Author Topic: Home Brew Analog Computer System  (Read 105942 times)

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Offline mamalala

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Re: Home Brew Analog Computer System
« Reply #50 on: February 15, 2013, 03:27:19 pm »
BTW, does anyone know an affordable source of PCB tin plate power?

There are immersion tin mixtures available. One is "SUR-TIN" from Bungard:

http://www.bungard.de/index.php?option=com_content&view=article&id=29&Itemid=80&lang=english#top9

Another one is "Seno Glanzzinn" (dunno if/under what name they sell it outside Germany).

I still have some of the Bungard stuff left, ready to be mixed for 1 liter or more. I could send it your way, but i'm not sure if that is at all possible, since it's a few nasty chemicals.... Sulfuric acid, uric acid, and some powdery stuff.

Strange that this stuff is so ridiculously expensive on Farnell. Here is German shop, for example:

http://www.octamex.de/shop/?page=shop/flypage&product_id=53&category_id=538bc6e72af65cf55e7fcba4ee8c099f&/Chemisch_Zinn_kaufen.html

Greetings,

Chris
 

Offline megajocke

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Re: Home Brew Analog Computer System
« Reply #51 on: February 16, 2013, 02:49:19 am »
Oh no, another audio forum refugee  :) How's it going?

Just fine! And you?

On the subject of analog stuff with lots of components, recently a friend and I have been working on a microprocessor controlled polyphonic analog synthesizer inspired by the Rhodes Chroma. Though I guess using digital computers is cheating...  ;)
 

Offline GK

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Re: Home Brew Analog Computer System
« Reply #52 on: February 17, 2013, 11:26:37 am »
BTW, does anyone know an affordable source of PCB tin plate power?

There are immersion tin mixtures available. One is "SUR-TIN" from Bungard:

http://www.bungard.de/index.php?option=com_content&view=article&id=29&Itemid=80&lang=english#top9

Another one is "Seno Glanzzinn" (dunno if/under what name they sell it outside Germany).

I still have some of the Bungard stuff left, ready to be mixed for 1 liter or more. I could send it your way, but i'm not sure if that is at all possible, since it's a few nasty chemicals.... Sulfuric acid, uric acid, and some powdery stuff.

Strange that this stuff is so ridiculously expensive on Farnell. Here is German shop, for example:

http://www.octamex.de/shop/?page=shop/flypage&product_id=53&category_id=538bc6e72af65cf55e7fcba4ee8c099f&/Chemisch_Zinn_kaufen.html

Greetings,

Chris



Thanks for the offer Chris, but you're probably right, shipping the hazardous chemicals overseas probably wouldn't be viable. Yes the Farnell (Element 14) price for the powder is ridiculous. I didn't know that you could buy it as a mixture. Does that have a finite shelf life? I know the powder only lasts several months once mixed.
« Last Edit: February 17, 2013, 11:34:13 am by GK »
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Offline GK

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Re: Home Brew Analog Computer System
« Reply #53 on: February 17, 2013, 11:33:19 am »
Oh no, another audio forum refugee  :) How's it going?

Just fine! And you?

On the subject of analog stuff with lots of components, recently a friend and I have been working on a microprocessor controlled polyphonic analog synthesizer inspired by the Rhodes Chroma. Though I guess using digital computers is cheating...  ;)


I'm fine also.

Lots of common ground between analog computing and analog synthesizer design  :-+ . I've always been interested in the design of analog synthesizers and once had fantasies of building one myself (polyphonic, with lots of keys) but I'm not musically inclined, so in the end it would be a bit pointless. 
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Offline mamalala

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Re: Home Brew Analog Computer System
« Reply #54 on: February 17, 2013, 01:51:10 pm »
Thanks for the offer Chris, but you're probably right, shipping the hazardous chemicals overseas probably wouldn't be viable. Yes the Farnell (Element 14) price for the powder is ridiculous. I didn't know that you could buy it as a mixture. Does that have a finite shelf life? I know the powder only lasts several months once mixed.

Yes, they all have a limited shelf life once mixed with water. It's usually around 6 months. If you keep it really cool, and use distilled water, it will last a bit longer.

