texts: Diode parallel to resistor on H-Bridge MOSFETs gates

texts:
I was looking at a TC4467's gate driver datasheet and there is one thing there that I haven't seen before when reading about H-Bridges. On the schematic of example H-Bridge motor control there is a diode in parallel to resistor on 2 of the gates:

I've read that it's good to put a Schottky diode in parallel with resistor to make turn-onss slower and turn-offs faster, but then the diode's anode is facing gate, not cathode as in the schematic above. What is the purpose of the diode here? Also, why are these diodes+resistors missing from the remaining 2 gates?


texts: What is the typical max voltage out of a PC speaker Jack?

texts:
I'm trying to use CD4051BCN chip to channel some speaker outputs from a computer. these chips handle analog voltages from +/-5V.
What is the audio line max/min Voltage coming out of the desktop PC? I just need the audio line this is without any amplification.

Would it be better to use a series of relays with higher voltage/current ratings?


texts: Bandwidth and Data Rate FSK Demodulations

texts:
I have a question about the data-rate limitations imposed from bandwidth for FSK signals. Suppose I transmit an FSK signal with frequencies as:

$$f_1 = 2400 MHz,$$ and $$f_2 = 2401 MHz$$

that is detected by a receiver. Assuming that the DC output voltage of the detector in the receiver is 100 mVp for 2400 MHz and 110 mVp for 2401 MHz. Without focusing on the circuit design, Is there any limitation on the rate at which I can transmit and receive this signal correctly? I always hear that the bandwidth limits the data-rate but I don't understand exactly why.


texts: Anyone ported the QP state framework for Arduino?

texts:
In reviewing possible approaches for my data logging project, I have found the book "Practical UML statecharts in C/C++" to be very interesting for more serious work with the Arduino. QP is a family of ultra-light, open source, state machine-based frameworks for embedded systems and they distribute code and ports for their frameworks (GNU GPL2) at http://www.state-machine.com/ where they have a port for the AVR and AVR mega using the WinAVR/Gnu C++ tool set.

Although the chip specific headers are appropriate, has anyone created a board BSP file or had any experience with these frameworks? I am just starting with the book, so any comments greatly appreciated.


texts: Harmonic's equations within Single Phase Full Bridge Inverter

texts: Is it possible to find the equations of certain number of harmonics (Ex : 3rd, 5th, ... 17th) in Single Phase Full Bridge Inverter theoretically, using the characteristics of the components of the circuit ? if yes, How?, i need some documentation about that.


texts: Switch mode power supply inrush current protection

texts:
I want to design a suitable PCB for my audio amplifier project.
The amplifier boards (both left and right channels) will use almost 4 amps at 24 V at full power. I want to use a switch mode based power supply brick (like a laptop charger) that is rated at 6 amps, 24 V but am concerned about the inrush current this power brick will face charging two 22000 uF capacitors at power on.

I'v done a little research and have found a NTC thermistor with a relay shorting the thermistor out over a time period is a common solution to this problem, so I used Falstad to simulate as best I could.

Note: the 5 ohm resistor is in place of the NTC thermistor as the simulator dose not seem to have one.

falstad link1

The 6 ohm resistor emulates the amplifier load.

The PNP transistor to the left is to discharge the 470 uF capacitor as soon as the circuit is powered off to 'reset the timer'.

Note: the 5 ohm resistor is in place of the NTC thermistor as the simulator dose not seem to have one.

However the load on the power brick still has a sharp peak of over 50 amps! is this accurate? (due to capacitor ESR ect..) and will my power brick handle such a spike?


texts:
My doubt will sound silly but I am going to ask it anyway.

Why is leakage flux represented as inductance in the equivalent circuit of the transformer?

As leakage flux increases, efficiency of the transformer decreases as a portion of the leakage flux may induce eddy currents within nearby conductive object such as the transformers support structure, and be converted to heat.

When represented as inductance, it only represents reactive power loss.

Shouldn't it also be represented as an inductor in series with resistor where the resistor will represent the active power loss?

Also, is the leakage flux a good thing as it reduces the fault MVA level?

Please clarify this, I am really confused.


texts: ATtiny power consumption with clock prescaler

texts:
I'm designing a battery-powered radio-linked sensor device which requires a long lifetime. Due to the project requirements I have very little onboard energy to work with; a single coin cell is the likely source and the lifetime requirement is at least a week.

My primary power savings will come from placing the device into a deep sleep mode and waking it with a timer every ten or so minutes to take a reading and transmit it. This means that for only 0.5% of the time is the device drawing any significant power; during the sleep state the consumption will be in the units of microamps at most.

The proposed process is as follows:

MCU is powered on.
The sensor is powered on by the MCU and a one-second grace time is given. The MCU is placed into a sleep state until the grace period elapses.
The MCU communicates with the device via I2C or SPI and gets a reading.
The sensor is powered off by the MCU.
The transmitter circuitry is powered on by the MCU.
The reading is transmitted.
The transmitter circuitry is powered off by the MCU.
The MCU triggers an external low-power (nA range) timer device which is configured to delay for approximately ten minutes.
The MCU puts itself in power-down mode to conserve power.
The external timer device triggers a pulse to a GPIO pin, which raises a waking interrupt in the MCU, returning us to step 1.

The ATtiny44A has multiple clock modes (section 6.2): an internal calibrated 8MHz clock, a low-precision internal 128kHz clock, and support for external clock sources and crystals. These can then be stepped down using the clock prescaler (see fig. 6-1 and section 6.3 for a description). I will be running the MCU at 3.3V.

As the processes performed by the MCU are not particularly time-critical, I'm trying to decide which of the following strategies are more optimal for low power consumption:

Use the internal calibrated 8MHz clock as-is with no prescaling, to minimise the time during which the MCU will be switched on. This has the benefit of speeding up the few calculations I'm doing on-chip and speeding up the IO with the sensor and transmitter devices. However, a potential downside is that other internal clocks are running at a higher frequency, and will remain running during the one-second grace period in step 2. My gut says that this is a poor choice since any power saved by quicker computation will be dwarfed by the one second of running the clock on idle.
Use the 128kHz low precision internal clock source. This increases computation and IO time, but may save power during the grace period.
Use the internal calibrated 8MHz clock with the prescaler set to 1/64, producing a 125kHz clock speed, emulating the low precision internal clock. I am unsure as to whether this is a useful option.
Use the internal calibrated 8MHz clock with the prescaler set to 1/256 (the maximum), producing a 31.25kHz clock speed. Again I'm unsure if this will save power.

Which of these, in the scenario described above, will result in the lowest power consumption?


texts: How can I replace the functionality of a button with an arduino?

texts:
Imagine I have a 5v wire connected to a resistor, a button, an LED, and a pin set to ground. When I press the button the LED goes on.

I want to be able to recreate a circuit like this without the button so that the LED can switch between on and off while the code is running. The catch is that I cannot change the 5v pin from 5v and I cannot change the ground pin to 5v. I need to either be able to change the ground pin to and from a high impedance state or use some sort of replacement for the button that the Arduino can control. Unfortunately it seems that digital pins cannot be switched between input and output while the code is running and I can't figure out any other way to solve this.

The reason I ask: I am trying to wire a PCB designed to be controlled by button presses so that I can control it with Arduino. By default the PCB has one 5v, one ground, and four buttons, depending on what button is pressed one of four things happens. I attached a wire to each button, and if I set one of those wires to ground its just like I pressed the button. But I need to be able to control which button is 'pressed,' and I can't figure out how to do that.


texts: How does a Rotary Encoder work without connecting it to 5V

texts:
Like in this picture:

I know we can hook 5v later externally to debounce but still, i heard it works without debounce circuit even if its bouncy. But how can it send signals if there are only output and gnd pins?


texts: Can I use the toner transfer tecnique to transfer the silk side to the pcb?

texts:
I have searched for a while information on how to put the silk side on the pcb ( without using an marker )

I have made an pcb with the toner transfer technique: You print with a laser printer over an glossy paper and then use the iron to pass the ink to the pcb on the cooper side, and after attack the cooper with acid )

Now i'm trying to pass the part that shows how components go on the pcb and they dimensions called the silk side on the side of the pcb that doesn't have cooper.

Question 1: Will the iron screw the pcb or is it any problems or danger doing this?

Question 2: Will the toner ink go off fast ?

Question 3: Is there another easy way to do this ? (Again without a marker )


texts: What's happening in my H-bridge? (N-ch MOSFETS)

texts:
I have made such circuit as shown in schematics:

I have connected 1k resistor between HB1 & HB2. When I connect GPIO1 to the +5V and GPIO2 to the ground(both sources do have same ground), I get only about 3.1V at the resistor. These are the voltages between D and S for all MOSFETs:
Q1: 11.9V (there is something wrong here, but I do not know what)
Q2: 3.1V
Q3: 15V
Q4: 0V

I have tried doing everything I can think of, including stupid things as rewiring. This is just simple H-bridge which should work. The 100ohm resistors at gate are there because I intend to use this with 100kHz PWM(after I prove that H-bridge works).

This is the MOSFET I use: http://www.infineon.com/dgdl/irlr2905.pdf?fileId=5546d462533600a40153566cbd072676


texts: PIC18F26J50 serial communications over RS485 link

texts:
I'm trying to figure out why my serial communication is not working. The design is  to use the UART of a PIC18F26J50 over a RS485 link. Here is the relevant part of the schematic.

