Lorenz Attractor (Horowitz design) - problems on pcb - Page 1
Forum section: electronics / beginners

author: qu1j0t3
author_rank: Regular Contributor
timestamp: September 28, 2020, 02:01:46 am
content: Hi allFor the past few months I've been working on the Lorenz attractor computer as described by Paul Horowitz:http://seti.harvard.edu/unusual_stuff/misc/lorenz.htm.I tested it extensively on a breadboard and it worked reasonably well. On the strength of that I decided to design a PCB from OSHpark with a few extensions (also tested by breadboard) such as four switchable integrator time constants, and a comparator based on X sign, with LED activity output and a 3.3v pulse output.When I assembled the PCB and the single fixed capacitor (C3,6,9 = 220pF), it ran fine (and fast time constant, as expected). Unfortunately after adding a switch and one switchable capacitor value, it stopped running reliably and indeed with the capacitor switched out, did not even run at fast speed. I have not found any errors in the PCB layout or switch pinout.Failure modes are: LED stays off; LED stays on; circuit sometimes runs for a couple of seconds with both capacitors switched in.One might think that some kind of parasitics from the PCB layout and the switch feature might be involved, but I can't think what. I also wonder if I am missing something with the integrator design (tried a 1MΩ resistor across each of the integrating caps—no change) or the integrator to buffer coupling.If anyone has any suggestions please speak up—this has been a huge investment of effort and I did not expect the PCB to behave worse than the breadboard.The KiCAD schematic:N.B. There are bypass caps on the op amps and comparator, not shown in this part of the schematic but visible on the PCB.PCB layout:

author: Paul Rose
author_rank: Regular Contributor
timestamp: September 28, 2020, 10:52:08 pm
content: You've probably already long since checked, but since it worked at first, and then failed after you put in the switch:Check that your 3x3 pad layout actually matches what the switch does.Check continuity with switch in various positions, make sure it is doing what you think it does.

author: qu1j0t3
author_rank: Regular Contributor
timestamp: September 29, 2020, 01:11:10 am
content: It never hurts to check again. I checked continuity with a meter again. Each switch has just 2 positions & the connectivity matches my schematic. Datasheet:

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 29, 2020, 02:11:30 am
content: You could start with making screenshots without overlapping texts, so they are actually readable.

author: qu1j0t3
author_rank: Regular Contributor
timestamp: September 29, 2020, 02:29:13 am
content: Can you specify what you were unable to read that is important?The silkscreening is just functional labelling, stuff that you could deduce from the schematic anyway.There are just 2 parts on the schematic whose labels overlap; D4 is an 1N4148; and D1 is a 4.7V Zener.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 29, 2020, 02:52:10 am
content: For me it's important to have all text readable.If you won't bother to sort out the text locations, I won't bother to look at the schematic. Simple as that.

author: qu1j0t3
author_rank: Regular Contributor
timestamp: September 29, 2020, 03:21:35 am
content: I've clarified the two parts which had overlapping labels. That's sufficient.

author: mawyatt
author_rank: Super Contributor
timestamp: September 29, 2020, 02:43:26 pm
content: There's a circuit based upon the Chua diode that invokes chaotic oscillation and produces a bifurcation result around two Lorenz attractors. Michael Kennedy published an IEEE article on such.https://people.eecs.berkeley.edu/~chua/papers/Kennedy93.pdfAt the time of Michael's paper we created and built a similar circuit (we synthesized the inductor with a gyrator), later the plan was to move this up into the RF/MW frequency. This was part of an "Analog Encryption" technique where serial digital data would be "encrypted" with the Lorenz Attractors coefficients and transmitted. A similar receiver would injection lock to the transmitted signal and recover the digital data from the signal by using the Lorenz attractors as "Encryption Keys". The idea was that if the signal was intercepted it could not be decoded without the proper Lorentz Attractor coefficients which act like analog encryption keys. We couldn't secure funding for the concept and a couple years later either MIT or Harvard published a paper on such.Earlier this year just for fun I created a simple SPICE version of the circuit and showed the bifurcated chaotic waveform hovering around the two Lorenz attractors. You can create different results by varying R between C1 and C2.Fun stuffBest,

author: qu1j0t3
author_rank: Regular Contributor
timestamp: September 29, 2020, 03:26:33 pm
content: Quote from: mawyatt on September 29, 2020, 02:43:26 pm@mawyatt Yes, I believe I have skimmed some encryption papers that used Lorenz.If this PCB can be debugged then it would provide a through-hole kit to experiment with the attractor (other people have produced surface mount kits for similar things). I also have a couple of spare OSHpark spins of it so I can give at least one away as a prize to anyone who helps locate this problem

author: mawyatt
author_rank: Super Contributor
timestamp: September 29, 2020, 04:02:43 pm
content: Quote from: qu1j0t3 on September 29, 2020, 03:26:33 pmI'm sure there are quite a few papers on this now, but back in early 90s nothing. The earliest I can find is this IEEE paperhttps://ieeexplore.ieee.org/document/982780. I wrote an article with measured results in the company newsletter somewhere around 1993 on this subject, and we tried to secure funding within the company and outside without success, so we never pushed this. We were just releasing the 1st MW single chip receiver in silicon at the time, so this took precedence and the Analog Encryptor was soon forgottenOn thing I remember from way back then then was Lorenz Attractors are very sensitive to component values, and a small variation could throw off the chaotic bifrunctation result. Also later remember a colleague had designed & built a low power SWPS that was producing way more "noise" than desired. Turns out this "noise" didn't look exactly like switching noise or Gaussian Noise, but was "Chaotic Noise". This SWPS was a Chaotic Oscillator created by accidentHope you can get your PCB working and have fun playing around with these Chaos circuits.Best,

author: BravoV
author_rank: Super Contributor
timestamp: September 29, 2020, 04:16:28 pm
content: Looking at the screenshots, this reminds me one of forum member work, not sure if this is related, check this out ->The Rössler attractor challenge.

