texts: Software controlled variable voltage AC supply with SSR relays

texts:
I have an autotransformer like this one :

I would like to control it with an arduino solid state relay like this one:

What would happens if I wire every output of the transformer together to the same output and accidentally turn on more than one relay at the same time ?

For example, the 80v, 120v and 150v turned on at the same time would output :

80 + 120 + 150 = 350v ?
(80 + 120 + 150)/3 = 116v ?
230v because this is the maximum input ?

Would it be dangerous ? I don't really understand how an autotransformer work. Any idea how I could achieve it safely ?


texts:
I have the following chip (DRV8833)
Technical documentation

The inputs work the following way

And i have connected it the following way (I think)

simulate this circuit – Schematic created using CircuitLab

It worked the first time i turn everything on and toggled the GPIO pins, but the second time i started everything up nothing works and the same thing has happend to me with a DRV8838.

So i must be doing something totally wrong to render the chips unusable but what?

I have checked all connections with a multimeter by putting a cable in the breadboard and testing the connection between it and the each pin on the chip (moving the cable for each pin).

I have also tried to connect the motors to the power source and they work.


texts:
I want to build myself an adjustable bench power supply with adjustable current limiting, mainly for fun but also because I want something to help me with prototyping. I have previously built small voltage supplies using linear regulators and pots, but I want something with the current control also.

I found the L200 and it seems to do what I want it to do:

Voltage between 0-24V
Current limiting 10m-2A (these are approx)

Here's an example circuit from the L200 datasheet:

My questions are as follows:

Is this a decent solution for such a device in the modern day? Are there better IC solutions than this one? Maybe one that uses less external components?
Is there an easy way to control the voltage/current with an MCU? Will I have to use digital pots to replace the analogue ones, or something, to do this?
When I want to set/measure the output current limit, do I simply short Vo to ground through an ammeter and adjust P1? (I am under the impression this is how you do it with retail PSUs, not sure if this works in the same way).
What kind of wattage resistors should I use? My naive calculation tells me that if the max current possible is 1.5A, then the max power dissipation in R3 is 1.5^2 * 0.1 = 0.225W, so most garden variety resistors would be OK. Is this correct?

Thanks for any help!


texts:
I'd like to SMD solder the JST 1.25mm connector below with horizontal orientation aligning it to the side of the PCB (ie. in the end the male header should be plugged to the connector from the side of the PCB not from above the PCB). As visible the pins on the rear side are raised from the bottom plane of the connector so they don't touch the PCB when the connector is layed on it.

Is this connector meant to be soldered the way I described, or is it just a through hole connector meant to be soldered with a vertical orientation? If the former is true, how to solder it, just put enough solder paste/tin under the pins to fill the space?

What is the proper name for this type of connector?

The product link where I bought the connector:
http://www.ebay.com/itm/231443803216

Rear side-1:

Rear side-2:

Bottom side:

Front side:


texts: Loading an FPGA pin at 20MHz in parallel

texts:
I'm designing a traction inverter controlled by the NI sbRIO-9627, which includes a Zynq-7020 FPGA. I am considering using a single FPGA pin to drive the external clocks of 14x ADuM7701 isolated ADCs in parallel at 20MHz. I am concerned about trace capacitance/inductance loading down the FPGA pin.
DC current
The NI sbRIO-9627 digital outputs are listed as capable of "driving ±3 mA DC loads," whereas the logic input current of the ADuM7701 is ±0.6uA (14 * 0.6uA = 8.4uA), so this should be fine.
Transmission line
According to the 1/10th rule, with ϵr=5 and f=20MHz, you'd need a 0.6708m trace to encounter any transmission line issues. However, maybe if there is a large mismatch between source and load impedances I could encounter problems.
Load impedance: From my understanding, the load impedance would be the parasitic pin capacitance, which is 10pF for the ADuM7701.
Source impedance: The NI sbRIO-9627 digital outputs "are routed with a 55 Ω characteristic trace impedance" which I would have to match, but I can't find information about its parasitic capacitance.
I could do an LTspice simulation of the source, transmission line, and load impedances to see if there will be any issues, however I don't know the characterstics of my PCB yet to estimate the transmission line.
Going forward
At 20MHz, should I be concerned about overloading the FPGA pin? Would the source/load impedances typically be small enough to ignore transmission line effects altogether?


texts: How to read the resistance of a digital potentiometer

texts:
I an designing a digitally controlled 5 band analog equalizer. In order to change the gains of each band i am using a few AD8403. I have it hooked up to a stmf3discovery which controls the CLK,SDI,nCS,nRS pins on the ad8403. I have the circuit configure as shown below just without the second pot in for testing purpose. Also the supply voltage levels are from 0v to 5 volts the test circuit does not have a floating ground at -2.5v

The problem / problems that im having is when I hook up a multimeter across A to B on any of the terminals I get a very large resistance in order of mega ohms and these pots are suppose to be 10k max. So I tried applying a 5v to the A terminal then grounded both the b and the wiper terminals and tried measuring the voltage across A to W and got a full 5 volts.

So the main question is do digital potentiometer not have a directly readable resistance? Do you have to measure it via Vout / Iout ?


texts:
I am trying to use this display with an STM32F0 using SPI. I begin by setting up the peripherals using the following

RCC->AHBENR |= RCC_AHBENR_GPIOBEN;
RCC->APB1ENR |= RCC_APB1ENR_SPI2EN;

GPIOB->MODER |= (0x2 << (2*12)) + (0x2 << (2*13)) + (0x2 << (2*15)) +
                (0x1 << (2*11)) + (0x1 << (2*10));

SPI2->CR1 |= SPI_CR1_BIDIMODE + SPI_CR1_BIDIOE + SPI_CR1_MSTR + SPI_CR1_BR;
SPI2->CR2 |= SPI_CR2_SSOE + SPI_CR2_NSSP;
SPI2->CR1 |= SPI_CR1_SPE;

In other words, I enable the clock to the peripherals, enable alternate funtions for the SPI NSS, MOSI, and SCK pins, as well as for the manually controlled D/CX and RST pins. I enable bidirectional mode and enable the SPI. I then initialize the LCD using commands adapted from Crystalfontz' Arduino example code (which I will not post to save space). However, once the initialization is done, the screen displays the following.

Clearly, this is not what I want. I attempt to fill the screen using the following functions.

void SPI_sendCommand(uint8_t command) {
    CLR_RS;
    while (!(SPI2->SR & SPI_SR_TXE));
    SPI2->DR = command;
    while (!(SPI2->SR & SPI_SR_TXE));
}

void SPI_sendData(uint8_t data) {
    SET_RS;
    while (!(SPI2->SR & SPI_SR_TXE));
    SPI2->DR = data;
    while (!(SPI2->SR & SPI_SR_TXE));
}
void setDisplayWindow(int x0, int y0, int x1, int y1) {
    SPI_sendCommand(ST7789_CASET);   // Column Address Set
    SPI_sendData(x0>>8); // X address start:
    SPI_sendData(x0);        // 0 <= XS <= X
    SPI_sendData(x1>>8); // X address end:
    SPI_sendData(x1);        // S <= XE <= X

    SPI_sendCommand(ST7789_RASET); //Row address set
    SPI_sendData(y0>>8); // Y address start:
    SPI_sendData(y0);        // 0 <= YS <= Y
    SPI_sendData(y1>>8); // Y address start:
    SPI_sendData(y1);        // S <= YE <= Y

    SPI_sendCommand(ST7789_RAMWR); //write data
}
void fillLCD(uint8_t R, uint8_t G, uint8_t B) {
    setDisplayWindow(0, 0, 239, 239);
    SET_RS;
    for (h = 0; h < 240; h++) {
        for (w = 0; w < 240; w++) {
            while (!(SPI2->SR & SPI_SR_TXE));
            SPI2->DR = R;
            while (!(SPI2->SR & SPI_SR_TXE));
            SPI2->DR = G;
            while (!(SPI2->SR & SPI_SR_TXE));
            SPI2->DR = B;
            while (!(SPI2->SR & SPI_SR_TXE));
        }
      }
    CLR_RS;
}

where CLR_RS and SET_RS clear and set the D/CX pin, respectively. These functions do not do their job, but are almost identical to the ones in the example code. My pins are set up as follows.

1  - GND                2  - Vcc (3.3 V)
3  - Open               4  - Open
5  - GND                6  - Vcc
7  - Vcc                8  - GND
9  - PB13 (SCL)         10 - PB15 (MOSI)
11 - Open               12 - PB11 (D/CX)
13 - PB12 (NSS)         14 - GND
15 - PB10 (RST)         16 - GND
17 - Open               18 - GND

I believe the issue may be with how I write data bytes to the SPI, as commands that don't take parameters, like putting the display in sleep mode, work, while commands that take parameters, like changing the brightness, do not work. Does anyone have any idea how I can get just a solid color to display on this?


texts: Electrical continuity detection [Manufacturing Solution]

texts:
I am designing a testing box that has as a specification supplying power safely to a product range that requires the following voltages: 24Vdc, 24Vac, 110Vac and 230Vac. I am intending to use transformers controlled by PLC's and a HMI screen.

However, I am stuck with a health and safety issue. Currently one end of the output lead could have live wire when disconnected of the product and therefore hurt the operator.

Is there any component that detects the continuity in a lead, and stops the current automatically when it has been detected that there is no path for the current to flow?

Many thanks in advance, any help would be appreciated.


texts: DC Motor as DC Generator + Output Polarity Switcher

texts:
I am working on a hobby circuit. And got a quick question.

I am using regular mini DC Motor as DC Generator. If the motor is rotated one side it generates few volts.
If the motor is rotated in opposite direction the output polarity is switched. Which is normal.

I would like to know how/what circuit to connect to output of Motor, such that if the motor was rotated in any direction, the polarity of the output after the circuit is same.


texts: What is the easiest way to amplify current from 20mA to 2 A?

texts: I am using an Arduino to control a solenoid that needs 2 A current DC but the Arduino only outputs 20 mA max. I have a bench top power supply that can supply 2 A but i need to find a way to use the Arduino to switch it on and off. I think BJT transistors might be the way to go but I am not sure which one i should use. I am open to any other suggestions but the simpler the better. A specific part no. and or circuit would be very helpful.


texts:
I have a fairly simple problem, but as I am a newbie in electrical circuits I was hoping someone might help me understand the principles of things.