Other relevant info:

RS485_RX is connected to RC7/RX1
RS485_TX is connected to RC6/TX1
RS485_DE is connected to RA2

Source code:

#define BAUD_2400       0
#define BAUD_9600       1
#define BAUD_19200      2
#define BAUD_38400      3
#define BAUD_57600      4
#define BAUD_115200     5

#define PARITY_NONE     0
#define PARITY_ODD      1
#define PARITY_EVEN     2

#define UART_READ       0
#define UART_WRITE      1

PRIVATE UINT32 speed_[] = {2400, 9600, 19200, 38400, 57600, 115200};

/*----------------------------------------------------------------------------*/

PRIVATE UINT16_VAL getBrgValue_( const UINT8 baud )
{
    UINT16_VAL value = 0;

    value.Val = (UINT16)((CLOCK/(4*speed_[baud])) - 1);

    return value;
}

/*----------------------------------------------------------------------------*/
PRIVATE VOID uartEnableWrite_( VOID )
{
    PORTAbits.RA2 = UART_WRITE;
}

/*----------------------------------------------------------------------------*/
PRIVATE VOID uartEnableRead_( VOID )
{
    PORTAbits.RA2 = UART_READ;
}

/*----------------------------------------------------------------------------*/

VOID uartInit( VOID )
{
#if 1
    UINT16_VAL brgValue;

    RCSTA1 = 0x00;
    TXSTA1 = 0x00;
    BAUDCON1 = 0x00;

    brgValue = getBrgValue_(BAUD_57600);

    SPBRGH1 = brgValue.byte.HB;
    SPBRG1 = brgValue.byte.LB;

    TXSTA1bits.BRGH = 1;
    BAUDCON1bits.BRG16 = 1;

    TXSTA1bits.TXEN = 1;
    RCSTA1bits.CREN = 1;
    RCSTA1bits.SPEN = 1;

    // enables rs485 transceiver direction control
    TRISAbits.TRISA2 = 0;

#else
#endif
}

/*----------------------------------------------------------------------------*/

INT8 uartSend( UINT8* buffer, const UINT32 bufferSize )
{
#if 1
    uartEnableWrite_();

    while (!TXSTA1bits.TRMT);
    TXREG1 = *buffer;

#else
#endif
}

The test could not be simpler:

VOID doUartTxTest( VOID )
{
    UINT8 b = 0x55;

    (VOID)uartSend(&b, sizeof(b));
}

/*----------------------------------------------------------------------------*/

VOID main( VOID )
{
    ANCON0 = 0xFF;              // AN0 to AN7  are Digital I/O
    ANCON1 = 0x1F;              // AN8 to AN12 are Digital I/O

    uartInit();

    while( 1 )
    {
        doUartTxTest();
        delay1s();
    }
}

Now, this is what I'm getting in RealTerm:

I expect RealTerm to get 0x55 several times. Can anyone, please, help?


texts:
I'd like to make a DIY kinetic energy harvester and wish to use the electromagnetic method to generate electricity. So far I know the following materials that I'm going to use:

NdFeB magnet
Induction coil made up of copper wire
Dry cell (for electricity storage)

And I wonder should I add a rectifier into the circuit before the dry cell is charged?


texts: What's the "accepted" way of driving LOTS of 2-digit, 16-segment, common-cathode displays?

texts:
I have a project that has 18 of these common-cathode displays, 36 digits in all, organized into three rows of 12 digits. My first version of the project used an Arduino and shift registers to drive them. I would shift out the 0th column of digits, latch them to provide power to the displays, then ground the 0th column. This would show the first character. Then, I'd shift out the next column of data, disable the ground on the 0th column, latch the 1th column, and provide ground to the 1th column to show it to the user.

It works, but it has a couple issues. It's very, very, very dim. I can make it brighter by holding each display on a while longer, but it doesn't go very far, and you can sense the low refresh rate when you look at it. Also, if I have a column that have very few segments active, they draw all the current I'm supplying and that column ends up being much brighter than the rest.

I have a ton (would you say I have "a plethora?") of MAX-7219 LED controllers, but there's a snag: the LED controller assumes a maximum of 8 segments per cathode. I considered using one LED controller to drive half of the segments on 8 digits, and another controller for the other half. This would (probably) work - I'd just deactivate the display on the upper half and activate the lower, then reverse the process a few milliseconds later.

I really want the drawing to be fire-and-forget. I have to generate the data I'm displaying, and this takes time. During this time, I can't really be burning CPU, flopping the displays. (Technically, I could do the flopping in a timer, but I'd have to stop the timer while I shifted out new data, and that timer might interfere with the LedController library, as well as the serial communications I'm using to get the data from a GPS module, anyway.)

So, is there a way that I can shift out 36 digits worth of data and completely forget about it for 100-1000ms, leaving the work of driving the display to someone else's hardware? I've even considered having one arduino to process data, then transfer it, somehow, to three - or even six - other arduinos for display.


texts: Helical wire antenna normal mode or axis mode?

texts:
I have bought theses two RF-transceiver CC1101 module from e-bay(image below), and I want to know if it is a helical antenna in normal mode or in an axis mode.

The specification doesn't say anything about it.

Can someone help me to detirmne this?


texts: Bridge rectifier protective resistor selection

texts:
I have a device with a supply voltage range requirement 12-24AC. The B80S bridge rectifier I am using recommends a 3.5 Ohm series resistor to limit inrush to acceptable levels. Initially I decided to go for 2 x 2.7 Ohm in 0805 (metric) package. While testing the prototype it rarely happened that one of those resistors failed when using 24VAC.

I am somewhat unsure about the single pulse peak power rating that is required for the resistors and would like some feedback.

About 400uF of bulk capacitance (calculated with respect to my load requirements) are used to smooth out the AC before hitting a 5V switching regulator.

A quick estimation, ignoring parasitics like AC transformer resistance, inductance and capacitor ESR:

At 24VAC and an assumed no load factor of 1.3 for the transformer I expect a peak voltage of

U = 24V * SQRT(2) * 1.3 = 44V

With 2 x 2,7 = 5.4 Ohm and completely discharged capacitors this leads to an inrush current of about

I = 44V x 5.4 = 8.15A.

So the dissipated peak power on the resistor would be

P = 44V / 2 * 8.15 = 180W

Having 400uF load capacitance, the pulse duration would be about

t = 5 * R *C = 5 * 5.4 Ohm * 400uF = 10ms

So I would need a 2.7 Ohm resistor with a maximum pulse dissipation of 180W for 10ms.

Maybe this is a somewhat unrealistic estimation since the parasitics will work in my favor, so I performed a simulation:

While this looks "better", this would still lead to a pulse load requirement of about 90W for 3ms. I don't know if 500uH as transformer inductance are realistic though. Since the customers will used totally different supplies this will vary anyway.

Looking at some Pulse Proof Thick Film Chip Resistor data sheets:

I would have to select at least a 2010 resistor type.

Does all this sound/look reasonable or am I way off?


texts:
I need to design a circuit capable of sending an on signal for 5 seconds and then shut off. The circuit needs to be initiated on power input from a usb port (5v ~200mA), and as I said output a few seconds of current before shutting off permanently, and then of course do the same again when power is switched off and on again.

Does anybody have ideas on how to set this up? I would prefer not to use any IC's like the 555 timer if possible, just basic components (eg capacitors, transistors...).


texts: How to convert Pulse Position Modulation (PPM) to duty cycle?

texts:
I can convert PWM to duty cycle since each frame starts with a rising edge. Then I count the on time, off time and take the ratio to find duty cycle.

However, for PPM signal, there is no start of frame or end of frame so I am stuck. That is even with the assumption that frame length is known.

There are some modules that claim they can convert PPM to Analog. One of them is PT01A WingXine which can convert PPM to Analog AND vice verse, there is only 1 single IC on there so I was wondering how it functions.


texts:
I want to assign the value of a generic that is an integer to a signal which is a std_logic type. My generic can take only two values, 0 and 1.

How do I do that?


texts: Power dissipated is maximum or minimum when step up transformer is used

texts:
The large scale transmission and distribution of electrical energy over long distances is done with the use of transformers. The voltage output of the generator is stepped-up (so that current is reduced and consequently, the \$I^2 R\$ loss is cut down). It is then transmitted over long distances to an area sub-station near the consumers. There the voltage is stepped down.

Here is what it looks wrong to me. If voltage is increased (stepped up) to decrease current \$I\$ so that power loss \$P=I^2R\$ is minimum. But doesn’t that mean power loss is maximum because \$P=\dfrac{V^2}{R}\$

[sorry for bad english]


texts:
I have two motors:

One from a DVD player and
Stepper motor.

I was wondering, if I use the DVD player motor to spin the stepper motor will I get an alternating current?


texts: Permeability: is webers per ampere-turn meter (Wb / At.m) equivalent to henrys per meter (H / m)?

texts:
Is webers per ampere-turn meter equal to henries per meter?

I.e. is \$\frac{Wb}{At.m}\$ equal to \$\frac{H}{m}\$?

-and if so, is there an easy way to picture the equivalence?


texts: How to avoid writing to and reading from 2D array at the same time vhdl

texts: Hi for something I work on, I must use an 2D array but I find it dangerious to write to and read from a certain memory location in the array  at the same time. How can I control this situation? When both reading and writing is necessary at the same time, I want to prioritize writing and instead of reading from that certain location, The old value should be kept in the signal to which I read from array and write. My narrating could be complicating. I am sorry for that.


texts: Can I secure a 12v battery to my bicycle to charge it? And then attach a 12v horn to it?

texts:
I'm from the Netherlands, so first let's clear this misconception up; I mean an actual bike, as in:
(source: fietsenverhuurschiermonnikoog.com)
.
Then I want to attach a 12 volt horn to it. I could just put it in the basket. It doesn't necessarily need to be charged while pedaling, or it can just be partly charged, but just that it runs out of power a bit slower. Then I'd like to attach a horn to it. And then have some fun.
Would this be possible? Thanks for reading my question. If I'm doing something wrong on here, please tell me.


texts:
In the 7905 negative voltage regulator datasheet, it didn't mention that it needs a minimum load current to operate.

The 7905 that I have is outputting -7 V but adding a ~2 mA load causes the voltage to drop to nominal voltage -5 V. Input is -15 V.

Does a 7905 need a minimum load or is it broken?


texts:
Hello I am trying to use 30 "tec-1 12706" peltiers along with my geothermal ground loop to cool machines. I have (2) banks of 15 in series and the two bank parallel to each other electrically. Power from simple 600v ac/dc full wave rectifier and (2) 1000 uf larger radial caps with high ripple duty rating. Scoped the power is 154.5 vdc with ripple equal to a normal quality regulated psu. 15 peltiers in series x 12vdc = 180vdc so 154.5 puts applied voltage at 10.23 each. I also measured across the series jumps to confirm. normale rating  I have used 7 200mm water blocks to form a sandwich. 4 block are supplied the entrance closed loop water from my geothermal at an incredibly stable 52.2 deg f. the other 3 blocks are connected to a manifold the supply 5 200mm radiators with 120mm 1300 rpm case fans. these radiators are mounted inside items like my server, my workstation, a cnc mill controller ect. Total heat load measured by btu = 500 x flow rate of water x difference in inlet outlet water using geothermal or totals 743 btu hour. Not much. If the peltiers are supply endless cooling at 52 f and the peltiers are all oriented correctly with undervolting why is there only 1 deg reduction from cooling water running through radiators. non energized cooling water, not geothermal is 78 deg f. that's cold side water blocks to radiators. this drops in 10 mins to 77f than creeps up to 80 f after and hour. the heat output to the ground loop is around 1200 watt or 4094 btu/h they seem to only make heat on one side with barely any cooling on cold side. non of them are heating on both sides. amps range from 3.4 to 38 each module. everything is in spec but the out come. Any ideas. I also jump stated the cooling process by cooling the water in system to desired level of 45 f. Then energized the tecs. 1 hour later back up to 80f. Flow rate to hot blocks are 2.1 gpm  divided by 4 blocks equal flow for .525 gpm each with the same divided by 3 for the cold side .7 gpm.

