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Beginners / Re: oscilloscope problem
« Last post by dcbrown73 on Today at 11:21:34 pm »If it's freezing up, I would check for firmware updates also. It could be a known issue that is already resolved in firmware.
Recent Posts
2
Repair / Re: TDS744A: 1M input impedance measures: Ch3 = 160Kohm, Ch4 = 706KOhm [resolved]
« Last post by TERRA Operative on Today at 11:20:54 pm »I use standard rosin flux cleaned off with alcohol and never have a problem. I'll be sure to avoid organic fluxes on ceramic substrates from now on though.
Also as a side note, the thermal paste on the hybrid module is important, so make sure you replace it after washing or you'll burn out the chips on the hybrid module!
Also as a side note, the thermal paste on the hybrid module is important, so make sure you replace it after washing or you'll burn out the chips on the hybrid module!
3
Other Equipment & Products / Re: Pace ADS200 soldering station
« Last post by bdunham7 on Today at 11:20:26 pm »Does that mean they changed:
- electronic board and/or other parts of hardware
- there is only new FW (so it can be applied to old stations boards)
Tip changes are OK, when old tips go I will get new ones with better performance but will it be any better without new controller?
Can existing users upgrade (just electronic board, or FW) ?
I would think of two changes that could be made, one simple and one obvious but maybe not simple.
First, since the thermocouple-in-series design requires that the power be turned off in order to read the thermocouple, reducing the frequency of the thermocouple reads would increase the power on time. In order not to lose the excellent tip temperature control under normal operation, they could have the system skip a reading or two whenever the tip temperature drops by a certain amount. So +/-5C they'd take the temp readings at the normal rate, at -5 to -10C they'd skip every other reading and -10C or more they'd just take a reading every 4th time, or maybe even less. Using this technique they might get the system to put out 20-25% more power according to what I was seeing in my earlier post.
The other obvious improvement would be either to get the thermocouple closer to the tip surface or to make all of the larger tips have a similar thermal resistance in this area so the controller can compensate by boosting the target when the power levels are high.
In any case, it would be great if they just told us, even greater if they made the improvements available through an upgrade. Now if their fix was to alter the transformer windings for a higher secondary output, then I guess we're all bag holders. They might not want to tell us in that case...
4
Repair / Re: TEK 475A VOLTS/DIV compensation problem
« Last post by David Hess on Today at 11:17:09 pm »I have had a few attenuator modules where the connection between the pin and the substrate was bad. I fixed them by using 2% silver solder to solder the pin where it contacts the hybrid substrate trace.
5
General Technical Chat / Re: Do you think an LED is a resistor?
« Last post by Someone on Today at 11:16:56 pm »Oh new words and definitions to play with. How about we take the IEEE dictionary as the authoritative reference:That was your long winded and dithering proof:non linear system has linear approximation around a small operating point....
STOP THE PRESSES!
... oh wait, that's the underlying principle of how spice AC analysis works.
Small signal analysis has nothing to do with what we are discussing here.
The resistance I talk about is the static resistance, not the dynamic or incremental resistance of small signal analysis.
Try again.So, we are now seeing the diode as a voltage dependent resistor. Let's see... what is the resistance 400mV? Let's zoom in:So to try and claim you're not relying on the well known small signal AC parameters is plainly incorrect.
[MASSIVE IMAGE]
I'd say it's about 23.2 kohm.
Let's see what is the resistance at, I don't know, 660 mV (about 5mA of diode current). We can compute it by hand of course, but on the graph we see it is 132 ohm.
[MASSIVE IMAGE]
Now, let's see if we can make something with these values...
[snipping conversational fluff]
Ok, exact same results, if we neglect a bit of rounding error in reading and setting the values.
Now, take your black boxes out of the fridge. Put the diodes D1 and D2, and the resistors R1 and R2 inside a black box each. Shuffle them around. And tell me: without looking inside the black boxes and without resorting to second order effects (like temperature dependence, or changing the other circuital parameters to change the operating points) can you tell me which are the diodes and which are the resistors, by simply measuring voltages, currents and powers?
If you dont like relying on small signal characteristics, perhaps "try again" with your explanation/justification.
Again, small signal analysis has nothing to do with anything I have written in that post.
Nothing.
I zoomed in on the V-R characteristic to find an accurate value of the static resistance. Not the dynamic, or incremental, or small signal resistance.
Then I used the static resistance at a chosen voltage or current to choose the limiting resistor that would have set the chosen operating point.
Then I showed that using a resistor with the correct static resistance value would give the same variables in the circuit..
If you want to waste a bit of time you can create in LTspice a voltage controlled resistor that has the same R=R(V) dependence of a 1N4148. You will then see that it will behave (secondary effects apart) as a diode, confirming that it's the variable resistance. that gives a diode its behavior.
