texts: Laptop's removable battery has 4 18650 3.7v cells in series, can I attach 8 more as external battery pack as 4s2p?

texts:
I have 4 years old HP gaming laptop with removable battery. I never kept the battery in the laptop. Right since the purchase, I stored the battery in a sealed pack in cold place, and charged it to 45% every 30-40 days.
I run the laptop via its charger which is connected to a PC UPS always. After power outage, laptop runs for around 30 minutes only on the UPS.
I wish to make a PORTABLE battery pack.
I have to attend long zoom meetings, on sometimes there are power outages. I wish to extend the original battery without changing the 18650 batteries inside it. I am planning to attach wires to the end terminals of these 4 18650 cells to attach a battery pack of 4s2p in parallel.
Do I need to cut the supply between the laptop battery's 18650 and the external pack? Or I can keep them all in parallel without any risk or loss of power?
If I have to cut off the supply, I was planning to do the following:
I know if the BMS detects 0 voltage, it will lock the battery. So I was planning on using 2 switches for this setup. 1st switch will allow the laptop battery to get parallel connection from the external pack (effectively having a 3s4p battery pack). Then few seconds after that, I will flick 2nd switch which will cut off the supply between laptop battery's 18650 and the BMS so as to keep only the external pack connected with the BMS.
Question 1) Is it practical, safe or efficient?
Question 2) What will happen if I switch to external pack ON THE FLY, while laptop is on and working? Will it show higher battery percentage immediately, or I will have to perform restart/standby to update it? I know for a fact that I ALWAYS remove the battery while the laptop is connected to the charger and working, it instantly shows no battery and I didn't face any problems due to that ever.
P.S. I am here to learn and only studied electricals till high school, I know the basics only so please don't start bashing! I will buy genuine Samsung 18650 batteries for the external pack, not cheap chinese ones.


texts: Using a large resistor instead of a flyback diode

texts:
In a video lecture a professor is explaining how to prevent an electric arc caused by the switching operation in an RL circuit. Here is the section (at around 18:26) where he explains it:
https://youtu.be/FYDLG_A2P1I?t=1106

I know that a flyback diode is used for this purpose:

... yet in his example he uses a very large resistor to create a path for the reverse current.

My questions are:

If a very large resistor is used, wouldn't it be a problem if a continuous switching is very fast comparing to LR time constant?
If a diode is used, would the inductor burn if the back emf current is too high? In almost all examples they just use a diode without mentioning any possibility about this.


texts:
I have STM32F7 (which has a Flexible Memory Controller capable of interfacing SDRAMs) and I want someone to check if it is able to interface this SDRAM - IS42S32800D (http://www.farnell.com/datasheets/1275293.pdf).

I have checked and it seems ok, but I want to be sure, because I have "one shot" to buy and do the PCB.


texts:
In a 16x2 LCD there are 16 columns and 2 rows of characters, each character is made up of a grid of 40 pixels. My question is, do each of these characters have their own driver that drive every pixel simultaneously or is it a persistence of vision method, where one row of pixels at a time is turned on one after another?

A corollary question would be where would I find any kind of documentation on the best way to control each pixel. Its more out of curiosity than anything, and i plan on making my own LED matrix and playing around on my FPGA but obviously I want to use the fewest pins possible. This got me wondering exactly how an actual display does it.

Thanks for any info.


texts: Meaning of zero load and full load in circuits

texts: This might be straightforward but it has been tough to grasp for me. When a question says to calcualate the power dissipated by the Zener diode under zero load and full load. What exactly does the concept of load mean here? I know load can be thought of as a well defined output, then the circuit connected is load or the power consumed is. But then, what is zero load and full load?


texts:
I am new to electronics so please bear with me!  I tried searching for help on this one, a lot of useful info on reverse polarity but I couldn't find much on this situation.
I am using a DC-DC converter that supplies 12 V and 30 A.  The DC-DC converter has a soft start, whereby it ramps up from 0 V to 12 V over some time, when the system is turned on.  During this ramp up, the system cannot draw more than 2.66 A until the DC-DC converter reaches 6 V.
I initially thought of using a time delay relay, of say 1 second, to ensure that the system started correctly.  However, I then thought I could use a P-Channel MOSFET as it looks to be a more elegant solution.
The idea of have is shown in Image 1.  The idea was that the MOSFET would conduct less than 2.66 A until 6 V is reached.  The problem I have is that I cannot find a MOSFET with a high enough gate to source threshold and low enough resistance, as at 30 Amps the resistance needs to be as low as possible.
I can only find high Rds, high Vgs(th) or low Rds, low Vgs(th) MOSFETs.  I can't find a suitable Rds high Vgs(th).
I therefore thought I could add a resistor to the circuit as shown in Image 2 to a low Rds, low Vgs(th) MOSFET.  The thought being that this resistor would also take some voltage, thereby effectively increasing the Vgs(th).  The problem is I don't have sufficient knowledge to know whether this would work, or the equations involved.


texts: Is it possible to wire a regular power supply cord to a sewing machine motor so I can use it for a Halloween prop?

texts: If it is possible to wire a regular cord (power supply) to a sewing machine motor (with a motor speed controller), what volt/amp supply do I need to use?


texts: LTSpice Simulation Problem - Controlled Rectifier Single Phase Dual Converter

texts:
So I am having problems simulating a Single Phase AC/DC Dual Converter on LTSpice. At the first converter I am getting the perfect output but when I take the voltage probe from the second converter output I am not getting the expected voltage output.

Frequency is at 60Hz, my load angle of the first converter is 60 deg and load angle of second converter is 120 deg.

Circuit Implemented in LTSpice:

The voltage output V(1) and V(3):

You can see that V(3) waveform has a drop somewhere 5/6th of the way before its actual drop at 360-60=300 deg (13.89e-3 s). It should be a complete inverse of V(1) with its conduction at 120 deg and 300 deg.

I used a Thyristor model from a book called "SPICE for Power Electronics and Electric Power" by Rashid, below is the sub-circuit:

.SUBCKT SCRMOD 1 2 3
* MODEL     A K G (anode, cathode, gate)

S1 1 5 6 2 SMOD
RG 3 4 50
VX 4 2 DC 0V
VY 5 7 DC 0V
DT 7 2 DMOD
RT 6 2 1
CT 6 2 10UF
F1 2 6 POLY(2) VX VY 0 50 11

.MODEL SMOD VSWITCH(RON=0.0125 ROFF=10E+5 VON=0.5V VOFF=0V)
.MODEL DMOD D(IS=2.2E-15 BV=1200V TT=0 CJO=0)

.ENDS SCRMOD

I'm not sure what exactly is causing the problem on the second converter output. Can I get some help in figuring out what the exact problem is on the second converter? And yes I've done a transient simulation for a longer time, up to 2s but the V(3) output was consistent.

I'm sure I have the correct model, I used a couple other SCR models from online obtained from the littlefuse website but the SCR Model from the book was better in simulating on LTSpice. Any help would be appreciated, Thank you.


texts: Questions about microbit and Nordic nrf51

texts:
My first question here and please excuse my English. I am playing with Nordic nrf51 Timer module (using a BBC microbit v1.5). I am using Timer1 to flash a LED. I stored a value to the capture register CC[1] which, according to the reference manual, will generate a event compare[1] when the Timer counter register reaches that value. The compare[1] has an offset address and whenever the compare[1] turns to 1 I toggle the LED and have to manual set compare[1] to 0 + clear the timer counter to count from 0 again. The pseudo code is something like this:
Timer_source=timer1;
timer_bitmode is 16 bit
Prescaler=9 => 16MHz/2^9= 31250 ticks per second
Write 31250 to CC[1] ( 1 second) => compare[1] event will be generated when timer reaches CC[1]'s value
set LED_pin as output;
Start timer;
while(1){
check compare[1] (timer address + offset) if it equals 1 => toggle LED, set compare[1] to 0 and restart the timer
}

It works as expected but I would like to make sure I understand it: the compare events each of them is it a register or just 1 bit of a register which turns 1 when generated?


texts: Fast (high) frequency hopping with off-the-shelf components

texts:
I am looking for the easiest solution to

synthesize 1.6 - 2.4 GHz (qudrature)
in steps of 4 MHz
settle within 10-50ns
precise timing control when to switch frequency (e.g., at rising edge of an external signal, frequency should be updated)
total integrated phase noise (jitter) between 1 MHz and infinity < 400fs rms
Cost and power is irrelevant (in a meaningful range) to the extend that they do not add significant complexity or add other problems (like thermal issues)

In considered the following solutions:

PLL. Settling time cannot be met
DDS: The best I found is the AD9914/AD9915 with fclk=3.5 GHz (i.e., fmax=1.75 GHz)
DAC/RFDAC: There are many options (AD9161 at 12 Gsps etc). However, they require that the digital signal is generated externally and high-speed samples pumped into the DAC. A high-end FPGA could implement DDS logic and spit out the samples. However, this has tremendous complexity. Besides, these high-speed RFDACs are 200 ball BGAs requiring 12 PCB layers, serdes and a careful design that would take many months to complete
DDS+Mixer. Let's take the AD9910 as an example followed by a mixer with fc=2 GHz. The issue is that the mixer needs to be an image rejection mixer and hence I need two DACs for each I and Q channel - a total of 4 DDS and 2 Quadrature!
DDS+I/Q Modulator: Basically the same as 4 but the output of the DDS systems is shared between the modulators (2xDDS, 2xIQ Modulators). This would be "ok" but it cannot control the phase difference between the I and Q branches for I/Q compensation.

Is there anything I forget? The AD9956 is a 400 MHz DDS system but claims:

  The AD9956 uses advanced DDS technology, an internal high speed, high
  performance DAC, and an advanced phase frequency detector/charge pump
  combination, which, when used with an external VCO, enables the
  synthesis of digitally programmable, frequency-agile analog output
  sinusoidal wave- forms up to 2.7 GHz

Two application circuits are given in the datasheet:

but I do not understand them. What would be the switching time from, say 1.6 to 2.4 GHz for these?

Is there any other hybrid DDS+PLL or DDS+Mixer system?


texts: Electrostatic charge changes crystal frequency

texts:
What are the reasons of this undesired effect:

I have a PIC with RTC (Real time clock) connected to an external 32.768kHz crystal for auto-calibration (according to PIC Manual handbook). The crystal is also connected with two 12.5pF capacitors (to ground).

Just after start up of the PIC, the flow of the time given by PIC is wrong (a second given by the PIC are 4 real seconds more or less) and it keeps so until I touch the cover of the crystal with the finger, then the time flow right. After shutdown and restart the problem appears again. I mean it is a problem with electrostatic charge. but why and from where comes the charges?