If i'm correct 30 tec- 12706 us made at 10.23 volts at 3.8 amps = 1368 watt equals 4667.809 btu hour, which i have on the hotside. and assuming 30 percent loss where is the 3267.467 btu/h cooling I'm not receiving going? something up and I don't see the solution. The tec-1 get cold by them selves but not as a thermally coupled unit . I used arctic silver and check their smear patterned for equal coverage, and the stack of water blocks are clamped using upper and lower 3/8 plate stainless and surrounded with 4mm stainless threaded rod. nut on bottom and thermally decoupled compression springs above using 7 lbs force each x 18. I got those numbers from manufacturer.    sorry for running on, but I intend to provide as much data as I can. This is a hobby lever build, but constructed by a profession in the field of power gen and geothermal tech. Thank you in advance for any help, I'm stuck?????????


texts:
I was looking at the datasheet of CD4048, a multifunction gate IC when I was a bit disturbed by the output circuitry, controlled by Kd in figure 2.

When Kd is pulled to negative, the output is supposed to be high-impedance (floating), no matter the logic of the 8 inputs, but the way they've done it disturbs me.

This looks like a short circuit. Am I missing something? Am I interpreting the schematic wrong? Is this normal? I feel like the schematic would make more sense if both gates were non-inverting instead.


texts: How can error correction codes reduce bit error rate, for same amount of energy

texts:
I am selfstudying error correction block codes and has a confusion about their performance.

Suppose we have \$r\$ information bits and we make \$k\$ coding bits in addition. I am given to understand that, for the same amount of energy per information bit, the coded system performs better compared to an uncoded system, where the channel is additive white Gaussian noise (AWGN) and modulation is BPSK.

This is demonstrated in a simulation, where the bit error rate (BER) is plotted against energy per information bit.

My question is, how does this come to be? When we code the \$r\$ bits, we in fact spread the energy over \$r+k\$ bits. Where as in uncoded case all the energy is used on \$r\$ bits alone. On the other hand the coded bit stream has \$r+k\$ dimensions whereas uncoded steam has \$r\$ dimensions.

Can someone please explain, mathematically, where the BER improvement comes from?


texts:
I'm thinking about an electric truck of 20tons total mass, accelerating to 100kph in 20s. Top speed 160kph. What electric motors would be needed for this? How much would they weigh?

I calculated on some site (http://www.robotshop.com/blog/en/drive-motor-sizing-tool-9698) that this would need a total of 2000kW and 17000Nm. Feel free to dispute this claim. Battery shall not be part of this equation.
Could this motor(s) that I need for this be lighter than 2 tons?
I only found 500kW motors of 1ton, I refuse to believe that for my numbers I need 4tons of electric motors...


texts: How can a logic 0 change a logic 1 to logic 0 given these circumstances?

texts:
This is a 4x3 numeric keypad. An output RB3, RB4, or RB5 may be connected to an input RB9, RB8, RB7, or RB6 by a pushbutton. The inputs have internal weak pull-ups. When the pushbutton in yellow square is pressed, RB3 and RB7 connect, rendering RB7 logic 0.

If a logic 1 voltage supply is provided by the input pins, how can a logic 0 of the output pins render the input pins a logic 0 if the output pins do not have open-drains enabled? A logic 0 is an absence of or a smaller voltage than that of logic 1. Shouldn't this be reversed in that the logic 1 voltage on the output pins render the input pins logic 1 as well when the pushbutton is pressed?

I don't know why I am having difficulty understanding this. Unless my understanding of voltage is skewed, I see know way to reverse the order of my way.

Thanks in advance for your help.


texts: The load resistance in a MOSFET current mirror vs CMOS

texts:
In class I have learned that in a MOS current mirror like the one below, we can say that the load seen by M1 is equal to r_o of M2. This makes sense to me since I have drawn the small signal model and the calculations add up.

When we compare it to the CMOS inverter like this next diagram, we cannot say that the PMOS is equal to only a resistance since there is v_gs applied, that comes from v_in on both MOS. This also makes sense.

After understanding this when I look at the current mirror again, the fact that M2 is equivalent to only a resistance is somewhat strange. Since there is v_sg2 applied much like in the CMOS example. So it looks like a mismatch of principle, it seems has though we are using double standards.
Where did I go wrong?


texts:
I am learning VHDL and came across this example of 2 functionally equivalent ways of implementing the same thing. But I am having trouble understanding how they are functionally equivalent.
My confusion is in the 3 concurrent statement picture. Since they are all executed at the same time that means that F3 gets set to (A1 or A2). But since A1 and A2 are getting set at the same time that F3 is getting set, doesn't that mean A1 and A2 do not actually have values yet when F3 tries to get assigned to (A1 or A2)?
Thanks


texts:
I'm working on a project in which I need 32 outputs from an MCU that only has 8 free outputs.

To accomplish my goal I have the following requirements:

I must be able to toggle more than one output at the same time
Data must come in as fast as possible
I cannot lose data packets
The data should be transferred in a reliable way

I though about using a 4-16 Decoder, but I cannot switch more than one output at the same time with it.

I can use I2C communication to expand my IOs pins, but I'm not sure if I'll have issues with timing and data packets.

One possibility is to use multiplexing.

I'm using a AM3359 ARM Cortex-A8 @ 25Mhz

Any other ideas?


texts: PNP high-side transistor switching with microcontroller

texts:
Up to this date I was working with NPN transistor  with micro controller and it was working fine. But here I need a PNP transistor.

Does any one can tell me is that the above configuration is correct and that the circuit can be used safely ?


texts: What is the simplest and cheapest way to interface with USB?

texts: If I wanted to make a simple device that communicates with my computer, say maybe a switch that could mute my computer when turned on and off and plug it in via USB, what would be the cheapest and easiest way to accomplish this?


texts: Small signal analysis of dynamic microphone preamplifier circuit

texts:
I am trying to do a small signal analysis for a dynamic microphone preamplifier circuit. The original circuit is using BJT but I did not have much experiences with BJT, so I switched all BJT to MOSFET.
Then I end up with the following circuit

I am trying to do a small signal analysis of the circuit but I am not sure if I am doing it right.

Then I combined resistors/capacitors for simplicity.

Here's my question

Is my small signal analysis correct?
If it is correct, is input resistance = Z1, and output resistance=C5 + Rload?
How do I find open circuit voltage gain? I know it's Vo/Vi, but I am not quite sure what to do next. Will it be easier to obtain from simulation?


texts: Use solar cell to power and communicate with chip in IR

texts:
I have a slightly movable (torsional (freely for infinite degrees around the z-axis) and translational (+- 40mm in the xy plane)) microcontroller in communication with a fixed one. I'd like to use it without having a dedicated battery. Cables would transmit too much mechanical force (own weight, spring-action), coils would pick up too much noise and require ac/dc conversion in the mobile component, so I was thinking about using a solar cell on the mobile component for power, and either a dedicated TX/RX part, or to solve the RX with the solar cell as well (there won't be much communication, so the (off-)duty cycle won't be much of an issue)

There are multiple papers about the principle, but I am stuck on a practical issue: the mobile component will need about 20mA @ 3.4V (~0.07W) continuously, and i cannot find the values i need to compute whether this is feasible in a small package.

A silicon solar cell has about 10% efficiency, but that is for full spectrum sunlight, and I would be using an LED at 950 nm (because silicon solar cells seem to be more efficient there - only some sources say the reverse, which might be due to NIR not having the most energy in sunlight -), and I’d ballpark an LED at 50% plus the solar cell would only get half of the light at any given moment, to account for movement, so I’d have to power the LED (array?) with 40*20 mA=800 mA, which seems a lot.

Also, I cannot seem to find upper limits for radiation densities for small-spectrum light on silicon cells (amorphous? Crystalline?) - is it the same as for full spectrum, ie 10000W/m2 ?

Alternative power conduits are welcome, but my main focus is on scaling the LED(laser?) and solar cell.

EDIT:
there will be plasma cutting and arc welding going on in the near vicinity, which is why i thought coils were out. The welding and cutting equipment is not related to the project i am talking about here, so neither can i use the resultant light, nor can i use the infrastructure (cables). The MCU itself is shielded, and has functioned properly. Currently it is powered by a small lipo unit i got from a minicopter. I experimented with the coils from an electric toothbrush, but got bad results for the translational movement (did not try with welder on ).
Movement is +-40mm in xy plane, and torsional movement is constrained to the x-axis. air gap of >50mm would be nice. There is no MCU is 10g, shielding is another 12g (though i'll try to shave that down as soon as i get my hands on thinner metal sheets), lipo is 7g


texts:
this is my first post here as I am just getting into this electronic engineering stuff. My question concerns the SR flip-flop or latch, the NOR gate version. I have been reading a copy of http://www.amazon.co.uk/Digital-Techniques-Tutorial-Electronic-Engineering/dp/0412549700/ref=sr_1_1?ie=UTF8&qid=1376179565&sr=8-1&keywords=t.j.+stonham.

The circuit I am looking at is below:

simulate this circuit – Schematic created using CircuitLab

R and S are inputs, Q is the output of the second NOR gate, Q' is the previous value of Q, and X is the output of the first NOR gate.

I understand that Q is a function of R and S and the previous output Q' but there is something I cannot get my head around.

The truth table for the function is

R    S    Q'  |  Q
0    0    0   |  0
0    0    1   |  1
0    1    0   |  1
0    1    1   |  1
1    0    0   |  0
1    0    1   |  0
1    1    0   |  0 /*don't care*/
1    1    1   |  0 /*don't care*/

What I don't understand is a comment in the book. It says that if the two 'don't care' inputs are disregarded then the output of the right-most NOR gate is the complement of the left-most NOR gate.

Now, I have of course seen the cross coupled NOR gates diagram of the SR latch which has a NOT Q output, so I know I am doing something wrong somewhere, but I cannot see where.

For each of the cases in the truth table, this holds true, Q is the complement of X. But when R=1, S=0 and Previous Q=1 this is not the case.

When R=1, Q is always 0. But Previous Q=1, so X is also 0. X and Q are the same in the case.

Please somebady show me the error in my thinking. Thank you.