I have a circuit with an inductor of L = 0,102H a resistor of 20k ohms and a voltage source of 10V. The question is how much current will 'accumulate' (if thats even how it works) and if I were to disconnect S1 (or flip it so that that the voltage source would no longer apply) what would happen to the body (represented as a resistor).. How much voltage there would be and how much current would run through it. Also in what manner would the current run?


texts: What is the purpose of Failure Mode and Effect Analysis?

texts:
Our embedded controller is Advanced Drive Assist Systems(ADAS).  It basically has Two software layers.  Application software and low-level software.
Our controller has many low-level functions such as different communications protocols, different types of memory, Digital outputs, PWM Outputs, and so much more.
What might be the benefit of performing Failure Mode and Effect Analysis(FMEA) on these low-level functions?  Is the purpose of this exercise to catch low-level software design problems?  Also, would this analysis help in debugging?
How to perform thorough FMEA on low-level software for a typical Automotive ADAS Controller?
For example, one Failure mode may be Loss of I2C communication or intermittent I2C communication.  How to come up with all possible potential effects of this failure?  How to come up with all possible Potential Causes of Failure?
How to identify all possible Failure Modes?


texts: Why should I use a logarithmic pot for audio applications?

texts:
Just got really curious about it reading this answer from Spehro Pefhany. There Spehro comments that one should use a logarithmic pot for audio applications. So I googled for it.

The best article I could find was one titled "Difference between Audio and Linear Potentiometers"[1] which now seems to have been removed from the original website.

There they said this:

  Linear vs. Audio

  Potentiometers, or "pots" to electronics enthusiasts, are differentiated by how quickly their resistance changes. In linear pots, the amount of resistance changes in a direct pattern. If you turn or slide it halfway, its resistance will be halfway between its minimum and maximum settings. That's ideal for controlling lights or a fan, but not for audio controls. Volume controls have to cater to the human ear, which isn't linear. Instead, logarithmic pots increase their resistance on a curve. At the halfway point volume will still be moderate, but it will increase sharply as you keep turning up the volume. This corresponds to how the human ear hears.

Well, I'm not satisfied.

What does it mean that the human ear isn't linear?
How does the log changes in the pot resistance relates to sound waves and how the human ear works?

[1] Original (now broken) link was http://techchannel.radioshack.com/difference-audio-linear-potentiometers-2409.html.


texts: FCC part 15 "must accept interference from other sources": what does this mean?

texts:
I've googled around a bit and here are the interpretations I've found in non-authoritative sources:

that the device is unable to filter out interference caused by
other certified equipment
that if there is interference, the device must not "complain" about it (whatever that means)
that if there is interference and your device fails to work, you must not complain about it (i.e. you cannot sue for failure to perform the function)
that if there is interference, the device can't do anything about it (though I can't think what it possibly could do about this other than actively seek out the source and shut it down, sci-fi style)
that the device is actually required to work correctly regardless of any interference

So what does this phrasing actually mean? Is it phrased poorly or am I misunderstanding it as a result of not being a native speaker?


texts: Is PCB testing of all nets after assembly required?

texts:
That is my first time asking an assembly house to produce 200 units of a PCB (and not the usual 3 or 5 PCBs). The assembly house came back to me saying that the testability of the board was bad and that they need to have 1.2 mm pads on the bottom side of the PBC for all nets... They require such large pads because beds of nails are a much more economical option than flying probe for 200-400 units since they can do it in-house.

The PCB we are talking about :

4-layer PCB (a few power supplies, a battery charger, connectors to screen and other accessories)
only surface-mount components
all components on top, 60 euros/PCB (bare PCB + assembly) for 200 units.
we are targeting 200 units at first, and probably 400 units total. (It is already revision 2 of the same board).
consumer product

I'm a bit suprised by this request from the assembly house. Using large pads or adding vias on all nets seem to be extreme to me. I'm also a bit surprised not to have noticed such testing pads on other products (if that's even possible to fit them sometimes?).

My questions are :

Is testing of all nets required for consumer products? Is it common practice? I was more thinking about some higher level tests (if the screen works, if all buttons works, if the battery charger delivers the good amount of current, etc.).
Is adding 1.2 mm pad on ALL nets common practice for PCB?
is it normal that the assembly house increases the assembly cost if they don't do the bed of nails? The cost of the bed of nails is almost as much as burning (fully) 40 PCBs...
I may be a bit naive there but they seem to say that they want to test all nets in order to check if resistors/capacitors/others are good. Is it so common that an assembly house mixed up components on a few boards?


texts: 240V 5A PCB traces - stitch double sided or not?

texts:
If I have traces connecting a relay to an terminal block (10A relay, 6A terminal, 5A expected maximum load) and I double the traces up on both sides of the board (mirror the traces on the top and the bottom) to double the current capacity of the traces (effectively turn 1oz copper into 2oz), is it best to leave them as they are or to stitch the traces together with vias?

The longest trace is just under 1".

Would the stitching adversely affect the current capacity of the traces and defeat the objective? Or would it allow for better heat management and thus actually increase the current capacity?

Or would it have no effect whatsoever?

And what of the effect of 50/60Hz through the two traces with FR4 dielectric between them? Would doubling, with or without stitching, have an effect?


texts: Help needed to select proper electric motor for constant drive

texts:
I need about 180 degree movement, back and forth in about one second. Maximum torque is about 2.2 kg ⋅ cm.

I have tried RC-servos (up to 20 kg ⋅ cm), but they all burn within first 12h (maximum drive time is always omitted from the specifications). The motor should be able run at least month without stops.

Low price is the key. DC motor with some sensors? Stepper motor? Other ideas? I would highly appreciate advice, which I can verify from specifications.

Edit: For clarification the servos died after over-heating. Nothing visible in gearbox nor in the electronics. So, most likely not from mechanical wearing out.


texts: Which is better for the 555, a smaller capacitor or a larger one?

texts:
As I understand it, there are many ways to combine two resistors and a capacitor to give the same time characteristics in a astable 555 setup.

My question is which is better, a larger capacitor or a smaller one? and does it effect power consumption?


texts: I'm building a 48V e-Bike. I want to use a Predator 212 to spin a 12V car alternator to use as a onboard recharger. How do I connect this?

texts:
I have 4) 12V LiPo batteries, rated at 16A-hrs. They'll be connected in series, to make a 48V system to power the motor on the e-Bike.
I also plan to use a Predator 212 (Harbor Freight engine) to spin a single wire AC Delco alternator as an onboard recharger.
How would I go about hooking this to the batteries to "recharge as I ride", so to speak?


texts:
I am attempting to use a SPI NOR flash memory IC that is said to support CFI (Common Flash Interface) and the JEDEC flash command set. This sounds great however I have been unable to find any documentation on what the JEDEC command set is specifically or how to interface with this device.

Does anybody know of a reference for this information?


texts: How often do AVR's actually glitch and need a watch-dog reset in the real-world?

texts:
Have you ever seen an otherwise happy AVR spontaneously glitch and require a reset?

Assuming:

a nice stead power supply that stays inside the specified range
a correctly sized decoupling cap directly between Vcc and ground
normal (not too noisy) household conditions

...what is the real-world MTB glitches?

I've had hundreds of AVR's running for years and I don't think I ever have seen a real glitch, but maybe I am just lucky?

Note that I know that you should always use a watchdog, I know. Don't flame me - but if the likelihood of glitches is very low, there could be applications where it would be reasonable to maybe not use the watchdog to get lower power usage in sleep.

Note also that I understand that the watchdog also protects you from firmware bugs, but I am only asking about spontaneous hardware glitches.


texts: Where do USB ports on laptops typically source their power when the laptop is charging?

texts:
Suppose you are at a coffee shop and your phone battery is low. You decide to plug it in to your laptop via USB to charge it. At this point the laptop's battery serves as our energy source for charging the phone.

But then you realize your laptop's battery is also low, so you plug your laptop in using the AC adapter it came with. So the coffee shop's electricity is charging the laptop battery.

Now, do most charging circuits in laptops switch to source power (specifically on USB ports) from the AC adapter or not? Would the current draw from the AC adapter increase as a result of having the phone being plugged in, or would it just take longer to charge the laptop battery to full capacity?


texts: I got Step down transformer which reduces voltage from 230 VAC to 40 VAC ~ 100 amp. I can weld with it while having no problems. Also I got another one step down transformer which is three phase, but has one single phase input, where it's now powered. Outputs about 600 amps 6 VAC. I've picked up 4.2 mm welding stick and it doesn't create arc it just melts down in seconds. How do I weld with this thing ?


texts: Cadstar : Define pad only on bottom or top layer

texts:
I currently design with cadstar and when I want to check my PCB layout I see my SMD pads defined both on top and bottom layer. I think it is normal because these pads are defined on the both side in the assignment.

Do you know how is possible to define directly on pcb if the pads are on top or bottom side ?

Thanks,


texts: Want to apply EE knowledge -- which microprocessor would you recommend?

texts: Here's my story:  I got my electrical engineering degree BUT I do not have a lot of experience with circuits (OMG, right? O_O).  Most of my education was about communication theory, so I really feel incomplete and want to apply my knowledge somewhere and start making something on a microprocessor.  It would also be a good skill to develop for the workforce.  Do you folks have any recommendations as to what type of microprocessor I should be working with?  PIC?  Arduino?  Others?  What is used most in the market and for production purposes? Does it matter?  I hear Arduino has a very good community for help, but I hear it is more for "hobbyists"?  Is that necessarily a bad thing?  Any insight is much appreciated.  Thanks!!


texts:
To supply 5V to a PIC in a 12-15V automotive environment, I have so far been using variants of 7805s, or the HV varieties of PIC. While they work, obviously they aren't really of sufficient protection for the environment. In particular reversed polarities, and battery 'jump starts' can cause problems of the destructive variety.

My circuits draw very little current (100mA is a typical maximum) and I solder through hole by hand, so I would avoid SMD

Can anybody recommend either a good way to protect a simple 7805 (or 78L05), or some alternatives to the 7805 that are more suitable for the environment? I have so far found a suggestion of LM2937, but this is relatively very expensive (some 10x more than a 7805)

As a side question, is there a good way to find automotive grade components? I usually use farnell's catalogue, but they don't seem to have 'automotive' in their parametric search so it is a matter of scouring datasheets, which is time consuming.


texts: Displaying a 2-digit integer on two 7-segment display

texts:
I'm having trouble displaying a binary number into a display. I'm not sure of how to split a number in binary into its individual numbers.

