texts: Using a MOSFET or BJT instead of solenoid

texts:
I'm trying to convert all relays and solenoids to transistors in a circuit to make it solid state. I have a small (150cc) 12V DC starter motor that is currently turned on by a small transistor turning on a solenoid, but now I want to use a larger transistor to be able to do the solenoid's work.

Would there be anything wrong in doing this? I realize I need to measure the motor's current draw while it is under load to pick an appropriate sized transistor. If this would work, would you recommend a MOSFET instead of a BJT for this application? I should also put a 1N4007 flyback diode on the motor's terminals as well, correct?

Thank you for your input.


texts: Are there flaws in the reasoning behind the Zedboard bypass scheme?

texts:
There is an eval board for the Xilinx Zynq-7000 FPGA called the Zedboard. When you look at the board you will notice a very interesting pattern of bypass capacitors. The designer has a technical note that explains why he/she thinks this is a good way to do bypass for a board like this.

Are there any flaws in the reasoning behind this bypass capacitor scheme?

Disclaimer: I will not answer my own question, as I really would like other experts from this community to bring their knowledge to the table. But I may do a measurement some day to find more facts - and may blog about it + add that here.


texts:
I'm looking for some simple schematic for movement detection.

I want to use it with a small hobby project of my own to detect if someone is moving the box, doesn't matter the direction. I'm looking for simple and (preferencially) cheap.

I'm not looking for accelerometers or gyroscopes. The most simple solution that I've found for this is a tilt switch, but I couldn't find if it's the simplest solution.

EDIT

I've found out that piezo sensors are also used as a vibration detector: What's the cheapest way to detect vibration with Arduino?

Do you think that it could work for me? In this case, the piezo could be attached to the plastic box.

EDIT 2

Following @Kortuk advices, here's the original idea and the one I want to be able to do:

I have a box with my system inside (in this case MCU, bluetooth and a USB connector). The box doesn't exist yet, so I don't know which kind of box could it be, this is just an hobby project to play with stuff that I've never played before.

My goal it's to have a pin that will be active when someone moves the box, and that could be change it's place, tap it or even moves the table where the box if. I have no problems with some false alarms, if the box it's going to be attached to a wall and some guy starts drilling the wall, the pin could be activated too.

I'm looking for the simplest solution.


texts: Application of Ohm's law to a single resistor and to a series circuit

texts:
For any given resistor following Ohm's law say a carbon resistor, it's resistance is independent of the value of current and voltage.

However, say we had a 5 ohm resistor in a circuit with a 10V battery. Ideally, the 10V potential would be dropped entirely across the resistor. This 10V potential is the work that would be done to move a 1C charge around the circuit by the definition of potential.

But, if say I connected another 5 ohm resistor in series with this, the drop across each resistor would reduce to 5V. How is it possible that for a given resistance whose value doesn't change (at relatively low current values) the work done to move a unit positive charge changes? After all resistance is the obstruction offered to the flow of current and hence the energy required to overcome this opposition for a given amount of charge should always be fixed?

 What aspect of this reasoning is incorrect? The only thing I could thing of would be that we are dealing with potential energy instead of potential since that would make since due to varying current leading to a reduced amount of charge and hence reduced potential energy. But I'm pretty sure that goes against the definition.


texts: Virtual ground circuit won't work as expected

texts:
I need a split rail circuit for a 741 op amp.

The circuit can be found here:

or here (the latter can be simulated).

I have simulated the circuit in three different programs an it always seems to work. However, when I build the circuit on the breadboard, it doesn't work. With 9V DC supply instead of getting 4.5V, 0V and -4.5V I get 9V, 4.5V and 0V. It seems as if the caps weren't even in the circuit. I checked the polarity and the value of the caps and even used different ones. Still don't get any virtual ground, the circuit acts as a voltage divider. A photo of the breadboard circuit is here:

The circuit is damn simple, it puzzles me why it doesn't work. Again, I checked polarities, power, etc. Any help would be appreciated!


texts:
I've been using these batteries for a long time and I've never seen such a feature.

There's a band on its outer wrapping having two ends: The white circle on the left side and the another one on the right side (not visible because it's under my thumb):

If you press hard on those ends, a bar slowly fills up and shows the current capacity of the battery:

This one is a brand new battery, so it shows full.

I didn't even try Googling because of the risk of hitting a lot of fake information (I don't know why but I feel so). Anyway, I trust here, so I asked here.

Any ideas?


texts: Differences between Solid Region vs Polygon Pour

texts: In altium you can define polygon pouring or solid region. It seems both are doing the same things. What are the differences ?


texts: Is it really OK to supply more current than what the component is rated for?

texts:
In this heavily upvoted answer the answerer states that it is okay to supply a component with more current than what it's rated for. The analogy is that (paraphrasing here) "If Johnny wants to eat two apples, he'll only eat two regardless of whether you give him three or five, etc."

However, one of the most basic circuits you can possibly make is to power an LED from some power supply. Since most power supplies provide a current that is higher than what most LEDs can handle, you must put a resistor in front of the LED in order to not burn it out.

So which is it?!? Can someone explain to me when/where/how it is/isn't okay to provide higher (and lower, for that matter) current than what a component is rated for?


texts: what will happen if the motor that is designed for delta connected in star connection

texts: I have a motor which is designed for 3 phase, 380V. The power rating of motor is 132kw and motor stator winding is connected in delta connection. If I connect the same motor stator winding in star connection with same 380 V line voltage, what will be the impact on motor line current and power rating of the motor.


texts: Can I use a 9 V power supply instead of 12 V for my piano keyboard?

texts:
I have a piano keyboard, the manufacturer says that it needs 12 V.
My original mains power supply (adapter) is not working and I only have another 9 V power supply.
Can I use it without risk?
Thank you

Here is an image of both power supplies (adapters):


texts:
For my project, I need to measure AC current for a 220V load (a more detialed description of the initial approach and problems can be found here.
I'm using an ACS724 for +/-5A; the next step will be to feed its output into a RMS-to-DC converter, more specifically an Analog Devices LTC1966.
With a DSO I tried to get an idea of the signal that comes from the sensor, and I get this :

No load connected (all wires entirely disconnected from the board)
With load connected

Which is pretty much as expected, except for the noise. The measurement for the 'load connected' case seems to be the sum of the right sine wave for the load and the 'no load connected' noisy signal.

