texts: Cheapest yet safest solution to measure AC lines? (1 phase as well as 3 phase)

texts: Any solution apart from using hall effect sensor to measure current through AC lines? The value measured will be later processed by a MCU.


texts: How to measure power/energy with analog circuit?

texts:
I would like to measure either power (running average, for example exponential average with a certain time constant) or energy (power integrated over time) with an analog circuit.

The setup I have is a pulse generator and the average output power and single-pulse energy are both important parameters.   However, measuring current and voltage with an ADC and then calculating power digitally is unlikely to work well since the signal is fairly broadband, so it would have to be a heck of a fast ADC.  I also would like to be able to measure single-pulse energy in a purely analog way for reliability reasons.

I think this must be a common problem in true-RMS power meters, but I have no idea how to approach it.  Thanks for your ideas!

P.S. The question is not how to do a bench measurement (no doubt there are off the shelf tools for that) but how to build a circuit that does the measurement that can be used as part of the device I'm working on.


texts: Glue/adhesive/epoxy for soldering a mems microphone

texts:
I have read a lot of articles on epoxy and glues for PCB especially with a ripped off pad. I am in the same situation myself and was hoping to get some suggestions here. .

The mems microphone looks as follows

The PCB still has metal connections jutting out, and i tried soldering without glue. The microphone works, but it is not held in place since the solder connection with the metal does not form a strong bond.
The way i see it there are multiple ways of dealing with the situation:

Buy a silver based epoxy, coat the metal and nearby area where pads originally were, and then solder the microphone using silver epoxy as pads. There is only one epoxy 8331 from MG chemicals which seems to be most preferred yet most expensive. Can anyone suggest a cheaper version?
Apply a non conductive epoxy and stick some solder pads if i can find one. Once the epoxy is cured, solder back the microphone. However this looks to be difficult task since i need to find solder pads matching the one on the board and i have not found any yet.
Simply solder the microphone and then make sure that the microphone connectors are touching the metals, and apply super glue to keep it in place. but this is not a clean solution.

I would really appreciate if anyone can give me a cleaner solution. Also names of epoxy/adhesives/glues will be helpful.


texts: How to trigger an SCR after a certain time since the start of a cycle of mains voltage?

texts:
I am looking for an Arduino code that uses PWM. Mine's a little different than most PWM programs however because I am looking to create some sort of reference point within the code to not only vary the duty cycle, but to control where my output pulse will trigger on the sine wave. It's a little hard to visualize, so here are a few pictures:

What I want to find:

What I've been finding:

The image above is the typical PWM code I've been finding, but it is irrelevant to my application because I will be triggering an SCR (which only recognizes the rising edge of the output pulse).
Below is a general idea of how I want to control the SCR firing angle:

So I'm thinking I will need some sort of reference point within the code to make the falling edge of the duty cycle be where my output pulse will trigger. That is my only clue how to attack this problem. Please let me know if I was not very clear on certain specifics with this issue.


texts:
Ive been posed with a problem regarding calculating the characteristic impedance of a shielded twisted pair with a drain wire. While I understand how to calculate this for a "normal" shielded twisted pair, Im struggling to understand how (if at all) the drain wire would affect the answer.

Background:

The application is a particle detector, in which space for cabling is at an absolute premium. People are losing hair over trying to find spare millimeters to route the cables for the elements in their areas. There is also a lot of repitition of cables, so shaving a mm off one type of cable for instance, adds up to a not insignificant saving over the whole detector.

In the section I work in, we are connecting hundreds of internal chips to the outside world over a CAN bus each. Grounding and shielding requirements dictate that CANH and CANL for the CAN line are contained within a foil shielded twisted pair. Management have however requested that we insert a drain wire into this twisted pair as a current return path (please see a basic image below), as it saves on the insulation mass of routing it as a single wire. We have found a company willing to produce this cable for us, but before we purchase any samples (which i could perform time domain reflectometry on), ive been asked to calculate the characteristic impedance of it. For information, the CAN speed is 125kbps, so it is my understanding that we dont treat it as a transmission line.

(conductors in red, foil shield in grey, and insulation in orange and yellow)

(The equivelant cross section if a seperate wire is used)

From the following reference page of cable design equations, I can see that even a jacket on the outside of the shield (as I have) affects the impedance equation, but I have been unable to find any reference explaining mathematically how a drain wire would affect the equation. Anecdotaly I would imagine that the impedance of the shielding will be reduced due to a larger cross sectional area, but cant say much more than that. From my googling, I havent come across any instances of someone trying the same thing, and personally ive only ever used shielded twisted pairs without a drain wire. It may be that theres a good reason for this, in which case im happy to go back to management and tell them so, but im stumped. Can anyone point me in the right direction please?

Edit: Have added a sketch showing a rough idea of how this saves space compared to having the return line in a seperate wire.


texts: What is this little board I've found in an ATX PSU?

texts: I have dissembled and old ATX power supply, and I've found this small board between the male AC input socket and the main board. What is it?


texts: MOSFET high side gate driving without driver

texts:
I'm building an H bridge form IRF3205 N MOSFETS to drive a TX coil for Wireless power transfer. I want to make the high side switching without a driver, instead I'm using a somewhat similar bootstrap configuration. For testing I use an active 10R load at 12 Vcc. The switching frequency is 100 KHz.

It works, but the problem is that the rising edges for the gate of Q1 are really slow due to the R1 gate resistor.

In the blue is VGate relative to ground and the red is signal from microcontroller. If one decreases R1, the edge rising time greatly improves, but at the expense of a lot of R1 and D1 heating because they conduct when Q5 is 'open'. What would be an efficient schematic to make a 'power efficient' gate driving circuit and since I'm not too experienced ir ringing causes, what could
 be the reasons for the ringing when the gate discharges?

Edit

I made this kind of gate driver.

Would it work? I would like to have not more than 300nS rising/delay times, so would need around 700mA gate charge current.


texts:
I have an idea for a programmable breadboard, but I am not sure of the feasability of it. My thought is to connect each strip of a breadboard to some type of circuit that can make arbitrary connections in software. This would eliminate a lot of the tedious wiring associated with quick prototyping.

I have a few ideas, all of which seem prohibitively cost or wiring heavy.

For a breadboard with N strips I could:

Use an array of analog switches for each possible combination of wires. This is not quite N^2, but its not far off. A lot of switches may get expensive fast.
Make M connections possible with 2M N:1 analog muxes. Not sure how feasable this is.
Set up a bunch of rows of parallel headers and use little jumpers to form connections. Probably cheaper than 1 or 2, but not programmable.

I started thinking if maybe there was a way to use an CPLD or FPGA to do something like this. At the very least if I had one with enough IO I could do some input->output following design that could get pretty close for slow digital circuits, but wouldn't handle analog very well.

What I really want is a chip that can take a large number of IO and let me program in arbitrary connections between them. Does something like this exist? Preferably easy to program, even from a pic or something.

The board I am looking at now has 3 rows on each side and two power rails so that's 64 distinct connection points, or 2016 analog switches.


texts: A very basic question about response time of an instrument

texts: Regarding a temperature transducer, what is meant by response time in this context? It says it can be set to < 30 ms or < 300 ms. Is there any trade of between choosing low or high response time?


texts: Simplified Electrical Impedance Tomography (EIT) setup

texts:
We are working on a setup to measure the terminal settling velocity of objects (spheres, metal, for example) in a vertical tube filled with some sort of fluid (Mud, water, etc.). Preferably, we want to measure the velocity of the object using a non-invasive measuring technique. One of the options we are investigating, is Electrical Impedance Tomography (EIT). By measuring the passing of the object at several locations, we can determine the speed (distance between two measuring points divided by the time it took to travel between them). The reason we want more than two points, is to be able to make sure that the terminal velocity has been reached (no acceleration noticeable between two speed measurements).
Traditional EIT setups have two rings with around 16 or so electrodes each. These map the position of the object in a 2d plane as it passes through the planes made up by each of the sets of 16 electrodes. This traditional technique works quite well, but really only provides two position measurements: this is what we want to avoid, as we want quite some more.
We are looking at simplifying this setup greatly. One of the options is to reduce the amount of electrodes at each measuring point to maybe two or three. Notice that we really only need to know that it is passing through that plane, it does not matter where in the 2d plane it passes through. With a simple Arduino setup we could then connect some of these 'electrode rings', perhaps even have two 'slave' Arduinos that handle the electrodes, and one master that handles the rest.
However, we are in doubt whether this would be able to measure the passing of objects accurately. It of course depends on the dimensions of the tube (D) and the object (d), but if that is in the order of D/d = 30 or 40: will the simplified electrode rings even notice the passing of the object (by seeing a reduced resistance)? We shall assume that the sphere stays somewhat in the middle of the tube, and will not move sideways too much. We can later analyse the 'resistance plots' and take the peaks of these plots as the point at which the object passed.
So, to sum up, our questions are:

Will this simplified setup (2 or 3 electrodes) even be able to notice the reduced resistance through the fluid as the object passes through?
If not, is there a minimum for the amount of electrodes per ring? Does the current really only travel in a straight line to the other electrode, or would it 'notice' an object passing through just on the side of this straight line as well?
Do you have any tips for us as for how to solve this problem of simplifying the setup?

Source for EIT (that we have looked at as well):
EIT with Arduino (Github)
Excuse us for our limited electrical engineering knowledge, we are mechanical engineering students ourselves.
Thanks in advance!


texts: How to implement a double buffer using an ARM Cortex M3

texts: I am a total beginner, but I have been working on a project to attempt to build my own microcontroller that outputs basic 2D graphics to an LCD screen.  In doing some research as to how this is commonly done, I have heard a lot about the benefits of double buffering. However, I have not been able to find any information into the logistics of implementing such a feature.  I was hoping someone could explain how it works in terms of data flow, and if it is possible to implement using only 1 processor (Cortex M3 SAM3S4C).  Is it possible to be filling one buffer while the 2nd buffer is being written to the LCD screen with only this one processor? Any and all advice would be greatly appreciated.


texts:
I have a AC source with some serial resistance. To maximize power transfer, the load connect in series should be 40 ohms (its a voltage regulator). However it need to take a DC voltage rather then AC, so I use a full bridge with a smoothing capacitor. But I dont know how to match the load (to 40 Ohms) with the capacitor present.. It always reduce the power transfer as it provided a parallel path..

