Recent Posts

Pages: [1] 2 3 4 5 6 ... 10 Next
1
I'm just lost on what is the end goal of all this trouble?
Resistors and their specs are built to purpose (usually). What is it in here for DIY?

I had a friend stop by last year, and I was showing him my 3458A and some other precision gear.  He said: "Why in the hell would anybody need THAT many digits!?!?!"  He was right of course, because in real life, we only need a good hand-held meter (Like a Fluke 87-V or similar) for day-to-day work.  I told him: "I have all of these digits of precision because it's fun, and I CAN".  It's the same reason that people jump out of perfectly good airplanes and climb very tall mountains; because the activity is challenging and exciting (and dangerous too).  In retrospect, I would also add that all human beings are learning until death, and in fact if we stop learning, then we might as well BE dead.  Knowing how components are made is the first step to knowing if they are made correctly and are behaving (or will behave) correctly in our circuits.  There are many amateur radio enthusiasts that still build their own gear, even though there are commercial transceivers that far exceed anyone's expectations.  But, DIY radios can explore the fringes of the art, where the commercial radio manufacturers fear to go, (because there is no money in it).  Amateur radio enthusiasts ("hams") have furthered the state of the art in many areas that simply would not have been done commercially.  And so, it is the same with precision artifacts and precision gear; DIY is a way to learn and/or understand the art, and (possibly) to push against the boundaries, which is where most great discoveries come from.  So, THAT's why we DIY.

The commercial guys (except for Edwin it seems) hold on to their proprietary IP with a "death grip"; and for good (business) reasons.  So, we must DIY if we are to learn about PWW resistors.  Who knows?  Maybe, someone will decide to make a DIY foil resistor (using Evanohm-S foil on a TCR-matched substrate of some sort).  For now, resistance wire seems the way to go for DIY (for now), and it also appears to be the best solution for very high and very low values.  There also needs to be a parallel effort in developing DIY hermetic packages.
2
Microcontrollers & FPGAs / Re: Small Lab (SLab) release
« Last post by Vic20 on Today at 05:12:56 AM »
USB power is diode connected to the 3.3V ST-Link regulator with no way to isolate it short of removing the diode.  The U5V vs E5V jumper only handles power to the uC regulator.

Yes, I noticed that.
You cannot prevent a path from the E5V line to the USB line although the diode gives some protection.
The best way to provide isolation is snapping the USB part of the Nucleo board.
Then power the MCU part of the board from E5V or VIN

There are several lines that go from the USB part to the MCU part of the Nucleo board, but during normal SLab operation only three are needed: MCO, RX and TX. You can use three optocouplers for them. MCO is needed unless you populate the oscillator components on the MCU side of the board. The requirement for the optos will be the 8 MHz MCO signal as the RX and TX signals are lower frequency.
Connecting RX and TX after snapping the board requires installing two solder bridges to have access to those signals on D0 and D1 or the Morpho pins.

During MCU programming you will need to provide a path for the SWIM signals: TCK, TMS, NRST and the Vdd sense. I think SWO is not really needed.

Quote
Even if E5V is fed from an outside source, parts of the board are still powered over the USB input.  When E5V is jumper selected, ST-Link loses the ability to control power to the uC.  I don't know what this capability is used for but it goes away.

The E5V jumper position just makes the external source on VIN or E5V power the main MCU. You will still be powering the ST-Link MCU depending on the voltages on the E5V and U5V nodes.

If you remove diode D2 and put jumper JP5 on E5V, then you won't never use USB power.
There will be a path from E5V to 3V3 trough a regulator and from 3V3 to the USB connector trough T1.
But the most important thing is that powering the ST-Link MCU from E5V has the potential hazard that something that blows E5V can blow the ST-Link MCU that is connected to the PC on the USB lines.

Quote
I had thought that having just 30 mA for the DUT was a little skimpy if I wanted to do transistor curves above that level.  I'm not thinking about 2N3055s but even 2N3904/5 are good for more than 30 mA of collector current.

I am going to break out E5V on my board so I can feed it from a 5V wall wart but I am planning to use it with USB power until I can't.  I always plug my projects into a powered USB hub, never directly into my PCs.  On my Surface Book, the powered hub is connected to the powered docking station which, sooner or later, gets connected to my PC.  I would have to do something incredibly stupid to break through an isolator and 2 powered hubs to get to my PC.  Even without the isolator, it would be tough to damage the PC.  I simply don't work at higher voltage levels.

Seems like a good plan.
Adding 100k resistors to the opamps positive inputs, both ADC and DACS, will provide some protection for the ADC and DAC lines. Using an external supply independent from USB will somewhat protect the USB power bus.
I know that it is good to be paranoid when dealing with protection, but those kinds of potential problems are always present when you deal with MCU demonstration boards.
3
Soo... Those 220uF 25V, are they what you feel they should have been, or do you actually have 25V instead of the underspec'ed 16V me and others were complaining about?
4
Beginners / Re: Your Help Needed designing affordable electric bike!
« Last post by rstofer on Today at 05:10:59 AM »
Most of these projects tend to start with treadmill motors:

http://www.ebay.com/bhp/treadmill-motor-dc
5
Beginners / Re: Your Help Needed designing affordable electric bike!
« Last post by rstofer on Today at 05:09:58 AM »
wait a sec. 300kg/cm ?I'm old school and that's like 20000 foot pounds ! That's 5 Chevy's!