It doesn't stop working completely, but the tin layer wont be that shiny anymore, and it takes much longer to deposit on the board. Also, it partially crystalizes. You can re-dissolve them by heating it up and mixing it well again.

Also, you have to solder the boards pretty quick once tinned. After a few weeks it will become virtually impossible to solder it anymore. You would have to give it a good scrub then, which probably will partially remove the tin layer completely. I used that stuff for a while, but don't use it anymore at all. It smells like foul eggs, has nasty chemicals, a limited shelf life, and it forces you to solder the boards quickly.

The "Seno Glanzzinn" comes in a brown bag, no liquids. I guess that would be rather easy to send. A pack is around 19 Euro, plus shipping. Let me know if you are interrested, i could then forward one to you. One pack is good for 1 liter ready-to-use solution, about 40 Euro-Card sized boards (160mm x 100mm).

However, you can get a can of leaded solderpaste, spread it on the boards and reflow that in an oven. Not the most beautiful thing, but it works well and protects the copper.

Greetings,

Chris
 

Offline GK

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Re: Home Brew Analog Computer System
« Reply #55 on: February 18, 2013, 12:39:47 pm »
Hmmm... The whole tin plate idea is looking less and less attractive. I'm probably being a bit paranoid about PCB leakage current in my integrators anyway and would be hardly worse off just using a conformable coat. JFET leakage currents will likely dominate anyway, and you shouldn't expect the computer to hold your solution in the "Hold" mode with the utmost stability over extended periods (eg. while going off to lunch) anyway.

That said, now just thinking aloud (way too late at night), how much luck would I have evenly/uniformly solder-coating a bare copper board if I melted a hefty roll of solder in a frying pan over a gas burner and somehow just skimmed/floated the board over the surface?
« Last Edit: February 18, 2013, 12:44:38 pm by GK »
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Offline notsob

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Re: Home Brew Analog Computer System
« Reply #56 on: February 18, 2013, 01:03:11 pm »
If you are looking at plating systems and supplies, I recently found these guys when looking for liquid electrical insulation (look at their plasti dip range), anyway I haven't used them but it may be worth contacting them.

http://www.caswellplating.com.au/store/store.php
 

Offline mamalala

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Re: Home Brew Analog Computer System
« Reply #57 on: February 18, 2013, 01:34:10 pm »
That said, now just thinking aloud (way too late at night), how much luck would I have evenly/uniformly solder-coating a bare copper board if I melted a hefty roll of solder in a frying pan over a gas burner and somehow just skimmed/floated the board over the surface?

Virtually none. You will always get an uneven solder coating that way. Just look at consumer electronics that is assembled using a solder-bath. There is a reason why you almost never see big chunks of copper plane solder coated that way there. They either go fo a "grid" type copper-pour instead of a solid copper plane, or they restrict the available tinable area with a solder mask.

If anything, you have to recreate the HAL process to get a somewhat even surface. This is basically just applying the molten solder to the PCB, and then using hot air to "level" (i.e. blow away) the excess solder. HAL = Hot Air Leveling.

So, if you don't care about an even surface, you can do it the way you proposed. Otherwise that method is good only for etched boards, i.e. when tinning only the traces instead of a whole bare copper area.

So, i would think that conformal coating would probably the best way to go. Cleaning in an ultrasonic bath, with suitable solvent. Maybe then dry the boards in an oven for a few hours before coating, to make sure that no moisture is trapped under the coating to be applied.

How were the boards "finished" in the commercial analogue computers? After all, these machines are a rather old thing.

Greetings,

Chris
 

Offline GK

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Re: Home Brew Analog Computer System
« Reply #58 on: February 20, 2013, 12:48:32 pm »
I vaguely recall seeing it done as you describe but couldn't say if it was Pease or Williams.


It was Williams:

http://cds.linear.com/docs/en/application-note/an124f.pdf

bottle cap was epoxy filled too.

I'm almost finished loading/testing the Time Base PCB. After that I'll be doing the Log Amp boards. I've already collected 10 coke bottle caps. I think I'll drill a ~5mm hole in to the top of each and inject araldite with a syringe.
 