Any advice would be helpful


texts: To prove that Close Loop transfer function is sensitive to perturbation in H(s) but not to perturbations in G(s)

texts: The feedback control system with high gain K is shown in figure


texts: LED on the collector without a base limiting resistor

texts:
am a beginner trying to understand transistors.
I am using a npn transistor.

I have a 6V battery.

The base and collector are connected to 6V
Emitter has the load (LED + 100ohm resistor) to the ground.
Current passes and the LED lights up. I understand, it is in saturation mode.
With or without a base resistor.

Case 2:
The base is connected to 6V.
The collector has the load (LED + 100ohm resistor) connected to 6V as well.
Emitter is connected to the ground.
The LED does not light up when powered.

Case 3: Further to Case 2: I use a 1K resistance with the base and the LED lights up.

Why does not the LED light up in case 2?

This seems similar to Emitter Follower LED Circuit - LED in Collector, Resistor in Emitter, but I did not get the concept.

Thanks.


texts: Verilog memory designs with multiple read/write ports - poor circuit performance when synthesized?

texts:
I am interested in designing (with verilog) some memory structures that have multiple (let's say 3) read/write ports. I've been doing some studying on architecture and what I've heard is that these are not trivial hardware implementations, and can create a lot slower circuits.

With behavioural verilog I would imagine it's quite simple, something along the lines of:

always @ (posedge clk) begin
    if (read_enable) begin
        out1 <= mem[read_addr1];
        out2 <= mem[read_addr2];
        out3 <= mem[read_addr3];
    end
    //something similar if I want multiple writes
end

Assuming it synthesizes, will I have a crappy and slow circuit, and why? Can it be alleviated by going with a more custom design using gates instead of behavioural coding?

Thanks


texts: High Impedance Input does not drop all voltage applied. Why not?

texts:
If you apply 3.3V to the input of a micro-controller, which is set as an input (hi-z), why does the micro not drop all of the voltage as is usually the case when applying a voltage across a resistance?

Thanks,
Gary


texts:
I'm an industrial designer, and am working on building a small electronic rover,

however I've been doing some research and I feel a little bit lost in terms of what
motor is best for me,

The device consist on a 4wd electric vehicle, (a dc brushless motor on each wheel)

Wheel diameter: 7cm

Weight carried: 100kg (mass 980N)

Top speed: 20km/h (results in about 2000rpm)

Acceleration: 0.4m/ss (value may vary)

After doing some research I plugged numbers in equations and figured out the following:

Total torque: 40N

Torque in each motor: 0.350Nm

Power required by each motor: 73 watts

Now, this means I need a dc motor which gives me 2000rpm and a 0.350Nm torque
As I have little experience with these motors, I can't seem to find any that match these settings,

The question is: Am I looking for something feasible by a dc brushless motor?

Follow-up question: What Voltage/Amperage values am I to expect from a motor of these characteristics?


texts: How to connect the third contact in the DC barrel?

texts: I was reading this question post What to do with third contact in DC barrel plug with only two input contacts about the third connector of the DC Barrel, and said that you can know if the DC Plug is connected or not. How can you know that? Did the third pin give you ground or voltage? For example if I have an also a USB connector to give some priority to one of the connections.


texts: ADXL345 generating interrupts without MCU

texts:
I wonder if it's possible to drive an ADXL345 without an MCU on the board. That is, to set the ADXL345 to generate an interrupt on activity without needed an MCU on board. Could the register values stay persistent? If so, it could generate an interrupt without an MCU.

Thanks


texts: Finding the cut-off frequency of a filter circuit at -3db from transfer function

texts:
I am having issue with finding the cutoff frequency from this filter circuit transfer function as i am stuck at the step shown in the picture attached. I am not sure if i have done the steps correctly so please correct me if i have done something wrongly. Thank you for your time!
Updated:
I like to apologize but i realize that i have incorrectly drawn the circuit previously which is why i was having difficulties getting the cut off frequency that i got. I have since corrected my working following Andy Aka methods and Tony suggestions . However i got a very complicated transfer function and was wondering if it could be reduced further or have i done some steps wrongly.

FACT method transfer function done


texts: need a circuit that can switch motor direction by photo or timer input

texts:
I have a reversible 115 volt ac motor that has its own internal limit switches to cut the power. It has 4 wires to the motor green-ground and red-hot ,black-hot, and white-neutral. If I have the red and white connected to power it turns one way and the black and white connected it turns the other way. I would like to know what sort of circuit I can use to switch power from the red wire to black wire and back depending on light levels or timer input. ie red wire powered by increasing light and black powered by decreasing light. It is for a door to be opened in the morning and closed in the evening.
Thanks


texts: Am I reading this MOSFET datasheet right?

texts:
Sorry for the lame question, but I am a software developer, and have only a limited understanding of analog circuits.
The ODrive uses the MOSFET NTMFS4935NT1G (since v3.2) in pairs.

This test says that you can drive a motor with ODrive continuously at 40A with using only the heatsink, and 75-90A when using fans.
However, when I look at the datasheet, it has the following picture (I have already learned on this site that I cannot just take the V and A from the datasheet and multiply them blindly):

(Note that the test is for the 48V variant of ODrive, and this is used in the 24V variant, but I expect at least the same order of magnitude with both ODrive boards.)
So if I look at 20A (because 40A is driven by a pair - red line), then this MOSFET cannot work in DC mode at all, and even a 10ms pulse can have only 2.5V. If I look at 24V, then it can drive only 0.005A, which I find hard to believe.
I would find it very strange if the datasheet would be wrong, as I can see similar values with the MOSFETs used by VESC for example. So what I can think is that 40A is the average current through all the 3 phases (all 12 MOSFETs), and so they receive a lower load. Another is that a heatsink matters so much, and that would mean that I have to do a thermal analysis for selecting MOSFETS.
So what is a quick rule of thumb selecting MOSFETs? Am I reading this datasheet right? I would need just a little more scientific method than ordering and building stuff and then touching the MOSFETs to check if they are too hot...
UPDATE
Thank you for your answers, it seems that I "complected" the breakdown voltage with the drain-to-source voltage. I was thinking that the more voltage I use as VCC to drive the load, the less current the MOSFET can survive. But now, that you have explained that VDS is the drain-to-source voltage drop, suddenly a lot of things make sense...
So, to check if I understand it now, lets assume that I want to drive a single MOSFET NTMFS4935NT1G to source 40A. Because I am a cheap bastard, I will not use a gate driver, but connect the Gate directly (with a current limiting resistor) to an MCU, which can supply 5V/10mA.

It shows that at VGS = 5V, at 40A there is a voltage drop of around 0.15V only. This is clearly in the ohmic region of the MOSFET, so I guess the power dissipated will be Rds(on) * Id^2.

This one shows that the on-resistance with be around 3.7 mOhm, which is very close to the values which are in tables in front of the PDF. 40^2 * 0.0037 = 5.92W, it needs very beefy cooling.

Finally the last graph shows that on 0.15V voltage drop, the maximum current is around 6A DC only. If I want to do 40A DC, then it goes over the Rds(on) limit, which I guess means that there is no way to cool the package so much to reach that. But at 20A it is below the Rds(on) limit, so maybe I can do 20% PWM or similar. (This result seems to be closer to the measured 20A maximum per MOSFET while driving a motor, which is not DC.) <- here I am not sure what does it mean physically to go above the Rds(on) limit...
Is it a correct reading of the datasheet now? (Ignoring that at 10mA, and with Total Gate Charge = 22nC, it will take several microseconds to switch on the transistor, where I think it is in the linear region, heating like crazy.)
Thanks!


texts: Need help to identify smd component of VGA adapter MSI GTX1070

texts: I did clean my VGA adapter MSI Geforce gtx 1070 with compressed air and one smd component has gone, now the adapter did not work. On another adapter I found out the marking on the component body and it is just - VT. I have no idea what is this. Could somebody help to find out what is this. On the PCB it is marked as U506.


texts:
I have this bridge rectifier (Image below). https://www.deantechnology.com/products/hvhp10k

How do I wire this? I know how to wire four pin bridge rectifiers but how do I wire this two pin rectifier?


texts:
Has anyone used small 2"- 4" epaper modules similar to these, and measured the actual energy consumption of them?

e.g. in J/erase/write or J per 1/4 rewrite.

Have you compared the power crossover point with any low power LCDs?

e.g epaper is more efficient at less than N writes/hour?

Compared with say this at 80uA or this at 450uA or your alternative suggestion.

Any other pearls of experience with them?

Yes I can read the datasheet current. The best info I have found is an old silabs app note indicating ~40mJ/update.


texts:
What template in Microsoft Visio would one use to lay out a digital design?

I draw up many schematics for the Adv. Digital Design course I'm in and cannot find the right template. Flow charts are too generic and electrical circuit templates are too detailed.

I just want to be able to draw boxes with wires/buses connecting them with the occasional logic gate.


texts:
I am working on pic24EP bootloader. My bootloader has it's own packet format to communicate with a python script to update the firmware of the microcontroller. The bootloader resides at the first free page after Interrupt Vector Table (0x000800). To make space for application, i have edited linker script of my application firmware so that application hex file wouldn't use any space in between 0x200 and 0x005BF0. The linker script of application project is given below:

/*
** Memory Regions
*/
MEMORY
{
  data  (a!xr)   : ORIGIN = 0x1000,        LENGTH = 0x8000
  reset          : ORIGIN = 0x0,           LENGTH = 0x4
  ivt            : ORIGIN = 0x4,           LENGTH = 0x1FC
  program (xr)   : ORIGIN = 0x6000,        LENGTH = 0x23FFE
  FICD           : ORIGIN = 0x2AFF0,       LENGTH = 0x2
  FPOR           : ORIGIN = 0x2AFF2,       LENGTH = 0x2
  FWDT           : ORIGIN = 0x2AFF4,       LENGTH = 0x2
  FOSC           : ORIGIN = 0x2AFF6,       LENGTH = 0x2
  FOSCSEL        : ORIGIN = 0x2AFF8,       LENGTH = 0x2
  FGS            : ORIGIN = 0x2AFFA,       LENGTH = 0x2
  FUID0          : ORIGIN = 0x800FF8,      LENGTH = 0x2
  FUID1          : ORIGIN = 0x800FFA,      LENGTH = 0x2
  FUID2          : ORIGIN = 0x800FFC,      LENGTH = 0x2
  FUID3          : ORIGIN = 0x800FFE,      LENGTH = 0x2
}

__FICD = 0x2AFF0;
__FPOR = 0x2AFF2;
__FWDT = 0x2AFF4;
__FOSC = 0x2AFF6;
__FOSCSEL = 0x2AFF8;
__FGS = 0x2AFFA;
__FUID0 = 0x800FF8;
__FUID1 = 0x800FFA;
__FUID2 = 0x800FFC;
__FUID3 = 0x800FFE;
__CODE_BASE = 0x6000;
__CODE_LENGTH = 0x23FFE;
__IVT_BASE  = 0x4;

__DATA_BASE = 0x1000;
__DATA_LENGTH = 0x8000;

It looks like my bootloader rejects firmware (hex file) at some point as it has address in between 0x200 and 0x005BF0 but i have edited the application linker script to only use addresses above 0x6000 by modifying variables: __CODE_LENGTH and program.