The PIC pins for the crystal are defined according compiler rules for external clock, could the problem comes from the PIC pins? (due to float possible state)
Is it a signal that some capacitor is broken? Or maybe the 12.5pF are not enough...
The crystal is placed only 1 cm from the pins, should it be even closer?

Note: question was updated following comments bellow -  original capacitors were 22pF, now I have changed to 12,5pF but the problem persist.


texts:
Is there a type of servo that can be de-energized and moved manually while giving input back on its position?

So say it's at 0 degrees, I turn it to 5 degrees and I get input back from it indicating it is at 5 degrees. Obviously it would have to be de energized or else you would not be able to move it manually

Thanks


texts: I'm looking to delay a clock signal with a pair of inverters (74HC04.) The circuit is 3.3 Volts, and the data sheets for the HC logic group only list 4.5 and 2.0 Volt tpd. Is linear interpolation sufficient to determine the propagation delay? As I recall, the curve is non-linear, so would the delay be more like what's shown for 4.5 or 2.0 Volts?


texts:
I am planning to do a high current (200A+) PWM in a PCB and I am afraid the PCB traces inductances will be a huge problem...so I have some questions:

1- How may calculate the trace inductance?

2- As wider the trace the less the resistance, but this works too for inductance?

I know there will be problems with the frequencies but I just want to get the feeling...


texts: Question regarding dielectric breakdown (especially for stun guns)

texts: This question occurred to me after looking at some models of stun guns.  What I noticed was that some of them like one I bought had metal extensions sort of like prongs, or like tiny metal cones.  I think the idea of them is to hurt an attacker in an additional way and to press the electrodes into their clothing.  What I thought of was if the extensions/prongs were not surrounded by clothing and there was a little air around them, would it not shock someone with clothing that has a higher breakdown voltage than the air gap between the electrodes?  In other words, for a million volt stun gun, would there need to be about 30 cm of distance between the electrodes, or they would need to be pressed with sufficient pressure so as to not leave any parts of the metal exposed?  In relation to that, does having pointed electrodes make the current flow out of the points and through clothing rather than around because the electric field strength is stronger near edges/corners of conductors?


texts: How do I reduce the brightness of an automotive lamp?

texts: I would like to know how to reduce the brightness of the running lamp in the tail lights of my tow car. It is a MINI Cooper and each tail light contains one single filament running lamp. These lamps also act as the brake lights in normal(not towed) driving. I believe the car's electronics change the voltage from say 5.5v as a running light to 12v as a brake light although I haven't confirmed this. Since I will tow this car with my RV, the running light feed from the RV will range 12v-14.6v. This high of a voltage will appear that the brake lights are illuminated and also create unnecessary heat within the tail light. I don't know how to calculate the proper size resister to safely reduce the brightness to say maybe half. There are two lamps, 21w each that are fed from one line. I have diodes in the circuit so there won't be any type of back feed into the car's electronics. Thank you for your help. Howard


texts: How to connect two points of the Board Shape with an angle of other than 45º?

texts: I'm drawing the Board Shape of my board and one of the corners the connection has an angle other than 45°.  Altium is not allowing me to make the connection, does anyone know how to solve this?


texts:
Occasionally I am faced with a problem where I am faced with a device that needs two of it's inputs to be shorted together for something to activate (Think smoke machine or gate motor).

This is the circuit I have been using:

simulate this circuit – Schematic created using CircuitLab

The idea is that the resistance of the mosfet goes down when a signal is applied which simulates the short circuit. My concern is that this feels very unconventional.

Is this an acceptable method of doing this? are there more professional methods?

note: it isn't as simple as sending a '0' signal. That often isn't how these systems work.

thanks.


texts: What safety concerns are there for discharging capacitors directly through a short?

texts:
If I discharged my caps on thick bronze rails connected to the caps by copper wires and nothing else, would that be dangerous? I'd like to safely discharge the caps as fast as possible for the highest amount of current I can get.
What's the best method to use multiple capacitors in a way to maximize the current safely while minimizing power loss?

Bonus Question: I said bronze, but I need the highest amperage possible while being sturdy. What would be a good material? Could copper be better?


texts:
Sign-extension works this way: You pad with zeros for a positive number and pad with ones for a negative number, because of two's complement, and left or right depends on endianness.

Did I understand it correctly? Do I need to know more if I'm looking to understand it as it is described e.g. in Pattersson (Comp. Organization)?


texts: How to supply power to a 12V solenoid from China, getting hot

texts:
I bought this solenoid from ebay and was wondering how to power it.

It says 12 volts as you can also see from the picture, but I tested it with putting a 9V battery straight to its terminals for a while, the solenoid and battery got hot after a while.

I measured it with a multimeter and it read 9.0 ohms. Putting the multimeter through it measured 0.53 amps. Both with 9V battery

If I had battery eliminator that gave 12V output, what other components would I need to make it not go hot? Do I need some resistors?

And is it possible to get its power usage to a minimum with it still opening using various components?

Can I add lots of resistors and the voltage remains 12?


texts: Minimum requirements to interact with PCI Express

texts:
I have a relatively simple project (from the user point of view) in mind. I want to develop a very simple PCI Express (x1) card that users can put into their system and toggle some GPIO's from a GUI program (e.g. to turn on/off some stuff). The project might sound stupid as there are better alternatives but I have decided to do this to force myself get good at stuff. So I want to do PCB design and programming (GUI and eventually a driver).

So my question is, what are the minimum requirements to have such a simple extension card?

Is it possible to do this with a STM32 controller? or Will it need FGPAs or dedicated chips/ASIC? I can imagine there is some sort of handshaking going on when a card plugs in into a PCIE slot or at boot time...

And where can I gather more information about this?


texts: IR photodiode doesn't show 38kHz carrier wave on oscilloscope

texts:
I have an IR photodiode, part number PDB-C134F, as shown here.  I'm trying to use it to retransmit a remote control signal that uses a carrier frequency of 38 to 40kHz.  However, when I connect the diode to an oscilloscope and look at the received signal, the carrier is lost.  I simply see a square wave encoding the data
(with a pulse width of 0.5ms and an amplitude of about 0.4V) but no finer square wave (which should have a pulse width of around 12us).  My oscilloscope is very basic (the Xminilab), but it is sampling at 2MS/s, and is rated at 200kHz, so I would think that it should be able to see the signal.  It can see a 40kHz signal that it generates on its waveform generator output.

In my test, the diode pins are connected directly to the scope inputs, and there are no other elements in the circuit.  I've also tested it after amplification with an opamp, and see the same thing.

Am I misunderstanding how this part works?  Or misusing it or the scope?

Thanks for any advice!


texts: Does the output voltage depend on the resistor?

texts:
If I have the function for the output voltage between node 1 and node 2 that is dependent on the input voltage, does R2 play a role in the function or is the output voltage just the Voltage over L1?

Don't mind the actual values of the parts, it's a general question
Thanks.

simulate this circuit – Schematic created using CircuitLab


texts: My son is doing a Science Fair project on dc voltage from trees. We are only getting about 1 volt when they are put in series. He's in 6th grade, what is a simple way to increase the voltage ?


texts: I cannot seem to understand this. Please explain the Kvl part for this as well.


texts: How is a series resistor limiting the voltage for a diode?

texts:
I try to understand some basic concepts, but I'm stuck with this question.
I have this schematic, with a power supply 9V, a resistor 450ohm and a LED.
Assuming the LED consum 16mA, this resistor have an voltage drop of: 7.2V
My questions is why this resistor "limit" the voltage with this voltage drop? I learn that resistors limit the current, not the voltage, so my power supply can deliver 1A, only 16ma would reach to the LED, so why I have a LED power by 9-7.2v = 1.8V and 16mA, and not power by 9V and 16mA?


texts: Transmitting ASCII 'A' over SPI Protocol

texts:
I'm working on a project that involves connecting directly from the TRS jack of an iPhone to a SPI port on a microcontroller.

So the iPhone is the master and the microcontroller is the slave

So let's say the left speaker channel of the iPhone is responsible for generating clock signals

Now how do I transmit for example a single ASCII byte 'A' from the master to the slave?

I can see that each time the clock edge rises ( let's say passes zero ),  both master and slave read off a new bit -- whatever the state of the respective MISO/MOSI

But how to byte-align?

Binary for 'A' is 0100 0001

How do we distinguish that leading 0 from the silence that preceded?

It seems to me that a sensible protocol would be to use 0xFF or something as a start Sentinel,  and have the next byte dictate the number of bytes ( between 1 and 256 ) in the packet that is to come.

And then these bytes get sent one after the other, may be followed by a parity byte.

Maybe each byte would have parity bit...?

As soon as this ' packet ' has arrived,  the decoder could start looking for another start Sentinel.

So that's how I would go about designing SPI.   so I'm trying to find some documentation that tells me how it is actually done.

But I'm getting really frustrated bouncing around Google / Wikipedia / IRC

Is there someone out there who understands this protocol, and wouldn't mind giving me a really simple example usage -- sending the single character 'A' via SPI


texts: What are the 3 box-symbols on the teensy2.0++ schematic?

texts:
I'm talking about the 3 boxes that form a column, near where it says 5V on the top of a lead and 3V below it. The lead comes out of the middle box.
The datasheet for the AT90USB1286 mentions nothing about this, only that there should be 22Ohm resists between D- and D+ (check) and a 1uF cap to UCAP (check).
USB1 supplies 5V (default usb power).


texts: How to achieve bidirectional DC-AC power flow with a Grid-tied Inverter?

texts:
Question:  How can I achieve DC-AC bi-directional energy flow control of a grid-tied inverter?

I want to control the bidirectional DC-AC power flow of a 3-phase grid tied inverter that I am developing. The inverter should perform DC-AC as well as AC-DC action so that I can either charge a battery from the grid, or transfer energy from the battery to the grid.

I have attached the topology I am currently working with.
This shows the overall system but the question is focused on the DC_AC bidirectional aspects.

_________________________________________________

Background information:

Here is the short description of the steps I completed.

I used Clarke and Park transformation to implement Phase locked loop(PLL).
Implemented Space Vector modulation for PWM generation.
Completed synchronization with the grid.
Now testing power flow segment
I used dsPIC33fj32mc202 microcontroller for implementing the inverter. Really it was a very hectic journey for me as I have to learn DSP assembly instruction of the microcontroller for fast calculating all the algorithm related to grid-tied inverter.

