I know I'm a bit late in following up on this, but better late than never! I got caught up in life and other projects as usual.
I've put up some more photos and videos, plus some preliminary schematics in this google album: https://photos.app.goo.gl/dzu7QLQbDr4ameMr8 Best regards On Saturday, December 23, 2023 at 2:10:19 AM UTC+1 Max Di Noi wrote: > Actually, that code works well! I had a typo on a pin config. Seems to > work well! Very pleased. I hope you find that snipped of code useful. > > > On 22 Dec 2023, at 17:58, Max DN <flata...@gmail.com> wrote: > > > Jörg, > > This is the code that I am using with DAC 4822 (similar to 4922 but with > internal ref.). I can generate some nice sinewaves with 1V or 2V amplitude > with the Teensy 4.1 powered by USB data cable and output displayed on my > Rigol oscilloscope. > > And of course, I can draw a circle. > > I think the code is as slim as can be, see below. However when I plug it > in the scope clock code, It doesn't seem to work well... I need to figure > it out. > > > //code > #include <SPI.h> > > //typedef unsigned int mcp4xxx_register; // 16-bit MCP48XX/MCP49XX > register for a single channel and 12-bit data > // > //const mcp4xxx_register mcp4xxx_channel_a = 0B0000000000000000; // for > all MCP4XXX > //const mcp4xxx_register mcp4xxx_channel_b = 0B1000000000000000; // for > MCP4XX2 only > //const mcp4xxx_register mcp4xxx_buffer_off = 0B0000000000000000; // for > all MCP4XXX > //const mcp4xxx_register mcp4xxx_buffer_on = 0B0100000000000000; // for > MCP49XX only > //const mcp4xxx_register mcp4xxx_gain_two = 0B0000000000000000; > //const mcp4xxx_register mcp4xxx_gain_one = 0B0010000000000000; > //const mcp4xxx_register mcp4xxx_output_off = 0B0000000000000000; > //const mcp4xxx_register mcp4xxx_output_on = 0B0001000000000000; > // > // > //const mcp4xxx_register mcp4822_channel_a = mcp4xxx_channel_a | > // mcp4xxx_buffer_off | > // mcp4xxx_gain_one | > // mcp4xxx_output_on; > // > //const mcp4xxx_register mcp4822_channel_b = mcp4xxx_channel_b | > // mcp4xxx_buffer_off | > // mcp4xxx_gain_one | > // mcp4xxx_output_on; > > const unsigned int steps = 512; > > unsigned int sines_of_steps[steps]; // sine values scaled to 0 ... 4095 > (2^12 - 1) > > const byte DACCSPin = 10; > > void setup() > { > int i; > > for (i = 0; i < steps; i++) > { > sines_of_steps[i] = round((sin(TWO_PI / steps * i) + 1) * 2047.5); > } > > pinMode(DACCSPin, OUTPUT); > digitalWrite(DACCSPin, HIGH); > > SPI.begin(); > } > > void loop() > { > unsigned int i; > for (;;) > { > for (i = 0; i < steps; i++) > { > SPI.beginTransaction(SPISettings(20000000, MSBFIRST, > SPI_MODE2)); > > digitalWrite(DACCSPin, LOW); > SPI.transfer16(0B0011000000000000 | sines_of_steps[i]); > // bits: DAC channel A, buffer off, gain 1x > (Vout=VRef*D/4096), output on, 12-bit data (D) > digitalWrite(DACCSPin, HIGH); > > digitalWrite(DACCSPin, LOW); > SPI.transfer16(0B1011000000000000 | sines_of_steps[steps - 1 - > i]); > // bits: DAC channel B, buffer off, gain 1x > (Vout=VRef*D/4096), output on, 12-bit data (D) > digitalWrite(DACCSPin, HIGH); > > SPI.endTransaction(); > } > > } > } > Il giorno mercoledì 22 novembre 2023 alle 08:55:55 UTC jörg ha scritto: > >> Pretty nice photos. >> I like it too, to disable blanking and to see the painting beam. >> I did some tests with the MCP4922, too, but it was too slow for me. >> Mabe you've found a better way (code) driving it. If you don't mind, I'm >> intersted in a code snipped and which lib you have used. >> I ended up in a AD5344, which works pretty well for me on the >> teensy40/41). So maybe I will give the 4922 a second try. >> And I'm curious about your powersupply approach. Especial the +-5V and >> noise. I'm using a switched one, which is too noisy. >> Last, I'm in the same problem, getting a sharp image an tweaking with >> focus, astig etc. >> So, if you get good results with the emitter follower, please share your >> experience. >> Cheers >> Jörg >> >> >> >> On Monday, November 20, 2023 at 9:37:35 PM UTC+1 GDR GDR wrote: >> >>> wow! while the technical details are all "greek" to me, the images look >>> amazing. I love the "artifacts" in them. I dont know how you took these, >>> but it looks awesome! I like it as it is! not sure how this looks like in >>> "motion" but looks great in the stills... can you post some more? cheers >>> >>> On Sunday, November 19, 2023 at 4:25:50 PM UTC-6 Anders Mikkelsen wrote: >>> >>>> I recently started playing with scope clocks again, after seeing >>>> David's circle graphics clock the better part of two decades ago and >>>> having >>>> had