EDIT:

Having thought about this, could the answer be that the 'problem' state I am considering is an unstable state; i.e. when NOR2 outputs 0, that 0 will also change NOR1 to 1, which would solve the problem.

Although that thinking led me to another problem, and that is that surely then, for a split (milli)second the outputs of NOR1 and NOR2 are the same before the change. The only problem I can see with this thinking is that I am tracking the changes in the circuit fairly slowly, when in fact the change should be instantaneous, i.e. that as soon as NOR2 changes to 0, NOR1 changes to 1 instantaneously.

EDIT II:

I am going to try to clarify tho confusion with my question here, and express the problem more concisely.

To clarify the variables:
S - Set as usual
R - Reset as usual
Q - Output as usual
Previous Q - The initial value of Q
X - The output of NOR1

The problem I was having can be looked at as a transfer between two states.

The first state:

simulate this circuit

Here R and S are 0, Previous Q is 1, so X is 0, which gives Output Q as 1, which is Previous Q, the circuit maintains itself as expected (R and S were both zero).

But in the next circuit I switch R to 1:

simulate this circuit

So now Output Q and X are the same, they are not the complement of each other.

This is where I think I am going wrong:

This last state is an unstable state, and so will not remain as such. Previous Q will instantaneously turn to0 and hence NOR1 will output 1, giving X as 1, the complement of Output Q.

I think the problem in my thinking was that I was looking at it as if it would take some time interval for previous Q to reach NOR1 and change X to 1, when in fact it would occur at the exact same time as Output Q changing to 0.

Hopefully that has cleared things up.


texts: How do I do point to point wiring on a protoboard?

texts:
I bought a small "fancy" protoboard from Sparkfun. It includes a solder mask and through plated holes(double sided).

Now I'm trying to do a simple circuit and I can't seem to figure out how to drag solder across the board. The solder mask keeps the solder out of where I want it to bridge and it ends up just going through the plated holes and accumulating on the other side.

How exactly do you do point to point wiring?


texts: How to build AC current sensor circuit for ESP-01 GPIO

texts:
I would like to build circuit that can detect current flow and provide suitable digital high signal to GPIO pin for 3.3V ESP-01 logic.
I started looking at the designs available on internet.
Option that drawn my attention is based on current transformer / Hall's effect combined with OP amp (or comparator).
Current from the main line is represented with the proportional voltage drop which is used as input for an OP amp. As I understand OP amp (with negative feedback) suppose to give amplified signal representation prepared for further processing or in case of comparator (positive feedback) digital representation could be provided.
But neither of those options can serve exactly my needs.
When OP amp is used as amplifier (negative feedback) I get amplified voltage representation for current flow.
Second option, using converter (positive feedback) gives saturated voltages, and thus it can give digital representation, but in that case, depending on the way comparator is configured you can get digital high during first half of sinusoidal signal and 0 during second half or vice versa.
In booth cases it is not what I need.
In short, I don't know how to use circuitry to process signal after OP amp/comparator and get suitable 3.3V logic HIGH state on GPIO when current flow is present.


texts: How to test voltage and current/amperes of solar panel with multimeter

texts:
I am testing the efficiency of solar panels in different temperatures with a multimeter. I am testing for voltage and amperes. However, how do I connect a solar panel to a multimeter to test it? From past recent experience I'm pretty sure you just connect the red and black wires to the multimeter, but when looking at solar panels it asks if I would like diodes and wires, and I don't know what those are. Please respond with links for a small solar panel, a multimeter for me to buy and how to test a solar panel with it. Please don't go over 25 CAD with the multimeter and 10 CAD for the solar panel. I would like a small one please, I'm open for a suggestions.

Solar panel link that confused me: http://store.sundancesolar.com/3-0v-100ma-round-solar-cell/

Proposal: https://docs.google.com/document/d/1e7Qd1Mnc-bzLgHIJ-wEY_OkftLELLZ2ulFH57DwvS3I/edit


texts:
I am designing a power meter based on ADE7758 and I'm using the official documentation for examples; I will also use an isolating IC for the communication between the ADE7758 and the microcontroller. I have some trouble understanding why is the ground of the +5V supply referenced to the neutral line in the diagram below:

The diagram is adapted from page 12 of AN-564 Application Note of Analog Devices and depicts a power supply design for a power meter.

The ADE7758 datasheet sheds some light on connection between digital and analog grounds, saying that these should be connected at only one point (page 9). What bothers me is that the voltage regulator's ground is supposed to be 0V for the digital circuitry, while the neutral rail may not be a good reference. I have not tested the circuit and before I go ahead and do that I would like to wrap my head around its working principle.

My other concern is what will happen if someone swaps the hot and neutral connections of the board; the microcontroller reference will be connected the the hot line and I want to avoid that.


texts:
I have a mechanical water flowmeter with reed switch output and I connect it to my low power, battery powered device to count pulses.

The reed switch is connected to my device via a 15 m long cable and it shorts the pulled up input (1M) of a comparator with hysteresis in my device - detection works okay.

The problem is that once in a year the flowmeter needs to be disconnected and inspected - while the long cable combined with large impedance, humid and electrically noisy environment causes the comparator to trigger and count a lot of false pulses. Even touching the cables triggers counting.
Changing the pull up value to 47k works great, but also increases the battery current a lot when the switch is shorted.

Currently the device is powered from 3 V coin battery, the comparator window is set between 1.4 to 1.7 V. I thought about moving the window into a lower voltage range, ie. 0.2 - 0.5 V - is it a good idea? Maybe there's a better solution? Battery life is the top key priority.

I'll only add that it's not my design, I'm just trying to fix someone's work.


texts: Software/Hardware Reset of MCU sometimes makes 24 Bit External ADC conversion goes wrong in Tiva C series

texts:
I have a strange problem and I couldn't find a solution for 1-2 month.

In my system I have a Tiva TM4C123GH6PM MCU and external 24 Bit ADC(MCP3919). My PWM pin generates 8MHz clock for ADC main clock. ADC conversion automatically starts with this clock.

My problem is that with software/hardware reset of MCU, my ADC readings sometimes goes wrong. It is like "fixed garbage value" comes from external ADC to me with SPI communication.

Only power off/on device solves problem!!!

As a result, there is a problem that occurs with software/hardware reset of MCU in run-time and the problem is solved with only power off/on device.

I don't know it is related with power-cycle issues sth. like this or not.

I really need your experiences with this issue.

Regards


texts:
Most software defined radio peripherals involve a FPGA. In designing a SDR peripheral, I would like to know whether its possible to design a GNU Radio Compatible SDR hardware peripheral without any FPGAs. i.e. Directly sending the output from the ADCs to a PC via USB. If possible, I think  My interest to eliminate FPGAs (at some other cost) is because FPGA soldering, design is a difficult process that is not properly explained by most vendors. If there is a way I could eliminate them from my design it will be great. My interest is to design something similar to this.

In the above image I found from TI, is it possible that we directly connect the output of the ADC to the to the PC via some sort of a USB connection? Perhaps, transmission is possible this way as well.

I would also like to know the exact purpose(s) of using FPGAs in SDR peripheral designs. Im sure there may be many. But I would like to know the most imperative ones.

UPDATE:

As suggested by Neil_UK in the answers section, if the limitation is not being able to transmit the raw ADC samples via a USB interface to the PC due to slowness in USB speed, What would be the highest practical bandwidth that we could have in a system that directly connects the ADC to a USB? perhaps a USB 3.0? is it only the bandwidth that will be limited by this decision? What other fundamental features would go missing if SDRs were desiged this way? (provided its not required to operate on signals e.g. demodulate them)


texts: What is a symmetrical differential amplifier?

texts: Can someone explain what kind of amplifier this is and how why it is called symmetrical? Also, an example schematic would be great.


texts:
I work with deaf athletes and need a training start light system, it needs to be a box approx 15 - 25cm long 10cm wide with three different coloured lights green, Amber, red
Battery operated from a lead 2meters long, switch or button operated - first press green light comes on, second press green lights goes off and amber lights comes on, third press Amber light goes off and red light comes.
I hope someone can help as it would greatly aid deaf sports


texts: Why short circuit occur when the hot line touches the neutral wire (aka ground)?

texts: The charges move from negative (hot wire) to positive/negative (neutral) to make the device work right? So why would the Short occur only when they are directly connected? Wouldn't they just flow freely to Earth? Or it's different when DC passes the neutral line? Or Because it was weaken by the transformer after passing the device?


texts: How does the shield of a coaxial cable work?

texts:
let's consider a coaxial cable with only two conductors (the core and the external metallic shield), and let's consider the case in which it propagates TEM mode at a certain frequency:

My question is: how does the shield operate in order to get 0 (or near 0) electromagnetic field outside the cable)? I always have been told that its shielding effect is due to the shielding property of very good conductors. I may understand this explanation, but I have a doubt: along the metallic shield there is a current which is equal and opposite to that flowing along the core. So, it should generate a circular magnetic field also outside the cable.


texts: Use of passive filter in oscilator circuit

texts:
I see on datasheet of a part that I want to use in my next design that is common to use an passive componente, like an inductor or capacitor, to avoid EMI issues in oscilator circuit.

Here is the datasheet:

So, my question is:
1 - What value of capacitor shoud I put in there? There is some calculation avaiable to design it?
2 - I have notice that many schematics come with an inductor in that place. Is that rigth?

Thank you a lot!


texts: current direction when the switch is connected

texts: At first,SW1 and SW2 are open,after ac produce a positive half current to charge the C1,then two switch close at the end of the positive half current.In this moment,the current from capacitor should flow to the inductor,then,what is the correct direction,a or b?


texts: I have a 2 mm radius steel ball and I want to charge it in a 0.025 Coulomb charge. Can I do that domestically or the charge is too high? And how can I do that assuming I don't have another conductive material that I know it's charge?


texts: I am trying to make an FM receiver. I have a radio transmitter and it's able to pick up and demodulate the signal from that when the transmitter is beside it, but the problem is when I try and pick up any other radio stations. The variable capacitor is between 10 pF - 60 pF maybe is this too narrow of a range? or would there be another reason for this?


texts: Transistor overheating in seconds when connected to usb power source

texts:
I am following this tutorial and have managed to make a working circuit but when I connect it to a high current power source such as a USB 3 port, the transistor gets so hot that I fear it may burn just after running it for a few seconds. This does not happen when connected to batteries. What am I doing wrong? I have calculated that current flow should be less than 1 mA because of the 5.6 kOhm resistor based on the fact that 5/5600 = 0.00089 A or 0.89 mA. The transistor is rated at 1.5A and 80V (here's a link) which is well below what I am providing it with since even USB 3 provides no more than 900 mA at 5V.