Now I want to control the bidirectional DC-AC energy flow.
I want to charge battery sometimes. I studied a lot of papers. But could not recover the information about how to change the power flow direction.


texts: Control power output of a stack of 4 Lead Acid Battery

texts:
I am currently working on a school project that have a stack of 4 (12V 20A) lead acid charged by adapter from wall outlet. With 4 individual batteries, if i put in series, i will have 12V, 24V, 36V, and 48V output. My questions is how can i control the specific individual battery that i want to use and not use the whole stack of battery to step down to a desirable voltage level.

For examples: 4 of the batteries now named #1, #2, #3, and #4

The load is only ask for 15V, so now i only need to use 2 from the stack of 4 batteries.
   In this case, i will use battery #1 and #2. Then, i step it down from 24V to 15V, while keep the other 2 batteries charging.

When i notice battery #1 and #2 draining out, i can switch my source to battery #3 and #4. Then, charge battery #1 and #2.

Thank you.


texts: Why this evaluation board use different track impedance than the right one? Ethernet PHY, routing

texts:
Im doing a design with a implementation of 1Gb ethernet switch, for that I bought a evaluation board to do it well.

The problem is that in the layout of the ev board I can check that the track impedance used to link the output of the chip (which has the PHY interface integrated) to the RJ45 connector is different than the right one which is suposed to be 100ohms as many routing guidelines for Ethernet say.

Here is the impedance calculation. (the values are taken from the layer stack and the design of the PCB that are included in the documentation associated with the user manual)

And here is the datasheet of the evaluation board that Im using:

http://ww1.microchip.com/downloads/en/devicedoc/50002587a.pdf

Any idea why the differential impedance (83,73ohm) is so far from the ideal 100ohms recommended in ethernet routing?

thank you all!


texts:
I have some code that takes in 2^X samples and outputs 2^Y samples, where X and Y are integers and Y is less than X. So for example X=6,Y=4, I ingest 64 samples and output 16 samples.

As of right now, X and Y are generics, but I would like to make them, or the ratio between then, or the log2 of that ratio a signal, so that I might change my operation at runtime via a register write or something.

In my internal processing, using the example values of 64 and 16, I have to do some addressing and counting, and to generate some of the addresses I have to do soemthing like this:

constant pkt_addr_pad : std_logic_vector(15 -Y downto 0) := (others=>'0');
-- In this example is is 12 bits of 0
.
.
.
raddr_short <= pkt_addr_pad & raddr (Y-1 downto 0);

to convert raddr which can contain values from 0 to 63, to raddr_short which only contains values of 0 to 15; effectively discarding bits 4 and 5, masking them to 0, whatever you want to call it.

I'm looking for the best way to be able to have Y change at runtime. obviously the timing for Y is relaxed, as it changes unimaginably less frequently relative to the actual address, and when it does change, the rest of my logic will be in an idle state such that raddr/raddr short won't be changing

I'd really rather avoid the whole:

raddr_short <= x"00" & "00"  & raddr(5 downto 0) when Y = 6 else
               x"00" & "000" & raddr(4 downto 0) when Y = 5 else
               ....
               x"00" & "000000" & raddr(1 downto 0) when Y = 2 else
               x"0000";

as I've actually 4 of these things running at once, and as such have arrays of slv16 for each of the raddr/raddr_shorts, as well as waddrs, and...

Although I guess I could put the MUX in a function to clean up the code, but there has to be a better way. maybe some thing liek:

constant zeros16 : std_logic_vector(15 downto 0) := (others=>'0');
.
.
.
raddr_short <= zeros(15 downto Y) & raddr (Y-1 downto 0);


texts:
I'm planning to try to build an electric go-kart. My idea was to use a 12V starter motor from a car to power it, since used ones are fairly cheap and easy to get. (I already have 2 of them to experiment with).

I've read that starter motors aren't a good choice because they aren't meant to run continuously and will get too hot. But I was wondering if I limited the current, maybe with external resistance connected in series with the motor, will that help to prevent the motor from overheating?

Starter motors normally draw a huge amount of current in order to have enough power to crank an engine, which needs a lot of force because of the engine compression. But I figure I wouldn't need to run the motor at full power just to drive a go-kart.

Could limiting the current help with this?

I thought of several different ways, including using heater elements or even just a long coil of wire for enough resistance. Since starter motors draw about 100 amps when cranking an engine, I figured if I limited the current down to maybe 40 amps, that might work to allow the motor to run longer.

How can I limit the current to a starter motor to 40Amps?

I need a cheap, simple way to do this if possible. A PWM motor controller isn't really option because it's hard to find ones that can handle enough current, and they seem to be expensive.


texts: Light detector linearity with varying wavelength

texts:
Given the same intensity of light, in varying wavelengths, which is typically more linear with their output: Cds (photo resistor) or a Photo transistor?

I would assume that the junctions in the transistor or photo diode would be much more sensitive to a smaller range of light frequencies, but I'm not finding any information to back this up.

Edit: I added an answer below from the research I was able to do after the initial answer.  Hopefully it is helpful to some.


texts:
I understand you can create a serial transmission between the Raspberry Pi and an Atmega328 using the GPIO:
http://www.raspberrypi.org/phpBB3/viewtopic.php?t=22736&p=293668

I'm interested in having more serial options, like the USB ports. I managed to do so, but with an Arduino board:
http://www.doctormonk.com/2012/04/raspberry-pi-and-arduino.html

I've searched a lot on this topic and got pretty confused. Is there a safe way to use the RPi's USB port for serial communications with an Atmega328? What would be the easiest safety intermediate circuit? Thanks!

(Note: Easiest as in minimal number of components, like transistors and resistors. Preferrably NOT ICs. This is to reduce size and ensure availability of components in my country)


texts:
I was simulating the below opamp integrator circuit with pulse current.As this is an inverting integrator I thought it would integrate the input current and give me a triangular waveform.

But after simulation in PSpice I got the following result.

Can anyone explain why the current flowing through capacitor jumping to 0 to 2u instead -1u to 1u.
Also why Vout is almost constant at 15v.

From my understanding, if dc current flows through capacitor then the voltage across through  capacitor will be ramp.


texts: Relay-like behavior without constant power

texts: I was wondering if there is someway to have relay-like behavior, but without constant power to the relay. For example, if my understanding is correct, if I wanted to control power from an outlet using a relay, it would either be normally on or off, but when power was applied it would switch to off or on respectively. Is there a way to achieve the same type of behavior but without constant power? For instance, a pulse of power would switch the "relay" to on, and another pulse would switch it to off?


texts:
I received SmallHD 5" display which was broken by supplying 14.4V by a mistake. It runs on 7.2V typically. The monitor is fine, just the backlight went bad. I replaced TPS61180 right off the bat but this didn't fix the issue. Right now I'm getting 15V on the output which is too low to drive 14 LEDs (7 in series, 2 in parallel).

I checked all caps and they seem to be fine. D1 looks good to me (can it affect the output voltage?).
I'm out of ideas for this one. The backlight is flashing once at boot and then it's off. I tried replacing the IC a few times, it's not the IC causing the problem. Do you have any idea or clue what should I check next? I don't know how LED drivers work so I hit the wall.
BTW. The part marked as Optional is not included in actual circuit.


texts: Simple way to avoid current draw on resistor divider sense?

texts:
This is a simple, but complicated question.

I measure voltage on several lines, more than 3'000. The lines can be up to 100V.

I only need to measure at certain time, and would like to avoid current draw from the sense lines when it's not being measured.

I was thinking to use a mosfet and detach the whole VSS from the bottom side of the resistor divider, but the AN are connected to sampling logic, which has internal protection diodes to 3V3, so it will still draw current.

Given that I have a lot of those lines and the application is cost sensitive, I would like to avoid to have a P Mosfet on each line with the resistors and zener that would be needed.

Is there some trick possible in here ? Maybe some component made for it I don't know about ?

Update:

The answer of Edgar Brown is valid, but is a bit complicated to drive the gate, given the voltage of the mos will vary.

Also I do not have space on the PCB to add mos between the two resistor of the divider (or would need to do quite a lot of re-routing).

I have another possible solution:

Q53 would decouple the sense divider from the ground and the other Q would decouple from the sensing IC.

If the gate of Q54 is driven as a open drain, Q53 would be driven first, bringing Q54 to a few V to VSS and then Q54 can be driven.

Only one resistor from all the Q54 gates to the Q53 Vd sould be enough?

Update 2

I think I found a better solution, adding a bias voltage before the VSense. Simply biased at the same voltage of the off state.


texts:
I have a circuit to solve:

In this approach, I inferred the V1 from the parallel connection of voltage source. For the second node, I have applied the KCL.

I also tried to do it another way, by modifying the source E4 ( pushing it to the branch with G2 ) and then tried to apply nodal analysis.

Equation was like :

(G2+G1+G5)*V2=E4G2+E1G1-J

V2=(E4G2+E1G1-J)/(G2+G1+G5)

As You can see, both results differs by 'G5' in denominator. What is wrong?


texts: What is the purpose of this transistor in an Apple Time Capsule?

texts:
While taking apart a 2009 Apple Time Capsule, I found a 2N3904 NPN transistor on a 2-wire cable with the emitter connected to one wire and the base and collector connected together and to the other wire. The transistor was physically attached to the back of the hard drive with Kapton tape. What is the transistor being used for?

simulate this circuit – Schematic created using CircuitLab


texts: Explanation for dual slope DVM voltage measurement

texts:
I want to design a dual slope integral digital voltmeter.After reading its working I got a doubt on its voltage measurement.

How can we say that our required voltage is the count of t2 time period as we have taken t1 time period as the time to charge the capacitor using input voltage(the voltage we measure.)


texts:
I was reading this PDF which tries to explain the concept of poles and zeros of Laplace transform.
My question is about FIGURE 32-5(b) on page #591.

I don't understand why the area is said to be zero when, as shown, it should clearly be some negative number. The mentioned PDF does try to give an answer which I don't understand.

Figure (b) shows one of the special cases we have been looking for.
When this waveform is multiplied by the impulse response, the
resulting integral has a value of zero. This occurs because the area
above the x-axis (from the delta function) is exactly equal to the
area below (from the rectified sinusoid). The values for σ and ω that
produce this type of cancellation are called a zero of the system. As
shown in the s-plane diagram of Fig. 32-4, zeros are indicated by
small circles.

You can consider it to be a follow-on question to this comment where @AJN tried to explain it further but unfortunately I still couldn't get it. I thought it'd be better to ask it separately. I'd appreciate if you could help me with it?


texts:
There are missing connector pieces in this PCB that I was working on and I swear that there was no connector there in the first place, so I ruled out me going insane.I circled the connectors in gray.  Are these connector pieces for something else off the board I have?

