pseudorandom noise generator uses? - Page 1
Forum section: electronics / testgear

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2021, 12:19:03 am
content: So I have a old HP Pseudorandom noise generator. I know its probobly extremely outdated and useless, but what exactly can this thing be used for in electronics?https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1967-09.pdfI can read alot about what it does and does not do but what I want to see is like some kinda useful test setup that can be made with this to test something as it would be used in a electronics laboratory, how did they think with this machine?

author: Algoma
author_rank: Frequent Contributor
timestamp: February 25, 2021, 12:47:06 am
content: There is certainly no shortage of natural noise that could be simply amplified as needed, but its certainly better to have control when testing products.

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2021, 01:11:00 am
content: but what do you do, feed it into a control loop to make disturbances? like with a amplifier?Like, can you give me a school problem that would be solved with this kinda thing in a lab setting? I remember something along the lines of "there is a remote sensor... something random noise margin threshold something".I remember finding this problem on a sample exam from MIT or something about a decade ago (very similar to where I went to school, in terms of tests) where they actually gave a problem that might be verified using something like this relating to some kinda remote sensor in a random math class that used symbols/math that i am recognizing when looking at these generators. something with noise margins and signal correlation causing a false reading or something?.. not my favorite class lol

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: February 25, 2021, 01:50:58 am
content: One application would be to test the autocorrelators used in dynamic light scattering instruments. The autocorrelators process the scattered light from a laser beam illuminating a dispersion of nanoparticles. Each particle scatters light with a phase difference relative to the incident light according to the particle's position. This changes the amplitude. The composite signal from millions of particles results in a scattered light signal from a detector that fluctuates in intensity with the random motion of the particles due to the constructive and destructive interference from each particle's contribution. Since random motion can be described as a normal (gaussian) random process, the light signal is essentially random gaussian noise with a characteristic time constant in the time domain or frequency distribution width in the frequency domain. This is discussed in the HP magazine on page 4. Since smaller particles diffuse faster, the detector signal will fluctuate faster than larger particles. Hence, the size of the particles can be estimated.I'm currently building an instrument that, in part, does the autocorrelation - so I'd have an immediate use for this noise generator!Incidentally, the first autocorrelators for light scattering also arose in the mid-60s.The generator also has "binary" noise which, up to a certain frequency, has a flat frequency response. This can be used for measuring the bandwidth of circuits.It is interesting to read how they generate the noise. They use exactly the same "trick" that Arduino fans use for generating audio via PWM - more than half a century before

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2021, 01:58:59 am
content: what changes with modern noise generators? I.e. my DDS has a noise generator in it. Not the pseudorandom noise though.Like what parameters would a researcher desire in a modern instrument. The bandwidth of this is low, only 20KHz. That has to be a big one. What else?Is there a randomness specification akin to distortion in function generators that can be compared to get a feeling of worth?

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: February 25, 2021, 02:13:13 am
content: Quote from: coppercone2 on February 25, 2021, 01:58:59 amThe bandwidth of the gaussian noise is abput 50kHz but it generates uniform noise up to much higher frequencies.One of the import features of this unit is that there is a signal that indicates when the pseudorandom sequence is starting again. Although you can get random noise generators based on natural random processes, the pseudorandom approach allows you to repeat exactly the same sequence. The disadvantage is that, at some point, the pattern will repeat.Of key importance to the randomness is that the value at a given time doesn't correlate with the value at any other time. Measuring the autocorrelation function would be a way to characterize the randomness.This is an interesting site:https://www.random.org/randomness/

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2021, 04:11:01 am
content: what could measure that value? I am installing a new IEC plug on it to remove the oval connector, hopefully this unit works. I think last year I plugged it in with some jerry rigged crap but I don't wanna do that, it will have a seat on my new rack.If you describe a simple experiment I might be able to find it. looks like it needs alot of TLC on the switches and maybe a look over the electronics.

author: penfold
author_rank: Frequent Contributor
timestamp: February 25, 2021, 05:00:43 am
content: I had no idea HP made such an instrument! Really wish I had one.You can use it to use it in many "system identification" techniques similar to what you may use a network analyser or frequency response analyser for. A bit of googling around "prbs system identification" should show up some interesting applications. But basically by using it as a signal source, recording the input and output during between the "sequence complete" pulses along with a little maths (see convolution theorem) and you've got a pretty descent setup for performing frequency response analysis... big applications for measuring lower bandwidth control loop responses and LF impedances (maybe batteries perhaps for state of charge/health measurement).To get good results, you need to be quite precise about trimming away the chaff and only using one single sequence's worth of signal in the convolutions - if you don't, its a bit like using a dodgy window function on an FFT.