The memory map of my micro-controller is below:

The size of flash is 256kB and page size is 1024 instructions (1024*4 Bytes). The Hex File is over here. And the linker script is over here.

EDIT:
I have solved my problem. Looks like PIC uses a slighty different HEX File Format than INTEL. The addresses in HEX file are 2 times the real address in PIC. So, i need to divide the address in hex file by 2 to get flash address of PIC microcontroller.

However, i have identify new issue with my system. I am not able to post a new question. So, i am adding it here. Now, my application(well tested) uploaded via bootloader works until any interrupt fires up. If any interrupt fires up, it hangs. All i can check is that it doesn't end up in any trap. Can anyone point me to right direction?


texts: Is there any emperical evidence which (dis)proves the threat of an EMP disabling an electronic safe lock?

texts:
The debate between whether to use a mechanical combination lock vs an electronic safe lock seems to be rife with claims with little evidence to back them up.

The pro-combination lock folks are erring on the side of caution to ensure that you have access to your safe contents when you need it the most.

The pro electronic lock folks say worrying about an EMP is moot because:

The e-lock is floating and not tied to the grid (they generally run off of two 9V batteries)
The actual locking mechanism which stores the combination in a PROM is behind the steel plate door of the safe which would act as a Faraday cage. Only the keypad is exposed on the exterior of the safe.
The required magnitude of an EMP to take out an e-lock is so large that your body would quickly succumb to the radiation exposure.

So, are the pro e-lock folks right? What would it take to take out an e-lock and would I be around to even see it?


texts: Design very big PCB vs multiple parts w/ connector

texts:
I'm working on a project which we need a long LED PCB (1,5m x 3cm) to bem inside a lamp tube. Currently we have small PCBs (around 20cm each) connected in series with exposed wires soldered by hands. We could also use a connector but it has to be cheap and also very small/slim not to affect the light effects inside the tube.

The other option would be to produce a single PCB for the tube. Is it possible to find machines that produce PCBs that big (for series production)?

If not, do you guys know good small connectors to put the boards together? We now need 8 wires between each board with <1A per wire.

I also thought of making the edge of the board with small pads so when putting the boards together one could sold them without wires. Is it possible?


texts:
We have a question about the power available to the home in the UK.
Our product draws a fair amount of current, so we have (so far) designed it to be powered by ~230vac single phase at 48A OR ~230vac 3 phase, 16A for each phase.
We bought IEC 60364-1 and read section 312.1.1 Current-carrying conductors in a.c. circuits.
We understand that we may encounter:
1 phase 2 wire, 1 phase 3 wire, 2 phase 3 wire, 3 phase 3 wire or 3 phase 4 wire.
Our specific question is what kind of coverage will each of these two options give us in the UK (or the continent)


texts:
On the Internet I found FSK demodulation connection diagram with LM565 . And I'm trying to connect up it in Qucs. At the output of the whole schema I get unclear result.

In my previous topic we were able to come to the right decision with FSK generation Topic1. So FSK generator works properly.

I suspect the error is in the circuit of LM565. In many articles there are different versions of internal circuit diagram of IC PLL LM565.
I did as here.
But I don't understand the element that is marked in red.

Look, please, what could be wrong?


texts: Choosing the correct power supply for the controller

texts:
For my project I need a Siemens controller. I can not choose one. And the problem is not about amount of  i/o pins or aviable programming blocks. I dont know which power supply characteristics will be best for me (24 AC/24DC or even 220 AC). In my control panel there is 220 AC everywhere. And maybe it is better to use a controller with 220 AC power supply. But in other side I can use 220/24 transformer and use a 24 AC power supply controller. The second case seems to be more safer.
How do you choose a controller in your projects? I repeat I ack only about power supply characteristics.  Is there any difference between theese two case except safety?

EDIT

To be more cleare I attached a picture.

It is how I see this. When someting happens sensor says it to controller and then controller opens a relay. Relay opens a contactor and my motor runs.

As I understand I can not open a contactor directly by a controller. So I need a  relay. If Siemens controller output is 5 V and my contactor is openned by 25 V I need relay 5/25 V. And then I think "I need relay in any case. So I need transformer 220/25 V. And if I need this transformer then why I dont use this 25 V as power suply for my controller?".
But also I can use relay 5/220 V. In this case I need not a transformer (if I use a controller with 220 power supply).

The best thing would be if I could control a contactor directly by a controller.

What is the best way? It is my first project with high vltages. Any suggestions are welcome.


texts: How practical would it be to field rewind a large power transformer that's suffered damage from a geomagnetic storm?

texts:
It is commonly accepted in power distribution circles that large (large substation-sized or larger -- smaller substation-class transformers are much more readily replaceable) distribution transformers are vulnerable to overheating due to geomagnetically induced currents (say from a solar storm or EMP event).  This damage appears to be largely heat-related insulation damage, though, and not something that renders the copper in the windings or the iron in the core unsalvageable though.  Given that, would it be possible to restore some functionality to a transformer put out of operation by geomagnetic current overheating by:

Draining and disassembling the transformer on-site
Unwinding the existing windings and removing the damaged insulation materials
Rewinding the windings using the existing copper and fresh insulation materials
Reassembling and refilling the transformer

, or is this not feasible/possible to do to restore some functionality? I'm not expecting a field rewind to be 100% as it won't be a shop-quality job, but wouldn't it allow limited service to be restored more quickly than having the transformer "dead" until a replacement can arrive, months or years from the event happening?


texts: How can I offset and scale a differential voltage signal

texts:
I have an HCPL-7840 isolation amplifier. It's input side is connected to some high voltage (~300V) power circuitry.

It produces a differential output signal that is nicely isolated from the power side. Each of the two pins that form the signal are between 1.29 V and 3.80 V with respect to the ground of the output side.

I want to take that signal and feed it to the analog components in my MCU, which is an ATXMEGA128A3U. It shares a ground with the output side of the isolation amplifier. And it accepts differential inputs. But it requires that both voltages be between 0 V and 3.3 V, and further that the differential voltage be within +/- 1 V.

How do I glue these things together? I have some understanding of how it is done for single-ended signals, answers to that problem are crowding out the answer to this problem in my search attempts.

I have two uncommitted DACs in the MCU that can output a reference voltage for what I want the new common mode level to be, if it helps.


texts: Measuring output of solar panels for science fair project

texts: I am in 7th grade and doing a science fair project using different solar panel arrays. I have 3 different configurations with 6 mini panels connected.  For each configuration, I have all the positive wires connected and all of the negative wires connected.  I am using a multimeter to measure the voltage and the amps.  If I multiply the amps times the voltage, will this give me an accurate indication of the output for each of the three configurations? Thank you in advance for your assistance!


texts: Programmable sensor signal reference voltage

texts:
I'm designing the front-end circuitry for an ADC. The ADC is to be used to read from sensors under two use conditions:

An externally referenced sensor, whose signal line will either be 0-5V or bipolar (e.g. ±10V). Note that the ADC supports bipolar inputs. No additional circuitry is required to support this scenario.
An unreferenced two-wire sensor, whose signal line will need to be pulled up to a 5V reference via a 1kOhm resistor within my front-end circuitry before interfacing with the ADC. A basic representation of this scenario is shown as follows:

simulate this circuit – Schematic created using CircuitLab
The user can install sensors of either scenario, so my front-end circuitry needs to be able to support both operating modes. My initial design was to use an MCP23017 (or another similar I/O expander) which could provide the 5V reference to the sensor signal line by setting that particular MCP23017 pin as a logic high output. Similarly, it could be set as a high impedance input to support scenario 1 (i.e. no affect on the sensor signal line). However, as the sensor signal line can be both negative and much higher voltage than the MCP23017 VDD, I don't think this method is suitable. Even if the MCP23017 pin could be set to a high impedance input, there's always the risk that the user accidentally enables the pullup reference on a particular input, damaging the MCP23017.
Could I use a similar approach, but instead use the MCP23017 pin (as an output) to turn on/off a transistor? If so, would an n-type MOSFET be the best option? What considerations need to be made to ensure the circuit is open (so far as reasonably practicable) for scenario 1 operation (i.e. no affect on externally referenced sensor signal line) and closed for scenario 2 operation (i.e. as close as possible to exactly 1kOhm series resistance to 5V reference)? Similarly, are there any other considerations from a protection perspective, allowing for bipolar inputs which are greater than 5V? I.e. the circuit should not be at risk if a -~20V signal is connected with the transistor in either the on or off state.


texts: TI LM25118 buck boost, variable power supply

texts:
For a part of my next project I'm required to make a variable power supply module. I have never designed a power supply and I would like to make my life as easy as possible. Thats why I would use LM25118 buck boost controller. The datasheet is a bit confuseing for me.

The input voltage varies from 3 to 6 volts (can deliver 4A). The output voltage needed is between 2 and 12 volts. The output voltage would be regulated with a potentiometer. I would like to look at the worst possible scenario when I have 3 volts at the input.

What voltage do I have to set to still get 1A at the output, while there is a 3 V input?
Is there a better solution? Like a controller from another manufacturer something else. I would need at least 1A at 5V out, 1A at 9V out would be great! (with 3V in)


texts: How would I go about generating a very small analog signal ( 0.06-0.08 V)

texts: I am looking to generate a small analog signal around  -0.08V to +0.08V. What is the best way to go about doing this?


texts: Choosing RC values for Active LPF to match signal input impedance

texts: I am design a basic 1st order Active LPF with unity gain and am new to this field. How do I make sure that I choose my R and C values to match the input signal impedance or does this not matter? What other factors should I consider? Does the RC time constant matter?


texts: Can a USB power source run 4 IR LEDs in series without a resistor?

texts:
USB is 5V, and the voltage drop across the 5mm IR LEDs I'm gonna use is around 1.2V, if I connect 4 IR LEDs in series and perhaps more in parallel, do I still need a series resistor?

