texts:
I have this circuit :

Two common base amplifiers for amplifying frequency in FM range (88 to 108 Mhz).

The Problem is, as seen in the figure, I am getting an output of 1.5 V for an input of 10 uV. That means a gain of nearly 150,000, which really bothers me.

Firstly, I would like to ask is whether this much gain or amplitude (1.5 V) is normal or is it too high. The schematic is the front end for an FM receiver and this output will be fed to a mixer for producing intermediate frequency.

Second and more importantly is the following sequence of events :

1) When I had a single common base configuration instead of two, the circuit was same (meaning I was taking output from only 1 transistor and second one was not in the picture), except the inductor in collector leg was 1 uH instead of 3 uH.

In this situation, the output was of the order of 500 uV or so ( See below)

2) Next I combined the two transistors as in the schematic above. This gave me an output of 1 - 3 mV depending on frequency. So far OK I guess.

3) Now as soon as I change even one inductor to 3 uH, the gain shoots up dramatically ( first pic). More importantly, this does not happen in EVENT 1, if I replace the 1 uH by 3 uH.

Can someone explain this, and more importantly address my first concern; Is this much amplitude OK ?

Thank You.


texts: mechanical relay output voltage doesn't change

texts:
As a followup to my previous question, where a 2222 npn transistor wasn't beefy enough to handle the load I was putting on it to activate a solenoid valve, I decided to try a mechanical relay board kit instead (which I realize is overkill for what I need, but it wasn't too expensive, and I figure I can reuse it eventually).

Like my previous question, I'm driving the logic with an arduino. I see the LED on the relay toggle, and I can hear the relay click when it's turned on or off. However, the output voltage (NO to COM on the 'relay 2' outputs) doesn't change when I test it with a multimeter. The voltage between any pair of output pins stays zero (NC to COM as well, all the outputs on relay 1 as well).

Is it likely that I make a mistake when I soldered the board kit together? I could try to re-do the soldering, but visually it looks OK to me (although I'm new to this), and things are functioning enough that I can hear the relay click when it's toggled.

Could I have fried both of the relays? It's a 'Omron Relay G2RL-14-DC12, SPDT, 12A, 12VDC'. Is there a way I can diagnose what's wrong with the board? I've prodded various through-hole pins on the underside of the board, and I can see a voltage across the LED's pins, but not the output pins. Is there something else I should test? Since I can hear them click, I assumed they're working, but maybe something else on the board is busted.

The output voltage should be the same as the input voltage, right? The multimeter says the voltage across the input pins is 11.7 when the relay is on (open), 11.9 when the relay is off (closed), 12.01 when the arduino is off too (why would it be different? I thought it was an isolated circuit).

Thanks for fielding my newb question :)


texts:
Clarification:

I appreciate everyone's input so far. The alternatives suggested are interesting, but for this application none of them seem better than the one presented here (except possibly switching M1 with a pnp). What I'm really looking for here is pitfalls with this circuit, rather than alternatives (for example, testing oscillation, input transients, output transients).

End clarification

I'm working on a relatively low power system (10's-100's of mW) that needs to operate from around 1.5V to 12V input. The current system can operate between 1.1V to 5V, but voltages higher than that will damage it. To be clear, it will use up to 100's of mW at both 1.1V and 5V. I've been having trouble finding an LDO thats small and also can handle such low input voltages, so I was wondering what the pitfalls were of just making a discrete one as shown below. The accuracy of the output regulation is unimportant, as long as it doesn't reach 5V. Assume the power dissipation of the mosfet is unimportant for now. It seems to work pretty well in spice. Currently I'm focusing on the DMP1081UCB4 datasheet here.

simulate this circuit – Schematic created using CircuitLab

There is some oscillation caused by the added base capacitance (5n at the moment), but this is probably acceptable for this application (although removing it would be good). The overshoot is also ok.

Green is the voltage output, blue going high represents the load switching from 3mA to 300mA, at 12Vin (which switches on at 1ms).

This is the same situation, except going from 0.3mA to 170mA (which is a more reasonable approximation of the load).


texts:
Newbie here. please be easy on me.
 I have a spotwelder project where i need to sense when the secondary is shorted. The working of the pcb is as follows,

my circuit detects the zero cross on the AC sine wave and triggers two Thyristors in a back-to-back configuration which switches on a MOT(Microwave Oven Transformer) at the peak of the sine wave, which is the typical way to switch on inductive loads to avoid inrush currents. I also have two taps on the secondary to measure the voltage during a weld to calculate the Weld current. All these are initiated at the press of a button which am hoping to automate when the electrodes touch a conductive material like here, nickel strip. I've checked the OFF-State voltage at the transformer and it read 1.05VAC and when the secondary was shorted it was 0.5VAC.

So with the best of my knowledge i think using op-amp as a comparator would be the ideal solution.

I could add the op-amp input parallel to section of the primary (like a shunt resistor) and monitor the voltage variation and use the output of the op-amp to trigger the thyristor through a arduino. I am not sure how to add the input voltage to the thyristor.

Would appreciate if somebody could help me here.


texts: Conversion of a Galvanometer to Ammeter and Voltmeter?

texts:
I am in 12th std and while reading my Physics textbook I came across a topic called "Conversion of a Galvanometer to Ammeter and Voltmeter." So I read it and found that to convert a Galvanometer to Ammeter we connect a very low value resistance in parallel to the Galvanometer and to convert it to Voltmeter we connect a very high value resistance in series with the Galvanometer.

Now my question is: What is the logic behind this type of conversion? I mean that why the low resistance is connected in parallel to the Galvanometer? Why can we not connect in series? Or why does it have to be low, why can't it be high?


texts: Motherboard RGB diode control and resistance?

texts:
I've recently acquired a new motherboard for my PC which features RGB strip control. That's well and good but I have particular need to control a single RGB diode with that same header.

The issue I'm facing now is that I'm not sure what form of resistors I need for my single RGB diode. I know I will need 3 of them. I plan to use a female to male connector then into a ribbon cable to the diode.

My motherboard is an ASUS HERO Maximus Alpha: LINK HERE

This is noted on the Asus page: *The Aura RGB-strip header supports standard 5050 RGB LED strips with a maximum power rating of 2A (12V)

Here is the data sheet for said diode:

How do I calculate the resistors required to control this LED?


texts: I am working on the re-design of an old board, but due to many reasons, the original design document is incomplete. So I sometimes have to figure out what an IC is. Here is one I couldn't figure out, and I would appreciate if anyone could give me some hint. The IC seems to be related to LED diode.


texts:
As per this building simple radio  it is the simplest AM radio receiver.

obviously this is very poor AM receiver.(but it was working for someone in comment)

I'm wondering what will happen when this receiver is very near to FM radios transmitter? will it work?

if no, How will the simplest FM radio receiver look like?


texts:
I am writing device driver for Samsung NAND flash K9xxG08xxM. I am not aware of exact part number as its staked board.  But Device ID of flash is

EC D5  51 A6 68

As per data sheet

I am having 16 Giga bits of Data which 2 GB ( 2 Giga Bytes ) of memory size.

But as per 4th Byte

    Memory size is =  Page size * No of block size  = ( 4 * 1024 ) * ( 256 * 1024 )
    = 1073741824

Which is 1 GB ( 1 Giga Bytes )

So what is the actual memory size from above device ID  ?


texts: I see sometimes that resistors are specified as current-limiting resistors, so I decided to see if voltage-limiting ones exist. When I do a search though, I don't see anything mentioning voltage-limiting resistors.


texts: I can't identify this component - is it a capacitor?

texts:
I thought this might be a motor start or run capacitor based on its size, but its markings aren't particularly revealing (to me).
Also I'm not sure if the resistor would be typical on a motor capacitor?
Unfortunately the stamped markings seem illegible, its not due to being a blurry photo (3rd image).

Lettering reads:
C800 (or C-800 or C•800)
KS 2018-1
CORNELL-DUBILIER
<patent #s>
NAF

As noted in a comment, its 4.7MΩ.

It's about 2x3 inches (50x75 mm).


texts: Confused why outputs of a priority encoder could be X instead of 0 or 1

texts:
So this is the truth table given for the Priority Encoder:

and this is its logic diagram:

I am extremely confused with the part where the outputs x and y are labeled as X (where D0 D1 D2 D3 are all zero). First of all, how could an output be a "don't care" term? What that would mean is that when D0 D1 D2 D3 are all zero, x and y are either 1 or 0. But that does not make sense at all. How could an output have an indefinite value when we have definite inputs?

As you can see from the diagram, x = D2 + D3 and y = D3 + D1D2'. So if you put zeros to all inputs it is clear that x and y should be 0. Then why is it shown as X in the truth table?


texts: I'm reading the datasheet of the G54/3 battery from Saft data sheet here. On page 2 the manufacturer show the plot 'restored capacity vs current and temperature'. But I don't really understand what the manufacturer means by the 'restored capacity'. Could anyone please explain what the 'restored capacity' is? Is it different from the capacity of a battery at certain temperature and certain (constant) discharge rate?


texts: Using NPN-Transistor as switch not working

texts:
I have following schematic:

simulate this circuit – Schematic created using CircuitLab

But the motor is not working, the NPN-Transistor does not seem to let any current through. What am I doing wrong? the transistor does work, I checked, but there may be something very basic wrong, electronics is not really my strong suit.


texts: Examining Q-V characteristics of a Capacitor using LTSpice

texts:
Consider the following circuit:

I want to acquire Q-V characteristics of the capacitor C using that circuit, with LTSpice. How can I do this? Does LTSpice provide a straightforward method for measuring Q, or should I find an expression involving electrical laws and that can be evaluated using LTSpice?

(I am using LTSpice v4.23)


texts: Measuring power consumption of Wiimote adapter not working, what am I doing wrong?

texts:
When I try to measure the power consumption of various Wiimote accessories, the multimeter only says 0.0mA, so I wonder if I'm doing it wrong.

Here's how I measure:

A more detailed explanation:

Like I said, I wanted to measure the power consumption of various Wiimote accessories, like Raphael of raphnet.net does here. He states he uses a modified Wiimote extension cable.

So, I modified an extension cable myself: cut it in half, with one side hooked up to the Wiimote, and the other to the accessory I want to measure, a Classic Controller for example.

The wires inside are connected to a breadboard. There I connect every wire together again except for the 3.3V ones, which I put a multimeter in between.

The colored lines in the illustration represents the wires. Red + yellow = 3.3V, black = GND, green = SDA, blue = SCL.

The multimeter (an inexpensive Uni-T 20B) manual says: "Break the current path to be tested. Connect the red test lead to the more positive side of the break and the black test lead to the more negative side of the break."