Is this normal?
Do these sensors need additional signal conditioning?
If yes, how?
Is it possible to digitally compensate for this noise once the signal is measured by an ADC?


texts:
I'm making a photodiode circuit, but the voltage drop across the photodiode is constant no matter what light levels it's in. Is this just a faulty photodiode or could it be some problem with the configuration of resistors? It sounds like a problem with the photodiodes, but it's happened with 2 separate PDs, which makes me hesitant.

The datasheet was wrong and it turns out I had it in the wrong way. Thanks for your answers though!


texts: Current between batteries facing wire with same pole

texts:
I have just started learning about electric circuits, so I hope you'll be patient :)

I am trying to solve for the current \$I\$ in the problem below, but (after much googling and reading) I cannot figure out how the current behaves between \$E_1\$ and \$E_3\$.

I discovered that \$-12+15i+25i+17+30i+10i-20+4i+6i=0 \implies i=0.17A\$, which is correct, but I cannot explain why \$30i\$ and \$10i\$ are positive.

Could anyone explain this to me, please.


texts:
I'm going to connect 12 potentiometers (100k) to a couple of cd4051 analogue (8->1) multiplexers and to 2 of Arduino (Uno) analogue pins.

Now I think each pot draws 0.5mA (I'm going to measure it to be sure) so around 6mA for all 12 pots. I think it is ok the Arduino permits 200mA as I know.
Also I read that it is recommended to use 10k potentiometers (because of the ADC) but I have also read that the 100k are going to work.
So is there anything I miss here? (before soldering all the power and ground terminals). (the multiplexer in the schematic is a single module)

simulate this circuit – Schematic created using CircuitLab


texts: Schmitt trigger low threshold calculation

texts:
I have this classical Schmitt trigger circuit from an old Elektor magazine.
It describes the following, when U1 is lowered (from a high state):

If the right transistor cuts off entirely and the left transistor is completely turned on, then there is on the emitter resistor about 9V / 11 = 0.8 V. Then one should add the BE-voltage, that the left transistor needs to conduct. The low threshold is thus 1.4V.

Where does the number 11 come from? Why does one need to add the emitter voltage to the BE-voltage?


texts: Altium: Using Find similar object to change all designator fonts at once

texts: I am trying to use Find similar object in Altium designer to change all designator font in my schematic at once. First I Right-click on any designator on the schematic and select Find similar object and Ok. this makes all designators in the sheet to be highlighted. Sch inspector is opened and I select FontId to change the required font. Later I expect that all designator fonts will immediately be changed but actually nothing is happened, Why?!


texts: Implementing a constant current source circuit that can be switched off by a voltage signal

texts:
How do I implement a constant current source circuit that is able to output 10mA constantly, ideally the load of the circuit would be a 100uF capacitor in series with 100 Ohms.
Is there a way to then have the current source switch off with voltage signal given to it?


texts:
Hi, I need a circuit to convert a linear ramp to an exponential curve, as shown below.
Can anyone help?

These are simple voltage ramps, not periodic waves.
Thanks


texts: NFC/RFID device sending URL to NFC-enabled smartphone at 20-30cm

texts:
I am very new to this so please bear with me.
I have read many questions but I haven't quite found a suitable one for what I would like to do.

I would need a NFC/HF RFID device able to send an URL to a NFC-enabled smartphone (with no app or extra-antenna installed) from a distance of about 20-30cm.
In case reaching 20-30cm distance requires 1-5W, I am happy to consider powered tags/devices.

Looking forward to hearing from you!


texts: Difference between Voltage source and Current source?

texts: So what's the difference between a Voltage source and a Current source? Aren't they the same? Because after all they are related with the formula \$V = IR\$. So it means that If we produce a voltage, there should be a current and vice-versa. So really what's the difference?


texts: Is resistor needed to drive NPN Transistor from EEPROM

texts:
I am using this EEPROM in read mode: http://ww1.microchip.com/downloads/en/DeviceDoc/doc0270.pdf

And am using this transistor: https://www.onsemi.com/pub/Collateral/P2N2222A-D.PDF

I need my EEPROM I/O to be connected to other loads, so I am using the NPN transistor in a switch configuration. However, I am unable to find the max current supplied by the EEPROM so I am unsure if I need to put a resistor in between the EEPROM and Base. (If resistor is too high the current supplied by the EEPROM won't be sufficient to drive the NPN transistor). So do I need a resistor? The load I am attempting to drive is a 555 timer.


texts: Verilog - Referencing Flattened Busses in Module Instantiation

texts:
I have a verilog gate-level netlist generated by Synopsys Design Compiler.

DC was directed to flatten all busses and ports when creating the netlist, and the module declaration is given below:

module DES_SBOX1 ( CLK, \ptext[5] , \ptext[4] , \ptext[3] , \ptext[2] ,
    \ptext[1] , \ptext[0] , \key[5] , \key[4] , \key[3] , \key[2] ,
    \key[1] , \key[0] , \ctext[3] , \ctext[2] , \ctext[1] ,
    \ctext[0]  );

My problem is that when I go to use this module in a testbench, I receive syntax errors because I am not sure how to reference the ports names (because of the back-slash.)

Here is an attempt at instantiating one of these modules:

DES_SBOX1 feistel( .CLK(CLK_tb),
                 .ptext[5](ptext_tb[5]),
                 .ptext[4](ptext_tb[4]),
                 .ptext[3](ptext_tb[3]),
                 .ptext[2](ptext_tb[2]),
                 .ptext[1](ptext_tb[1]),
                 .ptext[0](ptext_tb[0]),
                 .key[5](1'b0),
                 .key[4](1'b0),
                 .key[3](1'b0),
                 .key[2](1'b0),
                 .key[1](1'b0),
                 .key[0](1'b0),
                 .ctext[5](ctext_tb[5]),
                 .ctext[4](ctext_tb[4]),
                 .ctext[3](ctext_tb[3]),
                 .ctext[2](ctext_tb[2]),
                 .ctext[1](ctext_tb[1]),
                 .ctext[0](ctext_tb[0]),
                );

...and here is the error message from Modelsim PE:

** Error: C:\Users\Kristin\Desktop\des_feistel_90nm\testbench.v(14): (vlog-2730) Undefined variable: 'ptext'.

** Error: C:\Users\Kristin\Desktop\des_feistel_90nm\testbench.v(14): near "[": syntax error, unexpected '[', expecting ')'

I've also tried using the back-slash in the instantiation itself, like so:

 .\ptext[5](ptext_tb[5])

..but this also gives a syntax error.

I'm wondering what the significance of the back-slash is in the first place?

Any ideas of how to correctly instantiate this module are greatly appreciated.

Thanks in advance!