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Offline GK

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Re: Home Brew Analog Computer System
« Reply #59 on: February 21, 2013, 12:06:16 pm »
The Timebase board is slowly nearing completion. I decided in the end that I wanted much more comprehensive sweep waveform (x-axis) output options and provisions for re-trace blanking (z-modulation) for use when viewing problem solutions on an X-Y oscilloscope in the repetitive operation mode. These functions will be performed on a separate circuit board. As a consequence I modified the circuit a bit. The revised schematic is attached.

« Last Edit: April 30, 2015, 06:28:54 am by GK »
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Offline GK

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Re: Home Brew Analog Computer System
« Reply #60 on: March 01, 2013, 08:00:56 am »
A geofiz trip put me out in the middle of nowhere again for several days, but I'm now back in the shed. The timebase board is finished and works just as planned. Got it wired to a scope with more channels this time! (A DSO for now, until I finish calibrating two of my Tek 1A1 plug-ins for the 551 mainframe).
The two rotary switches (time [1s, 2s & 5s] and five-position multiplier) which select one of the 15 calibrated compute time settings (from 1mS to 50S) will be double pole types, with one half of each switching a diode decoding matrix and MPSA44 HV transistors to display/indicate the timebase setting on three Nixie tubes (and two neon lamps in bezels to indicate either ms or S), which I have salvaged from an old stuffed "panel" meter (along with a suitable transformer to supply the anode potential).


« Last Edit: March 01, 2013, 09:18:45 am by GK »
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Offline SeanB

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Re: Home Brew Analog Computer System
« Reply #61 on: March 01, 2013, 02:54:33 pm »
You need a new slip indicator. I got quite good at knitting them out of a big ball of bright red wool i bought at the sale section at a haberdashery. What chopper were you flying over the sand.
 

Offline GK

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Re: Home Brew Analog Computer System
« Reply #62 on: March 01, 2013, 10:42:13 pm »
Robinson R44 Raven I. I actually drove a ~6 tonne truck/mobile lab out there, battling sand dunes. When things didn't go to plan (as usual), instead of sitting around in the 40+ heat with sand up my arse, I managed to hitch a free seat on the chopper out to a hotel room for the night. Touched down right in front of the pub!
   
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Offline FenderBender

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Re: Home Brew Analog Computer System
« Reply #63 on: March 01, 2013, 10:55:58 pm »
Awesome work there GK :-+ Makes me feel electronically inept :'(

I'd say...

Yikes, I'm still trying to understand class-b amplifiers...
 

Offline GK

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Re: Home Brew Analog Computer System
« Reply #64 on: March 02, 2013, 08:59:00 am »
A DSO for now, until I finish calibrating two of my Tek 1A1 plug-ins for the 551 mainframe.


Done! Well, almost. The 1A1's are still way out of calibration, but I have fixed all of their faults and they are functional. Also spent the entire afternoon tracking down faults in the 551 mainframe, before I could calibrate it properly. My long run with ancient Tek gear and no dodgy electrolytic capacitors has come to an end. One "125MFD 350WVDC", of the -150V regulated reference supply, suddenly decided to go <100nF, giving me huge ripple on all of the regulated rails along with a really funky CRT display. Another PSU electro decided to low impedance instead and burnt out some parallel peak-current-limiting resistors between it and the bridge rectifier. I will have to compile a shopping list and do an electrolytic capacitor blitz on my old Tek mainframes one weekend  :-/O

But anyway, two 1A1 dual-trace plug-ins in a 551 dual-trace mainframe gives a 4 channel scope. The next step is to track down a pair of 1A4 plug-ins on Ebay to make 8 channels.................

 
« Last Edit: March 02, 2013, 12:55:56 pm by GK »
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Offline GK

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Re: Home Brew Analog Computer System
« Reply #65 on: March 02, 2013, 12:53:26 pm »
Robinson R44 Raven I.