Isn't this what I've done? I've set the multimeter to DC current measure (in the range of 20mA).


texts:
I am designing a PCB for a VFD clock I want to build and I have come across something in a schematic for a voltage regulator that I have no idea what it means.

I have circled what I do not understand in red. I'm curious as to what this is supposed to denote. I do not want to fry any chips or blow up VFDs.


texts:
I'm relatively new to electronics, so sorry for my awkward understanding of topics. I'm just trying to wrap my head around some basic concepts here.
From my understanding, in OFDM, the information that we want to send (with a high data rate) gets split unto multiple partial datastreams with lower data rate. Therefore, my question is if there's a minimum data rate that enables OFDM? Like, if the rate is too low, it's probably hard/impossible to split the data unto datastreams with an even lower rate.
I'm asking because I'm trying to trigger OFDM with my dev boards which send raw 802.11n packets at 1mb/s, but it's not working. So I'm thinking that the rate's too low for OFDM.


texts: Breadboard Power Supplies' Output Voltage Incorrect

texts:
I bought one of these inexpensive MB102-style breadboard power supplies (Elegoo brand) and the output voltage I measure is incorrect. It is supposed to be 5 V but it is only 4.24 V.

I thought it might be defective so I bought a second one made by a different manufacturer and it also does not produce 5 V. Instead, it produces 4.46 V.

In both cases the 3.3 V output voltage is correct.

So is this problem with the 5 V output voltage then typical of these MB102-style units? Is it an issue with the design perhaps, or just bad build quality? Or maybe it's because ~4.3 volts is often considered "good enough"?


texts: Should I care about IC input pin current?

texts:
When dealing with IC input pins, should I care about current flowing through the input, or is it the IC's responsibility to limit the current in its internals?

The situation I am thinking about is similar to driving a load with a transistor. It is my responsibility as the designer to limit current flowing through both the transistor and the load to safely operate both components.

So if I am driving IC input with an NPN transistor, should I care about currents flowing throught the transistor (and the input pin), or can I assume that these are limited internally?

As for a concrete example, suppose Microchip's 24LC024 EEPROM. In our project, we are driving the WP pin up/low with an NPN transistor.

Furthermore, what are the common "sink current" values for inputs? I couldn't find such parameter in the official datasheet.

Thanks for help!


texts:
The headphones A has an impedance of 32 Ohms.

The headphones B has an impedance of 250 Ohms.

Both of the headphones are similar by size.

Is it right that the headphones B will play quieter by 250/32=7.8, if we talk about the sound pressure level?

7.8 times is approximately 9 dB.


texts:
I need to solve these two exercises but I really have no idea where to start.
How should I proceed to solve this kind of problems?
I tried to find something on my teacher's files but haven't understood how to solve the exercises because there are no examples.
What is the difference between I(RMS) and I(with the dot)?


texts: Help me understand FFT and harmonic distortions

texts:
I'm new to FFT and harmonic distortions. I'm dealing with a power system where the phase currents are distorted.

Now I don't understand the concept of FFT and why the harmonics seen in FFT relate to the current waveforms. FFT shows how the current waveform changes in gain by frequency instead of time. How is it possible for something to generate a waveform across all frequencies by just looking at a waveform from one frequency? Could someone explain this in a more intuitive way instead of using mathematical language? Also, if harmonics are the changes in gain for other frequencies, why do I care about them if I'm running at a single constant frequency? How can these changes from other frequencies affect something from another frequency?

Also, is an RLC band-stop filter a good way of cleaning up the waveform by simply blocking out the frequency range where the harmonics are? How would you block out multiple frequency ranges since there's more than one bad harmonic?


texts:
Here is my circuit

For some reason my 3.3v regulator is over heating. The regulator is a TLV1117LV33. I've tried everything to try and debug the problem but can't seem to figure out what's wrong except maybe a short to ground somewhere on my board.
I've connected just a MicroUSB cable to the regulator and even that is causing it to overheat.
Could it be because of the capacitors I have on there?


texts: How to properly connect SMD component to inner layer

texts:
I have a four layer board. The stack is divided as follows:

Layer 1: Signal
Layer 2: GND
Layer 3: Power
Layer 4: Signal

I have SMD components such as an SMD fuse, but the Power layer is in Layer 3.

What is the best way to properly achieve this connection?

Do I need to place a copper polygon pour on Layer 1 as well as Layer 3 and then connect them using vias?

Or because it is a small connection I can get away with just using a top copper pour?


texts: What determines if a battery is charging or discharging in a circuit?

texts:
I have a basic understanding of DC circuits from high school and university physics courses, but those courses only covered circuits that discharge batteries.

I'm trying to build an rudimentary electrical system for the inside of a trailer. It'll be used for a few LEDs for lighting, USB ports for device charging, and an inverter for a few 110v outlets. The system will be powered from its own lead-acid battery (not charged by the car's alternator), that's chargeable via a solar panel on the roof, or by plugging it in.

I have no experience in this domain, and couldn't find the information on this (perhaps I just can't think of the right keywords to google). Fundamentally, what determines if a battery is being charged in a circuit, vs being discharged? For example, how can I ensure that if the system is plugged into a mains outlet, that the energy comes from the wall plug and not the battery?


texts: Why is the input pin to my multiplexer considered a capacitive load?

texts:
I am currently using CD74HC4067 multiplexer in my design.

I had trouble with my input signal and therefore conducted an experiment by measuring the input resistance of my multiplexer as the frequency increases. I noticed that as the frequency is increased from 1 KHz to a final value of 8 MHz that the input resistance decreases with the increase in frequency. I am guessing that therefore this is a capacitive load because impedance = 1/(jwc) where w is the frequency. But why would the input pin be capacitive as opposed to purely resistive for an input pin?


texts: Where can I get this connector / what's it called

texts:
It's for connecting an LCD to the driver board via a flex ribbon style cable shown below:

Also, is there any hope that I can solder this with a hot air gun?


texts: I2C data sampling is done at clock edge or level

texts:
I am trying to understand I2C data bus from this document. It explains the START-SLAVEADRESS-R/W-ACK-DATA.. as the master-slave take turns to get hold of the shared bus for mutual communication.

One thing that I could not understand is related to the sampling of the data at the SDA line. Is it done at the falling or rising edge of the SCL  line or is it done at the SCL HIGH or LOW level?


texts: How to multiply a voltage when its lower than 5V?

texts:
I am working with a power source of a range from 0-20V and I need to regulate the voltage to 12V. I plan to use a buck boost converter to stabilize the voltage, the problem is the input range is 5-32V. I need the power to not be lost when it's generating less than 5V.

What I am thinking of is multiplying the voltage if it is less than 5V but I don't know how to do that. I have looked into MOSFET switches but I don't understand how those work.


texts: How to convert serial input to Ethernet via an Arduino Uno and Ethernet shield?

texts: I'm working on a project for school, and the basic premise is to take a serial input, and convert that information to go over Ethernet. It needs to be able to switch between rs232/rs422/rs485 at some point, but I would just like a jumping off point if at all possible. I'm trying to use an Uno and an Ethernet shield, but may switch to a Mega. New to this but looking forward to learning!


texts: How to place an indicator light for 24 VDC Solenoid Valve?

texts:
I'm using Arduino and relay shield to control five 24 VDC Solenoid Valves.

Now I want to place an indicator light (LED) for each valve, so whenever the valve is open, the light comes on.

Do I need 24VDC LED lights in order to do so?


texts: How measure input impedance this differential amplifier in LTspice?

texts: How to measure the input impedance (shown in the figure below) of this differential amplifier with BJTs in LTspice?


texts: Amplifier Gain and Offset (Positive m and Negative b)

texts:
My question is regarding gain and offset of an amplifier.

simulate this circuit – Schematic created using CircuitLab

I've used various references however I believe the circuit I want to build is somewhat unique in which I want to convert an input voltage from a sensor which ranges from 2-4 volts. I want to convert the 2-4 volts so that my amplifier output is from 0-10V where 2V corresponds to 0V and 4V corresponds to 10V.

I read through the following post Can someone explain this gain & offset op-amp circuit? and read the famous TI document.

After calculating my "m" (gain) I essentially got m=4.8780 and after calculating my offset "b" I got b=-10.6439.I then proceeded to calculating the necessary resistor values other than Rf which I selected as 51.1k just because I needed to start somewhere in order to proceed with the calculation in this document.

Here's the problem, I'm generating error in my output (i.e. instead of out seeing 10V at the output when 4V is present at the input I receive 13V (that's a 3V diff and a significant error %). How can I remove or remedy this so that I get closer to a 10V output (same goes for 2V input. Instead of seeing 0V I see approx 3V at the output. I can post the math if someone needs to see it however looking at the equation I don't see which of the resistor is actually having a huge effect on this error. How can this be remedied?

Note: On paper the math works out however I'm wondering if Pspice/TINA Ti is having an issue simulating this.

Thanks in advance!


texts: Modify a kinect - Reconnect the two cards

texts:
I’m trying to make a Kinect camera smaller. There was a problem at some point and my client expect me to put the kinect in a vertical position rather than horizontal as it is supposed to be. The problem is that if the kinect is positioned in vertical, the skeleton detection doesn't work. I’ve opened and cut a part of the kinect and figured out that if I could put one of the card in vertical position then it could fit with their display.

The thing is that this card is connected with another card via this 14 pin connector.

I guess it could be possible to connect these two cards via some kind of cable so my card could stand vertically but I do not know how/what exactly! First of all, is it possible? If yes what kind of cable could I use?


texts:
I have to dissipate \$2W\$ from a voltage regulator. It's a 7805 in a TO-220 package. The datasheet is here.

It's the first time I have to pick those so I would like to have a review of the following decision because I'm afraid of missing something as this sound really complicated for me. So I will put you here my entire reasoning.

\$R_{thJC}\$ is 5 C°/W for the TO-220 package and \$R_{thJA}\$ is 50 C°/W (table 3, page 7). As I will need to dissipate 2W I will have without heatsink 100° of heat on the chip. The room is around 21°. \$T_{op}\$ is 0° to 125° so to be safe I definitely need a heatsink. In that case it will just go around 31° based on that formula \$Max_{ambiant}+ R_{thJC} \times W_{dissipated}\$ or 21 + 50 * 2

But now I'm blocked. For the example I will take this heatsink. He's rated as 40 K/W. I assume K is for kelvin degrees. In that case does it means he's rated as 233°C/W ? I've found that formula :

\$Max_{JunctionTemp} >= Max_{AmbientTemp} + (W_{Dissipated} \times (R_{thJC_{C°/W}} + R_{thHeatSink_{C°/W}}))\$

Which give me :

\$ 21 + (2.5 \times (5 + 233) = 595°C\$

So, there's something wrong as this would mean that the junction between chip and heatsink will be 600° hot ... What have I missed ?


texts: Controlling 8-bit DAC Output over I2C-- decimal to binary char conversion help

texts:
Clarifying my question a bit.  We're using a PIC32 board with an MCP4706 8-bit DAC, controlled over I2C.  If we write a binary value (e.g. 0b00000100) to the DAC, it outputs as expected.  However, we're trying to incrementally change the voltage output by the DAC, which goes into a voltage follower controlling a MOSFET that allows current to flow from a high-current source into a battery.

