texts:
I have started a small LoRaWAN network. I already have setup:

1x LoRaWAN gateway (LAIRD RG186, using EU863-870);
4x T/RH Nodes (Dragino LHT65, same standard);
LoRa Servers to cope with packets and complete the dataflow.

Everything went fine, I am able to log packets from nodes scattered across the field.

Having collected data since few days, I have processed data with success. Now I am processing related metadata. My question mainly focuses on RSSI and SNR and frequency plans.

If I draw a heatmap of packet counts, I can see that frequency plan changes and it is somehow homogenous:

If I draw heatmap with RSSI average, I get:

Which does not surprise me as node-T002 and node-T003 are most distant nodes in unfriendly environments (there are behind concrete walls).

But if I draw heatmap with SNR average, I get:

Which seems to points out that some frequency plan (867.5 MHz and 868.5 MHz) are disadvantaged before others. And this is somehow surprising to me at the first glance.

Anyway, I have not enough background on this technology right now to clearly spot what is happening. My first thoughts are:

There are some EMI (eg.: those frequency plans are to busy, maybe because to many other nodes emit on that frequencies);
There are some scale issue, those frequencies are disadvantaged in this peculiar setup because of something else than EMI.

My question is: Is there a know reason why this phenomenon occurs, how can I identify it and what could be done to mitigate it?

Or more concisely, recalling the title: What could potentially affect some specific LoRa frequencies among others and how to mitigate it?


texts: LED chaser using as few wires as possible

texts:
I need to create a cable that has 4 LEDs attached every 3m.
The cable will be 40m long and will have some control electronics at the beginning.
The purpose of the cable will be a LED chaser.

I've read whatever I could find here and elsewhere about LED chaser and they all focus on CD4017 and 555's. My requirement is anything that is efficient.

I was thinking of some cheap MCU and 15 miniature PCB's connected with SPI, but at best that would give me about 20 wires in the cable to create a LED chaser.

Is there a better way with less wires?? I don't need the complete solution I just need someone to point me to a better solution.

Anything is acceptable, LED driver chips, I2C, SPI, CAN, whatever can get me to as few wires as possible.


texts: TS832 audio-video transmitter lowers its input voltage

texts:
I have a TS832 audio-video transmitter, and in its datasheet it says that the operating voltage is typically 12V, but can range from 7V to 16V. I am powering the transmitter with a 9V battery.
I am measuring the voltage between its DC IN (+) and its DC OUT (-) pins, and it's 5.1V. Shouldn't that be the same with the battery's voltage? There's nothing but cable between the pins and the battery terminals!
If I ignore this problem and connect everything else correctly (camera, receiver, antennas) and connect the receiver to a television, I see nothing. That's why I believe that this problem is why the whole system isn't working.
The transmitter also heats up quite quickly while it's operating, if that helps.


texts: Term for errors that are constant for a measurement

texts: In my measurements, I am encountering errors that remain constant over a measurement but change from one measurement to another. The errors specifically are amplitude and phase errors resulting from different electronic components in a telecommunication chain. Are these errors called static errors or systematic errors in literature? I looked at their definitions but couldn't relate them to my case. Any suggestions on this would be appreciated.


texts: Legal obligations when designing electronics

texts:
I'm planning on releasing a USB powered device, basically a AVR ATMega2560 µC with a FTDI FT232RL chip powered by USB-C.

Although I'm comfortable with the safety of the device (has fuses, ferrite beads, etc.) I'm not sure what are my legal obligations regarding consumer safety when selling the product (Europe and US at least). I'm guessing that all components need to be RoHS certified, etc.

Is there a place from which I can start reading on the requirements so that I can make sure that the devices are fully compliant?


texts:
I want to build a simple and stable constant voltage source (voltage regulator) and current source. I built one using a LM317 but the output is not stable, it varies when temperature changes. Do you have any suggestions to improve the design?

CURRENT SOURCE

VOLTAGE SOURCE


texts: Are there cerifications needed to bring 5VDC LED Controller to the US market?

texts:
We are producing LED programmable controler, the power supply is 5VDC.
Do we need any certification (UL or similar) for the US market?


texts: "Breaking-in" lithium polymer batteries:Is there any research on that?

texts:
Well I just got new batteries for my RC glider and I'm thinking about what to do with its battery.

For those who aren't in the RC hobby the story goes something like this:

New kid buys a battery and hears that some people recommend breaking in the batteries. After that he asks the question on one of the popular RC forums.

Answers are usually something like "I have xxx batteries and  always break them in." or "I never spend the time to break-in my batteries, it's a waste of time." and then threads move to the argue phase where each side tries shows numerous older posts which back one side or another and then they dig up PDFs hidden on manufacturers' sites can be interpreted to recommend breaking-in while the other side argues that many other manufacturers don't mention breaking-in and in the end no conclusion can be made as we have one side with no solid claims trying to refute other side with no solid claims and this all seems so unscientific to me.

One combination that seems to repeat often is to discharge the battery at 0.5 C and then charge it again at 0.5 C for first five times as that will cause chemicals which are supposed to keep the battery stable during shipping to dissolve and provide higher maximum output current.

Such threads are numerous and key word combination that seems to bring them up is "li-po break-in" for those who want the pleasure of reading endless arguments.

Also a bit about the battery requirements:
Usually the battery is supposed to provide high current (10 C to 20 C is common, sometimes more), have low mass, low volume, charge quickly ( several C) and last for several hundred cycles.

So my question is: Do you know of any solid guidelines which explain if new batteries should be broken in, preferably backed by some research results or clear and unambiguous instructions provided by manufacturers.

UPDATE The particular type of batteries I'm using don't have electronics in them. They're just bare cells convected together and any electronics which sense battery status are external to the battery itself, so calibration of such electronics isn't the point here.


texts:
I am looking to find the correct kind of crimp pins that go in the controller nub of a Nintendo 64 controller. I have attached some pictures of what I'm looking for. I have read up on terminal pins and for whatever reason I can't seem to find this exact model. At first I thought they were some kind of Molex variety since it's widely used in arcade cabinets and the like, but the .062 female pins were too big and did not make a connection with the port in the console. Close, but no cigar.

Hope someone can lead me to a part number! Thank you for your help.

Pictures:


texts: How to connect multiple Raspberry Pi to an Arduino

texts:
If you want to make multiple Raspberry Pis to communicate with an Arduino, what interface can you use?

I have a sensor connected to an Arduino via I2C. Now I want to share the readings from the sensor with more than two Raspberry Pis. Each of the RPis will read the values and write them into a file. As long as I know you cannot use I2C or SPI, since the Raspberry Pis cannot be configured as I2c/SPI slave. Then what interface can you use?

I'm sorry that Raspberry Pi doesn't support I2C/SPI slave mode, though it must be useful.


texts:
I'm possessed of an inverter battery (12v 150AH rating) that has been out of service for a few months now. The reason it was out of service is the inbuilt charger provided with the inverter was not charging it.

I'm looking to construct a charger for it.

Will a transformer secondary of 15V or 18V suffice?
Can I use a sub-1A rating transformer? Is there a mathematical relationship between the battery AH rating, and that of the transformer in the charger?(There's an old Tandy adapter lying around here someplace that I can probably cannibalize ...)


texts:
I have a 9v source driving a comparator with a 5v source that is pulsing with 1s intervals, and a 2.5v constant source. with a pull up resistor of 10K to get make my vout 9v when my pulsing source is greater than 2.5v. This is working as expected. However, I'm trying to push the 9v vout into my 13ohm load which requires to be grounded. Is there anything I can do to keep the 9v vout switching and also use my grounded load?  Any help is much appreciated. He is a rough design of what I'm looking at in LT Spice.

In the picture (R4) is the load that I want to get the 9v to go to.


texts:
I have these two circuits:

With a 'normal' OPAMP (without capacitors), I do know how to calculate the amplification factor of the circuit (\$A=\dfrac{U_{uit}}{U_{in}}\$) . But how do I do it with those two capacitors? But also how do I calculate where the -3 dB point is of both circuits?


texts: What's the best way to geolocate a walkie talkie broadcasting on FRS channels using a UAV?

texts:
I'm researching methods to geolocate a fixed walkie talkie broadcasting on FRS channels. I need  to detect its location using a UAV. The UAV is fixed-wing, so it can not remain stationary. From what I've read so far, it seems like the best way to do this is probably to fly a pattern,  periodically take measurements of the signal strength and use trilateration to get a location to some accuracy. Can anyone give details on whether they think this is the best method, or if they would recommend a different method? What kind of location accuracy could I expect to have with that method? Are there any outside resources you could recommend related to this?
Thanks.


texts: 3 phase - Unbalanced loads from line to line

texts:
In the case of a 3 phase wye unbalanced configuration such as the following:

we can compute the amount of current going through the neutral wire using geometry, in this case it is \$\sqrt{(\cos(150^{\circ})\cdot 5 + \cos({30^{\circ}}) \cdot 20  )^{2} + (\sin({150^{\circ}}) \cdot 5 + \sin({30^{\circ}}) \cdot 20 -15)^{2}} \approx 13.23A\$

Therfore the amount of current going through the neutral wire is approximately 13.23A. So far so good, now, what would happen if I showed you this configuration instead:

In this case the red resistance is connected in between L1 and L2, thus increasing the voltage to \$\sqrt{3} \cdot V_{phase}\$, how much current is now flowing through the neutral wire?

How would I go about calculating the amount of current, how many degrees is it out of phase now, can I still use basic geometry as I did so in the other example?

Thanks


texts: Sampling rate analog to digital converter

texts:
I am a novice in microcontroller subject and have just learned that ADC converts analogue voltage on a pin of, for example, an Arduino, to a binary number. Since the ADC on the Arduino is a 10 bit ADC, we will have 210 discrete analogue levels. Does it mean that the number of samples during the acquisition time is 210 and the intervals between these samples gives the sampling time?

Edit:So here in the picture with two bits we have 4 levels. When I look at this graph I see the signal has been sampled 4 times equal to 22.


texts: It it safe to connect Li-Ion batteries in series and then in parallel?

texts:
I plan to use packs of 18650 Li-Ion batteries as power source for my hobby project.
I would like to combine two 4-packs connected in parallel. Each 4-pack connects four batteries in a serie. So there is total 8 batteries.
Assuming nominal voltage of 3.6V per battery each 4-pack will give 14.4V. Connecting two 4-packs in parallel will maintain 14.4V but double the capacity, at least that's what I expect.