Holy crap! I wouldn't have guessed that that crappy little thing was equipped with an engine almost 9 liters in capacity:

http://en.wikipedia.org/wiki/Lycoming_O-540


 
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Offline SeanB

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Re: Home Brew Analog Computer System
« Reply #66 on: March 02, 2013, 02:23:49 pm »
500hP is better........ http://en.wikipedia.org/wiki/A%C3%A9rospatiale_Alouette_III

You need a lot of power to keep from sweating in there.
 

Offline GK

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Re: Home Brew Analog Computer System
« Reply #67 on: March 27, 2013, 11:55:51 am »
Some major progress has been made in the construction of this computer, but I won't have much further fully functional to show until a bunch of back-order bits arrive.

Here is a little play in LTspice in the meanwhile   :D:

www.users.on.net/~glenk/bouncingball.asc
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Offline GK

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Initial baby steps to a TV-based oscilloscope
« Reply #68 on: March 29, 2013, 10:40:02 am »
Well perhaps this is a little more exciting than the above............................... ???

Since I started working on this analog computer project I've been pondering over what kind of X-Y oscilloscope would make the best display device. For example, something like this: http://www.analogmuseum.org/english/examples/bouncing_ball/  just isn't as impressive as it should be when viewed on a tiny CRO tube screen with a 10 by 8 cm grid.

So this afternoon I started investigating the idea of converting an old TV set with magnetic deflection into an oscilloscope. An old little TV set which has been sitting in my cupboard for the last 11 years unused was sacrificed for the purpose. The pics below show how far I got. To my delight, my basic theoretical understanding of how to undertake the conversion proved entirely adequate and the conversion is really going to be a piece of cake.

I started by reverse engineering the RGB driver board (plugged into the rear of the CRT) and disabling the video. I reconfigured the gun driver amplifiers so that I could adjust the intensity of each color beam independently/manually. In the photo below I just have the green gun operating; the others are biased to cathode current cut-off. I then identified the connections to the separate horizontal and vertical deflection coils and disconnected them from the sets circuitry. So, from that point on, I am only utilizing the TVs motherboard to provided the operating voltages for CRT.

The vertical deflection coil is actually quite sensitive. My AWA G231 oscillator was easily able to drive the coil for full scale vertical deflection on the CRT at frequencies of 1kHz or so and less. To approximate a current drive in this initial test, I am simply driving the coil through a low value series resistor. So long as the value of the resistor is low compared to the inductive reactance of the deflection coil (at the operating frequency) current drive is adequately approximated and a linear(ish) deflection appears on the screen.

For driving the horizontal coil, however, I had to knock something up. I initially assessed the deflection sensitivity of the horizontal deflection coil by connecting it to my bench power supply in the CC mode. By dialing the dc current through the coil up and down I could therefore manually move the dot across the screen. A current of approximately 1A was required to shift the dot from the center of the screen to the edge (with no current through a deflection coil the dot returns to the center of the screen for the respective axis).

I then made a really simple and crappy (but adequate for "proof of concept") single-ended class A, current-output power amplifier stage capable of driving +/-1A peak into the horizontal deflection coil. This amplifier stage was build up around an MJL21193/MJL21194 power transistor pair screwed down onto an adequate heat sink. This amplifier is shown in the photographs. Being single-ended class A a bit more than 1A is constantly drawn from the supply (note the current reading on the bench supply providing the +/-15V supply rails). By driving this horizontal deflection coil amplifier with my crappy little Jaycar "pocket" signal generator I has able to get some nicely linear Lissajous figures up on the screen. yahoo!

The next step was to knock up a crappy triggered "timebase". For this I used a 555 wired as a one-shot monostable. It is triggered (via a transistor switch configured as a crossing detector) by the AWA G251 oscillator output signal, providing the vertical deflection. For a linear ramp, a current source is used for the 555 one-shot and the linear ramp voltage across the timing capacitor is buffered with a BC550C (c-grade for high gain) emitter follower and then applied to the H-coil driving I-out power output stage input via a pot to vary the horizontal sweep width on the screen.

This allowed me to get a conventional, stable oscilloscope-like display of a ~500Hz sine wave on the screen, as shown in one of the pictures below. Note the feint retrace line though as I wasn't bothered to implement retrace blanking at this early experimental stage.