Here's a schematic of all that.  It's not perfect, but it gets out point across.

An analog pin measures the value output by a current sensor in-line with the battery, which controls the current flow, essentially.  Currently, our conversion between voltage and current is done arbitrarily, which is okay.  I'm looking to get steadily increasing values from the DAC, but I'm reading 0.00V at all time from the output unless I manually set the DAC value.  I'm adding some different code here:

// Control voltage sent to DAC as a function of Cvolt read from current sensor
void CurrentControl()
{
    double current;
    // Gets values for Cvolt and Bvolt
    getAnalog();
    // ARBITRARY CONVERSION, NEED TO CHANGE
    current = Cvolt*.0035;

    // Current should be between 8A and 9A at all times for safety
    if(current <= 8.0)
    {
        // if current is less than 8A, increase DAC value
        shift = shift + 1;

        // safety control; keep shift at 255 (max) if it tries to go higher
        if(shift > 255)
            shift = 255;
        // write value to DAC Vout register
        SendI2C3(DAC,0b00000000,shift);
    }
    else if(current >= 9.0)
    {
        // if current is more than 9A, decrease DAC value
        shift = shift - 1;

        // safety control; keep shift at 0 if it tries to go lower
        if( shift < 0)
            shift = 0;
        // write value to DAC Vout register
        SendI2C3(DAC,0b00000000,shift);
    }
}

.

.
.

// Send data to I2C line at given address
void SendI2C3(char addrs,char regis, char data)
{
    char ack;
    I2C_start();
    ack=I2C_write(addrs); //Address for LED is 0x50
    ack=I2C_write(regis); //0xFE for LED
    ack=I2C_write(data);  //0x20to0x7F standard
    I2C_stop();
}


texts: LM2596 voltage regulator not providing steady voltage

texts:
I was trying to simulate a 3 phase AC full wave rectifier, and wanted a 5V output.
I connected an LM2596 module to turn the rectified voltage into the desired 5V output and ran the simulation in LTSpice.
To my disappointment, I found that the voltage was not only higher than the expected output (it was about 6.7V at first), but was also constantly decaying (in 210 ms it went from 6.7 to 6 V.)
The rectified voltage was almost totally constant but the output voltage (that is, the voltage produced after being passed through the regulator module) was not, this suggests that there maybe some problem with the module.
Is there anything wrong that I'm doing that you can point out to fix this problem?
At the same time, suggestions are also welcome for building a 3 phase AC full wave rectifier, with 12 V input and 5V regulated output, without this module in a better way as well.
P.S. - Also can someone clear up why my rectified voltage (11.4V) is slightly lower than the input voltage?


texts: What kind of DC motor should I get for raising my blinds?

texts:
I have large blinds that cover sliding glass doors in my condo. Unfortunately, the draw string to raise / lower them pops out regularly. I've decided I want to automate the raising / lowering with a RPi webapp.

I have all the software working (basically just a webapp to enable / disable 2 GPIO pins), but I need to figure out which motor I should get. Here's what I've measured so far:

The draw string is a 19.5ft loop that goes through a pulley (picture here http://imgur.com/1KaIoke). It takes 1 full rotation of the entire draw string to raise / lower the blinds. The pulley is 1" diameter, and I don't want it to take more than 30s to raise / lower the blinds fully. Therefore, I determined I need
\$\frac{19.5*12}{2\pi*.5} = 75\$ rotations and therefore a \$150\$RPM motor.

Here's where the measurements get a bit shoddy. I took a luggage scale and wrapped the pulley around it to measure the amount of tensile force in the string. It came back as \$10\$lbs. Using \$.5\$" radius, I determined that I need \$10*.5*16=80\$oz-in torque.

So that leaves me with a DC motor capable of exerting \$80\$oz-in torque at \$150\$RPM, and that's about as far as I've gotten. I know I'll also likely need an H-Bridge and of course a power supply (I assume a cheap wall wart should suffice for this). I am going to 3D print the junction between the motor and the gear/pulley thing, but that's a question for another day. So far, I've been able to narrow it down quite a bit, but there are still seemingly endless options for DC motors (BLDC vs brushed, steppers, modded servos, I saw some motors used for pumps in cars). At this point I'm trying to figure out the most suitable type of motor for my application. Any help would be much appreciated!


texts: how the capacitor equation can be modified?

texts:
I have a 500 mF capacitor with a charge of 1 V and connect an 1 ohm resistor in series.

What will be the maximum current flowing through the resistor?  It may be 1A, right?

But the max capacity of this capacitor at 1 V is 500 mC, so how can we say that in our circuit the max current that will flow is 1 A from equation:

$$I = I_{max} \cdot e ^ {-{{t}\over{RC}}}$$

$$I_{max} = {{Q_{max}}\over{RC}}$$


texts: x2y caps and common mode chokes (using both)

texts:
I am designing a ultralow noise PCB board. Common mode noise has to be minimized, so I have a question

I am planning to use a CMC on power input and to further decrease the  common mode noise I also planed to use a x2y cap ( middle going to earth)

Should I place the x2y cap before or after the CMC ? Should I expect a decrease on common mode noise using those 2 filters ?


texts:
How can I add these two components (OPA192IDBVR and MMBT2907AL) to LTSpice?
If someone can help with step by step tutorial I would really appreciate. I tried googling, but most of them suggesting importing and converting PSpice models to LTSpice and it looks like that was doable before, but not now, or I'm not doing something properly...


texts: Problems with using potential dividers to scale 220V AC mains to 0 to 5V

texts:
I want to measure the 220V grid voltage using a microcontroller. I can either use a transformer to step down the voltage to 6V rms and use potential divider and dc bias to bring the voltage to uController friendly 0 to 5V range. Or I can use potential dividers without the transformers.

What problems will I run into if I use potential dividers to divide the grid voltage (and add DC bias) and interface them directly with my microcontroller without any isolation?

Edit:
I want to understand the implication of a design with no isolation. I am guessing electrocution is only a problem during production and testing. And it goes away once the circuit is nicely packaged in a plastic container.

Edit2:
What I am designing is a minimalist watt meter that only communicates wirelessly via wifi. Only thing exposed out will be a socket to plug the appliances in.


texts: How to charge double cell lipo battery with single cell charger?

texts:
My setup is simple: I have this bluetooth module with a built in single-cell Lithium ion/polymer battery charger. I have this double cell LiPo battery and I also have an arduino nano that I will have to supply with power.

The bluetooth module runs fine on 3.7volts so that would be fine with a single cell battery but the arduino needs 7volts to operate.

So basically how can I charge both the cells without adding any more major components? (Or how can I power this setup?)

Any help is appreciated as I am a beginner (über noob).


texts: Comparator with Hysteresis_Design Calculations

texts:
I need to design a comparator with Vih=1.3V and Vil=1.2V. Therefore hysteresis is 100mV. The circuit will be working on a 3.3V supply. During high state, the o/p of the comparator will be 3.3V and at the low state, it will be 0V. I will be using a comparator with push-pull output configuration. Please see my design calculations below.I would like to know two things
1)May I know my design calculation is correct or not.
2)For finding Vref where I need to plug the value of R1 and R2.In equation 1 or 2


texts: Charging an 8 V, 100 mA device via USB (5 V, 500 mA)

texts:
I have a shaver (Philips QP2530) which I would like to be able to charge via a USB outlet (in order to allow me to use it on a motorcycle ride from London to Tokyo, but that's another story!)

The shaver's standard power adapter output is 8 V and 100 mA DC

What would happen if I connect the shaver to a regular USB outlet (5 V, 500 mA)?

I calculate the shaver charger to be 0.8 W and the USB to be 2.5 W - but will the shaver only pull the wattage it needs as the voltage is higher?

Keen to hear your thoughts! I'm trying to teach myself about electronics, so bear with me if it's a stupid question.


texts:
I'm starting out with resistors and would really use some good guidance here. I've researched a lot but still the knowledge is quite dark in my mind and there's things I don't finish understanding.

For instance, I'm working on a project now which consist in converting a set of lights so that they'll work with a USB connector instead of a battery.

The set works with a single AA battery. So the input voltage is 1.5vdc. I've measured the resistance of the lights and the circuit and, unless I measured very wrongly, its resistance is of 178 kohms.

So using a Voltage Divider Calculator I get that if I need to input 5v and the 1.5v and the 178 kohms resistance and I get 76 kohms.

Now, I'm sure I'm doing something wrong. My idea is to get a resistor to bring down the USB 5v to the 1.5v the circuit needs and, when researching, I was pointed toward the Voltage Divider formula as the way to do this but I'm confused as to how it works.

I was playing around with another set of lights that use 3 x AA batteries and found it only had a 200 ohm resistor that connected the positive side to the light series. However, I wasn't able to measure the resistance of the light series itself. Still, both sets I'm talking about have just 10 white leds, so I'm imagining their load to be about the same.

This second set I'm also planning on converting to 5vdc but first I need to understand how to go about doing it; that is, how I can calculate what I would need in order to get a circuit that takes 1.5vdc and another that takes 4.5vdc and make each work with 5vdc. If anyone could point me out in the right direction and/or clarify certain concepts that I fear I've got wrong, I would appreciate it greatly!

Thanks for all your responses! And I really an VERY sorry that my question (and in fact all my knowledge on electronics) is very much all over the place! I am, as I said, starting out; I'm a very excited amateur that wants very much to learn but hasn't learned anything formally. So please bear with me!

After a couple of the comments, I went back and (yes, I forgot to say there was a circuit on one of the streams of lights) found a capacitor in the circuit, which I'm assuming is used in order to allow the stream to be powered by the single AA battery (1.5 v).

Now, the second stream only has a resistor after the 3 x AAs. As the number of LEDs there was the same as in the first stream and they were both warm white, I went under the assumption that both worked with about 3.5 vdc and a current that a AA can provide. So I tested the stream and found that, yes, it works with 3.5 vdc. So my target voltage is that. And I believe the current out of a 5v USB output will be OK if the original power source was a (or 3) AA battery(ies).

