Recent Posts

1

Projects, Designs, and Technical Stuff / 3-phase diode bridge - 6 separate windings

« Last post by Nix2 on Today at 11:11:55 am »

Hi.
I have a old Bester Magster 160 MIG MAG machine, in which I will replace the main transformer.
The problem is that the new transformer (photo on the right) has the simplest winding system, it has a secondary winding connected in a star (so only 3 windings), while the original transformer had 6 secondary windings (photo on the left) , connected to a specific diode bridge.


And here I wonder - this is a very interesting, but non-standard and rarely seen circuit (Google is also silent on this subject) and the bridge diagram/circuit is hardly legible... Is this a modification of the classic 6-pulse, 3-phase bridge rectifier?
Regards

https://ibb.co/n85L500

2

Beginners / Re: High frequency (50kHz) 16 bit PWM

« Last post by tooki on Today at 11:11:46 am »

I don't understand why you need LED flashes during exposure and can't drive LED with PWM passed through low pass filter?

Because I get a signal from the PLC and need to capture 2 images in fast sequence, with 2 different brightnesses.
So at the moment I set the PWM value that will change in 1/50000 of a second after the command. And then start the camera trigger by software. Between setting the PWM value and the CCD exposure starting is about 1 ms or even shorter (and probably not constant, the trigger is send over USB)
So the time is too short for LP filter to settle at a constant value during the exposure.

P.S. I can get away with the 10 bits I have now. Always on the lookout for a better solution.

You could divide the LEDs into two or more banks that you can control independently, adding another level of brightness control without needing more bits of PWM. (For example, alternate every LED between 2 banks, so that for lower brightnesses, you just disable one bank.)

Another thing you could consider is not using PWM, but some other encoding like PDM (pulse density modulation, which is almost the same thing as delta-sigma modulation). This would reduce the brightness error by spreading out the pulses within a 16-bit value.

It also seems to me you could use a DAC to control a constant-current LED driver. Modern audio DACs, for example, are often 24-bit at 48, 96, and 192kHz, more than enough. The question I don’t know off the top of my head is how long the latency is.

3

Repair / Re: 18V/3A HY1503 PSU - weird CC/CV behavior while charging battery cells

« Last post by iMo on Today at 11:10:37 am »

 
Yep, a full idiotizm may cost time and effort and money (and often life).. 

I've removed the long leads from the shunt (the 0.33ohm placed in rear part of the box) to my new switch on the front panel (creating a loop antenna) and all oscillations are gone.. (with 1n only in the 741 feedback). What is left are the couple of mVpp 100Hz ripples at the CV and CC opamp's outputs.
I will make the transient test next weeks.
Also I have to solve the 200mA/3A switching as well as I need the lower CC range as well..

4

Test Equipment / Re: SDS800X HD Bug Reports + Firmware

« Last post by electr_peter on Today at 11:10:36 am »

Bug with vertical zoom persists - can anyone confirm this behavior? Is it the same on other Siglent scopes?
To reproduce bug, set "Vertical ref" to offset and try zooming in on the top of square wave. See attached picture of a results from zoomong in, behaviour is incorrect.

There is a bug with vertical zoom functionality as described in topic Siglent SDS800X HD 12 bit DSO's. Screenshots describing situation are in a linked post.

SDS800X HD in zoom mode with Fixed Offset for Vertical Ref behaves strangely (1.1.3.6/3.8.12 FW) Utility > Menu > System Setting > Reference Pos > Vertical Ref [Fixed Position/Fixed Offset]

Setup - square wave 0V/3V input signal, edge trigger at 0.3V. Make signal full screen, then enable zoom mode and try to focus on the very top part of square wave. With vertical reference set to "Fixed Offset" zooming vertically "moves down" zoom box in level (!) and requires vertical offset adjustment.

Is it expected behavior? I don't see how this is useful.
IMO Vertical Ref option should not affect zoom mode at all and zoom mode should work as it currently does with "Fixed Position" setting.

The same issue remains with the newest FW 1.1.3.8.