(By the way, based on the amount of current draw, is it safe to run this from, say, an Arduino?)

EDIT: Thanks to Dave Tweed here is the actual schematic I am following:


texts:
I need to convert 12V (may vary from 11 to 14V - motorbike battery) to 5V 1A (microusb phone charger). I have the L7805CV positive voltage regulator.

Which capacitors I need to connect at input and output? Any other stuff is needed?

(I need the whole thing to be smallest possible)


texts: Limit switch for Linear actuator Do I need relays or not

texts: I am replacing the linear actuator in a handicap lift. The old wiring was disconnected when I acquired this lift.  The lift uses a limit switch to stop the actuator outward stroke at maximum lift. But no limit switch on the downward stroke.  What is left of the wiring contains 2 relays with a number of wires removed or cut.  I truly need some advise on what would be the best set up for this application. It utilizes 12v from the vehicle, and I am assuming a 2 way momentary switch. up and down. Possibly power on and off. Currently I am using a switch from my jeep, with no relays, but they limit switch is not part of the occasion.  I do have a wireless remove receiver that I would like to incorporate. But for the moment just safely up and down would be just fine.


texts:
Applying KCL at the node where I have drawn the currents in order to find Vin/Vs,
I am not getting the correct answer which however I did obtain using the Voltage Divider. My question is, am I using the KCL wrong way?

Using KCL: Vin/Vs = (R/Rs)

Using Voltage divider (correct answer): Vin/Vout = R/(Rs+R)

The way I approached with KCL:


texts:
I've been trying to flash an image of UBuntu 12.04 on the cubieboard using LiveSuit(3.05,3.06)
on my UBuntu 13.10 and also using LiveSuit(1.07,1.09,1.11) on my Windows7 64bit .

LiveSuit/PhoenixSuit fail to detect cubieboard every time I plug in my device in FEL mode.
I've been through most forums on cubieboard and they recommend the very same procedure but it always fails in my case.

1.Start LiveSuit/PhoenixSuit(LS/PS)

2.Turn cubieboard off/Unplug it.

3.Select/Load Image.

4.Press and hold the FEL button and plug the cable to connect Cubieboard to PC and release the button.

5.Upgrade should start automatically.

LS/PS never detect my device at the 4th step.
On UBuntu I've checked my drivers using lsmod | grep awusb and sudo modprobe awusb. Executing ./LiveSuit.run installs awusb vers. 0.5 in case of LS3.06 and awusb vers. 0.4 in case of LS3.05. So i guess my drivers are installed properly.Please let me know if I'm mistaken.

I'm not so sure about my drivers in Win7 though. My Device Manager shows a USB Device(VID_1f3a_PID_efe8) however it has an exclamation mark on it. The Device Status in its properties window says --

  This device cannot start.(Code 10).

Plugging the device in FEL mode causes no change in the devices shown in the Device Manager nor does it change the aforementioned Device Status. When the device is plugged in normally, a bubble appear on near the taskbar that says --

  USB Device not recognized.

Also, a usb device by the name of Unknown Device is added to the list of USB devices with the same exclamation mark on it as mentioned before. The device status of this device says --

  Windows has stopped this device because it has reported problems. (Code 43).

After a few seconds it automatically disconnects!

The windows compatible version of LiveSuit doesn't install any drivers though I think they come packed with it. There are 3 files that I believe are the setup files for the driver--

1.drvinstaller_IA64

2.drvinstaller_X64

3.drvinstaller_X86

I don't know which installer to run. I've executed all three but nothing happens apart from a blank cmd prompt window appearing on my screen for a second or two. There also some .sys files in another folder but they aren't executable. I've also tried to update drivers for the aforementioned devices using the device manager by pointing the browse option at the LiveSuit folder.All that happens is that another pops up that says--

  The best driver software for your device is already installed.

  Windows has determind the driver software for your device is up to date.

This is driving me nuts! Please help!


texts:
How to make automatic reset of slave timer in gated mode in STM32 mcu?

Summary:

I've done synchronization between 2 timers: Timer#1 is configured as a slave in gated mode, Timer#2 is configured as a master, it toggles its output compare channel, which is an input for slave timer.

The timer overview (AN4013 application note on timers) states that:
"the counter clock is enabled when the trigger input (TRGI) is high. The
counter stops (but is not reset) as soon as the trigger becomes low". And it works just like that: when output of master timer becomes high, slave timer starts, and when it becomes low - it stops, but not reset, which leads to undefined behaviour - after changing output from "high" to "low", line sometimes becomes low (as I need it to) and sometimes doesn't change (standing high).

So the question is, if it possible to reset slave timer on trigger becomes low?

PS: I'm using STM32F103C8T6 microcontroller


texts:
Currently I am using  VSMY7850x01 IR LED which is 850 nm this IR LED works perfectly for my project however  I want to change 750 nm for optimal quantum efficiency of my lens which is in the 750 nm, I asked Vishay but unfortunately they don't have this 750 nm IR LED. BTW, I am pulsing 5 A for 200 uS for this LED so it must be 5 A peak current.
My application for this is FLASH for taking photo.

If you have any idea which vendor has is much appreciated.


texts:
I need to glue a small heat sink on top of a DIP transistors array.
At the moment I have used this adhesive:

http://uk.farnell.com/fischer-elektronik/wlk-5/adhesive-thermal-conductive/dp/1211723

I looked for cheaper alternatives but I only found products that cost £10 for asmall bottle/tube.

I was wondering if anybody has any suggestion. do I really need to use these expensive adhesives or can I use something else?


texts:
I have a problem seeing characters written in /dev/ttyS8 on my PC terminal with this C code:

void main (void)
{
    int file, i;
    unsigned char receive[100]; // declare a buffer for receiving data
    char buf[20];
    size_t nbytes;
    ssize_t bytes_written;

    if ((file = open("/dev/ttyS8", O_RDWR))<0)
    {
        printf("UART: Failed to open the file.\n");
        return;
    }

    //
    struct termios options; // the termios structure is vital
    tcgetattr(file, &options); // sets the parameters associated with file

    // Set up the communications options:
    // 9600 baud, 8-bit, enable receiver, no modem control lines
    options.c_cflag = B9600 | CS8 | CREAD | CLOCAL;
    options.c_iflag = IGNPAR | ICRNL; // ignore partity errors, CR -> newline
    tcflush(file, TCIFLUSH); // discard file information not transmitted
    tcsetattr(file, TCSANOW, &options); // changes occur immmediately

    strcpy(buf, "This is a test\n");
    nbytes = strlen(buf);

    while (1)
    {
        bytes_written = write(file, buf, nbytes);
        sleep(10);
    }
    close(file);
}

I tested if maybe type of serial cable is a problem, but it behaves the same.
/dev/ttyS8 is my UART output, but I cant determine what I'm doing wrong. Any idea what to test will be helpful, or on what to pay attention when trying to do something like this.

Thanks for your help!


texts: MAX7221 experiencing 40C temperature rise above ambient

texts:
Each MAX7221 (2) in my current design is getting very hot.  I used the FLIR One to get a general measurement.  I observed a 40C rise above ambient.  I'm not sure what the root cause is.  Perhaps someone has experienced this as well.  I have attached the thermal image, see the cross-hair in the y-direction which represents one of the MAX7221.  In addition, I also included the schematic for reference.  Thanks, Brian

P.S.  I'm not how the schematic will look.  I was hoping to add a PDF version.

Max7221 FLIR Image


texts: Need help calibrating ADC input using a voltage divider

texts:
I have been using Arduino Nano analog input to measure voltages, in the range between 22-30 Volts.   The Nano's ADC expects a 0-5 volt range and has 0-1023 as its output.

Following the instructions found here:

Read Analog Voltage (www.arduino.cc)

Which basically states that all I need is this code:

int sensorValue = analogRead(A0);
float voltage= sensorValue * (5.0 / 1023.0);

5.0/1023 = 0.004888 volts per increment in analog readings.  Turning that around, voltage input divided by this value should give me the sensor value.

My voltage divider is 1 Mohm (R1) between the voltage input and A2, then 200K (R2) from A2 to ground

30 Volts measures as 4.2 Volts.  22 Volts measures as 3.1 Volts.

I think the range between 22 volts and 30 Volts doesn't present enough variation to the ADC - every single-digit change in the analogRead really make a big difference.

The result is that it is giving me some crazy readings.  It is definitely nonlinear, so I am having real trouble trying to get it to be accurate at both ends of my measurement range.  Each slight ADC increment makes too much of a difference in the measured voltage because I am not using the full 0-5V input range.

So I have been taking 10 readings in a row, at 500 ms intervals, then averaging.

And yet it is not working well enough.

One thing that seems to really matter is the power supply.  When I put 4.97 into the Vin it gets different readings than if I rely on getting power from the USB connection to the Raspberry Pi 3B.

Just yesterday I put it on the power supply for good - had been relying on the Pi all along.  But it still is not giving accurate readings.

--EDIT from Answers   (Thank you for showing me where to look)

Input impedance:  I'm trying 147/23.5 for the next attempt.  Getting 3.0-4.1 for the 22-30 range.  Same as the 1M/100K, basically, but lower resistances.

The reference voltage issue:  It measures 4.36 Volts on the 5V output from the Nano.  Vin is 5V exactly.

Here is an article I found that says the 5/1023 formula should use that actual value:

Measuring DC Voltage using Arduino

And another that confirms it:

Analog to Digital Conversion

SO NOW the immediate problem is how can I map 22-30 volts to 0-4 or so, thus allowing the utilization of more than just a few % of the allowable values?

Cross-posted at How can I seriously calibrate ADC voltage readings with Arduino Nano?


texts: Determining magnetic flux density of a closely wound toroidal coil

texts:
I am using David K. Chengs's Fundamentals of Engineering Electromagnetics book. In chapter 5/question 5.2, there is a given closely wound toroidal coil, and it asks what is the magnetic flux density at the inside.

This question is okay but at the end it says;

"It is apparent B=0 for r<(b-a) and r>(b+a) since the net total current enclosed by a contour constructed in these two regions is zero."

I understand, at r<(b-a) region, there is no current therefore B=0, but I did not understand the other part which is r>(b+a) how total net current is zero here?

Please see the picture of a question to understand better.


texts: Is it possible to power a peltier with 12 V and 1 or 2 A?


texts: Timer + voltage level translation circuit

texts:
I'm looking for a digital circuit whose behavior I will describe in a moment. It has one digital input (5V logic) and two digital outputs (12V logic). I'll hereby refer to these levels as 0 and 1, but keeping in mind the voltage difference between input and output. This circuit has to be as cheap as possible, with simplicity the second priority.