I may be wrong, though, and would very much like your help. But I've since read a couple of things (here and elsewhere) that may be of use to me. What is seemingly the easiest solution, although I don't know if it'll work:

  trying to power with 3.5V and how much current you need. If all you want is just to get replacement for pair of AA batteries, just put two 1N4001 diodes in series.

Will that work, do you think?


texts: What kind of microcontroller peripherals can help me to implement a timeout?

texts:
I am discovering the world of embedder software with microcontrollers.
My need is to check that an input of my system stays high for 2 secondes for example.

Since I am not very familiar with microcontrollers, I wonder what kind of peripherals can help me with this.
With a list of peripherals, I could check in my microcontroller specs (a Freescale MPC5553) which peripherals I could use for that.

Since the Reference Manual has 1208 pages, I won't be able to fully understand all peripherals features. So I'll probably miss some possibilities.

At the moment, the ideas I had are:

Do everything by hand with a GPIO that is checked periodically
Use a timer which decrementation is enabled with external input (if that is even is possible!) and that triggers an interrupt on timeout.
Learn what is the Enhanced Time Processing Unit (eTPU) of this specific microcontroller.

Thank you for your help.


texts: How do I know if part is compatible between manufacturers?

texts:
I found a schematic that uses the Arduino platform.  It uses shift register part number 7HC595.  I can buy a shift register locally, but it is a NTE74HC165.

How do I know if parts are interchangeable?


texts: Active resistor for gain Control for reference pin in instrumentation op amp

texts:
I'm using an instrumentation amplifier (AD8421 from analog device) to amplify very small signals in magnitude from 20uV to 500uV max. the problem I have with this is that the signals might have some offset voltage (depends on noises) of up to 100mV. Now because I need high gain to get the signals, these offset voltage can easily saturate my output.

In order to resolve this issue, I used an Op amp in reference pin to adjust the reference according to signal. The pic above shows my circuit. This works fine, but I need to change the value of R9 (in U3 LT1028) from around 100k to 1M. How can I do this according to my input signal? I thought of using a FET to change this but I can't figure out how to do this.

Some basic explanations: VG1 is my input signal, U1 Op amp is a HPF which is not really my question here, and U3 is my reference op amp amplifier. Also, R1 to R4 (on the left side of U1) are supposed to suppress these offsets for me but for some reason they don't do it. Also, the device is used for signal acquisition from rats, so the offset really depends on grounding of the animal body and that is something that may not happen always.


texts:
I have problems understanding the difference between electrical power and consumption. Can you help me understand what electrical energy consumption is?

Let's say that I have a bulb, on which is written 100 W. How much does this bulb consume in 1 hour? Can it have a power lower than 100 W? Can it have a power greater than 100 W?

I would like to know what is the relation between electrical power and electrical consumption.

I'm very sorry for the big disambiguation from my head. But I don’t know who else to ask. I hope that you will not consider my question as stupid, even if is so.


texts: Is voltage divider output affected by load resistance?

texts: Very basic question. Assume a voltage divider where both divider resistors are equal value, i.e. 100K. If 48v is the applied voltage, it's easy to see that we'll measure 24v across the "load resistor". However, when we add a load in parallel with the load resistor, doesn't this parallel circuit reduce the total resistance across the load resistor causing the output voltage to be less than the desired 24v? Thanks for enlightening a non-engineer!


texts: how to wire a mono audio signal to a 3.5 TRS stereo jack

texts:
A small audio project I am doing is producing mono audio right now. To stop annoying my family I added a headphone trs socket as an alternative for the (single) speaker. audio (-) is wired to the sleeve and audio (+) to the tip and ring, so that I hear it left and right. Unfortunately the signal on the left is coming out relatively quiet.

Should it work this way? Or should I just add a mono trs socket and the headphones will do the right-thing (TM) and duplicate the tip signal?


texts: In reference to this question, do you actually perform DRC on Gerbers? Or do you do it for the PCB (post-design or interactive) and trust that the generated Gerbers will be OK?


texts: Is primary memory buffering the only way to access I/O devices and secondary storage?

texts:
I'm not sure if this is the right stack exchange site to ask this question so sorry if it's not. If anyone can cite a good book which explains computer architecture in general (not for a specific computer), that would be helpful.

The question is asking if a hard disk is accessed by the CPU by first transferring a block of data from the hard disk into the RAM and then the CPU reads it from the RAM. The same happens with input and output devices, where RAM is always an intermediary store for all data transfer outside primary memory. Is this the case?


texts: How can I calculate how long I can run a 800w microwave on a 115ah leisure battery

texts: I would like to find out how to calculate how long I can run a 800w microwave from a 115ah leisure battery. Assuming that I was using the microwave for commercial use, therefore using the microwave in 1 minute usages 30 times in one hour for 4 hours


texts:
I currently have a 2:1 switch / multiplexer which is being used to switch between two different batteries which are to provide power to a small module on my board. The switch that I am using is the TS5A3154 and I am wanting to switch between the channels using  an output pin from my microcontroller (EFM32G222F128).

The issue that I am having is that the battery voltage is going to be approx. 2.7 - 3V which will be at both of the analogue inputs (NC and NO) and the supply voltage for this switch is going to be only 2.5 - 2.8V - due to V+ coming from a dual schottky diode which draws the current equally from each battery and also prevents on discharging through the other in the event of a battery failure so this part is needed.

Because of this small difference between the analogue inputs and V+, the Enable pin does not function properly (ie. when there is a high signal at the pin there is a high output when it should actually be off completely) and because of this I need to replace the switch with either a new component or a new solution which would only have a small voltage drop across it or be very low resistance.

I have already had a look around for alternative switches or multiplexers but it appears to me that the same problem would always be present for any alternatives that I looked at.

Low cost is also fairly important but at the moment I am more interested in any solution as opposed to a low cost one. The solution would also need to have a similar Enable function the current switch has in that the power to the module can be cut off at some point - either just by turning two separate things off or having one switch that would do it.

A schematic of what it currently is shown below might be of help for understanding a little more:


texts: So to get started on part a I am finding the REQ of the circuit by shorting it. Now to get from A to B in this circuit that is having R4 and R5 in series with R3 in parallel so REQ = (1/900 + 1/300)^-1 = 225 ohms. That is assuming R2 is skipped because it goes directly to ground after R3. To finish up the Thevenin Equivalent I need to find a voltage, but I have no clue where to go from this.


texts: What are the advantages of single-supply (low voltage) programming over high voltage programming?

texts:
I'm a student designing a simple board for a PIC18 microcontroller and am trying to determine how the ICSP circuit should be designed. The datasheet explains how there are two different programming modes: single-supply (low voltage) programming and high voltage programming.

I've been reading through the datasheet and searching online, but I haven't been able to find any advantages of using single-supply (low voltage) programming over high voltage programming.

What are the advantages of using single-supply (low voltage) programming over high voltage programming?

Additional info about my application:

The board needs to work with the PICKIT 3 and ICD 3 programmers
The board should preferably be able to remain self-powered while being programmed (to allow the programmer to remain plugged in during normal operation and used at any time without having to unplug the board's power supply)


texts: Method to lower voltage of a laptop charger

texts:
I bought an IMAX B6 LiPo Balance charger that needs as input 11-18V but I have an unused laptop charger (the laptop is gone) having 19V with 4.74A. What is the easiest method to lower the voltage to 18V or even a little lower? (if I connect it as it is to the IMAX B6 it says something about input voltage is too high).

Thanks!

Sorin


texts:
I am using usbasp with atmega16a. I try to use external crystal 16MHZ with 22p capacitor. With mistake i use this command to change the fuse setting.

avrdude -c usbasp -p atmega16 -U lfuse:w:0b00000000:m hfuse:w:0b10011001:m

The atmega16a is dead. How to fix it?

pls. Any solution:


texts: What happens when you assign the result of a reduction operator to a multi-bit wire?