-k


texts: Device is reset when switching power sources

texts:
I use a home weather station. It is powered by two AA batteries (2 x 1.5 = 3.0 V nominal). The problem is that it eats more than 1 mA and that is quite a lot of power and I must buy a new pair of AA batteries quite often. That's why I tried to connect the device to my computer's power supply, because the computer is turned on for many hours every day. I connected it using two low-drop Schottky diodes this simple way:

All connections (cables) and batteries are always connected to the device, the only changing part is that the computer is sometimes on and sometimes off.

It is only a partial success, as I face two problems with it:

I used a low-drop diode 1N5817 which should have only .25 V drop, but still the voltage seems to be significantly reduced, because the station's LCD display looks like the batteries are old even when they are new. (Old AA batteries have lower voltage than new ones. I have a lower voltage too due to the diode. The weather station apparently doesn't like that.)
The second and the main problem is that the weather station reset itself always on PC power-on. As I push power-on button on the PC, the weather station resets. And then works normally and its LCD display looks perfect. When I turn-off PC, the station switches to battery power and continues to operate normally without problems.

I understand that the first problem is caused by the diode. But what is the cause of the second problem? Is it something with the low speed of diodes? Are the batteries in device always shocked by momentary reversed current on PC power-on? Or does PC power supply which need some time to stabilize its output and the weather station goes mad because of momentarily receiving too high voltage? Can a capacitor help to fix that?

My limitation is that the solution must be simple and cheap enough otherwise it would be better to buy a new pair of AA batteries 4-6 times a year as I do now.


texts: ESD diode selection based on VCC of the IC

texts:
I have a question about TVS diode selection.
This kind of question is already discussed in previous questions.

ESD Diode - GPIO Microcontroller

Selecting a TVS for ESD protection

For protecting vcc line of a controller with nominal VCC = 5V, 5%, maximum vcc = 6V.
We normally choose esd diode with Vrwm=5V, for them Vbr = 5.8 to 7.8 and Vc = 12.5 to 15V (ESD9B5.0ST5G as a reference).

ESD diode manufacturer graphs also shows even though device is choosen from 5V operation, During testing, voltage across clamped can go up to ~50V(not sure can be lower but way higher than 5V), after some time they comes back to actual Vclamp voltage.

Is this ~50V clamping voltage is lethal to IC's(5V VCC pin)?

few answers i got it were first portion of ESD pulse where 8kV reaches is very low energy (few ns) and can't make much harm to IC's.
In addition to that most of the IC's have basic ESD protection (have esd protection diodes on all pins which will induct during high voltage events, designer's work is to limit the current passed to those diodes during transient event)

once this this high peak passed, higher pulse width portion comes which needs to be swallowed by esd diode.

we can't add series resisters in VCC pin of the IC, because it drops the voltage for the IC.

**

  So, in those cases just connecting ESD diode across VCC line is worth?

**


texts: way to display the data from a multi function meter

texts: I have a multi function meter and i want to collect the data and display it. My idea was to create a api for serial communication?? will the idea work or is there any other better way?? the meter uses modbus rtu rs485 protocol..


texts: VHDL synthesizing a module doesn't work, but simulating it does. Error: Bad synchronouse description

texts:
I am wondering why synthesizing this code doesn't work, but simulating does.
ONLY WHEN TRYING TO SYNTHESIZE I get the following error:

  Signal sig_enable cannot be synthesized, bad synchronous description. The description style you are using to describe a synchronous element
  (register, memory, etc.) is not supported in the current software
  release.

Here is my code:

architecture Behavioral of myModule is
signal sig_outSerial: std_logic := '1';
signal tri_output: std_logic := '1';
signal sig_enable: std_logic := '0';
signal sig_done: std_logic := '1';

component triBuffer
    port(
    input: in std_logic;
    control: in std_logic;
    output: out std_logic
    );
end component;

begin

U1: triBuffer port map(input => CLK_IN, control => sig_enable, output => tri_output);

process(tri_output, SEND)
    variable i: integer := 0;
begin
    if falling_edge(tri_output) and sig_enable = '1' then
        if i = 8 then
            i := 0;
            sig_enable <= '0';
            sig_outSerial <= '1';
            sig_done <= '1';
        else
            sig_outSerial <= inByte(i);
            i := i + 1;
            sig_done <= '0';
        end if;
    end if;

    if rising_edge(SEND) then
        sig_enable <= '1';
    end if;
end process;

outSerial <= sig_outSerial;
done <= sig_done;
CLK_OUT <= tri_output;

end Behavioral;


texts:
EDIT: I edited the question as it was my misunderstanding to think that the transistor was not getting into saturation.

I'm driving an LED with a microcontroller through a transistor with a PWM signal.

When the gate is grounded, no current flows, as expected. As soon as I start to drive the transistor (1% duty cycle), I get a voltage drop in TP8 of ~2V, with a 1% of the cycle at 0V. This turns the LED on at quite a high level of brightness, way more than 1% DC from the battery voltage would suggest.

As the duty cycle increases, the semiperiod at 0V at TP8 increases (as expected). The result is that VLED is something like (b), instead of seeing something like (a).

$$(a) Duty Cycle * 3.3V
\\
(b) DC_{value} + ((3.3-DC_{value}) * Duty Cycle)$$

My PWM frequency is rather low, as I'm using a low frequency clock to generate it, so it's only 128Hz, and I have an 8 bit resolution. The positive rail for the LED is the battery voltage, so it will vary from 4.2V to 3.XV. The MPN of the LED and the transistor are in the schematic (Transistor datasheet, LED Datasheet). The threshold voltage of the transistor is 2.1 in the worst case, so I can't see why is not fully switching.

Can somebody shed some light?

edit: I am expecting the voltage at TP8 to go to 3.3V, but it's 1.6V. If the pin is technically floating, why can't I measure 3.3V at TP8?


texts:
I am designing a Esp8266-based WiFi module and I'm not sure if I need one of those metal plates. They are suppose to protect a sensitive area from EMI/RFI, right? Also, how can I design one with custom measures and writing?

Here is an example:

This is with the shield on

This is with the shield removed


texts:
I am trying to control a brushed DC motor with PWM control through a MOSFET, below is the basic circuit for an idea. The PWM signal is given from a microcontroller to the gate driver IC which drives the MOSFET.

What is the nominal switching frequency? How to calculate the PWM switching frequency for this motor control circuit?

simulate this circuit – Schematic created using CircuitLab


texts: Can a single USB device emulate multiple USB devices?

texts:
I'm interested in the idea that my USB device can carry its own drivers.  I'd like the device the be plugged in, enumerated, and if a driver does not attach to it within a few seconds and initialize it, it also connects as a USB drive, and provides drivers on that drive.  Once the driver contacts the device, then the drive would be disconnected.

