Recent Posts

Pages: [1] 2 3 4 5 6 ... 10 Next
1
General Technical Chat / Re: Aliexpress dodgy GST tax
« Last post by Kim Christensen on Today at 12:41:56 am »
Probably because the concept of "free" or "cheap" shipping is BS.
In other words, the full/partial cost of shipping is built into the price and Aliexpress takes your country's tax rules into account.

2
General Technical Chat / Re: Admit your Brain lock
« Last post by joeqsmith on Today at 12:41:56 am »
Ladies.
3
Instead of MOSFETs and voltage switching, use bipolar transistors and current switching, or fast diodes and current switching.  The output level is then set by the easy to control DC current source driving the emitters of the differential pair, or driving the diodes.

That's an interesting approach, it also looks like it was used in some pulse generators such as the Philips PM5715, which I borrowed the idea of chained attenuators in the output circuit. I may try it too.

Tektronix used it on most of their pulse generators.  They used the diode version for vertical channel switching in oscilloscopes which gives some idea of the potential performance.
4
Metrology / Re: two LTZ1000 in "series" and attenuate to 10V?
« Last post by KT88 on Today at 12:35:18 am »
Summing two references in series should have the same effect as paralleling them - noisewise...
As the other comments hint - it comes with some complexity and pitfalls.
A slight advantage could be expected from the input referred noise of the Opamps not being amplified but attenuated - given an ingenious circuit could leverage that advantage.
However, the gain in performance would be disappointing as the Vz remains the major source of noise and in sum the reduction of noise in comparison to paralleling them would be negligible. (rule of thumb: a source with 1/3 of the aplitude of the main source only contributes 1/10 to the overall noise).
The seebeck related errors might still sum up...
5
Repair / Mastech 9803R Repair Help
« Last post by larrybud on Today at 12:30:26 am »
I purchased a Mastech 9803R benchtop meter off ebay for "parts or repair" and everything works on it except two odd issues, which I suspect are related:
  • Capacitance reads half the expected value
  • The voltage drop when testing a diode is twice the expected value

I opened the unit up, checked for the common culprits (bulging caps, cooked resistors, cold solder joints) but didn't notice anything.

First, does anybody happened to have a schematic of this thing, and if not, any advice on what to look for?
6
KiCad / Re: KiCad 7.0.9 Install On Windows 7 Easy!
« Last post by pandy on Today at 12:29:02 am »
I do have version 7.0.11, which I believe is probably going to be the last release of kiCAD 7, working quite well if you would like me to post it.


Sure - this thread is about going opposite to something called "planned obsolescence". I never get open source developers following agenda of companies like Microsoft - IMHO this is contradictory to open source philosophy - I you have working solution for 7.0.11 then please post it.
7
I realize that most people have moved on from this thread, but I still wanted to add a redesign of the EasyPDK programmer I did. Just to give back a little something to this community. It's called the PurplePDK programmer and is based on the easy-pdk-lite programmer.
The github repository can be found at  https://github.com/cross-bound/PurplePDK

Enjoy



8
General Technical Chat / Light fixtures periodically flickering in sync
« Last post by saratoga on Today at 12:24:05 am »
I have some light fixtures in my house that will periodically all start synchronously flickering at a slow rate (5-10 Hz) for a couple seconds and all stop at the same time.  They're definitely in phase and they all use the same model of driver, which has an annoying shape that would be hard to place with swapping junction boxes and cutting bigger holes in my wall. 

I tried bypassing the dimmer switch, but it has no effect.  10% brightness, 100% brightness, and no dimmer at all do it just the same, so not the dimmer switch. 

Since they flicker in sync, there must be a common source of interference to synchronize them.  Since they are dimmable, my theory is that some higher frequency signal on the power lines interferes with the phase cut detection circuit, causing the driver to lower the current briefly.  I don't have probes handy that can check mains power, and I'm not too excited about blowing up my scope anyway, but interference on the line seems a lot more likely than RF interference.

Would something like this help?

https://www.digikey.com/en/products/detail/qualtek/851-05%2F006/739530

And would it be up to code to put it in a junction box behind a light switch?  Or am I thinking about this wrong?
9
I prototyped a 0-6VACrms AC Sine Wave Generator Module (AC-coupled, bipolar output) shown in the below schematic.

Specs:

POWER SUPPLY (not on schematic): Single Supply 12VDC Regulated with on-PC board -12VDC Charge Pump Inverter, ICL7662. Maximum ripple on +12V rail is 600uV. Maximum ripple on -12V inverter rail is 900uV.

Principle of Operation: (per accompanying schematic & sequence of photos)

CD4047 provides a precise 50% duty-cycle, 100Hz square wave on +12V power so, it is a unipolar output 0-12V. 
That output is AC-coupled and level-shifted by OA#1 to swing +/-12V to produce a bipolar 24V Square Wave.
OA#2 Integrates that square wave into a Triangle Wave which is then fed to OA#3.
OA#3 Integrates the triangle wave into a Sine Wave which is fed to OA#4.
OA#4 Amplifies the Sine Wave to the desired 6VACrms (minimum) bipolar output required.

Objectives:

1)  Most important, operation from a single, well-regulated +12VDC power supply. (May also be operated from a single 9V battery with slightly reduced Sine Wave amplitude output.)
2)  Precise 50% duty-cycle square wave so, CD4047 was chosen. Op Amp square wave oscillators tested are too sloppy and imprecise.
3)  Dual integrators provide the easiest, most stabile method for producing a low-frequency, low-distortion sine wave while allowing the use of non-critical component values.  Phase shift oscillators and shaping filter schemes are too finicky and too complicated.  I like simple.
4)  Amplitude stability to 0.5% is very important. It is entirely dependent on the +/- rail voltages so the need for input voltage regulation is critical. An on-PCB MC7812 seems adequate. No temperature compensation or AGC is provided because the parts count goes way up along with the module's complexity and resultant BOM cost.

HELP NEEDED:  Open to any suggestions/criticisms/advice/revisions/corrections/re-design, etc. that could make this a better, low-cost product aimed at the student, beginner, hobbyist, DIY Homeowner markets.

What good is this thing and what is it used for?  Well, for those millions of people who have bought cheap DMM's and want to know whether their AC functions are working at least on the low voltage AC range(s), an economical AC Sine Wave module may be something they'd be interested in along with an economical DC reference and a precision resistor module.

Hell, they could verify that their cheap little DMM is worthy of trusting around the house, garage, hobby bench or, even coursework at school. Or, maybe if it
s not, buy a real DMM.

By the way, I'm an admirer of the DMM Check product but, it's too good and too expensive for the market I'm speaking of here.

Thanks in advance for looking things over.  SWING AWAY.... :box:

10
I had the scope a few years ago and am no longer quite up to date:
Is it still the case that you have to renew the hack as soon as you load new firmware onto the scope?
If so, then nothing has changed in the last 5 years...
Simply put, if you are on version 1.3.0.3 and you want upgrade You just need to

1. Go to the link in the first message
2. Download the zip file called Upgrading to 350MHz
3. Download only the 2nd video and watch it

it explains everything step by step
Pages: [1] 2 3 4 5 6 ... 10 Next