For example, if I want to display 25, I want to split this into "2" and "5" in binary.
I have 8 bits coming in and would like to split it into two 4 bit parts with the first 4 bits representing the first digit in binary and second 4 bits representing the second digit in binary.

EDIT: To clarify, I'm trying to do this using logic gates.


texts: Temperature compensation resistor value for oscillator circuit

texts:
I'm reading the CEM3340 datasheet, section "operation of the temperature compensation circuitry" over and over and still can't understand how do you choose value of the tempco resistor. In the typical application diagram the value is 5.6k. This exact value is hard to find, so I want to understand how do I choose the resistor value for another supply voltage, and what do I have to modify if I choose another tempco resistor value.

I understand why this resistor even needed: the transistor pair in the oscillator IC has temperature drift, so the resistor with 3500ppm drift would compensate by providing changing voltage (or current?).

The supply voltage in the typical application is ±15V, but I'm going to do ±12V.


texts:
For long version, include bracketed text.

I am 1.5 years into my career as an electrical design engineer doing MEP/architectural-type engineering, with a BSEE and I passed my FE exam. We do equipment design, power, lighting, feeding from utility, etc. I am very frustrated by my lack of progress and feel thoroughly unprepared by my degree education. Are there references or guides for having a better understanding of these concepts? I know it is a vague question, but after over a year, I still feel like I'm fumbling around in the dark with every task I'm assigned. Some contextual reference, ideally that can drill down to fundamentals, is what I need.

[Everyone at my job says college didn't prepare them for this position. My university was an IBM feeder school. I know how to make semiconductors from the molecular level upward, but still don't have a practical understanding of AC circuitry. I can make and program robots, and even process communication signals... It's incredibly frustrating. The problem I had, even in school, is the textbooks never made sense. I'm a visual learner, and I never forget when I truly, actually learn something, but I never really learned power. I could switch careers, but I like being able to help build hospitals, and I'd rather remedy my ignorance than try and work around it. It doesn't seem like my supervisors expect more from me than I currently provide, but it is incredibly demoralizing not being able to live up to my own standards. An example I just ran into is LSIG breakers: When are they required? Why? What regulators dictate their use? And isolation panels: How do I know what equipment should run through one (I am still bad at understanding the role of 1, 2, and 3 pole circuits). I was on a survey the other day and don't know what made one panel preferable to another (I am aware of emergency, critical, and differing voltages, but not how upper stream distribution panels are organized), or what might have been out of the ordinary in the space we were surveying. I dont know what to look for. How do you track panel loads for existing panels, how do panel loads affect upstream power, etc. I purchased the electrical engineer handbook, but it is more high level jargon, which would be fine if I had a better fundamental grasp on everything.]

Is there a resource for a straightforward holistic explanation of power systems? And is there a good resource for understanding AC power?


texts: Most households in this planet have multiple 'wires' - one for plain electrical power, one for telephone, one for internet and one for cable TV (there may be more).  I had heard of PLC (power-line-communications) before, is it not possible to merge all lines into one - so that every household can be 'indexed' and 'reached' using a single line, which is principally an electrical power line.  Does a power line serve better - only serving as a power line and not as a channel for communication (telephone, internet, cable TV etc)?


texts: Home-built machine: how to make the 110 V AC electrical installation part "by the book"? (safety, "code")

texts:
I am building a machine to manufacture optical components. The source of mechanical power is a 1/4 HP motor that's plugged into 110 V AC. Various parts of the machine receive mechanical power via belts and pulleys. The machine is a large square-ish box made of plywood. Inside it, there's the powerhead module containing the motor, hooked up to the machine via belts.

Grinding / polishing the optical components takes place on top of the machine. The process can be occasionally messy, with water-based slurry droplets being sometimes splashed over the top side.

Here are some images of previous machines made by other folks. The front/right/outside:

The back/inside, with the powerhead module, and the motor almost completely hidden behind the central plate of the powerhead (see the AC cable going to the motor over that plate):

I want to do the 110 V AC part "nice", or "by the book". Near the front/right corner (closest to camera in the first image) I want to add a panel (a small box), jutting out of the big box, containing: the main AC switch, a 16x2 LCD and microcontroller, and perhaps a circuit breaker.

I want the main AC cord to go inside the machine, lay close to the bottom edge back-to-front, then up the front/right edge, come out of the box through a hole, and into the front panel. There, it should go into the main AC switch. From there, it should split in two:

One branch should go into the circuit breaker, then back into the big box through a hole, and then into a regular 110 V AC wall socket mounted inside the big box. The powerhead should plug into that internal 110 V socket, for easy removal (the pulleys on the powerhead need to be adjusted or changed periodically).

The other branch should go into a 5 V "wall wart" supply, and then into the microcontroller connected to the LCD display. All of this branch should stay inside the front panel.

I've done lots of low-voltage electronics design, analog and digital. But I have very limited experience with mains voltage AC, building "to code", etc.

I assume there are some rules to follow when designing the AC part for a machine like this, but what are those rules? In terms of parts and components - should the internal AC wall socket be contained in a box of sorts? Should I run the AC cables inside conduits? (and what kind?)

I assume the rules can't be too different from building a house "to code".


texts: Logarithmic amplifier with high slew rate -- mutually exclusive?

texts:
Does anyone know if the basic construction of a log amp (with a diode or BJT providing feedback from output to input) is in conflict with any ability to reach high slew rates?

I've been looking (octopart, digikey, mouser) for a logarithmic amplifier chip with a slew rate of at least 350 V/uS, preferably higher (2 kv/uS would be good).  I'm seeing plenty of op-amps with slew rates in the Kv/uS range, and even a few instrumentation amps with respectable slew rates, but log amps with high slew rates don't seem to exist -- what I'm finding is log amp slew rates down around a few dozen V/uS; too slow by an order of magnitude.

Am I on the right track if, instead of looking for off-the-shelf log amps, I instead start with one of the high-slew op amps and use some sort of fast diode?  Is that the limiting factor, or is there something else I'm missing?

The application is single-ended, multi-channel, DC most of the time with infrequent and random input pulses ranging from a few mV to a few volts, rise times of a few nS, output same but log scaled. The output gets fed into an A/D converter; one goal of the log scaling is to bring the low-amplitude pulses up into a more useful area of the ADC's range; another goal is to attenuate large pulses to prevent clipping.

(Starting some notes as possible answers to my own question...)

Breaking out my Art of Electronics; starting to think that what I'm really looking for is a log converter; since the diode's nonlinear curve is mainly what I'm after, a fast diode plus a high-speed op amp does seem to make sense.  I'm worried about the noise from the diode, but don't remember how to quantify that.  Will study.
There is another SE question that looks related to the idea of the fast diode:
How to construct high speed logarithmic amplifiers


texts: Output Voltage Swing vs. Load Resistance of an Op Amp

texts:
What does the "Output Voltage Swing vs. Load Resistance" signify? Lets say I want to get a gain of 400 from an op-amp. I can use any one of the following combination

Gain = -(R2/R1)

Case 1: R2 = 400 Ohms; R1 = 1 Ohms -> Gain = 400
Case 2: R2 = 40000 (40K) ohms; R1 = 100 Ohms -> Gain = 400.

From op-Amp perspective, does the above scenario do something different?

Picture of "Output Voltage Swing vs. Load Resistance" for AD712 is attached below


texts: How to calculate the collector and emitter resistors in a differential amplifier with transistors

texts:
I'm refreshing my electronics knowledge a bit (after 30+ years), and I'm trying to build an audio amplifier from scratch without integrated circuits (transistors, and mosfets only).
I'm trying to build the input stage, which is a differential amplifier using 2 transistors. I'm currently simulating it with LTSpice, but I seem to amplify only the positive part of my input signal. I guess it's because of the values of the emitter and collector resistors.
I understand the principle of a diff amplifier, but I'm struggling with the practical setup.
Can somebody explain to me (or point me to a site) how to calculate those resistors?
I guess there should be current flowing through R2 while out1 should be at ground level, if no signal is applied?
I included my schematic and the waveforms.
Thanks a lot!


texts:
I want to calculate the integral of a voltage pulse. I have designed this circuit to do the integration. I am using a non inverting integrator:

The op_amp_2 is the voltage pulse. Comp_1 is used to discharge the cap once the pulse has ended. So that the integral of each pulse can  be found.

This is how the output looks like:

I wonder why the output falls down as the pulse ends. Is this because of the bias current of Op-AMP? I am specifically using a low bias (~pA) current opamp.

How can I avoid this?


texts:
I have used LiFePO4 batteries, only in discharge mode, by down to -15 deg C (charging was done 'back to the warmth'), and they worked fine. But from what I read it looks like Li-* batteries do not like to be charged by minus temperatures.

I would like to use large LiFePO4 cells with a solar panel by negative temperatures (typically -15 deg C, may be down to -30 deg C). I will have quite low charging currents, max 1 to 1.5Amps for a 40Ah cell. Do you think it may be OK to charge at such low rates (this guy seems to say no: Solar powered single cell LiFePo4 charger circuit ; but here it sounds like very low charge may be ok http://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures)?

Has anybody more specific experience with this? Or has anybody knowledge of a place where I may get military / space grade cells that accept cold if usual LiFePO4 is a no go, or alternative battery chemistry solution? FYI, here are the cells I use as by now:

http://www.batteryspace.com/lifepo4-prismatic-module-3-2v-40-ah-10c-rate-128-wh-----un38-3-passed-dgr.aspx


texts: How do single phase BLDC motors start in proper direction?

texts:
There are descriptions on internet of the single phase BLDC motors which are powered by Vdc (such as PC cooling fans 12V). Interestingly pictures shown describing outrunner type with equal number of poles and stator coils (usually 4 both). One detailed application note provided by Microchip :
Sensored Single-Phase BLDC Motor Driver
Here is a picture showing the motor and it's control using a full H-bridge:

Controlling full H-bridge is shown reversing the current flow in sync with Hall sensor reading.
What is confusing to me that there are no means to ensure proper direction of the rotation at startup. Even more confusing is the following text from this app note (page 4):

      The  toggling  from  Forward-to-Reverse  mode produces  a  clockwise rotation,  while  toggling  from Reverse-to-Forward    mode    produces    a    counter-clockwise rotation.