Upon a rising edge on the input, the first output should immediately go to 0, while the value of the second output is irrelevant (don't care).

Upon a falling edge on the input, both outputs should immediately go to 1. After an interval of time (around 200 ms, up to 50% tolerance on the timing is still acceptable), the second output should go to 0.

I built a circuit for this that would work if the input was 12 V, but other considerations forced the voltage level on the input to 5 V. I already felt my solution was getting complicated for a 12 V input, and just piling on a level shifter from 5 to 12 V would further complicate this circuit, so I'm trying to start from scratch and think of a simpler solution.

I think posting my circuit here would be counterproductive, as the natural reaction would be trying to refine it, and I think a good solution demands some outside the box thinking, but I will edit the post to include the circuit if requested by anyone.

Edit: by request, here is the circuit:

simulate this circuit – Schematic created using CircuitLab

The NOT gates are Schmitt triggers (HCF40106 in my circuit), which is why the circuit doesn't work properly with a 5V input: 5V is not recognized as a high level signal when the Schmitt triggers are supplied with 12V.

To fix the 5V issue, I thought of passing the input through the following circuit, but as stated above, I believe this is getting more complicated than necessary:

simulate this circuit


texts: Difference amplifier show fixed voltage on its output

texts:
I'm using a difference amplifier as shown on this page:

I double checked my resistors values, I have RA=10k and RB=56k. I'm using a 5V reference and a 0V ground.

On the actual board, I have V1=0.1V to V1=0.4V (this is adjustable) and V2=0.5V. However the output is always Vout=3.85V, even when I change the V1 voltage.

I double checked the resistors and LM324 pins, and see nothing wrong.

I also measured V+=V-=0.684 when V1=0.4V and V+=V-=0.542 when V1=0.1V

How could I determine what is the cause of the problem? Do you have any idea at what the problem could be?


texts: Sensibility and health hazards of reflowing computer PCBs in a domestic oven

texts:
This is a bit of a fringe question, SE-wise, but I think EE is the best place to ask it.

Some acquaintances of mine had a problem with their laptop - the graphics card stopped working. They've received (from someone else) instructions as to how to "reflow" it.

Unfortunately I don't have the link to the text (and it's not in English anyway), but the relevant bit instructed to heat the card in a convection oven set at 180 C for 5 minutes.

I was asked about my opinion about this fix and answered that while it's conceivable that it might work (my only idea was that it could perhaps remove solder connection defects, since the board is old enough to be pre-RoHS), I advised strongly against performing the fix in an oven still used for food preparation.

To my dismay I recently learned that the acquaintances in question went ahead and performed the fix, in an oven used for home cooking no less. Interestingly enough, it worked, at least for now.

Therefore, I want to ask the following two-part question:

What are the health hazards associated in performing this sort of rework in an oven used for preparing food, and how to deal with those dangers? I would prefer for the answers to concentrate on the possible contaminants left over in the oven, rather than, e.g. increased risk of catastrophic failure of the PCB's components.
How can this sort of rework be effective in rendering the board operational again?

Preferably, I'd like an answer that addresses both parts, but for obvious reason I'll also be satisfied with a quick response on only the first one.

UPDATE: Thank you for the answers so far. Since the most popular ones present opposing opinions, and the number of the respective upvotes is comparable, I think I should wait a day or two before accepting either. This is in the hope that someone would be able to provide concrete data relating to the subject.

UPDATE 05.01.2013: I'm still going to leave the question without an accepted answer for some time. Seeing as how none of the answers have hard data to support them, I'm a bit apprehensive with going the either way. Sorry for that.


texts: Bare bones dual 12V battery isolation circuit?

texts:
I'm putting together a bare bones dual battery system for the car so I can run an inverter from the second battery while the car is off.

Was thinking I could leave the starter battery as is, connect negative of aux  battery directly to starter negative and connect both pos terminals using a normally open 150 amp relay. then If I connect a 13V zener diode from the starter battery pos to one side of relay coil, the other side back to battery neg (via suitable resistor to limit coil current).

Connected directly across the aux battery will be my inverter so it receives power whether the ignition is on or off.

Am I correct that once the alternator charges the starter battery past 13V and the zener reaches breakdown and connects the two batteries in parallel the ongoing output of the alternator should prevent the auxillary battery from dragging the starter battery down to it's discharge level?

Does this all sound plausible or am liable to end up with fried electricals or a flat starter?

Edit: apparently I was mistaken in my assumptions of zener behaviour and didn't account for the voltage drop across the zener at breakdown. With this in mind was thinking that I could use whats left above the knee voltage to drive a transistor into saturation and the current through that to in turn close the relay - something like the following diagram.


texts: Problem with using power bank for modem with dc dc booster

texts:
I want to run a modem that needs 12 volts with a power bank.
I've used a DC-DC booster to increase the voltage of my power bank which is 5 volts up to 12 volts and there is no problem with that.
After I connect the modem and turn it on, it doesn't work. What I have noticed is that after turning the modem on, the voltage drops down to about 5 volts from 12.
I don't know what's wrong.
The booster module I used is XL6009 LM2577:


texts:
I am absolutely new to electrical stuff, and I am just trying to create my first project. I am basically trying to drive a strip of RGB LEDs (in a form of a Christmas tree) using attiny85. I have successfully programmed the attiny and connected it to the Christmas tree on a breadboard, and now I am trying to figure out a way to power it. Everything works fine when connected to 5V and ground pins of Raspberry Pi. But when I try to run everything connected to a small breakout USB-C port, it doesn't work, and I want to figure out why. According to what I read, USB-C without Power Delivery negotiations is capable of delivering up to 500mA of current. If I understand correctly from the attiny's data sheet, running on 1MHz with 5V it requires about 1mA. I am not so sure about the LEDs on the Christmas Tree and not sure how to check it.
Are my guesses correct, that my circuit doesn't work because it requires more power than USB allows to supply without a proper negations? If so, what are the alternatives I can use? Would it work better if I used simple micro-USB instead of a USB-C?
Thanks.
UPD:
The breakout USB-C board I am using: https://www.pololu.com/product/2585
On the diagram that board seems to already have 5.1k Ohm pull-down resistors on both CC lines of a USB-C connector. Looking at the board it self, I think, I can confirm their existence.


texts: Why is a high value resistor necessary for grounding a MOSFET gate?

texts:
New to electrical engineering. I am following an introductory Cambridge university course but not entirely clear on what the lecturer is saying, and have nobody to consult because I am self-teaching this part of the course under huge time constraints.
The diagram here has RG. I understand that the gate acts as a capacitor in a MOSFET, due to a metal oxide layer, which gives it essentially infinite input impedance. So, why not just connect the gate to ground with a wire? This ensures it's not floating, as charge buildup doesn't occur. Furthermore, the lecturer says RG sets the value of the input impedance from infinite to a finite value (and so should be suitably large for use in an amplifier), which I don't understand, because there is still the capacitive property of the MO layer to consider. I also don't understand why an infinite resistance is a problem in a practical scenario.
I tried to find similar posts: Why is this MOSFET's "pullup" resistor necessary?
seems like it might have relevant points (especially on the idea of not being able to just connect VDD and VDS). However I feel like I'm missing lots of basic details.
Question about mosfet gate resistor
says a high value resistor 'avoids capacitive coupling driving the transistor when it is otherwise not connected', and 'It is common practice to place a resistor... from the gate to ground, just to be sure the MOSFET will be off if the thing driving it... is letting the output float. Otherwise, very small currents from your finger, capacitive coupling, inductive coupling, or other things you'd rather not worry about can change the gate voltage of the MOSFET, resulting in unintended behavior'. What does it mean to let the output float, and what is capacitive driving?


texts: MPLABX syntax cheker errors in ASM mixed with C

texts:
I'm using XC8 for a project in MPALBX using a PIC18F26K80 and I'm getting lots of Unable to resolve Identifier errors in the editor:

The code works compiles an runs correctly but the syntax checker in the editor is driving me crazy, highlighting every line in assembler with these errors.

I tried a bunch of things that seemed to make it better, like using _asm right after the #asm directive, but it always creates some other kind of error instead.

Is there a setting I'm missing or is this just a sorry state of affairs and I have to live with it?


texts: Limiting wired low frequency signal transmission

texts:
I'm now considering TDA5051A to transmit information over the 230VAC power network. To avaid any interference between neightbours I will need to stop transmision beyond the appartment electrical network.

As I understand from its datasheet the transmission will be at the frequency about 132 kHz. From my point of view it will be enough to place some filter (i.e. place a ferrite bead at the apartment main inlet). But I'm afraid that this can suppress the signal in the areas where I don't need any suppression.

Graphics:

T/Rn - Digital transmitter and receiver.

Ground and neutral wires are not shown here for simplicity reasons.

In real world there is a transformer between HV power line and an apartment, please consider the line on the transmission towers as a 230VAC line.

So the question is: if the conception is correct - what kind of filter I should use if the signal is 132 kHz and main AC frequency is 50/60 Hz?


texts: How to increase the current output of a function generator?

texts:
I was wondering if someone could help getting me started.
I want to build a current amplifier that can amplify ~60mA to 10A while keeping the V_out = V_in.
This will be used to switch a power MOSFET (Qgate = 4050nC, Vgs_max = 15V) on and off with a square wave at 10V_peak, 1 microsecond pulse width and 25% duty cycle using a function generator.
Currently, the function generator can output 10V/(50ohm + 100 ohm) = 67mA or ~200mA with just R_internal = 50ohm.
There are already similar posts regarding the topic. However, they are mostly for much lower frequency than I need.
Thanks in advance!


texts: Can a Bluetooth 4.0 BLE device talk to a Bluetooth 2.1 device at the most basic level?

texts:
I want to develop an app on an Apple iPhone, that has Bluetooth 4.0 BLE embedded, that talks to a basic piece of kit with a bluetooth 2.1 chip in it?

Firstly - is it technically possible - if I only use the most basic commands of 4 to just 'know' if the 2.1 device is present?


texts: How can I measure back-EMF to infer the speed of a DC motor?

texts: I'm interested in measuring the back-EMF of a motor to determine a motor's speed because it's cheap and requires no additional mechanical parts. How can I measure the back-EMF when I'm driving the motor?


texts: Controlling two 4 wire fans using Arduino

texts:
If I am controlling two 4-wired fans using Arduino PWM.

Can I control them using the same PWM signal as shown without transistors?