Now that I know exactly what needs to be done to turn this old TV into a scope with 10-20 kHz bandwidth or so, I can begin with the electronics design proper. I am going to have to build class B I-out deflection coil driver amplifiers with several hundred volts of voltage compliance. I also intend to do away with the TV's original circuitry entirely, building my own PSU to deliver all of the necessary voltages for the CRT. For the gun drivers, I currently intend to make them digital - each gun either on or off in accordance with logic control signals with a common, overriding cut-off control input (for retrace blanking) and with a common brightness control that varies the "on" threshold of the thee guns in unison and thus the beam current and the resultant display intensity. A 7-position rotary switch will select the trace colour (3 bits actually gives 8 "colours" but one of them isn't very useful as it is black  ;D).

What I also intend to implement is alternative logic RGB inputs. This will allow, via multiplexing, the display of multiple traces off of different colours. So the 7-position rotary switch will rather be an 8-position one with the eighth input selecting external logic signals for the trace colour control. For example, I will eventually be able to run Bernd Ulmann's "ball in a box" simulation (as linked to above) on my machine, but instead displayed on my large screen TV scope, with multiple bouncing balls with different coefficients on screen at once displayed in different colours!

Also, as a bonus, my parents (on the big LCD-screen craze) pensioned off today a perfectly fine CRT TV with a screen twice as big as the one shown, which is due for delivery here tomorrow morning; another to be sacrificed for TV-to-CRO conversion  ;D





   
 

     
« Last Edit: March 29, 2013, 11:01:07 am by GK »
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Offline SeanB

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Re: Home Brew Analog Computer System
« Reply #69 on: March 29, 2013, 11:02:54 am »
Just use a scope to make a note of the drive to the LOPT and the drive to the transformer driving the line output stage, then just use that and nothing else aside from the tuning capacitors along with the appropriate HT supply. The PSU of the set can be cut out of the board complete, and used as a unit to provide mostly 130VDC for the LOPT, assorted low voltage lines like 12V, 26V and a 5V line for the low voltage stuff. Then you can have a much simplified unit.
 

Offline GK

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Re: Home Brew Analog Computer System
« Reply #70 on: March 29, 2013, 02:04:03 pm »
If I had a spare LOPT/trippler that is something that I would consider, but how long before these things are unobtanium and what would I do if the thing went poof a couple of years from now? They are a highly stressed part and failures are not uncommon. There is still heaps of this stuff around right now, but people (down here at least) are now throwing away their CRT televisions and computer monitors as if they were something one could catch rabies from! 

I was considering winding my own HV step-up transformer on a large ETD core (I have a kit of selected samples from the entire range) and making my own voltage multiplier. The multiplier could have its HV diodes and ceramic caps laid out on a spacious PCB. Spray half a can of conformable coating over it and it should last forever.

 

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Offline SeanB

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Re: Home Brew Analog Computer System
« Reply #71 on: March 29, 2013, 03:50:13 pm »
I can still buy LOPT's and triplers for Trinitron TV sets, the bloody things just keep on trucking, horrible bodges to replace GTO thyristors notwithstanding. If you are worried just use the LOPT and grab a few spares from similar sets, they all run off pretty much the same voltage (108-130V) and have near identical charactaristics, so can just be substituted when needed, just make a note ( place in plastic baggie and cable tie to LOPT EHT lead) of pins used for HT and GND along with the drive pin, and the values of the tuning caps ( put the caps themselves and the transistor in the baggie as well) needed.

3 Dead Trolls in a Baggie...........

http://youtu.be/nL24aNugo_4

 

Offline GK

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Re: Home Brew Analog Computer System
« Reply #72 on: April 02, 2013, 09:14:55 am »
Well I guess I could get my hands on a few spares if I really wanted to, but I still prefer to roll my own, just because I can.



-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------

I've completed the design for the horizontal coil driver amplifier. The yokes horizontal coil has an inductance of 2mH shunted with 70pF winding capacitance and a series resistance of 1.2 ohms and requires a smidge under 1.4A (accurately measured this time) peak for full scale deflection.