I'm going to draw 1-2A from above setup. I will use identical 18650 batteries and will charge them individually with smart charger, outside of above setup.
My  questions are:

Is it a valid circuit for Li-Ion batteries (are there any caveats)?
Can I expect the combined batteries to have the capacity equal to the sum of individual capacities? My reasoning is: If one 18650 battery has 3000mAh at 3.6V then serie of four should have 3000mAh at 14.4V. Times two gives 6000mAh at 14.4V from combined 8 batteries.


texts: Can I parallel unbiased photo-diodes for op-amp I-to-V?

texts:
Can I use several photo-diodes (unbiased mode), with different light sources for each, in parallel with a current to voltage op-amp circuit? I don't recall seeing it done that way but it seems to me that the currents should simply sum.

simulate this circuit – Schematic created using CircuitLab


texts:
I have a little problem: as I said I want to build kind of a big flashlight. With LED's and stuff.
I already know some things I need, LED's of course, a battery case, a switch and stuff.. but my problem are the more special parts, what other things do I need? The first I can think of is a resistance, but which one do I need? I suppose I will power it with a 9V-Battery (The LED will have orange light, so its about 2-2,3V if im right)

The other problem i have is about the LED itself. Does it simply have + and - or is it more complicated?

I mean I could just try, but I dont want to make any capital mistakes ^^'

I hope somebody here knows what I try to do and is able to help me a little.

Thanks to anybody who tries :D


texts: Determining imaginary axis crossing of a root locus

texts:
I have an equation \begin{equation}{\text{L}\left(s\right)=\frac{K}{s(s+4)(s^2+6s+64)}} \end{equation}

and I am trying to determine it's root locus by hand.When I try plotting it with matlab, the root locus seems to cross the imaginary axis at about +/-5.06

When I try to determine where the root locus will cross the imaginary axis by hand, I end up with two possible values for the imaginary axis crossing, either 5.06 like in the matlab plot or 3.52.
Is there some way of discarding a value for the imaginary axis crossing? Why do I end up with two values for the imaginary axis crossing but matlab only ends up with one?


texts:
Does anyone have a simple ESD generator circuit for pre-compliance testing (3KV-20KV)?

e.g. can it be built from the following?
http://www.ebay.com/itm/New-High-Quality-3V-to-7KV-Boost-Step-up-Module-High-voltage-Black-1PCS-/161938513435?hash=item25b4499e1b:g:4rkAAOSwZG9WjFLj

How can it be switched fast (~20ns) with an MCU?


texts: Is it safe to pass 240AC power through the ACS712 current sensor?

texts:
I'm trying to build a little Arduino circuit to automatically turn on a dust collector when my saw is on and drawing power.

My plan is to use an ACS712 current sensor (30 amps) to detect and transmit current changes to an Arduino and let the Arduino turn on a relay switch which should complete a 240v circuit to turn on the dust collector.

My saw has a 2000 watts motor which at 240v should draw around 8amps. I believe the ACS712 should not be overloaded by the amount of current drawn by the saw motor but I'm wondering whether its possible to safely pass the 240v Australia mains power through the ACS712 current sensor?


texts: How to prioritize which components in a circuit gets power

texts:
I'm sure this is probably very simple.

I have 2 power connections - a 5V 24A DC and a 5V 5A DC - a RasPi (1A power draw?) and the setup it's connected to (25A power draw). Normally both connections would be connected together and we'd have a total 29A which is enough for the entire circuit.

Sometimes, we might have to disconnect one of the connections temporarily - which in both cases means there's insufficient power - in that case I still want the RasPI to be guaranteed its 1A of power and the rest of the circuit uses the remaining power (they're just LEDs, and worst case they shut off until both power connections are available again; whereas the RasPi shutting down could mean data loss).

How do I do that?


texts: Electric shock from laptop due to capacitive coupling?

texts: If a person touches an exposed wire (the wire has a ground-prong) on the 20V side of a power cable while barefoot, I heard that it is possible to receive a shock of higher than 20V due to capacitive coupling. Could anyone explain how this is possible, if it's true?


texts: Can induction go through metal with holes?

texts:
I admit that I have already made this question in physics SE, but after a month of no answers, I realized engineering might be better suited to everyday applications.
I intend to use (Qi) wireless charging for a project of mine. It uses induction coils to transfer power wirelessly.
In my project, between the coils there will be a 1.5mm (0.04 inch) sheet of brass. The first question I had is if this would work. I tried using a 3mm copper sheet that I have, and sure enough the answer is negative, the sheet absorbs the magnetic field.
But what if I made holes in the sheet? Would some of the field penetrate then? Would it be proportional to the size and "density" of the holes? Or would the conductor still absorb the fields?


texts:
I'm little confused about oscillator settings for PIC18F2550. I have 20 MHz crystal (not oscillator) and I want PIC to work (if it is possible) at 48 MHz (both PIC core and USB).

This is part of a table from the datasheet:

In the table you can see that for 20MHz input crystal, if I want that uC is operating at 48MHz, I must set clock mode to HSPPL and MCU Clock Division to 2. At least that is how I understand the table. Is my interpretation of the table correct ?

This is how I've set up my mikroC project, based on that table:

Is this correct?  Will uC operate at 48MHz (12 MIPS)? Also, on the right side (field Oscillator Frequency [MHz]), do I enter 20MHz or 48MHz?

Also, I've noticed (if I'm correct) that I can get uC to operate at 48MHz with 4MHz crystal and 20MHz crystal. If there any benefit in using 20MHz crystal? Or should I be using 4MHz crystal?


texts: Torque-Slip Characteristic Stability Analysis for Induction Motor

texts:
I am having confusion for this stability question of induction motor.
The real question is here

I searched and searched online, keep reading and reading, but still not enough to answer my doubt.

My understanding (that I learnt from here http://electricalbaba.com/understanding-induction-motor-stability/#comment-2645
 ) on why point A is stable is like this: "If I increase the load torque, as the load torque increases, the new operating point has higher slip compared with that of point A which in turn means that speed of Induction Motor has decreased, and hence operating point A is stable".

Is this reasoning correct? But how about the condition that should be satisfied for the stability of the operating point A?

Hope some people can kindly help me.
Thank you!


texts:
This is from an example that comes with VUnit inside the array_axis_vcs fifo.vhd file.
  PslChecks : block is
    constant dx : std_logic_vector(d'left downto 0) := (others => 'X');
    constant du : std_logic_vector(d'left downto 0) := (others => 'U');
  begin
    assert always (not rst and wr -> not (d ?= dx or d ?= du))@rising_edge(clkw)
      report "wrote X|U to FIFO";
    assert always (not rst and f -> not wr)@rising_edge(clkw)
      report "Wrote to FIFO while full";
    assert always (not rst and e -> not rd)@rising_edge(clkr)
      report "Read from FIFO while empty";
  end block PslChecks;

My simulator is not able to understand these assert statements.
What kind of VHDL is this? How can this be written in "normal VHDL" so it works with my ActiveHDL 11.1? I have never seen block and assert always in my life in VHDL before this. I can't find these in the VHDL 2008 LRM as well.


texts: Application of Kirchoff's Laws to circuit with multiple loops

texts:
I want to find the current through the 20Ohm resistor in the following diagram, but am stuck with four equations and five unknown currents.

I can apply Kirchoff's current law to each of the nodes either side of 20Ohm resistor, which gives me two equations. Applying Kirchoff's voltage law to the left and right loops yields another two equations. However, I need another relation in order to be able to solve them simultaneously.

Can I assume two "Virtual Earths", so that the bottom rails are both at 0V? That would allow me to make another large loop around the entire circuit to apply Kirchoff's Voltage Law again. However, if this works, I'm not sure why it's a valid approach.

Does anybody have some ideas about how to solve this? Thanks!


texts: What would make a laser measuring device more accurate

texts: I was looking a varioos laser measuring devices (laser tape measures).  Most of them seem to be accurate within 1/8th of an inch. I'm wondering what the limiting factor for accuracy is. Is it simply a calibration issue? the quality of the electronics?


texts:
I have a basic series RC circuit with the following values.

Source: cos(2000pi*t)

Resistor: 1000ohm

Capacitor: 0.01uF

Upon measuring the voltages across each individual component I found that they are not adding up to zero. Is this supposed to be happening or perhaps I'm doing something wrong?

These are the numbers I'm getting with the multimeter.

Source RMS: 702 mV

Resistor RMS: 358 mV

Capacitor RMS: .88mV

For the life of me I can't see why I'm getting ridiculous numbers like this.


texts: Circuit doesn't seem to add up under Kirchhoff's laws

texts:
I'm supposed to do a full circuit analysis of the circuit above for homework, giving all voltages and amperages, but I cant figure it out because the elements don't seem to add up under Kirchhoff's laws. I'm pretty sure the directions shown for the sources and the resistors at the top are wrong. Any help would be appreciated.

To answer to the comments, under KVG:

L1: 0 = -v5 + v1 + v4

L2: 0 = -v5 - v2 + v4

The math here can't be correct so the positive and negative terminals on the top resistor seem to be wrong?


texts: DIP switch on Atmega32, are external pull-ups neccessary?

texts:
I'm connecting a DIP switch to an Atmega32 as shown in the diagram above. This works well in my application so far. However the common opinion seems to be that external pullups are necessary for a more robust implementation / less EMI susceptibility.

How can I decide whether or not the internal pullup resistors are sufficient for my application? Or is it safe to say "when in doubt use external pullup resistors"?


texts:
I'm using the hitachi 66720 controller for the diplay and there is a boost schematics which helps to provide enough current for the display. Here how it looks like:

I don't understand how transistor is used here. And why there is a thermistor?
The purpose is to stabilize the voltage in the Vci pin but not sure how this is done here.
I would like to see some explanations on this schematics.
Thanks


texts: Is it safe to connect an Arduino to the human body?

texts:
I want to create some project which uses an Arduino to collect and display ECG data. It uses two electrodes which are attached to the body (on the chest). The signal is then transmitted through op-amps to an Arduino ADC pin. The Arduino is connected just to a PC. Is it safe for both the human and the Arduino board to be connected this way?

Should I make some safety pracautions and if so, which?


texts: Can I swap a USB power sources for a 3-AAA battery source?

texts:
I'm putting some battery-powered lights into a boat, and I have the following question:

I bought a bunch of cheapo LED lights, as pictured:

They run on 3 AAA batteries.  They work fine using 1.2V NiMH rechargeable batteries, and I've wired them up just to share one set of batteries, rather than each containing their own (still works fine).  Rather than recharging batteries all the time, I figured it would be more convenient to get one of those USB LiPo power-packs for phones, and charge that when needed.

My question: Is anything bad going to happen if I hook up 5V USB power-pack in place of the (3.6V total) batteries?  If I need a resister in series, how do I tell what resistance I need?


texts: AVR Xmega - Can I simplify this port / peripheral init code?

texts:
Let's assume a function that gets a port as a parameter, it sets up the SPI module on that port and also sets the required pins to an output state.