Go ahead and try.
static resistance (semiconductor rectifier device) (forward or reverse) The quotient of the voltage by the current at a stated point on the static characteristic curve.
small-signal resistance The resistive part of the quotient of incremental voltage by incremental current under stated operating conditions.
small-signal A signal which when doubled in magnitude does not produce a change in the parameter being measured that is greater than the required accuracy of the measurement.
As I said in my opening statement, you're just playing with small signal analysis a well known and entirely un-novel method. There is nothing interesting here as most anything can be described as a small signal resistor (with bounds on some other dimension). So you're still wrong and trying to twist definitions to your liking while ignoring the consensus and the established science.
6
Projects, Designs, and Technical Stuff / Re: Coulomb counter IC for coin cell products.
« Last post by SiliconWizard on Today at 11:16:44 pm »The BQ35100 may do what you need, and a bit more.
https://www.ti.com/product/BQ35100
https://www.ti.com/product/BQ35100
7
Projects, Designs, and Technical Stuff / Re: Nichicon UPJ for switching power supplies - what's so special about these caps?
« Last post by mightyohm on Today at 11:16:32 pm »Thanks for the warning about stability. The board came with PL series caps, which are fairly low ESR. I figure that as long as I keep around the same ESR (and capacitance) I should be fine.
8
Beginners / Re: Convert US standard 115V to International 230V
« Last post by IanB on Today at 11:14:02 pm »Thank you all for the suggestions, this is very helpful. It is a stationary robotic gait trainer for those wondering, and this is an existing system that I am now involved in. I am a bit confused by those mentioning it already being transformer, could you please elaborate, for reference the 2 PSU I am using in the system are Meanwell HRP-150-24 and HRP-600-36 units.
Those power supplies are already universal voltage input units. You don't need to do anything, they will work just as they stand.
Haven't you looked them up already?
https://www.meanwell.com/productPdf.aspx?i=427
https://www.meanwell.com/Upload/PDF/HRP-600/HRP-600-SPEC.PDF
9
Metrology / Re: Analog frontends for DMMs approaching 8.5 digits - Discussions
« Last post by julian1 on Today at 11:13:30 pm »Hi Curtis, thank you very much for your detailed comments.
I wanted to ask, if you use COTS or custom RF cans and how you route the land vias, in the nanovolt thread, but didn't want to pollute the discussion with mundane detail.
In your research - did you find any makers of (fence and lid style) RF shields who can manage custom dimensions, in prototype quantities?
I should search on the manufacturers you list - Orbel, Lazerlok, Laird to see if they offer custom services.
To improvise - I did a Freecad step/dxf model for 0.8mm mild-steel sheet, and had it fabricated to try to prove the concept.
This approach should be OK for the larger LF magnetic (and thermal) guard cover, but is the wrong thickness for a rf-can.
I found a source of pre-tinned (for solderability) mild-steel in 0.2mm and 0.3mm thickness, but need to find a (local) service who can cut and fold the thinner metal.
Being able to pop the lid for access is probably needed as you note.
At this point, there's a trade-off between money spent on custom fabrication, versus extra time routing the pcb to accomodate fixed dimensioned parts.
The simultaneous aspect of mechanical design is a challenge.
Using EMI sniffer probes and then doing experiments, switching between a bench supply and DC/DC converter is a really good idea.
Perhaps small electric and/or magnetic probes could be made a permanent (pcb) feature, that remain under the RF cans?
So the probes would route and present to a DUT connection header outside of the shield can.
I purchased a set of near field probes to try to get a bit familiar with doing EMI tests, but there's no way to use them with the cans fitted.
Are there advantages in using JLC2116 versus other stackups, or even a basic manufacturing stack-up?
It seems like a good thing, if everything is well defined from a manufacturing pov.
Perhaps routing the fast digital signals (spi, adc control) with controlled impedance might reduce radiated emi, even if there are no timing/reflection needs.
For the dmm board, there are inner and outer layer grounds to shield (capacitive, magnetic) mostly orthogonal traces.
For the amplifier there are soic-8 footprints for jfe2140, and lsk389.
There is also a footprint for if3602.
I noted your comments about the thermal wander of the if3602 from the DIY cascode jfet lna thread,
So there is a 4-cycle sample acquisition sequence, that can measure and compensate the amp gain, against a small reference-voltage.
But use of if3602 is more in view as an alternative configuration like HP 34420a, rather than a general DMM and is not a priority.
Following Kleinstein's suggestion, I did some Allan variance noise tests with the jfe2140, posted in this thread, but still need to do it for the other parts.