How is it possible? All the toggling of the phase current does is to create repulsive force between stator coils and magnetic poles (knowing the polarity of the current position from the Hall sensor reading) but does not make the poles rotate in any "known" direction. These motors work similar to "switched reluctance" as the poles are driven to the position where their magnetic flux get fully aligned with stator coils flux. In this type of motors Magnetic flux lines of rotor magnets and stator coils are not perpendicular to define the direction of the rotation.
Do the PC cooling fans have equal number of stator coils and rotor poles? How do such type of motors start rotating in one direction only?
Thanks in advance for any input on this.


texts:
I am new to world of ARM trying to understand the core concepts been reading forum where ARM architecture and ARM instruction set is used interchangeably.  ARM architecture as i understand is a CPU architecture that many companies use it directly And some companies build there wont chip like apple which support ARM ISA .

The benefits provided by ARM architecture or instruction set ? Like low power and high performance/per watt ?


texts:
I've been thinking about designing and building my own bench-top power supply for general use. I envision the primary use to be with prototyping low-power analog/digital circuits with the occasional small DC motor and other electro-mechanical devices. The primary reason I'm doing this is to become more familiar with power supply design, and having a useful bench-top supply is an added bonus.

Target specs and device goals so far, recommendations/suggestions are welcome:

Powered from mains electricity (I live in the US, so I'm targeting ~120VAC@60Hz).
Mains isolated.
Variable voltage and current output, at least 1A max output current and 12V max output voltage. Preferably I'd like a 15V or 24V max output voltage as well as split supply, though these aren't critical specs.
Decent efficiency. I haven't quite spec'd out a target efficiency yet, but I would expect greater than 50% efficiency. I've heard of SMPS supplies going up to ~80-90%, possibly higher.

Since this is taken as primarily a learning exercise, I've been seriously considering if I should turn this project into one where I can learn more about using mains electricity directly. I'm hesitant to do so because I understand the very real danger involved with getting something wrong on mains and I could use a wall adapter (either AC-AC or AC-DC) or pre-built constant voltage unit to power my supply to reduce the risk associated with working with mains. I'm curious as to what you guys think about this, as well as any recommended resources I should check out before working with mains directly. If you have any suggestions for projects which would be better suited for a beginner working directly with mains that'd be great, too.

If I did choose to go with the direct mains method I think I'd starting out with a basic transformer to provide isolation and reduce the input voltage, then use some circuitry to get adjustable voltage/current.

The basic interface with the mains:

The main side is tied across the one side of the transformer, and the powered circuit is tied to the other side. The signal is then rectified through a diode bridge, and the output is filtered using a large capacitor in parallel with the load. If I wanted to, later down-stream I could use circuitry to further regulate the output voltage and current (something similar to what is done here).

The voltage across the load should be (assuming a sufficiently small load or large capacitor, as well as a near-ideal transformer):

\begin{equation}
V_L = V_{main} \cdot \frac{N2}{N1} - 2 * V_D
\end{equation}

Where Vmain is the amplitude of mains electricity (~170 V in the US).

This is a basic design which works in theory, but what real-world considerations do I have to take into consideration when designing the actual interface with the mains electricity? I know that a highly capacitive or inductive load will result in a poor power-factor, but since this is a general purpose power supply I'm assuming that whatever load gets attached down-stream will be designed to compensate for that rather than try to have the power supply do the compensation.

An alternative approach is to use a switched-mode design, but I haven't found many useful resources on how to design/implement one. From what I understand a SMPS uses much higher frequencies so the transformer can be smaller while still providing a semi-stable DC output. What I don't understand is how you're suppose to take the 60Hz signal from the wall and up that to a ~10kHz or even ~1MHz input for the SMPS transformer.


texts: Faulty display behavior using a Atmega328 due to (wrong?) logic voltage level

texts:
I have built a little circuit using a Atmega328P to drive a DD-32645C-2A display using a connector board. The display uses a SSD1303 driver.

So here is my circuit:

Pretty straight forward, I think. I use the C port to set the control pins of the display and the D port to send commands/data. Here is the code I programmed onto my MCU:

#include <avr/io.h>
#define F_CPU 8000000UL
#include <util/delay.h>

void inital(void);
void write_c(unsigned char ins_c);
void write_d(unsigned char ins_d);

int main(void)
{
    // set ports D and C as output
    DDRC = 0b11111111;
    DDRD = 0b11111111;

    inital();

    while (1)
    {
    }
}

void inital(void)
{
    PORTC &= 0b00000000;    // reset display pins
    _delay_ms(150);         // delay 150ms for reset
    PORTC |= (1 << 5);      // set RES to high

    write_c(0xAE);
    write_c(0x81);
    write_c(0xAF);
    write_c(0xA8);
    write_c(0x3F);
    write_c(0xA0);
    write_c(0xD3);
    write_c(0x00);
    write_c(0x40);
    write_c(0xC8);
    write_c(0xDA);
    write_c(0x12);
    write_c(0xD9);
    write_c(0xF1);
    write_c(0xDB);
    write_c(0x49);
    write_c(0xA4);
    write_c(0xA6);
    write_c(0xAF);
}

void write_c(unsigned char ins_c)
{
    PORTC = 0b00010100;     // set pins for sending commands
    PORTD = ins_c;
    PORTC = 0b00011111;
}

void write_d(unsigned char ins_d)
{
    PORTC = 0b00010101;     // set pins for sending data
    PORTD = ins_d;
    PORTC = 0b00011111;
}

Also not to complicated, I think. I set up my C and D ports as outputs and call my initialization function. This function resets the display and sends a series of command to set it up(I simply copied this routine from the display's datasheet). The other two functions simply send a byte of data using port D.

Now here's my problem: The setup routine seems to work fine, but my display looks like this(I apologize for my bad camera):

The first picture shows what I got initially, which is not really convincing. Now, after double and triple checking all of my connections and code for errors, I accidentally forgot to reconnect the VDD power(3.3V) to the connector board, which drives the display driver's logic(see page 5 of the connector board datasheet in the comment). And that result is shown on the second/lower picture above.

Still not perfect, but much closer to the desired effect. There should be on big blue rectangle and four smaller colored ones at the top. But still some pixels won't light up.

Has anyone a idea what is going on here? Not connecting the VDD pin for the display driver's logic doesn't make any sense to me, but makes my display work better.


texts: Trouble understanding rated values for a transformer

texts:
Say you have a 10 kVA 500/1000 V transformer and the transformer is operating at full load. My understanding is that then the load voltage would be |V1|=1000 V, and the load current would be |I2|= 10 kVA / 1000 V. But say we use the model of transformer below with an inductive load then V1>500V which its above its rated value of 500 V?

My question is therefore does full load mean that the primary voltage is at the rated value or the secondary? i.e that V1 is 500V but V2 is not 1000V?


texts:
I want to design a four layer PCB, where on the top and second layer are voltage up to 600V present. While I find many information about trace spacing, I don't find anything about isolation between the different layers. Is it possible and safe to have a voltage (difference) of 600V between two (or more) layers?
I'm planing to use a normal FR4 PCB and I know the breakdown voltage of 300V/mil. But is the breakdown voltage also safe?


texts: Should we use wheatstone bridges nowadays?

texts:
For measuring strain gauges, the Wheatstone bridge is the historical choice.

In a quarter Wheatstone brigde (\$350 \Omega \$ typically (?)), with a high input impedance amplifier, and some bridge power voltage \$V\$, the ratio between the bridge output voltage w.r.t. any resistor is 1/4, which is the same ratio in a voltage divider between the output voltage w.r.t. any resistor, compared with a stable voltage reference of \$V/2\$.

A voltage divider with a voltage reference would have a voltage noise of about 35.16 nV/rtHz (from a voltage reference of 35 nV/rtHz plus two resistors), and the Wheatstone bridge a voltage noise of 4.86 nV/rtHz (from four resistors), which should be enough (?) for most ADC systems (i.e. for 24 bit, 0-5V range: 300nV resolution).

And a voltage reference (\$0.02\%\$ initial error, \$2 \ ppm/C^\circ\$, AD, ADR4525), would be more stable and precise (?) about \$4\ ppm/C^\circ\$, than a precision resistor (\$0.005\%\$ error, \$2 \ ppm/C^\circ \$, Vishay, MR100), about \$8 \ ppm/C^\circ\$.

Hence, why bother using Wheatstone bridges?


texts: I'm trying to pick the components to use with this DC/DC Buck-Boost Converter. At page 13, the datasheet says, that for input voltages higher than 4.5 V I need to add an extra 2Ω/1nF RC snubber between SW1 and GND. And my concern is, what resistor size/package should I use? How do I calculate the max current that would go through that network at 1 MHz switching frequency? I know that I could calculate capacitive reactance of that capacitor to know the current, but that seems appropriate only for sine wave voltage, not for a PWM signal with rapidly changing duty cycle.


texts: USB hardware connection causing software reset

texts:
So I'm very new to USB (using 2.0) and I'm still working my way through various application notes and the official USB spec. Currently I'm working with the ATmega8U2 as my controller. In one of the AN that I worked through AN_146 USB Hardware Design Guidelines for FTDI ICs and it showed the following schematic

http://www.ftdichip.com/Support/Documents/AppNotes/AN_146_USB_Hardware_Design_Guidelines_for_FTDI_ICs.pdf

So my question is: what is RESET#, and does it hold the entire MCU in a "wait state" until it detects a USB connection? My main concern is the possibility The MCU will only work when a USB in connected to it, because this MCU needs to do more than just handle the USB Data logging.

Thanks for any feedback/advice. If you know of any great resources for implementing a USB Data logging application I'd appreciate some additional references/sources


texts: High current draw at start up of DC motor. How to understand if the battery can withstand it?

texts:
Suppose I have a solar powered plant like this one below:

simulate this circuit – Schematic created using CircuitLab

The solar panel charges the batteries and, when needed, the power is drawn from the batteries to power the load which in this case could be a DC motor or an AC motor depending on the application. For the sake of this example, let's say this is a 24V DC motor. Suppose the controller is just a switch.

By taking a look at the datasheet of some of the loads, most of them need a very high current at the start. For instance a centrifugal pump I took as example needs 78 A at the start.

