texts: DIY Lead Acid powered USB-C power adapter

texts:
I recently found a great appreciation for the long battery life of my newly acquired mac book pro and was thinking how I can scale that up even more (since I travel and work on site a lot), by building DIY "Power Bank" for the mac. So I have some very basic knowledge of electrical engineering (built a few small home Raspberry Pi Projects), and now just need some guidance with taking on this project. I'll keep it to a strict question-answer format for the things I am unclear about.

The plan is to take a 12V 7ah Lead Acid Battery and build the nessecary transformer/step-up module to get a USB-C output delivering 20.3 V @ 3A or 9V @3A (both work for my mac).

To get from the 12V to 20.3V, I'd thought I'd use this step-up module. Will this be able to do the job? Also, how do I specify on the step-up module the exact voltage that I want (In & Out).

Then I read here that one needs a pull-down resitor in order for the USB-C connection to be recognised and enable VBus, the post suggests that you "use a regular USB A male cable with an A to C adapter..." to achieve this - that makes sense, but how to I get power from the step-up module to the regular USB head?


texts: How to measure parastic capacitance of a trace

texts:
I have a 24 MHz, crystal on my board and datasheet of IC defines the load capacitance between 5-9pF. The reference design I follow don't use any load capacitor.

My traces look like this:

shorter trace is 3.3 mm long, the longer one is 8.6 mm long.

Referring to the application note here, I use a signal generator at 24 MHz. Output of the generator and a scope of my oscillator are placed to an end point of a path, the second scope is placed to the other end. But, I don't observe any voltage/waveform/phase shift changes at the oscillator. I tried it by applying ramp, square, and sine wave forms, but output is the same for all.

Could anyone explain how to measure the parasitic capacitance of the paths? What do I need to do after measuring the capacitance, say I measure 1pF at the short path and 4 pF at the long path, do I simply need to add them and then compensate the required capacitance by placing load capacitors?


texts: How to get values in terms of G in STM32F3 Discovery board

texts:
I am working on STM32 F3 Discovery Board. I am accessing accelerometer of the board. While doing so I am getting values for X,Y and Z axes.
But these values are some random numbers.
I want the output in terms of G (9.8).
The sensitivity of sensor is set to 2g.
The function I wrote for getting these values is as follows:
I am showing code for one axis only because it is same for all three axes.

USART_SendData(USART1, 'Y');
    //  tab=Yval;
    tab= (int8_t)Buffer[1];
        if(tab<0)
        {
        USART_SendData(USART1, '-');
            tab*=-1;
        }
        rem=tab/100;
        tab=tab-rem*100;
        s=rem+48;
        USART_SendData(USART1,s);
         Delay(5);
        rem=tab/10;
        tab=tab-rem*10;
        s=rem+48;
        USART_SendData(USART1,s);
         Delay(5);
        rem=tab;
        //tab=tab-rem*100;
        s=rem+48;
        USART_SendData(USART1,s);
         Delay(5);
        //  send(tab);
            USART_SendData(USART1, '\n');

             Delay(5);

I have also read in the data sheet of acceleromter used on the board "LIS302DL" that these values are stored in registers Outx, Outy and Outz but I am not able to access these registers.
Please help me to get the values in terms of G.


texts:
I'm using Nichrome wire for a heating application and just using some scavenged parts from a slow cooker.  What would be the easiest way to turn on/off the Nichrome?  I'm thinking of just having a microcontroller switch 120VAC via a solid state relay (SSR) which would feed the Nichrome wire directly.

Is there any inductance issues I need to worry about?  The nichrome is just one long strip and not coiled in any way.


texts: What's the function of the diode in this driver connected to a piezo buzzer?

texts: I can't remember the source of this image, but I found a similar image in an Ekulit catalog. One recommended circuit shows just a resistor in series with the piezo buzzer. But this one adds a diode. What's its function?


texts: Does the resolution of a DAC depend on the supply voltage or on the reference voltage? How would the possible voltage levels be calculated if we have, for example, a DAC with Vcc = 5V, Vref = 0.5V and resolution of 8bit?


texts: Nice three pronged plug for WS2811 LED strips?

texts:
I'm building a suit with under 1000 RGB LEDs on addressable WS2811 strips controlled by an Arduino---specifically I'm using at most 16m of these WS2811 strips.  Oh, the project is inspired by Jungle Smack's amazing creation and LED strip curtain displays, though it won't be nearly so bright.

Those strips are rated at 11.5A for 4m, and my largest segment will wind up between 4.8m and 6.4m.  So I'm looking at roughly 14-18A in the two large leg arrangements.  That's white at maximum brightness though.  I'll write the software to keep the draw well below that most of the time, as I'm running on batteries.  So that range only represents brief pulses.  I'd guesstimate that 7A represents a safe bound for typical usage because even that'll kill my batteries faster than I'd like.

Any recommendations on three prong connecters for this amperage?  The control wire obviously doesn't require much amperage, but running it in the same connector simplifies getting dressed.

As an aside, I suppose FastSPI requires at least 3k for this, OctoWS2811 even more.  So I'll find an Arduino-like device with enough SRAM, maybe a Teensy++ 2.0 or Teensy 3.0.  Apparently the FastSPI has massively improved support for WS2811, which had timing issues previously.


texts: How to simplify this block diagram to get the given transfer function?

texts:
Given this block diagram, I'm trying to derive the transfer function. I've tried moving the 2 branch to either side of the then getting something like this

But I'm not sure how to simplify it from there. Any guidance would be appreciated. Thank you.


texts: Wire gauges thickness/connector type for speaker level wire

texts: So I'm wondering what wire thickness is required for a homemade speaker level wire (200w amp head output over maybe 10cm)? And what connector type would be recommended for the wire type (I would like to connect 2 5cm wires together).


texts: sound to light circuit sensitivity and doubts

texts:
Are there problems with this sound to light circuit? first diagram is the original circuit designed by a famous person, second one is my similar copy, and last photo is the prototype board that I have been testing for hours with different values.

When the values of the original were used, I found it very hard to turn the led on, ie the mic was very not sensitive. After playing with many different values, I found that if I use 300k (10k original) for R29 and 100nf (1uf original) for C25, the sensitive increased to a point that a loud sound did flash the LED. The problem I think is that 10uf is too large for a 100nf to charge up with a short loud sound. am I correct?

Finally, I figured that if I connect collector of T10 directly to the base of T11, the sensitivity increase a lot. so what is the point of those 5 components?


texts: How to get power in dependent voltage source?

texts:
l've made a simple circuit using Thevenin's theorem, and then help me which node to formulate to solve the problem.

(I've written Thevenin's theorem, am I writing it correctly?)

Also, Vx is a voltage source, how do you get power from it? I learned to know resistance to save power.


texts: Battery voltage drops when connected to a motor

texts:
I was recently working on a quadcopter so I bought a pair of coreless DC motor. My intention was to use an Arduino (DIP chip) to control the speed of the DC motor (rated 3.7 V) through a transistor.

But I have noticed that whenever I connect the motor to the battery (li-po 3.7 V) the voltage drops to about 2.8 V.
I have tried a 5 V boost converter but the voltage dropped to 2.8 V again.

Can anyone please tell me the reason.


texts: instant current in very long transmission line

texts:
In reading the definition of impedance matched wiring a question popped into my head that I can’t seem to find the answer to. Assuming a 50 ohm impedance line that is infinity long, then in theory if I attached a voltmeter I am able to see 50 ohm resistance. However what keeps me bugged is what would be the current graph look like for a very long but not infinite transmission line that terminates in an actual load.

Suppose we have a very very long 50 ohm impedance matched transmission line that is connected in a 1k resistor (like a basic lamp circuit with very long wires). If I apply a 5 volt DC at the source, assuming an infinitely fast sampling ammeter I should first see the current of 0.1A before the current settles to 5 mA. Is this assumption correct or am I missing something. Thank!


texts: How do I debug a Arduino Uno with gdb on a Linux pc?

texts:
How do I debug (source code single step) a Arduino Uno with gdb on a Linux pc?
Please note that I do not like to use AVR Studio in wine or VirtualBox.

Question 1: Physical connection

How and what do I connect to the Uno board?
My guess is that since the Uno board is populated with a ATmega328, single step source code should be available?
I also guess that I can use either a AVR JTAGICE mkII or a AVR Dragon over the ICSP header?

Question 2: GDB server

Then I noticed that there is some projects like AVaRICE that seems to provide a jtag to gdb function, but there may be other projects?

Question 3: Where is the elf?

And if I get it up and running, where does the Arduino IDE hide the generated output like the elf file with debug symbols (there should be one)? Or do I need to generate a classic Makefile that just uses the Ardino libs?

I tried to find some info on what/how to use, but I have only found those clues that told me what I could do. Can someone push me in the right direction?


texts:
I need to send data over a wireless link, not far - max 50m. I have plenty of laser diodes, 1-5mW, with glass lenses that can be adjusted. I would rather avoid buying a 'receiver', since I can probably build one faster than it can be shipped. I understand that LEDs can generate a few microamps when hit with a weak laser beam. What's the best colour LED for this? And what's the best way to build a minimal amplifier?
I would prefer not using an op-amp.

My MCU responds to 3V3 and 5V, though I can probably make use of 1-2V as well.

Thanks in advance.


texts: Frequency Modulated Continuous Wave Radar: Basic Confusion

texts:
I was reading about Frequency modulated Continuous wave radar but still struggling to understand it.

I have a few  questions in the slide above. The blue line in the graph represents the transmitted signal and red the received signal. If the receiver output is pure sinusoid as is shown in lower graph why is its frequency vs time graph linear (red line). Shouldn't it contain a single frequency?
I also do not understand why the FFT of the received output gives us the range of the obstacle. And again, how its FFT gives us the velocity.
Could anyone please explain this to me.
The snippet above is from slides from TU-Delft, which can be found here:
http://www.slideshare.net/tobiasotto/principle-of-fmcw-radars


texts: About RMS in a non-sinusoidal electrical circuit

texts: I am trying to compute the root mean square current  with the main definition $$ \sqrt{\frac{1}{T}\int_0^T i^2(t)dt}$$ where the fourier expansion is given as: $$i(t)=I_0+\sum_{n=1}^{\infty}\sqrt{2}I_n\sin(n\omega t +\gamma_n)$$ so focusing only on squaring these $$I_0^2+2\sqrt{2}I_0 \sum_{n=1}^{\infty} I_n\sin(n\omega t +\gamma_n)+(\sum_{n=1}^{\infty}\sqrt{2}I_n\sin(n\omega t +\gamma_n))^2$$ Now when Integrating the first term would produce $$I_0^2$$ the second will vanish and well for the third I guess I need to extract only those that are square and the rest would be 0, but I dont really know how. I have thought of Cauchy product: $$\left(\sum_{n=0}^\infty a_n \right)\left(\sum_{n=0}^\infty b_n \right) = \sum_{n=0}^\infty \sum_{k=0}^n a_nb_{n-k}$$ But I am unsure since the sum starts from 1. Could you perhaps help me finish this?


texts: Will the power supply change the output in a Amplifier circuit?

texts:
Problem:
I designed this circuit for a project, but we have to use a biased power supply of +15v and -15v for the amplifiers.