texts:
I may just be having a mental breakdown, but what should be the value of 'f' after the following:

```Verilog
wire [3:0] u = 4'b0101;
wire [3:0] f = |u;

Should this not create an error? What am I missing?


texts: Flat line on output of single supply sawtooth generator

texts:
I have built the following sawtooth generator using LM358 opamps:

In simulation everything works fine, however in reality I get only flat line on output. Anyone got any idea what's going on?


texts: Does the following voltage regulator have a specific name?

texts: The reference voltage is taken from the potentiometer.


texts: Strange output from an AD595 in single supply mode

texts:
device under test

I've got a K-type thermocouple wired up through an AD595AQ to an Arduino in single-supply mode (12VDC to pin 11), with the addition of an RC filter across the thermocouple inputs (330ohm resistor, 0.1uF). In other words, the thermocouple+amplifier wiring looks like a combination of the below two images (from the datasheet and a guide on signal conditioning the AD595):

The Arduino receives input from a connection on pins 8-9 running to one of the analog inputs.

error symptoms

Testing the thermocouple with a multimeter on its own gives correct temperature of the measuring site, but reading the temperature off from the AD595 output gives strange results:

Reading from a multimeter at the AD595 output:

122mV-143mV # reasonable ambient temperature at 10mV/degC
1110mV-1150mV # nonsensical reading obtained with hand on thermocouple positive leg

9C-13C is the right temperature for ambient right now, with everything else powered off. However, when I turn the heater relay on, the output pegs at 111C.

I added another AC/DC supply so that the AD595 would be isolated from the heater, but it didn't change the behavior. Removing the filter on the AD595 input also had no effect.

What am I missing?


texts: GSM SIM900A battery power supply circuit

texts:
I want to power GSM SIM900A with Lead acid rechargeable battery 12V, 1.2Ah. The voltage regulator I am using is L7805 which gives a regulated output voltage of 4.9 V.

My GSM SIM900A modem is

My battery is

How should I design the circuit so that I get 3.2V - 4.8V with 2A for proper GSM module operation without destroying any components ?


texts: How to programatically simulate a click on a capacitance-sensitive button?

texts:
I am tearing apart a SONY HT-XT1, which has capacitive buttons to put it in a different case for a project:

(source: digitaltrends.com)
I've taken it apart already and am now met with a motherboard with 3 pads on it. Touch the pad and the switch flips. I want to be able to control these buttons with an arduino, but I'm not sure how exactly to proceed. If you touch it with anything like a long wire or a cherry switch terminal, it flips the switch. I'd rather have some electronic way to control this over some mechanical contraption. I've never worked with capacitive buttons before so I have no idea where to start. Any thoughts would be appreciated, thanks!


texts: how to define gpio4 pin in nodemcu using Espressif sdk

texts:
I want to turn on and off gpio4 on node mcu shown bellow.
from page 9 we have pin_func_select function ,but i cant understand the MTDI thing and how to enable the gpio4 pin from the functions bellow.
There is also GPIO_OUTPUT_SET, i understand the "select" enable the gpio and the SET sets the value.
But I cant figure out the languege of turning on gpio4.
Thanks.
https://www.espressif.com/sites/default/files/documentation/esp8266-technical_reference_en.pdf


texts: Connecting wind generator to 12V battery without regulator

texts: I've been doing a DIY  Wind energy generator. I'm also a newbie in this field. I would like to ask what will happen if I connect my wind turbine to a 12V rechargeable battery without a voltage regulator?


texts: Which cable connection will result in a greater loss of power?

texts:
I know that running a power cable (the cable is carrying 5V DC, I plug in an AC to DC converter to the mains) that is, for example, 50m will cause losses in the power output. So if you measure at the source it will be 5V but when you measure at the end it might be 4.3V.
However, if I connect a mains extension cable that is 50m (the cable is carrying 230V AC) and then plugs in my AC to DC supply (this DC power cable is only 5cm) to my mains extension cable. Now I measure the output of the AC to DC power cable (at the end of the 5cm power cable) will I still get 5V or will the mains extension cable incur losses along the 50m and thus reduce the output of the AC to DC power supply from 5V to 4.3V?
Which is better Scenario 1 or 2, in order to minimize losses?
The AC mains extension is coming straight from the house's wall socket. There is no AC converter. just a three-pin plug plugged into the wall socket.

Please don't ask to go and buy a 50m AC extension cable and test it. This question is asking about the principle of running an AC extension or a DC extension in order to reduce power losses. What if the cable is 5km long....?


texts: I have a little bluetooth to aux in my car which is battery powered. I want to hook it up directly without the usb cable hanging when charging. The problem is that I can't leave it always connected because when fully charged, it makes an annoying sound. I am pretty new so correct me if I'm wrong but, could I make a battery simulator/emulator circuit so that the device thinks it is always around 50%? That way it should not make any sound right? If there is a simpler solution, I'm open to ideas. Thank you in advance!


texts: How can I safely drive a relay OR sense a switch from a single terminal?

texts:
I am designing a device that uses an MCP23017 running at 3.3V to either check a "port" on a terminal strip as an input from a motion sensor or drive a relay/SCR/indicator from the same "port".  I'm space limited so the terminal strip needs to be dual-purpose and each "port" function will be selected in software whenever the device boots up.  It will, of course, not be an input AND output at the same time...

In "input" mode, GPA0 would be in input mode with pull-up enabled, and GPB0 would be LOW.  In "output" mode, GPA0 would be HIZ and GPB0 would control the output state.  Q3 would be 2N3904 (unless you have a better suggestion) and I need advice on a part number for Q2.

The relay and switch on the other side of the terminal strip are just there for visualization purposes to save space.  In input mode pretend the relay isn't there, in output mode pretend the switch isn't there.  They would not be connected to the same terminals in the real world.

Given the diagram below, can you offer some insight into the following questions?

Is this even feasible?
In output mode, would the 12V potential on GPA0 cause any problems over time? (It's in HIZ)
In input mode will there be much leakage from the mosfet and will that affect sensing the input state in any way?
Is 1N4004 the right choice for flyback diode?
Can you recommend a P channel mosfet that is as small as possible, can handle up to 500ma and won't generate much heat?
Are there any other issues you can spot or advice/recommendations you can give me?

I will likely add a resettable fuse on each mosfet drain as well.


texts: What is the purpose of galvanic isolation?

texts: Is it correct to say that the primary reason to have galvanic isolation (ensuring minimum clearance and creepage distance for required voltage of power circuit between HV and LV) between the HV power circuit and low voltage control circuit is to eliminate the possibility of creepage current or static discharge between the two?


texts: AC-Current to ground without a closed circuit?

texts:
I'm struggeling with the idea that there needs to be always a closed circuit for current to flow. The theory is that there shouldn't be a voltage drop across C2 and R2 and no measurable current at AM1 because there is no connection between ground and the rest of the circuit. So no AC current can flow.

That is all nice and good until I think about it in a physical way.

At the secondary coil electrons accelerate through the Lorentz force.

Charge beginns to build up at C1 and C2. The charge density at both cathodes should be the same.

Relation between charge density and electrical potential:
\$\Delta\phi\ = -\frac{\rho}{\epsilon}\$

Voltage should now build up between the cathode of C2 and ground (anode) because of the difference in charge density.

If we now think about the voltage/current relationship of the capacitor:
\$\ C * \frac{du(t)}{dt} = i(t)\$

Then there should be a measureable AC-current at AM1 even without a closed circuit?! Is that even possible?

Is there something critical I'm missing?

simulate this circuit – Schematic created using CircuitLab


texts: Need to produce two pwm signals with 180 degree phase shift and different duty ratios, frequency of both are 50 kHz

texts:
A sample picture of how the output should be is given below(in figure top square pulse has 50 percent duty and bottom one has 60 percent duty, 50 kHz is frequency).

Where should I start looking or which controller can be used to achieve this?
(Can I code these output directly?)(should I include more info?)


texts: Observing and exploring the relationship between current and potential with a USB multimeter

texts:
Preface;

Hi, I bought this cheap little USB multimeter/double-adapter accessory on eBay.
Today's question will be focusing on the multimeter aspect of this device.

The white USB cable is for charging the black/red Android smart-phone.
Both of which are relevant to the question.

(Unfortunately the tip of the cable is slightly damaged and may not always be making the absolute best connection.
- Apologies, it was all I had on me at the time).

If you're curious; the black USB cable is connected to a wireless network interface card.
Said interface is down, and doesn't seem to be actively consuming any resources.
It can probably be safely omitted from the scenario without affecting any other variables.

(It's main purpose here is simply to apply a small amount of physical pressure down on the white cable.
 - Ensuring a decent connection, and holding it in place).

TLDR;

There seems to be an inversely proportional relationship between;
the potential/voltage[V] and current/amperage[A].
(At the node being measured).

##In other words:##

 Min current[A] = Max potential[V];
More current[A] = Less potential[V];

##And vice versa.##

I recall being told to think of it in terms of a metaphor:

Where electromotive-force/potential-difference[V]; is like pressure/Pascals-per-square-inch; inside a hose/pipe.
And Coulombs-per-second/electric-current[A]; is like the flow-of-water/Litres-per-second; through said hose/pipe.

I'm not actually sure how accurate this analogy is.
But it seems to help with creating a mental image and an understanding of the mechanism of action.

(i.e. Block the tip of a running hose; water stops flowing; you can feel the pressure build up under your thumb; the hose becomes noticeably more tense.
Unblock the tip of a running hose; water resumes flowing; you can feel the pressure release under your thumb; the hose becomes noticeably more relaxed.)

The Question;

I'm sure this is a relatively elementary question for seasoned electrical/electronic engineers/technicians, but how accurate is this analogy?
What exactly is the relationship between current and potential (as observed below)?

FYI: (I noticed that ~4.98V is approximately the maximum voltage produced by this Acer laptops buss.
Apple computers and phone-chargers (just for instance) were observed producing a more ideal maximum of ~5.11V).

Fully 'open' circuit: Not charging: [4.98V/0.00A]

Fully 'closed' circuit: Charging: [4.89V/0.30A]

Half 'open' circuit ('loose connection'): Charging ('or trying to'): [4.80V/0.14A]

Fully 'closed' circuit: Charging: [4.88V/0.27A]

Half 'open' circuit: Not charging: [4.95V/0.00A]

Fully 'closed' circuit: Charging: [4.90V/0.35A]


texts: What happens when the chip enable active time limit is exceeded?

texts:
The datasheet of a FRAM chip (FM1608-120-P) says that "the device has a maximum /CE low time
specification that must be satisfied". The datasheet does not state what the consequences are when this limit is exceeded. Chip enable must be pulled low in order for the address to be latched in.

The maximum active time for the chip enable pin as stated in the datasheet is 10,000ns.

What happens when this limit is exceeded? Does it damage the chip? Or does it simply mean that the output will become invalid?


texts: Need oscillating servo/stepper motor guidance

texts:
EDIT: Additional Information below original post...

Looking for a 360 degree servo motor that has adjustable control for timing of steps
(or at the least timing per full oscillation) and can support (via vertical shaft) at
least 30 pounds of weight overhead (imagine a oscillating tower fan where the base is
the motor and the fan is the 30 pound weight with a vertical shaft at least 4 feet in
