Remember way back in the early 1970s when you would watch Star Trek? Remember how much you wanted to have a Tribble of your very own? Well, now you can! You just have to build it ... using the stone knives and bear skins of 1970s era semiconductor microelectronics. These are instructions for how to build your own purring, electronic Tribble (almost just like from Star Trek) using digital CMOS Schmitt Trigger NAND gates as analog oscillators. The instructions include theory of operation and construction, electronic schematic diagram, parts and tools lists, and detailed, step-by-step description of how to assemble the project.

Back in the late 70s, when I was in high school, I used to build these and give them to girls I had a liking for. I even managed to get a date or two from some of the recipients. Heh, the life of a high school science geek. Well, anyway...

The first few specimens I built used three 555 IC oscillators slaved to each other. After those first few I'd made of 555 chips I started thinking about how to make an equivalent circuit out of fewer, cheaper, more clever parts. Like 4xxx series CMOS inverter gates. After all, almost anyone can build a three-oscillator circuit using off-the-shelf oscillator IC chips (or a microcontroller, for the more sophisticated).

Step 1: Theory (such as it is) - waveforms

As noted above,this version of the electronic Tribble consists of three simple oscillator circuits: main "tone", modulation, and "breathing cycle". The main tone is at a few hundred Hertz, the modulation is at a couple dozen Hertz, and the breathing cycle is at about a third of a Hertz. The oscillators are made of a form of CMOS gates and simple RC networks.

Why CMOS? High circuit impedance and very low current requirements lead to long battery life and, as we'll see below, lower parts cost and better "character" in the finished toy. Why CMOS 4xxx series? Because they can be run from a wide voltage supply: from 3 to 18 Volts -- just the thing for a toy using a 9V battery as a supply.

Aside from its extremely low current requirements digital CMOS provides a few other advantages in this analog application. First, the extremely high impedance of CMOS circuits leads to increased "noise susceptibility" -- the opposite of noise immunity -- which is something that we want in this application. Nose susceptibility adds character to the Tribble. The extremely high impedance and low internal leakage of CMOS also allows us to use small capacitor values and high resistor values in our RC networks. Resistors (of a given precision and thermal dissipation capacity) generally cost the same regardless of their Ohmic value. The same is not true of capacitors; the higher capacitances tend to cost more, and be of larger physical size, than the lower ones.

But perhaps the main attraction of using CMOS gates is the satisfaction of knowing that you are using digital logic blocks to do an analog task. A corruption of logic ... so to speak.

Some of you may have seen oscillator circuits that use simple inverters, and you could certainly build our three oscillators from a single hex inverter IC, but then you would still need a way of multiplying (AND-ing) the outputs together. Worse, since the inverter circuits require two gates per oscillator they are not the most clever, parsimonious way to build this particular toy. Therefore, the IC that I've selected for this version of the Tribble is the 4093B quad 2-input NAND Schmitt Trigger. It can provide all three oscillators as well as do the multiply/mixing of the signals.

(Actually, I would have used a hex Schmitt Trigger inverter, the 40106B, if I could have found one at the store. As I'll show below an oscillator using a Schmitt Trigger needs only a single inverter. Perhaps I'll do that one another day because it is even more interesting than the current design as an example of Micky Mouse logic and applied bullshit.)

Figure 1 shows the voltage vs. time graph of the three signals we want to mix (and the mixed result). Red traces are the RC voltages. Blue traces are the outputs from the "inverters" (actually NAND Schmitt Trigers) of the stages.

Figure 2 shows the three signals multiplied (AND-ed) together.