From a theory point of view, if I consider the battery an ideal voltage generator, there is no problem. Furthermore, since 78 A are drawn for just a small time (suppose 1 second for the sake of argument) during the start up and then the load starts to draw the usual working current which is far lower than, 78 A, not that much extra-work is required from the battery after the startup.

However, batteries are far from being a perfect voltage generator, how can I understand if a battery is able to withstand such high current draw? A 120Ah battery in principle could easily do this since in theory it could supply 120 A for 1 hour (and in my case I just draw 78 A for a second) but I have some doubts that this reasoning could hold in practice.

Please address the following points in the answer:

What is the technical parameter in the battery datasheet I should be looking at? (Max current draw??)
What is an appropriate rule of thumb to address the start up current draw while not under/over sizing the battery package?
Are the reasonings above correct? (at least in theory)

Thank you


texts: Is there any way to connect 20-25V 1MHz digital input to arduino?

texts: I need to connect 20-25Volts 1MHz digital input to Arduino. Are there any possible ways to do it? I think, using optocoupler will be useless because of high frequency. Any other ways to solve it?


texts: Earthing (Grounding) neutral terminals in transformer and converter

texts:
In a TN-S system and for a configuration below (single-phase isolation transformer, rectifier and single-phase DC/AC converter) what should be earthed (connected to PE wire)?

I've been going through various sources and there are different views. In Ref1 it says that isolation transformer output is floating and should be referenced (grounded). Same as in Ref4, page 20 where neutral-ground bond is mentioned. However, Ref2 says in case of fault, "current path is contained within the secondary of the transformer, the RCD will not detect an imbalance and will therefore not trip. The operator is now in an unsafe environment with the potential for an electric shock as they may become the lowest point of resistance for the leakage current". Finally, Ref3 says "the inverters generate a neutral wire that is grounded in the auxiliary power supply", i.e. inverter output terminal 4 should be grounded. Not sure if this implies grounding rectifier terminal 4 as well. This reference is for rolling stock applications, so there might be some different general requirements. I could not find any recommendations on what to do when the inverter is supplying load (i.e. off-grid application).
Since the system is TN-S, neutral has been referenced to the ground at the source before entering the main panel. Do I need to re-reference neutral at every output terminal (transformer N, rectifier 4 and inverter 4)?
I guess, if there is a 400 V input, then it would make sense to reference inverter's output and create a TN-C system (Ref4, page 20).


texts: Trouble turning on relay using PNP transistor

texts:
I am having problems turning on this relay:
https://omronfs.omron.com/en_US/ecb/products/pdf/en-g6qe.pdf
Using a transistor whose base is connected to a digital signal of an Arduino Nano.
The schematic I am using is attached. I have tried both, BC558 (PNP) and BC549 (NPN) transistors. Neither of these works. I would've figured the PNP should work because it is a high side switch but it almost seems that the Arduino Nano does not supply enough current to switch on the transistor. That is because when hooking the transistor's base straight to a power supply it does work but once again the Nano just can't seem to handle it. I am pretty novice at this so I am looking for some help. What am I missing here?
Thanks in advance


texts:
Over a 200ms period of which this circuit regulates a 500mA current, the current drift downwards for about 0.4%.

At first I thought it was due to R202 temperature coefficient, but from my calculation the drift related to R202 should only be in the range of 0.05%.

R202 is a 2ohm, 2W, 2 point, 100ppm/°C resistor and from the touch it barely heats at all.

Any other idea where could be the source of the drift ? Solder of the resistor pads ?

The input at R198 is stable.

UPDATE 1:

To my surprise, this morning I restarted the circuit, it hasn't moved a bit overnight, and measured the drift, before touching anything. It was down to 0.1%, the night before it was about 0.4%.

Now as time pass, the drift is increasing little by little and I guess in 1h it will be back to 0.4%.

For my tests, I do a 200ms pulse every 1s and is constantly running. The circuit does heats up a little bit.

UPDATE 2:

Here is a graph with 3 measurements done at different times. As one can see, the first two have about 0.15% drift, the last one has 0.7% drift.

The drift seems to vary over time, and so far I've failed to understand the reason nor to find a way to influence the drift.

The circuit hasn't change between those measurements, I've played around with power supply, voltage rails, I tried to heat the circuit up, but no changes.

UPDATE 3:

Removing C121 and C122, affect the stability, but the drift remains the same.


texts: Do I always connect all GNDs together between devices?

texts:
I'm trying to interface with an RS232 port on a home automation system.  The RS232 port only has RX, TX, and GND pins connected (according to the documentation).

If I'm interfacing with an Arduino (and an RS232 to TTL converter), do I connect the RS232 GND with my Arduino GND and all the other GNDs?


texts: Is this method of charging a lead acid battery safe, or even good!

texts:
so I need to know if my method/circuit of charging a 6V Lead Acid Battery is safe or even workable! so this is the circuit and battery info!

simulate this circuit – Schematic created using CircuitLab

6V/2Ah Lead Acid Battery
Model - SD620
Type - VALVE Regulated
Voltage Charge Type - Constant - "Also it writes Constay, I think
it's a typo!"
Cycle Use - 7.25V - 7.45V
Standby Use - 6.8V- 6.9V
Initial Current - Less Than 1.2A


texts:
I am using a a TI TLV3202 comparator (U2B) with a bridge circuit as shown in the schematic below.

It is followed by a DG4157 analog switch. This is related to this question I had asked earlier.

After power-up and when RLS is approx. 50 k\$\Omega\$ range things seem to work - the voltage at TP13 varies with RLS. However, if RLS goes to approx. 1M or is open circuited, the voltage at TP13 goes to approx. 5V (as expected), but then STAYS at 5V, regardless of the resistance of RLS. In other words, it seems that the positive input of the comparator latches 'high'.

What could be causing this?? The lead length of the positive input is relatively long (~3 in) - could this be some sort of parasitic capacitance feedback effect from the output? If so, is there a way to address it without laying out the board again?


texts: Common emitter characteristics in the saturation region

texts:
I'm trying hard to understand the different modes and regions of operation of BJTs. The behavior of transistor in saturation region is so confusing. I've searched in forums but couldn't get a convincing answer. Here is what I've understood. Correct me if I'm wrong.

So a Transistor enters saturation region when the collector-base junction is forward biased. This happens when the base current increases causing a proportionate increase in the collector current and decrease in voltage across the collector (\$V_{CE} = V_{CC} - I_CR_C\$).

What happens after the transistor enters saturation? I know that \$V_{CE}\$ will be very small (around 0.2V) and the transistor will behave as a closed switch. But what exactly will be the collector current?

Can I now view this as two back to back forward biased diodes?

Why is the current will be maximum in saturation region? Why doesn't further increase in base current cause changes in collector current?

And if you see the \$V_{CE}\$ characteristics in the saturation region (see the image below), the curves are bunched together. \$I_C\$ actually approaches zero as \$V_{CE}\$ is around 0.2V (which is nearly the voltage across collector in saturation). But should we not have maximum current in saturation region?

I'm missing some crucial point. The characteristic curves in Saturation region are completely confusing. Help me understand this :(


texts: Going under specs for a linear regulator?

texts:
I have a Microchip PIC board (18F46K22) which has a VIN pin to connect to a power source (7vdc + supply).

What happen if I feed 3.3V to the VIN which goes through the 5V linear regulator (ST 78M05)?

The 18F46K22 is able to run on 5v or 3.3v supply. I would like to force the board to run on 3.3V so it will solve my logic voltage level issues easily.

I am asking because I can't find any information regarding going lower voltage than the linear is normally regulating.

Thanks!


texts:
And I have forklift battery 24V which is almost at the end of life. The 24V charger is very strong and heat battery and not working properly.
I have one 12V battery charger, which works very fine.
24v Lead acid battery has 12 cells in series. And I can read 12V on first 6 cells. It is safe to charge this first 6 cells and after then rest six cells with 12V charger?

Thanks


texts: Troubleshooting a faulty filter circuit in a PAL CRT display

texts:
I have an old CRT monitor (Phillips CM8833) which I am attempting to repair. When displaying a composite PAL signal, it only shows a black and white image, but it is still able to display RGB signals correctly.

The composite signal is filtered into chrominance and luminance portions, with the chrominance signal sent into a TDA4510 color decoder. The U and V output are fed with the luminance (Y) into a TDA3505 control chip (which can also switch between the composite/YUV and RGB inputs, hence the RGB is unaffected). Here's an overview of the circuit:

I see the indicated signals at test points 9 (input) and 8 (luminance) but not at test point (chrominance), which suggests a fault with the filter circuit between points 9 and 7:

Probing between R529 and R554 shows an AC signal of 150mV peak-to-peak, one-tenth of the amplitude at testing point 9. Measuring between C554 and C556 the AC component is down to less than 30mV peak-to-peak, and after C556 (testing point 7) it's indistinguishable from noise.

I've desoldered and tested all of these components individually, and all the resistors and capacitors appear to be within specification. (I've also replaced the TDA4510, as a precaution.) The inductor, S555, doesn't have a value listed on the circuit diagram or the parts list, but it matches the value of the color bands on its side (red, violet, black, gold, making 27uH).

I've been reading up on the operation of PAL systems, and I think that this monitor is using a bandpass & notch filter to isolate the chrominance and luminance signals. (The CM8833 service manual mentions adjusting S533 to calibrate the "4.43MHz blanking circuit in the luminance circuit", which suggests it's using a notch filter.)

C555 and S555 look to be forming a parallel-tuned bandpass filter, but using \$f= \frac{1}{2\pi \sqrt{LC}}\$ with 12pF and 27uH I get a resonant frequency of 8.84MHz, twice what I'd expect for a chrominance signal.

I'm left with some questions:

Is my analysis of C555 and S555 correct?
Are C554 and C556 serving as decoupling capacitors, or do they have some other function?
What are resistors R529, R553, and R554 doing?


texts: Differential pair output to voltage amplifier transistor

texts:
When designing an amplifier stage, like this, how does it work in a linear fashion?