length). Any suggestions for where to look for a baseline to mod or an off-the-shelf
solution?

Thanks for assisting in directing my ongoing efforts to build my prototype, peeps :)

I still have some primary concerns and questions unanswered in regards to the gearing, controls, etc for the oscillating motor and will continue those in more specific "Questions" posted as I think of them. I will post some google sketchup images of examples, as well. Thanks again and looking forward to hacking this project to completion :D

Google Sketchup Prototype:

I guess I'll fill out the images once I have 10 frickin points. :P

img src="http://goo.gl/fZykD" width="912" height="445" title="Google sketchup prototype Revision 1"

img src="http://goo.gl/kVBAi" width="1024" height="498" title="Revision 2"


texts: Combine power from power supply and LiPo battery

texts:
I am working on a hybrid electric power system project which currently has a 300W power supply and a 2S-910mAh LiPo battery. I would like for both sources to provide power if the load demand exceeds 300W.
I was wondering if there was any method for me to safely 'combine' the power output of the two sources.
Edit: to clarify the components used currently are not sized for any actual operations but to understand and verify power combination. Ideally the power supply wattage should be in similar range as the battery being used.


texts: How could this capacitor have been damaged?

texts:
During testing, a capacitor was found to cause an intermittent failure - going short circuit when heated.

The capacitor style is a through hole, radial lead, CECC rated 68nF MLCC. Our supplier makes these in small batches, so we assume they buy in SMT capacitors, solder leads + encapsulate them. It is not known if this is an automated process.

During sectioning, it is shown that there are significant cracks across the surface. Xray reveals these cracks are deep.

Question: What conclusions can be drawn from this analysis?


texts: what is exposed ground meaning in passive antenna layout?

texts: Could someone help me understand what is the meaning of exposed ground in pcb layout. I'm designing layout of my project and one of the component on it is passive antenna. What does exposed ground meaning?


texts: Why aren't garage door sensors retroflective on one end?

texts: Seems like they should be a transceiver + retroreflector, not transmitter + receiver pair. Is there a cost or safety reason for this?


texts:
In a lot of examples using STM32, HAL, where UART data is received by interrupt the code looks like:

Initially (to start the receiving):

HAL_UART_Receive_IT(&huart1, Rx_data, 1);

When an interrupt receive is complete:

//Interrupt callback routine
void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)
{
    ...
    HAL_UART_Receive_IT(&huart, Rx_data, 1);
}

I am wondering, is there a possibility that bytes are lost between the actual receiving and after the (receive complete) callback where the interrupt is started again.

Or is it assumed the interrupt handler above is so short the data will still be in the UART buffer?


texts:
I recently picked up and arduino nano kit and messed around with all the simple projects. I dont have much EE experience besides those so I have a question that might be pretty basic.

I am trying to make a simple travel lantern with a rechargeable Li-ion battery pack. It is working, but the voltage at the LED is below what I calculated it should be and thus the LED is dimmer than expected.

I'm using a 18650 3.7v Li-ion battery for power that is connected to a TP4056 charge/protect board. The TP4056 output is connected to a MT3608 step-up boost converter to boost the 3.7v up to 7v which powers the Nano through pin 30. I know that is not an efficient way to power it but I will be changing that in the future.

I want to use PWM to control the brightness using a rotary encoder and the push button to turn it on/off. The LED was salvaged from a flashlight I had around and after some research it looks like it is a cree xp-c which lists a forward voltage of 3.6v @ 350mA. To reduce the 5v max output of the arduino pins I made a voltage divider with R1 being a 100 ohm resistor and R2 being 330 ohms. This should cause the output between the resistors to be ~3.8v, but since the arduino puts out a bit less than 5v I expected ~3.6v output.

The issue is that I am getting 2.6v to the LED instead of the 3.6v it should be. I measured 4.5v from pin D6 to GND but only 2.6v after the divider. What could cause the voltage to be 1v lower than expected?

Here is the code I have on the nano:

int tempPin = 0;

volatile boolean TurnDetected;  // need volatile for Interrupts
volatile boolean rotationdirection;  // CW or CCW rotation
volatile boolean isOn;
volatile boolean buttonPress;

const int PinCLK=2;   // White
const int PinDT=4;    // Orange
const int PinSW=3;    // Brown
const int PinLED=5;

int counter = 100;

// Interrupt routine runs if CLK goes from HIGH to LOW
void isr ()  {
  delay(4);  // delay for Debouncing
  if (digitalRead(PinCLK))
    rotationdirection= digitalRead(PinDT);
  else
    rotationdirection= !digitalRead(PinDT);
  TurnDetected = true;
}
void isr1 ()  {
  delay(4);  // delay for Debouncing
  if(!digitalRead(PinSW)){
    isOn = !isOn;
  }
  buttonPress = true;
}

void setup() {
  isOn=false;
  Serial.begin(9600);
  pinMode(PinCLK,INPUT);
  pinMode(PinDT,INPUT);
  pinMode(PinSW,INPUT);
  pinMode(PinLED,OUTPUT);
  digitalWrite(PinSW, HIGH); // Pull-Up resistor for switch

  attachInterrupt (0,isr,FALLING);
  attachInterrupt (digitalPinToInterrupt(PinSW),isr1,FALLING);

}

void loop() {

  if(buttonPress){
    if(isOn){
      int val = map(counter, 0, 100, 0, 255);
      analogWrite(PinLED, val);
    } else {
      digitalWrite(PinLED, LOW);
    }
    buttonPress=false;
  }

  if (TurnDetected)  {
    if (rotationdirection) {
      counter+=2;
    }
    else {
      counter-=2;
    }
    if(counter > 100){
      counter=100;
    }else if (counter < 30){
      counter = 30;
    }
    int val = map(counter, 0, 100, 0, 255);
    analogWrite(PinLED, val);
    TurnDetected = false;  // do NOT repeat IF loop until new rotation
detected
    Serial.println(counter);
  }
}


texts:
Looks like brushless motors are more convenient - no brushes means no maintenance required. For example, power tools manufacturers often cite that graphite brushes need to be replaced every 50 hours of continuous use. I'd think that this alone should make brushless motors much more convenient. Still most power tools use brushed motors.

What's the reason to use brushed motors instead of brushless motors?


texts: Circuit to limit negative (falling) slew rate only

texts:
I am in search for a way to only limit the negative slew rate while leaving rising parts of the signal untouched. The signal will be anything from Subaudio till 20kHz, with potentially arbitrary waveforms and the amount of slew should be changable (via potentiometer, control voltage or current).

I found multiple ways of slewing both rising and falling edges, but nothing to slew only falling edges. I thought about some way to do it with positive and negative peak detectors and so on, but this gets quickly too complicated and to big for my intended applications (mostly a ±12V Audio environment).

The resulting slew can be linear or logarithmic, it doesn't really matter, for me it is more about getting unstuck with this topic.

The added slew is displayed in red (with different fall rates), the original waveform is the square wave.


texts:
I am creating this post as a second part to a recent post I have made: STM32F446 & External Oscillator
I have read other post about using a crystal that runs at 8 MHz rather than 25 MHz. Such as posts like this: Rectifying failed MCU crystal oscillator design
Could someone explain to me why is it preferable to use an 8 MHz crystal rather 25 Mhz? My project's sampling frequency is 44.1 kHz using I2S for the CODEC-MCU comms, I thought that having a 25 Mhz external clock would be fast enough to sample the signal by the guitar.
EDIT: How do you calculate the crystal frequency needed to hit the sampling frequency 44.1 kHz using I2S.


texts: Will replacing B23N20 mosfet with B4227 have problems?

texts:
I have the microphone amplifier and line Powerpod 410 R that after an analysis I found that one of the output mosfets is in total short.
The short mosfet is this IRFB23N20D, however I don't find it in my country Brazil, but I found this IRFB4227PbF. As I am new to amplifiers using mosfet, I asked for help, I have been reading the datashet of one and the other has some differences as the current supported my question is will I have problems replacing what I found in my country?
DATASHET's:
IRFB23N20D
IRFB4227PbF
IRS2092
OBSERVATION:
I'm sorry I use google translator, so I may not express myself well.


texts: How do I reliably connect power, ground and signal to a remote device?

texts:
I am building an arduino-based multi-event (light, sound, vibration) high speed photo trigger.  I'd like to house the arduino and display in one box, then be able to connect a remote sensor device to the main box.

+-----------+
|  arduino  |     5v, GND, signal    +----------+
|     +     |========================|  sensor  |
|  display  |                        +----------+
+-----------+

I had considered using a 3.5" TRS cable, but it seems there would be a risk of a short when plugging and unplugging the cable.  Is there a better connector/cable combination I could use to connect these together in a way that can be (dis)connected very easily?


texts:
I would appreciate some feedback regarding the design I came up with.
While I am not unfamiliar with electronics, this is the first time I actually designed something myself.

The purpose is to solve an issue with my Land Rover / travel trainer. The car sends out every 2 seconds a short electrical pulse of 100ms length, to check if a trailer is attached and if the trailer lights are still OK. With incandescent light bulbs this works just fine, as they need a moment to light up. Our trailer however has LED light, which cause the following problems:

The short pulse makes them flash briefly
The car does not recognize that a trailer is attached due to the LED lights high resistance.

My design is supposed to do the following:

V1 is the car's brake light output
R1 simulates an incandescent light bulb, so that the car 'sees' the resistance it is expecting
R2, 3 and C1 delay the TRIAC to turn on by around 150 ms.
The delay of 150 ms exceeds the duration of the pulse, the brake light will therefore only turn on when the brake light is actually activated.

I simulated the circuit in LTSpice, everything seems to work just fine.

What are your thoughts?

simulate this circuit – Schematic created using CircuitLab


texts:
I'm trying to figure out what's the best way to power a 64x32 RGB LED matrix and an ESP32 WROOM 32D using both a power bank (some 18650 2000mAh 3.7V in parallel + voltage regulator) and USB C (5V 3A). I would like to rely on the power bank when I need portable operation but I also want to be able to power them using an USB C cable (coming from any kind of power adapter capable of 5V 3A) when I have a wall socket available.
From my estimations, 5V 3A would be enough for what I'm using the matrix. Just in case I would need more current at some point, is there any way I can get more than 3A from USB C?


texts:
Is there a standard definition of the pictured ground symbol? It is distinct from an unmodified (without the rectangular box) symbol used in the same schematic.

Origin is USA, probably at least 10-20 years old, aerospace.


texts: Analog to digital conversion with variable VCC

texts:
I would like to build a circuit of a microcontroller reading an analog accelerometer, without the use of a voltage regulator. The problem would be that the battery's voltage will gradually decrease with time changing the VCC of the accelerometer and microcontroller.

In this case, the obvious problem when finding the step for the analog to digital conversion:

$$ step = \frac{VCC}{1023} $$

Is that the step is dependent of VCC and will change with it.

Is it possible to do analog to digital conversion with variable VCC?

(The accelerometer is the ADXL377)


texts:
I'm creating a portable test socket for electrical appliances that comes equip with a RCBO, power meter and possibly emergency stop button. My test socket will operate at max 240V AC and 10A. The purpose of the RCBO is to protect myself when I'm working on or fixing electrical appliances.

When searching for RCBO breakers, they seem to have different rated residual current varying from 10mA to 300mA with the most common being 30mA. I understand that in a household application where multiple devices are connected there can be some leakage current where the higher rated residual current RCBOs are used. However, in my case where the RCBO is connected close to a single appliance, which value is most suitable for me? And also to take note the 10mA RCBOs are almost triple the price of the 30mA version from my local supplier.