The declaration looks something like this:

void SPIInit(PORT_t *portname);

However, inside the function I'll also need to use SPIx with x being the specific port. For example, if the function gets called with PORTD, I'll to use SPID for the SPI module. Is there anyway to get SPIx from PORTx without using 'if' statements?


texts: Is it safe to plug the connection end of a capacitor?

texts:
I need to put a capacitor between my motor power supply and ground cables, and have covered the connection with resin for safety. Is it safe to do this?

It's an aluminium electrolytic capacitor by the way.

Many thanks for the help!

Oli


texts: Recommended Waterproof Cable Gland for Ethernet Cable?

texts:
I have a waterproof box that I would like to pass a pre-assembled RJ45 ethernet cable into.  What is the recommended cable gland size for this application?

Cable glands seem to all be specified with two numbers, for min and max cable diameter, but it seems like the specification should have at least three numbers, i.e. min and max diameters of cable for the part that seals, and a third number for how big a connector you can pass through during assembly.

I am looking for water protection of at least IP *5.

This is the sort of thing you could spend hours hunting through the 600+ results on farnell, but really, someone probably already has a favorite part number that is known to be cheap and just work.


texts:
Many books talk about the capacitances between terminals of the transistors, specially the capacitances \$C_\mu\$ and \$C_\pi\$ which are the base to emmiter and collector to base capacitances.

There are some methods to determine the high frequency behavior of transistors which rely on the fact that \$C_\mu\$ and \$C_\pi\$ are known. However, in most jelly bean transistor datasheets I've seen,\$C_\mu\$ and \$C_\pi\$ are not specified, instead \$C_{IBO}\$ and \$C_{OBO}\$ are the ones displayed on the datasheet. According to this SE question How are C(OBO) and C(IBO) defined? , \$C_{IBO}\$ and \$C_{OBO}\$ are the capacitances of the input and output of the transistor in common base configuration with the output open.

So my question is: How can I find \$C_\mu\$ and \$C_\pi\$ of a common transistor like the 2N3904? is \$C_{IBO}\$ somehow related to  \$C_\mu\$ and \$C_\pi\$?

Edit: I have noticed that the SPICE model for the 2N3904 includes much more parameters than the datasheet, can the capacitances that im looking for be extracted from the SPICE model?


texts:
I really love building LED displays and have a decent understanding of multiplexing at this point. However, everything I've built is just binary, on or off, and I've been interested in building displays with LEDs with 2 or 4 bits of brightness depth, which I believe is most easily achieved with PWM.

I've looked at drivers like the TLC5955 and TLC5947 which seem to do the job. With 24 or 48 channels, that's enough to cover a "row" of what I want to create.

I'm just uncertain if it is possible to multiplex with a chip like this. They have an open drain, so I wonder if I just shared all the Cathodes for each row on the chip, then I could just do a refresh cycle where I drop the anodes for each row to low on an update, and keep the others high.


texts: Convert low power Alarm Clock from 120V 60Hz to 230V 50Hz

texts:
I recently bought a vintage flip-digit radio alarm clock from ebay, because I plan to refurbish it and basically use it for the rest of my life. However I only realized that the device must be connected to mains when I had already bought the thing. I was assuming it would just work on 12V like most small electronic devices, but I guess because it's from the 70's I can't live in such luxury yet.

This is the clock I'm talking about.

The alarm clock is rated for US mains, so 120V 60Hz, and requires only 8W of power.
The ratings where I live (Europe) is 230V 50Hz, so I have a couple of questions that I would like to have answered. I searched the web but nothing could tell me the answer to my clock-specific questions.

Can I just plug the thing in my 230V supply? Do you reckon it has an internal converter or is it really 120V only?
I have found several cheap converters from US to EU power rated max. 100W, but they do not specify the frequency of the AC. Do you think these converters, which cost around $30, convert the frequency as well?
Is it a problem if the frequencies don't match? Will my clock run 16.67% slower on the 50Hz AC?
The clock is only 8W, so might the $30 adapter too imprecise (by lack of better words) when it outputs less than a tenth of its maximum power output?
What do you recommend?

Thank you for your time and I'm looking forward to reading your responses.


texts: Power ESP8266 (~200/300mA) from main 230V AC with a very small power supply circuit

texts:
I made a prototype of multisensor circuit with temperature, humidity, PIR, etc using a ESP8266.

My idea is to put each of this module in each house room. To achieve this
and I want to put the entire PCB in the back side of the plastic plate used to cover empty switches holes on wall switch plate (the 3 black plastic items in the photo below)

Each of switch hole cover is about 20x40mm and the available depth in the back of switch plate is about 40/45mm.
To avoid batteries I want to power the circuit using the AC 230V main power.

Can you suggest me the best way to power the circuit with the main requirement to keep PCB as small as possible?

using switching PSU?
using capacitor impedance?
other?


texts: What is the difference between differential resistance and resistance?

texts:
I came across that $$r_{diff} = \frac{dV}{dI}$$ is the differential resistance. What is the meaning of differential resistance, what does it tell us that conventional resistance doesn't tell us?

Also in this literature I'm reading, the authors choose to perform/read $$ r_{diff} - I$$ plots (differential resistance vs current bias) for a current biased circuit, while I traditionally am used to one taking I-V characteristic readings, so why do they take the first one? And also what does it tell us that I-V characteristic doesn't?


texts:
I am currently building variable voltage/variable current (lab) power supply out of an ATX switching power supply. I have done voltage regulation tweak of the TL494 so now it gave me variable voltage of approx 2V-15V.

Now, I want to add some current limiting capability as it is in lab power supplies (the other function of this will be short circuit protection because by tweaking the TL494, power supply lost its short circuit protection). Regulation range from 0-5A will be sufficient. (original rating on 12V rail was 15A).

I searched a lot, but all i can find is circuits using  bipolar transistors and low value sensing resistors sometimes with opamps.

My idea is to use simple circuit - P-channel MOSFET connected as high side switch and potentiometer to set required current limit. I have chosen high side switch, because i require common ground, e.g. ground will be connected to chassis.

Here is scheme:

simulate this circuit – Schematic created using CircuitLab

It will be kind of difficult to set desired current by potentiometer (because hreshold opening voltage is approx 4V and then the current will be climbing rapidly till full open transistor. I think multiturn potentiometer will be partly solution.

Is there any cons of this circuit?
Is there any better options to do current limiting with MOSFET?
Eventually, how can i add current limit signalization?


texts: Simple version of an internal op-amp circuit

texts:
I'm currently learning how op-amps and transistor circuits work and want to understand the simple version of an internal op-amp circuit. However, there are still some open questions.

The first stage here is a differential amplifier with R3 as the constant current sink. There may also be a transistor current sink or current mirror when I'm not wrong. T3 is a level-shifter (common-emitter, voltage-amplification). It receives a small current from the collector of T1, which is proportional to the input difference (U_pos minus U_neg), right? That means T3 creates an inverted voltage on its collector (output), which is proportional to that current. (I'm not exactly sure as T3 may also use the voltage from T1 collector?). However, why not using an NPN transistor? T4 is a common collector circuit that provides a small output resistance and amplifies the current (power-amplification).

Is my understanding correct?

The resistors I have used to simulate are not proper as the output gets into the negative saturation when I insert a small AC signal on the pos. Input. How can I calculate the resistors so that the output has a good range between Ub+ and Ub-? How can this circuit be improved (I'm aware of adding a better constant current sink made of a transistor)? I also saw some capacitors sometimes, would that help? Maybe a capacitor in front of T3 to remove offset?

Thank you!


texts: Are there any special tools used to adjust trimmer potentiometers?

texts:
Is there any special tool used to adjust trimmer potentiometers?
I have some similar to the one on the picture:

I've tried using small slot, Phillips and Pozidriv screwdrivers, but they all don't seem to fit nicely giving me impression that there is some special tool used to adjust trimmer potentiometers.

If there isn't any special tool, what has proven to work well for you?


texts: I am trying to identify this symbol as a part of personal research. I could not find any leads with Google Image search.


texts:
i would like to create simple circuit to drive an computer fan (12V, 0.5A) is the temperature is above 42 celsius and stop when the temperature decreased below 36 celsius. I am simulating in LTSpice.

The schmitt trigger does trigger when I want. The problem is that the output does not go completely to zero, therefore the pnp transistor never goes fully on and then there is not enough voltage across the "load".

I have read something that this might be due the transistor at the output stage of the opamp. But i really do not now how to fix this problem.

Could someone explain me how to properly drive the load?

greetings,

David

n002 = output of opamp
n003 = emitter transistor
n005 = voltage acros R5


texts: Why is no capacity indication on regular batteries?

texts: On every rechargeable battery there is an indication how big the capacity is (for example 2500 mAh). Why is this not the case with normal (nonrechargeable) batteries ? I tried to google the question but found no answer.


texts: Safest way to store a laptop that's rarely used? Plugged in or not?

texts:
I have a laptop (mid-2009 MacBook Pro: aluminum, non-user-serviceable battery) that I almost never use, but might need in the future.

The original battery was replaced by Apple a few years ago (The old one expanded)

Should I keep it plugged in or not? Which is least likely to cause the battery to turn into a fireball, like this one?

I don't have a yard or a fireproof safe, but one option is to store it in the oven (which I also rarely use), unplugged. However, as I understand it, totally draining the battery is also bad.

There was some discussion about this on HN, but I figured this site might have more expertise.


texts: Are there ARM controllers for small applications (like Cortex M0) available in small packages with maximum say 20 pins? I have the impression that in this area they don't quite are a threat for the usual suspects, like PIC and AVR.


texts: What is the compiled size of Semtech LoRaMAC node libraries?

texts:
I'm trying to determine if the microcontroller I intend to use for a project will have enough flash memory for my preferred SDK and also the LoRaMAC libraries.

Does anyone know roughly what the compiled size of the Semtech LoRaMAC library is for a LoRaWAN node?
The documentation doesn't say this, so I was hoping someone with experience of implementing it might know better.

Link to the library: https://github.com/Lora-net/LoRaMac-node

Additionally if anyone has any advice on implementing this on a CC1310 it would be appreciated.


texts: Is one circuit better than the other to drive the PNP transistor?

texts: Of the two circuits, would you prefer one over the other?


texts: Arduino Esp32-dev powering with 9V battery connected to pins

texts:
I can not find any example :( Is it possible that I power directly my Arduino Esp32 with 9 V baterry? Is it safe?