I'm a bit confused about how this linear equation (V2 = 20(V1) + 5) would work if all the amplifiers used a biased power supply of +15v and -15v.

V1 = -0.25v to 0.25v AC
V2 = 0v to 10v DC

Question: will this cut off the 20v output in the inverting Amplifier and change the equation to V2 = 15(V1) + 5.

Picture of the old circuit and the new circuit below

An Amplifier biased using +15v and -15v power supply

problem solved

Any answer would be greatly appreciated.


texts: How to interpret ADC values from L476RG ADC channel?

texts:
it is L476RG, I read the reference manual, I tried to read a 3.2v dc signal, I use HAL_ADCEx_Calibration_Start(&hadc1,ADC_SINGLE_ENDED);
int vdda=HAL_ADCEx_Calibration_GetValue(&hadc1,ADC_SINGLE_ENDED);
HAL_ADC_Start(&hadc1);
HAL_ADC_PollForConversion(&hadc1, 100);
int digital_result = HAL_ADC_GetValue(&hadc1);
HAL_ADC_Stop(&hadc1);

the vdda = 69 from the HAL_ADCEx_Calibration_GetValue function, digital_result=948; then I use formula float real_volt=vdda/4095.0*digital_result; I got a 15.9v result, where am I wrong? it is 12 bit ADC and single-ended.

Another interesting thing is, this is 12 bit ADC, but HAL_ADC_GetValue return a uint32_t, so sometimes this return value is very large, such as 65505 for a 2.4v input, there is no offset so the data should be no-sign, shall I directly extract the 12 bits on the right (right-aligned)?


texts: HC05 Bluetooth - why some use voltage divider and some not?

texts:
I have a bluetooth HC05 module on a breakoutboard w/pins for STATE/RX/TX/GND/+5V/EN.

Some tutorials say I need to use a voltage divider with 2 resistors, like these tutorials -
http://www.martyncurrey.com/arduino-with-hc-05-bluetooth-module-in-slave-mode/

Others say I don't -
https://alselectro.wordpress.com/2014/10/21/bluetooth-hc05-how-to-pair-two-modules/

(I only posted 2 tutorials but there's many others..)

I am using it without a voltage divider, and it appears to be working fine. Do I need to use a voltage divider? Why do some say to use it, and others not? Thanks!

edit - hc05 baud rate is 9600, it's being used to transmit very little data.


texts: Battery life calculation parallel vs series

texts: When I'm calculating battery life in series do I add up the mah  or is is the same as a single unit?  Ex. If I take 10x 3.2v cells @3000 mah and concert them in series, I will have 32 v @ 30,000mah or 3000mah.  How does this work for parallel circuits.  Thanks


texts: How do I know if a power supply will work with my monitor?

texts:
I've got a monitor which takes 19V 2A (AOC I2381FH) that I've lost the power supply to. I've got a power supply which will fit which says it produces 12V 2.5A which sounds like it might work.
Would I likely damage my monitor by using this? Trying to find a replacement supply seems difficult for it.


texts: How did I calculate the power for this source?

texts:
Let the circuit be:

Given that Ix = 5A and Vy = 10V, calculate the power absorbed or delivered by each source.

My solution:

10A source delivers 100W (P=UI= (-10 + 20)x10 = 10 x  10 = 100W). Correct

-10V source delivers 50W (P=UI= 10 x  5= 50W). Correct

20V source  absorbs 100W (P=UI= 20 x  5= 100W). Correct

0.5Vy source  delivers 25W (10 = Ix + Iy, Iy = 10 - Ix = 10 - 5 = 5  and P=UI= (0.5Vy)x Iy= 0.5 x 10 x 5) = 25W). Incorrect

My teacher said that the dependent source 0.5Vy absorbs 50W, while my answer is that it delivers 25W.

I couldn't figure out why my answer is wrong.


texts: Trying to find a spec sheet on an old Toko active filter

texts:
I'm trying to find the pin-out of an old low-pass filter I have. I must have lost my docs for it decades ago.  I've tried googling, but didn't turn up anything.

It's Toko part-number TK5429. I got it from DigiKey - probably in the 1990's. The writing on the little bag says "THB type Filter 14 KHz 7th order". The old DK part number is THB290.

The device has marked on it "B290 306I".

It has 5 in-line pins, a dot by pin 1.  Pins 1,2,3 are grouped together, and pins 4 and 5 are by themselves at the other end.

I know it's going to have +/- 15v, ground, and in and out, but I don't know which pin does what.

Does someone have an old Toko data-book?
Is there some non-destructive way to determine the pin functions?
Thanks!

Here's a snap-shot:


texts:
I am trying to make a transmission wire as light as possible and wondering how much I can overload it. I have a (300W) 12 amp load and a 22V DC source and need to transmit it about 1000 feet, which round trip I guess would be 2000 feet.

Normally with 12 amps you use 11 gauge transmission wire.

However, my understanding is that I can use as thin as 20 gauge wire without it melting and the only penalty I will pay is a 4 amp loss of electricity which is meaningless for my application.

Is this reasoning correct, or will my design fail for some reason?


texts: I am trying to use a Type-C thermocouple with a MAX31856 thermocouple IC.  This means that I must read the thermocouple voltage directly (in mV) and convert the voltage to temperature in software using a lookup table.  I cannot understand the formula given on page 20 of the MAX31856 datasheet on how to convert the "code" received from the 31856 to mV.  I am writing my program in python.  Can anyone explain to me the steps involved in implementing this equation?  Maxim tech support simply refers me to the datasheet.  Thanks in advance for any advice.


texts:
How do you extract the maximum amount of energy from a piezoelectric element?  (For energy harvesting purposes.)

The maximum power theorem would seem to say that you need to load it with a resistance equal to the piezo's internal resistance, but a piezo's internal impedance is capacitive rather than resistive.  So the load would have to be an inductor?  Or a resistance tailored for a specific frequency of vibration?  How would you use this to do something more normal, like charge a capacitor for powering other circuitry?


texts:
I'm working on modifying a board, while going through its schematic design I came across a section where a DAC output into the range of [0, +3.3V], which is then supposedly gained to +/-3.3V range, see extract below:

U24 is the an AD5662 DAC, with both VDD and Vref at +3.3V.

U25D is an OPA4170 opamp, with supply at +/-3.3V. It's in a non-inverting configuration. The transfer function is derived from:

$$V_{+}=\frac{1}{2}(V_{out}-3.3)$$, so $$V_{out}=2V_{+}+3.3$$

Two things that don't make sense to me:

Input range of 0 to +3.3V would be amplified to [+3.3v, 9.9V] according to this transfer function, since the positive supply is only at +3.3V,that would result in Vout to be constantly at the rail.
Since the input voltage is always positive, how can the output of the opamp ever be negative?

I would think that this is probably a mistake and that the left side of R61 should be connected to -3.3V, resulting in a transfer function $$V_{out}=2V_{+}-3.3$$, which would work as advertised.

However, the production board does indeed follow the schematic, and the opamp converts a strictly positive Vout (sinusoid with offset) from the DAC to a zero-centered signal. This wouldn't surprise me if the DAC output is capacitively coupled to the opamp. But R57 and C51 act as a low-pass filter, so I'm kinda stumped here.

Clearly this board's design works as advertised, but it doesn't make sense to me why. Can anyone point out where I'm making mistakes in my analysis?

Edit: Seems like I made a pretty silly mistake in my transfer function derivation, should be $$V_{+}=\frac{1}{2}(V_{out}-3.3)+3.3$$ to account for the voltage divider potential as being offset from 3.3 rather than ground.

Thanks all the for the help, I wish I could mark everyone's as solution.


texts: Mosfet \$\mathrm{V_{GS}}\$ not in datasheet

texts:
I have a datasheet for a MOSFET but can't find the \$\mathrm{V_{GS}}\$ to get the rated \$\mathrm{R_{DS(on)}}\$. It only shows the \$\mathrm{V_{GS}}\$ maximum rating which is the usual ±20V. The \$\mathrm{V_{GS}}\$ threshold is 4V.

Where is the \$\mathrm{V_{GS}}\$ that is required to the advertised \$\mathrm{R_{DS(on)}}\$?

AUIRF9540 datasheet


texts: How Verilog or VHDL projects are implement as physical chips?

texts: In real life, how would I implement a circuit design using Verilog and VHDL as physical chip? Do I send the code to some third party so it manufactures the chip, like with PCB printing providers?


texts:
I have found this image and wonder how to calculate or determine "Cm", because I like to simulate this circuit in LTSpice.
Also should I use a Mosfet or a voltage controlled switch?

Can someone help me?


texts: Why does the ssd1306 OLED controller have an unusual memory layout?

texts:
I've recently ported a driver for the ssd1306 OLED controller.  https://cdn-shop.adafruit.com/datasheets/SSD1306.pdf  http://www.ebay.co.uk/itm/0-96-inch-128x64-I2C-Interface-White-Color-OLED-Display-Module-for-Arduino-/382142082022

When writing to it, the 128x64 screen is arranged as eight horizontal sections of vertical bytes.

0 LSB
1
2
4
5
6
7 MSB

i.e. the top row shows the least significant bits, which the eighth row shows the most significant bits.

Each of the eight horizontal sections contain 128 bytes, which run from left to right.  So the whole screen is addressed as:

  0    1 ...  127
128  129 ...  255
...
896  897 ... 1023

Even if your turn the screen 90 degrees, the arrangement makes no sense.  (It's then 8 columns of bytes, but mapped top-to-bottom and then right-to-left.)

What reasons might have made this mapping of memory to display a good idea?

Update: One page 35 there is a "vertical addressing mode" which looks like a simple right-to-left raster, if you rotate the screen by 90 degrees.


texts: The source free RLC series/parallel circuit

texts: If the energy is dissipated more quickly in overdamped circuit then why it does have longest settling time?


texts: Help me check the values for capacitors in a reference design

texts:
I have the following circuit diagram from documentatoin for an MC34167 which I'd like to use in a project.

Am I correct in assuming the capacitors are all in pF? which would give me:-

330pF
4700pF
0.1pF


texts: Looking for an AC socket that mounts to a PCB

texts: I'm looking for an AC socket (U.S.) that mounts vertically (not right-angle) to a PCB for a smart power strip project. It should have through-hole or tabbed connections that I can solder into slots or holes in the PCB. I've been looking on Digikey/Mouser/Google for about an hour now and I'm almost convinced they don't exist. Am I using the wrong keywords? Has anyone seen such a connector?


texts:
I'm having a lot of trouble understanding how KVL is applied in a BJT circuit. Here's an example circuit diagram:

Assume I want to get Vc, so I think to myself that I must add up all the voltages on the right side of the loop to equal to 0. So I come up with this:

10 + Vc + Vce + Ve = 0

Vce is the voltage drop from collector to emitter, so I can substitute it like so

10 + Vc + Vc - Ve + Ve = 0

Which reduces down to 10 + 2 * Vc = 0

So Vc is just half the voltage of the battery (10v)? This didn't make any sense to me

After checking the solution manual, indeed KVL is applied but the equation is something completely different than what I had anticipated

Vc = 10 - IcRc

Where did this equation come from? And isn't Vc = IcRc according to Ohm's law? So we're subtracting the battery voltage from the Vc to get Vc?

