texts: Integrated voltage regulator chip versus discrete circuit utilizing op-amps and power BJTs for DIY bench power supply

texts:
After using the simple LM317 on breadboard variable power supply for a while, a need for a more rugged and reliable bench power supply has arose.

Short on money, i decided to build it as many other amateurs like me did.
The thing is that, for my current needs i don't need a giant digitally controlled multi-channel 500 watt beast or something like that.
 Instead what i really want is a low wattage positive and negative low voltage ouput -12v-0v-12v for example.
However i really like that my power supply to be safe, reliable and fool-proof as far as possible. So after searching the web here and there, i found many designs that from my point of view fell in one of two divisions:-

Ones that use discrete op-amps and transistors.
And ones that use integrated voltage regulators.

So -at least for me- i think that the ones with discrete op-amps and transistors are more prone to malfunctions and issues compared to the integrated ones with all of their internal over current and thermal protection circuits which would need to be discretely implemented in the bench power supplies that utilize discrete op-amps, however those designs have the advantage of ease of customization and more importantly that it is easier to have 0V output compared to 1.2V in integrated voltage regulator ones.

So i like advice to help me choose between circuits that utilize discrete op-amps like this circuit for example:-

Or ones that use integrated voltage regulators with their intrinsic robustness and low form factor.

Also as a side but related question i have seen many designs on the web that utilize negative voltage fed to the adjust or like pins to achieve 0V output from integrated voltage regulators like this single positive power supply:-

Or a positive and negative channels power supply that i really like its design because of simplicity (not because of laziness but to avoid the drawbacks that may come with complex designs especially when implemented by an amateur like me):-
And the question is

  Is it wrong or a system safety and reliability lowering act to feed negative voltage to adjust pin for LM317 for example?

I ask this question because the datasheet clearly states that the working output range is 1.2V-37V for LM317 for example, also no similar circuit is mentioned in the Typical Applications section except for the following one:-
And even in that circuit, however the adjust pin is tied to the negative rail, it does't regulate during this interval instead it is shut until the next half wave at least that what i understand.

So at last to sum it up which alternative is best suited for my needs, its pros and cons and suggested circuits if possible.


texts: Need a soft latching power on/off that starts OFF

texts:
I have spent a few days looking for a soft latching power on/off switch. I have breadboard-tested several designs, including at least these three:

Design #1

Design #2

Design #3

Testing:

I tested all 3 of them with and without load. As load I used a lux meter project (Arduino Pro Mini, BH1750 lux sensor and Oled display). The 555 alternative (design #1) is on the breadboard at the right. Power cables are at far right:

All of them work (with/without load), but ... all of them start frequently in ON position when connected to the power supply (with/without load, tested physically inserting/extracting the positive power cable from the breadboard).

Just think what may happen when main power returns after a blackout.

Question:

Do you have a switch design that guarantees starting at OFF when power is apply, just like a mechanical on/off switch? Bonus: One that does not oscillate when you keep the button pressed?

(I really like two separate buttons, if possible).


texts: Atmel SAMD21 DMA Transfer Complete Interrupt not firing

texts:
I have configured the SAMD21 peripherals so that incoming audio data from I2S will be copied into a memory buffer with DMA. As the controller allows linked DMA descriptors, I have two descriptors linked back to back, each writing to a different buffer.

  When a block transfer has come to its end, BTCNT has reached zero, the Valid bit in the Block Transfer Control register will be written to zero in the internal transfer descriptor for the active channel before the entire transfer descriptor is written to the write-back memory. The optional interrupts, Channel Transfer Complete and Channel Suspend, and the optional output event, Block, will be generated if configured and enabled. If it was the last block transfer in a transaction, Next Address (DESCADDR) register will hold the value 0x00000000, and the DMA channel will either be suspended or disabled, depending on the configuration in the Block Action bit group in the Block Transfer Control register(BTCTRL.BLOCKACT)

This excerpt from the datasheet coupled with the image suggests that the interrupt will be fired after each block transfer, implying the ISR being executed each time the next linked descriptor is loaded. But in my configuration, the ISR doesn't execute at all.
After I configured the linked chain to have a termination, the ISR fired after the block transfer of the chain. It seems like the interrupt fires only after a  complete transcation , not after each block transfer as the datasheet suggests.

Am I interpreting the datasheet wrong, is there a way to get the ISR routine to execute at each link?

static void _config_dma_for_rx(void)
{
    struct dma_resource_config config;
    dma_get_config_defaults(&config);

    config.trigger_action = DMA_TRIGGER_ACTION_BEAT;
    config.peripheral_trigger = CONF_RX_TRIGGER;

    dma_allocate(&rx_dma_resource, &config);

    // Configure DMA RX Descriptor A
    struct dma_descriptor_config descriptor_config;

    dma_descriptor_get_config_defaults(&descriptor_config);

    descriptor_config.block_transfer_count = 32;
    descriptor_config.beat_size = DMA_BEAT_SIZE_HWORD;
    descriptor_config.step_selection = DMA_STEPSEL_SRC;
    descriptor_config.src_increment_enable = false;
    descriptor_config.destination_address = (uint32_t)rx_values_a+ sizeof(rx_values_a);
    descriptor_config.source_address = (uint32_t)&CONF_I2S_MODULE->DATA[1];

    dma_descriptor_create(&rx_dma_descriptor_a, &descriptor_config);

    rx_dma_descriptor_a.DESCADDR.reg = 0;// (uint32_t)&rx_dma_descriptor_b;

    // Configure DMA RX Descriptor B

    dma_descriptor_get_config_defaults(&descriptor_config);

    descriptor_config.block_transfer_count = 32;
    descriptor_config.beat_size = DMA_BEAT_SIZE_HWORD;
    descriptor_config.step_selection = DMA_STEPSEL_SRC;
    descriptor_config.src_increment_enable = false;
    descriptor_config.destination_address = (uint32_t)rx_values_b +  sizeof(rx_values_b);
    descriptor_config.source_address = (uint32_t)&CONF_I2S_MODULE->DATA[1];

    dma_descriptor_create(&rx_dma_descriptor_b, &descriptor_config);

    rx_dma_descriptor_b.DESCADDR.reg = (uint32_t)&rx_dma_descriptor_a;

    dma_add_descriptor(&rx_dma_resource, &rx_dma_descriptor_a);

    dma_register_callback(&rx_dma_resource, rx_done_callback, DMA_CALLBACK_TRANSFER_DONE);
    dma_enable_callback(&rx_dma_resource, DMA_CALLBACK_TRANSFER_DONE);

    dma_start_transfer_job(&rx_dma_resource);
}


texts: Preferable mixed mode (SMPS + Linear) PSU topology

texts:
I'm designing power supply for my hybrid headphone amplifier. It will be powered from external SMPS of unknown quality. Amp's power supply contains linear part (linear regulator + rail splitter) and 70V charge pump for tubes (post-regulation is omitted on diagrams).

Which topology would provide better isolation of linear part from switched?

I have almost complete design using topology A, but now I'm in doubt if I should reroute it to topology B.


texts: How to get phase shift in this task and in general?

texts:
So the task says:

  In the serial circuit connected to the 50 Hz frequency alternating
  voltage, effective voltage values  = 220 V, known voltages L = 660
  V and C = 500 V. The current in the circuit is 11 A. Determine the
  ,  and , and phase shift φ between voltage and current

This is how circuit looks:

I have calculated Xl , Xc R L and by applying ohm's rule R = U / I = 220 / 11 = 20 Ω. Xl = UL / I = 660 / 11 = 60 Ω , Xc = Uc / i = 500 / 11 = 45.45 Ω , and then to find L and C I used formula Xl = wL , where w represents angular frequency, w = 2 * pi * f = 100 pi rad/sec, and the same for C, Xc = 1/ wC. And to find phase shift I used formula Φ = tg-1(X / R) = tg-1( ( 60 - 45.45) / 20) = 36.04 °

Can someone help?


texts: What is the best way to get a sine wave from a square wave?

texts:
I have square waves of different frequencies (1KHz to 20KHz), and I need to convert them to a sine wave of the corresponding fundamental frequency.

A RC ladder Low-pass filter was the first thing which I tried, It gave good results but the output peak-to-peak voltage (Vpp) varied a lot with the frequency. The square wave has a Vpp of 3.6V. But after filtering, the output Vpp of the sine wave varies from 3V to 2V as the frequency increases.

Is there any other better way to get a pure sine wave from square wave of same frequency without this voltage drop?

Thank you


texts: MOC3021 optocoupler not working ( or not working , a bit confused )

texts:
My Understanding

As far as my understanding of MOC3021 optocoupler goes, it should latch pins 4 and 6 whenever there's a current flow between pins 1 and 3.

The Confusion

Image 1 - D1 not glowing and D2 glowing

So, in this image no current flows between pins 1 and 3, however pins 4 and 6 is latched.

Same happens on the breadboard except that even the LED between 4 and 6 isn't glowing either on the breadboard ( unlike the simulation ).

Image 2 - D2 not glowing and D1 glowing

Same happens on the breadboard

Update : Yes increasing current works out fine

Actually it's part of an arduino circuit in which I would be giving an output from an arduino pin to this, and there won't be any LED ( not white one for sure as I came to know now that it requires more voltage ).

So, perhaps it would be fine with an arduino pin, this was just to check the components before hand.
Also , since MOC3021 has 15 mA forward current, so 5V would do the work ( as high in arduino pin would give 5V ).
I suppose even 3.3V would do the work.

Thanks all .

That's great piece of info Finbarr and jonk ( about white LED more forward current and choosing a specific opto isolator like why to choose MOC3021 or MOC 3022).

I am a newbie in this field , so it's great to get those tidbits of info.


texts: Dot convention inductors in series: equation confusion

texts:
So I'm really confused with mutual inductors and dot convention. If your answer is going to be a link to any website I can assure you I read them all and that only left me more confused. So here are my questions:

-> Should we write the absolute values of the mutual inductance? If so, why? Here is the example provided by my book:

They say that for the left side we have concordant coupling (mutual inductance positive) and therefore the series inductance is going to be:

$$L = L_{11} + L_{22} + 2 |L_M|$$

Why the use of the absolute value though? Isn't the coupling concordant and mutual inductance positive? What if it was negative, do you still have concordant coupling? I can see that if we apply the right-hand screw rule the fluxes have the same direction.

And for the right side discordant coupling (mutual inductance negative) and therefore the series inductance is going to be:

$$L = L_{11} + L_{22} - 2 |L_M|$$

Again: Why using the absolute value though? Isn't the coupling discordant (mutual inductance negative)? What if it was positive, do you still have discordant coupling? I can see that if we apply the right-hand screw rule the fluxes have opposite directions.