Pinouts

How to connect power to pins if I dont see "VIN" pinout?

http://mh.nodebb.com/topic/2/mh-et-live-esp32-devkit/12

Datasheet:
https://www.espressif.com/sites/default/files/documentation/esp32_datasheet_en.pdf

Could somebody help me please?


texts: I have been reading about motor controllers, and I found this article online (Introduction to Motor Drives and Encoders), but I am having a hard time understanding the diagram (figure below). Can someone explain the process of this control system in an algorithmic manner? I am really confused with the feedback part. I would appreciate any form of help.


texts:
To test the INA 155 I gave a sine wave of amplitude 0.2 V p-p 100Hz. It was operated at 5 V single supply. The reference pin was connected to 2.5 V from an op amp buffer. There seems to be no offset in the output whatever voltage the reference pin is given to. The gain was set at 10 with the pins 1 and 8 open circuited.

The circuit is working fine in simulation.


texts: What algorithm for feedback control to maintain heart rate on a turbo trainer

texts:
I am writing an application that will maintain heart rate within a specified range by adjusting the amount of work required on a turbo trainer.
I could cobble together something that would gradually increase resistance until heart rate reached the right level but I imagine reaching the desired heart rate quickly, not overshooting and maintaining it might not be a trivial exercise.
I imagine that this problem has been solved many times before and I was hoping for a relatively simple algorithm that I can implement without spending a long time fine tuning and improving it.


texts:
I have an LTI system with input and output related as per below:

$$
y(t) = \int_{-\infty}^t \! x(T-2)e^{-(t-T)} \, \mathrm{d}T
$$

and I need to find \$h(t)\$.

I am familiar with two methods of finding \$h(t)\$, namely, comparing the form to the traditional convolution integral and knowing that \$ h(t) = L[\Delta(t)] \$ and relating those forms, but each time, the \$(T-2)\$ bit trips me up.

For the first comparison method, if I set \$\lambda = T-2\$, then \$T = \lambda + 2\$. That puts the x function in an expected form, but turns \$ e^{-(t-T)}\$ into \$e^{-(t - \lambda + 2)}\$ and then I'm not sure how to proceed, given that the added \$+2\$ doesn't give the expected form of \$t - \lambda\$ alone.


texts:
I have a compliance audit that has been foisted on me from on high - as part of what an external consultancy has highlighted, I now have to prove that the indicator LEDs on a board I designed a long time ago are Class 1 laser compliant. Please do not point out how ridiculous this is.

I have the following specs for the LEDs in question:

peak wavelength (595 nm)
dominant wavelength (590 nm)
spectral bandwidth (15 nm)
luminous intensity (120 mcd)
viewing angle (defined as the angle across which luminous intensity is 50% or more of maximum - 140º)

Link to datasheet.

The Wikipedia article on laser safety has this chart of maximum allowed CW power at various wavelengths and for various classes. It states that it is only valid for weakly divergent or collimated laser beams, but since Class 1 devices must be safe to view using any optical equipment, I can make the assumption that they are valid for the case where there exists a lens that can concentrate all of the available optical power from the LED onto the retina.

My big issue is that I can't seem to work out how to go from luminous intensity to optical power. I can convert from luminous intensity to luminous flux - however not to radiant flux (which I believe is equivalent to total optical power).

Can anyone shove me in the right direction?


texts: How can I protect a MOSFET bi-directional switch

texts:
I need to protect a MOSFET bi-directional switch made with 2 of IRF540 (VDS 100V) against potentially over-voltages on inductive loads.

Because isolator is slow (say ~1mS), I am concerning about the moment when SW just opens or closes into inductive load (a motor).

The plan is to put some uni-directional TVS across mosfets with VBR < VDSS.

Should be bi-directional (because load can generate negative spikes)?
Should I connect the common? My guess is yes because in case of a event, I don't want to let the 2'nd mosfet to handle that too.

Any comments really appreciated!


texts: How to control the speed of a 12V DC motor with an Arduino?

texts:
I'm trying to figure out how to control the speed of a 12V DC motor with an arduino and a 12V battery.

I want to split the «power» and «control» parts of the circuit so the Arduino and sensors receive only 5V.

So far, this is what I've tried :

I am able to control the speed of the motor by changing the PWM of pin 3 on the Arduino. This opens the NPN transistor (BUF654).

The problem is that the speed of the motor doesn't change enough.

From 0% to 50% PWM on pin 3, the motor is stalled.

Above 50%, the motor is nearly reaching its maximum speed.

I wonder if I would be able to have a linear variation :

0% - 10% : very slow
10% - 20% : slow
20% - 50% : normal speed
50% - 80% : fast
80% - 100% : RELEASE THE KRAKEN!

Here are the voltage and current the motor draws when using only a battery, or the previous circuit :

+----------------------------+---------+--------+
| Directly on 12V battery    | 12.7 V  | 61 mA  |
+----------------------------+---------+--------+
| Arduino circuit (100% PWM) | 12.47 V | 60 mA  |
+----------------------------+---------+--------+
| Directly on 9V battery     | 9 V     | 54 mA  |
+----------------------------+---------+--------+
| Arduino circuit (60% PWM)  | 9 V     | 52 mA  |
+----------------------------+---------+--------+

What have I done wrong? Could the problem come from my motor?


texts:
Please help me figure out which inductor to use from this datasheet. Sorry - it's in Chinese as this is an Asian sourced IC and not sold in the US. (Use google translate if necessary - but, the meaning is clear enough from the digrams and tables. )

The formula for the inductor, given on page 3 is as shown below:

I'd like to use a single energy efficient LED like this     (I'm open to other white LED suggestions)

I'm using 2 alkaline AAA batteries.

Question 1
Based on the formula given above, should Vin be

2V fully discharged point of 2 x AAA Alkaline cells?

or

3V (= 2 x new Alkaline AAAs cells) to avoid over current?

Question 2: to calculate P for LED, I use 5mA at 2.9V = 145 mW - which is normal conditions for LED (page 2 from LED datasheet) - good assumption?

I came up with 580nH - is this correct?


texts: Ammeter time limits - how to understand them

texts:
On my multimeter, near the 10 A connector it says 10 A MAX 10sec EACH 15min. I usually measure currents less than 1 A so I never cared about this.

Is it correct to assume that if the measured current is lower than 10 A, I can take the measurement in more than 10 sec and I don't have to wait 15 minutes?

I measured only a few times a current of about 4 A and I'm sure I didn't follow those time limits and the multimeter is still working (so far).

I read the manual, there's nothing written about this.


texts:
I am trying to design a circuit to control mains equipment using a microcomputer, probably a Raspberry Pi.

The requirement is:

The main switch is open (up in the diagram) and (ideally) no current flows.
When the main switch is closed (down in the diagram), the Pi boots up. The relay R1 must stay open so the load is isolated.
Later, the relay R1 is closed by the Pi, under software control, so that the load is energised. The load stays on, even if the Pi shuts down.
When the main switch is opened, the load goes off and the relay R1 is opened, ready for the next iteration.

Is there such a relay type, that would be normally open with no input power, and and then latch closed?

Alternatively, I am thinking of another relay at C1, to open R1 at step 4. Is this a sensible idea?

Please advise on the type of devices for R1 and C1 if appropriate.

I am confident of cabling the mains switch, load and relay. Please note that this not about the Raspberry Pi. There is plenty of information available about using the Pi with relays and relay modules.


texts: For my project i want to connect 109 Li-ion cell in parallel then the battery pack of capacity increased to 3.7v 272.5Ah and convert by boost converter into 48V supply to motor. how to protect those cells.How to construct battery management system for my cause?.if there is any solution please guide to construct it or any product is available in market?


texts:
This is an assignment question:

A system is operating at 325VDC input, what is the required static leakage current during sleep mode in order to achieve Zero power?

I know there may be a lot of values for the leakage current which satisfy the requirement but I do not know a good or typical value for this. Although I saw that mostly the value will be in terms of micro amperes, I am still not sure about a value for this. Can I get help on this?


texts: Resistor-only solution to split 19V 3A to 3.3/5V and 12V 2A with common ground?

texts:
I need to quickly assemble a simple thing, a LED strip driver with ATTiny/Atmega. My powersource is (as always) a universal laptop brick (17-21V output @ up to 4A).
So AVR would be hooked into a number of ULN2003 to control overall drain (near 2A, 12V).
The problem is, it would take few days to deliver me anything better than a couple of resistors (have a lot of those here), so can make only a common-ground resistor divider.
Problems:

How to calculate the resistors to power both parts correctly?

(even worse) how to limit the current for ICs to about 500mA? Only resistors, remember. Maybe a bit of transistors/capacitors, but (almost? ideas?) nothing smarter.
.


texts: FT232 Chip as UART to USB freezes windows and and access denied

texts:
(Posting my own solution here)
I was trying to use a FT232 to communicate with my Atmega328p-AU (arduino uno's MCU) and even though I had several times made this connection which worked fine, this time, when I try to connect to it using Tera Term, this error shows up:

My connections are:


texts: Can I connect two different 1-Wire Devices to the same data pin on an Arduino?

texts:
I have used DS18B20 temperature sensors many times and understand that they can be daisy chained on the same data pin. Could two different sensors be connected in the same manner?

For instance, could I use the same data pin to read data from both a DS18B20 and a DS2417? Would there be any limitations concerning either the hardware or the code aspect?

Taking a look at the example code on arduino.cc:

if ( addr[0] == 0x10) {
      Serial.print("Device is a DS18S20 family device.\n");
  }
  else if ( addr[0] == 0x28) {
      Serial.print("Device is a DS18B20 family device.\n");
  }
  else {
      Serial.print("Device family is not recognized: 0x");
      Serial.println(addr[0],HEX);
      return;
  }

It is clear that there is at least some tolerance for different devices, however the DS18B20 and DS18S20 are both temperature sensors and aren't all that different


texts: Are the PIR sensor modules motion sensors or proximity sensors?

texts: I wanted to make a small project in which the lights of a room can only be turned on when there is someone in the room and it will turn off in absence of any person. I thought of using PIR sensors but from what I read it looks like they sense motion and not the presence (non-moving human) of someone.


texts:
I want to design a counter using logic circuits... The first counter ic takes it's clk from the frequency circuit... When the first dispay reaches 10.. The other clk should give signal for the second counter to give 1... What happens is that the second display gives 1 when the first is still at 8 so mainly it's 01..02...03...04..05..06..07..18..19..10..11..12..13
Any help?!


texts: How much current is flowing through this circuit?

texts:
Here's a circuit connecting 4 LEDs with 22 Ohm resistor. According to my calculation, I'm supposed to get 45 mA flowing.
Battery is 9 V. Voltage drop of each LED is 2 V. Resistor is 22 Ohm.
\$(9 - 4 \cdot 2)\ /\ 22 = 0.045 \$ or 45 mA.
However, if you look at the multimeter, it says 1 mA? I'm really confused.
I'm a total beginner, so I appreciate any help.


texts: How are op-amp gain vs frequency response curves generated?

texts:
I have been wondering this for a while. When we look at the electrical characteristics of a device such as an opamp there is a gain versus frequency plot.