I don't remember the numbers, but in a separate LNA project that I modeled a lot after your initial discrete jfet LNA design, I found lsk389 to be lower noise than jfe2140, but higher leakage (to be expected).
But shielding really needs to be improved first to gain confidence.
For supplies - at least for a first pass - I want to see if the design can be managed without dc/dc converters - and AZ ops for that matter.
I believe Shahriar Shahramian uncovered issues with the DMM7510 - even with the super low-coupling transformer used in that design.
I suspect fast voltage transitions on the rectifiers are a problem.
Adding LC filtering after rectification re-introduces coupling capacitance on the inductors.
So power supply issues are pushed-out as separate scope.
As fallback, I have a simple open-loop fixed-freq. push-pull, and resonant llc with zcs to test on a board, but they are a bit basic.
So for a power supply at the moment - the board can run with a scavenged 34401a mains-transformer (power input headers are designed to match).
Although this transformer is inadequate - with higher than expected coupling-capacitance and lack of a proper screen guard.
I did an experiment stuffing a small sheet of copper, between the two bobbins of Bel signal transformer, as a makeshift guard.
And this already works to reduces coupling (3x reduction from memory) better than the 34401a transformer, so it may something to explore.
If EMI can be measured qualitatively following your approach - with some sniffer probes. then trying out different supplies should be more of an option.
I wanted to ask, if you use COTS or custom RF cans and how you route the land vias, in the nanovolt thread, but didn't want to pollute the discussion with mundane detail.
In your research - did you find any makers of (fence and lid style) RF shields who can manage custom dimensions, in prototype quantities?
I should search on the manufacturers you list - Orbel, Lazerlok, Laird to see if they offer custom services.
To improvise - I did a Freecad step/dxf model for 0.8mm mild-steel sheet, and had it fabricated to try to prove the concept.
This approach should be OK for the larger LF magnetic (and thermal) guard cover, but is the wrong thickness for a rf-can.
I found a source of pre-tinned (for solderability) mild-steel in 0.2mm and 0.3mm thickness, but need to find a (local) service who can cut and fold the thinner metal.
Being able to pop the lid for access is probably needed as you note.
At this point, there's a trade-off between money spent on custom fabrication, versus extra time routing the pcb to accomodate fixed dimensioned parts.
The simultaneous aspect of mechanical design is a challenge.
The performance of the shields on the boards is quite good. I have used a sniffer probe made with five turns of magnet wire amplified 25x with two ADA4896 stages (about 30 MHz bandwidth) to get a qualititative feel for EMI around the board.
Using EMI sniffer probes and then doing experiments, switching between a bench supply and DC/DC converter is a really good idea.
Perhaps small electric and/or magnetic probes could be made a permanent (pcb) feature, that remain under the RF cans?
So the probes would route and present to a DUT connection header outside of the shield can.
I purchased a set of near field probes to try to get a bit familiar with doing EMI tests, but there's no way to use them with the cans fitted.
For the stackup, I used a 6-layer 1.2 mm board with the JLC2116 stackup.
Are there advantages in using JLC2116 versus other stackups, or even a basic manufacturing stack-up?
It seems like a good thing, if everything is well defined from a manufacturing pov.
Perhaps routing the fast digital signals (spi, adc control) with controlled impedance might reduce radiated emi, even if there are no timing/reflection needs.
For the dmm board, there are inner and outer layer grounds to shield (capacitive, magnetic) mostly orthogonal traces.
For the amplifier there are soic-8 footprints for jfe2140, and lsk389.
There is also a footprint for if3602.
I noted your comments about the thermal wander of the if3602 from the DIY cascode jfet lna thread,
So there is a 4-cycle sample acquisition sequence, that can measure and compensate the amp gain, against a small reference-voltage.
But use of if3602 is more in view as an alternative configuration like HP 34420a, rather than a general DMM and is not a priority.
Following Kleinstein's suggestion, I did some Allan variance noise tests with the jfe2140, posted in this thread, but still need to do it for the other parts.
I don't remember the numbers, but in a separate LNA project that I modeled a lot after your initial discrete jfet LNA design, I found lsk389 to be lower noise than jfe2140, but higher leakage (to be expected).
But shielding really needs to be improved first to gain confidence.
For supplies - at least for a first pass - I want to see if the design can be managed without dc/dc converters - and AZ ops for that matter.
I believe Shahriar Shahramian uncovered issues with the DMM7510 - even with the super low-coupling transformer used in that design.
I suspect fast voltage transitions on the rectifiers are a problem.
Adding LC filtering after rectification re-introduces coupling capacitance on the inductors.
So power supply issues are pushed-out as separate scope.