I think you're off by 3 orders of magnitude:

https://www.convertunits.com/from/kg-cm/to/foot-pound+force

It's around 22 foot-pounds.
6
Looking for something like this?

https://upload.wikimedia.org/wikipedia/commons/6/6d/Transistor_Clock.jpg

No ICs included ;)
Yes... But with better implementation.  ;)

That one seems to take the base clock signal from the mains. Not too exited.

It should be quite easy to build a 32.768 kHz xtal oscillator and build 15 divide by two flip-flops giving 1 Hz.
7
Thermal Imaging / Re: Best thermal camera for $300
« Last post by Fraser on Today at 05:07:48 AM »
Some sample pictures taken with the Irisys IRI4035 160 x 120 pixel camera.

These are as 'raw' as I could make them. No careful setting up or processing of the picture. Just nice and RAW  :) Te camera was started and set to auto, nothing else was done before taking pictures. Nicer looking pictures are possible at the expense of Delta V detail.

Note teh IRISYS camera software does a great job of smoothing and interpolating the image up to 640 x 480 but such would be an unfair comparison against the Lepton images.

160 x 120 pixels is enough, if inside the right camera  ;)

Oooops !  Pictures need to be changed from BMP so I will do that and upload ASAP.

Fraser
8
General Chat / Re: What did you buy today? Post your latest purchase!
« Last post by grumpydoc on Today at 05:06:03 AM »
On NASes... a Google search turned up this:

http://www.itinstock.com/dell-powervault-md1000-sas-sata-15-bay-drive-storage-array-san-2-x-controllers-33384

Yeah, the MD1000 is really just a box of disks, PSU's and a couple of SAS expanders - no "intelligence" as such.

Actually someone I knew built a NAS from something similar - in this case http://www.supermicro.com/products/chassis/4u/847/SC847E16-R1K28LPB - apparently the fans sound like a jet taking off.

I've finished for not - everything squeezed in and cables tied off neatly and an OS installed. My final view on the case it that it's OK, a bit pricy but OK - it does, in fact, have per disk activity LEDs - I didn't notice the tiny light guides in the disk caddies.

So there are just two outstanding issues:

1) The Toshiba N300 8TB drives, I realise that there are a few comments on Amazon to the effect that these drives are, or can be, noisy but I thought "no modern HDD is that loud". Completely wrong - these emit an irritating deep clicking noise on head movement. It was especially irritating when ext4 was doing its lazy table/journal initialisation - after a few minutes I just wanted it to stop. I see now why one reviewer said he dreaded turning his PC on, it was like listening to someone incessantly grinding their teeth. It's a bit better now the initialisation is done but I think that they are going to have to go back.

2) Thermals Undervolting wasn't stable, although there were some oddities which I need to look at. Keeping the lid on thermally needed a massive underclock. Sadly I think that the NH-L9i is not up to an 8700k. To be fair noctua say the cooler won't work with an 8700K citing a max TDP of 65W (but confusingly they do claim it is OK with 91W TDP Skylake CPUs).

Hence a re-think might be called for. The NH-L9i is probably the best, indeed almost the only, cooler for its 37mm height and so if it can't cut it I'm not sure what will (suggestions welcome). In another case I'd possibly try a higher airflow fan on the same heatsink but here isn't room. Liquid cooling probably isn't an option - even if you could get a block on the CPU it would not be possible to install a radiator (even outside the case which I thought might be possible).

Even in its current hamstrung configuration the 8700K is an impressive CPU. It is doing a software h.265 encode more than twice as fast as my mildly OC'd 4770K does and would be more than 3x as fast at stock clock speeds. More impressively the hardware encode (which I can't do on the Haswell chip) is managing 127fps which is about 25x faster than the earlier chip could do in software.

Ultimately I'm going to have to admit defeat, I think, on the idea of putting an 8700K in such a small box and probably move the 3770T motherboard into the U-Nas case. I think that will work well as the NAS server CPU and will be a really good match to the case. I just need to find the 8700K and its motherboard a new home so really I just need to buy a mid sized case (of which there are loads of nice ones without breaking the bank) and an ATX PSU (ditto).

9
Buy/Sell/Wanted / Re: WTB: Tektronix 7854 Vert Amp Bd 670-5832-00
« Last post by perdrix on Today at 05:04:54 AM »
I just checked my stash, and I have a 7834 vertical output board with a 155-0064 (gain code 4) still installed on it, but I don't know for sure that it works (I think it does, I normally mark them if they are dead).  I have the equipment and so on to re-do the vertical calibration but that doesn't help unless you are also in the UK (are you?) ...

The board is complete and the little carbon composition emitter resistors specific to that IC are still on the board with it (mounted on the back).  The terminators are also there.

Another possibility would be to contact Luis Cupido <[email protected]> who has a wire bonder.   He *may* be able to help, though I don't know if he can de-cap and re-cap the IC.

pm me if interested.

Dave


10
For a minute counting with discrete components search for "fet astable multivibrator". Carefully designed (voltage stabilization, quality foil capacitors, stable resistors, transistors kept at same temperature) you may achieve +/- few minutes a day :)
That wouldn't be a clock, but a counter.  :)
Pages: [1] 2 3 4 5 6 ... 10 Next