Suppose you're applying some feedback, the output may well be stabilized to zero, but the more "wrong"  \$R_C\$ is (in terms of base-emitter-voltage of \$Q_3\$ and quiescent collector current of \$Q_2\$), the more the differential pair is pushed away from its linear region. How is this dealt with properly?
Secondly, it is said, that the voltage \$V_o\$ is dependent on \$gm\$ of the differential pair, how is this meant?
Imagine there is a Capacitor for single-pole compensation between Collector and Base of \$Q_3\$ how does the \$gm\$ of the differential pair affect slew rate?
This is all a bit blurry in my head, please can someone help me clearing it up. Thanks

Edit: You can assume that the differential input is ideally 0, tied to gnd. At perfect conditions of \$R_C\$ the base voltage of \$Q_3\$ is exactly as needed to make \$V_o\$ 0V. But the slightest variation of either \$I_{C2}\$,\$R_C\$ or \$V_{BE}\$ of \$Q_3\$ make that impossible. So you could feedback \$V_o\$ to base of \$Q_2\$. But then you little by little leave the linear area of the differential pair with \$R_C\$ going "wronger". How can this problem be dealt with properly. And, as asked above, how is \$V_o\$ dependent on \$gm\$ of the differential pair?

Edit2: The amplification of the difference voltage of a diff-pair is as follows:

When I chose \$R_C\$ slightly wrong, I have a constant bias (\$v_{diff}\$) to achieve that \$v_o\$ is 0 (by feedback). Now when a signal is applied to the base of the input transistor, \$v_{diff}\$ is already offset and thus pushed further into non-linear region. How can this be avoided?

Edit 3: The problem could also be described this way: To get zero output through feedback, there will be \$v_{id} \neq 0\$ which would decrease linearity of the diff-pair since the incoming voltage to be amplified would rather alternate around a point left or right of \$x = 0\$ and therefore be in a more non-linear region. The worse the collector resistor of Q2 is aligned, the more linearity suffers. How can this be possibly avoided without having to look into the transisitors specification with a magnifying  glass, but rather have it work for various transistors?

Another main question is how the compensation capacitor is dependent on the \$gm\$ of the diff-pair. How do they interrelate?

The FETs are actually BJTs

I only know that this has something to do with slew rate, but I can't seem to find out what exactly.


texts: Isolate two audio inputs to amplifier circuits on ground connection

texts:
I am using an arduino to monitor the voltage of the input lines to a stereo amplifier connected to speakers. When the arduino detects voltage changes on Chan1 or Chan2 it activates an IR LED to change the state of the stereo amplifier and switch channels, power on, off, etc.

Chan1 and Chan2 are different sources (CD player, ChromeCast) coming to the stereo amplifier on RCA cables. The circuit below has a voltage divider to shift the voltage +2.5V with a small cap (C3) to isolate any DC. The circuit behind the voltage divider is a class-a amplifier based on this schematic

I've put Y splitter in the left channel of both sources. One branch of the Y splitter connects into the stereo and the other connects to J1 (CD player) and J4 (ChromeCast). Pins 1 and 3 of J1 and J4 both connect to a common ground. The arduino monitors the voltage levels on CHAN1 and CHAN2 on the base of Q1 and Q2.

This all works fine on my test bench with two different audio sources (phone and computer) and no stereo amplifier, but fails miserably when attached to the stereo amplifier. CHAN1 and CHAN2 cross-talk through the ground. Both CHAN1 and CHAN2 are detected as being on when only one source is playing. Even worse, when two sources are playing at the same time the audio of the other channel bleeds through the ground connection.

I've looked at this post about isolating ground between different elements of a guitar amp, but I'm not sure that this is the same problem I'm having.

How can I effectively isolate CHAN1 and CHAN2 from each other on the ground connection?


texts: How to join and connect two wires in one connector point professionaly in a high voltage PCB?

texts:
Regarding a HV (6KV) PCB design there is a part of the circuitry related to reed relay connection.

I have chosen a HV relay (datasheet) with flying lead connection in order to separate physically LV board from HV lines circuit.

The full circuit is only a signal distributor based on relays for input
multiplexing with output points. Hence, the HV PCB part could be very simple. I think it will only need connectors that receive the HV relay wires.

Full circuit consists of 8 points that:

Every point will be connected to B1 or B2 signal point towards Ai relay terminals.
But Every point (1..8) can't be connected (A1 and A2, A3 and A4, etc..) to B1 and B2 simultaneously. So it could fit well a DPST relay, but they do not exist for my electrical parameters. So we will use 2 relays per point: 1NO + 1NC or NO + NO. Hence we have Ai points, being i = 8 points x 2 relays.
Every one of the 8 points will have its connector interfacing the outside.
Important is that maximum current through these wires will be few mA.

This involves the two wires, A1 and A2 must be joined somewhere in the system before contacting external connector. Every wire would be like these red one:

So here is where I would like to know a professional even industrial way to join the two wires. I have never do it and I don't want to do sloppy job.

My first idea is:

to create a simple PCB
fit on PCB some special connectors that interconnect two signals internally (as a jumper) and
put then 8 jumpers, with correct distances, clearances, creepages, whatever HV could need, and route them if needed to the external connectors (they are not defined yet).

A second idea is the same but using a kind of typical female connector with N pins -if it exists- instead connector couples being separated by clearance.

Questions:

Is it possible that someone has ways/strategies for doing this?
Any suggestion for the appropriate jumper connectors, considering HV?


texts: Why does the instrument transformer distort the measured voltage?

texts:
I have the following instrument transformer for voltage measurement. The secondary winding is directly connected to the analog inputs at the ADC with \$R_l=300\,\Omega\$ connected across the secondary terminals.
I have found that the transformer distorts the measured voltage. Please see the attached waveforms recorded by the osciloscope

The red trace represents the voltage on the primary side and the
purple trace respresents the voltage at the secondary side.
Can anybody tell me why this behavior occurs and how to correct that?
EDIT:
I have studied a literature regarding the instrument transformers and I have found there that each voltage transformer has some inherent phase error and voltage conversion error. The authors of the literature stated that those errors are caused by the resistances and leakage inductances of both the windings. Basically the voltage drops on the resistances and leakage inductances causes those errors. Due to this fact the way how to minimize those errors is to minimize the voltage drops. The voltage drops will be minimized in case only small current will flow through those resistances and leakage inductances i.e. we have to connect high enough load resistance on the secondary winding. Based on that fact I have thought that the transformer operating in the open circuit conditions at the secondary side should achieve the smallest error. So I have done the same measurement as mentioned above in open circuit conditions and I was surprised that the phase error is greater than in case \$R_l=300\,\Omega\$.


texts: Relay not turning on when supply comes from LDO Regulator

texts:
I'm trying to turn on a 5V SPDT Electromechanical Relay. It is planned to be used with microcontroller application. Below is the circuit that I wired on a protoboard:

When connected like that and measured with meter, the BJT will drive the relay with current about 35mA, and the measured voltage across the relay is about 2.7V, but it won't turn on the relay.
The BJT already saturated so even if I reduce the value of 1k res, the collector current won't rise anymore.

At first I suspect that my LDO regulator either cannot provide enough current to kick start the relay or the regulator is not fast enough, so I also tried changing the input and output capacitor to a higher value like 47uF, 100uF but the result still the same.

If I just remove the regulator from the circuit and power the relay from the 6V battery directly (4x1.5V battery), the relay can be turned on without any problem.

Can someone enlighten me with detailed explanation?
What could be causing this phenomenon?
What could be the solution?


texts: Problem opening a PLECS blockset in MATLAB

texts:
A friend of mine sent his simulation of a converter for which he had used PLECS. It is in the format "example.slx".

I have MATLAB R2017b. I downloaded the PLECS block set for MATLAB and activated it using the trial license. But when I try to open his simulation, I get an error saying that the source file was made in a newer version (2017b). The problem is that even I have the same version of MATLAB.

I tried to then load the file and convert it to its previous version (2016b). After this, I was able to open the slx file, but there was just a plain yellow PLECS subsystem which was empty inside. How do I access this simulation?


texts:
I have a Surface Pro 3 and am on the run a lot so I'm thinking about getting a deep cycle AGM battery to put inside my car so I have a constant power.

I need to know and confirm some measurements regarding it so I can buy the proper battery.

power adapter says INPUT: 100-240V @ 1A, OUPUT: 12V @ 2.58A
So if I can somehow supply DC power (12V) directly from battery to the surface,
it would draw maximum of 2.58 A/h? if yes, if load is lighter then less Ah, right? and so under its heaviest use it would never pull more than 2.58Ah? and INPUT/OUTPUT rating kinda omits hour in Amp so that it actually means Ah?
If I'm just gonna use inverter to plug in via AC power then, with battery source being 12v, it would draw 100V / 12V = 8.33 so 8.33 x 1A = 8.33Ah? And what does 100-240V exactly mean? does it mean it is capable of pulling from 100 to 240V and if in US it can pull 110v? and in Europe it can pull with the help of only prong adapter 240V? if yes, then is it pulling 240V x 1A = 240W of power where in US it would only pull 110W? or does in Europe's case if it's pulling 240V then does A go down to 110/240=0.458Ah?


texts: How can I use a transistor (2n2222) to act as a switch with this 12V momentary switch?

texts:
I have a garage door setup that is basically like the following:

All I want to do is add a new remote switch into the system.

I basically want to add a circuit into the previous schematic in the following place (image cropped for space):

Bluetooth & Arduino

What I'm going to do is have a Bluetooth module connected to an Arduino.  When the BT receives a signal (from Android app) then it will make one pin (D10) of the Arduino go high (5V) for a moment then go low again.

I have all that worked out.
What I need now is a circuit that will "connect" the two new wires when the pin goes high.

I'm guessing the circuit will look something like the following:

simulate this circuit – Schematic created using CircuitLab

NOTE:
The schematic is more of a block diagram. I am just trying to show that:

The primary circuit (Bluetooth / Arduino) runs at 5V
The secondary circuit is the new circuit I'm proposing and will be powered from the same 12V source as the original momentary switch.

Why am I proposing using a 2N2222 (transistor)?  Because I know I have one available.

My Questions

What would that secondary circuit really look like?
Would I just use a resistor between the 12V input and the collector to drop voltage / limit current?
Is this possible using the 2N2222 and the proper resistor combination or is it just not feasible due to limitations of the transistor?
If it's not possible can you offer the proper components that should be used in that secondary circuit?


texts: AC line from inverter grounded to vehicle chassis

texts: What happens if a hot line from an inverter powered by a vehicle battery contacts the vehicle chassis?  This will form a circuit connecting the hot line from the inverter to the negative terminal of the vehicle battery.  Does the DC battery somehow accept the AC electricity, or does the current not flow, leaving the chassis hot?


texts: Vector Network Analyzer - The effect of increasing the number of measurement points

texts:
Does increasing the number of measurment points make the measurement time longer?