Note that the frequency ratios in the figures are not to scale.
you could just buy one from <a href="http://www.thinkgeek.com" rel="nofollow">www.thinkgeek.com</a><br />
Thaw would be boring ;)
True true :P
This is great! Do you have a video?
Nope. I don't have a video of the construction process nor of the device in operation. I don't think I have a sample device anymore. Gave it away.
Apparently the original tribbles had windup motors from clockwork toys in them - no electronics at all - the sound effects were put in afterwards (and I'm not even particularly interested in Star Trek!)
Could you clarify?<br><br>Tuning is managed by means of capacitance alone, or a combination of capacitance and resistance? Seems they should be interdependent values and some alteration might be achieved by means of preset variable resistors.<br><br>I have a slightly different project in mind and something that makes wibbly-wobbly noises at different tones and frequencies would be fun.
Yes, timing (or oscillation period) is proportional to the product of R and C: T ~ RC.<br><br>However, it is best to go with small C and big R for a given T because the cost of a resistor is basically independent of its resistance value while the cost of capacitors generally is higher for higher values of capacitance. Also, it is better to use low precision resistors (20%, if they are even still made) for this project because they are both cheaper and have more &quot;character&quot;.<br><br>None of the electronics in this project are intended to be precision in any way. After all, we don't want Tribble clones, do we? (Yeah, yeah, they are born pregnant, I know. But they weren't all identical in the show.)<br>
they also make good watch dogs for Klingons &nbsp;
Oooo!!! I lke the tribbles they make some peple laugh but they are great to have if you dont feel good kinda like a shmoo
it's not going to multiply and eat all my quadrotriticaley (cerial made of wheat)? is it?
Welder Guy, Multiplication may well be an hazard with these as they are built of NAND gates. AND is the primitive for the binary multiplication operation. It would only take two of the NAND gates that go into this beast to make a simple 1x1 multiplier: one for the A, B inputs (with NOT AB out), and the second NAND as an inverter to make the output AB instead of NOT AB. Of course, in the "authentic" Tribble configuration both A and B inputs would be tied, perhaps via a suitable RC delay, to V+ (they're born pregnant, you know). I make no warranties for the safety of your quadrotriticaley. David
i'm sorry dude but i have no idea what you just said in the paragraph. i understand electronics and electricity well but i don't understand gates. i'm still reading about it
whos the cute chick in the uniform! i love star trek
My wife. She says "thanks for the compliment."
Nice electronics, but I missed that episode of Star Trek. What were the treibles? Just furry, purry things that breed like rabbits?
Unit042, Yup. The episode was called "The Trouble With Tribbles" and it was in the original series. David
Oh. I was born in 1991, but my dad watches it because it comes on TV for free. I never liked it because there was hardly ever any starship fighting, and when there was, the Enterprise would be beat up and chased away by ships half it's size(70%, 40%, 10%, need more power to the sissy shields, scotty!). Oh, and Kirk is so stupid the way he constantly beams himself onto unknown planets and always gets taken hostage along with his entire bridge crew... does he WANT to die?!? But I'm ranting. My favorite episode/movie was the wrath of kahn (I think it's somewhere on the movie shelf....) because of the knock down drag out fight that the starships had. Didn't like the ear worm/leeches much--yuck.
Unit042, Yeah, the original series did have quite a number of irritating things about it. But, at the same time, its many of those same irritation points that give it the high campyness factor that is so enjoyable. Also -- and I guess this is probably true for many "old school" Trek fans -- I grew up watching the show and when I see old episodes from it I remember more than just the show itself. David
Campyness? I've not heard that one before.
<a rel="nofollow" href="http://tv.msn.com/tv/">http://tv.msn.com/tv/</a> has most of the old Star Trek episodes. I don't know if tribbles are there but it is worth a look for Trek fans.<br/>
duckythescientist, Thanks for the pointer. David
For the AND-ing, you could have used three transistors/MOSFETs in series with a high resistance, well, resistor going to GND, to provide a low while all MOSFETs/transistors are off. PS: as of this second, I've only gotten to step 1, but this looks like cool electronics, with oscillator modulating. i think I might try something like this.
Unit042, You are correct. I looked at using one of the CMOS ICs (I think its the 4007) that have simple transistors on them but decided that it would add another whole chip. There are pretty much an unlimited number of ways to build this three oscillator device. This version is probably about the 5th significant design variation I've used. It all started out with three cascaded 555s. David
Yeah, so many ways to skin a cat. I don't care which way is used, as long as the cat's skin comes off.
WOW great instructible this is how everyone should do it. Great job!!! A++++
