Recent Posts

1

Metrology / Measuring femto-level differntial capactiance changes

« Last post by charliehorse55 on Today at 05:52:37 am »

My dad is a semi-retired physicist and he's interested in building a gravitational wave detector. The idea is to measure the differential change in capacitance of 2 capacitors oriented at 90 degrees. Gravity waves push the plates of the capacitor back and forth, causing the voltage on the capacitor to change:

The 0.1 ohm resistor is to filter the low frequency components (mainly drift due to internal leakage).

We're aware that we won't be able to observe anything with an experiment that fits into our cost/complexity budget, but the idea is to develop the technology to understand what would be required for a full-scale system. By creating smaller and smaller test inputs (for ex. mechanically vibrating the capacitor), we can validate how sensitive the instrument is, and how much it would have to improve in order to observe gravitational waves.

Ultimately, the signal will be buried in a lot of noise and require signal processing techniques to extract, so the amplifier needs enough gain to amplify the inherent noise to cover the entire range of the ADC (with room to prevent clipping). So, the lower the system noise, the higher the gain.

Frequency: 50-4kHz
Gain: noise floor (100nV?) -> 1V for a 3V ADC = ~10 million V/V = 140dB?

• Should we use discrete transistors for some sort of input stage, or directly go into a low noise op amp such as LT1128?
• Is there a practical limit to how much gain you can put onto a single op-amp stage? The LT1128 has >75MHz GBW, which would imply for 4kHz a single stage could already have a gain >10,000. Such high value resistors add noise of their own?
• How many stages of amplifier should we use?
• The source impedance here should be the ESR of the supercapacitor, which is extremely low. Could a small signal transformer be used? Do they have any non-linear effects that might destroy a femto-level signal?
• How to implement the 50Hz filter on the input? The required value of R for Fc=50Hz would be something in the ~10 uOhm range, which would get dwarfed by the internal resistance of the caps. A simple RC pole would introduce too much noise through the resistor, right?

I have little-to-no experience with analog design, so I'm kinda jumping into the deep end with this!

2

Test Equipment / Re: LCR meter questions and maybe recommendation.

« Last post by indman on Today at 05:50:55 am »

But you have to make things clear and one thing is that the ST42 (in my eyes) is not enough to cover everything, but that is exactly what is always suggested.

Totally agree with this opinion. I have ST42 and it is a convenient and good tool when you need to quickly find out the parameters of SMD parts.
But it has, along with its advantages, also a number of limitations. For example, the upper operating frequency of the test signal is limited to 10kHz, unlike the DE-5000.
Shannon has promised to release a 100kHz tweezers, we will wait for it. The HV-15(16) tweezers, which were sold in the Russian segment, has an upper operating frequency of 250kHz test signal, which significantly extends its range of application. Yes, it costs twice as much as the ST42, but it has twice as much capability. The analog of this smart tweezers in your market is labeled LCR Reader.

3

Dodgy Technology / RooBadge - new mosquito, I mean kangaroo repelent from straya?

« Last post by dusan on Today at 05:45:58 am »

I've just seen advert for RooBadge:



And on VW official site:

https://www.volkswagen.com.au/en/roobadge.html

Some say it's april's fool joke, but VW insist on it being real, what are your opinions?

4

Projects, Designs, and Technical Stuff / Re: Part S10BdA1 datasheet

« Last post by sdancer75 on Today at 05:42:16 am »

I googled the part number without the word regulator and I got nothing :-) Thank you !!!

5

Projects, Designs, and Technical Stuff / Re: Are Logic Circuits Still Used or Micros

« Last post by T3sl4co1l on Today at 05:40:18 am »

Speaking of CPLDs, the major difference AFAIK is about resource allocation/organization.  Think, multiple PLDs in one chip.  Big wide min/max-terms arrays, the usual flip-flops, cascade terms, and one or a couple outputs (complements, cascade, clocked, etc.).