RBW value does change the time, but does sweep bother the time of taking a single sample?

I'm looking for disadvantages of increasing the number of points from e.g. 201 to 401 while measuring frequency response of a low pass filter.


texts: Looking to create a switch box for multiple audio aux inputs

texts:
I'm looking to create a circuit that will switch a 3.5mm audio input between 3 or more sources using multiple switches. I've made a quick schematic to try to explain my idea, but I'm fairly sure this won't work as the audio will use the ground of which ever input is switched on.

Thanks for the help & sorry for the beginner question.


texts:
Using a relay, if I found a 12v source on the ps3 motherboard that was on only when the ps3 was on. Could I attach a 12v relay switch to it and the connect some LEDs that run off another power supply so that when the ps3 turns on the LEDs do too?

Thanks


texts: Which particular transistor types represent triode and pentode vacuum tubes best?

texts:
If you encounter an old text which uses tubes instead of transistors, and if you are not familiar with the tubes, which one of the transistor from the following transistor tree would you think of to understand the circuit?

I sometimes encounter an ancient text but when I see tubes in the diagram I used to skip reading. Should I instead think of it as an NPN transistor or a particular type of MOSFET? Which particular transistor in the above tree makes most sense for a tube circuit?


texts: Do I need to fill in the vias under BGA pads?

texts: I have a very dense BGA footprint. There is no way I can place the via between the pads - the PCB manufacture's tolerances do not let me. Also, the thinnest allowable traces do not fit between the pads. One way to do this was place via right under the pads. But because of the via's hole right under the pad, I am afraid that I might not solder it properly (the pad diameter of the via is essentially equal to the pad for the BGA ball). Filling the holes with non-conductive material costs 5x more expensive. Should I look for a component with the larger BGA pitch, or not filling the via will be ok?


texts:
I was reading this article today about interfacing a microcontroller with a 4-wire resistive touch screen, and found myself a little bit confused.

The article suggested this could be done by using four digital i/o pins and two ADC inputs. Two of the four touch screen interface wires are for the X-axis and two are for the Y-axis. The pairs are operated on independently (e.g. the other pair is tristated by the microcontroller).

The operation performed by the microcontroller on each pair is to apply Vcc to one wire and apply Gnd to the other. The wire to which Gnd is applied is also connected to an ADC input on the microcontroller, and the voltage read is proportional to the position being touched along that axis.

What I don't understand is why the ADC would ever read anything but 0V since the microcontroller is driving that wire to Gnd. How does this work?

Here is the schematic from the article for reference:


texts: GSM module working when powered by laptop via USB but keeps restarting when powered by battery

texts: I am using a sim900 module in the following link and I connect it to my laptop using USB to TTL converter and the module works properly. But, when I connect the same module to 9V DC battery the module keeps restarting, and also if I power the module from my laptop via usb cable it also keeps restarting. So, please, help me out.


texts: PCB Crystal layout for DSPIC33EP512MU810-E/BG

texts:
I'm designing a PCB with 8MHz crystal for DSPIC33EP512MU810-E/BG (https://www.digikey.com/product-detail/en/microchip-technology/DSPIC33EP512MU810-E-BG/DSPIC33EP512MU810-E-BG-ND/2765491)
On the datasheet, recommendations say that my traces should not exceed 12mm but this is the best I can do since my PCB board is defined and can't be changed.The crystal is side by side with the uC.

I have a ground plane below the crystal and the GND polygon pour around the crystal is 7mil.
.
Do you guys see any issue with this Crystal layout ?
Thanks,


texts: I've read here that running the TLC5940 with no load can cause some issues with it drawing excessive power. The TLC5926 is a constant current driver rather than a PWM driver. It seems to me that since both of these chips have the ability to detect an open condition on any of its drivers it ought to do something intelligent with that information (like not try and sink current from that driver). Is the TLC5926 susceptible to the sane effect described in the e2e forum post with respect to the TLC5940? What is one supposed to do to deal with this phenomenon?


texts: Neutral and the earth are bonded at the main panel or the substation but why is only earth wire used for safety?

texts:
Typical distribution system can be illustrated as:

Here are my premises (and assumptions):

1-) Chassis in a house must be connected to the earth, not to the neutral.

2-) The earth and the neutral are connected together at the substation.

Imagine one lives in a house and there is no earth in the outlet. I have seen such apartments and never understood how they are allowed to wire houses like that.

Including this web-site, I encountered similar questions (so this might be duplicate but the reason is I didn't comprehend the given answers such as this one) but never understood one thing. And here is my question:

Is there an "easy" example showing the fact that connecting the neutral to chassis is a bad idea? An illustration of a scenario helps a lot.


texts:
I am curious about the working of a Faraday cage as the shield for EMI in many systems. As far as I studied, it depends on Faraday's and Lenz's laws.

When the electromagnetic waves are incident on the Faraday cage, which is highly conductive metal, it produces eddy current which opposes the incident magnetic field (according to Lenz's law), thus stopping the EM waves entering into the environment.

I think the above is how a Faraday cage works. Any other ideas? I am asking because when I surf through the internet, everyone is giving different justifications.

Also I need to know why we are connecting the shield metal to the ground in the PCB? I thought that connecting to the ground layer forms a bottom layer of the Faraday cage (as the ground layer is made of copper) and forms a closed metal. Is there any other reason for connecting the shield to ground?

Also I need to know that if the above is the reason for connecting the shield to ground, will it be efficient to connect the shield as below? If your PCB has 8 layers, normally 2nd and 7th layers are ground, so connecting the shield to the 7th layer instead of 2nd layer surrounds the signals in all above 6 layers and it will acts are cage of all the above 6 layers. Will it be useful?

Please shed some light on this. This confuses me a lot.


texts: Understanding current through batteries and Kirchoff's Law

texts: i've just started studying electricity a while ago , but there is something that i've been trying to understand and it's making a huge gap inside my head to understand electricity. Now in kirchoff circuits where you haven't got just one battery but more , how does current flow through the battery ? If it's through the electrolyte then if electrons can do that why batteries die then ? I'am just starting to understand it , thanks in advance and i owe whoever make me understand it


texts: LDO vs. DC2DC for 3.3V to 1.05V Converting

texts:
I have a reference design that uses an FP6367S5G 800mA DC2DC converter in the following circuit:

I have been thinking about the pros and cons for replacing this DC2DC with an LDO.
one of the main differences that I can think of is that the LDO has higher power dissipation, since the LDO transfers the excess power into heat while regulating.
the second important difference is cost.
Is it preferable to replace this circuit with the following LDO-based circuit?

This is the data sheet for the RT9186A LDO I want to use.
could be there any complication with this replacement (which I want to do out of cost-related choice)? in addition, I wanted to know how can I decide if the heat that would result of the LDO's bad efficiency can be tolerable or not, and if not, how to deal with that?
Note: the load for this circuit is VL805 ‧ VL806 - Super Speed USB 3.0 Host Controller, which unfortunately I can't share it's datasheet due to confidentiality concerns.


texts: Finding the no. of decoders required in cascading

texts:
I am trying to solve the following question.

  How many 3 to 8 decoders with an enable input are needed to construct
  a 6 to 64 line decoder without using any other logic gate.

I have a Digital Electronics textbook in which the author gives a simple cookbook method :

  If n is the number of input lines in the available decoder and N is the number of input lines in the desired decoder, then the number of individual decoders required to construct the desired decoder circuit would be \$2^{N−n}\$.

With above explanation, the answer would be 8. Then I checked the answer & it was given as 9. I have only answer & no solution & even answer also may be given wrong.

After bit of struggling, I come up with this design. Let there be 8 decoders cascaded. The 3 inputs of each of decoder would serve as inputs for target decoder. And one more 3 x 8 decoder connected to each of these 8 decoders enable line. So that makes 9 decoders.

Here is my design:

I would like to know:

Is my approach correct?
Where did I do mistake in understanding from textbook?
Most importantly, how to tackle problems like these. If inputs are in large number, it would be very difficult for me to come up with a design. Is there any standard formulae or any method?


texts: How does SMBus receive byte command protocol know what to send?

texts:
Im programming an I2C device to act as a PMBus slave. Looking at the SMBus protocols (which PMBus is built on) the Receive Byte command has a format described as follows:

+---+---------------+---+---+-----------+---+---+
| S | Slave Address | R | A | Data Byte | A | P |
+---+---------------+---+---+-----------+---+---+

My question then is how is a slave supposed to know which commands data it is supposed to be returning? Is it dependent upon a preceding communications transaction, like reading from a device to which the read location has already been set??


texts:
I have a robot. My robot has three main sensors one is a gyro from which i can get my yaw, pitch, and roll. I also have an encoder in the x and y axis. How can I use these sensors together to reliably get my (x, y) coordinate within half an inch.

Just to clarify

Given: I have a gyro, an encoder on my drivetrain, and an encoder perpendicular to the drivetrain.

Problem: Use these three sensors to reliably get (x, y) position accounting for rotation on a global x and y axis. What I mean by: Account for rotation is that my position should not change if I spin in a circle, only if my physical x and y coordinates change. The resolution I am looking for is within half an inch. I would like the (x, y) to be relative to my starting position and in inches.

Question: How in the world do I approach this, I'm a beginner when it comes to sensor fusion, sensors in general and most of robotics.


texts: Build a circuit to modify a printer's power supply

texts:
Can I in anyway build a simple circuit that would change the printers power supply to be able to power the printer in the photo?
I want to convert a 22V 455mA power supply output to 16V 500mA output to power the printer. How can I do it, and what components will I be needing?


texts: Does supercapacitor electrode need dielectric layer?

texts:
I am trying to build a super capacitor. I use Activated Carbon with Wood Glue, aluminium tin can as electrode, multi layers of tissue paper as separator, and table salt water as electrolyte.
No matter how many times I have tried in different ways, my supercapacitor is always conductive. I connect 3.7V battery, a Red LED (about 1.6V), and the supercapacitor in series. LED always lights up, doesn't dim at all. (I have taken out the RED led and powered the circuit with 1.5V battery, but nothing changes.)
I made a search about activated carbon, and it is said that they are electrically conductive.
Now I am thinking that electrode is conductive, activated carbon is conductive, salty water is conductive. Then why would this device build up charge at all? It is all conductive!
Should there be a dielectric layer between electrode and the activated carbon, so the current doesn't flow between positive and negative sides at all, and the ions of the salty water builds up in the pores of the activated carbon?
There is also bubbling together with hissing sound while the circuit is connected, but I guess I should be asking it separately.


texts: Altium Designer: How can you extract single members of a Harness?

texts:
For better readability of the schematics I wanted to do something like in this image(Distributing the I2C-bus):

But I get "Conflicting Harness Definition for COM-IF" as a compile error.
Am I doing something wrong or is this impossible to achieve?