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2021, 05:09:41 am
content: the back plane is made with wire point to point construction on a bunch of cards, it is quite a beast. I just wonder if the cards have sockets or if you need to desolder em. I only took the back panel off but I think from glancing at the manual it looks like they are carded, probobly more cinch knowing HP. Working on some other things before I have a better feeling about the wired backplane then those fucking PCB interconnects from spectrum analyzers.alright good to hear this stuff though because I was starting to wonder if i was working in a lab or an archeological dig, sounds like my gut instinct was right when I bought this like 4 years ago lol. i was kinda worried it would be like OMFG LOL MAKE ONE OUT OF AN ARDUINOsorry i gotta get it out of my system im waiting for the 50 amp pwm 5ppm accuracy class 10MHz constant current controlled arduino project using a toasters bread grabber to latch on the 4/0 cable.

author: penfold
author_rank: Frequent Contributor
timestamp: February 25, 2021, 06:00:54 am
content: Quote from: coppercone2 on February 25, 2021, 05:09:41 amWell... MCU and FPGA implementations are generally what gets used in the research papers on PRBS/MLS/"Random Signal" system identification, but it is bare-bones and still requires a fair amount of work still to "tailor" the measurement system around it, getting the acquisition synchronised with the waveform, being *incredibly* precise about trimming the data and balancing between sequence length and finding the best polynomial structure are just a few of them. What you've got avoids a lot of that rubbish and just makes a signal that should work for 90% of situations to give *descent* results.

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2021, 06:09:12 am
content: is this related to SETI?

author: Berni
author_rank: Super Contributor
timestamp: February 25, 2021, 06:34:49 am
content: There is a lot of old test gear out there that is today now possible to replicate a lot more easily due to advances in electronics tech.For example i have an old HP pulse generator from the early 80s. All it does is generate an adjustable fixed freqency or one shot digital pulses with an adjustable amplitude and offset. That is it. Nothing else. Its full of weird unobtanium analog ASICs. But i keep the old dinosaur around just because of how convenient it is. I just flip the power button, the incandescent power indicator lights up (No LED yet) and it starts spitting out whatever pulse shape i left it set for. Every parameter of the pulse is adjustable with a dedicated knob, be it amplitude, offset, freqency, on time, off time, rise time, fall time, one shot triggering etc... and it will make everything from under a Hz to 250 MHzTest equipment is not just about doing something that is hard to DIY, but its also about having a convenient, well tested and characterized box that does a single job really really well. You just give it power start using it. It will also typically be better thought out than a DIY solution, making it more resilient to damage (both electrically and physically) and have a proper user interface on the front panel to easily operate all of its functions.Same reason why people buy PSUs rather than building them, despite how easy they are to DIY.

author: coppercone2
author_rank: Super Contributor
timestamp: February 25, 2021, 06:41:35 am
content: yes, i have a 50Mhz beast pulse gen from wavetek. sounds like its gonna take off but that is easy to understand why you keep it around. the random generator seemed questionable, perhaps because I remember there being a random generator in C.Trust me I have no problem with most things its just it makes me think of rand(), it was bugging me thinking about how I need rand() on an analog output in my lab. its breaking the 4th wall or whatever the hell you wanna call it. to me its like meeting someone named "The". Did you talk to the? whos on first?? who framed roger rabbit?im eager to setup some kinda experiment with this, the laser sounds interesting, i need to see a setup.