Next example my book provides is this one:

By applying the same thinking pattern of the previous one we have discordant coupling (mutual inductance negative) and therefore the series inductance is going to be:

$$L = L_{11} + L_{22} - 2 |L_M|$$

HOWEVER, my book now provides this:

$$L = L_{11} + L_{22} + 2 L_M$$

I know that because \$L_M\$ is indeed negative this will lead us to the same result, however, why remove the absolute value now? Or are they assuming concordant coupling even though the mutual inductance is negative? Or is there a step I'm missing? This one didn't bother me so much because I ended up with the same answer.

However, the final case is where I drop the ball:

So here I had previously calculated the mutual inductance and found out it was indeed negative. The series connection also suggests to me that we have discordant coupling (by dot convention) and therefore the series inductance is going to be:

$$L = L_{11} + L_{22} - 2 |L_M|$$

But now my book gives the answer:

$$L = L_{11} + L_{22} - 2 L_M$$

And since \$L_M\$ is negative this will originate different values.

I feel so confused right now, I have no idea how am I supposed to solve problems right this because I keep getting different answers. Can someone help me organize my line of thought. I think I understand concept of mutual inductance. What I don't understand is this thing with absolute values and series connection and I don't really know what to do.


texts:
I have two distinct set of lines where one is an input, and one is an output. I want to hook them up to a shared set of lines that will connect to shared I/O pins, with a signal to switch between the input and output lines.

Basically, I want an IC that will let me split pins on a device that act as both inputs and outputs, and have a signal line to swap between them.

I know I can accomplish this with a bunch of tri-state buffers, but I'm hoping a more concise package exists for this.


texts: How to find an EAGLE routing variant which will be OK after final processing of polygons

texts:
I am laying out a PCB using EAGLE 7.7.0 for Linux (64 bit).

When I run the Autorouter (high effort) it runs 22 variants of the routing, and all 22 produce 100% complete routing.

Below the dialogue is the standard warning "Percentage may decrease after final processing of polygons".  Sure enough, it does: many of the variants, upon selecting them, turn out not to be 100% routed - one or more connections cannot be routed because the polygon ground fills have split into two parts which cannot be connected.

Is there anything I can do to make EAGLE check whether they really are 100% routable, before I permanently select one?  At the moment the best method I have is to undo the whole routing, recalculate them all, try the next, and so on.


texts: How can I couple relay chattering noise to a data cable?

texts:
How the chattering of relay causes noise ? Is it its on-off sound makes the noise?
I want to know how to couple a relay chattering noise to a data cable.


texts: Detecting a moderately-fast moving object from 1ft away

texts:
I have a small side project using Arduino (pro mini or nano) that would detect passing model race cars (and quadcopters) and counting how many times it passed through a selected location. I thought of using IR emitters and detectors (photodiode) to achieve this but I'm worried it might not be fast enough or it might miss some counts.

The setup would have a few (1 or 3) IR emitters on one side of the road and a detector on the opposite side, facing the emitters (or maybe the emitters on top, and detector on the bottom). They would be more or less 1 foot apart and the toys would pass in between (there is also an arch about 1ft and all of them should pass under the arch). I'm using these for the emitters and these for the detectors.

Only one car would pass through the track at any given time so there would be no issues arising from use of multiple cars.

The toys are about 4-5" length and width, and height of a quadcopter would be around 1-2".

Basically, just detect any brick-sized object passing through the arch.

Is there something I could do to guarantee a count and would IR even fit this type of application? Or should I use an alternative? If so, any suggestions?

Thanks in advance


texts:
First tests for the field oriented control (FOC) of a pmsm may be conducted only on an inductance or a stator, i.e. not at the rotating machine, e.g. when the machine has more or less high power I want to be sure that the controller works.
My question is if it is actually possible to control a three phase current in the phases of a stator or at a standing still pmsm, when the angle is generated by the software.
In other words explained, the set-up is the following:

I measure the phase currents ia, ib, ic
I generate a rotating angle in software for fixed speed
The currents ia, ib, ic are transformed in dq- coordinates with the generated angle
The transformed currents and set points for Id, Iq enter PI controllers respectively for d and q.
An inverse clark transform is performed for the outputs of the PI controllers using the generated angle.
Space vector modulation is performed to generate duty cycles
Duty cycles steer a 3 phase inverter in order to implement the phase currents in the stator windings

Could this actually work, or do I have a mistake in my understanding of FOC? Since the motor is indeed not rotating.


texts: Simple circuit with operational amplifier (intended to be ECG) not picking up actual readings, only noise

texts:
I have a major problem.  A couple days ago, I ran into an issue with my circuit.  The problem is that I can only get noise from my ECG, not actual readings.  I'm using opamp LM358, not opamp OP37 like shown in the schematic and breadboard below.  Here are my pics.

NOTE: In the schematic, I took out the diagram of the Bluetooth because it's wrong.  I don't know what I'm doing here that's wrong.  I'm not going to post Arduino code here because I know that the Arduino is processing everything fine (software problem ruled out)  I'm totally fine with the noise (that's easy to fix), but the fact that I can't get any actual readings from my ECG is what I've been to fix.  I'm a total noob at hardware design and I don't know much about circuits.  This is just supposed to be a simple design, so that's why I didn't place any capacitors or resistors in my breadboard.  I would appreciate it if I could get some feedback on this.  Thank you!


texts: I'm using an ATTINY85 for a portable application that uses a Lithium-ion battery; therefor I need to monitor the battery voltage so I don't kill the battery. Is there a way to go about this without using another pin? or using the reset pin? **NOTE: assume that there will be no regulated voltage such as 3.3V or the like. (this is because the circuit only uses one battery and should never go above spec; and saves on cost)


texts: Proplem with Code Composer Studio v6 with GCC

texts:
I have the following

Tiva C Board (TM4C123GXL)
Code Composer Studio v6 using GCC

Compiling this sample code:

/*
 * main.c
 */
#include <stdint.h>
#include <stdbool.h>
#include "inc/hw_types.h"
#include "inc/hw_memmap.h"
#include "driverlib/sysctl.h"
#include "driverlib/gpio.h"

int main(void)
{
    uint8_t ui8LED = 2;
    SysCtlClockSet(SYSCTL_SYSDIV_4|SYSCTL_USE_PLL|SYSCTL_XTAL_16MHZ|SYSCTL_OSC_MAIN);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
    GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, GPIO_PIN_1|GPIO_PIN_2|GPIO_PIN_3);
    while(1)
    {
        // Turn on the LED
        GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_1|GPIO_PIN_2|GPIO_PIN_3, ui8LED);
        // Delay for a bit
        SysCtlDelay(2000000);
        // Cycle through Red, Green and Blue LEDs
        if (ui8LED == 8) {ui8LED = 2;} else {ui8LED = ui8LED*2;}
    }
}

This sample code is provided within the TivaWare works fine with the TI compiler (following all the steps in the workshop pdf). When I choose to compile with GCC using, If I do not include the driverlib.lib file it says undefined reference to the functions used above. If I include it it says two errors on the four functions

error: C:/ti/TivaWare_C_Series-2.1.0.12573/driverlib/ccs/Debug/driverlib.lib(cpu.obj) uses VFP register arguments, Test.out does not

failed to merge target specific data of file C:/ti/TivaWare_C_Series-2.1.0.12573/driverlib/ccs/Debug/driverlib.lib(cpu.obj)

I think everything should be fine when using TI compiler but I want to try GCC.


texts: Consequences of inrush current out of specifications in AC/DC power supply

texts:
What would be the consequence of an inrush current bigger than acceptable limits at the output of a AC/DC power supply? We are currently using a MeanWell model (GST160A15) whose datasheet reports a maximum inrush current of 120A. We are using the power supply to power a control card. We just figured out that the inrush current flowing into the control card is in excess of 175A with a following negative pulse of ca 200A. The whole is happening into the Mhz frequency range. The measurements where taken with a Tektronix 100 Mhz oscilloscope and a shunt resistor - because the current measuring instrument we have just arrives in the range of 500 KHz.
We noticed that 1-2 power supplies out of 15 got broken in a time span of 6 months. Could the failures be entirely due to the inrush current over specs? Or are they other possible reasons? Please look at the attached measurement.


texts:
I just bought a 5 volt dual relay module for my arduino.  But now that I have it I was wondering if there is any way that I could control it directly from USB.

The pinout of the module is GND  ONE  TWO  VOC
This would make it really easy to just connect a USB cable to it.
Assuming I did that is there any way to send 5 volt through the USB Data+ and Data-?

Thank you


texts: MAX31855K reported temp dropping when AC current applied at ktype thermocouple location

texts:
I'm trying to use a Raspberry Pi, MAX31855K thermocouple amplifier, and solid state relay to control an espresso machine's boiler using a PID.

However I'm hitting a frustrating snag. I have everything hooked up and temps are reported properly (I'm reading temps using python libraries off the Pi). Heating up the probe reports a higher temperature, and vice versa, so I know the leads are hooked up properly.

The problem happens when I plug the espresso machine in the wall. The MAX31855K immediately starts reporting a temperature ~20F too low (instant temperature read drop). As soon as I unplug the machine, the temp returns to its accurate value.

I was using this thermocouple (http://www.auberins.com/index.php?main_page=product_info&products_id=307) which has a stainless steel sleeve, and appears to be a "grounded" thermocouple, which apparently the MAX31855K doesn't support - even though I'm following plans made by someone who used this thermocouple succesfully.

Fair enough, I bought a new k type thermocouple that is ungrounded - and same issue!!

At this point, I don't know what to do. Could the MAX31855K breakout board be defective? Anything else I could check? Here's a circuit diagram:

Thanks!


texts: Cost to run an Arduino device 24/7, simple maths question

texts:
I have built an Arduino window automatic closer/opener. When the device is on stand by mode, it draws 12V DC 0.025A.

My quesiton is, how much yearly I need to pay to have this on standby mode?

Would the equation below right?

12V, 0.025 A = 7.2Whour per day. It is then = 365*7.2 = 2628 W hr per year = 2.68kWhour per year.

If electrical cost in NSW Australia 27.56¢/kWh, so it will cost my 2.68*27.56¢ per yer = 72¢ per year.

Above calculation is based on the fact that the 240VAC to 12VDC is at 100% efficiency. I know it is never going to be 100%. Would I assume 90% ok?

So it will cost me 72¢/0.9 = 80.4¢

what do you think?

thanks all.

FYI, the reason did measure the AC current was because i was a bit dangerous and complicated to hoook up. but i did it at the end.

i found out at the end that it was drawing 220vac @ 3mAmp, so the cost would be about $1.7 a year.

however, when i open the electonic box. the 5 volt linear regulator was abit warm. and i wanna totoally minimise the heat. sill working on it


texts:
I had some fun with an RTL-SDR dongle, and I noticed this weird signal with no noticeable pattern at 119.9 MHz. What's even weirder is that the signal is symmetrical. What might this be? Or is this simply a hardware error?