Do I have to design my device to be a USB hub, with two USB devices that attach and detach from that virtual hub, or does the USB specification have a way to allow this sort of design without pretending to be a hub?


texts:
I want to connect a 3.5mm trrs audio connector to sim868.

The image above is my connector.
But sim868 has four pins as:
1- MIC +
2- MIC -
3- SPK-N
4- SPK-P
As shown in the picture above, the pins of this connector are as follows:
1-S
3-T
2-R
6-SR
I want to use this connector both as a microphone and as a headphone.
Can someone clearly guide me how to connect the connector pins to sim868?
The connector has one MIC pin but the sim868 has two MIC pins, what should I do?


texts: Looking for a dc 2pin connector with latch

texts:
I'm looking for a pair of connectors with following features.

about 10V rating (no high voltage)
5A
2 pins
latch which will prevent from accidential unplug
panel mount

I want to mount the socket on alluminium scheet.

I dig through internet, but the only connectors which I found (which comply with above requirements) is BNC. Can you help me and propose something else?

I'm not sure if i can use BNC as about 4Amps connectors, it's kinda unproffesional.


texts: Rules on grounding on a PCB with low voltage digital circuit

texts:
What are the most important rules for grounding in a PCB? Can anyone explain with reasons?

We are making a PCB for electrical power systems in our project. It has high switching converters and some digital circuits too.


texts:
I have a question regarding USB2.0 power negotiation. I'm in the process of improving the design of a support equipment PCB that utilises an FT232H chip.

The layout of the current board consists of two separate Micro-USB connectors, one directly connected to the FT232H and the other directly connected to another device (essentially a pass-through).

The FT232H is used as a usb-to-serial bridge to communicate with a camera that is also powered off of this USB connection. I use the FT_Prog program to make the FT232H negotiate 500 mA of maximum power (the camera needs more than the standard 100 mA) and it all seems to work very well.

However I would like to simplify the design from two to one USB connector, meaning I'd like to use an on-board USB Hub IC. The question that I have is how this power negotiation performed by the FT232H will work when it is 'behind' a USB hub. (i.e. a Microchip USB2422) I've looked into datasheets of many hub IC's but none seem to talk about the up-stream power negotiation. Do hubs automatically request the maximum?

The only real difference I can find is self-powered vs bus-powered. However I'm unsure what the current limit is on the VBUS pin when it is self-powered.


texts: Getting wrong data from SPI Flash SST25VF010A

texts:
I'm trying to interface an mcu (tm4c123) with external SPI flash memory SST25VF010A.
I execute the Read-ID instruction, but instead of gettting BF and 49 (manufacturer and device ids) - I get BC and 41.

Reading the status register also gives weird results - on startup I get 0x8 and after executing the write enable instruction, I get 0xC.
Looking at the datasheet and boot up values, I would expect it to be more like the opposite - 0xC on startup and perhaps 0x0 after write enable...

Here is my code:

void ConfigureSPIFlash()
{
    MAP_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOD);
    MAP_SysCtlPeripheralEnable(SYSCTL_PERIPH_SSI1);

    // Enable pin PD2 for SSI1 SSI1RX
    MAP_GPIOPinConfigure(GPIO_PD2_SSI1RX);
    MAP_GPIOPinTypeSSI(GPIO_PORTD_BASE, GPIO_PIN_2);

    // Enable pin PD0 for SSI1 SSI1CLK
    MAP_GPIOPinConfigure(GPIO_PD0_SSI1CLK);
    MAP_GPIOPinTypeSSI(GPIO_PORTD_BASE, GPIO_PIN_0);

    // Enable pin PD1 for Chip Enable
    MAP_GPIOPinTypeGPIOOutput(GPIO_PORTD_BASE, GPIO_PIN_1);
    MAP_GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_1, GPIO_PIN_1);

    // Enable pin PD3 for SSI1 SSI1TX
    MAP_GPIOPinConfigure(GPIO_PD3_SSI1TX);
    MAP_GPIOPinTypeSSI(GPIO_PORTD_BASE, GPIO_PIN_3);

    MAP_SSIConfigSetExpClk(SSI1_BASE, MAP_SysCtlClockGet(), SSI_FRF_MOTO_MODE_0, SSI_MODE_MASTER, 125000, 8);

    MAP_SSIEnable(SSI1_BASE);

    uint32_t r;
    while(SSIDataGetNonBlocking(SSI1_BASE, &r)){}
}

unsigned char SPI_transmit(unsigned char data)
{
    SSIDataPut(SSI1_BASE, data);
    uint32_t r;
    SSIDataGet(SSI1_BASE, &r);

    return (unsigned char)r;
}

void main(void)
{
    ROM_FPUEnable();
    ROM_FPULazyStackingEnable();

    SysCtlClockSet(SYSCTL_SYSDIV_4| SYSCTL_USE_PLL | SYSCTL_XTAL_16MHZ |SYSCTL_OSC_MAIN);

    ConfigureUART();

    ConfigureSPIFlash();
    UARTprintf("spi flash ready\n");

    uint8_t res;

    // send Read-ID command
    GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_1, ~GPIO_PIN_1); // CE low
    SPI_transmit(0x90);
    SPI_transmit(0x00);
    SPI_transmit(0x00);
    SPI_transmit(0x01);

    // get response
    res = SPI_transmit(0xff);
    UARTprintf("received: 0x%x\n", res);

    GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_1, GPIO_PIN_1);  // CE high
}

Any idea what I'm doing wrong?
Thanks!


texts: What quantity changes when the signal is amplified without changing SNR in this case?

texts:
This is a conceptial question and I want o ask via an example in my mind. So I neglect any other factors which are possible for the sake of simplification. Let’s assume an analog signal through a channel can handle 1V variation and has a noise level of 1mV.

And lets assume this analog signal will be sampled by a 10 bit ADC which has 10V input range.

We can directly couple this 1V signal and sample by the ADC or we can amplify the signal by 10 and match it to the ADC range.

