Recent Posts

1

General Technical Chat / Re: Do you think an LED is a resistor?

« Last post by Berni on Today at 05:54:00 pm »

There is so much to unpack here but let's consider only the last part.
A capacitor at DC can hold a voltage without passing current; try to do that with a resistor.
An inductor at DC can hold a current without a voltage (if ideal, and a small voltage due to small resistive losses if real). Try to do that with a resistor.
You can use these properties to create memory cells. Try to do that with resistors alone.
I am not well versed in memristors to give an elementary setting that shows their fundamental difference from resistors, but I am pretty confident  you got that part wrong, as well.

Have you looked up the Science Direct link I gave above? I am not redefining industry standard terms: diodes have been considered to be nonlinear resistors for decades. You just wasn't aware of it.

Yes and we have names for a resistive device that is designed to be very non linear, the industry standard term for that is a varistor instead of resistor.

If you just generalise all these things are being resistors, then you could also generalize all diodes as diodes (even tho they act very differently), then it falls apart even more as some TVS diodes exhibit a memrisor like behavior (they clamp down and stay clamped until you reduce the current, hence have memory of previous current). But that's besides the point. Diodes exhibiting electrical resistance is nothing special or ground breaking. Everyone in this thread knows about it.

The only problem is that you are throwing around the term resistor and resistance as being the same thing. They are not. The resistor is the industry standard term for a device that is designed to create the effect of resistance in a well defined manner. While electrical resistance is a physics phenomenon where something opposes the flow of current in a electrical circuit.

What is the point you are trying to make with this thread? That a diode has electrical resistance? Or that everything that exhibits electrical resistance should be called a resistor?

2

Repair / Re: LEM Baby Echo Mixer Amp Issue

« Last post by MathWizard on Today at 05:53:45 pm »

So it looks like an amplifier, but C5=100uF, is that there to delay the signal to the top output transistors and make the echo effect ?

I play guitar, but I haven't tried any effects circuits yet.

3

Test Equipment / Re: Magnova oscilloscope

« Last post by DaneLaw on Today at 05:53:23 pm »

The quite common Xilinx Ultrascale+ MPSoC
https://docs.amd.com/v/u/en-US/zynq-ultrascale-plus-product-selection-guide

Any info on how it's powered and if it relies on a separate AC to DC power brick with modern powering protocols?

4

Projects, Designs, and Technical Stuff / Re: Simple illuminated time display that can be driven over USB?

« Last post by sparkydog on Today at 05:51:42 pm »

https://www.mouser.com/ProductDetail/Display-Visions/EA-PLUGL128-6GTCZ?qs=UkDUCjYnTB3JUsCi7MJI3Q%3D%3D
https://www.mouser.com/datasheet/2/127/plug_seriee-1532082.pdf

OLed
Capacitive Touch
USB
GPIOs, RS232/485, SPI, I2C
easy to use ASCII commands

Er... that looked interesting until I saw the price. $130? For a tiny, monochrome 128×64 display? Uh... no thanks. At that price I might as well buy a waveshare 5.5inch. Sure, I'd also need a PI or the like to drive it (or figure out how to run a second X server), but it's bigger, full color, and 1080p... for a lower price. (In fact, that plus a Pi Zero is still a lower price.)

5

Test Equipment / Re: DMM Input Capacitance

« Last post by 2N3055 on Today at 05:49:11 pm »

I measure 10-40pF across the jacks of 5 multimeters on DCV. Most are around 35pF except 34401a measured 680pF quite high. Adding test leads does not add much.
34401a 177pF and 112pF to PE.

I find DMM input capacitance an issue if measuring low impedance HVDC, say 500V I've seen multimeters blank out or crash when connecting the (+) probe and even a tiny spark can be seen. It's a bit scary. A few product recalls over this (Fluke included) where the MCU reboots due to the EMI of that.

Also important is the common-mode capacitance, the other electrode being the multimeter's shield and your hand, or your workbench, or the grounded metal the multimeter is resting on. The input capacitance from each input (+), (-) to shield is not symmetrical. Mains-powered bench multimeters can have a Y-cap to PE.
This is a problem at RF especially if the DMM is cheaper and has no foil shield.

This is about common mode capacitance, i.e.  measuring from T+ of the meter to ground (P.E.) and then comparing it to T- to ground (P.E.) in your lab.

6

Beginners / PCB review and RF layout

« Last post by SierraFox on Today at 05:46:55 pm »

Hello!
I'm working on a GNSS/GPS tracking device that will transmit its location on 915mhz to a handheld unit and I'm hoping I could get some advice on my PCB.
U1 is a microcontroller and the transceiver for the 915mhz channel. U2 is the GPS receiver. AE1 is a ceramic patch antenna connected to U2 via a U.FL connector.
U3 is a 3 volt LDO and U4 is a li-ion charger.
J2 is an SMA connector to connect a whip antenna for 915mhz.
J3 and J4 are the U.FL connectors.
The battery is going to be a AAA sized li-ion battery (10440)
The left and right halves are separate boards and the back view of the PCB is flipped. I also attached screenshots with and without the ground plane visible for clarity.
I feel like the layout is quite garbage, but I also don't know how to make it better. I also don't know much about layout for 1.5ghz signals. The RF traces are 0.8mm wide and have a clearance on either size of 0.15mm.
I would love some advice and please ask if you want more pictures or details.

7

Beginners / Re: Help identifying these possibly RF/Microwave components?

« Last post by xvr on Today at 05:46:44 pm »

142ЕН2

Only Russian DS (Google rejected to translate )

8

Microcontrollers / Re: Reset esp8266 when alarm circuit path *broken* with minimal power draw at rest

« Last post by langwadt on Today at 05:45:36 pm »

I wouldn't discount the pull-up route altogether, at least without a bit of experimentation. You can use a very high value resistor and end up with negligible current use.

a very high value resistor would likely make it noise sensitive

9

Beginners / Re: display current on scope

« Last post by jpanhalt on Today at 05:44:58 pm »

First, I had to cut the ferrite toroid core without breaking it.  That's where my experience glassblowing came in.  Use a thin, non-reinforced cutting wheel in a Dremel.  It needs to be kept wet, of course.  Any twisting on the first cut will fracture it.  I used a wet, cellulose (not plastic sponge) and cut through the sponge where the wheel entered the ferrite.  Then lap it using fine "color coat" wet carborundum paper.  Finally, the flat piece was done.  One could easily see on the oscilloscope how performance improves as the gap gets less.

I agree on the Hall sensor.  I had read about how current rapidly increases as the core saturates, and wanted to see it.  Coilcraft kindly gave a a calibrated inductor, and my my results were close enough to predicted for an old organic chemist.  I thought I was old then, but not compared to my current age.  

10

Repair / Re: Ksger T12 Sudden Death

« Last post by floobydust on Today at 05:44:39 pm »

That is a crappy control board, problem is the 3.3V regulator U5 has no proper heatsink and it roasts and croaks, runs too hot.
Carefully check that you have 24V in and 3.3V out for that IC. It's not an official KSGER controller board I think. Really old ones or bad copies had problems with reliably making a 3.3V rail.

edit:
One mod is here, power the IC input from less than 24V:
https://www.eevblog.com/forum/reviews/ksger-t12-help-me-identify-this-wire/msg5182668/#msg5182668
https://www.eevblog.com/forum/reviews/stm32-oled-digital-soldering-station-for-t12-handle/msg3048556/#msg3048556