Will cooling fans help?


texts: MOSFET N channel power switch: high side doesn't work and low side would need multiple MOSFETs

texts:
I'm experimenting with a MOSFET that controls power to another component so that I can remove all current from it when it's not in use and save power. In regards to that, this question is awesome: Switching DC with MOSFET: p-Channel or n-Channel; Low Side Load or High Side Load?

But I'm running into some snags when it comes to practical use.

First approach:

simulate this circuit – Schematic created using CircuitLab

I was able to switch this off fine, but when it was on, I was only getting half voltage out. Turns out I was using an N channel MOSFET wrong, and it's not good as a high side switch like this.

Ideas to fix:

I could move the MOSFET to GND of the LED array with a 100 ohm resistor on the gate. I believe this would allow it to act like a switch in the manner that I really want. However, the addressable LEDs still draw a decent amount of power when their GND is disconnected! It seems the return path goes down the CLK and DAT lines. This is not a problem when VCC is disconnected. This means I would need three MOSFETS, one for each of CLK, DAT and GND, driven by one pin.

I could use a P-Channel on the high side, but to turn it off I need to supply voltage. When turned off, I want to be conserving power with the micro controller in a super low power mode . In that state wasting current holding the MOSFET closed seems wasteful, and I'm not the micro controller could do that in sleep mode.

Both those options seem kind of inelegant. What I seem to need is a simple 4 pin component (VCC, GND, GATE, OUTPUT) that can connect VCC and OUTPUT when I pull GATE high. Does such a thing exist?

What do you think is my best bet for making this work with the fewest/simplest components?


texts: What happens to the output of Optocoupler input voltage is negative

texts:
Here is an example of circuit using VIshay Optocoupler 4N25

5V to 3.3V GPIO Output (Inverted)

schematic http://www.savagecircuits.com/attachment.php?attachmentid=294&d=1430452949

Logic
+5V Input ---> 0.0V output GPIO LOW

+0V Input ---> 3.3V output GPIO High

What happens to the output if my input is -5V???


texts: I am beginner in Robotics.I want to make serious start from scratch with interest but confused from where to start.So can anyone give some suggestions for 1.As a beginner in robotics ,are there some simple and basic robots or circuit designs which I can make by myself in the home(so that I can gain practical knowledge of robots)? 2.or should I first read books (can anyone suggest some good reference book names,articles ,links,video series)?


texts: Source Conversion: Combining series current sources

texts:
I have done 1.1 and gotten 9V and 3k Ohms for the equivalent source. I am trying to do 1.2 without first converting to voltage source and I come across this situation:

How would I combine the two current sources that I have circled into one current source, without converting them first to their equivalent voltage sources.


texts: SIM908 GPS STATUS "Location Unknown" Error

texts:
I'm using a SIM908 module on a custom board and am having trouble getting the GPS location from it. Everything else works on the module. I can send SMS, make calls and send and receive data from a webpage. But GPS doesn't seem to work. I am using the antenna pad directly on the chip with a passive antenna.

When I call AT+GPSSTATUS? I receive Location Unknown no matter what I do. I tested this outdoors with clear view to the sky. I expected it would at least give Location Not Fix but Location Unknown seems to indicate GPS is not on, even though I call AT+CGPSPWR=1 and AT+CGPSRST=0 and get "OK" back almost every time. A few times, it has returned ERROR GPS READY, which I can't find anywhere in the datasheets, but I assume is due to not having reset the SIM908 while testing new code.

I have posted my test code below. Am I missing something?

// DDDR initializations (not included)
// UART Initialization
uart0_init(UART_BAUD_SELECT(UART_BAUDRATE, F_CPU));
sei();
_delay_ms(500);
// GSM Power on
PORTD |= (1<<PORTD3);
_delay_ms(1100);
PORTD &= ~(1<<PORTD3);
_delay_ms(2300);
UWriteString("AT");
// Returns: "AT" and "OK"
// So far all good
_delay_ms(1000);
// GPS Power on
UWriteString("AT+CGPSPWR=1\r");
// Returns "OK"
_delay_ms(10000);
UWriteString("AT+CGPSRST=0\r");  // Have tried with =1 with no luck
// Returns "OK"
_delay_ms(10000);
// VERY LONG DELAY
_delay_ms(30000);
_delay_ms(30000);
_delay_ms(30000);
_delay_ms(30000);
_delay_ms(30000);
_delay_ms(30000);
// GPS STATUS
UWriteString("AT+CGPSSTATUS?\r");
// Returns: "Location Unknown"
_delay_ms(10000);
UWriteString("AT+CGPSINF=2\r");
// Returns: "2,160745,0.000000,N,0.000000,E,0,0,99.989998,187.000000,M,-187.000000,M,,0000


texts:
I'm looking for some advice on driving an 8Ω 2W speaker near full power from a 3.3v DAC. I've put together a current amplifier using a rail-to-rail op amp and two BJTs, but it's not supplying as much current as I thought it might.

In an ideal scenario, I was hoping to be able to drive the speaker up to ~1.25W, but in reality I'm only getting about 0.3W when putting 3.3v into the positive input of the op amp.

3.3V / 8Ω = 412.5mA = 1.36W

Wondering if anyone has any suggestions for improving this circuit or any alternatives. The DAC is providing a 3.3v output and my available power supply is 3.3v so I would prefer any amplifier I use to have a unity gain.

Thank you!


texts: Transistor letting 12Volts through collector->emmiter withouit being damaged

texts:
I have made a simple digital amplifier using 2N4401 Philips switching transistor.

simulate this circuit – Schematic created using CircuitLab

I have tested this amplifier on 5 VDC and it has worked (though the effect was very weak). However, if I plug 12 volts from the power supply, the 2N4401 lets all the current through (even when base is disconnected). It doesn't seem to be damaged though, since 5V behaves normal.

I must say that I'm a little bit confused by all the tables in the datasheet. I'm not sure what should the resistors be - I can't see what is the maximum current allowed for the transistor.

The pull-down resistor is here to make the transistor close faster (so I was taught). But again, I don't know how to calculate the resistance so that the transistor never gets more than necessary current.

It might be that the transistor was somewhat damaged. But it's still closes and opens as expected if there's 5V over collector-emiter.


texts: ISIS Proteus - Simulating a buzzer using an Atmega 8535 Micro controller

texts:
I am new to micro controller programming.

I am programming a Atmega 8535 micro controller using AVR Studio and simulating the circuit using ISIS Proteus.

In ISIS Proteus, there is a buzzer output device.

I need to know how what the schematic layout needs to be to play a sound using the buzzer. Just a simple layout that will demonstrate the use of the buzzer would be appreciated.


texts:
I am designing the data logger of a solar-powered automatic weather station that will be installed in farms. It's used to gather data from environmental sensors (wired) and send it to a host using the cellular network.

One of these sensors is a Solar Radiation sensor. Its sensitivity is 15uV. I am designing the analog front end and already filtered the mains 50 Hz that may be present due to nearby power transmission towers.

My question is:

What are the other external noise sources that are present in a farm that may interfere with my system?


texts:
I have Danaher Motion SS451 (120V, 60 Hz, Single Phase, 72 RM, page 10 in manual below) synchronous motor that was consistently blowing a 3 amp fuse. I replaced it with 5 amp slow-blow fuse and everything seems to be fine. My question is this:

The manual states "It is not necessary to consider high start currents... since starting and operating current are, for all practical purposes, identical."

How can this be true if the operating current (per the manual) is 0.8 amps and it was blowing a 3 amp fuse?

The motor is operated with a phase-shifting network ("C Connection", page 11 in manual below).

Manual


texts: Where the appropriate word size is selected for the operand?

texts: This question is about a 32 bit Intel Chip using x86 assembly. My question specifically is what happens when you do the mov reg, mem instruction where the memory operand is a word (16 bits) from DRAM. Every time DRAM gets read for a memory access, a lot more than a word is being read right? So is the memory controller grabbing a subset of those bits from DRAM- depending on the operand size- and only sending 16 bits to CPU? Or does the CPU receive more than 16 bits and has to isolate the 16 bits itself? An entire double word (32 bits) isn't moved to the register, right? I'm assuming you're not getting 2 extra bytes in a register that you didn't want. So what's in charge of giving the correct memory operand size?


texts: Searching for a suitable method to detect peak heights of nanosecond pulses

texts:
My goal is to digitize an analog signal and measure the maximum pulse peaks via an ADC device. The signal has the frequency (pulse-repetition-rate) of f = 100 kHz. Furthermore, the analog signal consists of narrow pulses that exhibit pulse durations around ~30 ns. In addition, peak voltages of the pulses are not constant and change in time. Below, you can see the illustration of the signal:

(Note: Actually, pulses are not rectangular-shaped. They have the form of a Gaussian pulse.)

The problem is that comparing to the period of the signal, pulse durations are very short. So, I think that it is a real challenge to accurately capture the each pulse and detect their peak voltages via an ADC component. I don't know which ADC meet my requirements to detect pulse amplitudes, since I couldn't decide the required sampling rate and bandwidth of ADC.

I don't want to use GSPS-ADCs, since their prices are really high. Can I use kSPS range ADCs to detect pulse heights? (e.g. only one sample for one pulse) I think this method requires the accurate synchronization of ADC clock to analog signal, am I right?

Can you guys give me some design advice to chose a proper ADC to digitize such a signal?

Thanks in advance.


texts: When changing rotor current in alternators, the pf and inductive part of the current changes but the resistive part does not. Why is this so?

texts:
Given a current for an alternator $ I = I_R - jI_X $
When the rotor current changes, the excitation changes so the magnitude of the generated voltage changes.
The current changes, but only the inductive part $ I_X $ while $ I_R $ stays constant and it is the change in inductive part which leads to the new power factor.
Why is this so? This is what a friend told me while I was solving something in an alternator. She didn't explain much to me about rotor currents, but just told me that only the inductive part of the current really changed. I don't get this. I tried searching about it in Google but I can't seem to comprehend anything I've seen.
She didn't have the exact concept in the references but gave me this from Theraja.