If we assume the SNR remains the same before and after the amplification, what do we obtain better by matching the signal to the ADC range by amplification? What improves? Can you give some insight by using my example?


texts: Sensor input calibration for wider range

texts:
I get minimum voltage output from my sensor as 2.2V and max voltage as 2.65V. I want to change this voltage to 0-5V range so that the controller ADC can calibrate input in a wider range.
How can I do that through a circuit?
The microcontroller is a PIC 16F877A.
Can someone guide me, please?


texts: "Overall frequency excursion del-f in MSK  is minimum frequency spacing between symbols 0 and 1 that allows their FSK representation to be coherently orthogonal". What is meant by being coherently orthogonal here?


texts:
I'm using a QC2004A 20 x 4 LCD (blue back ground/white text) with a PCF8574 I2C backpack in a GPS trip logger. I leave the trip logger in the car. When I start the car, the trip logger starts automatically. Everything works fine except on days when the car is hot inside. When first started up the LCD is all white (like if the contrast potentiometer is set incorrectly). As the A/C cools the inside of the car, the LCD returns to normal.

Is this heat slowly killing the LCD or will the LCD be OK?

The QC2004A data sheet I have shows:

Operating Temperature -20°C~70° (158°F)
Storage Temperature   -30°C~80° (176°F)

While the car is warm, I doubt the temperature exceeds the specs.


texts: Why MOS transconductance is not zero even when drain current is constant?

texts:
I am trying to plot transconductance \$ g_m \$ of the MOSFET below when \$ V_{gs} \$ varies from 0 to 1.8V.

The schematic is below. The drain current is fixed to a constant DC value 1uA by a current source.

From the definition of transconductance \$g_m = \frac{\partial I_{ds}}{\partial V_{gs}}\$  and with this case \$I_{ds} = 1 \mu A \$ and is a constant current so \$g_m \$ should be zero.
However, as seen from the plot gm is not zero at all.

I am running DC anaylysis and plot \$ g_m \$ from the result browser in Cadence Virtuoso.

Could anyone explain why \$ g_m \$ is not zero in this particular case?

PS. I added other curves:


texts: Quantifying white noise with a spectrum analyzer

texts:
The setup of my problem is as follows. I have an experiment in which I want to apply a noisy voltage with a white (flat) spectral density over a large frequency range, say 0 to 7 GHz for example. Not only do I want it to be white, I want to be able to tune its amplitude A. I plan to do so by using an AWG and generating Gaussian noise with zero mean and a variance of square root A; one can derive that for gaussian noise with a vanishing mean

$$S(f) = \sigma^2 = A$$

Moreover, I have access to an AWG with a sample rate of up to 50 GSamples, so the frequency range should be attainable as well.

One problem I now have however, is that I need to quantify how well the amplitude I set on the AWG actually corresponds to what is produced. This is because I do not actually generate a new time trace with different amplitudes, I simply produce 1 trace (I can make it 16 Gpoints long) and I change the peak to peak voltage it places the points into. That makes it a bit unintuitive to see what V_pp corresponds to what A.

So my idea was to use a spectrum analyzer and simply measure the spectral density that is being output for a specific V_pp. It'll allow me to verify that the spectral density is actually flat as well. So this is what I started doing, but I am running into trouble due to my limited understanding of how to operate the spectrum analyzer.

The problem is that I do not know how to choose the resolution bandwidth and the video bandwidth in such a way that the resulting spectrum is as accurate as possible. What I mean by that is that, by changing these bandwidths, the actual amplitude of the spectral density measured by the spectrum analyzer also changes, quite considerably. So how do I decide which values make the most sense?

From what I read about the spectrum analyzer, the resolution bandwidth allows for the discrimination of signals with closely spaced frequency components. So as my noise is supposed to be white, should I make this bandwidth as small as possible, to discriminate as many frequency components as possible?

Similarly, the video bandwidth determines the capability to discriminate between two different power levels, as far as I understand. Should this then also be set as low as possible?

It seems obvious to me that my interpretation of the above cannot be correct, as in that case most scenarios would simply boil down to setting these bandwidths to low values. There has to be something more nuisances that I am missing, and this is what I am asking your help for.

As an aside, I will be applying the voltage to a resistor to produce a current, which will be used to produce a flux, which will be sent through squid loops in a Josephson junction. So I suppose there is also the question of if the noise the spectrum analyzer sees (both in the frequency domain and the amplitude domain) is trivially related, or if there are filters and such which complicate things entirely. However, I think at this stage this is not too important. Knowing exactly what signal I sent in is a good starting point before thinking about what arrives.


texts: Why does my O-scope show capacitor charge starting negative?

texts:
My wave generator has a 50 ohm output impedance. I'm using a 10kohm series resistor and a 100nF capacitor. I calculated the RC time constant to be (10050)(100E-9)=1.005ms. A safe value for charging and discharging should be 5*(time constant), so 5.025ms. My function generator has a square wave with a duty cycle of 50%, so I want the full period to be 2*5.025ms=10.05ms. This corresponds to requiring a frequency < 1/10.05ms, or f < 99.5Hz.

So I set my wave generator to: Square, 50% Duty, 99Hz, 2.5V Amp, 2.5V Offset:

Now when I look at the voltage across my capacitor on my oscilloscope, instead of it starting at 0v and charging up to 5v, it shows that it starts at -2.5v and charges up to 2.5v.  The circuit simulator I compared it against, however, shows that it goes from 0v to 5v like I expected, with the same source of 2.5v amplitude and 2.5v offset.

So why is my o-scope showing -2.5v to 2.5v across my cap instead of 0v to 5v?


texts: Use Sainsmart SSR to control AC outlet with Arduino?

texts:
I am looking for a way to control an AC outlet with my Arduino Uno.

I have looked around and found the following: http://amzn.com/B0057OC66U

I heard you can use this to control 16 AC outlets with this an arduino but I have not found any sites that explain how to do this. How can I do this? If possible, please explain for a beginner.


texts:
A common question, here and elsewhere. Is C++ suitable for embedded systems?

Microcontrollers? RTOSes? Toasters? Embedded PCs?

Is OOP useful on microcontrollers?

Does C++ remove the programmer too far from the hardware to be efficient?

Should Arduino's C++ (with no dynamic memory management, templates, exceptions) be considered as "real C++"?

(Hopefully, this wiki will serve as a place to contain this potential holy war)


texts: Multi channel variable speaker design problem

texts:
As part of my my consideration of possible solutions to my multi channel variable speaker number problem arising from my attempts to restore radio functionality to an old hotel intercom system (see previous post on the subject if interested) I have been considering how to distribute say three audio streams delivered to multiple locations (by way of three/four cores per location), where a switch at those locations can be used to select an audio line.

My inexperience is leaving me slightly unsure of what approach to take in terms of the big picture / over all design. Basically what I want to achieve is this...

BUT... I want it for many (10+) rooms (the room being the right hand side of the diagram, where the switch and speaker is).