I have couple of questions regarding measurement of frequency response in practice:

1-) How is an opamp's frequency response obtained in reality/on bench? Do they sweep or measure the output voltage for each frequency input and obtain the plot? Or do they apply an impulse or step input to the input, obtain the response and do the math and plot the frequency response?

2-) If they do the sweeping freq. method but not the impulse or step input method; where is the second one used in practice? I mean is the step input or impulse input used in any case in the engineering world to obtain the frequency response? Or are these only used on paper(mathematical modelling or simulations)?


texts: Increase headphone impedance using resistors

texts:
I have an LG-V30 cellphone, which has an integrated headphone amp with two modes for audio reproduction depending on the headphones you plug in.

Normal mode for headphones under 50 ohm, low output, amp disabled.
High impedance mode for headphones over 50 ohm, high output, amp enabled.

I'm using Takstar 82 Pro headphones which according to the specs are 32 ohm (plus-minus 15%).

These headphones have a detachable cable, and I have two different cables, a short cable (1m) and a long cable (2m). When I plug the headphones with the short cable, the cellphone detects them as under 50 ohm, but when I use the long cable they're detected as over 50 ohm and the amp gets enabled, resulting in higher sound level and just better sound overall.

I have measured the apparent resistance of the cable by measuring the ohm between the tips.

Short cable: 0.4ohm
Long cable: 1.5ohm

Questions:

Is it possible that the higher resistance of the longer cable is somehow fooling the phone into thinking the headphones are of higher impedance?
Can I somehow add in-line resistors to the short cable to simulate the resistance of the longer cable, so I can use the headphones in high-impedance mode with the short cable?
If so, which values would those resistors be?
Will this mess up audio quality the way inline capacitors would?

Notes:

I am aware there are other headphones with higher impedance, but I want to use these specific model.
The behavior of the cellphone cannot be changed by the user.
My knowledge in electronics is somewhat basic, so be gentle :)


texts: Why is the Image Sensor Board routing different?

texts:
The below posted is a open source camera project Elphel PCB layout images

I have took their  353 model camera, which is mounted with an Onsemi sensor

I only know that for high speed signals we go for curved traces to avoid reflections ,in this case i see the complete card routed with curved traces with out any kind of angular bend

Not only this card i also have seen few image sensor boards from fairchild and omnivision having routing done with curved traces than angular, why so ?


texts:
I'm trying to find the datasheet of an 8-pin DIP IC:

I tried to search each line separately and both of them together but to no avail.


texts: Notation on schematic for circuit with n-channel switch

texts:
I am designing a circuit with a load that will consume up to 2A @ 5V. I decided to use a slide switch rated at 100mAh to drive an N-channel MOSFET for the (relatively) high current, since a slide switch rated for 2A is significantly bulkier.

I understand that when using N-channel as a switch it is connected on the low side between the load and GND.

I'm just wondering about best practices for separating the circuit GND from the load GND that needs to go through the MOSFET. I'm guessing I should use different net names for those two GNDs.

Which one of the grounds should I call GND? The external "raw" one? Or the one that goes through the MOSFET? I already have a dozen GND nets/symbols in my circuit that should be going through the MOSFET
Should I use different symbols for the two grounds? Or same symbol with different net names?
Does anyone have an example schematic with a similar circuit I can look at for reference?

I am mainly asking about best practices and ensuring maximum readability. Thanks!


texts: What happens to inverter if running motor controller without load (motor)?

texts:
Consider running a 3 phase BLDC motor controller having 20KW inverter fed by 100V whence designed for high amperage. What happens if we turn it on and start gradually increasing duty cycle of the MOSFET gates PWM without connecting motor leads?
Or a somewhat similar situation but more complex - connecting 3 phase motor but one phase wire is broken ...
What can we observe on the phase output leads if we connect oscilloscope probe A-B, or B-C etc...? What happens to the inverter bridge MOSFETs ? Can this (no load) case be used to test at least some of the inverter specs?
I think the conducting MOSFETs will not have a half bridge closed circuit for the current to run but, if so, I am confused about what happens if 2 phases are conducting but one is broken (unbalanced inverter's load)?
Thanks in advance for any meaningful ideas as this question tests our understanding of the nature of the power inverters.


texts: On NAND or NOR flash, is program time completely independent of byte values?

texts: I know that the erase value of NAND and NOR cells is all 1s, and the process of programming involves clearing bits. Is the program time of some x length data always the same, regardless of the number of 0s in that data? For example, does it takes less time to program 11110000 than it would take to program 00000000?


texts: Software alert when doorbell rings. Doable?

texts:
I am looking for a way to send alerts to my Linux laptop each time the doorbell rings to avoid those unpleasant times when a visitor ends up waiting minutes outside my door when I am alone and have headphones blasting full volume, rendering my doorbell-hearing powers useless :x.

Now, I am relative noob to all things electrical, which this project will most definitely involves. My brief search on Google indicated something called Arduino holds the key for me. So,  would love some pointers as to whether such a thing is doable, and if yes, how should I proceed?


texts: Convert CMOS-level signal to microphone-level (0..3V --> -1..+1V)?

texts:
I'm building a microcontroller circuit that feeds its output into a microphone input of an audio recorder. The output is a square wave. (Think old-style 3.5mm Square credit card readers).

What can I use to covert a signal in the range of 0..3V to -1..+1V? I'm looking for something like MAX232, but with lower voltage levels.

I could just use a voltage divider and feed 0..+1V to the audio, but I understand that many audio input circuits use AC coupling and the recorded waveform can have unpredictable DC bias. This is undesirable, since the waveform encodes information in zero-crossings.

The question really is about a circuit that can generate negative voltages without a separate negative supply, but for completeness, I can add a few more details. The application is a kind of old-style telemetry format. The data rate is fairly low (~2,000 zero-crossings/second, or 2kbps). The client audio circuit is usually (though not always) a digital recorder. The client records my input and (usually) saves it as a digital sound file. Clients' expectations are that third-party programs can extract original digital information from these files. Sometimes, instead of recording my signal directly, the client feeds my signal into an audio-frequency radio TX (think walkie-talkie) and records the signal from the RX.


texts:
I'm developing a home automation system, and using a triac to power on/off some lights.

My problem is that lights from other rooms when switched on/off are producing noise/spikes and flashing the lights turned on by the automation (triac).

I added a snubber like this, and it is all good now. My point is how to calculate the ratings of the RC components.

The answer is "calculate the necessary power dissipation, and after that the RC", but considering that spikes are randomly and in rare situations I'm using a 0805 resistor and a 0805 capacitor.

My voltage is 220Vac. The resistor has Umax = 150V. I'm using it and it is working as expected. Aparently the lower voltage is not a problem for the spikes.

Can I desconsider the resistor Umax for spikes, and use it definatevly in my system? I'm assuming the RC will dissipate a very low energy.


texts: How to send a packet every n clock cycles in verilog?

texts:
I am fairly new to Verilog and in general Digital Design. I am working on a project which has a state machine. The module, in a particular state, receives a read request packet from some other module and I have to decode the required read response data size and send back as many data bytes in the payload. Now I have to do this every n clock cycles.

I am finding it difficult to understand where should my count be updated and where should it be assigned the next count value? Here is the general structure of my code.

    always@(posedge clk_i or negedge resetn_i) begin
    if (resetn_i == 1'b0) begin
        reg_read_en         <= 1'b0;
        reg_write_en        <= 1'b0;
        count               <= 3'b111;
        next_count          <= 3'b111;
        state               <= S_INITIAL;

    end else begin
        state               <= next_state;
        count               <= next_count;
    end

This is the sequential block.Now in my combinational block

always@(*) begin

    next_state  = state;
    next_count  = count;
    .......
    ........
    M_PASSIVE:begin
                        if(count == 3'b000)
                        begin
                           //Update some registers with new data values
                        end else begin
                        next_count = count - 3'b001;
                        end

I am unable to understand does this wait the required count no of cycles and then update the reg values or I am missing something here.

I would very much appreciate some clarity about this.

P.S. Pardon me if I am missing some fundamental aspects of behavioural design regarding difference between sequential and combinational blocks.

Here is a complete code of what I am trying to do. Essentially I want to read a packet, turn of reading of packets, wait 7 or 8 clock cycles or N clk cycles and then send a read response with the data in the registers which are assigned to output ports continuosly.

    always@(posedge clk_i or negedge resetn_i) begin
    if (resetn_i == 1'b0) begin
        reg_read_en         <= 1'b0;
        reg_write_en        <= 1'b0;
        count           <= 3'b111;
        state           <= S_INITIAL;
    end else begin
        state           <= next_state;
        count           <= next_count;
    end
end

always@(*) begin
    next_state  = state;
    next_count  = count;
    case(state)
        S_INITIAL: begin //not enabled
            if(enable_i == 1'b1) begin
                next_state = S_ENABLED;
            end
            reg_read_en         <= 1'b0;
            reg_write_en        <= 1'b0;
        end

        S_ENABLED: begin
            if(enable_i == 1'b0) begin
                next_state = S_INITIAL;
            end

            case(mode_i)
                M_PASSIVE:begin
                    reg_read_en =   dnoc_packet_ready;
                    //pkt_type  =   dnoc_packet_pld_header[]
                    if(dnoc_packet_ready)
                    begin
                        reg_read_en = 1'b0;
                        if(count == 3'b000)
                        begin
                        reg_write_en    =   1'b1;
                        read_resp_tx_data_size = 3'b001;
                        read_resp_tx_qpe_dest  = 6'b000010;
                        read_resp_tx_mod_dest   = 5'b00000;
                        read_resp_tx_c_routing  = 0;
                        read_resp_tx_pld_header = 17'b00100101000000000;
                        read_resp_tx_pld_address    = 32'h0001;
                        read_resp_tx_pld_data   = 256;
                                                        //count = 3'b111;
                        reg_write_en    =   1'b0;
                        end
                        next_count = count - 3'b001;
                    end
                end


texts: Difference between USB host & device when connected to the Intel PCH chipset

texts:
I know USB 3.0 Host & Device connector port has the same pin count (VBUS, D+/-, TX+/-, RX+/-, GND), but what is the difference between USB host & device when they are connected to the Intel PCH chipset?

I am using a USB3380 controller to convert the PCIe to USB device port. I would like to ask if there are any other controller out there which can replace USB3380. Texas Instruments TUSB7320? Renesas uPD720202? Cypress EZ-USB FX3? I know TI & Renasas chip are PCIe to USB host controller; can they be used for my purpose?