The original problem can be found here (Problem #1)


texts: difference between using reset logic vs initial values on signals

texts:
Let's say I have a signal, I can either assign a initial value of zero OR I can set it to zero upon RESET. I've seen my co-workers using the two method interchangeably. I just want to see others opinion on this.

Assume in my code the flag signal is a flip-flop

Example (using initial value):

architecture arch of xxx is

    signal flag : STD_LOGIC := '0';

begin
    process (clk) begin
        if rising_edge(clk) then
            -- do something
        end if;
    end process;
end arch;

Example (using reset value):

architecture arch of xxx is

    signal flag : STD_LOGIC;

begin
    process (clk,rst) begin
        if (rst = '1') then
            flag <= '0';
        elsif rising_edge(clk) then
            -- do something
        end if;
    end process;
end arch;


texts: What happens to the final voltage of capacitors (v_o) when another voltage source is applied?

texts: I am just trying to find v_o final, since 40V has been applied to capacitor for a while, I know that it reaches steady state and acts as a Open circuit. When the switch moves to b, I know it's initial voltage will be 40 V but how does the 80 V source come into play as the capacitor charges. Is final voltage 80v -40V = 40V?


texts: Need help with a simple solar battery charger

texts:
I need some help with a circuit that I'm trying to build for an engineering class. We are making these solar cars to practice soldering, and most people just used solar but I want to make it better. My plan is to add rechargeable batteries to it, so that the solar panel will charge the batteries. I don't know too much about electronics components and circuits, so I need some help.

I currently have

1W, 6V, 167mA solar panel (I also have 2 cheap 1v panels)
1N4001 diodes
5v motor
4 AA 1600mAh NiMh batteries
switches

However, I am not limited to these. I have a Radio Shack available to me.

I drew a picture of how I suppose it should look. I got a lot of the info from this article. One concern I have is, will the 6v from the solar panel destroy the batteries? Would capacitors work in place of that? Also, where would the ideal place to put the switch be?

Any help is appreciated, thank you!


texts:
Currently I use a LT3083 as a constant current source more or less according to the datasheet as given in the first image. Instead of a single set resistor however is use a fixed resistor in series with a variable resistor connected via a cable to the case of my device which is generally not recommended as I'm told.

In the future I would like to set the current with a DAC if possible like this:

Unfortunately, the datasheet does not offer any more details to this configuration and it only works as a voltage regulator. How would I have to modify the second schematic to create a DAC controlled current source with the LT3082? Is this even possible?

Thanks!


texts: ioProx ID card continually getting fried

texts:
My work uses ioProx proximity ID badges to get into the building, whose specs can be found here. We use the P10SHL.

My card is continually getting fried. I have gone through about 8 cards in a three year period, and my last card only lasted two weeks. The culprits are probably my cell phone and wireless car keys.

I'll be getting a new cell phone this summer, but in the meantime, is there anything I can do to shield the card to prevent it from getting fried?


texts:
I've set up an audio amplifier using TDA7297 and Raspberry Pi's 3.5 mm audio jack.
And I'm using omxd, a daemon for omxplayer, and playing mp4 video files. The audio output has been set to jack.

But the problem is that there's a strange noise in the background of audio. (The recorded audio is http://vocaroo.com/i/s0c0RC3uJE2o and http://vocaroo.com/i/s0Ek3z3ltDSO. One is main audio+noise, the other is just noise with the main audio paused.) This problem occurs when the grounds of both systems (RPi and external audio amplifier) are connected. When disconnecting the grounds, this noise disappears.

But I need the common ground to use logic levels, control audio via MCU, use SPI, etc.

I tried simple RC low-pass, high-pass, band-pass, band-stop, notch, ... filters, but no help!

So, any suggestions !?
What causes this noise !? And how can I eliminate it !?


texts: Nyquist Diagramm, Open loop transfer function and stability

texts:
This is a general question about how to determine if an electronic system is stable. A system is unstable when the closed loop transfer function goes to infinity, ie when the denominator of the transfer function goes to 0.
If I consider a linear regulator, the system can be represented as follow :

where the closed loop transfer function is :

It is possible to get the open loop transfer function by opening the closed loop of the system as follows :

And we get from Va and Vb the open loop transfer function :

So we can write the closep loop transfer function as follows :

In order to get the closep loop transfer function to go to the infinity, we need to have :

Then in a nyquist diagram the point of instability in this case is not the "-1 point" but the "+1 point" ???? What do you think about it ?

Thank you very much and have a nice day !


texts: Electrical isolation problems when routing between pads of SMT resistors/caps

texts:
According to answers to this previous question, routing traces between the pads of SMD caps/resistors, as shown in the picture, is not dangerous as long as trace to pad clearances are obeyed and the possibility of crosstalk is accounted for.

That being said, this type of answer sounds incomplete to me: while the clearance between trace and pads may be ok, the via under the SMT component and bottom of the SMT component are separated only by a thin layer of solder mask, and it seems unsafe to rely on that kind of insulation. This source seems to agree (about solder mask being bad at insulating, not about the trace between pads question), and IPC-2221 also states something to that effect: "Complete reliance on coatings to maintain high surface resistance between conductors shall be avoided."

So, shouldn't one also consider the possibility of this insulation failing? Wouldn't that make this kind of design choice bad? Could I estimate how much voltage a SMT component can handle between its bottom and a trace underneath it?


texts: Number of read and write ports on L2 and L3 cache

texts:
I have an Intel Core i9-9900K processor (some specs here) and I'm trying to figure out how many read and write ports each level of cache has, for a personal project. I cannot find this in any online literature.
The one value I have found is that the L1 cache has 3 ports: 2 read and 1 write. Please correct me if I'm wrong.


texts: Non-inverting amplifier clips to unexpected voltage

texts:
I'm trying to build a circuit where I control a small DC motor using an Arduino. My goal is to be able to sense the load on the motor, and shut it off or reverse when the load is too high or the motor is stalling.

My idea was to use a shunt resistor and a op-amp to sense the current through the motor and control it accordingly.

I'm powering the motor using 3.3v. The no-load current is ±10mA while the stall current is ±80mA.

I've build the following circuit (non-inverting amplifier):

Where:

Rsense = 0.1Ω, R1 = 2k, R2 = 1M

The op-amp I'm using is the LM324AN, which I power with 3.3v

effectively resulting in:

The voltage I measure over Rsense is in the range of 0.0011V and 0.0082V (which is as expected).

The problem is the Vout. I would expect this to be between ±0.5 and ±3.3v (the voltage it's supplied with). Since the Gain = 1 + R2/R1 ≈ 500.

However Vout is not coming above 2.06V. It seems some clipping is happening, which I expected. But I expected it to happen at 3.3V and not 2.06V.

Is there an explanation why the Vout is not coming above 2.06V?

Thanks, R.


texts: What is the amplitude of the output voltage?

texts:
The question with its answer is as shown below:

However, I have solved it as follows:

Am I right or not?


texts: Why can't I connect an external clock oscillator to an ATMEGA64A-AU?

texts:
I've decided to change my crystal oscillator for one of those smaller (and also expensive-er!) SMD clock oscillators on ATMEGA64A-AU.
I've found this image on the web, which seems right:

So I built my schematic like this :

But I've got all sort of abnormalities in my MCU when I set it to use the external clock.  When I set it back to internal oscillation, the micro controller works like a charm!
I searched for an open source project which used this kind of clock and I found Pro Micro - 5V/16MHz:

The schematic of this board makes me more confused.  The open hardware schematic is using a crystal oscillator but the board is using a clock oscillator, I guess they forgot to update the schematic. Why they use two 22PF capacitors above the clock oscillator? Two 22PF capacitor usually use for crystal oscillators.
How can I make this clock work?
PS: I don't have an oscilloscope.
UPDATE1: I realized that the red board is using a crystal not clock, but my chip is a clock oscillator.


texts: What kind of switch do I need to emergency stop a dc motor?

texts:
I have a DC motor - 48v - 1000w - ~20A and I'm controlling its speed using a PWM.

When I plug my 48v battery, the only protection I currently have is my main Mosfet that acts like a switch. If the gate is not opened, no current is flowing.

If the Mosfet burns for any reason, it currently means the motor will run at full speed which is very dangerous.

So I was thinking about putting a switch between my 48v battery and my DC motor. Thereby, I'll be able to turn on/off manually if something bad happens. Another solution could be putting a relay and control it through a small signal with my arduino board.

I can't find on the internet what's the best solution. Especially because I can't find a switch or a relay that can support ~30A - 48v with a decent price.

Any suggestion? Thanks!


texts: Can you control a motor's general speed by oscillating from 3.3V to 0V?

texts:
I'm doing a project where I will take a Raspberry Pi Zero and build a model RC plane with two small DC drone motors.
The frame of the plane houses a battery, the Pi Zero, and the two motors (in the back.)
It's basically a 3D-printed paper airplane with two motors.
The idea is that the Pi will host a WiFi network and a website on that network. I'll be able to connect to the WiFi, navigate to the page, and control each motor to make it turn and fly.
I was hoping to be able to control the motors' speed by changing the voltage output of the Pi, but I soon realized that you can only output 3.3V or 0V.
If I switch between 0V and 3.3V very quickly, will that change the general speed of the motors?
I don't have any room on-board for a motor controller, either.


texts: Design of a nichrome heating element - achieving predetermined power dissipation

texts:
I want to make a nichrome heating element with 1500 watts of heat being produced while running on 120v AC. This will be part of a air heater as a fan drives air over a circular coil of nichrome wire.

My first thoughts where that this would be very simple with Ohm's law. I'd simply divide 1500 watts by 120 volts to get 12.5 amps of current. Then knowing v and i and Ohm's Law i'd figure out r by 120v/12.5a = 9.6 ohms of resistance needed in the element.

But after reading more on the behavior of metals resistance as temperature increases also tends to increases the metals resistance, my first attempt seemed less valid as a way to truly determine how much heat this thing is really going to produce. According to this the 9.6 ohm element will make less heat than what what I thought.

The book I read, All About Circuits, describes the current through a metal conductor as voltage increases more like the graph of y=sqrt(x), rather than what I thought originally with constant resistance and linear voltage and current y=x.

How do I figure out the cold resistance of this element with out actually building it and fiddling with the resistance till I get the 1500 watts?


texts: Discrete time domain, Is cos(2n) periodic?

texts:
I have just started out learning the basics of discrete time. I would like some help to understand if cos2n is periodic or not.
I know the discrete time formula for periodicity: x[n] = x[n+N].
I Also know that ω=2πf, ω=2π/Ν.

I searched the web and i found a solution that goes like so:
x [ n + N ] = C o s ( 2 n + 2 N ) therefore 2 N = Ω = m 2π, m ∈ Z, (at quora.com).
I do not really understand it, i think that m integer does not fit in the standard formula i know of: ω=2πf. Can you solve it using a step by step guide for 'dummies'?


texts: Need help finding inputs and outputs of a relay

texts:
I have here the diagram of a table for a 9-1415389-1 relay.
The mechanics of the relay I understand for the most parts, however I need an in-deph explanation of the inputs outputs;
What is A1, A2, 11, 12, 14? what goes into it and what goes out of it?


texts: Using Zener diode for circuit protection on RS-485 network

texts:
I'm examining an RS-485 driver circuit that uses what look like Zener diodes between D+ and gnd and D- and gnd.  Anode is connected to gnd, cathode to the D+ or D-.  So in this arrangement the idea is for the diodes to shunt current if gnd goes above D+ or D-?  Circuit is at http://resplendid.com/rs485connector_withdiodes.png.