PCB Details

This PCB belongs to a Sharp 1999 TV.  Was connected to four other small PCB one the buttons for the TV, the other the jacks on the TV, the speakers, and deflection coil.


texts: I have 3 Li-ion cell of 2000 mAh. I want to charge them in series and with charging I want to connect load with it load is of 1 A and charger which I am using is of 2000 mAh, 12.6 volts. Does it make any harm to the batteries? One more thing it will be plugged in for 24/7.


texts:
I am trying to create an RF remote that has 6 buttons but the RF encoder only has 4 inputs.
Is this possible and preferably I would not like to use a separate chip.

This is what I am using:

http://www.farnell.com/datasheets/56726.pdf


texts: Techniques for digitally copying video laserdiscs

texts:
I’m attempting to design a system that can back-up the information stored on a video laserdisc by interpreting the RF signal generated by the photodiodes within the optical deck of the player.  The RF signal is a frequency modulated analogue output with several carriers (with the highest frequency being around 10 MHz).

There are other projects around that attempt to sample the analogue signal using high-speed ADCs to capture the sinusoidal output in its raw form but, due to the Nyquist, you require at least 20 MSPS (preferably somewhere in the region of 40 MSPS for accurate sampling).

It occurs to me that this may be inefficient.  The information is encoded on the laserdisc as a series of pits and gaps that cause the RF signal to swing either positive (pit) or negative (gap).  The analogue nature of the RF signal is therefore caused by the laser moving in and out of the pits.
This means that, by passing the signal though a high-speed comparator, I could recreate the digital nature of the encoding on the disc.  Since a laserdisc is analogue (unlike later technologies such as CDs) the length of the pits and gaps is the important information.

Since sampling at 40 MSPS at 10-12 bit resolution requires a lot of bandwidth I’m searching for a better method that takes advantage of the fact that the original signal is only 2 states and that only the width of the signal is important.  I’m not really that clued up on sampling theorem.

What sampling technique can I use to efficiently capture the RF based on the fact it is a digital signal where the width of the pulses is important?


texts: why the power absorbed by RL load in half wave rectifier is I^2R not V^2/R nor VI

texts:
why the power absorbed by RL load (resistor in series with inductor)  in half wave rectifier is I^2R not V^2/R nor VI.
V , I are with RMS value.


texts: Omitting USB 2.0 pins on a USB 3.1 connection

texts:
I am in a situation where my project requires the use of a slip ring so wires can freely rotate. I will be limited to the number of wires that can run through it, which is a total of 12.
I have a USB 3.0 device that I want to connect through the slip ring using USB-A 3.1 and USB-C breakouts on each end. I don't need to have the redundant row/reversible plug option so I will only be working with one row (A1-A12). The device I am connecting will only be using a 3.0 port, never 2.0. Through some reading, I found that the D pins shown below exist for USB 2.0 compatibility:

It seems that they are only there to transfer data if the plug is connected to a USB 2.0 port. Can I safely omit the USB 2.0 pins in this situation? Doing so would free up two wires on the slip ring which are important for connecting another device.


texts: Calculate expected voltage around a resistor

texts:
It's been a few years since I first studied the Ohm's law at school.
Now I'm really getting into electronics, and I must admit a part of it still puzzles me.

I know this is kind of a strange question, but I have no clue how to express it otherwise, so I'll just lay out my reasoning.
The following train of thoughts is wrong and/or incomplete.
Please stop me whenever I'm wrong (even for the sligthest thing), and complete this reasoning.

Here it comes:

Let's make a circuit with:

6V battery (typically 4 AA batteries)
2k ohms resistor
LED, for the sake of doing something

Circuit map:

simulate this circuit – Schematic created using CircuitLab

From Ohm's law, we know that the current in the circuit will be of (considering only resistor has any resistance)

\$ I = \dfrac{V}{R} = 3mA \$

I do understand that the current is limited due to the resistor... crystal clear.

The book tells me that, if I measure the potential difference between both sides of the resistor, I will have something between 0 and 6 volts.

Sounds legit:

can't be 6 volts because the two ends of the battery are connected, therefore lowering the potential
can't be 0 volts, since the current does not freely move around, due to the resistor; resulting in one side being more negatively charged, and the other more positively charged, since the electrons can move faster to an end of the battery than through the resistor.

What I don't understand (and if my whole reasoning is right until now), is:
How can I calculate the expected voltage around the resistor ?


texts: Altium: how to assign a net class to unconnected pins?

texts:
I have PCB with a clearance rule for nets that can be exposed for higher voltages:

In the schematic I put a blanket around the area I need to be assigned as higher voltages nets (I called this class "Line"):

However the unconnected pin (pin 12 of K2 relay) has no net assigned - no net class consequently. So in the topology the clearance is not corret:

Until I put some arbitrary net label (NC1).

This can be solved for simple cases like mine. But if there will be an IC with many unconnected pins needed to have a net class - it will be a tricky thing.

Any thoughts?

UPDATE

As Matt suggested I tried to put Net Class directive directly to the pin as the following: strange but this didn't work, the pin still has wrong clearance.


texts:
How do I use a PWM unit and/or microcontroller to have transistors progressively all turn on and then progressively all switch off? It's for what will most likely be an 18-pulse inverter.

Essentially, I'll have 18 transistors (2 rows of 9) and I'll want the top row to come on progressively, then the bottom row, then I'll want the top row to switch off progressively followed by the bottom row. That being one cycle, I'll need to have that happen 60 times per second.

I think I can use a PWM/motor controller to do this and/or a microcontroller, but not sure where to look to firmly understand the schematic.


texts: Create Transformer Center-tap From 2nd Secondary

texts:
After ordering this 200VA, 32V transformer, I realized that it doesn't have a center tap on each secondary, which I need to have. (duh on my part) So I want to use 110V across the 220V primary leads to give me half the voltage at each secondary, resulting in a single secondary of 32V and a center tap.
I know that this works because I have done it and observed that the output is 32V RMS with a center tap, but I want to make sure I'm not throwing away half the VA rating by doing so. I read TONS about transformers trying to get a definitive answer to this, and I think that the core saturation and the secondary wire size and associated voltage drop and heat are the main concerns, along with the fact that the ratio of number of turns is proportional to the ratio of the voltages and inversely proportional to the ratio of the currents in the primary and secondary. So on those points, I think I'm not reducing the usable 200VA, with the possible exception of secondary wire heating.
To illustrate what I mean using the image below, I would wire-nut the middle black and red primary wires together and connect 110V across the top red and bottom black wires. And on the secondary, I would connect the middle blue and green wires and use that connection as my center tap. I would use the top green and the bottom blue wires as my supply rails and there would be 32V RMS across these rails. If that's confusing for me to say rails, I'll add that I'm using a bridge rectifier and 2 shunt capacitors to make them into +/- 45-ish volt rails for an amplifier.

Yes, I know that this is NOT standard, and this is not for a commercial product, so please don't reply simply that this is not standard or that it will void my warranty.
There is a similar question here with 2 answers to my question, but unfortunately those two answers contradict each other exactly. Also, here is a question with a very promising title, but the answers don't answer my question. The other similar questions don't have answers which address the current-rating-doubling part.
Please weigh in if you know whether I can safely get the full 200VA in this way.


texts: Microchip's XC8 Linker doesn't recognize some custom section names

texts:
Slightly related to this one: https://softwareengineering.stackexchange.com/questions/254734/microchip-xc8-how-to-pack-code-against-an-upper-limit

I can relocate code just fine, but I'm having some trouble with constants:

Example code:

#include <xc.h>

unsigned char buffer[16];

__section("SecConst1") const unsigned char constants1[] = "const1";
__section("SecConst2") const unsigned char constants2[] = "const2";
//__section("SecText1") const unsigned char constants1[] = "const1";
//__section("SecText2") const unsigned char constants2[] = "const2";

__section("SecText1") void fill_buffer1(void)
{
    unsigned char i = sizeof(constants1);
    do
    {
        i--;
        buffer[i] = constants1[i];
    }
    while(i);
}

__section("SecText2") void fill_buffer2(void)
{
    unsigned char i = sizeof(constants2);
    do
    {
        i--;
        buffer[i] = constants2[i];
    }
    while(i);
}

__section("SecText") void main(void)
{
    while(1)
    {
        fill_buffer1();
        fill_buffer2();
    }
}

Linker Options:

-L-aClass1=1200h-17FFh,1800h-1FFDh -L-dClass1=2 -L-pSecText1=Class1 -L-pSecText2=Class1 -L-pSecText=Class1

If I build it with no linker options, or if I only specify the functions (as above), it builds with no errors and I see all of the section names in the map file, so I know they're all there.  But if I specify where to place a constant, the build fails because that section name was not defined.  If I switch to the other set of constant declarations (swap the comments), then those names are suddenly not defined.

I feel that this is a bug in the toolchain, and I've told Microchip about it via their support site, but does anyone know of a good workaround?

I'd rather not specify the address of every constant directly in the source code because the complete project has a lot of them and they can all change size and contents from one version to the next.

I'm using a PIC16F1454, but I'm pretty sure that doesn't matter for this problem.


texts:
I am trying to measure average current draw of low-duty cycle, low current devices.

For example, a Bluetooth Low-Energy device might draw 16 mA during the radio transmissions (for a millisecond or so), and background / idle current at other times, say 3 uA.

These transmissions happen infrequently.  So taking a current reading with a DMM that updates once per second gives wrong readings, because the DMM does not have a proper anti-alias filter, so the reading depends on whether one or two radio transmissions happened during the DMM's sampling period.

To measure this current I have been using a custom-designed circuit, an external shunt with an RC across it, where the RC is set to several seconds.  Then I measure across the "C" on a low-voltage range of a voltmeter.

Are there any ammeters with proper anti-alias filtering?  I have tried Keithley sourcemeters and HP34401 meters, and neither will do it.  (The Keithley has a triggered current measurement mode, which at least gives a stable reading, but this won't give an accurate average reading.)


texts: Applying voltages to conductors in a passive-matrix LCD

texts:
In the picture the horizontal and vertical lines are the conductors and the intersections are the pixel positions
I want to turn off the pixels which I've filled
So for that I've to apply an electric field across these pixels
For one pixel I have to apply voltage to conductor 1 and a
And for the other one apply voltage to 2 and b
But when these  conductors are conducting ....then the pixels which I've shown with just a circle also get turned off.
How exactly is then an entire frame buffer drawn on the screen?


texts: Can you change the parameters of all of a certain kind of component in LT Spice?

texts: I was wondering if there was a function in LT Spice that I don't yet know of that would allow you to either select a bunch of components, or all of a certain kind of component (capacitor, resistor, etc.) and set them to a certain value?  I was simulating the output of a voltage multiplier with many capacitors and I was going to try a few different values for the capacitors.


texts: How to non-destructively test unknown LED strip?

texts:
I have a tiny LED strip that I took out of a smashed LCD in my Digital camera. I remember lighting up the strip in the past but can't remember how.