Whereas FPGAs are, more or less the same per cell, except with a tiny LUT instead of an AND/OR array.  Often 4x4, simple RAM lookup, but bigger ones go 6x6 or more.  But rarely the, like, 12x7 or whatever array CPLDs may have.

PLDs in turn, I guess, arise from the input pins; you want to matrix all possible combinations, since it's a small chip, and you can offer some reasonably powerful functions that way.  So, kind of a lot of options, but feasible for just a single chip.  Then, suppose you put a few of them together, well, then you get a CPLD, right? etc.

FPGA interconnects I think tend to be more complex, including crossbar matrices and buffering, and just more routes to choose from, cells to place (including potentially routing through cells to reduce bus contention), etc., which is really where the timing comes in.  Compared to CPLDs, there's just less to route between dozens or hundreds of CPLD cells, vs. thousands in FPGA, but that really just means you have more responsibility to set timing constraints, and less freedom in them (fewer cells, and permutations thereof, in a critical path), but because FPGA cells are faster than PLDs per cell, it's about even either way.

Tim

6

Test Equipment / Re: Siglent SDS2000X-HD Specific Questions

« Last post by Kowolski on Today at 05:38:56 am »

Thanks for that so far. Makes sense.

Is there anyway to get the non public solution? I assume I can get PM's in here. If anyone sees this and can shed light via PM or any other way how to hack the upgrade I'd be huuugely grateful.

7

Microcontrollers / Re: ATMEGA 644P AVR Programming Help Needed

« Last post by pcprogrammer on Today at 05:30:59 am »

It might be that when in the board IC2 the 74LS165N is causing problems. When you use your zif socket to program the MCU there is nothing else connected to the SPI pins so the programmer will be able to control the pins as intended. On the board there are other connections to the SPI pins that might give trouble.

Another issue can be with the supply voltage when also connecting the 5V on the six pin AVRISP connector and trying to power the whole board from it. The voltage might drop due to to much current drawn.

Like qpass wrote with avrdude showing everything written and reading the fuse bytes back correctly the MCU seems to be correctly programmed, and when not working the problem will be on the main board when it does not work as expected.

It could be the crystal that is defective and the MCU is not running due to this. Checking this without an oscilloscope or frequency counter is hardly possible.

8

Other Equipment & Products / Re: best mini electric screwdriver?

« Last post by Andrew LB on Today at 05:25:10 am »

Every mini electric screwdriver i've owned/used have been garbage. Either the motors are too weak or the bits themselves are of poor quality and get rounded off or cam out, ruining the screw head. I bought a set of Proxxon micro screwdrivers about 10 years ago and use them a ton and not a single one in the set has been worn out from use. Wera and Wiha make some good ones too.

9

Repair / Re: Fluke 179 problem measuring resistance

« Last post by neskor on Today at 05:23:57 am »

I can see there is a slight discoloration on the top of Fluke 642998 ASIC, maybe went south???

10

Projects, Designs, and Technical Stuff / Looking for a source of high quality (EZ-Hook/BusPirate) jumpers

« Last post by amaschas on Today at 05:21:23 am »

I recently bought a BusPirate 5, and it ended up coming with an auxiliary probe kit that partially solved an issue that has been driving me crazy for years. Namely, the dupont connectors used for every set of jumper wires I've owned does not really fit the pins in test hooks and probes designed to help interface to IC pins or hard to reach connectors such as the EZ-Hook. The connectors on this probe kit were very different, seemingly an exposed pin with a bit of heat shrink to prevent shorts.



I immediately started looking around for jumpers that used this connector style, but the closest thing I could find were these EZ-Hook products that are not only continuous linked sets with a minimum of 25, but also outrageously expensive. What I'm hoping to find is a set of multi-color jumper wires in the style of standard jumpers like these with dupont connectors, except with these higher quality connectors that offer a much tighter connection to various pins:



Failing that, I'm hoping maybe someone can point me to some similar connectors that would let me construct my own jumpers in this style. Any recommendations would be appreciated!