As fallback, I have a simple open-loop fixed-freq. push-pull, and resonant llc with zcs to test on a board, but they are a bit basic.
So for a power supply at the moment - the board can run with a scavenged 34401a mains-transformer (power input headers are designed to match).
Although this transformer is inadequate - with higher than expected coupling-capacitance and lack of a proper screen guard.
I did an experiment stuffing a small sheet of copper, between the two bobbins of Bel signal transformer, as a makeshift guard.
And this already works to reduces coupling (3x reduction from memory) better than the 34401a transformer, so it may something to explore.
If EMI can be measured qualitatively following your approach - with some sniffer probes. then trying out different supplies should be more of an option.
10
RF, Microwave, Ham Radio / Re: WSJT-X on Pi
« Last post by metrologist on Today at 11:09:50 pm »And
Nope!
pi@raspberrypi:~/Downloads $ sudo dpkg -i wsjtx_2.6.1_armhf.deb
(Reading database ... 113061 files and directories currently installed.)
Preparing to unpack wsjtx_2.6.1_armhf.deb ...
Unpacking wsjtx (2.6.1) over (2.6.1) ...
dpkg: dependency problems prevent configuration of wsjtx:
wsjtx depends on libgfortran5 (>= 8.3) | libgfortran4 (>= 7.3) | libgfortran3 (>= 6.3); however:
Package libgfortran5 is not installed.
Package libgfortran4 is not installed.
Version of libgfortran3:armhf on system is 4.9.2-10.
wsjtx depends on libgomp1 (>= 6); however:
Version of libgomp1:armhf on system is 4.9.2-10.
wsjtx depends on libqt5serialport5 (>= 5.7); however:
Package libqt5serialport5 is not installed.
wsjtx depends on libqt5multimedia5-plugins (>= 5.7); however:
Package libqt5multimedia5-plugins is not installed.
wsjtx depends on libqt5widgets5 (>= 5.7); however:
Version of libqt5widgets5:armhf on system is 5.3.2+dfsg-4+rpi1.
wsjtx depends on libqt5network5 (>= 5.7); however:
Version of libqt5network5:armhf on system is 5.3.2+dfsg-4+rpi1.
wsjtx depends on libqt5printsupport5 (>= 5.7); however:
Version of libqt5printsupport5:armhf on system is 5.3.2+dfsg-4+rpi1.
wsjtx depends on libqt5sql5-sqlite (>= 5.7); however:
Pa
dpkg: error processing package wsjtx (--install):
dependency problems - leaving unconfigured
Processing triggers for gnome-menus (3.13.3-6) ...
Processing triggers for desktop-file-utils (0.22-1) ...
Processing triggers for mime-support (3.58) ...
Errors were encountered while processing:
wsjtx
pi@raspberrypi:~/Downloads $
Nope!
pi@raspberrypi:~/Downloads $ sudo dpkg -i wsjtx_2.6.1_armhf.deb
(Reading database ... 113061 files and directories currently installed.)
Preparing to unpack wsjtx_2.6.1_armhf.deb ...
Unpacking wsjtx (2.6.1) over (2.6.1) ...
dpkg: dependency problems prevent configuration of wsjtx:
wsjtx depends on libgfortran5 (>= 8.3) | libgfortran4 (>= 7.3) | libgfortran3 (>= 6.3); however:
Package libgfortran5 is not installed.
Package libgfortran4 is not installed.
Version of libgfortran3:armhf on system is 4.9.2-10.
wsjtx depends on libgomp1 (>= 6); however:
Version of libgomp1:armhf on system is 4.9.2-10.
wsjtx depends on libqt5serialport5 (>= 5.7); however:
Package libqt5serialport5 is not installed.
wsjtx depends on libqt5multimedia5-plugins (>= 5.7); however:
Package libqt5multimedia5-plugins is not installed.
wsjtx depends on libqt5widgets5 (>= 5.7); however:
Version of libqt5widgets5:armhf on system is 5.3.2+dfsg-4+rpi1.
wsjtx depends on libqt5network5 (>= 5.7); however:
Version of libqt5network5:armhf on system is 5.3.2+dfsg-4+rpi1.
wsjtx depends on libqt5printsupport5 (>= 5.7); however:
Version of libqt5printsupport5:armhf on system is 5.3.2+dfsg-4+rpi1.
wsjtx depends on libqt5sql5-sqlite (>= 5.7); however:
Pa
dpkg: error processing package wsjtx (--install):
dependency problems - leaving unconfigured
Processing triggers for gnome-menus (3.13.3-6) ...
Processing triggers for desktop-file-utils (0.22-1) ...
Processing triggers for mime-support (3.58) ...
Errors were encountered while processing:
wsjtx
pi@raspberrypi:~/Downloads $