I have been trying now with my bench supply to power it up but can't get it to light, I'v gone as high as 3.7 volts with no lighting, I fear I may have already destroyed it, but if I havn't how do I go about testing it without blowing the LEDs?

Image to indicate scale and layout, dots on paper are 2mm spaced:


texts:
As a now-professional EE, I'm slightly embarrassed to be asking what I feel like is a simple question. But I'm stumped and google isn't giving me good answers.
I'm trying to PWM a string of LEDs via a low-side NMOS switch (a PMV40UN2). On the surface this seems like a simple thing to accomplish. However what I'm seeing is that the LED string is always on, regardless of the state of the MOSFET's gate.
Here's the circuit:

My first test was to pull out the LEDs + resistor and throw in a 10K resistor from 12V to the FET's drain, to see if it was a bad solder joint or something else on the PCB causing the issue. Here's the plot for the gate (yellow) and the drain (purple) in that setup:

So the MOSFET is properly pulling its drain to ground when +12V is applied to the gate. Perfect. Now we look at the same test points with the 10k resistor still in palce, but with the string of LEDs and the current limiting resistor added back in:

I can see the drain trying to go high in the off-state, but for whatever reason it's not able to do it and instead stays low. The result is what I originally saw, the LEDs are always on.
I'm an RF engineer by trade, so I don't deal with DC all that often. However it's pretty obvious something simple(?) is going on here that's totally going over my head.


texts:
I'm making a circuit which basically should turn on a led when it's dark and turn it off when there is more light. To test the light I've used a photoresistor, and to turn the led on/off a comparator (an LM339N). Here's my circuit:

My problem is that the led DOESN'T glow and there isn't any voltage/current on the comparator output. Why!? I checked it out, all the inputs works fine, their voltage is not 0.

Well, the generator is actually 10V, but it shouldn't matter I think (even with 5V it didn't work).


texts: Why my charging circuit always heat up and malfunction?

texts:
I am working on troubleshooting bunch of overheating PCBs. I found that 2 components on my charging circuit always heat-up or malfunction even after replacement.

The first problematic component is the Power management chip LTC 4085 which connects the Li-ion battery, voltage converter chip, and the wall adapter. 5V coming from the wall adapter and is passed to the LTC 4085 chip. When the charger is connected, the battery charging voltage is 4.2V from pin 14. When charging is off, the battery voltage is supplied to the converter chip. The problem with this power management chip is, I always get the wrong output on Pin14 to the battery. I have replaced the chip, cleaned up the solder pads underneath but still many failed to have the correct output (either 0V or >4.2V).

The second problematic component is the voltage converter chip TPS63001, convert 5V to 3.3V. This component always heats up. However, it has the correct output. Again, I have tried to replace the components that heat up and clean the solder pad, but the issue is still there.

I have also tried adding a noise filter capacitor on the charging cable to make sure the input voltage is steady around 5V.

Here are the schematics of the design:

Thank you for the responses so far. I am still struggling with this issue.

Here are the link of LTC 4085 and TPS63001 datasheet:

http://cds.linear.com/docs/en/datasheet/4085fd.pdf

http://www.ti.com/lit/ds/symlink/tps63002.pdf

I have also tried the following method trying to locate the issue recently:

Increase my R11 to 100Kohms, which connected to Pin12 on U1. This reduces the battery charge current from 1.2A to 500mA.  I previously found out that the recommended charge current for my battery is around 800mA. 1.2A can be too big.. However, after I switched to the 500mA settings. I still get some board to heat up.

Any input will be highly appreciated!

Thanks

One more update on the schematics..

The current board doesn't have these components( Q5 and R40 which connect to Pin 11 from the LTC 4085). Can this be a factor of heat up and malfunction issue?


texts:
Recently I was experimenting with the NAND-gate representation of an adder circuit and tried to implemenent it without crossing wires. So I got this:

The carry is negated, but when chaining two of those together to a full adder, the negated carries can be combined with a NAND gate to give a normal carry. My questions are now: Does this design have any advantages or disadvantages compared to other ones (e.g. the one Wikipedia shows https://en.wikipedia.org/wiki/Adder_(electronics)) and is it used anywhere (I searched, but couldn't find it)?


texts: home audio: How much current flows through my speaker amplifier's output?

texts:
In a recent project I used relays to electronically control a multi-room speaker selector. I wired these relays in parallel with the physical switches in the box.

When I was designing it, I wasn't sure how to analyze how much current could be conducted. The amplifier is rated for 2x 25W RMS, speaker impedance 8 ohms; thus the theoretical maximum current given by P = I^2 / R is sqrt(25 W / 8 ohm) = 1.77 A. In practice, when I attempted to measure AC current at high volume with a multimeter, I saw <100mA. I didn't have a scope at the time, but I imagine that because it's not a sine wave, it'd be better to use an oscilloscope and measure the voltage across a shunt.

I ended up using relays rated for 2A contact current and random ~24 AWG wire I had on hand. The project works very well, but I'd like to better understand what is actually going on.

Is the theoretical current above correct? Why is the measured current so much lower?
Each room has an "impedance matching volume control." Does this mean that they simply put a resistor in series with the speakers, so that when multiple channels are on, the amplifier doesn't see <8 ohm impedance? (I can't find much information about how these work.) That could explain the low current.
I'm frankly a bit surprised that a small amplifier like this can drive 5 rooms/10 speakers at a pretty high volume. The speakers and in-wall volume controls were professionally installed before we moved in. Is it likely that there is actually some powered amplification hidden in each room?


texts: Are BLE modules capable of working with a CR2032 battery?

texts:
I keep reading that the Bluetooth Low Energy modules are capable of working with a CR2032 battery for years, but their consumption is around 20mA and the max discharge of a CR2032 is around 3mA (200uA standard). How could this be possible?

I'm pretty sure it has something to do with the pulse discharge current, but the datasheets usually don't have a lot of information about that. In this case how can I determine the relation between the discharge current and the duration of the pulse?


texts: Help understanding ARM Cortex-M4 SBC instruction

texts: Page 88 of the ARM Cortex-M4 Generic User Guide says "The SBC instruction subtracts the value of Operand2 from the value in Rn. If the carry flag is CLEAR, the result is reduced by one." Why the result is reduced by 1 when the carry flag is CLEAR rather than SET? I think the SBC instruction subtracts the value of the carry flag from the result of subtracting operand2 from Rn, therefore the result is reduced by 1 when the carry flag is SET. Am I wrong?


texts: Matching different voltage levels using op amp

texts:
I'm new in electronics and have a "simple" question: how can I match different voltage levels by using op amps?

Let me explain better:
My input signal is something like this:

And I have to provide an output signal like this:

How can I do that? I'll be thankful with the name or the designation of the circuit that can operate in this form so I can search and read about it.


texts: Elimination of transistor in 12V Switching Circuit

texts:
The below given circuit works fine, I am switching 12V voltage using a microcontroller GPIO.

P-CHANNEL MOSFET (load connected between Drain and Ground):

When the microcontroller output is LOW, the transistor is OFF and the gate of the P MOSFET is HIGH (12V). This means the P MOSFET is OFF.
When the output of the microcontroller is HIGH, the transistor is turned ON and pulls the gate of the MOSFET LOW. This turns the MOSFET ON and current will flow through the load.

How can I improve the circuit? Can I eliminate the transistor (2N3904) shown in the schematic?

Do I need to use N channel MOSFET, by any chance?

Also I am using P channel MOSFET which has Max. Drain-Source Voltage of -12V (?). If switching Voltage is increased to 15V, can it still work?


texts: Is it possible to speculate on the completion of an adder from the first row?

texts:
I've seen speculative adders that take an extra clock cycle something on the order of once in 10^5 additions.  Often papers on speculative adders claim to need the information from stage 1 and stage n, but always error check entirely from stage n.  See page 73, where G from stage 1 of  bits 1, 3, 5, and 7 are needed; but on page 74, the error check uses G from stage 2 of bit 3, and stage 3 of bits 5 and 7.

If a carry is propagated, it will change G=0 at stage 1 to G=1 at subsequent stages.

This speculator checks if G=1 at the lower half even bits (1, 3, 5, 7…yes, starting from 0) and P=1 from those bits + n/2 for n bit length (e.g. +16 for 32-bit).  If any such pair are both 1, it detects the computation is in error, and muxes the final stage back in.

Just curious why it's like that.

The 64-bit speculative adder decreases delay by 24% when it predicts properly, and increases delay by 66% when it errors.  Most papers claim error mandates an additional clock cycle; from what I see, error requires an additional 1.18 clock cycles.


texts:
I want to build a smart wall where people can touch a 2 sqft region of the wall and it will detect who touched it and which cell they touched. The wall itself is made of plywood and I have access to both sides. You can think of it like turning the wall into a giant board game, where I have some server behind the wall and when it's a player's turn, they tap a couple of areas to move their game piece. The resulting move is displayed on their mobile phone, so it does not need to be displayed anywhere on the wall.

Given my requirements:

~50cm omnidirectional proximity detection
Ideally I can place it on the back of the wall, rather than in front. I only have control of the wall itself, setting up additional sensors elsewhere in the room is not feasible.
Uniquely identify each player for stats tracking. Players can wear some sort of bracelet if it helps the sensor, but it should not be much heavier than a LiveStrong bracelet; the hands must remain totally free.
As cheap as possible. My budget is < $30 per 2 sqft cell.

How can I build this smart wall?


texts: Characteristics to look for in a bench power supply to use in microcontroller development

texts:
I'm doing some microcontroller development, mainly for education and as a hobbyist.

So far I have powered it all from USB-power or 5V wall warts and regulated it down with 1117's or similar regulators.

At his point I want to be able to drive my projects from different voltage levels, both for testing and to be able to use different voltage levels as power source. I also would like to be able to draw more than the odd 1A you can get from the USB port. (Not mainly for the controllers but for some peripherals)

My thought is to get a variable bench power supply.

Are there any certain things I need to consider except the obvious power/current ratings?