it in the back of my mind since. This was prompted by Teensy 4.1 >>>> becoming available again on the market, and the official port of the SCTV >>>> codebase for this platform. I got it up and running, and explored some >>>> aspects around the design, I thought I'd share some info with the group in >>>> case anybody else can benefit from it. >>>> >>>> Firstly, off-the-shelf flyback transformers for low power auxiliary >>>> supplies work very well in Baxandall oscillators to make the required >>>> voltages at minimal cost and complexity, without using any custom parts. I >>>> used a Wurth 750310787, but many others are available. A buck converter >>>> can >>>> be wrapped around the circuit to get good line and load regulation, and >>>> the >>>> resulting BOM cost is less than 5 bucks. An off-the-shelf gate drive >>>> transformer can be used to drive the filament, providing the required >>>> isolation and power handling for a few bucks more, making a very simple >>>> and >>>> cheap design. >>>> >>>> Secondly, the LT DAC in the design can be replaced by a much more >>>> affordable (and easy to solder) MCP4922, without taking a hit on the DAC >>>> update rate. A comparison of the two parts would suggest that the 20 MHz >>>> maximum SPI rate of this part would significantly impact performance, but >>>> in practice it ends up working at around 500 KSPS as well. The issue with >>>> the original part is that it relies on 24 bit SPI transfers, which are >>>> again implemented as an 8 bit and a 16 bit transfer, and the overhead from >>>> reconfiguring the SPI peripheral and waiting for the receive buffer to >>>> fill >>>> is significant. The MCP allows native 16 bit operation of the peripheral, >>>> and use of the transmit FIFO to make the transfers without any >>>> intervention >>>> from the firmware once a set of XY coordinates are passed. I also >>>> experimented with porting the code to run on an RP2040, which works well >>>> so >>>> far. I haven't assembled the RTC part yet, but everything else seems to >>>> work with minimal changes to the code. The biggest effort was figuring out >>>> how to do efficient SPI transfers, which required some raw register >>>> access, >>>> and clock tree reconfiguration for synchronous operation of the SPI >>>> peripheral (which is not the case with the Arduino default clock frequency >>>> for this board). >>>> >>>> Thirdly, I did struggle a lot with getting a sharp image without having >>>> a lot of interaction between focus, brightness and astigmatism. Part of it >>>> came from feeding the cathode from a high impedance point in the divider, >>>> but a major factor turned out to be the source impedance of the anode >>>> drive. Most circuits I've seen drive the anode from a potentiometer fed >>>> from the deflection design. Most CRTs seem to draw an anode current that's >>>> significantly higher than the screen current, often by an order of >>>> magnitude, and this current causes the anode voltage to drift around as >>>> the >>>> brightness is adjusted. I initially used the high value of 1 Mohm for the >>>> pot, which exaggerated this issue a bit as well. In electrostatic CRTs, >>>> the >>>> final anode together with the first set of deflection plates forms a >>>> cylindrical lens, that affects both image geometry and beam focus. I >>>> looked >>>> at some oscilloscope schematics, and found some that use an emitter >>>> follower to buffer the output of the astigmatism pot to deal with this, >>>> and >>>> I'm just waiting for some parts in order to try this out in my design. >>>> >>>> I tried it with a range of old CRTs, and most of them struggle with >>>> getting a sharp dot near the edges of the screen. I suspect this is partly >>>> due to my sagging voltages, but I'll see if the improvements address it. >>>> Does anybody know what to expect in terms of corner spot size for typical >>>> non-PDA electrostatic CRTs in the range of 30 - 100 mm screen diameter? >>>> This is at 1200 V, and with enough beam current to make the scope clock >>>> image readable in a room with normal indoor lighting. >>>> >>>> Some pictures attached in order to compensate for all the words. >>>> >>>> AM >>>> >>> > -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to neonixie-l+...@googlegroups.com. > > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/23535526-26bb-432a-b809-8c3e83918727n%40googlegroups.com > > <https://groups.google.com/d/msgid/neonixie-l/23535526-26bb-432a-b809-8c3e83918727n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. 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