How effective in general are Zeners at this type of overvoltage protection?  On an RS-485 transmission line I would think some pretty large voltage spikes could be induced, wouldn't the diodes blow up pretty easily with a large spike?  When blown, to they fail open or closed circuit?  Maybe putting some MOVs on the bus would be a better idea?  In general what's a good protection scheme for an RS-485 network that's going to be used outside?

Thanks,
Fred


texts: Single motor + Timer. Lift and reverse hand. Single joint robot arm

texts:
I need help trying to design a single jointed robot arm that will lift to almost flat on a wall, back down to a right angle position on a timed sequence, repeatedly. It would pause for a few seconds at each position (sketch below)

The hand would weigh approximately 1 kilogram on the end of a 45 cm rod.

I am unskilled and am trying to make it as simple as possible to learn. Thanks in advance for any assistance.


texts: Is it possible to have STD_LOGIC_VECTOR range constraint applied bottom-up?

texts:
I know that entities can use unconstrained array types (such as STD_LOGIC_VECTOR) in their port list, which will be automatically sized to match the signal connected in the port map when instantiated (and possibly different sizes for each instantiation).  Within the entity attributes such as 'LENGTH and 'HIGH can be used to discover the actual instantiated range.

I have such an object, which is a parallel -> serial converter (accept any size input, wider inputs require more clock cycles to spit out).

Is it possible to make range inference work in reverse, that is, to have the range specified in a subcomponent, applied to an unconstrained signal in the parent component, and propagated from there to other components?

Further details:

My application has a number of data source subcomponents producing data streams of various width, arbitration logic to sample and serialize these sources round-robin, and parallel->serial converters doing the actual serialization and handshaking with the bus arbitration logic.

Right now I have the signal widths specified as constants in a package, but this means whenever any stream data format changes, I have to change both the source subcomponent and the package.  I'd really like for the width to be specified in the source component only, since the downstream components adapt to any width.


texts: How to amplify a signal containing square pulses at milivolts to a couple volts

texts:
I was on it for a time. I'm planning to generate a signal containing square pulses from a smart phone's audio output. As I can get any shape of audio signal from smartphone's audio output, I want to encode digital data into audio signal with square pulses.(Surely pulses represent 1.)

I wrote an application and generated desired signal, everything is OK so far. But I measured peak value of pulses, it's approximately 20 mV. The problem is: this needs to be amplified to a couple volts such as 3 V so that digital devices can read the data properly.

One solution was using transistors, but I couldn't find any kind of transistor having such low threshold voltage.

Transformers also won't work because data is rare and very little part of the whole signal.

I couldn't come up with another solution.
Please help me, what is the simplest way to get this?

EDIT:
OpAmp's will help, I guess. Thank you


texts: Power supply and circuit breaker for a bursty device

texts:
I have a device (a strobe light) which draws up to 15 A for up to 50 ms at a time, but doesn't allow duty cycles over 0.1. This means that the average current is at most 1.5 A.

For instance, if you drive it for 10 ms, it will ignore all inputs for the next 100 ms.

The question now is: how do I choose a power supply for this light? I assume allocating 15 A for this device alone is a major overkill, but how do I know if weaker power supplies will be able to keep the voltage at 24 V during the 50 ms strobe time? Other devices depend on this voltage as well.

The second question is which circuit breaker do I choose for this device? C2 breakers should be able to handle 2 to 20 A for short amounts of time, but how do they handle repeated bursts?

The strobe light is the Smart Vision Lights' ODSXP30:  http://smartvisionlights.com/downloads/datasheets/ODSXP30_Datasheet.pdf

The power supply I intended to use is the Weidmuller's CP SNT 250W 24V 10A: http://catalog.weidmueller.com/catalog/Start.do?localeId=en&ObjectID=8708680000

Assume other devices besides the strobe light can use up to 8 A.

Edit:

To clear up some points from the comments:

The 50 ms pulse duration limit is enforced by the strobe controller integrated into the light. It also enforces the duty cycle limit and therefore the average current limit. That would mean that the max RMS current is 4.75 A.

The 15 A pulse is limited to 50 ms by the strobe controller integrated into the light. The controller also enforces the 0.1 duty cycle / 1.5 A average current limit.

The power supply is a pretty much standard simple DIN rail AC/DC converter for 220/24 V.

Here is a quick simplified schematic:

simulate this circuit – Schematic created using CircuitLab


texts: What are the differences between shift register ICs?

texts:
I'm learning Arduino and one thing that caught my attention was the use of Shift Registers to expand the number of digital pins.

I've seen many tutorials that use 74HC595 Shift Register, but my local store does not sell this exact Shift Register, but does sell many others like:

74HC166
CD4015
74HC165
74HC164
CD4014
74HC595 SMD

They all seem to be 8-bit shift registers.

I want to use them to light some LEDs using an Arduino. I imagine they have very specific purposes, but over all, could I use any of them in my project?

What is the main difference between these Shift Registers?


texts: Connecting mixed-speed multiple serial devices to two microcontrollers

texts:
I'm trying to figure out the best way to integrate all devices flawlessly on the 8051 based microcontrollers. If each device was the same low speed, then I could multiplex each and every one of them within the timer routine by itself and forget about the serial interrupt, but one device needs to run about 10x faster. But I found a bottleneck...

INTERRUPTS

Surely the optimal way is to have an interrupt for the serial routine and one for the timer so everything supposedly executes cleanly. I drafted rough code below:

Org (Timer)
(insert software uart routines here)
reti

Org (Serial Interrupt vector)
push PSW
mov PSW,#SERIALBANK
jbc RI,gotabyte
jbc TI,sentabyte
exitserial:
pop PSW
reti

gotabyte:
  mov CHAR,SBUF
ajmp exitserial

sentabyte:
  inc R1
  cjne R1,#ENDOFBUF,notend
    ajmp exitserial
  notend:
  mov SBUF,@R1
ajmp exitserial

But there's a major problem. It seems that I can either receive and send data correctly on the higher speed device while having all the lower-speed devices out of sync (just because the serial interrupt has priority and delays execution of the timer handling the remaining UARTs by the time it takes to finish its interrupt), or I can have all low-speed devices work correctly while the high-speed device is out of sync (just because of the opposite situation... timer runs right at a bad time while the serial routine attempts to send or receive data). Trust me, I even ran a timer and have the TI and RI flags checked at a much higher speed than that of the UART and that even returned inaccurate data.

So I thought of an idea

Based on my past circuit boards and the hardware available to me, I'm thinking of offloading most of the serial routines to another 8051 based microcontroller (AT89C2051) since much of the serial data coming into the main system is almost immediately discarded after processing (such as checksum).

Question is, how do I best do data transfer between the two microcontrollers?

As It stands, I can make extra uarts and have all run at a slow speed on the main microcontroller, but I'm trying to think of a way to send the data back and forth reliably over three wires without introducing serious lags on either side to the point where data on any device is out of sync.

One may suggest SPI but that involves having one microcontroller stall until the clock line is set. Making it a UART line won't work because the smaller microcontroller that's connected to the high-speed radio might lose characters because the serial routine will constantly interrupt data flow.

If my idea of using two micros is best for my situation, then can someone point me to a good asynchronous data protocol I can go for using only three wires?

For clarity in my diagram, S1 through S4 are individual sensors, and RIN and ROUT are connections to the radio module. DIN, DOUT and DCLK are Data In, Data Out, and Clock, but those names could be changed later.

Both micros are run by independent 22.1184Mhz crystals with 33pF ceramic capacitors connected between each crystal pin and ground.


texts:
I am studying BJT frequency response, particularly low frequency response, and I am not getting a clear picture of calculating the effect of an emitter bypass capacitor.
My question is: why is the impedance looking through capacitor not simply like this:

$$ [(R_S //(R_1//R_2)) + \beta_\text{re}] // R_E $$

Where am I going wrong in applying Thevenin's theorem for calculating Rth?


texts:
Around 10 years ago we bought 3 dimmers for lighting at a venue. In the last year all three showed the same problem: one or multiple resistors of the dimming circuit (6 channels per dimmer, therefore 6 of those dimming circuits). In the internet I have found a schematic which fits the device. In this excerpt of the schematic R31 is the blown resistor.

I have replaced the resistor and the capacitor (C30) in one of the three and it seems to work fine for now. However I'm concerned about whether the cause is can simply be aging of the components (the resistor or the capacitor) or if there has to be an external cause for the problem (e.g. overloading / overvoltage input from the grid / etc.) as the three showed the same problem in a quite short time-period.

It might be noteworthy that the devices have never been cleaned and therefore were quite full of dust, so they might have gotten quite warm over time...


texts: How to limit current in order to power small car radiator fan with laptop charger?

texts:
I'm trying to do a makeshift small grinder/sander out of a car radiator fan, but I want to power it up with a laptop charger for convenience.

Since it's a salvaged fan, I wasn't able to look up its schematics, I only know it takes 12VDC input (as most car radiator fans do).
These fans typically go from 10-15 Amps while running, with up to 25 Amps inrush.

The laptop power brick is rated at 18.5 Vout, 6.5 Amps, 120 Watts.

I connected it as-is for a short period, and everything works fine, I get satisfactory RPM and torque on the fan. However, I wouldn't want to leave that setup running for a long time, for multiple obvious reasons.

I'd like to be able to have some sort of potentiometer as well, in order to be able to regulate its speed.

So far, I've only come up with this:

Limit 16 Volts on the laptop output via triac voltage regulator or similar (at this point around 16v)
Static resistor rated at 100 Watt / 3 Ohm maximum (at this point making sure it'd be around 16V 5A)
Variable resistor (pot) rated at maybe 100 Watts / 100 Ohms (resistance is less important than wattage at this point)

The problem with this setup, is that those kinds of resistors and pots are hard to come by, and usually expensive.

Can anyone come up with a better / more intelligent solution and suggestions?

Most answers I found are related to more common uses, at usually lower amperage.

I have moderate experience with electrical appliances, what I don't know I'm willing to research, so don't hesitate to go wild.


texts:
I am a computational biologist and am working on some aspects of control theory in biological systems. Since control theory concepts are not well known among biologists, I need a good standard reference for certain terms. I was thinking of citing a control theory textbook. Now I have a doubt regarding the definition of overshoot.

The book — Modern Control Engineering by Ogata defines maximum overshoot as:

  The maximum overshoot is the maximum peak value of the response curve
  measured from unity. If the final steady-state value of the response differs from unity, then it is common to use the maximum percent overshoot.

It does not say what maximum overshoot is, when the final steady state is not unity. In my analysis, at present, I am defining overshoot as the max value above the tolerance zone normalized by the steady state value. I am not sure if this fits the above definition (steady state being scaled to unity, however I do not report the steady state anywhere).

When I google overshoot I see images that have labelled overshoot differently which is either of these two:

The dynamic maximum
The difference between the maximum and the steady state.