Would a base version of an el cheapo brand for 50€ be sufficient or do I need better filtering/protection?


texts: Lorentz forces on loop cancel each other out so how do eddy current brakes work?

texts:
Let's take the pendulum example. When it passes through the magnetic field, eddy currents are induced. Those currents flow in circles and now with the presence of current and magnetic field lorentz forces are created against the pendulum.

However, if the current is flowing through a loop the forces cancel each other out because of the symmetry of the circle. I understand that the same doesn't apply for torque and I think that's the key to the explanation. And even if I'm right and that really is the case, a detailed answer would help others studying about eddy currents understand how the forces actually stop the pendulum.

Also, what would happen if the pendulum was superconducting?


texts:
RoboCup Junior uses an IR ball which emits pulsing infrared light (before this it was a steady beam which sensors could not differentiate from environmental sources). A presentation  outlining the possible methods of detecting the ball mentioned the use of TSOP1138s and microcontroller programming.

What would be the best way to use an Arduino/ATmega to read the pulses? The timings involved are very small, and with an interrupt I am unable to use timing functions.

EDIT: After a little mucking around it seems like I should have used the TSOP1140 instead. If anyone can explain how these little guys work it would be great help, but in the meantime I shall wait for my order to arrive.


texts: How to transform a streaming IP video into a CATV signal?

texts: I wanted to create a circuit, where a network cable was connected, and then the eprom, connected to a video stream in IP, after that streaming, it was converted to RF (CATV). What kind of things should I start to learn and where. I know that for example this messes with QAM or TDM Modulation (only if you want to transmit more than one channel on the same frequency). But unfortunately I can't find anything about this type of content on the internet. Where on the internet, or in reading, could you find more about this subject?


texts: Help identifying component (LED matrix PCB)

texts:
I have a led matrix PCB without a driver and I'm trying to figure out how to control it. I'm having trouble identifying one of the components on the PCB.
Here is a scheme of a part of the PCB:

These 6-pin parts have WDFN-6 package or similar. They have labels AP1 (I also met APN for the same parts). Here are the pictures:

I thought it might be a Dual LDO Regulator or something similar, but it doesn't match the actual scheme.
Please provide any thoughts on what it might be.


texts: Why would a breadboard have a conductive plate underneath it?

texts:
So for my electrical engineering classes, we were tasked to make an operational amplifier.

However, on the day of testing the instructor showed me that the bottom of my breadboard (which he had given me) was one big conductive plate, and that some of my wires were pushed far enough into the breadboard to make contact with it, creating a connection between any wires touching it, as well as a capacitive connection to the entire rest of my circuit.

He said that this broke the design specifications of the circuit, and I got a much worse grade than I first expected.

Can someone please explain to me why anyone would design a breadboard like that?


texts: How can I use a comparator in a circuit?

texts:
I am learning about how to use Operational Amplifiers as comparators. I understand that comparators are used to compare an input signal to a reference voltage. However, I am having a hard time visualizing this.

Say that I wanted a comparator with a reference voltage of 0 V (therefore, the output will be either positive or negative depending on whether the input signal is positive or negative, respectively). How could I draw a circuit like this?

I hope my question is clear.


texts: What is affecting the power supply current rating?

texts:
My question is generally specific on how to determine the current rating for a power supply? does the current is always constant? or it's according to the load of the circuit? Also does the maximum current rating of the power supply is determined according to the power rating of the components used in the circuit?

What will happen if I connect an 4 Amp LED to a transformer based 10 Amp power supply of the same voltage rating?


texts:
I have to develop a driver for a 3 phase brushless DC motor @ 24V with max current per phase of 5A. I want to use an Arduino Zero for testing.

My idea is to use the Allegro A4963 IC. This is my first attempt with 3Phase motors.
For what I understand the IC needs only a PWM signal and then it does itself the commutation of the 3 P-MOS and 3 N-MOS, right?
Thanks


texts: TLP383 ltspice XVII model not working because of encryption?

texts:
I tried to test the model of the TLP383 in ltspice which I downloaded from toshiba. TLP383
I added it as I always did with my models downloaded from the internet.
But this time ltspice gives me the error:

Unknown SPICE device type "1" in "17f62b..."

So I wanted to ask if somebody also experienced something like this or if anybody got a working model of the TLP383?
Thank you for your help.
Best regards.


texts: What is the software used in this image(semiconductor simulation)?

texts: If I interpret this correctly, this means there is some nice software to simulate various properties of semiconductors. Does anyone know what it is or alternatively what packages do the same thing?


texts: I know these packages have different thickness, but I have a hard time to find a TQFP landpad spec. Is it using the same landpad as for QFP (reflow soldering)?


texts:
I am trying to create a sawtooth waveform using microcontroller/counter and DAC. Instead of getting a nice smooth ramp, I am getting a ramp but with impulses and other noise. I am using AD7533 DAC and AD8055 Op Amp. The 10 bit input comes from a microcontroller. I am interfacing the DAC using figure11 from dac's datasheet:

Considering the note under the drawing, I decided to omit R1 and R2 from the circuit and made it the following way:

When I measure the signal at the negative terminal of the OpAmp, I get this reading:

which is not that attractive. Changing Vref does not make much difference. At Vref=5V the signal on the negative OpAmp input looks like this:

When I measure the signal on the OpAmp output pin, it looks like saturated:

So, two questions:

Am I missing some trivial components? Why the signal looks so bad?
Why OpAmp gets saturated if I do not do any gain? Moreover, the signal is withing 0-3V range and the power on the OpAmp is 5V.

EDIT:
So, I considered suggestions from the comments (shorted R2 and added negative rail to OpAmp power) and there I am getting this waveform:

It still looks very noisy and when I zoomed it in, the ramp also looks to float up and down:

Theoretically, since my range is about 3.3V peak to peak, and given 10 bit resolution, the output signal should have resolution of 3.3mV. Whereas, the noise is as bad as 100mV.
Any practical approaches on how to fight this noise?

Also, my next stage is going to be AD8531. I will use it as a high current G=1 buffer - the output from the AD8055 will be connected to +in of the AD8531. Do I need to place the load resistor to ground between the two amps, or connect the output to the input directly?


texts: How “safe” is it to put a higher voltage into a small DC motor?

texts: The main board in my old rechargeable philoshave failed.  Not wanting to give up easily, I soldered direct onto the DC motor (as pictured).  The motor is rated for 3.6V (pictured), but I get a much better cut if I “overclock” the motor by about 20% in terms of voltage - i.e. 4.5V rather than 3.6V.  Is this safe to do ?  The motor doesn’t seem to be running hot after a few minutes under load (in this case a shave).  What are the general guidelines / tolerances allowed for this sort of thing ?


texts: Replacing a 8 ohm Speaker with a Piezo. Will it work?

texts:
Like Replacing a piezoelectric speaker with an electromagnetic one, but the other way round.

simulate this circuit – Schematic created using CircuitLab

A DC squarewave will turn on and off ASW (Analog SWitch) for a buzzing sound from a constant voltage. The 4K7 pulldown is for discharging the cap. when ASW is open.

I want to use a piezo for the simplicity they provide.
Are the schematics equivalent, sound-wise?


texts: How could I set up a circuit that keeps track of strikes in a baseball game using D flip flops in Multisim?

texts:
What I want is two LED lights and a push button.  When the push button is pressed the first time, the first light lights up.  When it's pressed a second time, the second light lights up.  When it's pressed a third time, both lights turn off.

I set up two D flip flops.  The first Q output connects to the second's D input.  The push button is hooked to the Clock on both flip flops, the push button which is hooked to a power source.  After going through my logic with K-maps, I determined the following:

D1 = Q0'Q1
D0 = Q0'

Q0 is the first flip flop and Q1 is the second flip flops.

So I set up the gates as necessary.

Here is where the problem is.  The lights have a strange behavior.  Sometimes one turns on, sometimes both turns on.  I'm obviously doing something wrong.


texts:
This schematic shows the circuit that I'm trying to build. At the moment I'm not using V2, as I'm having a problem with V1. From my understanding the diode should drop the voltage by about 0.7V, and the resistor by 1.1V, reducing the Voltage from 2.6 to about 0.8V. The voltage is only dropping by 0.7 V with the LED's lit, and by 0.2V without the LED's. Can someone please explain why, and what I'm doing wrong?

The reason I'm using a 2nd circuit, is that I want V2 to supply extra voltage to switch on the LED's in V1. There are other LED's in the V2 circuit, and I want them all to switch on at the same time. The LED's need about 2.4V to be fully lit. Thanks in advance.

simulate this circuit – Schematic created using CircuitLab


texts: Shielding a signal with both GND and supply?

texts:
What happens if a net is shielded by GND on one side and VCC on the other side inside an IC? Assume that the 3 lines are on the same metal layer.
This is an interview question and I would like to know if this actually serves any purpose or was just a googly question.


texts: Two Gas Discharge Tube in parallel; a fast acting gas acting tube and a gas discharge tube

texts:
I want to know what happens if we put two gas discharge tube (fast acting GDT and a GDT in parallel), and a tvs diode in parallel. Would there be an issue in putting GDT in parallel?

Datasheet of Fast Acting GDT

Datasheet of Second GDT


texts: Can I expect SMD components from a same manufacturer to be identical?

texts:
I'm working on a project which requires at-least 2,000 ambient light sensors, and instead of using a microcontroler to manage and monitor the whole system I just want to amplify the output of sensors with a transistor array and use it for actuation of solenoids.

As a beginner I'm a bit confused, and I don't know whether I can treat each individual cell(from sensor to solenoid) identical to other.


texts:
I have got a short length (1m) of standard fat CAT5 shielded cable that runs inside a piece of equipment before the signal exits via a bulkhead connector to a PC. It's the old kind that is a real pain to put a tight radius bend into. I was thinking of replacing it with thin CAT6 cable that has a very flat cross section and is extremely flexible.

The question now being, am I likely to experience any RFI problems from the cable to the surrounding electronics boards? It will run close to or on top of a single board computer. Data rates are low and the SBC connects with 100Base-T


texts: Where is the ground reference when using a thermocouple?

texts:
I am using a MAX31856 to read thermocouple voltages. I have an ADG707 differential multiplexer feeding the MAX31856 from various ungrounded thermocouple probes (see diagram below). I am using the multiplexer in single sided mode (Vdd = 3.3v, Vss = gnd).