EDIT: This picture is from an oscillating signal generator/MP3 tansmitter from AliExpress (2SC9018) and it looks pretty similar:

The only problem is, that when listening to the signal (In FM, AM, etc.) you cannot hear any music, any speech or any patterns that would sound digital.


texts: Filter 50Hz hum picked up by the oscilloscope

texts:
I am measuring huge 50Hz oscillations on my oscilloscope, but I am not entirely sure the probe  is generating those by behaving like an antenna (an ADC at the same point gives stable values but it's not sampling fast enough to give a definitive answer).

Would adding a capacitor in parallel to the probe (tip and gnd) filter out that noise (22nF in parallel to 1Mohm in my case)?

I will answer that question as soon as I test it (for the sake of others too, it appears there are not a lot of answers to that question online, and no good one), but I would like an intuitive or step-by-step description of what is or would be happening.


texts: TS2950CT50 Voltage Regulator +5V confusing specs / usage

texts:
The datasheet for the TS2950CT50 voltage regulator only provides information on the series TS2950C and TS2951C. From what I can tell, TS2950CT50 is a model within that series, which is a fixed +5v regulator. But the circuit diagram in the datasheet only shows how the model TS2951A can be used to provide a custom voltage output. But it gives no information on how I might use the TS2950CT50 (which I think is purely a +5v fixed model, is that correct?)

Please can someone give me a circuit diagram of how to use TS2950CT50? The input will be between 10 and 15 volts. I will be drawing current between 1mA and 90mA.

Thanks


texts: Repair MRAM that's been exposed to a magnetic field

texts:
Is there any way to repair MRAM that has been exposed to a magnetic field?
I've got a bit stuck (3rd bit) on my MRAM. Probably due to exposure to a magnetic field.
Is there any way to fix this short of completely desoldering the MRAM and replacing it?


texts:
I picked up my first "from-scratch" DIY electronics project in a long time, building a 2-tone door bell on stripboard with a basic 555 circuit.

For the most part everything went well. I assembled the circuit and measured up before going out and getting a snug fitting plastic enclosure (since it will be mounted close to the door).

I made one vital mistake, I forgot to include the 555 IC in my measurements, which is now protruding from the IC holder I soldered in - and now the 9v battery is poking out of the enclosure and blocking the lid!

I feel I have three options:

Meticulously unsolder the IC holder and solder the 555 directly to the stripboard
Run the 9v battery clip outside the enclosure and strap the battery to the outside of the box
Re-measure and buy a slightly larger enclosure

I'm not experienced at soldering; my current efforts have been reasonably neat but the components have had to cope with some excess heat as I occasionally fumbled with the solder. I'm very tempted to give the resoldering a go, but does anyone have some advice on how to keep the component cool while I solder the pins? Are there any other things I should watch out for when soldering an IC without a holder?


texts: Can I connect two taps of a tapped transformer together to make a center tapped transformer?

texts: I want to get two 8 V AC from this transformer which is outputting 0, 8, 16, 24 V / 1 A.


texts: Voltage regulator IC with positive and negative voltage output

texts: I need to save space on PCB and have to convert voltage from +48 to +9, -9 and virtual ground. Is there a single IC that could do that?


texts:
I want to measure weight of 200kg using load cell.
i have to use 4 load cell ( each capacity is 50kg).

My question is : is this possible to increase the capacity of load cell from 50kg to 200kg by connecting it in series.

if possible then please share me the any reference schematic that how to i connect it with series.

Thank you


texts: Impedance frequency response for a DC motor

texts:
Consider the following impedance frequency response for a DC motor :

Its equivalent circuit is :

Clearly, from the response, there exists a capacitor, inductor, and resistor, but my problem is how to determine that the resistor is connected in series with the inductor and all of these elements are in parallel with the capacitor.


texts: Transistor Biasing of high side switching network for PWM control

texts:
simulate this circuit – Schematic created using CircuitLab

iagramI am attempting to create a high side switching circuit for a string of LEDs wired in parallel. There are multiple strings, all wired together, which share a common ground, so low side switching is not an option.

I have found a schematic for a high side switching network, which looks promising. However, I am unclear on how to determine the proper value of the resistors. Any help would be appreciated.

The intent is to control the circuit with a PWM signal from an Arduino, Rasberry Pi, or similar.


texts: Where is this LED getting its timing from?

texts:
So this little board when connected to 5v and GND start blinking different colors in different orders and with different timing for colors to stay on!
There is nothing on the board other than the LED and a resistor! How on earth does the LED know when to turn on/off? and how do the colors change?
Please note, this is not an RGB LED.

Please see the schematics here.


texts: Amateur radio practice exam question about voltage drop

texts:
So the question is as follows:

"Your mobile HF transceiver draws 22 amperes on transmit. The
manufacturer suggester limiting voltage drop to 0.5 volt and the
vehicle battery is 3 metres(10 feet) away. Given the losses below at
that current, which minimum wire gauge must you use?"

and the options are as follows:

A) Number 8, 0.05 V per metre (0.01 V per foot)
B) Number 12, 0.11 V per metre (0.03 V per foot)
C) Number 10, 0.07 V per metre (0.02 V per foot)
D) Number 14, 0.19 V per metre (0.06 V per foot)

I believe that the answer is option B as it is the highest voltage drop that is below .5 volts for 10 feet of cable. But the answer key states that answer C is correct.


texts: What does this symbol mean in PCB Layout?

texts: I came across this USB TX lines in pcb layout. Yet to figure out what do those circles at the joints mean?


texts: Reading voltage (0-5V) using the Arduino Uno analog input and overvoltage protection for this pin

texts:
I need to measure the voltage on the 0-5V power line using the Arduino UNO analog input.

As I understand it, this can be done simply by connecting the "+" power line to an analog pin, without using any resistors? If not, do I need to pull the + to GND?

Can I protect the input of the arduino from overvoltage?


texts: Voltage in RC circuit with unknown frequency

texts:
We were given the task of finding the voltage drop across R1 of the circuit below with the following alternatives:

5.8V
4.8V
4.0V
10.0V

All given information is contained within the image, i.e. no frequency is specified.

My intuition tells me that the only way to solve this is to consider the capacitors as resistors with a resistance equal the given reactance and solve it as a DC circuit where the voltage drop over R1 becomes 3.2V, i.e. none of the above.

I have a hunch that the alternatives are wrong. However, if anyone have any ideas on how to solve this, let me know.

The correct answer is apparently 5.8V.


texts: How much mains leakage does an Ethernet connection to a PC induce, and what is the operating leakage path?

texts:
It seems that some users on another Stack have reported GFCI nuisance trips caused by mains leakage through twisted-pair Ethernet cables connected between computers on different branch circuits, or more specifically, between a computer with a Class I, chassis-mounted, supply conforming to IEC 60950 connected to a grounded receptacle with UL 943 Class A GFCI protection, and a switch that is a Class III appliance with a Class II power supply, connected to a grounded, but unprotected, receptacle on a different branch circuit.

While, conceptually speaking, the idea that there could be a leakage path through the data cable makes some sense, and I have seen Ethernet reference circuits that have termination RC networks from the port-side center-tap terminals in the magnetics to chassis ground as well as a 1nF capacitor between chassis and signal grounds, it seems to me that it would be very poor engineering for this leakage path to allow the mains leakage current to rise to a magnitude exceeding the IEC 60950 standards.

What is the magnitude of this Ethernet-connection-induced leakage current rise, what factors in the design of the equipment involved control this rise, and can someone describe to me the precise leakage loop involved?


texts: Does the UPS specifications make sense to you as far as battery current go?

texts:
I have following UPS: https://www.cyberpowersystems.com/product/ups/pfc-sinewave/cp1500pfclcd/

It has max power of 1000W
It uses 12V battery

at 12V it has to draw 83.33 amps in order to output specified 1000W. This is the battery: https://www.cyberpowersystems.com/product/ups/replacement-batteries/rb1290x2/ . Does it look like it can possibly support such current?


texts: Identify SOT-563 device with top code 49K

texts: Please help me to identify this SOT-563 device with top code 49K


texts:
I am trying to build this circuit

The N-MOSFET(FQP30N06L) is controlled via an Arduino Mega and sourcing the 5V from the Mega as well.
I have tested that the leg is getting 5V across but when I add the relay it lowers the voltage a lot.
This is the relay I am trying to flip. My ultimate goal is to control a larger 120V AC heating element. Thanks for any help, or suggestions of a different relay.


texts: I need to create a PCB with a transformer on it, and in this case, I unfortunately can't solder on a regular one. I was wondering if there was anything akin to a 2d transformer, or just generally a coil I could print onto my PCB. I know that spirals are used in Radio-Applications, but I'm not sure if you could use something like this as a regular coil.


texts: How do I model a resistor array in SPICE?

texts:
I am currently building a library of SPICE simulation models that is going to include resistor arrays.

These arrays exhibits both absolute tolerances and relative tolerances. Usually, the relative characteristics are better than the absolute characteristics. For example, the 4 resistors of the LT5400 from Linear have an absolute tolerance of +/-7.5% and a relative tolerance of +/-0.010%. Same story for the temperature drift : they have an absolute drift of 25ppm/K and a ratio temperature drift of 0,2ppm/K.

I would like to model these arrays in order to estimate the impact of temperature drift and component tolerances on my signal acquisition chain. For this purpose, I already found those two links that are useful for discrete components : Simulating component tolerances and Estimating temperature drift effects. However, they won't help me on how to model relative tolerances and relative drifts.

How can I take into account in my SPICE model both absolute tolerances and relative tolerances of resistor arrays ?

PS: there is a model of the LT5400 in LTSpice, but I have not found a way to access the source model. Thus, I have no idea how to use it in monte-carlo analysis or temperature stepping.


texts: What does radio frequency "potential" mean?

texts:
Page 1-2 (Naoki Shinohara: Wireless Power Transfer via Radiowaves)

  During the same period, when Marchese G. Marconi and Reginald
  Fessenden pioneered communication via radiowaves, Nicola Tesla
  suggested the idea of wireless power transfer and carried out the
  first WPT experiments in 1899 [TES 04a, TES 04b]. He said “This energy
  will be collected all over the globe preferably in small amounts
  ranging from a fraction of one to a few horse-power. One of its chief
  uses will be the illumination of isolated homes”. Tesla actually built
  a gigantic coil that was connected to a 200 ft high mast with a 3 ft
  diameter ball at its top. The device was called the “Tesla Tower”
  (Figure 1.1). Tesla fed 300 kw of power to the coil that resonated at
  a frequency of 150 kHz. The radio frequency (RF) potential at the top
  sphere reached 100 MV. Unfortunately, the experiment failed because
  the transmitted power was diffused in all directions using 150 kHz
  radiowaves, whose wavelength was 21 km. After this first WPT trial,
  the history of radiowaves has been dominated by wireless
  communications and remote sensing.