Also do I need fly-back diodes across +ve and -ve pins of each connector or only one fly-back diode or no fly-back diodes at all?

do I need to add 10 uF cap or so, across each connector to remove noise?


texts: Why is any lumped parameter system modelled with an ODE?

texts:
I'm studying Control Theory and the book jumps from a input-output representation of the system to a ODE model. Initially, the book derives that any causal system can be represented as:

\$y(t) = g(x(t),u(t),t)\$

Where x(t) is the state and u(t) is the input. Right after that, it defines a lumped parameter system as one where the state is a R^n vector and just assumes that:

\$ \dot{x} = f(x(t),u(t),t) \$

Does anybody have any idea as to why this is true?


texts:
I am trying to confirm a suspicion/understanding about electrical signals, and especially One-way CONTROL signals i.e. specifically NON-Power type signals in electronics like,

Trig/Echo pin in UltraSonic Sensor,
Digital IO line on an application specific IC/Sensors feeding into a microcontroller via high speed buses.
High Speed USB Camera connected via Serial Tx/Rx

which DO not EXPLICITY require a DEDICATED Ground (unlike power signal which requires a ground connection to function), but IMPLICITLY always return via Ground/PCB Ground Plane to the point of origin.
In short, what I am trying to confirm is that, no signal (control or power) is ever one way, and MUST find a way back to its origin to complete its journey. In practice, we observe this on PCBs with ground planes, as every signal will find its own path back, usually right under the trace, on the ground plane underneath.


texts: System Generator: How to configure the CORDIC divider block?

texts:
He all, I was wondering how should be the parameters fo the CORDIC divider block in order to get proper results.
In this example I´m trying to get 0.1/0.2 = 0.5 but I don´t get it and I don´t know why?
Please, does anyone know how to do it?
Thank you!!!

EDIT:
To take a look to the parameters of the CORDIC block see this question:
System Generator: How to configure the CORDIC divider block. Understanding the block parameters


texts: What does "Voltage Holding Characteristic Minimum" refer to for a supercap?

texts: In supercap datasheets (e.g. this, extract below) there is a column in the ratings table called "Voltage Holding Characteristic Minimum". What does this refer to?


texts:
I am trying to verify a design written in VHDL using SystemVerilog's assertions.
I have a problem when I have a non-defined signal'X.'
Just for example here is the code of a comparator:
entity FP_comparator_V2 is
port (
    comp_in1                    : in    std_logic_vector(31 downto 0);
    comp_in2                    : in    std_logic_vector(31 downto 0);
    less                        : out   std_logic;
    equal                       : out   std_logic;
    greater                     : out   std_logic
    );
end FP_comparator_V2;

architecture behav of FP_comparator_V2 is
   -- signal, component etc. declarations

begin
   -- architecture body

    process(comp_in1, comp_in2)
    begin
    if comp_in1 = comp_in2 then
        equal                   <= '1';
        less                    <= '0';
        greater                 <= '0';

    else
        equal                   <= '0';
...

   end if;
    end process;
end behav;

and the assertions
property FP_Comparator_V2_1_1;
@(posedge `assertion_check_clk29M4912 or negedge `assertion_check_clk29M4912)
    (fp_comp_intf.Comp_in1 === fp_comp_intf.Comp_in2) |-> (fp_comp_intf.equal);

endproperty

DS_3_4_69_1_1:
assert property(FP_Comparator_V2_1_1);
cover property(FP_Comparator_V2_1_1);

property FP_Comparator_V2_1_2;
    @(posedge `assertion_check_clk29M4912 or negedge `assertion_check_clk29M4912)
        (fp_comp_intf.Comp_in1 !== fp_comp_intf.Comp_in2) |-> (!fp_comp_intf.equal);
endproperty

DS_3_4_69_1_2:
assert property(FP_Comparator_V2_1_2);
cover property(FP_Comparator_V2_1_2);

When Comp_int1 and Comp_int2 have defined values the simulation works fine.
If one of them have an undefined value also works fine.
When both signals have an undefined value it gives an error.
For example:

Comp_int1= 48xx_xxxx; Comp_int2=47xx_xxxx
==>Equal = 1

I suppose it compares bit by bit so Equal should be '0.'
Please if you know a book or a website explaining the behavior of signals after synthesis or the logic behind undefined signals I would be thankful if you put it in a comment.


texts: Is there a motor designed to be constantly overloaded?

texts:
So I'm very, very new to electronics so this may be a really dumb question but here goes. Is there a motor that either a. is designed to be constantly overloaded or b. run in such a way that overloading it will not cause it to fail?

Here is the thought experiment that I would like to solve. Imagine an electric winch towing in a truck with say 1,000 lbs of force, though capable of towing in with let's say 10,000 lbs of force total. The truck is just in neutral and not providing any force in the opposite direction.

Now, imagine that the truck was put into drive and started pulling on the winch with a force of 1,100 lbs of force. In this situation the winch would be overloaded (is that the right word) and the truck would start to increase it's distance away from the winch.

Next, imagine the winch being able to sense this increased force by the truck (let's just assume that this is possible through the use of other sensors and microcontrollers) and then automatically increases it's towing force to 1,200 lbs. At this point that truck will now be pulled back in towards to winch.

Let's assume that this push and pull process continues indefinitely until the truck runs out of gas and is eventually towed all the way in. Also, let's assume that the force the truck exerts in the opposite direction NEVER exceeds the maximum 10,000 lbs total towing capability of the winch. Also, let's assume that the winch should always exert a pulling force. Meaning that we should not ever have it halt even when being overloaded by the truck.

Are there such motors out there that can operate effectively under these conditions? In my mind it seems illogical that motors would be designed for these types of purposes but I'm not sure.

Anyways, despite being very, very new to electronics here is my current thinking on this problem. From what I've read simply overloading a motor isn't the problem, but instead the overheating caused by overloading is the problem. And any time a motor is overheated beyond specifications then failure can occur. However, if a motor is overloaded while operating at only 1/10th (or some other small percentage) of it's total capabilities then the heat caused by overloading will probably not be too much for the motor to handle, right?

Like, I said this may be a really dumb question but it's one that I'm curious about and could not find the answer to anywhere else. It could be that this type of action is impossible from a physics standpoint as well, but I'm unsure. Thanks in advance for the help!!


texts:
Why does the change in poles does not affect the torque?
Even if number of poles increased the torque remained to be the same.


texts:
I'm designing a circuit that uses an optocoupler to isolate a relatively noisy H bridge from the USB circuitry also present on the board. Clearly in this case I will have two grounds - what is the norm for dealing with these in terms of ground planes?

My initial thought is to have 2 ground planes, 1 on the USB side and 1 on the H Bridge side of the board (isolated from each other), but could this cause problems with capacitance if one of the grounds were to rise above the other?


texts: Finding maximum source impedance for A/D converter (SAM3X8E ARM Cortex-M3)

texts:
I would like to find out what is maximum recommended source impedance for A/D converter on Atmel SAM3X8E ARM Cortex-M3 microcontroller.

I tried to follow the example of this excellent answer, which also explained the maximum recommended source impedance for Atmel AVR 328P MCU (being < 10k). There are even quotes from datasheet in the linked topic, giving this answer specifically. Therefore I also checked the Atmel SAM3X datasheet, hoping to find this information. But I had no luck spotting the answer from page 1317 onwards, which deal with ADC.

I might add that I intend to use 12 bit resolution capability of the ADC.

How should I be searching for this information and where to find it?


texts: Heater - how to define power needed taking into account air thermal dissipation

texts:
My objective is to heat a liquid inside a bottle. I have a air gap of 2 cm between the bottle and the heating element (resistive layers).
The heater and the bottle is surrounded by a bottle insulator, so the volume of air to heat is fixed.
I did the calculation to know how many power I need in order to heat my liquid from 18°C to 37.5°C in 5 minutes with these formulas, taking into consideration weigh of the bottle, delta temperature and specific heat of glass material.
Q = cp * m * dt

Q is heat required (kJ)
Cp = specific heat (kJ/kg K, kJ/kg°C)
Weight of bottle and liquid inside (kg) = 750 g

Then I deduced power needed:
P = q / t

P = power (kJ/s, kW)
T = time (s)

P = 9.75W
My questions now are:

How can I calculate the thermal dissipation between my heater physical element and my bottle of liquid as I have a air gap of 2 cm between both elements
How can I deduce the real power I need with my heater element to be able to heat my liquid ?
What is for you the best solution to heat my liquid in term of heater technology ?

I looked on google and I was able to determine my R factor for the whole assembly = 0.5 (due to air which is playing as insulator).
But it's really hard to understand how to do this calculation and the steps of the calculation...
Can you help me ?


texts: Attempting to Understand Transistor Specs and Pick One

texts:
I'm trying to find a transistor that will power on with very low input. The entire circuit is running on 3.3 V, DC and needs to use little current (Max 50 mA). The resistance between the power supply and the "base" of the transistor will vary between 50kΩ to 120kΩ when on. Here's an image showing the circuit:

In the image you can see 2 of 4 sections that will be present. They are all the same.

What transistor should I use?


texts: What is the "DanTherm" model in the SOATherm library in LTSpice?

texts:
LTSpice's SOATherm symbol has a "user-defined" option in the models list but I can't find any documentation on how to use it.  Out of curiosity I opened the .lib file and there is a user-defined model listed with the following parameters:
.subckt UserDefined D G S D2 G2 S2 Tj Tc

* The following two lines are customized for each DanTherm model *
.param Tambient=85 RthetaJA=50 Cheatsink=0
.param Imult=0 Iexponent=0 R6=0 C6=0 R5=0 C5=0 R4=0 C4=0 R3=0 C3=0 R2=0 C2=0 R1=0 C1=0

It seems I could define these values using a .param statement in my simulation - problem is I have no idea what the "DanTherm" model is.
So far Google has found what seems to be an HVAC brand by this name, but nothing about thermal modelling.  Is anyone familiar with this model?


texts: Why does my 2N7000 show a gate current of more than 4mA?

texts:
I have the following circuit:

simulate this circuit – Schematic created using CircuitLab

The D1 is in fact a character LCD backlight (with 4.2V input voltage and a maximum current of about 300mA). R2 is a peculiarity of my test setup, where I control the gate voltage using a potentiometer.

When measuring the current into the gate, I find that my multimeter shows 4mA to 5mA. The current drawn by the LCD with R1(*) in place like that is about 90 mA.

I wonder why there is such a large gate current. The datasheet of the 2N7000 suggests (but I might well be reading it wrong) that there should be a maximum of 10nA of gate current.

I tried the setup with two different voltage sources: A lab supply current-limited at 500mA and, after making sure that the setup doesn’t draw more than 100mA in total, 5V from my computers USB port. Both have shown the same behaviour.