Lastly, without a USB3380 controller, can I connect/design the USB device port directly to a Intel PCH chipset?


texts: Shorting a high voltage electrolytic - damaging?

texts: I have a high voltage (400V) electrolytic capacitor, and I sometimes discharge it by shorting the terminals with a screwdriver. I get a fat spark and a bang. However, apart from minor damage to the terminals/connections, does doing this cause any damage to the capacitor?


texts: How does impedance analyzer input capacitance influence the measured result?

texts: I work with an impedance analyzer, measuring impedance spectra of ionic conductors. I would like to know how the obtained data can be affected by input capacitance at higher frequencies (1kHz-1MHz). A person said that I cannot properly determine dielectric properties because the high input capacitance of the meter (on the order of 100 pF) does not allow measurement of solid samples that usually exhibit lower capacitance than the input capacitance. How can I see this input capacitance influence?


texts:
I would like to know about the workings of mobile phone battery chargers. I know the basic principle, you take a transformer to bring it down to 9/6/3.7 volts then a bridge rectifier circuit and a capacitor input filter to rectify it into DC. Then you apply it to the battery. But I know this should not be enough, I need at least two things,

Protection against back current flow
Switch off power when the battery is fully charged.

Can someone point me to something simple (apart from this http://www.extremecircuits.net/2009/07/mobile-phone-battery-charger-circuit.html)


texts: Can we connect battery negative terminal to oscilloscope ground?

texts:
I want to test my setup with 200Ah battery and check the outputs on oscilloscope. While testing can I connect battery ground to the oscilloscope ground?

Is there any safety risk, as oscilloscope internally connected to earth? If I connect to battery's negative terminal, it will be connected to earth. Will it cause any hazard? Battery is of 12 V.


texts: How can I find a correct crystal replacement for this circuit?

texts:
I need to replace a crystal component (16.257 MHz, one of its legs broke off and cannot solder it back on) from an old video card that is wired up like the schematic below (the resistor / capacitor / frequency values differ, it's just for reference on how it is connected) :

Now I read that there is such a thing as a series-resonant oscillator and a parallel-resonant oscillator, but I don't know under what category this falls. However given the schema above, I would like to find a drop-in replacement.

When I search for a replacement part on Mouser, by providing the frequency:

https://www.mouser.be/Passive-Components/Frequency-Control-Timing-Devices/Crystals/_/N-6zu9f?P=1z0wnq5Z1z0z7l5

I noticed that some of them say "load capacitance = 20 pF" others say "load capacitance = series".

I also noticed different form factors. The ones listed here all have a very low form factor,

while my broken component had a larger profile:

What kind of replacement could I choose? Does the housing (form factor matter) matter, and what about the load capacitance difference or other properties I should be aware of?


texts: Finding power absorbed by a voltage source

texts:
I would like to find the power absorbed by the voltage source B.
I know that \$P=VI=RI^2=(0.5\Omega)\left( \frac{4-E}{1\Omega + 0.5\Omega}\right)^2\$.

What is the "right way" to find it?

Edit: Basically it gives me three options: \$E=1[V], E=0[V], E=-2[V]\$, and I need to find \$E\$ such that B absorbs the maximum power. Textbook's solution is \$E=1[V]\$.


texts: Terminating resistor considerations for half-duplex RS-485 over 80-200 m cable at 115 kbps

texts:
I'm designing a system where we are communicating with a device (ultrasonic anemometer) which is at the end of a cable which could vary between 80-200m.
The sensor communicates via RS-485 half-duplex. There is mention of terminating bus resistors possibly being required. On the sensor, there is a 100R terminating resistor between TXD- and TXD+ which can be enabled or disabled.
Can this system be deployed without a terminating resistor and not have any problems? I read that 'long' cable lengths increase the requirement, however in the context of the guidance, long is relative.
I have used this calculator but there are some parameters which I do not know and I have made the assumption that the 'network cable' is similar to that of which is being used, such as: Bit Rate of Transmission Technique (bits per baud), UART Controller Sampling Rate (Clock cycles per baud).
My questions are these:

Is it standard rule of thumb for terminating resitors to match cable impedance?
If yes, how do I calculate cable impedance? (Example cable)
How do I determine if terminating resistor is required?
What is the tolerance of the terminating resistor for it to serve a purpose? (i.e. if the cable length varies, do I need to calculate a new resistance each time or is there +/- metres leeway)
Is 200m considered long in this context
Is 115k baud considered high-frequency in this context?

Thank you for your help in advance.


texts:
I'm working on a circuit to activate a relay with an Arduino, adapted from this schematic:

The relay is a RTE24005, which has a 5V coil.
When I use the 5V and ground from the Arduino it works perfectly.

When I use a wall wart power supply instead (5V, 550mA), it fails to switch.
The only real difference I can tell is that the wall wart isn't the same ground as the the input from the Arduino.
Does this make a difference?

Is there something else that I'm missing?


texts: Does the AD8495 thermocouple amplifier allow for grounded thermocouple probes?

texts: I recently purchased a MAX31856 thermocouple-to-digital chip for a project. However, I discovered that the chip does not support grounded thermocouples. I am looking for an alternative and the AD8495 appears to be the only similar option. However, I cannot tell from the datasheet whether it supports grounded thermocouple probes. How can I tell?


texts: What's the simplest high voltage AC square wave oscillator?

texts:
I'd like to have such an AC square wave oscillator putting AC through a load - which can go to 60 VDC and deliver no more than 50 mA with sharp, fast rise times and very "square". I would hope a topology exists.

The biggest request/demand I have is a circuit which would use the least amount of components, especially ICs if there would be any ICs then please a topology with ICs that have the least amount of pins. In other words, I am looking for an oscillator which can be thrown together onto a breadboard rather quickly. I need an actual circuit, not an output from a function generator.

Frequency: 3.9 Hz Duty: 50% Load: Resistive, no smaller than 1 kΩ

Squareness, sharp and fast rise times are just desires. I'm sure people won't suggest an oscillator which is slow enough to turn a square into a triangle wave.


texts: How do I switch on after the current (out of a power supply) has established?

texts:
I have built a case containing a Raspberry pi which controls a bunch of 12V based devices (using a relay board).

I am using a PSX3-C12AFC model power supply that takes my mains and drops it to 12V.

As per someone else's advice here, I have opted to use a simple car USB charger (for lighters) to go from 12v to 5v.

I would ideally like to have no power switch on the system at all: I plug it in the mains, and it starts up the Raspberry pi.

However, I'm concerned that the surge from either PSU (or combination of both) is not healthy for the raspberry pi. So far, I've been connecting the PSU and manually connecting the USB cable to the pi to avoid any funky business.

I'm looking to automate this with some form of circuit/device that would only give current to the Pi after the current has properly established.

I am not an EE, and can do moderate DIY stuff. Can anyone point me to the right resources to achieve this? Or even what the circuit I'm looking for is called?

Thanks.


texts: Connecting Solenoid valve in the emitter of the transistor

texts:
We are working on a circuit in which we are controlling two way solenoid valve (24V, 10W). We are using 3.3V based controller. The solenoid valve is connected to the controller via TIP 122 (NPN Darlington) transistor.
When the solenoid valve was connected in the collector end of the TIP 122, it was working fine. When the valve was connected to the emitter of the transistor, it was not switching ON.
Why there is discrepancy, when connecting the valve on the emitter end. In the end the transistor has to turn-ON and has to allow current to pass between collector and emitter end.
Answer: When connecting load across emitter and the ground: The VBE required to maintain the forward bias will go away as voltage will drop across the load. If VBE is set at 0.7 V, and then as soon as the voltage across load becomes 0.7V transistor will no longer act as a switch. As their will not be potential difference across VBE. Th


texts: Charging an RC circuit with two different Voltages?

texts:
I am giving step input voltages of value 10V and 5V to an RC circuit.

Will it take equal time to charge the capacitor to its's final value?

OR

5v will take more time to charge and 10v will take less time for charging the capacitor to it's final value.


texts: How to build a 75 ohm to 50 ohm converter

texts: I need help to build a simple converter to match a 75 ohm feed line to a 50 ohm antenna. Please help :-(


texts:
I am making a PVC electric go-cart. I want to know which is better: a 12V motor or a 24V motor?

I want good speed and good torque, because I don't want it to struggle with my weight (I weigh around 210 lb). So what's better for this project?


texts:
Using a simple PCB with copper on both sides but naturally in between, is it feasible for a hobbyist to make through-hole vias like this:

It seems there is copper in the via itself, isn't there?

If it is not easy to do, what would be the best solution? Simply fill the hole with solder? Or should I put a miniature wire or some component's lead to connect the two sides?


texts: Voltage Divider with two current sources

texts:
I'm having trouble with this circuit. I'm trying to find the current through and voltage drop across the resistors when the switch is open and closed.

When the switch is open, I've found that the voltage drop across the upper resistor and lower resistor is 10V each. I'm not sure how to deal with the second current source when the switch is closed.

Any help is appreciated!


texts: Does my PWM led circuit controlled with NodeMCU and Mosfet work properly. What should I do to improve it? How to calculate for each components?

texts: If I understand it right, when there's is signal from ESP, the PNP and NPN be ON, and Vgs=0. If they're OFF Vgs=+12V and the LED will shine. R=1K is to limit the Ib of NPN, and R=10K is the resistor pull up for the Gate. for the 2 Resistors=4.7K is to limit the Ic,right?


texts:
I must have missed an article, lesson at uni, or something obvious because I'm struggling to work out how to write some firmware to use a gas gauge to get out a rough percentage of battery remaining, e.g. "56%".

I'm primarily hardware-focused by trade and so whenever I've integrated them into professional products, the firmware has been handled by either a colleague or a contracted company. Now I'm just doing a design at home by myself and because of reasons, I've gone straight to using this STM part (instead of using a Sparkfun Module or something with pre-written and easy firmware) - because I actually want to learn, not just get something working.

So basically I was just after some advice on how they generally work. Obviously each part is probably unique in their own way, but in general I know:

They monitor the through-current with the shunt resistor
They monitor the battery voltage by tapping off the + and - terminals
They monitor charge/energy/power flowing in and out of the battery, by combining these two measurements and some math

My question is: how do I get a percentage read-out from this? Especially since batteries all have different capacities and there is surely no way the GG knows what size battery I have plugged in?

I'm guessing I have to plug in a fully-charged battery when the system first "fires up" (for example, 400mAh), and then work out the percentage myself in the firmware by constantly subtracting/adding the charge that has flown in/out from the total 400mAh. The bit that confuses me a little is that this then assumes a fully charged battery was first inserted into the system but this definitely isn't always the case - Li-Po/Li-Ion batteries are usually shipped at ~50% charge (if I'm not mistaken) and would be installed into products straight away before being fully charged, thus making all these calculations wrong and pointless.