What does radio frequency potential mean here?


texts: RMS and average value of a DC signal - Which is the correct way to eliminate the inaccuracies due to incorrect measurement setup?

texts:
I have a 5V DC signal and there are some ripples on top of the DC signal in the range of 50-100mV (maybe due my measurement inaccuracies or the switching noise coupling from other sources.)
In that case, to properly capture the accurate value of the DC signal without the AC noise ripple, should I use the RMS value of the scope measurement to capture it or the mean (average) value of the scope measurement to capture it?
My objective is to avoid the ripple due my the switching noise which couples, kind of like common mode noise. Which is the correct thing to do? And please explain why?


texts: which stepper motor driver is best for robotic arm?

texts:
I am  building a robot arm am using TB6560and datasheet,with stepper motor 17HS3001-20B datasheet.

I have problem with the stop current setting i.e. when stop the driver tb6560 reduces current supplied to motor by 50%.

This reduces the holding torque in stop position(when no signal is given by arduino).

I want increase holding torque as well as torque in running condition .

Is there any setting in tb6560 to set dip s2 for required current setting ,because tb6560 board that is only have two option i.i 20 % and 50% of running current.

Should this problem can resolve with TB6560 or I change driver to TB6600 or any other driver like L298 ,A4998 or any better solution .

I am using 12/24 volt and max 3A.

THANKS


texts: 9V 1A adapter and 2*3.7V battery IRF9630 produce sound and gets very hot 9V battery not (metal detector)?

texts:
I am not an expert at electronics.I am trying to build a pulse induction metal detector. I have this circuit

from that Book

I am using it with stm 32 blue pill but I have to stabilize the 9v supply to make works perfectly so i tried to use a 9v 1A adapter instead of 9V battery The transistor gets very hot and produce sound like beeps and after a while it is about to burn.I investigate the circuit on oscilloscope  it produces a similar output on both cases adapter and 9v battery.

I thought it is a problem of logic level(between stm32 and PIC) so i tried to convert the 3.3V to 5V using open drain but it produces the same unpredictable performace.

finally it do the same with 2*3.7 li-ion battery What should i do to overcome this problem to be able to drive the circuit with 3*3.7 through 9V regulator to stabilize the circuit.Thanks.


texts: Timer1 on ATtiny85 not working as expected

texts:
I am trying to use Timer1 on the ATtiny85 (Adafruit Trinket) to blink an LED every second. The prescaler value is 1024, and the compare register value is 28. I loop through this 279 times to get a delay of 1 second.

$$\frac{1024\ . 28\ . 279}{8\ .10^6}\simeq1$$

With the code below I get something like 8.5 seconds. I set -mmcu=attiny85 and -DF_CPU=8000000UL when compiling. What could I be missing.

#include <stdint.h>
#include <avr/interrupt.h>

#define TIMER_OVERFLOW_COUNT 279

volatile uint16_t timerCount = TIMER_OVERFLOW_COUNT;
ISR(TIMER1_OVF_vect)
{
    timerCount++;
}

int main(void)
{
    DDRB = 1 << DDB1;
    OCR1C = 28;
    TIMSK = 1 << TOIE1;
    sei();
    TCCR1 = (1 << CS13) | (1 << CS11) | (1 << CS10);
    while( 1)
    {
        if( timerCount >= TIMER_OVERFLOW_COUNT)
        {
            timerCount = 0;
            PORTB ^= 1 << PORTB1;
        }
    }
    return 0;
}


texts: Determining Vo in a diode circuit using iterative analysis

texts:
simulate this circuit – Schematic created using CircuitLab
Say  we have this circuit. Then we were asked to find Vo using iterative analysis. We were told to stop when the estimate is accurate to within 15mV. I just want to confirm my understanding of the question.

Is the 15mV the Vo that we should be aiming to get?
And so,  if it is, we should be looking for the values of Id or Vd, right?
What will be the right approach here? Could I first assume Vd to be 1/2Vout (Since I could find Id when I know Vd) and then just adjust it till I get to 15mV?

My KVL equation is: (Id is based from the exponential model of the diode)
$$ Vout = V1 - iD(R1) - 2Vd $$
The following are given:
Is (reverse sat. current) = 1fA
Ideality factor = 1
Operating temp = 27 C


texts: Variable voltage supply (0V , 5V, 7V, 10V, 16V) rotary switch

texts:
I need to build a variable voltage supply that can generate 0V,5V,7V,10V,16V. My idea is to use a rotary switch and zener diodes. So far I got all the outputs correct with little difference from my desired output.

My question is, are the values of my resistors and capacitor correct? How can I solve for the right value of R1, R2 and C1? What (value) of the transformer do I need to buy? What do I need to change? I am just a newbie and been studying electronics for a few weeks and I need to buy these components immediately. Thanks!


texts:
I am trying to identify components with RefDes EC1 and EC2 in this circuit (the boxes at the top with markings 100-10Z). I have done a lot of searching and EC is not even an accepted RefDes EC.

I think the component might be a SMT Inductor, but I don't really know.


texts:
I'm want to create a project with a LED strobe with IR LEDs.

As LEDs the Osram SFH 4249-UV will be used in strings of 15 LEDs and 32 strings parallel.

This results in a Vf of 34.5 - 45 V and a If of 32 A in an 0.3 ms flash.

The pulse frequency will be between 1 and 100 Hz and the current is most likely to be between 0.5 and 1 A.

Due to the fact that I'm not experienced with current sources created with shunt fets I read there is a high possibility of oscillation. I'm looking into using the CPH6442-TL-W from ON semiconductor since this one is capable of a drain current > 1A with Vds of 50V at 1 ms.

How can I prevent oscillation and where do I have to look out for selecting a opamp?
how does a fet shunt current source work?
Does is switch really fast on and off or does it increase the Rds?

I was thinking of the following circuitry:

Update: thank you all for the ideas and recommendations. I have found a BUK6D43-60EX mosfet that would be sufficient but when I calculate the maximum power I get with a thermal impedance of 6 K/W a junction temperature of 135°C at a ambient temperature of 60°C (T-junction = T-ambient + R-ja * (Vcc-Vled-Vsense) *If). This seems really insufficient and generating a lot of heat. I know I can switch te mosfet for a BJT or IGBT but I'm not so familiar with these components other than I know a BJT would have a much higher error since the base current also goes though the sense resistor.


texts:
I am looking into building this stereo amplifier based on this circuit: 2 x 22 Amplifier

However, as I am pretty new to circuit building, I have a question about the ground lines: Do i tie all of the ground lines to the earth ground on the power supply? On the schematic, it shows +12v in, and out to "GND", and i am not sure if I should use the common ground line by itself as the end point, or if i should ground the common to earth. Any help would be great, and apologies if this is somewhat redundant, thanks!


texts: Lightest weight option to provide short bursts of power (250W x 4 seconds)

texts:
I'd like to mount mount a small pump to a surfboard to provide a small push to help catch waves. Normally to catch a wave you have to paddle furiously for about 4-5 seconds. So that's about ~ 1000 joules of total energy. I'd need about ~25-50 such pushes.

One of the most important things here is the total weight -- to prevent the board from becoming dangerous, the board is ~7lb and addons should be ~4lb max.

The engine will be probably 12-16amp. What would be the lightest-weight option for providing these bursts of energy? 16 AA-sized batteries would weigh about 1lb; Would a supercapacitor be lighter?


texts: GSM regulations for 850/900 MHz band and 1800/1900MHz

texts:
I understand that GSM regulations establish that transmissions power for two bands must be as follows,

-Class 4 (2 W @ 850/900 MHz)
 -Class 1 (1 W @ 1800/1900MHz)

But I also know that lower the frequency higher the range for equal transmission power. In that case, does it mean 1800/1900 MHz band has lesser range than the first? And also essentially result "better" than Class 1?


texts: How to create footprint from IC diagram when no recommended layout is given?

texts:
I'm a student trying to create a library part in Altium for an Analog Devices AD8232. Most IC datasheets give a recommended footprint to use, but the AD8232 datasheet only shows the IC itself:

I have been searching, but have been unable to find a recommended layout for this footprint.

If you were designing the footprint for this device, how would you determine the pad sizes to use?


texts:
I am seeking to activate the DFU mode in the B-L072 Discovery Module using the Murata CMWX1ZZABZ-091 module. https://www.st.com/resource/en/user_manual/dm00329995.pdf

I have kept BOOT0 pin to HIGH and connected a USB cable to the CN11 USB connector. But STM32prog does not detect the DFU bootloader. Also the device manager does not detect the board. Tried using DFuse also, then uninstalled that and started using STM32prog and did all as asked under the STM32prog PDF UM2237.    I also shorted the SB16 & SB15 points to enable the USB DP-DM connection.

Also, uploading code by USART is also not working. Connected an external USB-UART to PA9 & PA10. The USART also does not connect.

What am i missing here? Any help would be deeply appreciated...


texts: How to connect a 4:1 balun to a a log periodic antenna?

texts:
I'm following a plan for a home made LTE/4G UHF antenna here: https://www.thingiverse.com/thing:3221812
...because it looks to be of a very similar to design to a very expensive 4G anntenna I know works very well.
However it's not completely clear how to wire it up. It looks like it has two element arrays on opposite sides, and that they appear to be wired from the pointed end (with shorter elements) rather than the opposite end.  I assume the LTE mast should be at the pointed end of the array? And that it should be vertically polarised like a normal dipole?
If I also add the 4:1 balun (I've no idea what this actually does!) I'm not sure how this is actually wired to the antenna elements and coaxial cable and what is classed as "earth" in this setup?  Does earth just mean the outer shield of the coax cable?


texts:
I have some difficulty reading specifications for PTC heaters, more specifically the ones on here. I understand that a PTC heater does not, inherently, rise above a specific temperature. In the previous link, does that mean that the "Temperature Rise Reference" column specifies the max temperature?
If not, how would I calculate it?


texts: How much change is allowed after a device has been FCC certified?

texts:
We are trying to decide between two different DACs in the same family that are pin compatible.  One DAC is about 3x more expensive, but has higher resolution and will definitely work.  The second is less expensive, but has lower resolution.  We will have to do more extensive testing to verify that the lower resolution DAC works for our applications.  We are a startup and would like to sell our product out as soon as possible.  If we pass the FCC test with the higher resolution DAC, and switch to the lower resolution DAC later would we have to retest?

The rules I found on the FCC site said that if the part is electrically equivalent we would not necessarily need to re-test, but I am not sure if changing DAC resolution is considered "electrically equivalent".

