough: when it goes down, the current is shut down and the voltage goes up temporarilly. But before the current is shut down and the voltage goes up, you can see a small downwards spike that's caused by the current injected from the command signal through parasitic capacitors. Because it's very fast, it gets through (it's coupled even through very small parasitics).
Next I connected a serious 100uF/50V capacitor with 1cm leads. You wouldn't normally want to use less than 100uF for decoupling a usual circuit. The improvement is clear:
Now comes a 470uF/16V one, which is a little better, but not by much:
Here is a 2200uF/10V:
And a bigger 2200uF/35V:
same, with 1 inch leads:
You can begin to see that indeed, very fast spikes are filtered by the electrolytics worse than slower variations. That's what ceramics are for. Long lead lengths do add inductance (especially on the bigger capacitors where the leads are spaced farther apart -- it's area, not length that gives inductance) and spikes do get noticeably larger. You also couldn't see the effect of leads on the first capacitor (4.7u) because, well, look: 500mV per division sensitivity there versus 20mV per division here.
So if you want to get rid of those fast spikes, electrolytics are by no means totally useless as some might say, but a ceramic does a better job, especially if it's a low-inductance SMD (surface-mounted device) that has no leads.
Here is a 100nF ceramic disc capacitor, rated for 2kV (it's quite big for a ceramic, 1 cm in diameter), with ~1cm leads:
Oops! :D It looks like the 7805 is oscillating when 100mA are pulled from it and a 100nF capacitor sits on its output. It's something that's mentioned in some datasheets, but not in all. Many voltage regulators are stable with low or high capacitive loads, but not with medium ones, and it also depends on load current. You can see some nice stability graphs in the TL431 datasheet from TI if I remember well.
The nasty thing is that it's a high-frequency oscillation, about 5MHz. It can go totally unnoticed if one doesn't have an oscilloscope, and low-frequency circuits would start acting in all sorts of weird ways. Plus, you don't want radio-frequency oscillations if you don't need them, because they could radiate and interfere with stuff. If they don't radiate directly from the circuit board, then signal and power wires on outside connectors are incredibly good antennas.
RF oscillation aside, a very important thing must be noted: no more fast (10-20 ns) spikes. You can see the fast voltage drop is slightly longer than with the electrolytic capacitors. That means better high-frequency filtering. But don't expect any low-frequency filtering from such a small capacitor - There's still a 1.2V drop.
At this point I soldered a 10nF SMD capacitor very close to the switching transistor. The oscillation is now much weaker, and you can see it's dying out - that's just my luck, the supply could have oscillated with 10nF just as well, and I would have had to find another value.
Notice the slightly deeper 1.5V drop (smaller capacitor), but still no fast spikes. It actually works better that the 4.7 uF electrolytic, which is almost 500 times bigger :)
Here you can see the steep drop that's not nearly as steep as with no capacitor:
The samples have been highlighted. It's at least 20 times longer.
Here is the 100nF ceramic added in parallel:
Interestingly enough, there's no more oscillation. Well.
Here's the tantalum added:
There's that strange shape again, and hey, there are spikes. They were always there, but just as with the 4.7u, we were looking on a 500mV/div scale, and now the filtering is so good we had to zoom in to 20mV/div and the spikes are now revealed. I have a suspicion that the spikes might be coupled inside the oscilloscope, which is also a signal generator and outputs the switching control signal. So I have to generate the signal somewhere else, but I already took all the screenshots for this article and packed all the stuff up before realising this now, so hell. I also really don't get why adding the tantalum speeds up the initial drop, it probably has something to do with the regulator, not the capacitor.
Anyway, here's a zoom-out with just the ceramic 10nF SMD capacitor:
Now here's the same, with a pulse frequency 10 times lower:
Damn it, it WAS oscillating :))
You can see two modes of oscillating, one high-frequency on turn-on and one low-frequency on turn-off. They both die out, but it's still not good for supplying a circuit.
Here are both ceramic capacitors:
Just as with the faster pulse repetition rate, the high-frequency oscillation is gone; but the low-frequency one persists, and it's interesting to note it's slower when both caps are added.
The tantalum capacitor kills it for good, but gives that weird shape on turn-on:
Here's a zoom-in of that:
Here's the turn-on for the "normal" 100uF electrolytic:
And the turn-off overshoot, complete with command feed-through spike:
Until now I've been switching between 100mA of current and almost nothing. This is quite hard for the supply to deal with, hence the 2V drop when the current was turned on with no cap.
So I added another 50 ohm resistor directly on the output, so I would switch between 100 and 200mA.
Here it is, with the 10nF SMD capacitor:
High-frequency oscillation with 100mA (strange, it didn't use to do that!), which ceases with 200mA (I was talking about stability graphs earlier). The effect might be caused by the fact that, as you let more current through a transistor, it becomes faster, and this happens inside the regulator chip.
The 100nF ceramic stops the oscillation:Here is the 10uF tantalum:
And here is just the 10nF SMD (first graph in this sequence), with the repetition rate increased 10x. It does look similar:
But it wasn't oscillating at 100mA before I connected the 50 ohm resistor! wtf? To answer, here's a graph after shutting down for 3 minutes to take a wee:
Yes, it's the regulator chip temperature. You can actually watch the oscilloscope as the chip warms up (it does get pretty hot with 150mA average current, significantly hotter than with just 50) and suddenly the mild, damped oscillation turns into the ferm one I was puzzeled by. Then put your finger on the chip and it ceases. Or just blow hard. Fun.
I took out the SMD cap and here is what I got:
and a zoom-in:
The spike dropped from 2V to a little over 100mV, as a consequence of switching 100mA next to the existing 100 as opposed to "suddenly waking up" the regulator in the first case. Also compare the graphs taken with the tantalum cap. The peaks are smaller in this case also.This is normal, and almost no datasheet specifies transient performance ("load regulation") with the current step starting from zero, just because their numbers would be awful :)
Next I had to debunk a myth related to electrolytic capacitors. It seems that electrolytic caps get worse as they get older: their capacitance decreases, their ESR increases, their ability to filter decreases. So I took some capacitors I had lying around that I had taken out of some old monitors for the specific purpose of testing them. Now the time has come! :)
I should point out that said capacitors come from a scrapyard and have been rained on repeatedly. The other components on the PCB had their leads severely coroded. Compare with fresh off-the-shelf 10uF tantalum and 100uF electrolytic seen a few graphs above.
220uF/100V (higher voltage ratings supposedly have lower ESR -- good) :
330uF/250V (very big, 1 inch diameter, 1.5 inches long)
This last one was quite big, very light, and different construction from others. Obviously filters less well, but that's acceptable, I guess it was designed to sit in the mains input circuit.
Well, there you go. Dirty old rained-on electrolytics filtering very well, quite better than new ones I might say. Of course, if they've leaked or grown internal pressure, scrap therm.
Now to try some film capacitors. These are big, but designed for high voltage, high current use, and I guess they also have less leakage than electrolytics.
Here is a huge 1.5 inch, 3.3uF/400V from the same scrapyard:
I guess the capacitor itself is resonating and I'm getting those damped sinusoids. I can't be sure until I pulse it in a passive circuit.
Here is a smaller 330nF/250V with its leads spaced about 1 inch apart:
This also seems to shoot up when the current is increased, like the previous two caps, and unlike all others. I'll investigate this further some other time.

In conclusion: when in doubt, use a bigger capacitor.