author: SilverSolder
author_rank: Super Contributor
timestamp: September 29, 2020, 04:29:51 pm
content: Is this a single layer PCB? - I was thinking, if there is a ground plane on the back, might have introduced extra capacitance somewhere, messing with the circuit (and your head)?Another suspect might be capacitance between traces to the switch, or internally in the switch?

author: qu1j0t3
author_rank: Regular Contributor
timestamp: September 29, 2020, 05:03:31 pm
content: Quote from: mawyatt on September 29, 2020, 02:43:26 pmI had a look at your simulation results and they are just beautiful.Maybe there's a way you can share your circuit with me, it could be interesting to realise it on actual CRT displays. Due to my …uh… interests, I have access to a lot of XY monitor hardware.

author: qu1j0t3
author_rank: Regular Contributor
timestamp: September 29, 2020, 09:33:05 pm
content: Quote from: SilverSolder on September 29, 2020, 04:29:51 pmDouble layer, but very sparse. There's no ground plane at all—something I thought might turn out to be a problem.Not sure about capacitance between traces, but the circuit ran pretty well on a breadboard. I don't think extra capacitance should be a problem around the switch, as it's literally switching integrator capacitance in and out, from 220pF up to around 1µF?

author: SilverSolder
author_rank: Super Contributor
timestamp: September 29, 2020, 09:44:41 pm
content: What sort of frequencies does this circuit run at? E.g. what are the max and min frequencies you would expect to see here?Assuming you copied the working breadboard circuit perfectly, consider that the breadboard might have had MORE capacitance than your PCB. I seem to recall something like 2pF- 5pF per connection point?The smallest capacitor in the design is only 220pF. It might be pretty easy to affect that value by 10% or even more going from breadboard to PCB. The value may be critical?Do you still have the breadboard set up?

author: qu1j0t3
author_rank: Regular Contributor
timestamp: September 29, 2020, 10:21:33 pm
content: Frequencies are low, basically < 1kHz. The frequencies are directly controlled by the integrator time constant i.e. the integrator capacitance.While I chose to put a small 220pF as the fixed capacitance (tested on breadboard), the switches are intended to parallel that with 0.5–1µF. Any variation simply slows or speeds up the integrators. (Also note that the circuit ran well on the pcb with just that fixed capacitance (no switches installed).)A signficant imbalance between the integrators might be a problem, but it's not obvious where that imbalance would come from on the PCB. The capacitors themselves have all been matched.A worthwhile experiment might be to parallel the fixed capacitors with 47nF (also tested on breadboard) and see if that makes it more reliable.The breadboard has been torn down.

author: mawyatt
author_rank: Super Contributor
timestamp: September 29, 2020, 11:15:00 pm
content: Quote from: qu1j0t3 on September 29, 2020, 05:03:31 pmShould work pretty much as shown in the simulations schematic on a simple plug-in board (without the startup current source which just "kick starts" the simulation). The original circuit was over 25 years ago so hard for me to remember the exact details. You can use a standard inductor and compensate for the ESR, or replace with a gyrator based synthetic inductor which requires another Op-Amp. Any GP Op-Amp should work, I used the OP-07 in the simulations because the model is pretty good. Use a 10K multi-turn pot for R to allow adjustment of the various chaotic modes.Spend some time studying Michael Kennedy's various papers on the subject, as well as papers on the Chua's diode and Chaos theory, fascinating stuff indeed. BTW Dr. Chua also proposed the memresistor way back in the 70's I recall. He looked at the 3 fundamental electrical components, the resistor, capacitor and inductor, then postulated that there should be a 4th, the memresistor....brilliant researcherBest,

author: qu1j0t3
author_rank: Regular Contributor
timestamp: October 06, 2020, 01:08:40 am
content: Bit of an update. After some thought and playing with the board, I realised that the two factors that seemed to make it unreliable were reducing capacitance to 220pF, and also running at 15V. If I run at a lower voltage, e.g. 8-10V, it seems more reliable. This made me wonder if I am hitting slew rate limits with the integrators. A back of the envelope calculation estimated slew rate with 15V input and 220pF at up to 7V/µs (e.g. input resistor 10K like the multiplier outputs). The amps are spec'd at 13V/µs which might be just too close. This configuration did run on the breadboard with the same amps (LF412). I may try slightly faster amplifiers as I was happy with the speed at 220pF as a "fastest" setting.closeupsetup

author: qu1j0t3
author_rank: Regular Contributor
timestamp: October 07, 2020, 10:31:37 pm
content: Swapping out the LF412's for ADTL082's (8SOIC on adapters) did not work. The circuit does not run with the new amps. (As far as I can see, the adapted pinout is the same.)

author: jdjohnsn0w
author_rank: Newbie
timestamp: July 18, 2023, 06:34:07 pm
content: This is an old thread but my circuit wouldn't work until I used film capacitors for the integrators.

author: TimFox
author_rank: Super Contributor
timestamp: July 18, 2023, 07:03:17 pm
content: What type of (I assume ceramic) dielectric capacitors was replaced by film?Polypropylene or polyester (Mylar)?