Sometimes the Maxium chip can read the theromocouple and other times it cannot. However, when I take the mux out, everything works correctly. My first guess is that this has something to do with the thermocouple not sharing the same ground reference as the multiplexer. My concern is that since the thermocouple lines are floating relative to the mux power supply, they may be floating in and out of range of the mux inputs. Is this correct or is there something else fundamently wrong with this configuration? If it is a floating ground issue, how can I remedy it.


texts: Can I make a latch using 2 AND gates, instead of NAND gates?

texts:
I have seen that, generally, a simple latch is made using either 2 NAND gates or 2 NOR gates.

Can I make a latch using 2 AND gates ?


texts: How can I design this pull up without wasting current/performance?

texts:
I want to move the low side enable switch of my H-bridge onto the high side, because for safety reasons it's better to turn off the tap than plug the drain. I'm powering a 24V, 35W BLDC, so it's nothing too serious. Rather than adding a 36V supply to my board only to drive a high side NFET, I decided to go with a PFET, however its logic is inverted, and I want the H bridge to turn off in the event the enable line de-energizes. That way, it fails safely.

This is the design I came up with:

The transistor is by default off unless an enable signal is applied to Q2. If Enable should droop or get disconnected, the H bridge will be disabled.

The issue is that since the H-bridge will be on most of the time, there will be a current through R1 to ground. Since I don't want to waste my battery, is there any way I can pick a large R1 to minimize that current, without trashing the gate drive of Q1?


texts:
I want to light up an LED strip via an Arduino (ESP8266)

The Arduino’s GPIO has a maximum output of 12mA. It is not enough to power a 5m length LED strip.

An obvious solution is to use a transistor to increase the current. I’ve followed an internet tutorial that used a TIP31 transistores, but my lights were too dim. The solution provided on this answer (RGB LED strip is too dim) is to halve the resistance to 200ohms and even that may not be enough because the current needed is about 2A per channel (6A total). They pointed to me that I could use a Darlington pair to increase even more the current and I’ve decided to try it out but before I could try someone said that it could burn my LEDs.

I can’t replace this LED strip in less than 3 weeks (shipping to my city is hell) and I would like to do it safely.

So um trying to figure out which resistor and which transistor I should use.

Some formulas I already know:

amps needed per channel: (#LEDS / 3) * 20mA => 2A
watts needed: V * I => 12V * (#LEDS / 3) * 20mA => 24W * 3 => 72W => 90W to be safe

This is the suggested circuit that someone said it will work and someone else said it would burn my LEDs

So I’ve decided to learn how to choose a transistor and a resistance, I’ve found this datasheet for the TIP31 but I can’t decode its math.

Can someone help me with that?


texts: Do I need to insulate down conductors in a lightning protection system?

texts: When we install seperate down conductors in an external lightning protection system, do we need to fully insulate it or need to insulate in touchable areas? Is there any requirements in IEC 62305 standard like that or generally are they insulate it?


texts:
I have a simple parallel RLC circuit (R in series to L and C which are in parallel to each other). I am using a 0.01 micro farad CK05 capacitor a 100k resistor and a 10mH inductor.

I measure a resonance frequency of 17.1kHz which is close to the theoretical resonance frequency of 15.9kHz.

My problem is in the bandwidth. I am measuring a bandwidth of approximately 1.5kHz giving a Q factor of approximately 11.4 while the theoretical value  is bigger by an order of magnitude i.e. 10 times larger (using \$ Q=\omega_0RC \$ for parallel RLC circuit I calculated Q=~100).

I measured the bandwidth by varying the frequency and measuring the frequencies where \$V=\frac{\sqrt{2}}{2}V_{max} \$ (using the cursors and measurement options on a digital scope).

What may be the reason for this kind of error?

below I added a picture of the components I used, from left to right:
resistor capacitor and inductor. I used an ohm meter and measured the DC resistance of the inductor to be 66 ohm.


texts:
Can a transistor be used to interrupt a signal? I know a common use is to switch power to another device. But my question is if I have a PWM signal applied to the emitter and the base pulled up, will the PWM signal make it through the transistor to the receiving device? Will pulling the base low disable the signal? Is there a better way to accomplish this interrupt without a relay?

To clarify, the signal is coming from a 3rd party device (RC receiver) and is used to control an ESC. I want to place a microcontroller in between to cut the signal off for certain conditions.


texts: How to select a DC-DC converter topology?

texts:
I've been simulating a switched mode 12V to 170V boost converter, and it has been quite the learning experience. If my observations are correct, power losses in the circuit not only increase as the square of input current (as usual), but also as something around

$$ \frac{1}{(1 - duty\,cycle) ^ 4}$$

for a given load, inductor and switch. So... that's obviously a pretty big deal.

I am aware that a switched mode full-bridge with an HF transformer can wrangle really large amounts of power from a rather low voltage source to a rather high-voltage one, given appropriate selection of core, windings, switches and switching scheme. I am also aware of the flyback converter arrangement and various other similar high-frequency converters, such as the Cuk regulator and SEPIC regulator. So on to my questions.

In general, how does a professional decide what DC-DC topology s/he will use for a given application? And, more specifically, is there a clear cut-off in terms of Watts or duty-cycle that professionals generally use to know when they need to get away from a simple boost converter design?


texts:
I am planning to generate +/-9V using LT1026 as shown.

These configuration is shown in datasheet of LT1026 Charge pump        (page 5).

But my question is if I add one more IC in parallel if I need more current to supply more OP-AMP IC's, Is it good option?
What precaution I can take to implement precise noise-free circuit? Please suggest. Should I remove the 1K bleed resistors to save current?

Thank you in advance.


texts: How to determine wattage of a resistor I found

texts:
In general is there a way to know what the wattage rating of a resistor is?  I have a large bin of resistors of varying resistances and physical sizes.  I assume size correlates to wattage as a larger resistor would be able to dissipate more heat.

How would I go about determining what a safe wattage is to pass through a resistor?


texts:
I have two cats and want to track in which of the 6 rooms of my flat (about 96 square meters) they currently are. Later I would like to trigger an alarm if they get into a "forbidden" room. The cats are currently not wearing a collar, but I tried it once and it could work, even though they are not very thrilled about it.

I would prefer an affordable solution and if possible no equipment on the cat itself - especially nothing that need to be charged.

I first thought of RFID, placing a passive tag on each cat and a sensor on each door. But I don't have any experience with it and don't know if it is even possible to detect if the cat is sitting in front of the door or actually crossing it - and how the direction (entering of leaving the room) could be tracked as well.

Another idea was to use small Wifi modules like the ESP8266, track the signal strength of two independent WiFi networks and calculate the position, but I don't think it's accurate enough, and there are many APs around here.

Do you have any idea what might work?

[Edit]

After some misunderstandings I'd like to clarify some parts

I'm not looking (necessarily) for a cat-specific solution. It doesn't need to reasonable as well (neither it has to be the next big thing). I want this, even though everyone may think it's stupid.
Yes, cat's can somehow be trained. That's not the point. I want to look on some display and check where they are. That's all.
It should be (if possible) const- and energy efficient. (i.e. no autonomes patroling drones ;))


texts: Implementing the I action in an analog PID controller

texts:
Can I implement the I action in an analog PID controller as follows?:

simulate this circuit – Schematic created using CircuitLab

And am I right when I say that the voltage follower is used to prevent distortion in the input impedance of the second opamp?


texts: Open and Short Circuit tests of Transformers

texts:
I have knowledge that a transformer in

Open ckt is used to find Copper loss and
Short ckt is used to find Iron loss

But I don't know how to interpret the result of such tests?

Further what do each of the following measurements indicate for open and short ckt tests?

Power measured in Wattmeter
Current in Ammeter
Voltage in Voltmeter


texts: How do I calculate the total resistance of this potentiometer circuit?

texts:
Can somebody explain to me how to calculate the total resistance of the circuit in the picture?

I do not understand how to deal with the potentiometer and the red line. Does the current flow over \$R_{2.1}\$, bypassing \$R_{2.2}\$ and going on to \$R_3\$ and \$R_{\text{B}}\$? So would it be \$R_{\text{total}} = R_{2.1} + (R_{\text{B}} \parallel R_3)\$?


texts:
I would like to power a Wemos D1 mini with AA batteries for a project.
I'm really new to the subject but as I understood the board runs with 3.3V.
You can power the board through the 5V pin because there is a built in dropout there.
To get 5V I thought of using 4 AA batteries (4 x 1.5 = 6V) and mount them with a resistor to lower the voltage to 5V.
What I don't understand is how the resistor is acting on the overall system.
Does it increase its lifetime or does it disperse all extra voltage into heat ?
In other words, if I use more batteries with bigger resistor, does my circuit gets longer lifetime  or should I stick to the required voltage ?
As I understood I could use 3 AA batteries (4.5V) it would work but I would opt for more lifetime if possible (Also I already bought boxes for 4 batteries ;) ).
Is there any best pattern to decrease voltage effectively ? (Diodes, ..., ?).
Thanks


texts:
Update:

All I want is, when the signal is higher than reference voltage, LEDs to light up(brightly).

For this, I was planning to use an op-amp as comparator (left circuit) but everybody told me to use a comparator instead.
However there is some differences between operating of these two devices which confused me.
I have drawn(on the right) the way I think it should be with a comparator after my readings. But I am not sure.

If you think I can use an op-amp comparator (left circuit), then I noticed that with GND connected to -Vcc terminal of this op-amp, the current flows through LEDs even the signal is lower than Vref.

I would expect the output to be 0 V and so no current flows through the LEDs. However this is not the case. You can also to explain this to me.

LM741 is not a must component, I know it is a very ancient op-amp but I am so stuck in these concepts that not able to choose another one.

simulate this circuit – Schematic created using CircuitLab

Original question:

I am a little bit confused about the usage of LM393.

Is this comparator IC somehow different than opAmp comparators? For them, I was able to understand easily because the load was directly connected to output. So when V+ > V-, the output goes high and when V- > V+ output goes low. Just like below,

But for this LM393, it looks different. I have read some:

  If the voltage at the inverting terminal is greater than the voltage
  at the noninverting terminal, then the output of the op amp will be
  drawn down to ground, allowing electricity to flow from VCC to ground,
  turning on the output device. If the voltage at the inverting terminal
  is less than at the noninverting terminal, then the output of the op
  amp stays at VCC allowing no electricity to flow, since there is no
  electric potential difference across the output device.

  This means that when the inverting terminal voltage is greater, the
  load connected to output can be powered on. When the noninverting
  terminal voltage is greater, the load connected to output will be
  powered off. So if an LED is connected to output, it will turn on when
  the inverting voltage is greater and turn off when the noninverting
  voltage falls below the inverting voltage.