Can someone please let me know what is the correct definition of overshoot (not percentage overshoot)? I need a good citable reference (a book or a review).


texts: how does the filter capacitor work in a rectifier circuit?

texts:
My question concerns the following schematic

PICTURE NUMBER 1

If the Capacitor and the LOAD are in parallel, this means that there is more
  than one path for the current to flow, therefore, the unfiltered direct
  current from the rectifier will split between the two branches and part of it
  will reach the LOAD. My question is how is this prevented? Does really the
  unfiltered current split, or first it builds up the capacitor until it's fully
  charged, than it further processes towards the LOAD?

PICTURE NUMBER 2

Here's what I do understand and what I don't. First, the rectifier's operation
  process is fairy straightforward, it transforms the INPUT AC into rippled DC
  at the OUTPUT.

PICTURE NUMBER 3

I want to simplify the first schematic on the top.The purpose of the Filter Capacitor is to remove the ripples from the DC  as much as possible in a manner that it will appear smooth on the LOAD, but on the schematic is shown that the unfiltered DC passes the LOAD because of the parallel circuit connection. Please explain to me what I got wrong about all this. Thanks in advance.


texts: Why do commercial components have a temperature range of -40 to 85c?

texts:
Why not -50 to 90?

How was the temperature range of -40 to 85c chosen to become the industrial standard? (Some products may have a different operating temperature range, but for the majority, the chosen spec is 85 to -40)

Is there any scientific paper that shows this is a good range to qualify component?


texts:
I have a small kit whose schematic is here,  it has an LM386 (or equivalent) with an FET preamp stage.
The FET went bad, and in searching for a replacement for the now obsolete part, I found that the [datasheet for that FET (2N5638)]https://www.onsemi.com/pub/Collateral/2N5638-D.PDF) says it's a chopper.
Is there an advantage to using a chopper FET over a boring JFET in a low-level analog preamp stage?
Schematic:


texts:
I was wondering what are the best rechargeable battery solutions for working in low temperature environments, ie. from -20 to -10 Celsius degrees. From what I have figured out, Li-ion batteries cannot be charged at temperatures lower than 0 Celsius degree. Lead acid batteries can be charged from -20, degrees but they are big, dont offer high capacity and cannot have many discharge cycles.
I was wondering what would be the best solution here? I have heard that there are battery packs that provide heating coating that one can power up in order to heat the battery, but was not able to find any.
I would appreciate all hints and help.


texts: TRIAC AC dimmer circuitfor resistive loads and dependency on LOAD resistance

texts:
First I have to say I am a not an expert at LTSpice and analog electronics.

I need to drive a 115V 700W (around 19 ohms) heater with a 220V mains so due to the pure resistive load I thought to use a simple TRIAC AC dimmer.

I did a replica of the most common circuit in LTSpice and I simulated it with increasing loads from 19 ohm to 108 ohm (6 times) due to the heater resistance which should grow as its temperature raises. I expect up to 3 times with a max temperature of around 500 degrees ( p = p0*(1+alfa*deltaT) => 1+4*10^(-3)*(500-20)=2,92~=3, but just to be sure I simulated up to 6 times.

The simulation measures the RMS value of the voltage at the heater resistance  ltspice sources and its values are somewhat dependant on the load resistance and this worries me (see raw values and plot).

Is there any thing that I can improve in the circuit in order to avoid that the output voltage depends on load resistance ? I would not like to blow up my heater with too much voltage :)

RMS Values measured

Measurement: volt

step  RMS(v(test))    FROM    TO

1 121.876 0   0.3
2 123.154 0   0.3
3 124.334 0   0.3
4 125.427 0   0.3
5 126.443 0   0.3
6 127.387 0   0.3
7 128.268 0   0.3
8 129.093 0   0.3
9 129.865 0   0.3
10 130.59  0   0.3
11 131.272 0   0.3
12 131.915 0   0.3
13 132.522 0   0.3
14 133.096 0   0.3
15 133.641 0   0.3
16 134.157 0   0.3
17 134.648 0   0.3
18 135.095 0   0.3
19 102.798 0   0.3
20 103.287 0   0.3
21 103.758 0   0.3
22 104.198 0   0.3
23 104.604 0   0.3
24 104.98  0   0.3
25 105.344 0   0.3
26 105.687 0   0.3
27 106.046 0   0.3
28 106.372 0   0.3
29 106.698 0   0.3
30 106.985 0   0.3
31 107.298 0   0.3
32 107.587 0   0.3
33 107.875 0   0.3
34 108.105 0   0.3
35 108.392 0   0.3
36 108.649 0   0.3
37 108.883 0   0.3
38 109.083 0   0.3
39 109.329 0   0.3
40 109.546 0   0.3
41 109.786 0   0.3
42 109.972 0   0.3
43 110.18  0   0.3
44 110.391 0   0.3
45 110.545 0   0.3
46 110.732 0   0.3
47 110.911 0   0.3
48 111.053 0   0.3
49 111.255 0   0.3
50 111.41  0   0.3
51 111.591 0   0.3
52 111.714 0   0.3
53 111.879 0   0.3
54 112.053 0   0.3
55 112.189 0   0.3
56 112.32  0   0.3
57 112.449 0   0.3
58 112.581 0   0.3
59 112.703 0   0.3
60 112.831 0   0.3
61 112.955 0   0.3
62 113.073 0   0.3
63 113.196 0   0.3
64 113.322 0   0.3
65 113.41  0   0.3
66 113.522 0   0.3
67 113.642 0   0.3
68 113.732 0   0.3
69 113.837 0   0.3
70 113.928 0   0.3
71 114.035 0   0.3
72 114.124 0   0.3
73 114.23  0   0.3
74 114.304 0   0.3
75 114.389 0   0.3
76 114.491 0   0.3
77 114.581 0   0.3
78 114.659 0   0.3
79 114.717 0   0.3
80 114.815 0   0.3
81 114.881 0   0.3
82 114.998 0   0.3
83 115.06  0   0.3
84 115.135 0   0.3
85 115.193 0   0.3
86 115.271 0   0.3
87 115.34  0   0.3
88 115.422 0   0.3
89 115.483 0   0.3
90 115.542 0   0.3
91 115.619 0   0.3
92 115.675 0   0.3
93 115.734 0   0.3
94 115.822 0   0.3
95 115.888 0   0.3
96 115.928 0   0.3


texts: Question about Discrete-Time Signal Frequency

texts:
I am running through my old Digital Signal Processing textbook in preparation for a course in DSP, and in the following example from my textbook, I am not sure why:
cos((5pi*n)/2 = cos(2*pin + pi(n/2)) = cos(pi*(n/2))

Can someone explain why x1n = x2n?  Is there some trigonometry that I am not getting?


texts: Battery output power calculated from internal resistance - explanation, relation to heat generation and actual power?

texts:
On a battery manufacturer specification (https://www.scib.jp/en/product/cell.htm, "High power 10Ah cell") it says: Output power 1800W* (SOC:50%, 10s, 25°C), *This value is calculated from the internal resistance.

How is this power rating calculation from the battery's internal resistance carried out exactly?

How does the above calculated output power relate to the heat generation rate (W) of the battery that is also calculated from the internal resistance?

And how does this theoretical output power (typically) relate to the actual battery output power available to the user in practice?


texts: How to Receive STM32 UART echo command using HAL libraries?

texts:
I am using a STM32L Discovery board (monted device STM32L476xx), for a transmit and receive UART operation using HAL libraries. I am using a FTDI chip for serial to usb conversion as I am unable to use the Virtual Com port of the STM.

I have got the HAL_UART_Transmit function working but can not get the similar receive function to work.

My UART handle Definitions
    void MX_USART2_UART_Init(void)
    {

    huart2.Instance = USART2;
    huart2.Init.BaudRate = 9600;
    huart2.Init.WordLength = UART_WORDLENGTH_8B;   // changed from 8B
    huart2.Init.StopBits = UART_STOPBITS_1;
    huart2.Init.Parity = UART_PARITY_NONE;
    huart2.Init.Mode = UART_MODE_TX_RX;
    huart2.Init.HwFlowCtl = UART_HWCONTROL_NONE;
    huart2.Init.OverSampling = UART_OVERSAMPLING_16;
    huart2.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
    huart2.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
    if (HAL_UART_Init(&huart2) != HAL_OK)
    {
        _Error_Handler(__FILE__, __LINE__);
    }

}

I used the following for Transmit function which prints a string.

char bufftr[] = "check\n";
len = strlen(bufftr);
HAL_UART_Transmit(&huart2, (uint8_t*)bufftr, len, 100);
fflush(stdout);

But I can't get a echo working where I transmit what I receive

char test[100] ;
while (1) {

        HAL_UART_Receive(&huart2, (uint8_t *)test, 4, HAL_MAX_DELAY);

        len = sizeof(test);
        HAL_UART_Transmit(&huart2, (uint8_t *)test, len, 100);

    }

This outputs seemingly random characters of the correct length.
Please let me know how can I can I get this to work and also how to get UART transmission through the virtual COM port


texts: Trying to find value of two capacitors using resonant frequencies in three conditions, but wrong formula is derived

texts:
I was trying to find capacitance of two capacitors in the following way.

Connect each capacitor individually to a same inductor and find resonant frequency in each case.
Connect the same capacitors in series , to the same inductor and find the resonant frequency.
Then calculate the capacitance using following way

we have

\$f_{1} = \frac{1}{2 \pi \sqrt{L c_{1}}}\$ , \$f_{2} = \frac{1}{2 \pi \sqrt{L c_{2}}}\$, \$f_{3} = \frac{1}{2 \pi \sqrt{\frac{L \left(c_{1} + c_{2}\right)}{c_{1} c_{2}}}}\$

Solving these equations, we get

\$\left\{ L : \frac{1}{4 \pi^{2} f_{3} \sqrt{f_{1}^{2} + f_{2}^{2}}}, \  c_{1} : \frac{f_{3} \sqrt{f_{1}^{2} + f_{2}^{2}}}{f_{1}^{2}}, \  c_{2} : \frac{f_{3} \sqrt{f_{1}^{2} + f_{2}^{2}}}{f_{2}^{2}}\right\}\$

I tried to substitute the values for f1, f2 & f3 ( f1 = 2500, f2 = 2030, f3 = 3200 ) . Interestingly  , I got a result which is numerically correct , but with a difference of \$1e^{-6}\$.
That is, instead of micro farad, I get values in farad,
Also, instead of millihenry, I get value in nanohenry

I was trying to figure out why this difference in occurred .

The completed IPython notebook can be found at https://gist.github.com/harish2704/5fe08c80c96307973a11f724a218950d

it will be a great help if someone can help me


texts: Saturation Points for Mosfets; driving gate with 3.3V output

texts:
I'm still new to this so please go easy on me :)

I'm looking at using N channel Mosfets to act as a switch between my microcontroller (ESP8266 breakout board) and LED Strip. Here's the schematic:

When I was reading about how mosfets and transistors work, I saw that for it to be saturated, the potential voltage between gate and source pins (or base and emitter in transistors) needs to be higher than the value listed under V_GS(th). Could I do this with the 3.3V output of a ESP8266 GPIO pin? The datasheet for the two mosfets I was considering using are slightly confusing me.