Is there something I'm missing? I can't find any detailed information on how to actually "use" these chips. Any help is much appreciated :)


texts: Does the code on an ATTiny execute while it is being programmed by ISP?

texts:
I'm using an ATTiny84 and I have both a switch and a pin header attached to the MOSI pin. I am reading the value of the switch in my program, and I'm using the pin header (along with headers to MISO, RESET, and SCK) to program the chip with my Arduino. I won't be pressing the switch while programming the chip.

When I start programming the chip, will the code already on my ATTiny restart execution, or will it wait until RESET is no longer held low? All I could find in the datasheet is that the pins "are tri-stated when a reset condition becomes active" which I don't understand.


texts: STM32F469 FMC Memory Mapping Inconsistency

texts:
I'm learning ropes with STM32 and everything was going pretty well until...
I have STM32F469i-Discovery (Touch DSI 800x480, SDRAM, QSPI Flash etc.) Have ton of docs - datasheets, manuals, PCB schematic and so on.
So now I got to the stage where I need to interface SDRAM IC with FMC. I used STM32Cube_FW_F4_V1.26.1 collection of examples, specifically \STM32Cube\Repository\STM32Cube_FW_F4_V1.26.1\Projects\STM32469I-Discovery\Examples\FMC\FMC_SDRAM.
According to code comments/documentation, my SDRAM is executing this example script correctly (LEDs indicate all good). So it works. But I don't understand how and why.

So the datasheet of 469 clearly indicates

But when I use debugging and breakpoint, I find only garbage at address 0x60000800 (taking SDRAM offset into account). Instead, the correct values are under 0xC0000800, which is FMC Bank 5 as per datasheet.
main.c has
hsdram.Init.SDBank = FMC_SDRAM_BANK1;

at the same time, main.h has
#define SDRAM_BANK_ADDR                 ((uint32_t)0xC0000000)

My only question can be summarized as:

Can anyone give a reasonable explanation and/or provide a link which makes this clear as to why FMC bank 1 gets mapped onto FMC bank 5 addresses?


texts:
I'm working on a project to run a 12 volt 12 amp DC gearmotor via PWM output from a controller.  I am using a Crydom solid state relay to power and motor and trying to figure out what diode is correct for this application.  I have read about using a zener diode for fast operation.  Is this the proper type and how do you size the diode to this application?

Thank you

Edit:
Motor: Leeson M1125273: .13 Hp, 12vDC, 12.0 A

SSR: Crydom DR2220D30U: Max Turn-On: 75 usec
                        Max Turn-Off: 100 usec

PWM F is 100 Hz


texts:
I'm currently trying to create a system to open my apartment's door (using the buzzer) using my raspberry pi, and thought that using an optocoupler would be the best solution - although I'm a complete novice.

The only optocoupler that I've been able to find locally is this one, however I'm pretty lost on whether or not this would be suitable for my project, and if so I'm not sure what kind of resistor I would need to buy to be able to use it.

The Raspberry Pi has a 3.3V source voltage, and I was using this site to try to calculate what ohm resistor I'd need, but I sadly don't see the forward voltage on the specifications of this product.

tl;dr: Is this optocoupler suitable? If so, how many ohms would the resistor I buy need to be?

Thanks for your help, and sorry for the probably trivial question.


texts: Someone has a circuit for a isolated driver (both input and output) to my project?

texts: I'm working on a self-oscillator Buck converter. My simulation on PSIM has a perfect output, as you can see. But I need a more realistic simulation on another software (with Spice models), so I need a driver circuit with the input and output isolated. I think a opto-isolated driver could work, but I don't found a circuit model to do this. Thank you!


texts:
I'm looking at designs for notch filters for an audio system. I want to filter out 10kHz and attenuate by 40dB. I found this topology online:

I'm unfamiliar with transfer function calculations for something this complicated. Could somebody walk me through this please?

I believe that once I have the transfer function I can figure out what the values are.


texts:
Can someone point out the mistake I'm making in reading this graph (which is from the ADI Blackfin 70x datasheet)

If a driver was set high, to 1.8V, why would it be unable to source current? I'm reading up from 1.8V on the X-axis and going up to the middle Voh line, then over to the Y-axis.


texts: Circuit Analysis: Difficulty in obtaining a current through a resistor?

texts:
I'm solving a problem that requires I compute some impedances, and then the current through a resistor. I obtained some of the impedances*, but don't know how to get the second part (current).

Question

4.A

For question (A), I partitioned the circuit mostly using intuition. I just kind of chose the left RC to be \$Z_{1}\$, the middle capacitor to be \$Z_{2}\$, and the right-hand RC to be \$Z_{3}\$. The first impedance is wrong, I'm not sure why.

$$Z_{1} = \frac{Z_{C}}{Z_{C} + Z_{R}} = \frac{\frac{1}{j\omega C}}{\frac{1}{j \omega C} + R} = \frac{1}{1 + j\omega CR} = \frac{1}{1 + j(\frac{1}{RC})CR} = \frac{1}{1 + j} = \frac{(1 - j)}{2} = \frac{1}{2} - \frac{1}{2}j \rightarrow \frac{\sqrt{2}}{2} \angle \frac{-\pi}{4}$$ Actual solution is \$ \frac{\sqrt{2}}{2} R \angle \frac{-\pi}{4}\$
$$Z_{2} = \frac{1}{j\omega(\frac{C}{\sqrt{2}})} = ... = 0 - jR\sqrt{2} \rightarrow R\sqrt{2} \angle \frac{-\pi}{2}$$
$$Z_{3} = \frac{1}{\frac{1}{Z_{R}} + \frac{1}{Z_{C}}} = ... = \frac{R}{2} - j\frac{R}{2} \rightarrow \frac{R}{\sqrt{2}} \angle \frac{-\pi}{4} $$

4.B

Here is where I have trouble. In order to compute \$I_{2}\$, I decided I should try using: $$I_{2} = \frac{V_{1} - V_{2}}{Z_{2}}$$ with:

$$ V_{1} = V_{s} + 0j $$
$$ V_{2} = V_{1} \times \frac{Z_{3}}{Z_{3} + Z_{2}}$$

However this quickly blows up in my face and becomes a huge problem I can't manage. The given solution simply states:

$$I_{s} = \frac{V_{s}}{R} = \frac{V_{s}}{R}0.271 \angle \frac{\pi}{8}$$

and hints that it used some Norton equivalent circuit. How can I solve for this current using a Norton equivalent circuit? What am I missing about the problem?


texts: Ethernet Magnetics CT pin shorting issue and the fix

texts:
We have a design where a voltage mode 1GbE PHY is driving the magnetics and the link is intermittent. Upon inspection it turned out the CT pins on the primary side of magnetics are all shorted as shown in the picture. Now in order to do the rework (only for testing)  our only option is to do via drilling to remove the short but in the process we will lose the caps C4,C58,C60 and C10 from the circuit.
There are two questions:

Will the circuit behave as it is now due to this shorting connection?
If we did do the rework and remove the CT shorting which will force us to disconnect the CT caps, will the Ethernet still function?

Thx in advance


texts: Why is solder not sticking to the PCB pads after using the hot air gun?

texts:
I'm training how to use the hot air gun at my hobby electronics station. It's a brand new machine. I can solder easy enough but the hot air gun is well so far only useful for wire shrink tube.

Here's what I do: I turn it on both to 395° Celsius. I use the iron to put solder on the pads, then I add flux before using the hot air and heat the solder ball up, put the part down, and all looks great. Then the part and solder ball comes off the PCB pad. What am I doing wrong?

The PCB is one of those cheap kits on eBay. It has a bunch of SMD resistors and an LED that lights to show it works afterwards. Any tips or demos related to what I'm doing wrong actually any information would be greatly appreciated.


texts:
I'm getting some conflicting information regarding the BigEasy stepper driver. I have a 24VDC 14.6A electromagnet that I need to toggle. I have a few Arduino Mega's and a box full of BigEasy stepper drivers that I would like to utilize to accomplish this as I'm extremely short on time.

I know the BigEasy can take the 24VDC but what about the 14.6 amps?


texts: Are "Apk" and "Amp peak-to-peak" the same thing?

texts:
Folks,

What is the difference between "Amp pk or Apk" vs "Amp pk-pk (or Amp peak to peak?)"

Are they the same thing?


texts: Why is my mixer circuit lowering the signal?

texts:
I have made a really simple mixer, to be used with both audio and control signals in a modular system:

This should if I understand it correctly give "about" 1:1 (1:0.99 in simulation) ratio beetween an input and the output. I've done a falstad simulation and there it looks "as it should" with a ratio of 1:0.99 which I think is close enough.
Link to simulation: Falstad Mixer Simulation, the caps have been disconnected in the simulation. You can change the input from DC to AC to see how it would react on audio signals

But when I try it out IRL the signal is much lower (less than half) after going through the mixer than when bypassed, and that 1% in the ratio cant do that much can it? I did a test with adding 1v on the input and when I plugged it in it sank to 0.1v (about), the source was a nonbuffered voltage divider if that could be the reason for that? Also trying audio signals, less than half volume, and control signals half the range.

The question: What am I missing?

I'd appreciate any ideas on what to try next, and common errors that I might have missed. Thanks.


texts: Connecting RFM12B transmitter to Arduino Leonardo

texts: I need to connect RFM12B radio transmitter to my Arduino Leonardo. I've found a library, but I'm not sure about the pinouts. Also I've noticed that this module should get 3.3V. Of course there is 3.3V pin for VCC, but digital outputs also has to be 3.3V. Can I use for this purpose simple resistor divider?


texts: How to read the datasheet of an ultrasonic sensor?

texts:
I want to use ultrasonic sensor for a personal project. I need a waterproof sensor like this but I cannot figure out how to calculate the measurement range. Sometimes on these sensors is written that the minimum range starts from about 25cm.

For my purposes I need a sensor which is able to measure from about 10cm. How to do it? HC-SR04 is very good for my idea, but it isn't waterproof.

Google can't help me this time.


texts:
I`m planning to buy a toroidal transformer for driving an LED. The LED needs 36 V and around 1 A.