Our device uses RFID, so it is an intentional radiator, but the DAC is not related to the RFID circuit.


texts:
I have a piece of equipment that pulses a 4.5V motor for a 500ms forward, then 500ms backwards.  I have no control over the board creating this function; however, I want to modify the signal to only pulse forward on the first action, and backward on the next.  Therefore, I want to intercept the wires going to the motor and create a small project that can achieve this.  I have tried to bread board a single latch relay to flip flop the signal; yet, my pea brain cannot get around the logic to make it work correctly.  I have also tried to draw up a schematic with a dual coil latch relay, and no luck.  I understand this is a broad question, yet I have googled this to death and have found no where to start.

Edited:
Signal coming from the controller are pulses of (4.5v 500ms -4.5v 500ms) each triggered event.  I want (4.5v ~500ms) first trigger event and then next pulse (-4.5v ~500ms) next trigger event and reset to first.


texts: Is it possible to realize an 1:16 impedance ratio Transmission Line Transformer on a single core?

texts:
I would like to build a wideband amplifier with a 1:16 impedance ratio Transmission Line Transformer (TLT) at the output. The input port of the TLT accepts a differential signal and provides a differential signal at the output too. The load impedance is 50 Ω. I wonder if this problem can be solved using a single ferrite core and if it is possible, how?

I know that the Guanella 1:4 impedance ratio TLT, which is a popular configuration, can be built on a single core. Higher impedance ratio TLT's on a single core is rarely presented in the literature, I haven't found any relevant information so far.

(Image: Chris Trask - Transmission Line Transformers: Theory, Design and Applications - Part 2, Fig. 14.)


texts: What does "capacity achieving code" mean?

texts:
I am an electrical engineer passed several courses in information theory and coding theory, however as I think now, I see that I have not understand the basic ideas in these concepts till now.

We know that each channel has a capacity that is achieved by a specific input distribution. For example an AWGN channel has a capacity of $$\frac{1}{2}\log{(1+SNR)}$$ and is achieved for input distribution of Gaussian. Now I want to transmit 0 and 1 with equal probabilities through this channel. Obviously I cannot reach capacity, as the distribution of input is not Gaussian.

In the books we see that ... code is capacity achieving, I cannot understanding what does this term "capacity achieving code" mean. Can anyone explain more?


texts: Why 2 electrolytic capacitors and Schottky rectifier at power supply?

texts:
I am trying to design and improve the power input part of my circuit to supply power to a motor driver that controls 2 DC motors. I did some research and i found this circuit but i cannot fully understand why these components have been used. I am using DC batteries to supply 12 V at VS and VIN goes to the VIN input pin of the Arduino UNO.

I read about power supply decoupling capacitors; electrolytic capacitors filters out low frequency signals and ceramic capacitors act as a low pass filter.

I have the following questions:

Why use 2 electrolytic capacitors instead of just one?
Why no ceramic capacitors has been used? Has this been omitted intentionally?
Why is a high value of 470uF used? I searched and found that many power supply decoupling capacitors are less than 100uF for my application where the supply is only about 12 V DC.
The Schottky diode is the most intriguing to me. It is a rectifier, so is it also helping to smooth out the DC signal? Shouldn't it be connected in series instead of in parallel?

Thanks for any help.


texts: Having trouble understanding amps, watts, voltage, and how they all work

texts:
I read that watts is amps multiplied by voltage.

But then I read that it depends on the wattage ... what determines wattage? I thought that the outlet supplied voltage potential, and the device uses that. How do amperes, watts, etc. come into the whole big picture?

I also found that you need to know how much resistance is in a circuit to determine how many amps equals how many volts. How would one know the resistance beforehand throughout an entire circuit before figuring out wattage? I thought wattage was force.

Then I read that a volt is what "pushes" electrons, but then I read that wattage is a force equal to one joule per second.

How does it make any sense to understand that voltage is the power when wattage is considered force? There's two forces?

Assume I do not know the wattage, what is the amperes of one volt then?

I have tried books, Google searches, everything - it doesn't add up to me.

This doesn't make sense to me, and it's greatly complicated. Ironically, I've done some small electrical projects not knowing this, and it's unclear to me.

Can anyone make this clear(er) to me?


texts: How to design the capacitors used with Crystal Oscillators?

texts: I have seen circuits involving crystal oscillators connecting two capacitors between each of the crystal legs and ground. I would like to know how to design the value of these capacitors for different crystal frequencies.


texts:
I am having a pipelined scheme and I want to have a register at the output for my result.

So, I am using this code:

 always @(posedge clk, posedge reset) begin
      if (reset) begin
          //do staff
      end else begin
         if (state_5) begin
            output <= ....
         end
      end
   end

however for timing reasons, I want the result to be available on the same cycle. If I change my code to this:

always @(posedge clk, posedge reset) begin
          if (reset) begin
              //do staff
          end else begin
             if (state_5) begin
                output = ....
             end
          end
       end

results are available in the next cycle as well.

If I change into that:

always @(*) begin
             if (state_5) begin
                output = ....
             end
          end

I am ok with timing. My question is , does this code infers a register to be used?

my output is defined as output reg.


texts:
I'm looking at this mealy machine:

and this state table with the boolean expressions at the bottom.

If you look at the \$S_1\$ boolean expression, it says \$S_1 = \overline S_1 S_0 B + S_1 A B\ \$.

Shouldn't it be \$S_1 = \overline S_1 S_0 B + S_1 \overline S_0 A B\ \$?

Why did they miss out the \$\overline S_0\$?


texts: What PWM inputs are needed to drive a 3 phase BLDC using the HIP4086 IC driver chip?

texts:
I am building a motor controller for a BLDC (w/ Hall sensors) using a Teensy. My circuit looks like the typical application diagram in the datasheet (https://www.intersil.com/content/dam/Intersil/documents/hip4/hip4086-a.pdf):

My micro controller correctly reads in the Hall sensor inputs and can identify which position the rotor is in. My question is, if I want to pull (for example) Phase A high (+), Phase B low (-), and keep Phase C floating, what PWM should I be writing to the pins AHI, ALI, BHI, BLI, CHI, and CLI. I know this is probably clear in the data sheet, but I am having trouble understanding the switching logic of the triple half bridge.


texts: Current limitation to capacitive voltage divider

texts:
For an AC capacitive voltage divider, I would think the amount of current that could come from the divider would be limited by the absolute size of the capacitors. The flow of current should be a function of how much charge can be stored in each capacitor.

The only reference to such limitations i can find on Google is here: https://forum.allaboutcircuits.com/threads/capacitive-voltage-divider-downsides.28895/. Ultimately the relevant commentary is a redirection to Wikipedia but I can't find anything pertinent there.

Given a capacitive voltage divider with an AC source, does the absolute size of the capacitors in the divider limit the current to the circuits attached to the divider¿ what is the relationship¿ (will kirchoffs laws predict this¿)


texts: What could be a good project to realize neural network in hardware (VLSI) for a beginner?

texts: As a beginner how can I start implementing neural network using CMOS technology. I have come across implementing neural nets that mimic basic gates.


texts: How is the "I" current calculated in this circuit?

texts:
I found Vo with these processes
[10 - (- 2)] / (1200   4700) = 2.033mA
1200 * 0.002033 = 2,43V
Vo = 10 to 2.43 = 7,57V
but I can't find the "I" current. Can you help me?


texts: How to calculate the input impedance and transfer function

texts:
I have the following circuit, that is used as a signal conditioning circuit in a audio system project.
I am trying to calculate the transfer function and the Zin(input impedance) and Zout(output impedance)

in Zin, I know how to calculate the impedance of the rc filter but im getting confused because there are one more resistor of 10M that makes the offset of the voltage.
So, how can i calculate the transfer function,Zin and Zout of this circuit?


texts:
Is there any difference in applying a 50-ohm female SMA PCB mount connector to an antenna as opposed to a pig-tail connector to a microstrip patch antenna?

The difference is in terms of the performance of the antenna, such as the resonant frequency shifting, BW, gain, axial ratio


texts:
I'm working on a mobile computer unit with a Raspberry PI 3 motherboard. The computer unit needs to run on battery so i can bring it with me anywhere. I'm going to solder both the battery pack and power supply (buck or buck boost) myself, since it need to fit as perfect as possible in a custom made 3D printed case.

I have decided to use LiPePO4 battery cells, either 2 (6.4VDC) or 3 cells (9.6VDC), I guess 3S is best since I only need a buck converter to get 5V contra 2S that may need buck boost. I'm thinking of soldering a) power supply and b) cut of (high voltage/low voltage) on the same PCB.

But I'm not so very experienced with electronics other than I have some basic electronic education, so I'm wondered if someone has some advice or inputs to this project. I have mainly three questions.

Is it better to use 2S or 3S battery to this project, I'm then thinking of efficiency of power supply, as far as I understand 6.4VDC is closer to Vout (5VDC) so it will be a more efficient power supply than Vin as 9.6VDC. Runtime is importent, so more efficiency power supply is longer runtime.
I'm looking for power supply circuits that can deliver 2-3A, is it enough to run just the RPI 3 board?
I have found several DC/DC converters that delivers 2A@5VDC, but these use Linear Technology IC that are pretty expensive, I have been told multiple times that LT's IC is overrated, what other IC brand can I search for?

And if you guys have been doing similar projects with RPI 3, or have other advice, please inform me.


texts: Can I feed my level shifter with a voltage divider?

texts:
I need to level shift 3V3 to 2V8. I have a 2V8 source but that'll require some patching wires on testpads and as such I would like to avoid it.
I'm wondering: would it be safe to feed the SN74LVC245AN the required 2V8 by using a voltage divider (two series resistors) to convert 3V3 to 2V8? It is for a temporary setup which will be used shortly.
I use this chip to shift my 9600 baud 3V3 serial to a 2V8 serial on a SARA-N3. I need to perform a firmware update and made room in my PCB design for the ALT uart to be accessed but forgot about the 2V8. As such I need to convert 3V3 to 2V8 serial. I don't know if the update process requires bidirectional data transfer and as such a simple voltage divider over the TX->RX probably won't be good enough.
The pad on my PCB is quite small, just enough to hold a volt meter probe on it to test for an activated SARA-N3.


texts: Problems with high-side current sensing with 12V comparator and logic

texts:
I am designing a system with circuit protection using high-side current sensing.
Expected shut-off current is in the range of 1~3 Amps.
The current being sensed is 12V so I have designed a circuit that automatically
shuts off a power transistor when excess current is detected. To avoid having to
use voltage shifters I am using 4000-series logic gates that run at the same 12V
supply which do the detection and shutoff. My problem is that most comparators
can't operate with their inputs close to their upper rail (i.e. power) voltage
and need to be brought into their linear ranges in order to do compares accurately.
Those that do seem to be expensive and my board needs to have 14 of these automatic
shut-off circuits on the board. But by their nature, high-side current sensing means
that the voltages that will be monitored are small fractions of a volt below the
upper rail voltage. Since the comparator needs to run with say 1.5V above measured
voltage ~12V then it needs to be supplied power of at least 13.5V. So it looks like
this might be a case where some sort of solid state voltage generator is called for.
I am aware that RS232 transceivers can generate the higher voltages needed for line
output and sensing line input using an on-chip device (called a charge pump). Is anyone aware of such a discrete device for creating a voltage that is higher than supply by some known amount for use by other onboard devices? It would be similar to an LDO regulator except that it produces a voltage above supply.