author: Berni
author_rank: Super Contributor
timestamp: February 25, 2021, 07:35:02 am
content: Id say this turning digital pseudorandom noise into analog noise is mostly just a neat specialized use case of it. Generating very flat noise over a wide bandwith in analog can be difficult, so this was likely a good way to generate such flat noise with the tech of the time.Keysight still produces modern versions of this equipment:https://www.keysight.com/en/pd-1000004569%3Aepsg%3Apro-pn-81134A/pulse-pattern-generator-335-ghz-dual-channel?nid=-536902258.536882047&cc=SI&lc=engThe actual intended use for these PRBS generators is testing communication channels. The PRBS pattern generator sits on the transmitting end while the receiving end has a oscilloscope drawing an eye diagram, or a piece of equipment called a BERT (Bit Error Rate Tester) that can recognize the pseudorandom sequence, lock onto it and predict all the bits coming in because it knows the algorithm used to generate it, this way it can recognize any errors in the bit stream and count them. This way you can get a quantifiable measure of the reliability of your transfer link. The transfer link being a telephone line, HDMI cable, Card cage back-plane, RF wireless link etc... So for this reason pseudorandom pattern generators kept being made for higher and higher speeds into the 10s of Gbit/s, but the modern ones also have memory so they have become general purpose digital pattern generators (Basically a DDS signal generator without a DAC on the output)

author: coppercone2
author_rank: Super Contributor
timestamp: February 26, 2021, 04:38:08 am
content: oh right thats how the problem was, something about getting a function that had some probability of causing something like saturation in an amplifier. like it got an auto correlation to some kind of profile, or maybe interference was given by some correlation.

author: coppercone2
author_rank: Super Contributor
timestamp: February 28, 2021, 03:05:23 am
content: lol this thing is spitting out boards like an aircraft carrier. So much mica, thank god. Seriously.It started as little mod to put a IEC connector on it but I decided to clean up the contacts, and wash the PCBs everything save that big can. This frequency thing seriously looks like a tall boy beer can with a knob on top.I am scared to look in the manual lol, looks like the physics package for an atomic bomb.One of the switches in there looks like its a fucking organ pulled out of the thing, or maybe a space station infested by the zerg, and the other one looks like some kind of weapon.I wonder if it works.If that switch needs more maintenance then being drenched in deoxit, I will need to make the camera they had on the set of the matrix to remember where all the wires go.

author: coppercone2
author_rank: Super Contributor
timestamp: February 28, 2021, 07:48:46 am
content: after carefully scrubbing every card and drying it, then polishing the contacts with a deoxit covered q-tip and spraying some deoxit into the cinch connectors, I have turned it on and it appears to work.Just needs 3x 1000uF capacitors replaced because it has some real old stuff in there (well, I will at least measure ESR) and I need to improve the wiring a little bit (replace with teflon wire, I did a hack job with PVC and a battery soldering iron working ontop of the washing machine, for a quick test). Everything else is pleasantly mica and styrene .adventure awaits

author: coppercone2
author_rank: Super Contributor
timestamp: February 28, 2021, 07:20:39 pm
content: Hooked it up to a speaker this time and damn it sounds creepy. Sounds kinda like old sound fx from games like wolfenstein 3d if the frequencies are set right. If you play with the sequence length and the frequency you can get things that sound like odd tones.Thought I was playing that old missile defense game (the one from the arcade in terminator 2) for a second. The effect is most impressive at around 50Hz.

author: Berni
author_rank: Super Contributor
timestamp: February 28, 2021, 07:42:38 pm
content: That is because a lot of old chiptune audio chips used a LFSR based pseudorandom generator to generate broadband noise. This was often used for various noisy sounds effects or short bursts used as drums in music.

author: coppercone2
author_rank: Super Contributor
timestamp: February 28, 2021, 08:20:43 pm
content: yeah lol I hooked it up on too high power level to a really bassy cheap blu tooth speaker and it started shaking the washing machine and scared meUsed a real BNC to phono connector