The problem is this leads to a design that looks more like this:

That's three 'rooms', but with a maximum design consideration of 4 audio channels and 13 'rooms' this means over 50 amplifiers. Small amplifiers are cheap, but still, I can't help feel it's a bit of a mad design!

Trying to come up with something more sane, I considered this:

BUT... The system should obviously survive usage, and here the impedance of the load applied to the amplifiers will change dramatically as variable numbers of speakers are turned on and the audio lines tapped... Obviously it's going to halve just from a second speaker being brought online with the same channel, and whilst it's not a likely use case, what if someone went round turning on 10 or more speakers all on the same channel!? The impedance of the load is going to be REALLY low now, and I have no idea if it is allowable to have such a variable impedance load for an amplifier. I do realise it's not normal or ideal, but is it acceptable if the amplifier is big enough to handle it?

I'd really appreciate any comments and/or help with the above questions or any suggestions for an alternative approach. I'm obviously more than happy to put time and effort into researching and working to expand the ultimate solution, but it's not currently clear to me which direction to go in at the moment!


texts: Why does the CAN bus use a 120 ohm resistor as the terminating resistor and not any other value?

texts:
I know the reasons for using terminating resistors on a CAN bus and how important it is.

But why 120 ohm? How did this value come up? Is there any specific reason to use 120 ohm?


texts: How can I measure rotation on a cog wheel?

texts: The cog wheel is 40 mm in diameter and is being rotated by a motor at 2.5 rpm. This cog wheel is inside a turntable that is used as an exhibit stand. Rotation will only be between 0-360 degrees i.e one cycle only, and then back to 0. I need to measure the degrees of rotation on this cog wheel. any suggestions will be really appreciated. thanks.


texts: I am looking to install a home PC computer for the car.  I am concerned about voltage regulation.  The car voltage can range from 10 - 14V, so would the standard PC power supply have voltage regulation built into it for powering the PC components or would I have to find a voltage regulation circuit board to take the PC power supply out put and feed it to the PC?  Or have the voltage regulation circuit board placed before the PC power supply?  Ultimately I want a touch screen display, wireless internet, solid state hard drive, keyboard and mouse, sound ran through the stereo.  I've been looking at raspberry pi setups or iPad mounting kits, but think I want to do this since the car's wireless internet would link up with the home network and download my iTunes podcasts and latest movies and tv shows.


texts:
I want to transfer data from my Smartphone to the RN4020 Bluetooth module. The easiest way is to use MLDP service. But I don't want to use it as CMD/MLDP pin is connected to +3.3V.
And the only way to exit from the MLDP mode is power off/on.

That's why I'm looking for another way.
It should be possible to create private service for that. But I don't know is it necessary to update/create the firmware for the private service?

Thank you very much.


texts: Is there a basic circuit to trigger a single short pulse when turning a device an? Something like a circuit providing the derivative of a signal?


texts:
I'm wondering if I can use an X or Y rated film cap for high frequency DC link filtering/snubbering.  The system will be a rectifier+inverter, so the cap in question will go on the DC link between the rectifier and inverter.  There will be a big bulk cap (>3mF) to deal with low frequency ripple.  The job of the X or Y cap is to do localized filtering for higher frequency noise.

The reason I want to use an X or Y cap in the DC link is that the X & Y caps typically have UL approval while caps listed as DC link specific rarely have UL approval.  To achieve UL approval on our product we will likely need UL approval on our DC link caps.  Assuming the X or Y cap meets all the voltage and current ripple requirements, is there anything else to consider when using an X or Y cap in the DC link?


texts: NPN transistor to short RF remote switch button

texts:
simulate this circuit – Schematic created using CircuitLab

Hi,
I am trying to replace RF remote switches with transistors and want to control them using raspberry pi GPIO pins.

Here as you can see, the grounds are different, so the circuit is not working. If I try to connect the raspberry pi ground to emitter of transistor it works fine. But my problem is, if i connect emitters of 2 transistor 2 same raspberry pi ground, it would short those 2 pins. I am not sure about the circuit on the remote, so can't short those 2 pins. Can I use another transistor to connect the ground to the emitter, for which base is  connected to the same raspberry pi GPIO pin? What is the best way to do this? I know optoisolators are better way, but i don't have them presently. Please suggest if i can achieve using trasnsistors.


texts:
Hi all,

I am trying to figure out a way to connect two fpga boards (like in the image) for a Morse code decoder/encoder. Our first plan was to make the decoding and the encoding in the same board with a mode select option, but when we sent our project proposal to our instructor, he said it was too simple for a final project and as a suggestion, he said that we can try to connect two boards and that it is a simple task, that we can find some example on Internet. However, all we could find was about boards with ethernet connection. We have our seven segment display code and a sample sequential circuit design with clock to take input and display it, but we could not figure out how to connect two boards. Any suggestion/advice would be greatly appreciated.


texts:
I am planning on using an MLX91206 to measure the current draw of a set of Peltier elements. They draw up to 17.3A at 24V.  However I would like to measure their current draw without interfering by placing sense resistors.
So I decided to use the MLX91206.  Could someone please explain how to connect this thing to an Arduino?  A rough pinout diagram would be really useful.


texts: Different behaviour of FTDI231XS on two PCBs with same circuit

texts:
I have designed two PCBs, both using a FTDI231XS USB to serial chip to program an ESP32. Both boards have the same circuit design to control the FTDI231XS chip. One board was hand soldered (board A); the other has been manufactured (board B, with smaller SMD components).
Board A works without a flaw. Board B won’t however be recognised by my computer (serial port is not shown, computer has all the needed the drivers and is completely updated). The message that the attached USB device is broken is displayed as soon as the PCB is plugged in (under device manager it shows the device couldn’t be reset).
In my humble opinion the circuit design to control the FTDI231XS should be correct, as it has been taken from the ESP32 thing by Sparkfun.
Here is the circuit in question (board A and B):

And here are photos of the PCB designs.
Board A (I know that in this photo USB D+ and USB D- are interchanged, during soldering I rechanged it. Also, only the USB type B connector was populated during testing):

Board B (machine soldered):

To your information, I know that my board design is not perfect, I am still a beginner in this field and so very thankful for constructive critic besides an answer to this problem.


texts: What is this type of flexible contact strip called?

texts:
The LCD below is from a cheap digital clock which was (obviously) damaged (broken glass).

The electrical connection between the PCB and the display was realized with this pink strip.

Its flexible...

...and consists of alternating rows of conductive and insulating material between the pink boarders.