Another problem I see is that, if the comparator is running at a higher voltage than
the logic then the 4000-series logic gates might experience inputs that are higher
than their power supplies. A possible solution to this problem is to run all of
the logic at the higher voltage as well. I am loath to use a higher valued current
sensing resistor to bring the sensing voltages down into a comparator's linear range
as it would make them burn a lot more power as well as lowering the voltage that is
available to drive the load that is being controlled.

Any advice or insight is appreciated.


texts: Capture Olympus 5800PR US pulser/receiver data on my laptop

texts:
Im tryng to place some ultrasound experiments at school and i have this pulser available (Olympus 5800PR), the problem is that i dont know how to capture the data on my laptop. I know i have to set an adc to do this but maybe there are easier ways to do this, preferable the cheapest ones.

Hearing suggestions.. tnxs.

Oz!


texts:
I'm doing an assignment on circuit analysis with phasors and it's brought up a point of confusion for me on how Phasors convert to rectangular form.

My textbook defines phasors as $$v(t) = V_M\text{cos}(\omega t + \phi) = \text{Re}[V_Me^{j(\omega t + \phi)} ]$$

and says that they can be written in phasor notation as $$ V_M\angle \phi $$

That makes plenty of sense to me. However, in my homework, when I have to add phasors and convert them to rectangular, the solution has them being represented as

$$ V_M\angle \phi = V_M\text{cos}(\phi) + jV_M\text{sin}(\phi) $$

This difference seems contradictory to me. The book seems to imply that phasors are only expressing the real component of the function, but when it comes to problems, phasors are now both the real and imaginary components? I know I have some conceptual misunderstanding somewhere, but I just can't identify it.


texts: effect of Capacitor when dc voltage source connected to it

texts: What happens to capacitor when capacitor is fully charged upon connecting to dc voltage source, will it behave as open circuit ?


texts: The best way to attach a heatsink to a SMD component?

texts:
There's a SoC I want to throw a heatsink on. What's the best way to do this for maximum heat transfer and longevity?

I know of thermal pads, thermal adhesive, and thermal paste -- but when it comes to the standard black plastic packages, I have no clue which of the options would be best.


texts:
I'm looking for replacement IC for CD4054, but I can't find any other part that would work like CD4054 in level shifting. What I would need (from CD4054 description):

The CD4054B may also be utilized for logic-level "up conversion" or "down conversion". For example, input-signal swings (VDD to VSS) for +5 to 0 V can be converted to output-signal swings (VDD to VEE) of +5 to -5 V. The level-shifted function on all three types permits the use of different input- and output-signal swings. The input swings from a low level of VSS to a high level of VDD while the output swings from a low level of VEE to the same high level of VDD.

Does anyone know what can be used instead of CD4054?

EDIT 1:

It was suggested that this question was off-topic - why? How I can't seek recommendations for specific product, if only some product (or products) can do what is needed? Also level shifting as described above, is not some niche application that no one will ever need. Same with CMOS 4000 series.


texts: BJT common collector amplifier with a voltage gain sligthly higher than one

texts:
How could I explain why a common collector amplifier has a voltage gain higher than one ? In a lab session, I built this circuit :

With Vg=30 mVpp and Vcc=15V, students were asked to give the voltage gain of the circuit in function of frequency. In class, we derived the small-signal equivalent circuit and concluded that the voltage gain must be sligthly lower than one. Well, I was pretty confused today because the mid-band voltage gain is roughly 1.15.

As the teacher always says, it doesn't matter if the experimental data don't fit with the expected values given by the small-signal model, but we must be able to explain the differences between theory and our observations. The thing is, I'm out of words. It seems to me that it is impossible to have a gain higher than one, Ve must be lower than Vin.

If you have an idea, even only an hypothesis, any help is welcome.

Values related to the circuit :

Rg=1K

R1=22k

R2=10k

R3=1.2K

R4=500

Ccc=100u

C1=C2=10u

Vcc=15V

Vg=30 mVpp


texts: SRAM: Purpose of Upper and Lower Byte Enable when Data Bus is greater than 8-bits?

texts:
What is the point of an upper byte and lower byte enable on an SRAM if the data bus is already 16-bits?

Is it related to multiplexing? I had always assumed that SRAMs were either designed with either multiplexed or dedicated data and address buses. Maybe I am wrong and they all have dedicated buses and how you wire them up determines whether or not they are multiplexed. Seems like you wouldn't save many pins or traces that way though. It would only save them MCU pins, but would not affect the SRAM pins or the number of traces running between the two ICs.

I am looking an an MRAM Datasheet, though this seems broadly applicable to all SRAMs:
https://www.everspin.com/family/mr5a16a?npath=258


texts: How to find input impedance for this op amp?

texts:
The simulation gives an output voltage of 1.427V and Av of 10. Based on the equation Av= -R2/Ri, Ri should be 7kΩ. However, when I calculate the total impedance using R3+(R1//R4), the impedance is only 5.833kΩ.
What is the correct way to calculate the input impedance? Why can't I combine R3, R4 and R1 together as Ri to feed into Av equation?


texts:
An old Sony VPL-CX11 stopped working because one of the fans (the lamp's one) was so rusty that couldn't rotate. In the front of the projector there are two fans, one for the lamp and the other for the power electronics.
The projector seems to read the state of every fan and the lamp's temperature and auto-shutdown then something is not working properly.

First I used lots of WD-40 and after some manual forced rotation the fan start working again, for about 1 month.

Now the same problem appeared, so I decided to replace the faulty fan with a new one. The thing is that the color's wire are not the same, so I am not sure how to connect it. Measuring the resistance gives little info since there is an IC between the terminals and the motor.

As you can see in the picture, the old fan (this is for the power electronics) has Yellow, White and Orange (or Brown) wire colors. The new one has Black, Red and Yellow.

If I make the following connections

Yellow-> Yellow
White -> Black
Orange -> Red

fans start spinning but projector shuts down unable to detect the new fan.

Any other arrangement prevents the new fan from spinning.

Some other color arrangements seems to let the lamp turn on, but since the new fan is not spinning, after a minute the lamp becomes hot and the projector turns off automatically. This is weird because it means that the protection reads a "proper signal" and thinks that there is a fan that is spinning.

Some extra info:

After measuring the voltage across the old fan terminals, the values are:

Orange-Yellow: 8V
Orange-White:  8V

The old fan draws around 0.07 A at 8V and the new one 0.15 A, but I don't believe that this is the problem here.

Any ideas would be highly appreciated!


texts:
For all those out there with solenoid experience I'm looking at a project using them for the 555 contest. The spec on most solenoids is ounces of force (at least in the price range I'm looking at). Aside from my disgust at the imperial units, I can fathom what the units mean, but not what kinds of things that amount of force could accomplish.

What kind of actions could 24 oz of force achieve? Is it closer to denting a peach or denting a bowling ball? Is it depended on distance? Drive current? Anything else? Thanks for all your help!


texts: How to determine the capacitance from the capacitor charging current

texts:
Consider the following circuit, and the recorded current curve (amp-meter current_in).

How do I correctly determine the capacitor's (C_1) capacity, without looking at the time constant?
My idea was to calculate the integral of the capacitive part of the current and divide it by the voltage VG1. This does not yield the correct result. What is wrong about my approach?

//Edit
I tried to derive the current at the amp-meter:
\$ I = V_G1/(R_1+R_2) + (R_2*VG1*\exp(-t(R_1+R_2)/(C_1*R_1*R_2)) +1/(R_1(R_1+R_2)) \$

Is that correct? Is the RC-circuit a high-pass?


texts: What is the trick to soldering to aluminum bases (like are found on the older Luxeon LEDS?)


texts: Can i use 12 v solenoid valve directly connect with the 12 v battery?

texts: Can I connect 12v solenoid valve directly to the 12v battery?


texts: protecting a sensor component from high spikes when switching power on

texts:
I have an electrical scooter which has a "Hall Effect Sensor" in the handle-bar, measuring the magnetic flux to determine the amount of "gas" or gauge.

This sensor tends to burn out quite frequently. I replaced it with a potentiometer for a while which worked out great. The only problem is that I can't control it (safely) wearing gloves, and I can't drive in the current temperatures without gloves... So I'd like to give the hall sensor a go again, but add some circuitry to protect it against voltage peaks. I measure 5 Volts across the gnd and "plus" pins. I'm not sure how high the spikes can go, but the serial array of 6x12V batteries delivers more than 80V in total (The 12V Lead-gel batteries actually deliver more than 13V each).

I have found quite some delay-start circuits on Ebay, but they only cover one channel and need a 12V source. I'd need 3 channels (since I don't have a clue what is actually spiking) and I don't have a 12V supply at hand (at least not linked to the switch, bridging one battery would not help).

Adding a capacitor over the sensor might work as a buffer, but it also might decrease it's responsiveness, unless I only apply it to the plus and gnd pins and assume the sensor pin is not spiking.

Adding an extra manual switch would be a last resort, which could also be easily forgotten.

Any other ideas for ways to protect it?


texts: Can I replace electret microphone with audio connector and expect similar results (sound levels)?

texts:
Last night I built a circuit that allows me to obtain sound via a SEED Grove Sound Sensor and input it into my MKR Zero for frequency analysis.

It's as simple as this:

simulate this circuit – Schematic created using CircuitLab

You just talk or whistle into the mic and it outputs frequency values.

It works very well but it picks up ambient sound of course.

Sound Sensor Schematic

I examined the Sound Sensor schematic and noticed that it is a very nice amplifier circuit using an lm358.

Now, I'm wondering, could I build that same circuit and replace the electret mic with one of these audio connectors and expect a similar functional experience when I connect an electric guitar?

If you need more details on those see product listing at https://amzn.to/2CkTO0g

Basically, I'm wondering if that amplifier circuit will work to increase the levels from the guitar input enough for the MKR Zero code to read it in the same way as the microphone is being amplified.

Or should I expect that the guitar input would be at a lower level and require more amplification?


texts:
I recently came across this question in a series of articles about cross coupled pairs by Razavi:

In Figure 6, M1 and M2 are biased
and balanced by I1 and I2 ^ h I I 1 2 = .
At t = 0, Iin jumps from zero
to a small positive value, I0. We
intuitively expect that VX rises and
VY falls. However, viewing the XCP
as a resistance equal to -2/ , gm we
obtain V g XY = -( /2 m) ( I u0 t), concluding
that VX should descend
and VY should ascend! How do we
explain the discrepancy between
these two results?

based on the figure in the image.