(The net label is because Altium sometimes requires one on a Harness for whatever reason to eliminate compile errors so I also tried it here, but no success)


texts: Are there any pins that need to be wired in certain ways for the ESP8266 to work?

texts:
So I'm making a PCB for a project so I don't need to use a node mcu and only need the esp8266 but I not exactly sure if there are any pins that should be wired obligatorily for it to work.
Here is my schematic. (It's just an external button  wired to the ESP8266)

Will this work like this or are any pins that should be connected so it powers up and its programmable?


texts:
I'm working with the LM431, and have successfully observed it regulating voltage in a series pass configuration.  The goal is to regulate an input voltage of up to 0-5V to a maximum output voltage of ~3.6V.  Essentially, its the circuit shown on this EDABoard thread:

(source: elektroda.net)

http://www.edaboard.com/thread126488.html

The values are:
R1 = 1K
R2 = 2.43K
Rbase = 100 Ohms
Capacitor is not present on the cathode of the LM431 for the following trials (trying to eliminate as much as possible from the circuit to determine what is causing the current draw).

I've looked around for similar questions, and haven't seen much on the use of the 431 as a series regulator although you'll see this application in other 431 family datasheets, as [shown here][www.onsemi.com/pub/Collateral/TL431-D.PDF] .  There are also other questions like this one which address the use of the 431 in a standard shunt scenario.

In testing, I've noticed that if I pull down the input of my circuit (collector of the BJT, or "V+" in the schematic above) through a resistor (1K) to ground, and apply a voltage to the output (emitter of the BJT, or "Vout" in the schematic above), I see a significant current into the reference pin of the 431.  I disconnected R2 from the reference pin of the 431 so that there was no current from the output to ground through the reference divider network, and took the following measurements:

Vout (at BJT Emitter) | Iref (into reference pin on LM431)   :
R1 = 1K, R2 = Infty, V+ = 0V

3.2V | 524 uA
2.8V | 420 uA
2V   | 202 uA
1.5V | 486 uA
1V   | 0 uA

From the datasheet, I thought that the maximum current into the LM431 reference was 4uA, and I am confused by what I am seeing.  I tried a few different LM431 samples, and the same results occur.

Any insight into why the LM431 sinks so much current through the reference pin in this scenario?

EDIT - An NMOS FET between R1 and the reference pin will effectively shut off all current to the device, configured as follows:
Gate - Tied to V+
Drain - Tied to R1 (other side of R1 is at Vout)
Source - Tied to Vref
Hopefully this helps others trying to figure out how completely turn off an LM431 (or similar variants).


texts: Interpreting basic contact and switch behaviour in a control system diagram

texts:
This might sound a stupid question but in a control system using buttons and contacts I have a bit confusion when it comes to picturing the real device. As an example if we have the following diagram:

There is Start button and NO contact called M. Now what is latching here? Button or the contact?

Is the Start button or the contact M latching type? I mean does it stay ON when I push and release my finger or I need to hold my finger pushed all the time to make it conduction current? Similarly for the contact M does it latch or does the current needs to pass all the time to energise it?


texts: powering a circuit with USB micro; what to do with unused pins

texts:
I want to power an old board (mostly TTL ICs) with this through-hole USB micro AB connector. I will have to create the pads for the pins with a scalpel, so the main question is: can I just connect the DATA and ID pins to the ground, or must I leave them unconnected (e.g. cut them their own little pad)?

A side question: I plan to use a dedicated charger; But would grounding the pins (if allowed) prevent powering this board via a PC USB port? Board needs about 300mA.


texts: Are pull-up resistors needed for shift registers (constant current sink drivers)?

texts:
I'm wondering if pull-up resistors are strictly necessary when using shift registers to control motor drivers or LEDs.
I have two STP16DPPS05 low voltage 16-bit constant current sink drivers, one controls four Allegro A3906 motor drivers which in turn drive one bipolar stepper motor each (so a total of 16 lines), the other drives 16 LEDs directly.
It's my understanding pull-up resistors are needed to ensure solid logic level high for input pins (or pull-down resistors for solid logic level low) but these aren't really GPIO pins even though they are sink drivers. I would have thought all the lines are either on or off according to control signals and any input is ignored.
As you can see in the images the shift register for the motor drivers has pull-up resistors but the shift register for the LEDs does not. I'd like to be consistent so I'm not sure which one is better.


texts:
If this is a differential folded cascode CMOS amplifier

simulate this circuit – Schematic created using CircuitLab

(where the "first" stage is nMOS and the "second" one is pMOS), can the following be considered as its dual?

simulate this circuit

It doesn't matter the different DC sources disposition and their values. My question is: is the second circuit built following the same cascode principle of the first one?


texts: What would be the ASMD chart (or State Transistion diagram) for the UART transmitter?

texts:
Here is the diagram of the UART design. I am trying to write a SystemVerilog code from the
ASMD chart of the UART transmitter.
I have done the the UART receiver ASMD chart below.

I know that the transmitter is quite similar to the receiver.


texts: Unipolar transistor as current amplifier

texts:
MOSFET or just FET: Common Source, Common Drain or Common Gate

Can be Unipolar Junction Transistor used as a current amplifier (or just voltage amplifier, because Gate's extremely low current)? If it is, how?


texts: Regulate, convert to DC and store current from home made AC generator to charge laptop

texts:
I am working on a small experimental project, learning more and more about electricity and electronics.

So, I have found this broken mixer and, surprisingly, it has a 300W engine with magnets that produces current when rotated. Just what I needed.

Now, what I intend to do is make it capable of charging a laptop battery, at least. The laptop's charger

needs 100 V ~ 200 V and 1.6 A (50 ~ 60 Hz) AC and
outputs 19 V and 4.5 A DC.

Now, I need to take some decisions and understand several things better

First, I need to decide if I should make my generator output at least 100V and provide at least 1.6 A to the laptop's charger then let the charger take care of the battery. Looks like the simplest and most secure solution. But if the generator creates 19 V and 4.5 A and sends this directly to the laptop, less work is necessary to rotate it, I guess. Why would I produce high voltage then have the charger reduce it?
No matter, what option is better, I need to know: how to regulate the current, how to transform the voltage as needed, how to store it temporarily, at least to keep it steady.
I have read a little bit about diodes, Zener diodes, regulators, induction coils, transformers and capacitors. Now, I have to find out how and in which order to connect these (I have bunches of them, of all sizes and colors) in order to achieve something like what I want.

So, what should I do?

Convert the AC current to DC using a diode bridge, and add a smoothing capacitor
Regulate it with a Zener diode (and required resistors to limit current flow) or a regulator (preferably to 12 V)
Convert the voltage from the regulated one to 19 V then use a capacitor to keep the amount if energy steady and provide it to the charger / battery?

or maybe

Use a regulator to stabilize the AC current
Convert the voltage to 100 V and use a capacitor to store it

Maybe this looks like I am asking for a circuit scheme (which would help, too) but I also want to understand every step


texts: Nodemcu sleep mode works but still consumes too much power

texts:
I would like to reduce the power consumption on my ESP8266 devices with a built in USB to UART.

I used this function :
  system_deep_sleep_set_option(0);
  system_deep_sleep(5 * 1000000);

This function works ok and reduces consumption to 0.1mA if I use Nodemcu with the serial connector.

However, it only reduces consumption from 90mA to 20mA when I use the Nodemcu which has USB connector (Lua Nodemcu WIFI Network Development Board Based ESP8266).

The difference between the two is that the second Nodemcu has a UARTtoUSB module. So I suppose that this is what causes the power consumption during the sleep mode.

Is it possible to make the second one only consume 0.1mA as well ?


texts:
I'm trying to understand better the whole clock system mechanism in TI's MSP430.

I understand that when doing this line of code I'm assigning REFO as the clock reference to the FLL/DCO

UCS_clockSignalInit(
   UCS_FLLREF,
   UCS_REFOCLK_SELECT,
   UCS_CLOCK_DIVIDER_1);

However, according to documentation I can pass to UCS_clockSignalInit other values among those is UCS_DCOCLK_SELECT and do the following:

UCS_clockSignalInit(
   UCS_FLLREF,
   UCS_DCOCLK_SELECT,
   UCS_CLOCK_DIVIDER_1);

This is unclear to me. From what I understand the function call sets the DCO as the reference clock to the FLL/DCO itself. Can someone explain to me how/why is this possible.


texts:
I recently got an ESP32 development board. I also found the schematic to this board online but I got an question. Can someone explain to me, what this part of the circuit is doing?

Schematic: https://dl.espressif.com/dl/schematics/ESP32-Core-Board-V2_sch.pdf


texts: Why is the potentiometer setup in this configuration in this 555 circuit

texts:
I just started learning about chips and signals using the book Make:
Electronics, in one of the circuits, used to generate a pulse in Monostable mode

a potentiometer is used to vary the pulse length. What I'm having trouble understanding is why the right pin of the pot is connected back to the wiper and not to ground, I built the circuit on a breadboard and indeed when I connect it to ground the circuit does not function properly.


texts:
I'm trying to convert an amplified microphone output (it is from 0-5v, biased at 2.5v) to a linear response that correlates with db SPL.

From my research, the output of the microphone directly correlates to the sound pressure, which is all fine, but I need to represent this in db. I am reading values from the mic with an arduino, which only has 10 bits of precision, meaning I cannot rely on converting the values into db on digital side because of the huge dynamic range that db covers which would mean very little of the db range would be represented inside the 10 bits since db is logarithmic to sound pressure.

So, how would I go about modifying the analog signal so that the output represents db SPL? I have read about logarithmic op amps but still don't fully understand how they could be used in this situation, or if they are what I'm looking for.