[above image was altered in contrast/brightness to highlight the alternating strips]

What is this kind of connector called? Is it only used for displays?

I am pretty impressed that the connection is reliable just from the very slight pressure between the strip and the PCB. Also, its easily removable from the display. There seems to be some conductive layer on the glass, from where the signal goes into the displays internals. This connection seems to be damaged for the three rightmost signals, where the glass is broken.


texts: Confusion understanding a transducer manual for wiring

texts:
In the Setra Model 270 transducer manual the following instructions are given:

Do they mean that the excitation negative terminal should be separate with the output signal's ground? And the shield is connected to the excitation negative terminal? Is my way of wiring correct below?:


texts:
I have a board that have 3 relay. I have 3 function for Set / Reset / Toggle a relay that get a special relay number and do action on that as below:

void SetRelay(byte RelayNo) //index 1
{
    switch (RelayNo) {
        case 0:
        S_R1;
        break;
        case 1:
        S_R2;
        break;
        case 2:
        S_R3;
        break;
    }
}

void ResetRelay(byte RelayNo)//index 2
{
    switch (RelayNo) {
        case 0:
        R_R1;
        break;
        case 1:
        R_R2;
        break;
        case 2:
        R_R3;
        break;
    }
}

void ToggleRelay(byte RelayNo)//index 3
{
    switch (RelayNo) {
        case 0:
        T_R1;
        break;
        case 1:
        T_R2;
        break;
        case 2:
        T_R3;
        break;
    }
}

I send a packet to board something like:

Relay Index: Index for activate a special relay.

Function Name: A index for witch function must execute for special relay index.

Schedule Time: Is is a time in millisecond that a function must be fire for special relay index.

A sample packet:

That mean the board must active

Relay index 1 must be fire in function number 3(ToggleRelay) in 2000 millisecond
Relay index 3 must be fire in function number 1(SetRelay) in 1000 millisecond
Relay index 1 must be fire in function number 2(ResetRelay) in 2200 millisecond

If just want to fire a relay with one function its must work with system timer, BUT anybody have suggestion for how to do that with more than one function?


texts: Some questions regarding the SPI configurations to interface with nrf24l01 radio transceiver

texts:
I am looking at the product spec of nordic nRF24L01 transceiver module and trying to figure out how I can use with the STM32's SPI. The MCU that I have is STM32F4 nucleo and it's got 4 SPI peripherals with SPI1 and SPI4 running at 42MHz and SPI3 and SPI2 at 21MHz and the radio module itself supports the data rate of 250kbps, 1Mbps, and 2Mbps.

So considering this:

any SPI peripheral would be more than enough to run this radio module since, for 42MHz, the data is sampled every 42MHz (23.9ns) whereas each data from the radio module comes in at 250kbps (each data every 4us)? Is this what you'd mainly consider while deciding about which peripheral to use? But then the enhanced shockburst packet is 32 bytes long. How do I picture this?
any reason as to why the max SPI frequency is fclk/2? Does it have to do with full duplex transfer?


texts: how to determine max peak of switching regulator in frequency domain (radiated emission)

texts:
I want to know how do I determine what should be the switching regulator peak in frequency domain(Radiated emission) , and where should I measure (Output or on inductor , capacitor).
Lets do below example which I am working on: LM34936EVM which has switching freq of 300khz and out of 12V
Below is near filed snap shot using 20mm H field probe on top of inductor. I am using Rigol DSA815 which I am not very familiar with. (please let me know if I have to change setting or if you want more data with finer loop)

I want to know if this switching regulator is normal or not.


texts: Is superposition theorem the only method to calculate the \$I_0\$ in this circuit?

texts:
When I learned the superposition theorem, the book provided this circuit to me, and taught me how to use the superposition theorem to find the value of \$I_0\$:

simulate this circuit – Schematic created using CircuitLab

However, I want to ask that why should use the superposition theorem to find the \$I_0\$ in this circuit? Must we use the superposition theorem to find the \$I_0\$?

I mean, is the superposition theorem the only method to calculate the \$I_0\$? If I have no idea about superposition theorem, that is, f I don't know what the superposition theorem is, I don't know there is a method called superposition theorem which can be used to calculate the \$I_0\$ value. Can we still use other methods to calculate the \$I_0\$? If yes, can anyone show me how to calculate the \$I_0\$?


texts:
I currently working on a new design that should support Ethernet IEEE1588 PTP. I was looking for Ethernet 1GBit PHYs with IEEE1588 support when I saw this on TI website:
http://www.ti.com/interface/ethernet/phy/products.html#p1323=10/100;10/100/1000;100&p2192=IEEE%201588%20PTP;IEEE%201588%20SOF

It appears that there is a difference between IEEE1588 PTP and IEEE1588 SOF but I can't see what the difference is (if there is any).

Do you have any idea about what the difference could be ?


texts:
Is there a way to estimate the magnitude of the current that would flow through the protective earthing of an electrical equipment in case of a fault?

I recently had an equipment fail in this manner and it tripped a 10 A circuit breaker.


texts:
Hi, I'm trying to find the resistance Rx in the picture.

Now, usually I would assume that (if channel length modulation is non-zero), that this would be 1/gm2 in parallel with ro2. However, I remember that was when our drain of M2 was connected straight to Vdd (AC ground in small-signal). But in this case, the drain is no longer just AC ground, Rd is there.

I'm assuming the Rx in this case won't just be 1/gm2 in parallel with ro2 will it?


texts: How can I detect if a garage door is opened or closed?

texts:
The Problem:

I want to be able to detect if a garage door is opened or closed with my Arduino. I don't know what kind of sensor would be suitable for this task. The Arduino and the unknown sensor will be placed approximately 4 meters from the garage door.

Some Context:

I live at the second floor of a house and last weekend the garage door left opened the whole night by mistake. I want a method to detect the door is opened. My first thought (I'm newbie in electronics) has been to place the Arduino I own in the garage, and putting some sensor detect the door is opened and then send via wireless to another Arduino place at the second floor that the door is opened and reproduce some sound to warn the garage door is opened.


texts: Can i just regard VSS as gnd when they both exist in the schematic?

texts: I always regard VSS as gnd when there is only one exists in the schematic, but if they both exist, like this schematic, in the schematic, can I just regard VSS as gnd? Because VSS and ground should connect to the ground, but if they all connect to the ground, why are there both VSS and GND in one schematic?


texts:
How do I detect a pattern of 4 pulses from 4 different signals? I want to be able to detect every time I see for example the pattern circled in blue. When I detect this pattern, I want to output a digital high signal. The pulses can come in different orders (as can be seen by the middle group of 4 pulses). I can only create my circuit using transistors, capacitances, resistances, current sources and voltage sources.