I think I am confused about the pull-up part in LM393. In my design, I want to feed 2 leds in parallel from the output of the comparator, so I guess I will need 20+20 = 40mA in total from this output. Does LM393 give the opportunity to have this much current flow?

If so, where the reference voltage(which I want to compare with a signal and when signal is above that reference voltage the load gets current) be connected?


texts: Interfacing thermistor with PIC24 10-bit ADC

texts:
I want to interface a 103AT-2 thermistor directly with the PIC24 10-bit ADC. I am interested in the temperature range between -10°C (where thermistor resistance is 42.47kΩ) to +70°C (where thermistor resistance is 2.228kΩ) and accuracy needed is 0.1°C.

I have explored something in the online and even in this forum under "Selecting Bias resistor for thermistor". For Bias resistor Rb selection, if I take geometric mean of the minimum (2.228kΩ) and maximum resistance (42.47kΩ) values, Rb is 9.70kΩ. I rounded this to 10kΩ.

Below is my schematic which is without a constant current source. The circuit includes a 10kΩ pot in series with Rb for calibration.

My question is: How can I build a constant current source, so the current flowing through the voltage divider would be constant, irrespective of the thermistor resistance?


texts: Placement of RF module for better performance

texts:
I am using a standard RF module (i.e., Bluetooth-module-on-PCB), which has a PCB-trace-type anntena. It is in turn to be soldered onto my main PCB. The whole thing will be powered by a standard Li-ion battery.

Which of the following two placements of the RF module would perform better, in terms of offering optimal transmission/reception?

(I prefer Placement B for logistical reasons but I am unsure about the effect of the RF module antenna's proximity to the battery, which I'm guessing will act as a huge ground plane.)

  Placement A:

RF module placed on top of my main PCB (which I'll make sure to keep out the copper pour/traces, etc. in the area directly under the RF module's antenna)

  Placement B:

RF module turned upside down and placed between PCB and battery.


texts: What is the most accurate and cheap way to figure out the distance between two points electronically?

texts:
For a project, I have an idea that involves getting a position for a person throughout a house. I am trying to figure out someway of triangulating the person's position, by having a bunch of little receivers sitting around the house. Each person will have a 'beacon' in their pocket, which sends out some kind of signal that the receivers can use to figure out distance, and therefor have the ability to figure out the location.

That is where I am stuck. What kind of signal could be used to accurately figure out distance, and still be cheap to get/create?

Size IS important, as the beacon would need to fit in a pocket. The receivers can be bigger, but not too big as to look out of place in the house.

Any Help?


texts:
Im curious about optocoupler.

What is optocoupler,why and how it is used in electronic circuits ?


texts: Why Non-parallel but full case statement uses ROM not the MUX?

texts:
as far as I know, when the items in case are not parallel

it would compose a priority routing network not the multiplexing network.

In other words, it should uses multiple 2-to-1 MUXs to represent priority in between the case items.

For example, below code has non-parallel case items 3'b11 and 3'b1??.

module non_parallel_but_full_case
(
  input wire [2:0] s,
  output reg y
);
  always @*
  //below case is not parallel but full case
    casez (s)
      3'b111: y = 1'b1;
      3'b1??: y = 1'b0;
      default: y = 1'b1;
    endcase
endmodule

Therefore, I've expected the synthesized circuit may have MUXs not the ROM.

However, when I tested the code in the vivado and its RTL description shows ROM not the MUX.

Why the non-parallel case uses the ROM instead of the MUXs?

=====================================================
Added question.

module decoder_2_4_if (
  input wire [1:0] a,
  input wire en,
  output reg [3:0] y
);

  always @*
    if (en == 1'b0)
      y = 4'b0000;
    else if (a == 2'b00)
      y = 4'b0001;
    else if (a == 2'b01)
      y = 4'b0010;
    else if (a == 2'b10)
      y = 4'b0100;
    else
      y = 4'b1000;
endmodule

The above code generates the multiple cascaded 2-to-1 MUXs.

However, the same logic implemented by the case statement uses the ROM.

module decoder_2_4_case (
  input wire [1:0] a,
  input wire en,
  output reg [3:0] y
);

  always @*
  case ({en,a})
    3'b000, 3'b001, 3'b010, 3'b011: y = 4'b000;
    3'b100: y = 4'b0001;
    3'b101: y = 4'b0010;
    3'b110: y = 4'b0100;
    3'b111: y = 4'b1000;
  endcase
endmodule

In two examples, the result can be statically determined, and it would mean that two modules could be implemented by the ROM.

Then why it generates the different schematics?


texts: If I need to find an MOSFET spice model with a particular length and width, where do I start?

texts:
I was using a 180nm NMOS and PMOS but now need to use an NMOS with about L=.36u and W=100u. I have two models but I dont think I can just change the length and width to any value.

How can I check if I can scale my current model to that size with a parameter, or what parameters do I check to make sure I can do that? I dont really see a "Wmin" or anything like that in my model, but I am sure there could be different names for them

Where do I go about finding a mosfet model knowing those two parameters I want to fulfill?

I am trying to use this NMOS in a diode connected configuration, and I was told that that size I am looking for would help get it deep into weak inversion

Right now I am using a TSMC .18u NMOS

.MODEL CMOSN NMOS ( LEVEL = 49
+VERSION = 3.1 ....


texts: why does the negative lead to a solar panel go black,oxidise.?

texts:
I have an 40watt solar panel connected to a 12v battery via 6A twin flex.
After 3 yrs the neg lead has gone from bright copper to black tarnished.
Can anyone explain why this should be, cheers.


texts: Why do we have 2 representations for load (shown below) in a power amplifier?

texts:
OR

I get confused when i see two different ways to connect load resistor in a power amplifier.

Why do we have two such representations (RL in series with collecor Vs RL connected across collector and ground)?

The closest answer I find is, for an AC signal both representations are equivalent. If so, can we connect (any) load in any of these ways? Is there any other consideration i'm missing out?

Any help would be appreciated.


texts: How to power STM8(S105C4) chip? Is decoupling needed?

texts: I have a MCU STM8(S105C4) with which I need to design a PCB to power from a USB. But I don't know how to power it. I've tried searching the specification for this MCU but all that I could find is that the input voltage should be from -0.3 to 6.5 V. The interesting thing it that for STM32 MCU's that the specification has a power scheme included. If anyone has any ideas that could help me out, that would be great.


texts: how to solve the phase shift of a ne555 timer

texts:
Why is the first pulse wave is not the same as the rest of the wave in this 555 timer?
Is there any way to remove the wave before 2 ms or is there anyway to make it same as the rest in the graph.


texts: Accessing structures concurrently modified by ISR

texts:
I have the the following situation: An STM32L476RG (ARM Cortex M4F @ 80MHz, 1MB Flash, 128kB RAM) parses some string data coming in over UART. The project uses mbed-os. The parsing of the data is done in an interrupt-based manner, meaning an ISR is in place which reads the just received character and has some stateful parsing logic to extract data from it. While doing so, it modifies an working-object which gradually gets filled up with the parsed values.

When the parsing process is done (all values filled), the working copy is saved into another global object of the same type. This is so that the application has an object with valid values and doesn't have to access the working copy of the ISR-based parser, which might change anytime. The structure in question is about 204 bytes big.

Code looks like (high level)

struct MeterState {
    double valueA;
    double valueB;
    double valueC;
    char id[64];
    //more..
}

volatile MeterState isrWorkingCopy;
volatile MeterState lastValue;

/* called in an ISR context by mbed-os whenever something is received on the serial */
static void SerialParserHandler() {
    uint8_t data = (uint8_t) meterSerial.getc();
    parse_data(data, &isrWorkingCopy);
    //check parsing finished..
    if(parsingFinished) {
        //save finished object
        lastValue = isrWorkingCopy;
    }
}

/* called by application to get last valid data */
void MeterState GetLastValue() {
    return lastValue; //copy structure to as return value to stack
}

However, here comes the crux of the problem. Due to length of the object and given some certain timing, it may be possible that:

Appcode calls GetLastValue()
Function starts copying the huge structure to the stack of the caller.
Mid-term gets interrupted by the ISR
ISR overwrites lastValue with new data when parsing is finished
GetLastValue() is resumed after ISR
Resulting returned value is half the old half the new value

See e.g. compiler output for GetLastValue(), it is implemented by a memcpy():

--
08015f3c <_ZN13ElectricMeter16GetLastValueEv>:
 8015f3c:       b508            push    {r3, lr}
 8015f3e:       22d0            movs    r2, #208        ; 0xd0
 8015f40:       4901            ldr     r1, [pc, #4]    ; (8015f48 <_ZN13ElectricMeter16GetLastValueEv+0xc>)
 8015f42:       f004 fa5f       bl      801a404 <memcpy>
 8015f46:       bd08            pop     {r3, pc}
 8015f48:       20001d38        .word   0x20001d38

Basically overwriting and getting the value is non-atomic. I'm not quiet seeing how it's possible to make it atomic so that the above scenario doesn't occur anymore.

I cannot just use a Mutex-based locking mechanism to atomatically exchange the lastValue because I cannot lock a mutex inside an ISR. The ISR must be non-blocking.

I also thought about temporarily disabling interrupts around the getter method as such

MeterState GetLastValueSafe() {
    __disable_irq();
    MeterState s = GetLastValue();
    __enable_irq();
    return s;
}

However, doesn't this have the possibility (as small as it may be) that the parser misses a character (which might screw up parsing and constitute a lost data value)? If the IRQs are disabled and the handler doesn't get invoked, the character is basically lost, as I understand.

Is there any sane way to solve this general problem of ISR concurrency with large structures?


texts: Why isn't solid permalloy used for common mode chokes?

texts: When reverse engineering a common mode choke from a line filter I found a wrap of very thin metallic foil inside the plastic housing of the toroid core. A little research on magnetic materials indicated to me, that the core material has to be some kind of permalloy because the L/N² value is exceptionally high, about 40uH/N². And then I asked myself the following question: wouldn't it make sense to build the core from solid permalloy instead of the thin foil? After all the only benefit of the multilayer construction I see is the reduction of eddy current losses. Why would I want to reduce them in a common mode choke instead of exploiting them?


texts: How to measure the temperature of a fridge with arduino?

texts:
A want to make a system with arduino to measure the temperature of many fridges and send SMS if temperature is over limits. I am wondering how to measure digital temperature without putting  wire inside the fridge. One easy solution is if fridge has alarm for high temp (I can connect a wire on  alarm and when it is on it will send SMS). What about if
 1)  fridge has not alarm, but has LCD temperature
 2) fridge has not alarm and LCD