I found a toroidal transformer which has a 230V Input and two 18V 0.83 A Outputs. Can I simply sum the outputs by connecting both positive outputs and both negative outputs to my LED?


texts: Need an isolator or similar to fix my design issue

texts:
I have an arrangement where 0-80 VDC signal is provided as input to a measurement board for measuring this DC signal. But somehow along with this 80 VDC signal, there is noise coming in the circuit rated 1500 V peak to peak. this noise signal is damaging the multiplexer circuit present in the board. Now, i want to prevent this noise signal from coming in to PCB and isolate PCB.
I have looked at plenty of isolators  in the market but none of them have the following specs:
Input voltage: 0- 80 VDC and output voltage : 0-80 VDC max. Basically what I want is output voltage same as input voltage without losing it for measurement.
Please provide me some ideas if you have one. If you know about any isolators , please provide me PN#.
If you know  i can do something else except the isolators , please suggest.
Thanks


texts: Output Resistance of a High-Swing Cascode Current Mirror

texts:
I am wondering how to calculate the output resistance of a High-Swing Cascode Current Mirror from small-signal parameters, see question High-Swing Cascode Current Mirror for the circuit.

First I transformed the output stage of that circuit to a small-signal representative, see circuit below (only considering gm and gds, since they have by far the highest impact). Since the output resistance is measured by shorting the inputs, the voltage controlled current sources deliver actually zero current and play no further role in the analysis. Therefore, the output resistance should be R_DS4 + R_DS2.

I simulated the High-Swing Cascode Current Mirror and got the following small-signal parameters (bias voltage and output voltage of 1V):

\$
gm_4=297.8uS \\
gds_4=3.118uS \\
gm_2=290.8uS \\
gds_2=2.267uS
\$

If I calculate now the output resistance as above, I get:

\$
1/gds4 + 1/gds2 = 320718.4\Omega + 441111.6\Omega = 761830\Omega
\$

But that seems totally different than what the simulation says, which is \$ 50M\Omega \$! I calculated this output resistance in cadence by typing 1/deriv(I_D4) in the calculator (Plotting I_D4 over V_OUT).

What am I doing wrong?

simulate this circuit – Schematic created using CircuitLab


texts: Malodorous transformer and the cleaning thereof

texts:
I’ve bought a lab power supply of the variable transformer type, that unfortunately smells of cigarette smoke. I’ve tried airing it.
I need a gentle method for cleaning the outer windings that won’t hurt the enamel. My initial thought was bicarbonate of soda on a slightly damp toothbrush. Bicarbonate of soda is a mild abrasive and has odour absorbing properties.


texts:
I am trying to design a circuit involving an LMC555 CMOS timer operating as a monostable multivibrator. Essentially, I want a momentary switch to turn on a set of LEDs for ~20 seconds and then turn off. Details about the circuit can be found at http://www.electronics-tutorials.ws/waveforms/555_timer.html.

Based on my requirements, I am running this circuit off of a 9v battery. Ideally, I would like this circuit to draw as little current as possible when it is inactive (hopefully ~20uA or less) so that the battery might last a year or so (the circuit will only be "active" about 0.1% of the time). After building the circuit, I measured the current from the battery to be roughly 200uA, which is well inside the spec of the part. However, I wanted to see if I could make this much lower.

In order to limit the current drawn when the timer is off, I tried to design a latching circuit that would stop current from flowing to Vcc when the output is 0v (and the switch hasn't been pressed). The design is heavily influenced by Kevin Darrah's video "Low Power Arduino! Kill Power Circuit Tutorial" on YouTube.

The actual circuit I built looks something like this.

When I implement this circuit on a breadboard, I get weird results. When connecting pin 2 (trigger) to the NMOS/PMOS, the pin is pulled to ground and the output stays high. Doing a little more investigation, about 6 mA is flowing into the trigger when the 555 timer is completely off (which seems incredibly odd). It appears the circuit misbehaves whenever the trigger is connected to the MOSFETS. I have gotten this circuit working by manually connecting this wire to 9v/Gnd but find that the circuit draws 3mA.

Anyways, can anyone help explain why this circuit doesn't work in practice? In addition, if you could recommending a new method of deceasing the current to the chip that would be awesome. If you need more information or other measurements, I can provide those as well. Unfortunately I'm stuck with using the LMC555 so I can't perform any drastic changes to my design in that respect.


texts: Is there a lower form factor alternative for common female header pins

texts:
I am looking for an alternative for the usual female header pins, one that has a lower profile than the traditional 8.3mm/0.33in high female header pins.
Adafruit has a low profile Female headers but when attached with the tradional male heade pins it still stands tall.
It doesnt have to be a through hole component, I found one that i really like but i am failing to search its name.
It from the raspberry pi POE HAT, a good thing about this (for my case at least) is it can be set on the other side of the board thus lowering the profile even more
but if there are others please do tell


texts: Specifying relay for breaking injection molding control circuit

texts:
I have an application which requires me to break a 24v signal running with low current (60ma being the absolute max). The signal stays on allowing a large hydraulic motor to close a mold with great force. If an obstruction is in the way, it will damage the mold when the hydraulics are activated. The goal is to use a PIC advanced 8 bit microcontroller running at 5v to sense a condition when there is an obstruction and signal the relay to open. My problem is finding the proper normally closed relay and determine how much response time is needed. It would be helpful if the relay could also work of 5 volt power rail and not exceed 0.5 amps of current to open.

Sadly the relay will be need to be placed inside the injection machine and will need to work in a normally closed manner because the object sensing device is only used on one job and will not always be set up to due to space constraints. The object detection system is a vision system to sense plastic parts that get stuck once in a while. It uses a Webcam hooked to a pc that sends a uart packet to the pic to trigger the relay. Currently the injection molding job operates without any protection so fail safe isn't the primary concern. I want to use the pic at 5 volts because I can easily use one DC power rail for the both energizing the relay and powering the pic. I don't have microcontroller experience aside from pic advanced 8 bit running xc8.


texts: Help me understand this circuit - unexpected LED behaviour

texts:
I'm well out of my depth here – please be kind!
My kids and I have set up the circuit below and the LED is lighting up unexpectedly.
When the switch is off, so is the motor BUT the LED is on. But when the switch is on, the motor is on but the LED is off.
How would you explain to kids (around 10 years old) what is happening in the circuit?


texts: What can happen with the PCB foil while SMD resistor destructive overheat?

texts:
I need to protect the gate driving circuit by putting the resistor between the gate and the control circuit:

During the testing of the mockup MOSFETs can go be destroyed which leaded to high voltage on the gate circuit.

I'm going to place 0805 SMD resistor (R19) which will be destroyed in milliseconds as well (as it will be exposed to 50 W continuous overheating). However it will be much simplier to replace just this resistor insted of looking up for the whole circuit for destroyed elements which was a real pain.

My concerns are:

If R19 will be overheated and destroyed - will it break the circuit? Or it is possible that it will go to short circuit (as FETs usually do)?
If the resistor destroyed - how likely that the PCB will be destroyed too? I'm using 35 um foil.


texts:
When using an external xtal/osc with an AVR, you get several startup time options when setting the fuses, such as:

6 CK/14 CK + 0 ms
6 CK/14 CK + 4 ms
6 CK/14 CK + 64 ms

Now... does anyone know if these startup times apply when resuming my AVR from sleep (SLEEP_MODE_PWR_DWN)? Or is it just when starting it for the first time. I want to use a 32.768 kHz watch crystal to keep accurate time, but it seems to me that if there are these startup time issues each and every time after going to sleep then that would make for very unreliable time-keeping.

Using an ATtiny85 if it makes any difference.


texts: If current flows through lowest resistance path, why circuits with grounding still work?

texts:
Okay, this may sound stupid.

Current (conventionally) flows from the positive to the negative terminal of a source. This also means that the source's negative terminal is on lower potential than the positive terminal.

My question is, how come when you touch a hot wire in a circuit, current suddenly flows to the ground (through you) and potentially kills you, but when you don't touch it AND the circuit is grounded (let's say on the negative terminal), current flows back to the negative terminal and doesn't leave the circuit to the ground?


texts: How to prove that the \$3\$ nodes have the same potentials?

texts:
The question of symmetry.

The each resistor has the same resistance(given by \$r\$).
Why a current doesn't flows between the each endpoints of the middle \$2\$ resistors?
The text book only states of it with "symmetry of middle vertical line".
Proving that node \$(1,2),(2,2),(3,2)\$ have the same potentials is enough to show that the above claim is correct I think.
Can anyone tell me some hint(s) to prove the sameness of the potentials? so that I can deduce it in my own.


texts: How much current does a microSD card use?

texts: I am building a uC board which uses an 3.3V microSD card as a storage medium. To design the switching power supply for the 3.3V, I have to know what my total current draw from the supply will be. I have average and peak current values from datasheets for all my other parts on the board, for example, SDRAM, LCD, etc., but can't find general info online about the microSD card.


texts:
My switching PSU gone silent dead.
There is voltage at DC side of diode bridge rectifier so the input filter and protection are in good condition. Where should I look next to check which component are broken?
Note: this model using KA7500B as PWM controller.
Update 1: there is no voltage supply to PWM controller ICs. Diode and transistor seem fine when I check with multimeter in diode mode (see some forward voltage and not short-circuit)
Update 2:
for referencs I found some reverse engineer work for similar product here

I'm not sure how it's work at standby supply part. what to do when there are no voltage output?


texts: Should each trace carrying RF be 50Ohm in characteristic impedance? How?

texts:
I have to translate a VHF (160MHz) receiver schematic into a PCB. After looking here and there, I am a bit confused.

It seems like the main issues with RF are

to avoid stray inductors and capacitors, by avoiding close tracks (capacity up), wide tracks (capacitor with ground plane underneath), and long tracks (inductance up)
to avoid signal reflections by avoiding sudden changes in "characteristic impedance".

[Please do tell me if I missed others]

I only have a vague idea of what characteristic impedance is (this wonderful video helped a lot though), but it sounds like it's the impedance of the equivalent RLC circuit.

It should be dependent on the length and the frequency of the signal, how come it isn't?
Intuitively I should calculate the characteristic impedance of each pad-to-pad trace and make sure it is always 50Ohm. Is that the case?

An online calculator gives (for 18um thick copper, 4.7 of permittivity, 0.5mm thick substrate) me 0.9mm of width to get 50Ohms. Does that mean I should route all traces at this width, keeping them short but without having them too close to eachother, and then I have nothing to worry about?


texts:
I want to build a centralized system which will be getting values from many sensors around an agricultural field.

The field's large area leads to long wires going from sensors to the central controller. I do not wish to use repeaters in between. How far (in metres) can those typical 5 V cheap sensors (specifically PIR sensor) transmit without the output fading too much?

I understand that this  distance of signal travel depends on current delivering ability of the sensor and also on the resistance of the transmission wire. So say if I use a high impedance op-amp at the input, hence solving the current problem, how far would I be able to sense the signal from sensors considering that much electromagnetic interference is not around?

EDIT: Sensor Link: https://m.alibaba.com/product/62366227634/Free-shipping-Motion-sensor-Human-Body.html