GWJax, Thank you for the acknowledgment! Heh, I just worry that if I make another instructable that it won't come up to the standard I seem to have set for myself. The trick is to do the project twice and write the instructable on the second assembly so you know in advance what is going to be tricky or need added detail. Anyway, that's what I did with this one. David
Well I guess you just have to do the next project 3 or 4 times to get better then, just kidding it's still great! Still would like to see more but if this is the last then it must go into my favs. hehe you hould have put this into the robotics contest befour it closed. maybe next time. Jax
Jax, I don't anticipate this'll be my one-and-only contribution to the Instructables site. Hmm, robotics contest, eh? I guess the fur would have really flown. David
Very nice, well-written Instructable, the informative kind that makes this site so interesting. Loved the stone knives and bearskins reference, too.
Great instuctable...this would make a great gag hair piece...kinda looks like my uncles...lol
Great job! Now THIS is what an instructable should look like. Excellent documentation, lots of pictures and detailed drawings to explain, and in-depth detail in the text on a somewhat complex subject without being boring. This is magazine quality, in my opinion.
Retro, Thanks for the positive review. I was not sure what the correct level of detail would be (its my first Instructables posting). Glad I got it right. I have the instructions in "article" format already since I wrote them offline and then posted them part-by-part on the site. If any magazine is interested in them (MAKE, are you listening?) they need but ask. David
Yay Tribbles! This is quite like a kind of stuffed toy I make, although much more sophisticated. Mine is <a rel="nofollow" href="http://www.instructables.com/id/Big-Warm-Fuzzy-Secret-Heart/">here</a> - it is merely a cell phone vibrator motor activated by a fabric pressure switch, so does not have nearly the character yours does, but it's the same family. My friend and I even taught a workshop on making these simple ones, at the recent <a rel="nofollow" href="http://www.makerfaire.com/">Maker Faire</a>.<br/><br/>Another more fanciful related toy is the <a rel="nofollow" href="http://www.instructables.com/id/Snailbot-Races/">Snailbot</a> (original by <a rel="nofollow" href="http://www.evilmadscientist.com/article.php/snailbot">Evil Mad Scientist</a>).<br/><br/>I've also made a more complicated Tribble using a Qprox touch sensor chip and a wire antenna sewn to the inside of the fur covering. The touch sensor works, I believe, similarly to your variable capacitor (my understanding is that it's a capacitance sensor), and I used the same tiny vibrator motor which in this case is triggered when the Tribble is petted. I don't have an instructable on that as I only made one so far and it was kind of sloppy; I took it apart to see what I'd done so I could make another, and that's where THAT project is at just now. I do plan to write it up when I make the next one.<br/><br/>I will probably have to make yours, too, just to round out my Tribble-making powers (I will post a picture). The instructions look super clear and detailed! It will also help improve my electronics knowledge which is still pretty small. <br/>
I love how Kurk got rid of the Tribble problem. Scotty: "Well, we beamed them to the klingons ship cap'tn"
I have a commercial variation one that was called a<em> Dreeble</em>, it came out in the 80's I think. It had 3 switches inside and if you pressed lightly it purred, too hard(more then one switch activated) it squealed. Looks just like that one too (but how do you tell one Tribble from another?)<br/>
nnygamer, I remember those. Didn't get one. David
David: Cool stuff! (Nostalgic comments w.r.t. 40xx-series CMOS elided...). Have you tried making a variable "squashable" resistor out of black conductive foam? (You would eliminate C4 and put the foam in series with R3.) As often as not, you get the foam for free with the CMOS part, which is in keeping with the elegantly minimalist approach of your design. - ff
ff, Nope, I've not tried making a variable "squashable" resistor out of black conductive foam for the third oscillator stage. Let me know how it works out if you give it a try. A few of my earliest Tribbles had a FET as part of the third oscillator stage. The FET's gate was connected to an "antenna" that responded to the presence of external electric fields (such as found on people) and would change the oscillator's pitch. These early models also had a switch in them to bypass the pushbutton and leave the Tribble on continuously (or to lock it off). The behavior of the FET circuit was amusing when the Tribble was left on. At first it would purr in its regular "breathing" cycle but, as the charge on the antenna leaked off, it would settle down to a sort of quiet "snoring". If someone then went near it the Tribble would suddenly "wake up" and revert to its regular purring / breathing cycle. Almost like a living pet. I think I still have the first one I built somewhere (lost in an unlabeled box out in the garage, no doubt) and it has a FET circuit in it. David
Nice! One observation - one of your R3s in the layout drawings s/b R4 ...
ncorison, Thanks for catching that. I've fixed it. David
<em>Back in the late 70s, when I was in high school, I used to build these and give them to girls I had a liking for. I even managed to get a date or two..</em><br/><br/>Heeheehee. Great job on this. It's how electronic instructables <em>should</em> be done.<br/>

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