Now, intuitively I expected that Vx would fall and Vy would rise as a positive current is flowing into Vx, doesn't that imply Vy has a more positive potential? Or is this a sign convention thing?


texts: How to improve timing on this design using so much BlockRAM?

texts:
I'm building a small RISC FPGA CPU on an Artix-7 (Arty A7-100 (xc7a100tcsg324-1) board.  It runs fine, most instructions take three clocks (non-pipelined), but due to crazy net delays, can only run at 100/50 MHz.  100 MHz for RAM which governs the speed of other signals.  Most of the lowest-slack paths are those connecting to the RAM. I used the Clock Generator Wizard to create a dual output clocking IP.
The problem is that I'm using almost all the BlockRAM on the device, so my signal fanout looks like this (e.g. this is the signal fanout for ram_dinb to the BlockRAM, other connections are similar):

At 100 Mhz, the timing requirement is of course 10.0 ns.  My Net delay here is 8.907, which seems absurdly high...  but when I highlight and zoom in on these paths, they meander all over the place, so  no wonder the net delay is so high...
So I studied a bit and even tried using the many horizontal BUFHCEs available, but this immediately failed because I used the Block Memory Generator to create this 256K-word RAM, it looks monolithic, even though it spans the entire die.  So for example if I wanted to use this on a single BlockRAM primitive in region X1Y2, I might use something like:
wire clk_ram_12;    // region X1Y2
BUFHCE #( .CE_TYPE("SYNC"), .INIT_OUT(0) )
BUFHCE_ram_12 (
  .O(clk_ram_12),
  .CE(1'b1),
  .I(clk_ram) // from the MMCM
);

Except that the Block Memory Generator interface only allows for two clock connections at the module level, not to mention all the other signals like data, address, etc.
RAM256 ram (
    .clka(clk_ram),
    .wea(2'b00), // Never write to port A because it's connected to the program counter.
    .addra(pc),
    .dina(18'b0), // Never write to port A because it's connected to the program counter.
    .douta(ram_douta),
    .clkb(clk_ram),
    .web(ram_web),
    .addrb(ram_addrb),
    .dinb(ram_dinb),
    .doutb(ram_doutb)
);

I feel like I'm missing something fundamental here.  Is there any way I can speed this up?  Or am I hopelessly painted into a corner with this BlockRAM?  Even if I create a clock tree using BUFHCE and BUFG primitives somehow, it still doesn't solve my problems for other signals, like data, address, write-enable, etc.  I've been reading Xilinx user guides for two days now with no promising ideas.


texts:
I was sitting around and suddenly wanted to convert my old blender into a lamp. The control panel would act as a dimmer switch. (And maybe the pulse button would be a big hit at raves.)

Can I just remove the motor and sub in a lightbulb socket?

For purposes of this lamp, I would prefer not to burn down my house, cause fuses to blow up in my neighborhood, destroy the power grid, etc.

I'm total n00b when it comes to circuitry, though I have soldered replacement parts onto PCB boards with success. Sorry if I'm not providing enough information or my question is just...wrong.  :)


texts: About MKP Capacitors for Inverter Welding Machine

texts:
I need your help with capacitors...

I'm restoring a 160A inverter welding machine, model Fimer X164.
One of the capacitors has cracked and I need tochange that..

Information about the capacitor on the board (i.e. exploded):

PILKOR 10nF 300V-Y2 PCY2 130 MKP

I can't find an identical capacitor but find similar values.

I have

1- 10 n K 400 RIFA 404 FVN

2- RIFA 271 Y 522 250V MP

Can I use capacitor 1? Or what do you suggest as a replacement for this capacitor?


texts:
I am looking to ways to best store my miscellaneous batteries, which consists mostly of AAA/AA batteries (both alkaline and NiMH), a few Lithium batteries, and assorted button cells. I think I have the environmental conditions sorted (cool, dry place, no direct sunlight, out of reach of children, etc), but I have a few specific questions:

Would storing cylindrical batteries so that their end contacts touch (see below) cause issues, or is this an OK way to store them? I know they won't complete a circuit (the container they are in is plastic), but I was wondering if I might nonetheless get corrosion (or other effects, like more rapid discharging)?

I presume that storing cell batteries loosely (like this - see below - note that there will be many more cells in that box over time) is a bad idea, as they could (if jumbled around) create a short circuit, correct? If so, is there a good way of storing them (except to keep them in the blister packs in which they originally came - which take up an inordinate amount of space!)?


texts:
Can someone explain how this part of the circuit works? Why do they use PNP (Q5), NPN (Q2, Q3) transistors with inductor (L1) and diode (D1)? The Li-ion charger is a BQ2954.
The description for pin 14, MOD says:

Current-switching control output

Pulse-width modulated push/pull
output used to control the charging current to the battery. MOD
switches high to enable current flow and low to inhibit current flow.
(The maximum duty cycle is 80%.)

Thank you for help.


texts: How to generate a short, slightly stepped up pulse?

texts: Given a 3v power source (2xAA batteries) and a microcontroller, what's the simplest cheapest way to generate a 3.6v 30ms 500mA pulse (to control a solenoid)?


texts:
I have more than one lamp and i need to make a program to commissioning.
I've already did it whit a single lamp but now I don't know :

How to make addresses for multiple lamps (in my case A3 is programming all the 3 ballast),
should i save it in a eeprom?

Whenever i put the lamp on or off the master should understand if she has ( if she doesn't have master must provide )

address
group

How should I implement DTRcommand for multiple elements?

I know I need Terminate Initialise Randomise elements but I would focalize to the controls part, 'cause i don't know how to structure and organize them.

Which commands should I use to verify if my lamp is addressed and without group?

I gladly accept every ideas and informations from you,
thanks very much!
If we can (since i didn't find some very useful guide, or suggest one) we could make a small library in order to create a very practical guide for Dali and his commands.
Thanks for helps


texts: First production run - design PCB for through-hole or surface-mount?

texts:
I am nearing the stage after testing everything on a breadboard where I'm ready to fire up Eagle CAD and start developing my circuit board. This will be my first ever circuit board design. My question now is: Should I design for through-hole or just go straight to surface-mount?

I have a pretty good soldering station (Weller WSM-1), so I think if I use reasonably large SMD components I should be able to hand-solder things with no problem. On the other hand, with through-hole components it would be impossible to not be able to solder them. The board is very basic, with just one ATtiny85, three resistors, a bunch of LEDs, two ceramic capacitors and a 32.768 kHz crystal. The crystal is another point I'm unsure of: Every electronic device I've opened up has these as hand-soldered through-hole, even if the rest of the board is all surface-mount. Why is that? Are 32.768 kHz crystals not available in surface-mount packages?

I would really appreciate any input on helping select the best way to go on the board design (through-hole vs surface-mount). I'm thinking that in the unlikely even that my board becomes popular, having it as an SMD board would facilitate production at a plant that can do automated assembly. On the other hand, I have no idea if through-hole manufacturing would be a cheaper option for certain quantities.


texts: Can you use a CAN FD transceiver for low speed (fault tolerant) CAN?

texts:
Fault tolerant CAN (ISO11898-3) is terminated differently than high speed CAN (ISO11898-2). Therefore the signal levels for dominant and especially recessive bits differ.

Newer CAN FD compatible transceivers can have baudrates up to at least 8 MBit/s, but none of their datasheets specify minimal baudrates or compliance with ISO11898-3.

Is it safe to assume they are backwards compatible or should I look for some kind of feature indication in the datasheet?

The only problem I can think of is the dominant timeout function of some transceivers. If the baud rate is too low, it might cause problems with longer strings of dominant bits.


texts: Having a non constant current in a constant-current LED driver

texts:
I am using the TPS92511 LED driver as follows :

It is not on a PCB but a veroboard with wires so it is not a perfect circuit.

I have chosen Riadj to 4.9 kΩ which should give me something around 300 mA according to Table 2:

I chose Rfs to 22 kΩ which should give me a switching frequency of 500 kHz according to Table 1:

The inductor reference is 74477020, the diode reference is GF1D and the LED reference XMLBWT-00-0000-0000U2051. Its forward voltage is 3 V.

I can drive the current with the DIM pin thanks to a PWM obtained by a microcontroller. The PWM frequency is about 20 kHz but I have also tested the circuit with 1 kHz.

I have two problems :

Whatever value I choose for my PWM, the consumed current is not constant but always oscillating by several mA, which results in a LED that is flickering.
If I drive the DIM pin high, or set a very high duty cycle, the consumed current is not the 300 mA I am expecting, but around 30 mA.

Is it a normal behavior?
Do you think there is something I am doing wrong?

Thank you for your help. :)


texts:
the following in-amp IC is 8-lead plastic SO, but there is no indication about which pin is first pin (oreintation is not printed on the IC ) any information about how to determine it is good enough.

Picture:


texts: How do I solve for the gain (MOSFET+Capacitor)?

texts: So I came across this circuit in my analog electronics course. I am not sure on how to account for the capacitors and I couldn't find a similar circuit anywhere else. So how do I solve this circuit for gain?


texts: Can touching connections between each WS2812B-LED result in a shock

texts:
WS2812B LED-strips are ran at 5V, and can consume up to 60mA per LED. This can quickly add up to a few amperes.

Would I receive a chock if I'd touch the connections between each LED while the strip is powered up? I'd guess so, since the current flows between the points -- however I've seen videos of people touching the strip while powered up.

Is it safe to touch the connection points while the strip is powered up?


texts: I am currently trying to create a circuit which will convert a 75 ohm Green RGB line with sync (sync on Green) to just Green. I will attach a very basic diagram. My question is will the latency cause me any problems. As you can see one Gs line goes straight to the subtracter and one line has to go through a sync stripper and op amp. Will the two lines be in sync so the "sync" line can be subtracted from the Gs line to create an G signal?


texts: Short life of LED parallel to Solenoid as indicator

texts:
I have a relatively simple circuit: 12 V to a switch; on the other side of the switch is a solenoid and an LED in parallel. Nothing special about either component; the LED is a 20 mA typical LED rated for 12 V and the solenoid is a solenoid on an LPG gas line. The idea is when the switch is flicked, the solenoid does its thing and the LED lights up to indicate the switch is on. The LED is just from the switch to ground.

The problem is that the LED doesn't last more than a month. I can put it a brand new LED in and flip the switch and it'll light up, but after a couple of weeks the LED will die. After the first time it dies, I can turn the switch off again and then slowly ease the switch back on and the LED will gradually come back on (weird behaviour that I can't explain?). However this only works a couple of times and after that the LED is dead.