author: DrG
author_rank: Super Contributor
timestamp: February 28, 2021, 08:51:36 pm
content: Quote from: Berni on February 28, 2021, 07:42:38 pmAt one point, there was the mm5837http://synton.nl/wp-content/uploads/2017/04/mm5837.pdfSadly, it looked a lot better than it sounded. Excited to build a cheap masking noise generator, I could distinctly hear a 'click' when it recycled. A complete flop from my pov.It was such a pain that this fellow wrote a PIC675 'replacement'https://electricdruid.net/white-noise-source/. Having no 675 on hand, I translated it to 202 and pumped it into an amplifier and it worked well for many years.Code:;----------------------------------------------------------------------; Translation of a white noise generator from PIC12F675 to PIC10F202; Original code from: https://electricdruid.net/white-noise-source/;by Tom Wiltshire; GP2 pin 3 (on 8p pdip has the output to be consistent with the; MM5837 - other output pins are possible;----------------------------------------------------------------------LIST P=10F202include "p10f202.inc"__CONFIG _MCLRE_OFF & _CP_OFF & _WDT_OFF;; RAM VariablesCBLOCK 0x08; LFSR 1, a 31-bit registerLFSR1_1LFSR1_2LFSR1_3LFSR1_4; LFSR 2, a 23-bit registerLFSR2_1LFSR2_2LFSR2_3; Temporary storageTEMPENDC;----------------------------------------------------org 0x000movwf OSCCAL; note: use default OPTION reg valuesmovlw b'11011100' ; for GP2 outOPTION;**** Setup GPIO inputs/outputs ****movlw b'00000000'movwf GPIOmovlw b'00001011' ; GP2 as output (pin 3 on 8p pdip)TRIS GPIO; Set up initial values of the registersmovlw0x45movwfLFSR1_1movlw0x57movwfLFSR1_2movlw0x9FmovwfLFSR1_3movlw0xF2movwfLFSR1_4movlw0xD7movwfLFSR2_1movlw0xC8movwfLFSR2_2movlw0x79movwfLFSR2_3MainLoop:; 31-bit LFSR with taps at 31 and 28swapfLFSR1_4, W; Get bit 28movwfTEMPrlfLFSR1_4, W; Get bit 31xorwfTEMP, F; Shift the XORd bit into carryrlfTEMP, F; Shift the registerrlfLFSR1_1, FrlfLFSR1_2, FrlfLFSR1_3, FrlfLFSR1_4, F; Output the noise bitmovfLFSR1_1, WmovwfGPIO; 21-bit LFSR with taps at 21 and 19rrfLFSR2_3, W; Get bit 19movwfTEMPrrfTEMP, FswapfLFSR2_3, W; Get bit 21xorwfTEMP, F; Shift the XORd bit into carryrrfTEMP, F; Shift the registerrlfLFSR2_1, FrlfLFSR2_2, FrlfLFSR2_3, F; Output the noise bitmovfLFSR2_1, WmovwfGPIOgotoMainLoopEND

author: coppercone2
author_rank: Super Contributor
timestamp: February 28, 2021, 08:59:27 pm
content: One of my first projects was a white noise generator that used a zener diode and 2 op -amps, you can dead bug it and fit it next to 2x 9v batteries in a altoids tin with a BNC connectorIt is scaresly bigger then the dual op amp dip package, you can fit all the parts under neath if you wire it up point to point using the DIP chip legs as a scafolding/lattice (use through hole resistors and axial through hole ceramic capacitors)

author: DrG
author_rank: Super Contributor
timestamp: February 28, 2021, 09:04:34 pm
content: Quote from: coppercone2 on February 28, 2021, 08:59:27 pmYeah. There's also the 'trick' using 2 legs of an npn - right?

author: coppercone2
author_rank: Super Contributor
timestamp: February 28, 2021, 10:00:07 pm
content: not sure, I think this is what the HP unit does, I read something in the manual about a transistor being used

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: February 28, 2021, 11:38:11 pm
content: Quote from: coppercone2 on February 28, 2021, 10:00:07 pmI think you are referring to this:Quotei.e., the unit can operate as a true random source if you want it to though it is primarily intended for a pseudorandom source.

author: coppercone2
author_rank: Super Contributor
timestamp: March 01, 2021, 01:26:01 am
content: it has a RF-type can with the noise source in it. Did not look inside of it.The other weird part is a board with what looks to be 2 glass tubes inside of what looks like those big power resistors (the hollow ones). I think the manual said it was a relay card of some sort, but I don't know why it would be made like that.Its page 8-32so they wound a coil over the relay or something like that. Not really sure.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: March 01, 2021, 02:27:34 am
content: Can you post some photos?