(*): Don’t nail me on the value of R1. R1 is constructed of four 10Ω resistors in parallel, each with a tolerance of 10%. I just now measured 4Ω (8Ω before changing batteries on the multimeter) for that construct.


texts: Opamp creating a DC offset at high frequencies

texts:
I am measuring a 4th order filter that consists in the cascade connection of two biquadratic Rauch sections.
All my measurements went well except when I try to measure signals with high frequency (4 kHz.) Then the measurement "gains" a negative DC offset.
Is this because of some internal capacitances of the opamp?


texts:
I need to design a circuit that will operate in a car, and the circuit needs to know when the vehicle is turned off. The circuit will run from its own battery, and it will basically be an alarm to alert a driver he/she needs to remember to do something before leaving the vehicle. I originally thought to just plug into the cigarette lighter, as most modern cars shut this down when the engine is stopped. But some do not, and in that case my intent was to just sense whether any AC (from the alternator) was riding on the DC. So now, if the DC voltage goes away, OR its AC component goes away, I can assume the engine has been shut down. Now there will be some cases where my circuit won't be usable, and I'm just trying to identify and minimize these cases. An electric car, for example, will shut down at a stop light, so if that car normally supplied voltage to the lighter socket when the whole vehicle was shut down, my circuit would not be usable in that case. I'm also not sure at all how cars with 24 or 48VDC batteries handle their lighter. They may use 12V regulators or switching supplies, which means I'm never going to detect an alternator through that.

So the questions are, what bases have I not covered, and are there any solutions to the NFG cases I'm missing.


texts: Question concerning equivalent capacitance

texts:
For the question above, i'm confused as to why the 6uF and 3uF capacitors have the same charge.

Also, for part b, would you have to find v(t) at the 10uF capacitor? If not, what would be the other approach?


texts: enclosure fabrication resources for the upscale hobbysist

texts:
I recently saw a beautifully made 1RU 8Ch microphone pre-amp that was in a beautiful enclosure with a  very pro looking faceplate and so on. The engineer
wouldn't share who made it for semi-obvious reasons.  This was the only pic I could find. Does anyone know where you can go for pro looking enclosures that don't completely break the piggy bank?


texts: Which type of surface finish to use for low-temperature SMD soldering?

texts:
I have designed a two-sided (components on both side) 4-layer SMD PCB that I will reflow with my solder oven. To do so, I am planning to use high-temperature leaded solder (MG Chemicals 4860P, ~250 C) on one sided and then reflow the other side with low-temperature silver-based solder (Chipquick SMDLTLFP15T4, ~165 C). Reference to the idea: https://www.instructables.com/id/Making-double-side-boards-in-reflow-oven/
I noticed earlier that the Chipquick solder does not want to reflow or stick to the PCBs I normally order from PCBWay or JLCPCB with HASL (leaded) finishes (default). The leaded one reflows extremely well.
I was wondering what type of surface finish would be optimum for both types of solder. Surface finishes offered are: HASL with lead, HASL lead-free, Immersion gold(ENIG), OSP, Hard gold, Immersion silver(Ag), ENEPIG and None(Plain copper).


texts:
I have a US-style power strip that is thin enough that plugs can overhang the edge. It is easy to do this accidentally.

I think that if you were to overhang a plug, and then accidentally touch the plug with one hand and a grounded object like the radiator pipe with the other, you would be creating a circuit like:

The safety page on my oscilloscope manual warns that 30 V AC (rms) can cause a fatal 30 mA AC (rms) current through a human body, so presumably the 120 V AC wall power can drive 120 mA AC; at which point the average resistance of the human would be 1 kOhm. If the appliance were a 60 W light bulb, it would be 240 Ohms, reducing the current to 97 mA AC, still fatal.

So, my best guess is that this power strip is unsafe. Is this correct?


texts: Concatenation with shift operator on concatenated array

texts:
I am relatively new to SystemVerilog and have found myself having to dig through quite a bit of it for work. I have come across a statement as follows:
module Foo (
    output logic [65:0] data_out;
);
logic [65:0] block;

// do stuff

assign data_out = {<<{block[65:0]}};
endmodule

I cannot find any description of the use of the << operator within the concatenation as in the assign data_out = ... line above.
Opening up ModelSim and simulating the following dummy code,
module test_module;
  logic [7:0] data = 8'b11110000;
  logic [7:0] data_out;
  initial begin

    for(int i = 0; i < 8; i+=1) begin
        $display("data[%0d] = %b", i, data[i]);
    end

    assign data_out = {<<{data[7:0]}};
    for(int i = 0; i < 8; i+=1) begin
        $display("data_out[%0d] = %b", i, data_out[i]);
    end

    $finish;
  end
endmodule

I see the reported output:
# data[0] = 0
# data[1] = 0
# data[2] = 0
# data[3] = 0
# data[4] = 1
# data[5] = 1
# data[6] = 1
# data[7] = 1
# data_out[0] = 1
# data_out[1] = 1
# data_out[2] = 1
# data_out[3] = 1
# data_out[4] = 0
# data_out[5] = 0
# data_out[6] = 0
# data_out[7] = 0

It seems that the {<<{...}} line has somehow swapped the endianness of the data array. Is the behavior of the {<<{...}} syntax somewhere described?


texts:
I have already asked this question in the ADI forum, but I haven't got the answer yet, so I will just copy the question below. I hope somebody could help me with it.

I want to use AD8310 for measuring very low amplitude DC voltage in high dynamic range. I connected AD8310 to differential output of ADL5391. With potentiometer connected to OFLT pin of AD8310 I trimmed input ofset for gaining maximum dynimic range. BFIN pin is unconnected. Everything works fine but I cant understand why slope for DC coupling is 480 mv/decade whereas for AC coupling 240 mv/decade, it narrows dynamic range twice. Is it possible to make slope 240 mv/decade for DC coupled connection?

https://www.analog.com/media/en/technical-documentation/data-sheets/AD8310.pdf


texts: Will multimeter show a voltage in an electric field?

texts:
I think that it won’t because there is no current entering the meter with which it can measure. Correct?

Also, is it the same reason why the meter won’t show a reading even though one probe is in air and one is at a battery terminal?


texts: How does a first-timer set up a correctly-grounded workbench / work-station?

texts:
I'm new here, and new to electronics in general. (for the most part … my [awesome] father had me building some simple Heathkit robots and panels with him when I was a kiddo, but I'm getting into it “4srs” for the first time right now.)

I've been doing a lot of research, a lot of reading, and trying to build a base of fundamentals … and meantime, before I know enough to actually start building anything, I've been putting together a simple workbench for myself with all the necessary tools. I've learned a lot, but the following still puzzles me:

How do I ESD-safe my working- / soldering-station, in general? What general advice (as well as specifics!), can you give me? (This is all especially important, as my home-lab is an extra bedroom with carpeted floors, I'm temporarily working on a folding table with horrible resin-polyethylene tops, and I live in a dry climate! I get shocked all the time, and I'm pretty sure I'll fry basically any IC I touch, if I don't get this all nailed down right from the start.)

For example, some specific questions:

To what do I connect the grounding-setup, as a whole? (The mat, or the wrist-strap, or whatever.) I've been told everything from a water-pipe (would have to run a wire to the ceiling, there's nothing down low in the room), to the center-screw of a wall-outlet (really!?) … and, practically-speaking, how do you suggest I do so? Wrap a bare/stripped copper wire around the screw, or around the pipe? Or what?
I know I should be working on an ESD-disappating mat, with an ESD-disappating wrist-strap on at all times. To what do I connect these? Do I connect them together, i.e. to a common point, as well? (From my still-fledging understanding, there should be a single shared ground amongst all points in the circuit, which I suppose includes your body if you touch a conductive part of the board, so …)
Is the “ground”, as discussed in terms of dissipating triboelectric potential / electrostatic charge, the same as the “ground” in circuits I'm working on? i.e. should I be connecting “ground” in any circuit, with a wire, to the same grounding-system we're discussing here? Or is that a separate ground? I've also got a bench power-supply with a ‘ground’ banana-socket, which I'm sure will be used for circuits, so I suppose … if the answer here is yes, I should wire that to this common-ground as well?
The bench multimeter I've acquired has a grounding screw on the back, next to the three-prong power-plug. Should that grounding-screw also be wired to the common-ground discussed here, i.e. the same as my wrist-strap? (Also, why the hell is there two grounds on that, then; one as a screw, and one as the third prong in the power-cable?)

(Edit: P.S., I'm speaking here of grounding in terms of protecting circuits sensitive components, and precise measurements, from ESD. Not of safety-related grounding involved in high-voltage or high-current applications. That's outside the scope of my goal, here.)


texts: Is it possible to extract pcb layout from an already made PCB?

texts:
Is it possible to remove all the components from a PCB, take pictures of it, and use any software to extract the PCB layout, or at least make a copy of the same layout?

If so, which softwares can do this?

If not, what other way can I copy the same design.

Note: The PCB design is my own. It is a complex 2-layered PCB, but I have lost all the Schematic and PCB layout files from my computer a long time ago.


texts: Replecating Multisim simulation in Altium simulation set up and probset up issues

texts:
For uni we were asked to get familiar with NI multisim and after having a look at the website, I got to wondering if I could achieve the same simulations in Altium. So I recreated a circuit that was given to me in an NI Multisim tutorial in both; however, for the life of me I can't get the same simulation results in Altium. I have put the layout and results (I am using transient simulation) of both below. What am I doing wrong?
Multisim:

Altium:


texts: PCB chip/trace antenna located away from board edge?

texts:
I'm looking to design a system that will require a 2.4GHz antenna. The only problem is, every single reference design I find has the antenna situated on at least one board edge. Unfortunately due to the nature of the design I don't have a board edge available.

Is there any reason I couldn't have the antenna in the center of the board if I ensure the surrounding area is well grounded?


texts: How is power consumption from a battery controlled?

texts:
Sorry if this is a amateur question, but I don't understand how to control power from a battery. If you just wire it up to the load, it seems it will draw the fastest possible current, possibly burning out the device.

A lead-acid battery is powering an electric motor. The question is, how to throttle the power so that I can run this motor at different speeds?

Example: 62 cells in the battery. Each cell is rated for 5,530 amps over 68 minutes, or 565 amps over 20 hours. Average voltage is 2.0 V.

I want to be able to choose the fast or slow discharge rate. What is the device that allows me to do this? Btw I took those numbers from a submarine example, Type XXI, but you have to go to the German version and use google translate to find the good data.