Any ideas on how to rectify this? I'm thinking the LED is getting ruined by spiking voltage but am not sure and don't know how to fix it if this is the case.


texts: I'm a beginner medicine student and I've got a question out of curiosity, why in defibrillators lifepak 12 or other versions..paramedics or dictors set energy for defibrillation and cardioversion in joules but for pacing is in milliamperes. Is there any explenation for that?


texts:
I looked for a relaxation oscillator for my project. Then I found this:

I tested it on simulator, and it works fine. But I need to calculate the frequency of this oscillator to put capacitors and inductors, correctly, accordingly to my project. How do I get the formula to calculate the frequency of this oscillator?


texts: Why this transistor logic as switch is not working?

texts:
I am new to transistors and have read little bit about them.  Please let me know if need to supply additional information to debug this issue related to transistors.
Something about my project:
I opened remote of a RC car and extended wires out of backward, forward, left and right switches.  So when I ground anyone of then the circuit completes and it sends signal to the car.  I wanted to close the circuit using one of the I/O pins of BeagleBone Black.  The output voltage on these I/O pins is about 3.3V.
I found out that I can use transistor as a switch but after a putting all the things together the circuit remains closed even without supplying base voltage to transistor as shown in the diagram.  I am also showing the calculations used by me to get the resistances required at the Base terminal.

Transistors can be used a switch when you supply base current.  The circuit remains closed without supplying any base voltage. In short the collector emitter terminal are closing the circuit from one of the remote pins with ground.  I wanted the circuit to close when I turn one of the pins on the BeagleBone high.  I am doing something wrong but I don’t know what I am doing wrong. Any suggestions in the right direction would be greatly appreciated.
I think it might be because the Vcc is lower than Vbe but I could be wrong.

simulate this circuit – Schematic created using CircuitLab
Edit1:
I tried using different resistors to see what happens.  R1=680K ohms and R2 as 140K ohms.  This time around the transistor was alteast not conducting any current.  But something interesting I noticed, whenever I touched R2 it was completing my circuit and sending signal to the car.  May be a grounding issue.  Is trying a Darlington transistor or low current transistors which has high hFE work?
Solution:
So as per one of the comments. I tried another transistor and values of R1=5k and R2=100Ohms and it works as expected. whenever P8_13 goes high the remote sends signal to the car.  The way I figured out was by connecting one of the remote's wire directly to collector and ground to emitter and it was still conducting. Ideally it shouldn't unless we supply base current.  So as soon as I changed the transistor it was not conducting so I changed resistance values accordingly and now it works great.  I am going to accept Jim's answer anyway because of the great comment.


texts: Charging Lead Acid battery using SMPS - unexpected voltage measured at battery

texts:
I am trying to charge a discharged 12 V Car Lead Acid Battery using a SMPS. According to voltage information provided for charging lead acid battery (https://batteryuniversity.com/learn/article/charging_the_lead_acid_battery), I have set the output of SMPS to 14.2 V.
However, as shown in the diagram attached, when I measure the voltage across battery it is showing 12 V instead. However, at junction, the voltage is shown as 14.2 V.  The junction is simply a joint between wires coming from battery and the charger wires.

So, I had some questions:

Is 12 V being read due to fact that as battery sinks the current, the voltage reading at its terminals drops?

As per the information provided for charging battery, the voltage range is 2.30 - 2.45 V/Cell or 13.8 - 14.7 V for Car Lead Acid Battery. So is this the open circuit voltage of the charger, or the voltage which should be read at the battery terminals when the battery is being charged?


texts: Questions regarding DC-DC converters powering transducers

texts:
Several of these transducers requires isolation as recommended here in their manual:

The transducer models are uni-polar 0-10V output which require 24VDC power supplies. So at the moment there is a hand made unit by a non-expert where six transducers with six isolated power supplies are wired and soldered as follows(for ease I only draw three of them):

A 12V 5A SMPS power supply feeds the six boost DC-DC converters. Each DC-DC converter supplies 24V to each transducer.

Here is the DC-DC converters being used.

My questions are:

The transducer datasheet doesn't say anything about power
consumption or max current for the 24V power supply. And the max
current the DC-DC converter can supply is given as 50mA:

Is there a way to determine whether
    this current is enough per traducer? The units work at the moment
    but I'm not sure if it is properly sized.
 2. In the datasheet of the DC-DC converter an LC filter is
    recommended at the input:

Should such a filter be inserted in front of each DC-DC converter input or is it enough to use only one as in the drawing here?


texts: How much power do power stations in parallel supply?

texts:
In modern power systems, the power is supplied by effectively connecting multiple generators in parallel. However, not all these generators are equal, some stations supply more power than others (I assume). What determines how much current is drawn from one generator or another? They all must be synchronized to the same voltage on each phase, and are all connected to the same load.

If I reduce this to a problem in circuit theory, and consider two ideal voltage sources and a load all in parallel, then the current drawn by each source is undefined unless I resort to symmetry arguments. My best guess is something to do with source impedance, since if you include these in series with the ideal voltage sources, then the current is no longer undefined.

Thought experiment: Say I got my home-brew alternator, running at a few dozen kV, and connected it to the power lines, what would happen? Would a massive over-current be drawn by the grid, or would the grid somehow "know" that my generator couldn't supply much and draw a lower current than if a full power station was connected?

How do power systems engineers predict and model this stuff? Is there some special terminology and links I could follow regarding this? Surely this is important, especially considering that these days we hear more and more about "giving back to the grid" via home generation of power.


texts: Can the BlueSmirf Gold bluetooth module communicate logical HIGH/LOW instead of serial?

texts:
I am wondering if the BlueSmirf Gold can set HIGH/LOW commands instead of serial communication?

I am writing a small andorid app to control something via the BlueSmirf. I know how to establish serial communication using it, and how to transmit data by following the Bluetooth Chat example

public void write(byte[] buffer) {
        try {
            mmOutStream.write(buffer);

            // Share the sent message back to the UI Activity
            mHandler.obtainMessage(MESSAGE_WRITE, -1, -1, buffer).sendToTarget();
        } catch (IOException e) {
            Log.e(LOG_TAG, "Exception during write", e);
        }
    }

But I want to send HIGH (1) or LOW (0) instead of serial communications. I believe that if I will be sending 0 or 1 in the current setup it will not set it to low or high. Any ideas on how I can achieve it?

Thank you


texts: Can someone check this so I don't fry someone's gps/transponder?

texts:
I am helping someone out over at aviation stack exchange -- they want a signal led for their gps receiver to do a preflight check to make sure it is working.   They basically want to be able to press a button and see if the tx line is hot (as it should be) with a signal led.   I suggested they use a transistor so as to not draw too much current from the tx line.   Here is a link to the original post:

  https://aviation.stackexchange.com/questions/42812/how-can-i-check-that-the-gps-receiver-is-sending-data-to-the-transponder/42826#42826

  Here is a link to the datasheet of the PNP transistor i use:
  https://www.centralsemi.com/get_document.php?cmp=1&mergetype=pd&mergepath=pd&pdf_id=2N4402.PDF

  And here is what I suggested.   Is there anything in this circuit that would damage their equipment (or any mistakes I made in the circuit)?

Your GPS puck (GlobalSat BR355) runs on 5v and the UART line idles high (it is pulled high when there is no traffic).   The first thing you need to do is find the power lines that go to the gps puck -- connect wires to these lines (5v and gnd) and run them to the spot where you want the button/led.   Then make this circuit:

The value for R1 should be 120 ohms (which will yield a little under 20ma of current through the LED, assuming your led has a voltage drop of 2.1v (which the ones in the link I provided do have))

Just wire these components up according to the picture and solder them together -- I'll leave how to mount the switch and the LED up to you but make sure once you are done you cover all the exposed wire with glue and/or electrical tape and/or liquid electrical tape so they don't accidentally short out.   Also make sure no exposed wires within the circuit are touching where they shouldn't touch (especially make sure you separate the pins of the transistor because if they accidentally touch the circuit will not work and you may damage your gps receiver -- long story short be careful in your wiring and make sure nothing is touching that shouldn't.

P.S. if you want you can move the button between 5v and LED1 if that makes it easier for you to mount; that would look something like this:


texts: Confusion with cut-off frequency calculation using Thevenin equivalent of an RC low pass filter

texts:
When I was trying to see the effect of load at the output of an RC low-pass filer I found myself in some sort of confusion. Below is an RC low-pass filter circuit with another R as a load and its Thevenin equivalent:

LTspice simulation in time domain shows that these circuits are giving same outputs at any frequency. Therefore I thought the cut-off frequency of the Original circuit must be the same as its Thevenin equivalent.

To verify it I first plotted the frequency response of the Original circuit as below:

As you see in the above plot, the Vout starts from -6dB and there is no -3dB in the entire plot for a cut-off frequency.

Then I plotted the frequency response of the Thevenized equivalent as below:

Above plot shows the -3dB point corresponds to 2.3Hz cut-off frequancy.

And finally I used the cut-off formula fc = 1/(2 * pi* R * C) for the Thevenized equivalent circuit and found fc = 31.8Hz.

What is going on wrong here?

All three ways give different results. Which one is the right one?


texts: How does Power over Ethernet classification work?

texts:
In this TPS2372 PoE PD there is a table about how to set up classification of the device. I think I understand the concept of classifying PD devices, it's to tell the supply equipment the power demand the PD needs.

But there are a few scenarios that in which I'm not sure what will happen.

Why does there seem to be a minimum power for certain class (e.g. PD class 2, 3.84W - 6.49W min to max)? What if the PD device idles down and is using a low 0.5W power? What would happen then? Must I design to ensure that it doesn't go below that?
What would happen if the PSE can't deliver the power requirement of the PD device, so the PD device is on a higher classification than what the PSE can deliver. Would power still be given to the PD device but only the highest it can go? Where does the responsibility of protecting both equipment from damage due to lack of power? Is it the job of the PoE PD controller to outright not give power, or its further down the line where the PoE PD controller send a signal to the microcontroller/processor that not enough power is available (designer's responsibility), or simply the PSE will just straight up not give power?


texts: Wet Sponge or Brass Sponge for solder tip cleaning?

texts:
There seems to be a lot of differing opinions out there on what is best practice. A lot of people seem to be shying away from the wet sponge due to the thermal stress it imposes on the tip. I have personally always used the brass sponge only, but my Hakko station came with both a "wet" sponge and a brass sponge for cleaning.

What are the differences between the two cleaning devices? How should I decide which one to use given the type of work I do?


texts: I have this ADS6125 ADC it has internal registers which can be programmed. The programming interface is LVCMOS I am planning to programm the registers with a 10 kHz clock frequency. How tight does this lines have to be matched? Should I use terminations?