The composite current driver amplifier I have come up with (schematic attached) forces -Vin across resistor Rsense (lower right hand side of the schematic). The current flowing through Rsense is the deflection coil current. The small signal bandwidth is 35kHz and the large signal bandwidth (a coil current of 2.8Ap-p) is a fraction over 2kHz. The large signal bandwidth and slew rate is constrained by how much "compliance" voltage the I-out driver amplifier has. I settled on +/-40V rails as a sane compromise between bandwidth and worse case power dissipation, which gives a clipping threshold of approximately 35V.

The small signal bandwidth is constrained by how much feedback can be wrapped around the deflection coil whilst maintaining stability. The first attached plot shows the loop gain and phase of the current sensing feedback loop enclosing the deflection coil. The second plot shows the voltage and current waveforms for the coil driven to full scale deflection (2.8Ap-p) by a 1kHz squarewave input.
   
I'm currently laying out the PCB for this circuit. Should have it knocked off in a couple of evenings. Then I will start considering the design of the current driver for the vertical deflection coil. It will be a fair bit different as the vertical coil has completely different characteristics (140mH inductance, 62 ohms Rs, 180mA peak for full scale deflection).

   


   
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Offline GK

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Colour CRT convergence adjustment
« Reply #73 on: April 10, 2013, 09:59:12 am »
I'm making steady progress with the deign and construction of the electronics for this magnetic deflection CRT XY oscilloscope, but right now I'm still playing around with the crappy/bodged/experimental/test bread-boarded circuits on the bench.

I'm having an issue with the beam convergence when wishing to display additive colours. Displaying red, green and blue traces independently works fine, but I'm having an issue when wanting to mix red with any of the other colours (eg red+green for a yellow trace). At the moment, the green and blue beams are, for all sakes and purposes, perfectly converged, but the red beam will only accurately converge with the others when the focus control is right at one end of its travel - but display focus is optimal at roughly mid position.

So, obviously, I need to adjust/calibrate the convergence for red beam. My CRT here is of the modern type in which the individual beam convergences are adjusted by means of rotatable pairs of magnets on the neck of the CRT only. There are no coils nor electronic compensatory circuits at all. I've attached a picture of the neck of the CRT and the rotatable magnet assemblies.

However, I'm not sure what the correct procedure is and I'm a bit paranoid about screwing things up! Any ex-TV service technicians out there who can offer advice? To the best of my knowledge, for this type of CRT, the convergences are adjusted for a single point in the middle of the screen with no currents applied to the deflection coils. However if someone could kindly outline the magnet adjustment procedure before I take a crack of it I'd be quite appreciative!

I've also attached screen pictures of the 7 binary (a beam either on or off) colour combinations as they are currently generated, with the less than optimal focus setting required to keep the red gun converged with the green and blue. The colors don't appear as vivid in photos as they do in real life, unfortunately.




 
« Last Edit: April 10, 2013, 10:01:25 am by GK »
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Offline GK

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Re: Home Brew Analog Computer System
« Reply #74 on: April 10, 2013, 10:21:45 am »
Some major progress has been made in the construction of this computer, but I won't have much further fully functional to show until a bunch of back-order bits arrive.

Here is a little play in LTspice in the meanwhile   :D:

www.users.on.net/~glenk/bouncingball.asc


Some more playing around............ Just for fun I used the ".wave" LTspice directive in a modified version of that simulation to record and save the simulated X and Y signals into the left and right channels of an audio file. This enabled me to connect the headphone socket on my PC to an XY oscilloscope for a visual display, playing the audio file with windows media player.

I modified the simulation for a much quicker solution time (10mS instead of 1s) and used alternate-write multiplexing to simulate and plot the trajectories of two bouncing balls in unison; one having a slightly higher mass than the other and subjected to a slightly stronger constant for gravity. I simply couldn't do a slow simulation such that the "balls" (CRT beam dots) could be observed slowly bouncing about on the screen (which I could have videoed), due to the high-pass, low frequency response of my PC's audio and there is some significant waveform distortion due to the AC coupling, but it makes a nice demonstration of a PC emulating an analogue computer nonetheless  ;D.   

 

 
« Last Edit: April 10, 2013, 10:26:09 am by GK »
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