In particular, I want to address why does excitation change the reactive component in general and not the resistive component? Yes, the power factor changes but I don't get the reasoning behind linking the excitation to only the reactive part whether it be current or power. Is there any specific formula that relates excitation or field current to reactive components?


texts: What's the relationship between harmonic distortion and intermodulation distortion?

texts:
So if you take a sine wave and put it through a non-linear transfer function, it experiences harmonic distortion, which produces other sine wave components at integer multiples of the original.

If you put 2 or more sine waves through the same non-linear transfer function, they experience intermodulation distortion, where the newly-produced partials are at sum and different frequencies from the originals.

But it seems strange that the 1-sine-wave case should be fundamentally different from the 2-or-more case.

As transfer functions with odd symmetry produce only odd-order harmonics, I thought maybe harmonic distortion is actually a form of intermodulation, where the single tone intermodulates with its negative frequency component, producing only odd harmonics (-10 and +10 are spaced 20 apart, producing intermodulation tones at 10+20 = 30, 10+20+20 = 50, 70, etc.) but that doesn't really work, because then why do even-symmetric transfer functions produce even-order harmonics and destroy the fundamental?  And what happens when you distort a complex exponential that doesn't have a negative frequency component?


texts: VHDL - displaying 4 digits on 7-segment display

texts:
I wrote a vhdl code, that would display 4 digits on cpld 7-segment displays. I used a state machine to select the display, and with ... select instruction to select a set of bits given to the current display.

entity disp is
    Port ( clk_in : in  STD_LOGIC;
           an1 : out  STD_LOGIC;
           an2 : out  STD_LOGIC;
           an3 : out  STD_LOGIC;
           an4 : out  STD_LOGIC);
           g : out  STD_LOGIC;
           f : out  STD_LOGIC;
           e : out  STD_LOGIC;
           d : out  STD_LOGIC;
           c : out  STD_LOGIC;
           b : out  STD_LOGIC;
           a : out  STD_LOGIC);
end disp;

architecture Behavioral of disp is
    type states is (s0, s1, s2, s3);
    signal present_state, next_state: states;
    signal outp: std_logic_vector (0 to 3);
    signal counter: integer range 0 to 199999:=0;
    signal tym: std_logic:='0';
    signal clk_out: std_logic;
    signal WY : std_logic_vector (6 downto 0);
    signal WE : std_logic_vector (3 downto 0);

begin

--state machine
process (present_state)
begin
    case present_state is
        when s0 =>
            outp <= "0111";
            next_state <= s1;
        when s1 =>
            outp <= "1011";
            next_state <= s2;
        when s2 =>
            outp <= "1101";
            next_state <= s3;
        when s3 =>
            outp <= "1110";
            next_state <= s0;
    end case;
end process;

--frequency divider
process (clk_in)
begin
    if (rising_edge(clk_in)) then
            if (counter = 199999) then
                    tym <= not tym;
                    counter <= 0;
                    else
                    counter <= counter+1;
            end if;
    end if;
end process;

clk_out <= tym;

--state changing
process (clk_out)
begin
    if (rising_edge(clk_out)) then
        present_state <= next_state;
    end if;
end process;

an1<=outp(0);
an2<=outp(1);
an3<=outp(2);
an4<=outp(3);

--set of bits for 7-segment display
WE <= an4 & an3 & an2 & an1;
with WE select
WY <= "1000000" when "0111", --display 0
           "1111001" when "1011", --display 1
           "0100100" when "1101", --display 2
           "0000000" when "1110", --display  8
           "1111111" when others; --display nothing

g <= WY(6);
f <= WY(5);
e <= WY(4);
d <= WY(3);
c <= WY(2);
b <= WY(1);
a <= WY(0);

end Behavioral;

I do something wrong with the with ... select instruction input, because Xilinx shows an error for the bolded line saying "Cannot read from 'out' object an4 ; use 'buffer' or 'inout'". How to solve this problem?


texts:
I understand that voltage is relative to ground, so that can be negative.
However, I'm currently looking at current-sensors (ACS712 current sensor) and in the performance characteristics table, it specifies the Optimized Accuracy Range.
In the case of this sensor, it's being specified in Amps, ranging from -5 A to +5 A

I can't find anything explaining how you could have a negative amperage. As far as I know, electric current is the rate of flow of electric charge within a (part of a) circuit.

How could the flow of charge sensed by the sensor be negative?


texts: Identifying a USB charging port without enumeration

texts:
Is there a low cost and reliable way to identify a USB charging port?

I plan to charge a device via the USB port. The USB Battery Charging Specification 1.1 allows 1.5A current draw when connected to a Dedicated Charging Port (DCP) and 500mA when connected to a Charging Downstream Port (CDP). A DCP is typically a wall wart and a CDP is typically a computer.
As far as I understand, a DCP is identified by shorted D+ and D-lines, a CDP id identified by D+ and D- being pulled to ground through 15k resistors.

It seems like identifying these ports takes quite a bit of extra hardware. I could probably bias the D+ line and connect D- to an ADC input to look for a DCP. And some similar arrangement to check for a CDP. I assume I would also need to disconnect the bias and ADC when done to not interfere with USB communication.
The USB pads on my mcu are not 5V tolerant and are dedicated USB pads (I'm using an LPC1343).

Identifying the non-standard Apple and Sony chargers would be an added bonus, but not critical.

Does anyone see a simpler or better way to do this?

From this datasheet


texts: What free IDE does everyone use for the stm32?

texts:
I'm currently using Atmel SAM series. The choice was easy: IDE is Atmel Studio which is very good, free and I used it for developing AVR before. The debugger I have is the Atmel ICE which I also used for AVRs and it supports the ARM series as well.

What makes the STM32 series interesting is the very low cost for the chips and the development boards. However, what IDEs people use for developing? I am interested in something that is completely free as mainstream as possible so it will be easy to find help when needed and also to make sure the tools stay up to date. I could find a definitive answer on Google or on ST's website so if someone is already involved with developing on this platform I would appreciate if you share the data and your opinions.


texts: Can signal arrival times be a function of receiver bandwidth?

texts:
Lets assume that the speed of light is exactly \$3\!\left(\!10^{8}\!\right)\text{meters}/\text{second}\$. Suppose we have a transmitter on the surface of the earth emitting a signal at 1000 MHz and that there is a receiver \$3\!\left(\!10^{8}\!\right)\!\text{meters}\$ above the surface of the earth that is receiving the signal (line of sight, straight line distance, normal to the surface of the earth). The bandwidth of the signal is 2 MHz and the signal is a precision timed signal such that arrival times at the receiver can be accurately determined by an on-board computer. When the receiver's bandwidth is set to 10 MHz the arrival time is calculated by the on-board computer to be \$1\!\left(\!10^{-3}\!\right)\!\text{second}\$, which is what it should be with the speed of light and distance as given above (ignoring atmospheric effects). Lets suppose when the receiver's bandwidth is changed to 20 MHz the arrival time is measured at \$1.5\!\left(\!10^{-3}\!\right)\!\text{seconds}\$.

Two questions:

1.) Taking the atmosphere into consideration and assuming non-ideal (i.e., real world) receivers and transmitters, is it possible to have different arrival times for different receiver bandwidths as described above? (Atmospheric multi-path should not be dependent on the receiver's bandwidth setting.)

2.) Could "noise power" affect arrival time calculations based on the receiver's bandwidth setting?


texts: 12 vdc arc suppression on 12v solenoid contacts, switching a car starter motor on and off

texts: Would anybody be able to advise the best way and components required to minimise contact burn up, on a car motor starter solenoid which is being repeatedly opened and closed? This is a lure machine utilising a car 12v starter motor, with a 12v car battery as the power source.


texts: RF transformers in first, second and third IF stages, how and why are they different?

texts:
Many websites about RF transformers talk about IF transformers to be implemented in first (green slug), second and third (brown, black or orange slug) 10.7 MHz IF stages. Other than this, I don't see any elaboration on why transformers with different impedance ratios would be used for the cascaded stages.
So what is the difference and why is it important?


texts:
Yes, yes, I know that it must be between 1 and 4 clock cycles of a target device. But... We don't know it if clock is provided by internal rc generator or external quartz. So is there any possible way to find the fastest allowed spi frequency?

And one more question. I've read that we can provide external clock source when programming. But how can we tell to AVR about this? I thought that it always uses internal rc generator when being programmed.


texts: Using connected PC keyboard input for VHDL Simulation

texts:
I am working on a project for school that will involve an input from a push button or related device. We have only a few Spartan boards available, but we have access to Xlinx Vivado to simulate an FPGA instead. The goal is to analyze data on differing lengths of time that the button is held down.

I want to know if I can program the simulation to accept input from the keyboard attached to the computer in place of the push button.

If not, is there another simulation software I could use?
Or is there a way to log the output on the Spartan board so I can download it later and analyze the results.

Thanks

Edit: How do I do this in the testbench?


texts: Design Considerations for Raspberry Pi Expansion Boards

texts:
I am venturing into the space of designing expansion boards for Raspberry Pi's. I have done this for Arduino boards but RPi's are a different beast.

From personal experience I have already had problems with damaged UART pins on the RPi and I am keen on finding ways not to repeat his experience.

Considerations I have come up with:

The IO pins are sensitive and needs protection. It can be as simple as Zener Diode to ensure the voltage stays at 3.3V and a current limiting resistor. Example Circuit
The GPIO pins are 3.3V , can source about 16mA and can only do about 50mA in total. The 3.3V rail is limited to 50mA and not suited for powering external components. Instead the 5V rail with +500mA can be regulated to supply more
The GPIO's are not suited for hot-swappable expansion boards and need to be powered down before installed.
External Power supply for extension boards are recommended.
Expansion boards can stacked but the limited current on the 3.3V rail could be an issue.

Considerations in question:

ESD - How well does a Rpi deal with people handling it.

Any other suggestions will be mush appreciated.

Extra Links worht looking at:

GPIO Protection Circuits


texts: Liquid level switch with normally open contact

texts: If something is described as a "liquid level switch", and contains a normally open contactor, would this imply that a dry sensor would cause the contactor to open, and a submerged sensor would cause the contactor to close? I get confused on the term "normally". To me, "normally" being dry or wet depends on the application, I suppose.


texts:
I'm trying to assign Parameter set for one of the DDR3 SDRAM chip pins. For some reason I can't assign parameter to the group of pins.
For example, if I do this way, then the program cannot assign parameter:

And when I try to do Design>Update from schematic I don't see anything related to parameters

But if I assign the pins separately, I can see the changes by doing an Design update. Like this:

I checked all the settings related to Parameters sets and I still can't make the pins grouped. Maybe someone knows the solution for this problem?


texts: What is "flush mount socket" in this 40yr old Tek scope?

texts:
EEVblog Dave shows us flush mount socketed IC's in this Tektronix 213 Portable Oscilloscope teardown, but it is hard to see and understand what exactly is a flush mount socket. Can someone explain how it is done and why?