IRLB8721 - https://cdn-shop.adafruit.com/datasheets/irlb8721pbf.pdf

IRLZ44N - http://www.irf.com/product-info/datasheets/data/irlz44n.pdf

I'm asking because under the max value they only use tiny currents. IRLB8721, they use a drain to source current (Id) of 25μA and the max Vgs (needed for mosfet to turn on right?) is only 2.35V. For the IRLZ44N it's 2V with 250μ. So are these logic level Mosfets? Would they work?

Another value I'm not to sure about is Vds. They set it equal to Vgs in the values above, but for figure 3 where you can see other (higher) Id currents, they set it to 15 and 25V. Is this relevant?

IRLB8721:

IRLZ44N:

I would be really grateful if someone could help me clarify this.

On a side note, is it necessary to use resistors between the microcontroller and gate? How would I do this, and for what function?

Thanks so much!


texts:
I need to find a way to detect when a door is opened and i want to register that through a wifi connection. So the 'door detection' module should send data to a PC over wifi when a door is opened.

There may be better solutions to get this working, but the first thing that came to my mind is an arduino board. Is there an arduino board that is easily capable detecting when a door is opened and sending data on detection to a PC (wireless)??

Or are there better alternatives?


texts: Is it possible to have 5V power and VTREF in SWD programmer for ARM?

texts:
I'm trying to use the Segger JLINK edu mini( https://www.segger.com/products/debug-probes/j-link/models/j-link-edu-mini/ ) to program a board that is also powered by USB. It has a pin out shown on the page linked above and also comes with a 20 pin cable suggesting it can do all the things a 20 pin SWD connector can do including power 5V from USB. The little USB stick itself has only a 10 pin connector.

What I'd like to do, is get 5V out of the Jlink edu mini to power my board. My VTREF is 3.3V but it needs input power from somewhere. The 20 pin JTAG pin out does this - I am wondering is there a way to output 5V using this smaller 10 pin connector and if anyone has run into this problem?


texts: Measure voltage on 48 batteries at once using microcontroller

texts: I am looking to design a microcontroller that can measure the voltages on 48 batteries. Some of the batteries will have floating voltages as the device is wired in a parallel string of 8 columns, with 6 batteries in each column. I would like to see if there is a way limit the amount of wires, so I don't have all these wires everywhere. I am looking for any basic information on where to begin or maybe a basic single line diagram. Thank you for the help!


texts: Formula to find out the resistance per meter of a specific gauge of wire if I already know the resistance of a different gauge of wire per meter?

texts: So if I know a 30 gauge wire's resistance at 1 meter, how can I figure out the resistance of a 29 gauge wire at 1 meter long of the same material? Or 5 gauge, or any other gauge? I need a formula, not a chart. Working with multiple materials, and I know the resistance of them at different gauges, but need to find out how to get the resistance per meter of varying gauge sizes using math.


texts: When charging rechargable battery, should we care about watts and ignore voltage and current?

texts:
I know this might be a silly question, but it's from a beginner.

Let's say I want to charge a rechargable lithium-ion battery, so when I charge it should I only check the watts and ignore voltage and current specific values? I mean the current is about how much electrons are flowing, and voltage is how much potential energy is stored in each electrons (this is how I understand voltage and current, correct me if my thoughts are wrong), so I thought that if I charged a battery with 10 watts, 1 amp and 10 volt, then the battery will be charged well, but if I charged the battery with same10 watts, but 2 amps and 5 volt, won't the battery be filled with weaker electrons? I mean this time the battery will be filled with less-energy electrons than the previous example, so should I look at the volts and amps when charging or the watts is enough?


texts: Oscillation frequency of ring oscillator

texts:
I have the following problem, that may be very simple, though I'm not quite sure.

MY ATTEMPT
Well, if we interpret all the sum of the delays as the period of the oscillation then the answer becomes awfully simple (maybe too easy).
\$f=\frac{1}{T}=\frac{1}{15 \text{ns}+15\text{ns}+15\text{ns}+10\text{ns}+15\text{ns}}=14.286 \text{MHz} \$
I arrive at an answer of 14.29MHz. However, this solution seems way too easy and simple, so I'm wondering if I am understanding the problem correctly?
Can anyone help me tell me if I am on the right track, or if I am way off?


texts:
Can some one explain the concept of transistor terminal impedance? What is it, and why is it important?

Any links to useful notes/resources will also be greatly appreciated.


texts: Why the sign for \$4Ω\$ resistor is positive using KVL even though it dissipates heat?

texts:
I would like to know why the sign for \$4Ω\$ resistor is positive as the equation in the image shows

\$-I1∙8Ω+I2∙4Ω=0\$

Even though the equation is formed using KVL why the sign for \$4Ω\$ resistor is positive when it actually should be negative since it dissipates heat?


texts:
I am considering replacing a SD card in a tiny embedded system  (Cortex M4 running a RTOS) by some kind of dedicated flash storage chip. However, I am worried about the chip's endurance.

The embedded system uses FATfs and writes about 100 bytes about once every 1 minute. My understanding is that this use case is ok in a SD card: that's about 2 block writes every minute, so 10 million block writes over the product's 10 year life. That seems reasonable if I use a SD card with 40k 128kB blocks and about 1000 writes per block.

However, this assumes some kind of wear levelling, since a few disk sectors will be overwritten much more. The FAT data structures come to mind.

My question is, how would I go about replacing this SD Card by a flash chip like this? I'm particularly worried because I see no mention of wear leveling in the datasheets of flash chips. Should I migrate to another filesystem? Write raw bytes? Buy a chip with built-in wear leveling?


texts: What is the method to measure the state of charge of a battery when it is :- a) Idle b) Connected to Load c) Charging. Is there a device like a multi meter which can achieve this?


texts:
I have this circuit and I do not understand the purpose of the diode connected to the ground.
This is a Bluetooth device (works at 3.3v) that has a 4x 18650 battery pack and a USB charger. When you plug in the USB it supposedly charges the 18650 batteries. (4x 18650 batteries in series)

The diode(?) is connected via the yellow wire from battery ground, onto the board, goes passes a few capacitors and arrives at a chip with marking "MPEK 2517 A023" (or AO23) and an inductor right beside that chip.

When no USB is present the end of the yellow wire inside the white socket measures 0V. when USB is plugged in it measures about 2.1 volts steadily
decreasing while the voltage steadily increases. (about 0.0001 volt every 2 seconds)

Can someone explain the purpose of this diode? thanks


texts: How to make a symmetrical DC power source?

texts:
I have been tasked with creating a logic probe that reads High/Low/High Impedance, but what works in simulations, isn't working in practice.
This was my idea:

I made a symmetrical power source using two resistors and a virtual ground, and fed the 741 OP AMP using these +VCC/2 and -VCC/2. The idea was for the probe voltage to be compared to half VCC, that way we'd get a -VCC/2 to +VCC/2 voltage output, and if there was high impedance, both LEDs would be off.

What ends up happening however, is no voltage output. I think the problem is in the symmetrical power source, because whenever the OP AMP is connected to the circuit, the perfect VCC/2 equilibrium between the two resistors is gone, and it goes to like 4v or whatever when feeding it with 5v.

Any ideas on why this circuit doesn't work? I have tried searching for ways to create a symmetrical power source, but all of them give me the same simulation results, so i figured it wouldn't change on practice.


texts: How does this power supply circuit work? (MCU + LM317)

texts:
I've been studying this schematic that I found while searching the web. I understand the point of PWM - it allows us to vary the average voltage fed to the op-amp precisely. The filter R1,R2 and C1 integrate the PWM waveform.

But what is the point of the op-amp? It looks like a non-inverting amplifier to me, with the gain set by R6 and R7 - if I'm not mistaken. But why does the integrated DC voltage need amplification?

Perhaps, I don't understand that part because I don't understand how the Lm317 is working in conjunction with the MCU. I understand that LM317 drops a reference 1.25V between the OUT and ADJ pin (which should be across R5 in reference to the circuit) and the Vout is defined as 1.25(1 + R2/R5) + I(adj.) * R2. (from datasheet)

Since the only variable is I(adj) in the above equation, am I correct in my understanding that the integrated DC voltage is actually changes the current and hence the output voltage?

Any insight would be appreciated.


texts: SMT resistor arrays are available in convex or concave form. What are the dis/advantages of either?


texts: How to calculate current on different resistors

texts:
I hope this is not a wrong place to ask. I've just started studying electrical engineering and I have (a newbie) question and would really appreciate it if you guys could help me.
So I have this curcuit and I have to calculate all the currents in this curcuit.
R1 = 400 Ω  R4 = 400 Ω
R2 = 0.8 kΩ R5 = 1.2 kΩ
R3 = 1.8 kΩ R6 = 2 kΩ
V = 36 V
I already calculated the equivalent resistance which is 1600 Ω and current in the curcuit which is 22.5 mA. I don't know how would I calculate current through R1, R2, R3, R5, R6.


texts:
What I am trying to do is set pin PC0 of PORT C as output to light an LED.
The code I am using for that is:

//SET PORT C
//PC0 = RELAY STATUS LED - O/P
//PC1 = RELAY CTL LINE - O/P
//PC2 = PUSH BUTTON - I/P
//PC3 = SPARE - O/P

DDRC |= _BV(PC0) | _BV(PC1) | _BV(PC3) & _BV(PC2);

//SET PC0 = HIGH

PORTC |= _BV(PC0);

But the above is not working. I have checked my connections and can't figure why is it not working. It should be a fairly simple thing.

The only reason that I think could be affecting it is that I also have an ISP connected to the AVR ⇒ PC6 being used as the reset line by it.

Any ideas why the above won't work?


texts:
In my system I measure signals with interesting bandwith from DC to 2 kHz. I have an analog low-pass filter with 200 kHz cutoff frequency in order to filter noise. The ADC samples the signal with 500 kHz. The signals are then used for a feedback controller that runs in a task with 20 kHz. So my questions are the following:
Can I expect alias on the signals used in the control task of 20 kHz?
Should in this case a digital filter at the sampling rate of 500 kHz applied that has a maximal cutoff frequency of 10 kHz (Half of control task rate)?
Would it be possible to apply a further low pass filter with 10 kHz cutoff frequency in the 20 kHz program task?


texts:
I'm trying to make a circuit that charges a capacitor to 63%, a comparator go high, charge another capacitor and turn on a mosfet (2n7002) which discharges the first capacitor.
My problem I connect the mosfet (Q1) to C1 the max voltage is much lower than expected (as if R3 and Q1 forms a voltage divider). I tried testing this circuit on a protoboard.

Here how I expect this circuit to work (Vcc:5v R2:17k ):

1- switch closes; Q1 (acting as a switch open)

2- C1 charges ; comparator (U1) output 0v

3- when C1 is 63% charged U1 outputs 5v

4- when c2 is 63% charged Q1 'closes'

5- C1 discharges; U1 outputs 0v, Q1 'opens'; C2 discharges through D1

6- back to step one

U1's output is supposed to be connected to a micro controller(Pic and arduino).


texts: Fail circuit with N MOSFET, what is wrong?

texts:
I have a circuit with two DC power lines coming from BATT A (1A) & BATT B (2A) (two outputs of a power bank). There is a sliding switch on the power line of BATT A. I would like to keep only one switch to control both power lines.