Added screenshots (with descriptions) of the vertical zoom in Fixed Offset and Fixed Position Vertical Ref modes. Screenshots show a sequence of zoom ins and manual offset adjustments, trying to get to the top part of square wave. Observe position of zoom box in top part of the screen - clearly Fixed Offset has some issues while Fixed Position works.

Also, I am not sure I like the way scaling of Reference waveforms works while not in zoom mode (Vertical Ref does not affect Reference waveforms), but at least it is not buggy.

5

Microcontrollers / Re: STM32G0 dma can't read const data from flash in boot memory space

« Last post by voltsandjolts on Today at 11:04:01 am »

linker setup that remaps flash to adress 00000000

You shouldn't use linker settings to remap flash, that's the job of hardware in the mcu. Linker should use the default 0x8000000, as David says.

That way &spidat will give real hardware addresses required by the dma unit, whether spidat is in flash or ram.

Also note that keyword 'const' by itself is not a guarantee that a variable is only stored in flash.

6

Beginners / Re: High frequency (50kHz) 16 bit PWM

« Last post by tggzzz on Today at 11:02:12 am »

But unless you need computer control, it is probably simplest to just use a PSU to set the current.

That is the problem the PC needs to set the brightness and it should be stable within 1 ms.

Apparently you only need two brightnesses, but to switch between them.

Have two slow speed DACs each controlling separate "DC" currents. Use a fast digital signal to divert the currents into either the LEDs or a different load.

Consider a long-tailed pair with the DAC controlling the emitter "tail" current. One collector would have the LEDs as a load, the differential signal on the base would direct the emitter current through one or other of the collectors.

In this diagram one collector resistor would be replaced by the LEDs. Ignore the marked voltage "outputs"; your output is the current into the LED


The current would be switched orders of magnitude faster than 1ms, so the LED response would dominate the timing.

7

General Technical Chat / Re: Submersible missing while visiting Titanic wreck

« Last post by EEVblog on Today at 10:59:09 am »

I watched the new The Grand Tour (Top Gear) road trip special through Zimbabwe, and Hammond did a joke about the sub. I guess it's old enough to be funny now.

8

Repair / Re: 18V/3A HY1503 PSU - weird CC/CV behavior while charging battery cells

« Last post by xavier60 on Today at 10:53:49 am »

Maybe it's oscillation in the output stage. If so, the signal should be a bit stronger on the anode of D12.

9

Repair / HP 6654A Opt.J23

« Last post by kjk24 on Today at 10:53:22 am »

Hi,

the Powersupply HP 6654A has Option J23 Label on the backside.
Has someone more information for the Option J23 ?, i found this but its only a sellers information
6654A-J23
Output voltage: 0 to 60 V (0-80V opt.J23)
Output current (40°C): 0 to 9 A (0-6A opt.J23)

I repair it for a while now.
The voltage is higher then expected and current is to low.
I cant calibrate it with the standard eeprom setting becouse the calibration constants dose not fit to the values what the device produce during calibration.

i changed the calibration eeprom settings to fit with the Voltage what the PS generate (~75V).
like this i can calibrate the Voltage and overvoltage. But the current is strange, when i start the calibration the first current point is around 0.4A and the second point it shows UNR and the current is only 5.6A with a 0.11Ohm Resistor.

i made the calibration Basic Programms to python and use a Agilent GPIB interface to reprogramm the eeprom Settings, i attatch it. (you should know what you do with the scripts !! have a look into it first !)

has some one A unit and can readout the eeprom constants for me please ? i can assist how to doit.

thanks a lot.
greetings KK

10

Projects, Designs, and Technical Stuff / Re: Energizer Ultimate Lithium: sudden failure of only some cells

« Last post by MK14 on Today at 10:51:53 am »

I have a SONY radio that uses 4 AA cells in series. There obviously is a quiescent drain as a LCD clock is run when 'off' - and I've measured it as 0.15mA.

Does everything in the device use the full voltage of all four cells?

Maybe the LCD clock, runs from 3V, from just 2 of the AA batteries, as first hinted at, by the second post, I quoted (6V could be too high for that part of the circuitry and/or increase the quiescent current, by a fair bit, probably double).

Is the '0.15mA' quiescent current, coming from all 4 batteries, or just two of them? (presumably the ones which end up at near 0 volts, eventually).