The video at 7'46" and a picture:


texts: Is it dangerous to short circuit D1 on STM32F4 Discovery Kit?

texts: I damaged D1 on my STM32F4 Discovery board. Afterwards, I removed D1 and shorted there. Now, it works. Can I use it or is it dangerous?


texts: is a water inlet valve water resistive by design?

texts:
I cleaned a leaky washing machine water inlet valve with wd-40, pressurized water, pressrized air, drain opener(caustic soda+ sodium chloride), vinegar and alcohol and gave it a massage gun session using all frequencies after the water.
Should I dry it before reinstalling it or is it safe to dry it superficially and reinstall it right away?
I was thinking about putting it in the fridge then let it under the sun for a while.
C-136/14-14-10
334913600 5220FR125LE
220/240V 50/60Hz


texts: Different ways to digitally control an adjustable SMPS

texts:
I want to make a battery powered, adjustable SMPS for use in situations when I cannot have an outlet near me, so I would like some more information or suggestions about this topic. The SMPS chip I am basing this off is a LM2733.

The power source would be a LiPo, voltage output 3V to 25V, and at most 500mA.

There are a few ways I think I can control a SMPS chip digitally: one is a digital pot controlled with a MCU via SPI or I2C. A 1024 step pot would give me 20mV stepping, which is more than enough. What I saw in datasheets is that the pots are only able to go up to 5V for the digital resistor. Would that be a limiting factor in such a design? This way seems the simplest and least demanding way from what I see.

Another way would be using a DAC, but I am not sure if it would need to go faster than the switching speed of the SMPS, because in data sheets I always see the voltage dividers before the output capacitor. Problem is that I do not know what the feedback pin wants to see. Does it want the entire ramp up and down from the inductor and compare it to the reference voltage, or does it just find the average voltage of each cycle?

I know it is similar to {this question}, but I'm looking for some more information or discussion.


texts: How a usb device identify a purpose made powerful USB charger?

texts:
I know that by standard no device should ever try to draw more than 500mA from USB.

But a lot of phones and tablets can somehow identify their purpose made chargers and draw far more than 500mA from it.

How is this done?

I see two solutions, one digital and one analog.

Digital solution is to build some logic into the charger and use data lines to handshake.

Analog solution is to use a 5.2V or higher charging voltage so the logic is as simple as "if input voltage is greater than 5.0V, then it's our VERY powerful charger, forget about 500mA limit".

I'm using a LTC3556 power management chip. The input current limit can either programmed via I2C or by adjusting a resistor.
http://www.linear.com/product/LTC3556


texts: Basic PNP transistor on a microprocessor output pin

texts: I have a 5v microprocessor that needs a PNP transistor between it and the common anode of an LED display, as it can't source enough current to drive all of the LED's without burning up. I understand in principle how the transistor connects, but seeing as I'm a computer programmer and not an electrical engineer, I'm having a little trouble finding the exact part number or specifications that will work in this application (all this talk of bias voltage, forward and reverse biasing, etc. has me thoroughly stuck). The display should suck around 400 mA through the transistor, worst case, and everything runs on 5 volts. Lastly, will I need any resistors (aside from the LED resistors) on the transistor and if so, how do those work?


texts:
In discussion a friend mentioned:

  In the original implementation of PAL and NTSC they used the AC current as a means providing the frequency for the TV. As the different mains had different frequencies, they designed the TV standard to have different frequencies.

I wasn't sure about this so I wanted to check.

My question is: Is the design decision for different frequencies in PAL and NTSC related to the AC mains power frequency?


texts:
I am required to design a current DAC (64 element NMOS) that sinks the current of another current DAC (16 element PMOS).

The specs are as follows:
1. The smallest current output from the PMOS DAC is 6uA.
2. The smallest step size of the NMOS DAC is 6uA/256~25nA (that is the spec I am provided with)

Additional information:
1. The controls to each NMOS element are clocked at a maximum frequency of 15o MHz. (Feedback clock, as this DAC is used to fine tune the frequency of a PLL).

I am having trouble deciding how to bias the NMOS elements to sink 25nA each. I could really use some help, thanks!


texts: I'd like to know if my own version of a cell balancer will do the job

texts:
I have two 3.7v cells in series to make a 7.4v battery. I want to make my own active balancer because I don't have access to buying any cell balancers.
I'm using a transformer with 2n turns on the primary side connected to the 7.4v part, and I have 2 different secondary coils with n windings on each, which are connected to diodes which are connected to the individual cells.
From my understanding, if one cell is less than the other, the total battery voltage divided by two should charge the cells at different rates since one cell will pull more current from the transformer because of its lower voltage drop.
I'm not that good at electronics as I'm limited, but I'd like some input on this.


texts: Sharing sensor analog output with multiple ADC for digitization

texts:
I am using a pressure sensor, MPVZ4006GW6U, and I have an unique requirement where by I need to share this sensor's output with multiple ADC (say ADC128 from TI) for digitization. Each ADC is interfaced with different microcontrollers for processing the digitized values and hence the need.

Will there be any functional issues when an analog signal is fed to multiple devices?
Does the analog signal sharing arrangement disturb the sample and hold stage internal to the ADC?
What are the things to be taken care of in the layout while T-routing this analog signal?


texts: Way to power a monitor that requires 12 V 2.5 amps with a PC USB port

texts: I am looking to see if there is a way to power a monitor like this: (https://www.amazon.com/gp/product/B07774L6TT/ref=ask_ql_qh_dp_hza) over one (or two) of the PC's USB ports, so theoretically it would be a two wire setup, 1 HDMI, 1 USB for the whole display, no need for an extra wall outlet. I have seen USB 5 V to 12 V step-up cables but they seem to only deliver 2 amps which it looks like this monitor may need 2.5 amps.


texts: Voltage reduction issues in an existing circuit

texts:
In the above diagram, I am trying to reduce the input voltage of 7.4v to no more than 3v, which is the maximum rating for the M2 motor. This is for a boxmag used with an Airsoft gun, specifically an M16 style 5,000 round boxmag. The idea is to operate the gun and the boxmag off the trigger switch of the gun. I have had this circuit in use in other boxmags, but recent events has shown that a potential problem with overheating of the resistor can occur and thus result in frying the resistor.

My current components are listed below,
Motor (M2)
Diode (1N4001) (Had to replace the original Schottky diode)
Resistor 5 ohm, 1/2 Watt, 5% tolerance
Switch DPDT

The switch must be able to achieve two modes of operation, 1] constant power for priming the boxmag, and 2] selective power for operation off the gun's trigger switch. The diode acts as a control gate to prevent damage to the motor, or that is how I understand it anyways.

I ran some calculations using available data to determine the resistor's rating, these are the calculations below,

The motor has these statistics,
Voltage range: 1.5 to 3 volts
Current: 0.18 to 0.25 amps w/o load, 0.70 amps +/- 15% at max efficiency
Output: 0.31 watts

If I understood everything correctly, the device (M2) has a resistance of 10.57 ohms, which when entered into the formulas and calculated out, should have brought me to 2.37 volts at the motor, but since the circuit keeps frying the resistor, I'm not so sure anymore.

Therefore, my question is, how can I address this issue such that I will achieve the correct results without risking frying the resistor?

Any assistance to achieve my goals is appreciated. Thank you.


texts: Capacitor for handling startup current of DC-DC converter shows different behavior

texts:
I’m using a 5V DC-DC converter to step-up a coin cell (Nominal Voltage: 3V) to 5V which did not work. I suspected that the high startup current of the converter was causing the Cell voltage to drop, hence the converter never really starting. To confirm this, I used a power supply with 3V voltage and 1 Ohm resistor in series to measure the input current to the DC converter.

As I suspected, the starting current was very high than what the Coin Cell could provide. Below is the plot of voltage drop across the input resistance I got on my oscilloscope. Since the input resistance is 1 Ohm, the current is equal to the Voltage drop e.g. 100 mV = 100 mA. (CurA = Starting Peak Current AND CurB = Input Current after Converter starts up)

Someone suggested to put a high capacitor in parallel to the input voltage to the DC converter to reduce the input current. I used a 1500 uF capacitor in parallel but opposite to my intuition, the input current further increased from 292 mA to 384 mA as below:

I’m placing the capacitor in parallel just between the input supply to the DC converter. What is wrong here? My assumptions or values of capacitor?


texts: AT42QT2160 capacitive touch controller inverted Cs voltage - no touch detected

texts:
I'm trying to make my own development board for the AT42QT2160 Touch controller, since the original one was discontinued. I've designed the PCB with 8 buttons and a slider consisting of 8 sections. It's a two-layer slider/button, which means the X-line is on the one side of the PCB, and the Y-line is on the other. (See more here, page 50). With a scope, I see my touches just fine, but the IC doesn't detect any.

When I measure the X pulses with a coin as specified in the datasheet, I get the correct pulses. However, when I measure the Y voltages, the voltage makes a positive incline instead of the negative decline. I believe that is the reason I can not read any touches. What did I do wrong?

I've already specified the number of keys as well as resolution via I2C.
Microchip support suggested adding a front panel, but I have already tried that. It only affects the sensitivity, based on the thickness.

My measurement of the Cs voltage:

The datasheet's Cs voltage measurement:

The schematics:


texts: Dual primary / dual secondary transformer heat up

texts:
I've built this 220v DC motor controller. I use a 2x110v - 2x15v transformer to power up the stator.

The transformer is a Myrra 45064 with the primary windings connected as follows: pins 1 and 9 connected to the mains, pins 4 and 6 in short.

On the secondary windings, i've connected pin 12 and 19 to a rectifier, and 14 and 17 in short.

When I plug it in at 220v AC, the transformer heats up very fast and outputs ~12V out of the expected 30V. Didn't keep it powered more then 6 seconds.

I thought that this pin configuration should connect the 2 halves of the transformer in series and output 15+15V.

Am I connecting them wrong, or there could be another cause for the high current through the transformer?

