Recent Posts

11

General Technical Chat / Re: What did you buy today? Post your latest purchase!

« Last post by cosmicray on Today at 11:32:24 pm »

An assortment of enameled wire sizes (22-32 AWG) from Remington Industries.

12

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

« Last post by Sredni on Today at 11:31:38 pm »

To the OP.
Are you sure you are talking about a 'normal' diode, and not a 'special' type of (apparently chaotic) diode?

I am talking about ordinary signal diode, power diodes, zener diodes, tunnel diodes.
Have any of you even opened the Science Direct link I gave before?

From here (a page that is apparently invisible to many browsers)
https://www.sciencedirect.com/topics/engineering/nonlinear-resistor

Nonlinear Resistor
Nonlinear resistors have a common characteristic that their constitutive relationships are described by nonlinear algebraic equations.
From: The Electrical Engineering Handbook, 2005
 

From: A.C. Fischer-Cripps, in Newnes Interfacing Companion, 2002
3.3.7 Log amplifier
A non-linear resistor is connected into the feedback circuit. In practice, this can be a diode, but a transistor connected as a diode is used since the forward biased transfer function is more accurately exponential. The exponential nature of the forward biased diode leads to a logarithmic decrease in gain of the circuit as the input signal is increased.



From: A Gavrilović OBE, in Electrical Engineer's Reference Book (Sixteenth Edition), 2003
32.6.3 Surge arresters
The zinc-oxide non-linear resistor material used in modern surge arresters exhibits a very high impedance at normal applied voltage whilst at a voltage only some 50% higher a very low impedance is provided. The extremely non-linear relationship between voltage and current shown in Figure 32.20, has rendered obsolete the spark gaps which were a feature of previous arresters based on silicon carbide.
 

From: I.D. Mayergoyz, W. Lawson, in Basic Electric Circuit Theory, 1997
EXAMPLE 5.5 A Voltage Regulator Circuit
Consider the circuit shown in Figure 5.31, where a load resistor RL is connected in parallel with a nonlinear resistor characterized by the v1(i) curve shown in Figure 5.32. This curve exhibits “voltage saturation.” In other words, it has an almost horizontal (flat) portion which starts from small current values. We would like to find all currents and voltages in this circuit.



[note1: you know what is that curious component represented by a resistor symbol with two lines? It's a zener diode. A special kind of nonlinear resistor]

[note2: the above book as a section titled "Non-linear resistive circuits" where nonlinear resistors are introduced and diode and zener diode are used as examples of nonlinear resistors]

From YIN Jijun, ... LI Peng, in Unified Power Flow Controller Technology and Application, 2017
6.1.1.2.4 Metal oxide surge arresters
Gapless metal oxide surge arresters are used in a UPFC. In the simulation model, they can be replaced by nonlinear resistors. The nonlinear volt-ampere characteristics of valves are shown in Fig. 6.5.



From: Nasser Tleis BSc (Hons), MSc, PhD, CEng, FIET, M-CIGRE, in Power Systems Modelling and Fault Analysis (Second Edition), 2019
10.4.8 Passive damped resonant limiter
Fig. 10.10 illustrates one phase of a three-phase damped resonant limiter circuit that uses only passive components.



The limiter consists of an isolation transformer whose primary winding is connected in series with the ac system and a capacitor is connected across its secondary winding. A nonlinear resistor, for example, a varistor, or a fast-closing triggered switch, is connected in parallel with the capacitor, and a damped tuned filter is connected in parallel with the capacitor/varistor. Under normal unfaulted system condition, the secondary circuit appears as a capacitor at 50 Hz that, when transferred to the primary of the transformer, is equal to and hence cancels out the transformer’s leakage reactance. Therefore, at 50 Hz, the limiter appears as a short circuit except for the resistance of the transformer.
 

So, I hope there will be no more discussion about the usage of the term "nonlinear resistor". It is not a novel invention by Chua alone. It is a well known and estabilished term that encompasses, among others, diodes, transistors connected as diodes, zener diodes, varistors, incandescent lamps, neon lamps, etc. etc. etc.

I think we are left with the doubt if nonlinear resistors are... resistors. No kidding.

13

Projects, Designs, and Technical Stuff / Re: LTSPice LoopGain2 Circuit Stability example does not make sense.

« Last post by moffy on Today at 11:31:30 pm »

Looks like one heck of a considence right, but I can't explain how I get a real phase margine from the negative. For instance, do I substract 180 degrees from it? why?

No coincidence, look at the phase difference at say 1kHz, one is +90 degrees the other is -90 degrees, they always are 180 apart, and 180 degrees just means that one signal is inverted with respect to the other, just invert one of the voltage sources and they will agree.

14

Projects, Designs, and Technical Stuff / Re: Passing 2 wires into a hot water cylinder

« Last post by themadhippy on Today at 11:31:00 pm »

I can install into the immersion heater cap?

Make a water/pressure proof probe that you can stick into it. Place the sensor inside that.

If theres an immersion heater theres a 99% chance theres already a water tight tube going into the cylinder for the existing  stat

15

EEVblog Specific / Re: EEVblog 1611 - Top 5 Jellybean 7400 & 4000 Logic

« Last post by cosmicray on Today at 11:29:18 pm »

I see so many posts and reports of hobbyists like me burning their microcontrollers or SBCs or at least a few I/O pins on them, by not thinking about this stuff at all.  I wish someone with a wide enough viewership would point this out, because the solutions are so easy and easily available.  Starting from the current-limiting resistor (which relies on the ESD or other diodes to voltage rails), to transistor open collector outputs with pull-up resistors, to level translating transceivers, to digital isolators.

74ls07, buffer, open-collector, very useful for translating voltages.

16

RF, Microwave, Ham Radio / Re: WSJT-X on Pi

« Last post by mag_therm on Today at 11:22:39 pm »

Read the answers here.
https://stackoverflow.com/questions/76696292/libc6-dev-depends-libc6-2-31-13deb11u6-but-2-36-9-is-to-be-installed
Try to do, as root, the package update as described at the end of the answers. Watch the update messages as they flow past.
(I am Fedora here, the commands are different but the o/s is very similar)

You can copy the error lines one by one and paste into your browser as I did above.

17

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.

18

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!

19

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 accurately 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...

20

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.