I the following circuit with a N-Channel MOSFET (RFP30N06LE) to be able to control the power line of BATT B using the state of power line of BATT A ?

I have a problem with it, I get 2V on the motor driver when the SW1 is open. Moreover the MOSFET M1 became quite hot.

The goal was to use M1 as switch for BATT B managed by SW1. Do you see any error that can cause my problem ?

Thanks for your help :)


texts: Why the voltage drop is so high in my Half-Bridge SMPS?

texts:
I have been building an offline Half-Bridge SMPS of about 300W with a friend of mine. We need a variable range from about 10V to 30-35V. We finally got it working and we could achieve 10A at 30V.

The problem is when we have no load but a 1K resistor at the output of the SMPS, the voltage goes up to 45-48V and we cannot go below 32-33V, but when we put a load of only 1A the voltage suddenly drops and the maximum we can get again is about 30V but with high current as needed (but we got around 8Vpp of 100KHz ripple).

The SMPS is working at 100KHz, we drive the MOSFET through 1:1 driver toroids and we get around 12V at MOSFET gates (we are using IRF840). The duty goes from 5% to 50% with a 375ns dead-time.

Our problem is that a drop of about 15-20V when we put a load is too much, we get around 50V with no load and when we put a load we can't get higher than 30V (even when we calculated the transformer for a 40V output). We used the book "Power Supply Cookbook from Marty Brown, 2nd edition".

Here you can download a PDF with the complete schematic and the PCB. The transformer has 33 turns on the primary side and 12 turns on each side of the secondary. L2 is a toroid from a PC power supply with 70 turns. Also, the efficiency oscillates between 40% and 50%, I think the problem could be there but I don't know what is causing such a low efficiency.

EDIT:

Here are the measurements with a 20% duty cycle:

T4 Primary side:

T4 Secondary to ground - 100mA load (minimum load):

T4 Secondary to ground - 3A load


texts:
I have a device with a SNx5HVD251 CAN transceiver. I opened the datashett and read the following parameter:

IOS(SS) -  Short-circuit steady-state output current

Below are two images of the datasheet that I put together here:

I didn't understood the relevance of this parameter or what it means.

1)For example, if I have VCANL at 12 V, CANH Open . It means that the  current over CANL line will be at maximum of 200mA ? Or, it means that CANL line can support at maximum of 200mA ?

2)The CAN line will be passing through a relay. (The relay will not switch during communication, but the CAN line need to pass through it). So, how relevant is to take this value of current into account when I need to specify my componentes ? A relay with less than 200mA is much more cheaper, so I need to know the relevance of this parameter.


texts: Ammeter show half of the real current draw

texts:
I have a couple of ammeters from China, they have 2 connectors:

Con 1: Yellow voltage sense, Black and Red to power the ammeter.

Con 2: Thick Red and black for current sense.

They are designed to run with two different voltage sources but i'm connecting everything from same power supply, the problem is the current is being cut at half, for example i set my load to 2A, the bench power supply shows 2A draw, but the ammeter show just 1A and the voltage is correct (24V in this case)
I also have tried other unit but both does the same thing. They have U and V pot to ajust the values but that doesn't help since it's already calibrated and at max position.

Suggested connections:

I connect like that but the power meter will connect to the battery, so just one power source and one load, so red and yellow are connected together.

My connection:

The fact this is made with two power sources causing this problem?


texts: Step down variable high voltage DC input to low voltage DC output

texts:
I'm looking to find a system that will help me step down a high voltage DC input to a low voltage output. The problem is that the DC input in question is not very stable in terms of voltage and varies depending a number of situations out of my control.
The DC input could be from anywhere to 150V to 230V but is, for the most case going to be in the range of 200V-230V.
We need a safe way to convert the power to a stable 6V-12V DC, after this we can employ other systems to get a stable low voltage. I've had a look at existing systems but am having trouble finding anything within the correct range.The power requirements are low, no more than 1A at the specified output voltage, so a absolute max of 12 watts but usually much less.
Any recommendations or processes that combine new or existing systems would be helpful. We are currently looking at options so are not set on anything in particular.


texts: How do I replace a capacitor with a resistance?

texts:
I'm studying Fourier transformations, and their relationship with electrical circuits. In the example below the capacitor is replaced by a resistance, in that way we can use the voltage-divider principle to find an expression for \$Y(j\omega t)\$, in terms of \$X(j\omega t)\$.

This is where I'm stuck, as the author leaves no reasonable explanation as to how the capacitor was turned into a resistance. Can someone provide an explanation as to how it was replaced by the resistance \$\frac{1}{j\omega100\cdot 10^{-9}}\$?

I should add that I know about the relationship \$i(t) = C\frac{dv(t)}{dt}\$


texts: Byte-Banging 2 8051's using port addresses

texts:
Currently I have two microcontrollers setup in which entire ports are connected to each other (P1.1 connected to P1.1, P1.2 connected to P1.2, etc). I also have two pairs of extra GPIO pins connected as signal lines.

What I want to achieve is a way to send and receive a byte in as little time as possible.

Let's assume that the master requests the slave to add 1 to a number and the slave responds:

Here's my code so far for the slave microcontroller:

SLAVEDATA equ P1
SLAVEACK equ P2.0
SLAVECMD equ P2.1

jnb SLAVECMD,$  ;wait for command
mov SLAVEDATA,#0FFh ;tristate to allow input
nop             ;wait how many uS?
mov A,SLAVEDATA ;see what number came in
inc A ;add 1
mov SLAVEDATA,A ;produce result
setb SLAVEACK   ;send acknowledgement
jb SLAVECMD,$   ;wait till remote lowers comand line
clr SLAVEACK    ;clear acknowledgement
;transaction complete

And here's the code for the master:

MASTERDATA equ P0 ;Master's P0 connects to slave's P1
MASTERACK equ P3.0 ;Master's P3.0 connects to slave's P2.0
MASTERCMD equ P3.1 ;Master's P3.1 connects to slave's P2.1

mov MASTERDATA,#20h ;Set number to 32
setb MASTERCMD      ;tell slave to increment
jnb MASTERACK,$     ;wait until its done
mov MASTERDATA,#0FFh ;tristate port to allow input
nop                 ;delay by how many uS?
mov A,MASTERDATA    ;Get result here
clr MASTERCMD       ;tell slave were done
jb MASTERACK,$      ;wait until slave understands this

While I believe this code mostly works, I'm just not sure how long to make the program wait between the time the port pins are set to high and the time valid data is read on the pins.

If I don't wait at all, then I will get incorrect data. I believe it has to do with the FET's inside my AT89C4051 and AT89S52 that I am using but the manual does not indicate how long I should wait.

Both micros have the same crystals, capacitors and PCB track arrangements for the crystals and capacitors.

Each capacitor is 33pF ceramic

Each crystal is 22.1184Mhz which came out of the same package

Each PCB track in which the leads of the crystal are connected to is 1.9mm wide.

How do I calculate the minimum number of NOPs in my code so that valid data can be captured on the port pin after tristating it?

Also, because each micro has the same clock driving circuitry, could I replace the stalls (waiting for acknowledgements for example) with three nops? or will I still experience a minor clock drift?


texts: Output Voltage of OP Amp is not equals to Acl x Vin in LTSpice

texts: I have recently downloaded LTspice and when I am testing the LF351 and LM741 OP-Amp, I realised that the output voltage does not equal to the gain which should be -50. I have looked at the data sheet and the Vsat of the LF351 is around 13.5V and the LM741 is 14V. I am trying to get the design desired output which I think should be -25Vp but none of the OP-amps gave me the output. So, I am wondering why the gain is not (-R2/R1) in this case. Thank you in advance.LM741 OP-Amp


texts: I'm working with 12V 6.5A power supply, should I be worried?

texts:
I'm an electronics novice and I'm working with 12V at 6.5A.

(I'm activating the power supply with a series of electro-mechanical relay switches controlled by an Arduino. The power supply lights up a series of LEDs)

If I touch a bare wire at this rating, would I sustain a serious injury?


texts: What component most limits a camera's frame rate?

texts:
I have a quick question here when I started wondering how they made slo-mo cameras: What is the part that most limits frame rates in average smartphone cameras? Is it the CCD chip, or a component in the phone that stores the image that limits the frame rate the most? Or something else entirely?

Thanks for any answers!


texts: MEMS oscillator how to wire them and can they replace crystals?

texts:
My question is: Can a MEMS oscillator replace a crystal oscillator?

If answer is yes, how I can wire them to XIN and XOUT? How should I select capacitor? And since they don't have crystal capacitance load, shout or equivalent ESR in their datasheet specifics, how I can choose correct oscillator?


texts: Regulated power supply from thermostat to zigbee module

texts:
I have a thermostat that outputs a DC power supply for a communication daughter board.  When I read it with the voltmeter, it reads ~3.9v, but the zigbee module that I want to use requires 3.3v regulated.

Since its a tight squeeze inside the thermostat, I have to stick with SMD components.  I looked at the the MCP1703 in the SOT-223-3 to do the job, but in the example schematic, the input voltage is 9v so I'm hesitant to use the 1uF input and output filter caps that they used.

Do I need an oscilloscope in order to do this right?
Can I just use the example caps even though my input voltage is ~3.9v rather than 9v?
How "clean" does my output voltage need to be for a typical zigbee module?


texts: Creating a 1PPS signal froma a 10 MHz CMOS Output Signal

texts: Is it possible to "create" a 1PPS signal using an Agilent 8165A signal generator? We currently don't have a way of testing a 1PPS signal directly, so we're looking at "making our own" for the time being. The thought process is to use an atomic clock that can provide a precise 10 MHz CMOS output at 3.3 Vpp. That signal would then go into a signal generator's External Input connector. Using the signal generator, our goal is to take the input and create a pulse that meets a specific pulse-width, specific rise time, and can amplify the signal to a 10 Vpp. I have already connected the 10 MHz reference to the signal generator, but I am lost on what to do next to get the specific pulse-width to mimic a 1PPS signal. I could use any inputs or ideas on how to get started to create a specific pulse-width.


texts: 74AS TTL to CMOS pull up resistor and maximum speed (or lowest delay)

texts:
Hello I have to pilot a CMOS input 5V chip device with a 7474 flip flop with the lowest possible delay to minimize clock jitter. Signal is about 11.3 Mhz

I have two options:

1) 74HC74 (CMOS compatible) with maximum speed of about 30MHz

2) 74AS74 with a pull-up resistor with theoretical maximum speed of about 100MHz

I would use 74AS74  because this should have one third of propagation delay vs 74HC74 (hence one third of clock jitter probability, I suppose), but I would need a pull-up resistor to reach CMOS input voltage levels.

I was thinking of about 1K ohm of pull-up from the 74AS TTL output to the positive 5V rail, giving a safe 5mA load.

Questions:

1) which is the lowest safer pull-up resistor for a 74AS piloting a CMOS device? Websites recommends from 10K to 2.2K from TTL to CMOS. I would use 1Kohm. Is it 470ohm still safe and better?

2) 74HC74 run at 30Mhz, 74AS74 run at 100Mhz. But which is the maximum speed (or propagation delay) of a 74AS74 with a pull-up resistor? Does the pull-up resistor jeopardise the 74AS speed advantages vs 74HC?