P.S.: The schematic on github shows a 3 port primary winding, however, the board is built with the connections done as explained above.


texts: HDMI Development: What Would Cause Thin Pink Lines?

texts:
I recently designed a board which produces an HDMI output for an oscilloscope so it is viewable on an external monitor. My prototypes seemed to work just fine with one or two mod wires. However, after adding these mods to the copper and re-spinning the board, I am getting fine pink vertical lines spaced evenly across the entire screen, mostly visible in the white areas:

It's a bit difficult to see in the above image, but you can see it if you zoom in on the white line just above the blue language ribbon, and also in the white arrow beneath the "Training Signals" text.

It can also be seen in some of the text, as in the image below:

The lines appear to be approximately 10 pixels from the start of one to the start of the next. The video format is 800 x 600 @ 60Hz.

I have tried reflowing the solder joints, re-cleaning the board, baking it, etc but I am still seeing the issue. At this point I am fairly confident that it is not a connection issue and instead has something to do with the display data itself, be it timing or something else altogether.

What would cause such evenly-spaced pink lines to appear on an HDMI monitor? In case it is important, I am using a Xilinx FPGA as the controller, some Cypress SRAM for the frame buffer, and the TFP410 for the HDMI transmitter.


texts: How to minimize the gates in implementation?

texts:
I am a computer science student, and several times have been asked to implement an expression with the minimum number NAND or NOR gates. I could never get the exact procedural thinking about it and always guessed the solution sometimes leading to the wrong answer.

Can you tell me how we can we take it as a procedural problem? Or is it just practice and guess for such questions? As an example how can an XOR gate be implemented with 4 minimum NAND gates, how would I approach that question?


texts: Bode plot of circuit with unknown values

texts:
I have the two following circuits with unknown values for \$R_1\$, \$L\$ and \$C\$, \$R_2 = 1\text{ k}\Omega\$. I have attempted to find the transfer functions for these circuits and ultimately want to produce two Bode plots from this. The purpose is to determine the configuration of a "black box" circuit by performing tests with either a DC source or signal generator and viewing the result on an oscilloscope. The circuits below are two of a number I want to test. How could I tell which circuit is which just by these tests.
My thoughts were to perform a frequency sweep from \$1\Omega\$ to \$1000\Omega\$ and then compare \$V_{\text{in}}\$ and \$V_{\text{out}}\$ and plot frequency response from that. But with unknown values I could get anything.
Is there any test I can perform with either a DC source or signal generator that would allow me to determine the configuration of either circuit? More broadly, for any black box with 1 resistor, 1 inductor and 1 capacitor what tests could you perform with a DC source or signal generator to determine the configuration?
Circuit 1:

Transfer Function 1:
$$H(j\omega) = \frac{R_2}{R_1 + \frac{1}{j\omega C} + j\omega L + R_2} \to \frac{j\omega C R_2}{1 + j\omega R_1 + j\omega^2 L C + j\omega CR_2}$$
Circuit 2:

Transfer Function 2:
$$H(j\omega) = \frac{R_2}{\frac{1}{j\omega C} + j\omega L \parallel R_1 + R_2} \to \frac{R_2}{\frac{1}{j\omega C} + \frac{1}{\frac{1}{j\omega L} + \frac{1}{R_1}} + R_2}$$
\$V_{\text{out}}\$ is across \$R_2\$.
What I can't figure out is how do I produce a Bode plot if I don't know the values of \$R_1\$, \$C_1\$, and \$L_1\$?
The Bode plots I have seen so far do not include unknown values so I am not sure of what to do next, do I treat the knowns as 1?


texts: Are PLCC Chips/Sockets always the same pitch?

texts: I'm hunting down a socket for a PLCC-84 chip and none of them mention pitch spacing.  Is that because PLCC is always the same spacing between pins?


texts: Why does the current not flow directly to ground?

texts:
I'm working on an assignment for a digital circuit in a basic logic design class so I'm sorry if the answer is obvious! The title question is incredibly vague, but I wasn't sure how else I could title it. Please let me know how I can rename it to a better one.
The boolean expression I'm trying to model is B AND (E XOR H). (Please excuse the seemingly random variable names, they are named that way for the assignment.) To my understanding, the circuit itself is essentially an XOR gate with an extra condition of A. So I used this video as a reference guide to create the schematic below.

I was able to model this on this virtual breadboard simulation, and the picture below is currently what I have on my circuit board, where switch S1 is for B. It works perfectly for almost all of the cases except for when all the switches are on - then the LED still stays on.

I've narrowed the issue down to transistor C on the breadboard, or Q1 on the schematic. The 5V being delivered goes through both the transistor and the resistor, causing D1 to turn on. However, from my understanding of the original diagram that was shown in Ben Eater's video, if Q1 and Q2 are closed, then shouldn't the current go directly to ground and Q3 should be turned off? In my implementation though, Q3 stays on. Could anyone help explain why that is?
Edit: My resistors all have a value of 330 ohms. I ended up leaving R1 out and replaced it with a wire because when I included it, the simulation refused to run properly for some reason.
Edit 2: Here is the breadboard file for the simulation to download if you happen to have the virtual breadboard simulation downloaded as well.


texts:
I have an Arduino that I want to drive using a 12 V source. Of course, this can be achieved using a voltage regulator or similar solution. Notably, there is a loss in the conversion (at best, this is roughly 5 % with the best switching regulators), which is acceptable. That is all fine.

However, I also know that I need to drive a few LEDs. Let us for now ignore the fact that the LEDs work with 3 - 3.6 V and that the source, being a lead-acid battery actually differs in voltage depending on charge. Assume that I have a LED with exactly 3.5 V drop and place two in series with the Arduino, producing a voltage distribution as 3.5 V, 3.5 V and 5 V.

In the below circuit diagram, the Arduino is modelled as a resistance (commonly called an R-duino), but I suspect it is not very accurate.

Exactly, what will happen? My guess is that since LEDs are passive and the Arduino consists of active components, the current draw will be decided by the Arduino, causing the LEDs to shine more brightly when the Arduino draws more current and shine less when the Arduino is in sleep/idle. If we disregard the losses in cables and such, could this solution be considered having 100 % efficiency? If not, then where are the losses (note that light emission is desired and not a considered loss)?


texts: digital chip trigger output high on change input

texts: I need digital chip (low power consumption, can't use arduino or simular devices) which will put output pin high for a few ms when there is digital change on input pin (from hight to low or from low to high). Digital chip or circuit has one input and output pin. I don't know name of these device or where to look?


texts:
I want to locate a lost car key. It’s a 2004-vintage classic metal transponder key (not just a fob as is used in modern “pushbutton start” cars) which uses the immobilizer system (125 KHz?) to identify the RFID circuit in the key handle.

I can get to within probably 6” (15 cm) of where I suspect the key is. The area is quite large but the depth to search is fairly shallow. Manual searching has thus far failed. There is metal in the search area so a metal detector or magnet are useless.

I am thinking to output to a loop antenna the 125 KHz (maybe sweep either side of that a little) and use an audio tone (ie, 1 KHz?) and listen for changes when the key is in range. No need to communicate (challenge/response) with the key.

I’d like to use existing equipment and not build everything from scratch (ie, use a cheap sig gen rather than build the oscillator).

I have a spare key to experiment with.

A new key and programming is more than US$200 so I’m motivated to try something fun and geeky...

I’m looking for design ideas and assistance (directions only—I can build it) re. circuit details and components.

Thanks.


texts: should AC ground (earth) and DC ground be connected?

texts:
I have a power supply (AC --> DC) powering an microcontroller and DC electric motors. I also have the same AC powering a speed controller, which feeds to an AC motor.

Should I be connecting the ground from the DC power supply, to the earth ground on the AC?

Thank you!


texts: USB 5v temp control for stainless steel wire micro heat elenent

texts:
First, I am new to electronics.
Is it possible to build a usb or battery powered heating element to heat 1ml of water?
How much wire. Needed to hear to 60 deg. c.
I need to control temp and also cycle temp.
Searched but not many examples for this specific scenario for a novice in electrinics.
Any feedback most appreciated.
Cm


texts: How have my neighbours’ appliances been damaged?

texts:
In the aftermath of the recent storms in the UK, one of my neighbours reported a flash and loud bang from his local transformer station, and the power briefly cut out.

After that, several households reported their appliances malfunctioning, including a hair-dryer getting dangerously hot, the smell of burning from sockets and boilers and Xboxes no longer working. The power company cut off power while they investigated and are now repairing/replacing everyone’s appliances at their expense.

So what would have caused this to happen? I can only imagine a spike in voltage as I understand that breakers and fuses blow on too much current, but I can’t believe there aren’t some safety mechanisms to prevent this from happening.


texts: Problem with understanding EPROMs and how they're written to

texts:
I've got a problem understanding how an EPROM (UV-erasable) works.
This question may seem very dumb, but what would happen, if I just try to write contents to an EPROM, which has already been written to? Will it just not work? Or will the contents on the EPROM be corrupted? I don't really understand why I can't just overwrite the whole thing, without erasing it first through UV-Exposure.
Maybe somebody with a better understanding of this can explain it to me. Thanks in advance for your help.


texts: What are the maximum number of RGB LEDs that can be hooked up to just one of these I2C RGB LED Drivers?

texts:
So this is LP5036 by TI (Datasheet), a 36 channel RGB LED driver I2C interface-able with a micro controller, which means it can drive upto 12 RGB LEDs individually up to my understanding.
But using special circuitry with transistors/ multiplexing/ GPIO driving, how far can this driver be harnessed to the maximum extent? How many maximum number of RGB LEDs can be individually controlled using just one LP5036 ?


texts:
I'm trying to design a NFC loop antenna according to the following specification:

http://www.ti.com/lit/an/sloa135a/sloa135a.pdf

In the design the loops are placed on the top layer of the PCB, same as rest of the circuitry. However, when mounted with the back of the PCBS against a flat surface and the RFID tag on the other side of the flat surface, the antenna loops are father away from the tag than they could be.
My questions are:

Is there a downside to moving the antenna loops to opposite side of the PCB? That it, bottom layer.
Are typical NFC-antennas equally effective with the RFID tag placed under or over them? I believe they must be due to the fact that field lines should be symmetrical on the back and front.