texts: What does zero Iq means in reverse voltage protection ICs

texts:
I was looking for reverse voltage protection circuits for my circuit. I happen to stumble upon an IC LM74610 combined with a NMOS seems to offer a good Reverse voltage protection. As i am skimming through the datasheet to see if it can work within my system, there is this term that they advertise "Zero Iq". what does this mean? are there circuits that dont want this or is a a general good thing for all circuits?

Also why is RVP always placed on the positive end of the source of power?


texts: I'm trying to debug an I2C device, and the wave is looking really weird. Why is it curved?


texts:
simulate this circuit – Schematic created using CircuitLab

I have a hall sensor that can measure current up to 25 A with analog output 0~5V. I am using Arduino mega board for programming. There are in total 30 hall sensors and where Arduino mega has 16 analog channel. Because of this I am planning to use multiplexer circuit.

Questions:

Is the above circuit right to build multiplexing circuit?
How are multiple analog output values read?
What is the purpose of selector pins S0, S1, and S2? It says that depends on state of pin it read value. Is it true or false? I mean to say, if S0, S1, and S2 are all 0, it reads analog output of hall sensor 1; if S0 = 0, S1 = 0, S2 = 1, it reads HS4. Is that correct or not?
Is it correct that using multiplexing, I can read one value at a time, but with multiple IO connected?


texts:
Why is it that in full wave rectifiers do you divide the secondary coil by half as stated in this book:

(Source)

What concept am I missing?


texts: TCA9548A I2C switch register functionality

texts:
I'm developing a little program to control the TI DRV2605LEVM-MD evaluation module, similar to the TI Haptics Control Console, but specific for this board. It consists of a MSP430 microcontroller, a TCA9548A i2c switch and 8 DRV2605 haptic motor drivers connected to the switch.

While I'm actually able to make the motors run and play effects, I'm having quite a hard time figuring out how to read the driver's registers through the switch.

My actual poor idea of an i2c switch is basically an ic where you can activate or deactivate any channel/s to send i2c communications to the slaves, so my approach until now was:

A) Enable the needed channels

B) Configure those channels as outputs

C) Activate the desired channels

D) Send i2c query to the slave connected to the active channel.

This has been working so far with no problems, but now I need to read from that channel instead of write, and I've not been able to make it work with the same approach.

Reading the switch documentation, I've find the following register description:

Register 0: The Input Port register (register 0) reflects the incoming logic levels of the pins, regardless of whether the pin is
defined as an input or an output by the Configuration register. It only acts on read operation. Writes to these
registers have no effect. The default value, X, is determined by the externally applied logic level.
Before a read operation, a write transmission is sent with the command byte to indicate to the I 2 C device that the
Input Port register is accessed next.

Register 1: The Output Port register (register 1) shows the outgoing logic levels of the pins defined as outputs by the
Configuration register. Bit values in this register have no effect on pins defined as inputs. In turn, reads from this
register reflect the value that is in the flip-flop controlling the output selection, not the actual pin value.

Register 2: The Polarity Inversion register (register 2) allows polarity inversion of pins defined as inputs by the Configuration
register. If a bit in this register is set (written with 1), the corresponding port pin polarity is inverted. If a bit in this
register is cleared (written with a 0), the corresponding port pin original polarity is retained.

Register 3: The Configuration register (register 3) configures the directions of the I/O pins. If a bit in this register is set to 1,
the corresponding port pin is enabled as an input with a high-impedance output driver. If a bit in this register is
cleared to 0, the corresponding port pin is enabled as an output.

So, I think I understand at least what register 2 and 3 does: register 3 is used to tell the switch if you're going to use a channel as an output (write) or input (read), and register 2 reverses that behaviour. But for the first two registers, I have no clue.

I know I need to write to register 1 in order to enable that channel, then configure it as I/O writing to register 3 and finally raw-write to the switch to activate the channel, but this is for a writing operation. Raw-write is a concept that I do not understand, as this is my first experience with i2c and everything I've read so far involved register write.

Can anyone help out with this one?


texts:
I'm working on a circuit that uses two 555 timers. At the electronics store, they gave me a handful of 555 chips, I only noticed the difference when I finished my circuit: the R1 value is shorted out, my R2 value is 150 Ohms, and the electrolytic cap is 10 uF. (see the schematic with R3, D1 and D2 replaced with a single piezo speaker).

The thing is, if I put in the 555 chip marked LM555CN, it appears to be 'always on'. But, if I use the Texas Instruments chip marked NE555P, the circuit works as expected, that is, it generates an annoying screech on a piezo speaker. What is the difference between these two seemingly identical chips? Is it a quirk in the TI chip that it works when R1 is just shorted out? And lastly, is there a way around this problem other than me sitting at the electronics store picking out the TI chips?

Also note - the piezo speaker doesn't have any oscillator in it, that is, when you apply raw power to it, it just clicks once and sits there, that's why I have the second 555 timer, and it's not an option to change out the speakers at this point.


texts: Why am I getting negative base current in LTSpice simulation?

texts:
When I was trying to bias an NPN transistor I noticed that the base current Ib is negative in LTSpice. So for the sake of simplicity I only apply voltage to the base-emitter junction. As you see in the figure above LTSpice shows this current negative. Infact when you bring the cursor on R3 the arrow points +V2.

Isn't the direction of Ib is from +V2 to GND in an NPN transistor?
Here is one example in tutorials:
http://www.zen22142.zen.co.uk/Design/cct/sw1.gif

I'm confused..


texts: Remote dissable a micro type B USB connection to device

texts:
I need to control the shutter and image download from a wired remote camera. The camera has 2 pinout ports.  One to control the shutter and the second is the micro-type B  USB post to download image files to a computer.

I need a circuit that controls the power line of a USB Micro-B. The USB has 5 pinouts. The circuit allows to manipulate the shutter and the image files download process from a of a remote wired SLR camera.

Connecting the USB directly to the computer does not work for me because the camera disables the shutter function when power in detected from the USB port. Therefore, I must rely in a circuit that will allow open and close the USB power line with a transistor with logic connected to a microcontroller.

I have included a primitive diagram and image of the USB type-B.  Note that the USB wiring has 2 wires for ground and another ground ID. I am not sure which to which line needs the transistor attached.

UPDATE 1 NOTE:  In response to comment. I rewrite the title because it misleads to think that i want to power off the device or the computer. I just want to disable the USB connection with logic.

UPDATE 2 NOTE:  From comments and responces here leads me to consider this might fall under a software related solution. To anyone interested in this type of scenario. I have posted a separate thread in stackoverflow https://stackoverflow.com/questions/55680572/need-to-disconned-the-usb-from-software-in-win10

simulate this circuit – Schematic created using CircuitLab


texts:
I want to power my project(AVR uC + RF transceiver) with a fake iPhone charger whose internal is the same  as this one, but with a smaller input and output capacitor. I therefore suspect that the output will be similar: source (under Counterfeit iPhone)
The oscilloscope traces show the output signal (yellow) and frequency spectrum (orange). The left images provide high-frequency information on the output voltage. The right images show the low-frequency information on the output voltage.
 How to smooth the output? Bigger input and output capacitors, buck converter, filter or extra rectifier + filter stage?


texts:
I'm new in this forum, but I think this is the right forum to ask my question.
I'm working on a project, where I need to store datas on an SD card. I use an STM32L443 microcontroller. The controller communicate with another device through UART communication, and save the datas to the SD card. The program works correctly with a no name SD card (I don't know the manufacturer, because I get it from smoebody). If I change the SD card to a 8GB Sony SD card, or to a Maxell 4GB SD card the controller doesn't recognize the card sometimes. Somtimes recognize, somtimes don't recognize. When I connect to the Debugger and go to debug mode, the program works fine and recognize the cards everytime.
In this situation I don't debug the problem because the problem doesn't present in debug mode.
If the program run free without debugger, and pull down the NRST pin manually to ground to restart the device, everytime recognize the cards.
Can You help me? I think that the NRST pin influence it, but if this pin influence why don't influence with the no name SD card?

The project was generated form STM32CubeMx and the programming environment is System Workbench for STM32. I know that similar question exist in this forum, but he answers that I get there, isn't help for me.

Please help me.
Thank You for the answers,
Szabolcs

P.s. I tested with a buzzer that where fail the program. Inside of the SD_PowerON function exist a while loop. When the cards don't recognize this while loop run infinitelly and never go out from there.

/* Send ACMD41 SD_APP_OP_COND with Argument 0x80100000 */
while(validvoltage == 0)
{
  if(count++ == SDMMC_MAX_VOLT_TRIAL)
  {
    return HAL_SD_ERROR_INVALID_VOLTRANGE;
  }

  /* SEND CMD55 APP_CMD with RCA as 0 */
  errorstate = SDMMC_CmdAppCommand(hsd->Instance, 0);
  if(errorstate != HAL_SD_ERROR_NONE)
  {
    return HAL_SD_ERROR_UNSUPPORTED_FEATURE;
  }

  /* Send CMD41 */
  errorstate = SDMMC_CmdAppOperCommand(hsd->Instance, SDMMC_STD_CAPACITY);
  if(errorstate != HAL_SD_ERROR_NONE)
  {
    return HAL_SD_ERROR_UNSUPPORTED_FEATURE;
  }

  /* Get command response */
  response = SDMMC_GetResponse(hsd->Instance, SDMMC_RESP1);

  /* Get operating voltage*/
  validvoltage = (((response >> 31) == 1) ? 1 : 0);
}


texts: Transients and shielding in power transmission/distribution lines?

texts:
I've been lurking for some time on the board here - but hadn't had occasion to ask a question until now:

Does anyone have experience with power distribution networks and their impacts on sensitive instrumentation?

I've got a 12.5kVolt line within a few feet (4) of a dielectric (aka capacitive or E-field) sensor used for detecting moisture.  What sort of shielding is standard for this type of line?  (I don't know total power through the line.)  I'm concerned that transients on the line may cause improper behavior in the sensor.

Nick answered below about sensitive instrumentation in the face of interference - but I'd like to better define the interference itself.


texts: Is there any Low cost sensor or sensory circuit which can figure out the Traffic density in a Junction?

texts:
My idea is to implement Automatic and Dynamic Traffic Control System.

I want to get the Vehicles density that were stopped along in all the roads in a particular junction. I want to get the binary information.
For ex:
 If I get 1111s that means it has the highest traffic.
 If I get 0001s that means it has very less traffic.

Something like this. I am Ok if I get the information in any other format. I can redesign my implementation.

Based on the information I will change the timings for each road to clear.

I have implemented the logic using a simple flash software. But I need to implement this on board for the demo purpose. The sensor should cost low. Or any other circuit from which I can get information is also very helpful.


texts:
QUICK INFO:
I am currently studying about closed and open-loops systems.
BACKGROUND STORY:
Imagine a big antenna is placed on a hill and there is a lot of wind. You want to turn the potentiometer so the antenna turns EXCATLY 65 degrees to the left (just an example) however, the external wind forces (disturbances) turns the antenna additional 2 degrees which leaves you with an antenna that has turned 67 degrees to the left. A closed loop system would subtract the disturbance from the TOTAL RESPONSE (in the input) and make up for the additional two degrees.
QUESTION:
What do you call the response after the subtraction from the TOTAL RESPONSE that your are left with? Furthermore, what would forced response be in this scenario and would natural response be you turning the potentiometer?


texts:
There are tools to calculate the width of a trace for a certain amount of current, but what about polygons?
Do you know a tool, possibly for Eagle Cad, that quickly calculates the maximum current or at least the area of the polygon?
If I have the polygon area, then I guess I can calculate the current using the formulas from trace-width-calculator:

Area[mils^2] = (Current[Amps]/(k*(Temp_Rise[deg. C])^b))^(1/c)

Then, the Width is calculated:

Width[mils] = Area[mils^2]/(Thickness[oz]*1.378[mils/oz])

For IPC-2221 internal layers: k = 0.024, b = 0.44, c = 0.725

For IPC-2221 external layers: k = 0.048, b = 0.44, c = 0.725

where k, b, and c are constants resulting from curve fitting to the IPC-2221 curves

EDIT 1:
Example polygon:


texts: How to connect 2 3v3 lines in parallel from different dc/dc converters?

texts: Is there any way, to connect 2 different (but same output voltage) dc/dc converters? One of them works on 5 to 40 Volts, and one on 3 to 5.


texts:
What is the better choice to get opensource SPICE simulator on Linux?
I am fan of Proteus (Windows) is there any alternative like it?


texts: Can I make an embedded logic analyzer for FLEX (flex10k) devices using SignalTap by JTAG?


texts: What is the difference between the electrical components on a micro-chip and ones on an eyes-observable circuit?

texts:
For example, an IC or "microchip" where everything must be micro-engineered on to it uses the same electrical components such as resistors, transistors, etc.

But I looked around online and noticed that transistors are actually eyes-observable(i.e., you can see and touch them, and there are some on my comp's motherboard).

But so they must be micro-implemented? Are they the same components, only micro?

I don't understand this, and it would be nice if someone could make sense of it.


texts:
I am trying to understand a charge pump circuit here but one part has me scratching my head and this sort of scenario happens a lot with me in electronics. It’s a question of what happened first??

If you look at the image below:
I understand the left image where the capacitor is basically in parallel with Vs and GND so this configuration is charging it up to VS .

In the next drawing, If I understand correctly, the Capacitor is connected in series with VS thus giving you 2VS. Then, because VS goes through the mosfets Drain -> Source thus connecting VS to what was previously the GND node of the capacitor

How did the mosfet turn on to let that through?

It seems like to get 2VS the mosfet has to have BEEN on, So basically a catch22 , which happened first? I don’t understand.

I think an answer might be if you switch S1 to off position first, that way the gate is not grounded and the source is still at ground and then the cap begins to charge the gate and once the mosfet is on then you flip S2 off and it works as described to give you 2VS ???

Any insight would be much appreciated.
Thanks.


texts: Where do I place a decoupling capacitor when the power supply is intermittent?

texts:
I'm building a low power obstacle detector.
I have an infrared LED and a IR photoresistor wired up to a BLE Nano (a tiny bluetooth IC) running off a small 3v coin battery.

My code basically does this.

digital-out 2 ON (powers the photoresistor)
take a reading from analog-in 1 (reading 1)
digital-out 1 ON (turns on the IR LED)
take a reading from analog-in 1 (reading 2)
digital-out 1 OFF
digital-out 2 OFF

if reading 1 and reading 2 are different I know there is something reflecting back IR.

The problem I'm having is that reading 2 seems to be picking up noise and often reports a different value to reading 1 (even when I know no IR has been detected). I believe this effect grows as the battery drains.

I would like to place a decoupling capacitor either on the LED circuit, the photoresistor circuit, or both.
Because I want this to be as low powered as possible I'd rather not have current constantly going though the photoresistor as most of the time I will not be taking readings. I can't seem to figure out where I would place those capacitors or even if this is the correct solution.

Any help (even if it's a simple "this can't be done") much appreciated.


texts:
My question is: How can capacitors pass AC without or with minimal voltage passing?
If the current is caused by a voltage (potential) difference and current is just the voltage (or charge) passing per unit time across a cross-sectional area of the wire, then how can just current pass without voltage at high frequencies? What is flowing then?
This idea has confused me and I thought about how could it be possible.

Another similar idea that I had trouble with is how can an inductor pass voltage and not current at high frequencies? If voltage is passing, then how can current not be flowing across the inductor? How can voltage flow without current?
These are the 2 concepts that have been troubling to me.
The closest thing I could find on this subject is this: https://www.researchgate.net/post/Does_the_current_flow_through_a_capacitor_and_if_so_why


texts: Add line in to electret microphone and mute the microphone when plug is connected

texts:
I have a megaphone with an electret microphone. I want to modify the megaphone so that I can optionally conntect a notebook's headphone out to the megaphone. So I want to add a line in connector to the megaphone, but at the same time keep the electret microphone.

The electret microphone operates at 3.1V. I found a 20 dB PAD for line to electret microphone input circuit which is working well if I completely remove the microphone.

I have a 3.5mm audio jack connector (mono) with a switch. The switch closes when an audio jack is inserted into the connector. I want to use that switch to "activate" the line in and mute the electret microphone.

What I tried first is to short-circuit the microphone with a transistor when the switch is closed:

C1 = 10 uF
R1 = 10 kOhm
R2 = 1 kOhm
T1: NPN transistor
M1: Electret microphone

This in almost working as I want it to. But there are two problems:

The microphone is not completely muted, it's just turned very quiet. I want it to be completely muted.
I'm not sure if short-circuiting the microphone without any load will drain the battery or worse will damage the microphone amplifier. The microphone has a resistance of about 1 kOhm.

My next idea was to use a transistor and an inverter to cut off the microphone when the switch is closed:

However I don't know which part or circuit to use as an inverter.

How could I solve this problem? Is there an inverter I could use? Or another circuit design? Thank you!


texts: Nyquist-Shannon sampling theorem on non infinite signals

texts:
Can we sample and recover signals with non infinite "length" using the nyquist shannon theorem? For example if we have a signal

$$ x(t)= u(t+5)-u(t-5) $$  and we know that its sampling period T is less than 10s (T<10). Can we recover it using the nyquist theorem? If not , what could we do to recover it?

Edit: I have taken the fourier transform of this signal and it is : $$X(ω)=2i(\frac{1}{iω}+πδ(ω))sin(5ω)$$ which can lead to finding the period as $$\frac{2π}{5} $$ and actually see that if f>= 5/π it can be recovered. But this may not be possible because i used the theorem although we are on a finite signal


texts: Solar Inverter shows different power on AC vs DC side

texts:
Apologies for my ignorance, there probably is a fairly simple explanation for this, but I've never claimed to be an EE and the basic stuff we got at school is err.. long shelved in some dark part of my old brain I'm afraid =)

Anyway, the situation is as follows: a while ago I had a PV installation installed on my roof and the inverter has a basic web-page that shows me some internal statistics. The only ones I'm really interested in are AC-Power out and Total Energy over the day. However, I've got 2 -- differently sized and differently oriented -- strings of PV panels and I always wonder which one 'does best'. For fun I started logging the numbers in a .csv file so I could make some graphs out of it and a such I started having a closer look.

It turns out I don't have a power-number for each string, but I do have a Current and a Voltage number for each. I seem to remember that Power = U x I, so when I sum both multiplications I should get the output power even with some losses due to whatever process is going to convert 'random DC' to 240V AC. (The thing gets warm, so there's at least that).

Turns out, that the input-side is consistently lower than the output side, so somewhere along the road the inverter adds energy to the mix?!??! I'm willing to believe a lot of things, but this seems unlikely =)

An example:

As can be seen:

String 1 gives me 0.60A x 259.8V = 150W
String 2 gives me 0.65A x 352.8V = 230W
AC(out) is at 1.94A x 228.6V = 443W

The input side sums to 380W, yet the output side gives me 445W according to the machine itself (it seems some rounding is going on).

Where does the 'extra' 65W come from?

Writing all this down I seem to remember there was something with a SQRT(2) conversion when figuring out peak AC voltages, but I'm not sure that applies to Power here?!?! Pout / Pin gives me about 1.17 while SQRT(2) is close to 1.41

PS: the inverter is a Sununo Plus 4K-M with Power Factor: 0.9 leading~0.9 lagging (I have pretty much no idea what the latter means but I've got a gut feeling someone is going to mention it =) And yes, it was a fairly cloudy day.


texts: convert pwm to analog signal with a load of 0.7A

texts:
I have a question, an easy one I believe. I am designing a small module which may take control of an analog model train as soon as the train is detected.
When the train is detected, a uController must screw down the dutycycle to either 50% or 0% (frequency is fixed) to slow the train dowm to either half speed or a full stop
The voltage on this piece of track has to be analog (0V - 12V). Use of an unfiltered PWM signal on the tracks is not an option. The first section would be 12V DC, if a train would transition from the first section onto a section which has PWM every conducting wheel might trigger a short circuit spike between 0V and 12V. The system might get away with such short circuit spikes, but I believe it cannot possibly be any good and therefor I consider it a bad option.
Also driving analog trains with PWM is very undesirable. 1st digital trains do not understand a PWM signal and they will simply not work. It is common for people to have a digital train driving around among analog trains.
PWM'ing a train can be done on 20kHz or above (due to horrible high pitch sounds). This has horrible driving qualities on analog trains. Digital trains do use these frequencies, but these trains also come with cruisecontrol and an advancde PID (or something similars) system to deal with this.
By far the best way to achieve a good PWM controller is by varying the frequency alongside the dutycycle.  < 10% Dutycycle you use 20Hz and 100% dutycycle is done @ 100Hz. Though trains drive wonderful on this method. The train's LED may flicker like an Xmas tree (glowbulbs work fine though) and sadly not every train has room to accomodate an anti flicker circuit. It is also not desirable if you need to do this with every train.
The detection is done via an optocoupler. When a current flows through the 2 diodes, they create a 1.4V drop over the led of an opamp which then pulls the currentSense line down to 0V. This informs the uController that a train has entered the section.
This circuit is designed for oneway traffic.

The opamp should correctly filter the pwm to an analog voltage. But I want it to drive a load of about 0.7A max without experiencing a noticeable voltage drop.
At the moment I have a rail to rail opamp in supply, but it cannot provide the desired 700mA.
Questions:

Disregarding any potential heat development, can I simply add a mosfet or a transistor such as the TIP120 darlington behind the opamp without screwing up the voltage level on the tracks? Or will this affect the voltage level in a negative way (which I suspect)
Is it a good idea to pick a stronger opamp such as this one from Mouser which can drive up to 1A
Is it a good idea to use this circuit (with 5V instead of 12V) to 'replace' the potentiometer of an existing buckconverter (essentially I'd be controlling the output of a buck converter using this circuit as input)

Also. I am yet to learn how to run a simulation of a schematic, so no I have not simulated anything.