3) at the end: to minimise jitter driving a CMOS is correct that any 74AS with pull-up resistor is better of any 74HC device?

PS: don't want to use 74AC or other logic families. Question is only about 74AS vs 74HC.

Thanks


texts: 'P.V.' marking on 1940's electrolytic capacitors

texts:
I am replacing the paper and wax capacitors in a tube radio of 1949 vintage. Puzzled by the initials P.V. where I'd expect to read VAC or VDC. Can anyone explain this puzzling jargon?
For some reason that's beyond me, this was by far the clearest image I could capture of the elusive thing.


texts: Powering and dimming white LED from single-cell 3.7 rechargeable lithium battery (with a 3.3V Arduino mini)

texts:
I'm designing a circuit for a handheld project that runs from a 1-cell rechargeable Lithium battery (18650 or prismatic). The circuit powers an Arduino Mini Pro running at 3.3VDC.

The Arduino board contains logic to:

operate a miniature 3V DC motor through PWM using a low power H bridge (dual-channel L9110S - only 1 channel used);
operate a red LED through PWM;
operate a white LED through PWM;
go into deep sleep and periodically blink a red LED when battery level is too low (below 3.5V).

The circuit also foresees the possibility to recharge the built-in Lithium battery by means of a USB charger (through a mini / micro / type C connector).

I designed the functional prototype with an Arduino nano running at 5VDC, so I could even power the white LED from the output pins. And that works flawlessly.

Porting everything to 3.3VDC and single-cell Lithium battery power, things get more complicated.

Powering the red LED will probably still work, either directly or by using a switching transistor driven by the PWM signal (works with BC547B).

Powering the white LED won't work out of the box as the forward voltage is in the 3-4V range. Even with a switching transistor, I'll be out of luck.

I tried looking for step-up (boost) DC-DC converters and LED driver ICs, but they're either over-dimensioned (I only need approximately 500mA), or they don't support (or like) variable load, or they overheat with very low load, or they can't be sourced unless by the 1,000s. Some chips that have an EN pin allowing in principle to be operated through PWM are the B6288 from various brands and the MT3608 (Aerosemi) which seems to be the same. They're found in inexpensive buck-boost and boost converters such as this one.

So far I have also seen LED driver ICs with built-in charge pumps (e.g. the MAX8822, TPS61085 - see Fig. 20 on the data sheet). The circuitry they need is rather complex so I sense I'm over engineering things.

My initial plan was to power the Arduino by means of a Mini 360 DC/DC step-down converter. It is based on the LM2596 which has a duty cycle of max. 90%, which translates to a 10% input voltage dropout. In this setup I will be able to use 60-80% of the battery capacity at most.

Another option would be to first boost the input voltage to 5VDC (would solve the white LED voltage issue) and then use a buck converter to power the 3.3V electronics. It even appears that there are 5VDC boost modules that have a built-in battery charger circuit (I suppose they're used in 1-cell power banks). These combined boost/charger modules seem to require a 5V 1A power supply for charging.

How could (or should) I approach the LED powering and dimming in this setup?


texts: Does the "drain" wire in a microphone audio cable serve any purpose the shield does not?

texts:
I'm helping a friend with an audio installation, and he asked about the requirements for the microphone cable:

  "Wiring Requirements: 2 Conductor shielded cable, 22 gauge with a 24 gauge drain wire.

The requirements imply that a 24 gauge drain wire is a necessity, but if the cable is properly shielded, is the drain wire a necessity? Other than providing some additional strength to the cable and/or an easy way to connect to and solder to the grounded shield, does it serve some additional purpose?

It is intended for an unbalanced electret microphone; I'm interested in other uses if not applicable here.


texts: Zener diodes multiple breakdown voltages

texts: How could there be zener diodes with different breakdown voltages since the chemical bond of the Si atom with the B- atom has the same strength in all occasions?


texts: RF output power too high because of PSU cable

texts:
We have a situation where an integrated 868-920MHz RF chip is programmed to output the chip maximum of 14 dBm power. From professional chamber/measurement equipment 16 dBm is measured in the carrier band.

From measuring the setup in different positions, it seems the extra power stems from the incoming wall charger cable. The charger is 5V/3A fully approved by CE/FCC.

The antenna is a somewhat isotropic PIFA. From seperate measurements the extra power does not seem to come from directivity of the antenna.

I can understand the small RSE power magnitudes that we normally measure, but how do we amplify the actual carrier power by this much?


texts: Layman explanation of "dynamics" or "dynamic behaviour"

texts:
I often read the term dynamics or dynamic behaviour in electrical engineering especially in control systems course

What is meant by it?
Is it means that the system whose internal state/properties change with time?please kindly explain with practical example application


texts: Via Stitching on 2 Layer PCB when top layer is not fully ground pour

texts:
I am designing a 2 layer PCB for an LED module and need advice on EMC/EMI. I know EMI is more to do with fast rise and fall times and not frequency but I will post details anyway. The PCB will have a 5V regulator switching at 400 kHz, several switching LED drivers at frequencies between 600-900 kHZ and the microcontroller clock (no crystal oscillator) will be at 32 MHz. Data signals will be in the range of 100 kHz. We have had EMC compliance issues in the past on other PCBs where especially the clock signal caused EMI that violated the toughest European standards. So I am trying to use all the design options available to pass EMC requirements.

However, we also want to keep costs down and go with a 2 layer PCB if possible. The bottom layer will be a ground pour. The top layer will have DC power trace to feed power into all components. It will have all signal traces, LED power traces, and the rest will be filled in with a ground pour.

My question relates to via stitching. I have heard it can be used to reduce EMI, but to be honest I don't have alot of experience in this department. Even at 10 times the clock frequency (320 MHz) the wavelength is 0.9 meters, which is more than 3 times the length of the PCB. So my questions are as follows:

1) Will it help to do via stitching here in your opinion?

2) If it will help, since I only have 2 layers and cannot do a complete GND pour on the top layer, can I run a GND trace around the entire perimeter of the top layer and run all the vias along that trace? There will also be a ground pour on the top layer but this is a fairly densely populated board and the ground pour will cover only a fraction of the top layer. Will this trace around the perimeter on the top connected to GND work as a Faraday cage like via stitching is supposed to, or am I confused?

3) Since wavelength is 3 times the length of my PCB, can I just space the vias 2mm apart or so? Or will spacing them really close also cause issues? Can you recommend any appropriate spacing for the vias?

4) If you have any other suggestions for minimizing EMI please do share them with me.

Thank you for any help you can give.


texts: Connection battery charger IC to battery protection

texts:
I'm trying to design a battery charger with protection for 2 cells in series. I'll try to work with this charger:

together with this protection IC:

Sorry for the dumb question but I'm quite new in this field. What are PB+ and PB- terminals?


texts: How to drive a LED strip from AC power supply?

texts:
I have a LED strip (5050) and a sine-wave AC power supply of a sufficient wattage and the voltage regulated in a sufficient scale. What would be a good design of driving the LED strip from this supply? I want to keep it simple.

My idea was to:

setup the voltage of the power supply to the level required by the output luminosity.
include a rectifier to keep "no-power" time as short as possible.
connect a capacitor parallel to the LED strip to prevent flicker and not to shorten LED strip life (because it's 50 Hz AC power). Is there a way how to calculate the capacity of the capacitor based on the LED strip power consumption? I know it has to withstand the max. voltage it connects to.

Is there anything else to make it better or more sustainable?

Edit:
This is a minor importance, but the final goal is connecting several LED strips in series and the power supply would be 220V AC electrical grid. The circuit will be with circuit breaker and an Earth leakage circuit breaker.


texts:
I would like to know how we determine the IEC 6100-4-2 level for a product.
There are 4 levels, and I don't know what level take.
It's for an encapsulated system with mechanical ground separate from the electrical ground with ESD protection capacitors.


texts:
I've been continuing to play with small circuits and Im trying to sort out how to calculate the resistor for the base of this transistor.  The transistor is a pn2222 (https://www.fairchildsemi.com/datasheets/PN/PN2222.pdf).  Its my understanding that the resistor for the LED should be calculated much in the same way I would without the transistor.  In this case, I know the LED drops 2.48 volts and draws 46mA.  So my resistor for the LED is 54 ohms and I used a 47 ohm resistor.

I've tried many different formulas to try and figure out what the base resistor should be used and I can't seem to get it right.  From my reading this is important because too much current could open the transistor too far and block the current coming from the collector through to the emitter.

I tried using this formula...

R = Voltage x hfe / LED current
R = 4.3 x 35 / .05

That gave me 3010 and when I use a 3k resistor I only get about 30 milliamps of current to the LED.  Shouldn't I get the full 46 as I see when the LED and resistor are plugged directly into the power source?

Also - in the above circuit I subtracted .7 volts from voltage since that just seems to be what everyone was doing.  In reality, when I check the voltage drop from collector to emitter and base to emitter I see .8v and .6 v respectively.  Shouldn't this be factored in?  What about the voltage drop of the LED?

Im lost.

Update - Thanks for all the comments.  Im really new to this space and still learning so it's been very helpful.  I've moved the LED and it's series resistor to the collector leg of the transistor.  The more I think about this, the more I see that Im dealing with two parallel circuits on the same power supply as I've drawn out.

If this is the case, I can see how having the LED as part of circuit 2 would impact the power required to drive the transistor.  Having it in it's own leg on the collector means that I can deal with it separately.  I've also measured the voltage drop from base to emitter and verified that it's right around .7 volts which seems to match the value everyone else has been using for transistor voltage drop.  At this point Im just trying to sort out the math for driving the transistor to saturation.  What Im not confused about is which spec on the sheet I should be looking at in order to figure this out.  For instance, the spec sheet lists saturation values for for collector-base as well as base-emitter.   Im getting the feeling that Im getting too far ahead of myself here.   Just by moving to this new configuration and having a 3k ohm resistor on the base it seems to work, Im just trying to prove out why that works now.  Thanks!


texts: Can I wire a 12V car battery to the 12v cigeratte lighter plug?

texts: I have a van for summer travel and I am considering wiring up a car battery directly off of a 12V cigarette port which is rated at 20A by the car company. If both batteries were well charged at the time of connection, would it probably fry the fuse of the cigarette port very easily? The cigarette port is switched off by a relay every time I put the car into sleep mode.


texts: The \$I^2R\$ loss in transformer is eddy current loss or copper loss?

texts:
As the title say, this is what my text book say. I use Hughes Electrical Electronic Technology 10th edition

  The varying flux in the core induces e.m.f.s and hence currents in the core
  material. These give rise to \$I^2R\$ losses. These losses are called eddy-current
  losses

However then when I search through the internet

I found this and it says

  Copper loss is I2R loss, in primary side it is \$I_1^2R_1\$ and in secondary side it is \$I_2^2R_2\$ loss,  where \$I_1\$ & \$I_2\$ are primary & secondary  current  of transformer and \$R_1\$ & \$R_2\$ are resistances of primary & secondary winding. As the both primary & secondary currents depend upon load of transformer, copper loss in transformer vary with load.

and

  Hysteresis loss and eddy current  loss, both depend upon magnetic properties of the materials used to construct the core of transformer and its design. So these losses in transformer are fixed and do not depend upon the load current

They are kinda contradict each other. So, what's the right definition for copper loss and eddy-current loss