Thank you for your time.


texts: What are the multiplication factors for switching frequencies in 3 level NPC, TNPC and 5 level inverter topologies with 2 level Fsw as reference?

texts:
I am trying to compare losses of 2 level inverter topology with that of 3 level NPC, TNPC topologies.
However, it may seem not a valid comparison if the switching frequencies of every topology remains same. Because with the same switching frequency the losses in NPC and TNPC will be definitely more than 2 level due to more number of switches than 2 level topology.
Hence, I can go for a reduced switching frequency in 3 level NPC and TNPC topologies. But I don't know the factors by which amount the switching frequency in NPC, TNPC can be reduced with 2 level switching frequency as reference value for valid loss comparison.


texts: What voltage should I use to heat a 36 gauge nichrome wire to 100 degrees Fahrenheit?

texts: I am making a foldable brass hanger, with a brass tube I will solder to the base. I am going to be using Nichrome 80-250 36 gauge wire, but I am not sure how many volts I need to get it up to 100 degrees Fahrenheit. If anyone could help me calculate this, I would be super thankful.


texts: How to define VHDL entity with two architectures?

texts:
Currently I have one 'adder' entity with two architectures: (1) RippleCarryAdder (2) CarryLookAheadAdder.

I put all the definitions in one single VHDL file as below:

entity adder is
generic (N: integer := 16);
  Port ( Cin : in  STD_LOGIC;
      x : in  std_logic_vector (N - 1 downto 0);
      y : in  std_logic_vector (N - 1 downto 0);
      s : out  std_logic_vector (N - 1 downto 0);
      Cout : out  STD_LOGIC);
end adder;

architecture RippleCarryAdder of adder is
begin
  ...
end RippleCarryAdder;

architecture CarryLookAheadAdder of adder is
begin
  ...
end CarryLookAheadAdder

Using ISE 14.7 Xilinx I can see that the tool has difficulty to properly distinguish two architectures associated to 'adder' entity. It only recognizes the last architecture specified in the file (in this case 'CarryLookAheadAdder').

I guess there is something with file domain, or maybe some rules that govern the architecture declaration which I am not aware of. Strange that the VHDL documentation has not talked about multiple architecture and file structure. Should I use two files, and copy entity declaration in both of them? Can you point to a page that properly discusses multiple architectures format supported by Xilinx ISE? (for example configuration keyword is not supported and I have to resort to another format to bound architectures.)


texts: Delay and Stablity in Negative Feedback Systems: Confusion

texts:
Below is a block diagram that shows an op-amp in negative feedback with feedback network made from resistive divider:

The encircled block is Op-Amp with 1 and 2 as its inverting and non-inverting pin respectively. I am assuming ideal conditions.

This would always be a stable system unless there is a delay in the feedback path. If we give a step input to the system and if the delay of the system is small then there would be no overshoot above the input step voltage but as we go on increasing the delay the system would start to overshoot and for higher delay it can become unstable. Below are the diagrams that show the system with delay and its response to the step input:

For this system with ideal delay, I read that if the delay \$T_d\$ is greater than \$\dfrac{\pi}{2} \cdot \dfrac{k}{\text{unity gain freq}}\$, the unity gain frequency is the \$\omega_u\$ in the diagram above, than the system would become unstable and its output would start diverging.

For the second order system the block diagram is shown below, here the delay element is first order, let's say it is some RC delay:

The delay element has a single pole at \$p_2\$. I read that this system is unconditionally stable with delay being \$1/p_2\$. From the above requirement of the delay, we can state that unconditional stability means the delay \$T_d\$ for this system always remains less than the above limit which is \$\dfrac{\pi}{2} \cdot \dfrac{k}{\text{unity gain freq}}\$.

Since the delay is of the order of \$R \cdot C\$ of the delay element and the \$R \cdot C\$ value can be made arbitrarily large, I think it is not always guaranteed that the delay will be restricted within this limit and hence system should go towards instability whenever the delay exceeds this limit.

Could someone please explain this apparent paradox about why the system is unconditionally stable even when the delay could be greater than \$\dfrac{\pi}{2} \cdot \dfrac{k}{\text{unity gain freq}}\$.


texts: I have a conveyor belt under which there are electromagnets to hold a piece of steel during movement. At the end of the belt the pieces must be unloaded with suction cups. Over a certain speed the electromagnets do not discharge sufficiently quickly, making resistance to lifting. How can I speed up the electromagnet discharge process?


texts: I can't figure out this circuit. How do I obtain the three currents?

texts: I can't figure out why i2 is 0. I tried applying KVL on the mesh with the voltage source but I didn't get anywhere (perhaps I applied it incorrectly? i don't know if the current travelling through that mesh is i2 or not). I also don't know how to obtain i1 and i0 once I obtain i2. (i'm guessing the voltage is the same on the 2 and 5 resistors? but i could be wrong). A little help would be greatly appreciated.


texts: Electrically detecting a not connected input

texts:
I have a 0-30V DC signal and it can be physically disconnected from a circuit. I need to detect and generate a TTL output when this signal is disconnected.

The "detector" circuit and the signal will share a common ground.

The thing I can't figure out is 0V (GND) is also a valid "connected" state for that signal. Using standart approach of a pulldown for detecting unconnected state is not going to work.

Edit: Thanks for all your input. Additional information:

Signal is not digital, varies between 0-30VDC. Sorry for misleading tag, removed that.
Which side I need to detect: I need to detect at receiver side and also need report that to sender.
Impedance of source: Low, but going higher than 50mA load will going to disturb other things that depends on this signal.
Pulling down lower than 0, higher than 30: I actually thought that but it is not seems feasible since I don't have these.
Pulling to middle: 15V is valid signal, can't use that.
Injecting signal: Nice idea, but receiving side need to be "basic" as possible and I can't modify freely the sender side.

Is there any way to detect this electrically? Thanks


texts: How use DMM thermocouple probe hands-free to monitor heatsink temperature?

texts:
I suppose this is more of a lab practice question than electronics per se, but I wonder if there's a standard-ish way to mount the K-type thermocouple that comes with my Fluke DMM so I can monitor the temperature of a power transistor and/or heatsink over time, hands-free?

I'm certainly open to a special-purpose thermocouple or other sensor that could be screwed or perhaps preferably clamped in place so I could follow the temperature changes without having to poke the little temperature probe tip in there each time I want to take a reading and wait the minute or so it takes to stabilize on the right temperature.

Is there something the pros do for this sort of thing?


texts: What is the relationship between Power Generated in the grid and Voltage delivered?

texts: I am trying to understand how the grid works. Lets say we have some gas turbines, where we have a combination of air and fuel being used to turn turbine blades which in turn drives a generator to generate lets say three phase power. This 3-phase power is essentially 3 sinusoidal voltages out of phase with each other by 120 degrees. Now lets say that the load demand on the grid were to increase, then we need more power, so probably more air and fuel are used to make the turbines spin faster. What is the effect of this on the three phase power being generated. My understanding is that the three phase power will be 3 voltage waveforms each at 120V RMS and out of phase by 120 degrees with a frequency of 60 or 50 Hz, depending on where you live and it this three phase power should remain constant. So how is more power being generated at the turbine/generated affecting this output voltage. I don't understand the relationship between the power generated and voltage.


texts: Things to avoid when using voltage regulators?

texts: My project has components that operate at 3 different voltages (9, 5 and 3.3). I would like to only deal with one power source. Is it alright to feed one 12 V power source to 3 voltage regulators? Is there a smarter way of getting everything powered from a common source? I want to avoid placing the components in series.


texts: Can we create a depletion region  (just like in diodes) between two dissimilar metals?What would be the use of that?


texts:
I have a problem with connecting STM32F429 with a DAC (AD9748). I found that STM32 has pins PA4 and PA5 that could be used as DAC_OUT. I have been trying to look for this interface and I am not able to proceed forward.

I would be really grateful if someone could help me proceed.


texts: Switching PSU and residual noise on the rails

texts:
Is it ever possible to totally eliminate (at reasonable cost) switching noise on the power rails from either a switching PSU or DC-DC converter? At least, down to the sub-mV level.

I'm measuring it using an oscilloscope with a high impedance probe.


texts: STM32 USB programming using the OTG interface

texts:
I'm new to ARM based STM32 controller. The Controller which I'm using STM32F427VIT6. It has USB OTG FS interface where I need to program it using the USB interface. Is it possible to program or I have to use UART interface to program the controller.

Please help me on this.


texts: Photoresist PCB - Traces always gets washed away with developer

texts:
I have a positive acting presensitized UV-curable PCB board (link). I'm using the manufacturer-provided developer.

Supposedly, the parts that get exposed will get washed away by the developer. However, I observed that my traces are always the ones that get exposed no matter what arrangement I do. It seems like the "minority" always gets exposed.

What am I doing wrong? Is this the normal behavior for photoresist PCBs? I'm always using the same developer all cases.

Please ignore the scratches and blurry impressions. These are test runs. Left is first run, right is second run.

EDIT: added included pamphlet


texts:
I’m trying to design an off grid solution that would allow me to charge a Tesla (240v@48a) without having to buy a ton of batteries (since most car charging would be done at night)

I would like to buy a generator that is dedicated to this purpose. The problem is I need a way to turn it on when needed and off when charging is done.

My first thought was to buy an inverter that would be sleep until current is needed the have it turn on the generator when it wakes up. Problem is the inverters that I saw need a 50amp breaker limiting the incoming AC current. The line from the charger to the generator needs a 60a breaker.

My next thought was to use the inverter to start the gen then use a transfer to switch to a dedicated line between the charger and gen. Problem is that the line between the inverter and charger would need to be limited to the inverter rated wattage (say 1.5kW) and I’m not sure how that would be done.

Is there another way to monitor the charger outlet to see if there is need for power to control a relay that would control the generator?


texts: Homebrewed phototransistors - unijunction versions

texts:
Back in the days, when phototransistors were hard to get (especially in some parts of the world like the communist eastern block), one could brew their own by just filing/sawing off the top of a TO 18 NPN or PNP to expose its junction. The the collector-emitter pair would serve as a photosensitive device.

Since I'm just an amateur, I'd like to know whether it's possible to obtain something out of an unjunction transistor via the same treatment (e.g. the universal 2n2646 is an ideal, cheap and common candidate). The goal would be to obtain a light controlled saw-tooth/relaxation oscillator (probably an on-off modulation might be the most intuitive behavior).

Later edit:
I managed to build a simple audio saw-tooth oscillator with a home-brewed unijunction phototransistor. To test it, I used both visible range and IR light from a remote control, and, as in this question's hypothesis, the transistor seemed to shift its curve slightly, the only testimony being the modulation of the audio frequency by the strength of the light shone onto the exposed junction. Anybody interested can try it out using such a circuit.

UPDATE A theoretical back-up of the observations/hypothesis of this question is provided here.