I plan to use a hysteresis comparator in some fashion to compare the signals to some threshold voltage (so as to account for a small amount of noise after filtering). But I don't know how I can compare 4 signals at the same time.

Any help would be greatly appreciated! Thank you so much!


texts: How to calculate resistor and capacitor size for snubber circuits

texts:
I have a 24 VAC Contactor that I want to drive with a microcontroller through a photmos. How do I calculate the proper size resistor and capacitor for a snubber circuit? Here are some of the specifics. Thank you for your help!

Microcontroller - 5V DC 40 mA max on the output pin.

AQV252G Photomos
http://www.futureelectronics.com/en/technologies/electromechanical/relays/solid-state-relays/Pages/9530346-AQV252G.aspx?IM=0

Transformer Data - 24 VAC 40 VA Transformer

Contactor Data

Contactor Nominal Coil Voltage 24

Maximum Pickup Volts 18

Drop-Out Volts Range 6 - 15

Nominal Inrush VA @ 60 Hz 20

Nominal Sealed VA @ 60 Hz 5.25

Nominal DC Resistance - Ohms ± 10% 16.5


texts:
I wanted to use timers in TM4C123GH6PM (in TIVA C series TM4C123G Launchpad evaluation kit). So I decided to use GPTM TimerA0 in periodic timer mode. I defined the address of the registers of GPTM and followed the steps given in the section 11.4.1 One-Shot/Periodic Timer Mode of the datasheet in page 722. I want a LED to blink after every 3 seconds (connected to PORT F-pin 1). But the LED is always ON. Are the address of the registers to which I am referring wrong? Or something else is the issue with the code?

//TIMER Registers
#define RCGCTIMER        (*((volatile unsigned long *)0x400FE604))
#define GPTMCTL                  (*((volatile unsigned long *)0x4003000C)) //timer zero
#define GPTMCFG                  (*((volatile unsigned long *)0x40030000))
#define GPTMTAMR                 (*((volatile unsigned long *)0x40030004))
#define GPTMTAILR                (*((volatile unsigned long *)0x40030028))
#define GPTMRIS                (*((volatile unsigned long *)0x4003001C))
#define GPTMICR                (*((volatile unsigned long *)0x40030024))

//PORT F Registers
#define GPIO_PORTF_DATA_R       (*((volatile unsigned long*)0x400253FC))
#define GPIO_PORTF_DIR_R        (*((volatile unsigned long *)0x40025400))
#define GPIO_PORTF_AFSEL_R      (*((volatile unsigned long *)0x40025420))
#define GPIO_PORTF_DEN_R        (*((volatile unsigned long *)0x4002551C))
#define SYSCTL_RCGC2_R          (*((volatile unsigned long *)0x400FE108))
#define SYSCTL_RCGC2_GPIOF      0x00000020  // port F Clock Gating Control

void initializeTimer()
{
    RCGCTIMER |= 0x00000001; //To use a GPTM, the appropriate TIMERn bit must be set in the RCGCTIMER. Here it is TIMER0

    //Periodic timer mode

    GPTMCTL &=0xFFFFFFFE; //TAEN is set 0. Timer A is disabled.
    GPTMCFG = 0x00000000; //Write the GPTM Configuration Register (GPTMCFG) with a value of 0x0000.0000
    GPTMTAMR |=0x00000002; GPTMTAMR &=0xFFFFFFFE; //TAMR is set 0x2. Periodic Timer mode is used (first bit1 is set 1 and then bit0 is set 0 in two statements)
    GPTMTAMR &= 0xFFFFFFEF; //TACDIR is set 0. The timer counts down.
    GPTMTAILR = 0x02DC6C00; //TAILR is set to 48,000,000 Hz
    GPTMCTL |=0x00000001; //TAEN is set 1. Timer A is enabled.
}

void initializePORTF()
{
  volatile unsigned long delay;
  SYSCTL_RCGC2_R |= 0x00000020;     // 1) F clock
  delay = SYSCTL_RCGC2_R;           // delay
  GPIO_PORTF_DIR_R |= 0x02;         // PF1 output
  GPIO_PORTF_AFSEL_R &= 0x00;       // No alternate function// 1) F clock
  GPIO_PORTF_DEN_R |= 0x02;         // Enable digital pins PF1
  GPIO_PORTF_DATA_R |= 0x02;        //PF1 Set to 1. LED is ON
}

int main()
{
    initializeTimer();
    initializePORTF();

    while(1)
    {
        //did TATORIS in GPTMRIS become 1??
        if((GPTMRIS | 0x00000001) == 1)
        {
            GPTMICR |= 0x00000001; //Set 1 to TATOCINT. Writing a 1 to this bit clears the TATORIS bit in the GPTMRIS register and the TATOMIS bit in the GPTMMIS register.
            GPIO_PORTF_DATA_R ^= 0x02; //Toggle PF1. Toggle LED
        }
    }
}


texts: Preparing Input and Selection voltages to a Multiplexer

texts:
I am trying to make a fast switching circuit that is able to switch a current (0-20mA) supplied by a current source (open-circuit voltage 100V) between two channels (i.e. switching between two pairs of electrodes). The load has a low resistance (100-250 ohhm). The current signal is composed of square pulses of (5-20ms) duration, one pulse every 300ms.

I have a CD4067BE 1x16 multiplexer operated at 15v/0v Vdd/Vss to minimize its on-state resistance. At 15v, channel selecting voltage should be at min. 11v for logic 1.

my questions:

How to limit the input voltage coming from the current source to MUX such it does not exceed 15v? can I use zener diode without any harm to the current source?

I am using MCU signals (0-5v) to control selection inputs of the MUX. However, at least 11v is needed to activate selection. What a driving circuit do you suggest?


texts: Does usb to serial multi port communicate only for one port at a time?

texts:
In my work place there is a usb to serial multiport connected to a PC which controls servo motors ect. The 8 port(rs232) multiport is connected to the PC via a USB cable. My question is: Can these ports controlled at the same time from the PC or one port at a time? If for instance I have data transfer to COMport1 can I establish data transfer to COMport2 at the same time?

Here is a device similar I'm talking about:
http://www.sunix.com.tw/itpd.php?cid=2&kid=4&gid=10&pid=764

or here:
http://www.serialgear.com/4-Port-Serial-USB-CM-41042.html


texts: how to create high frequency RC phase shift sinusoidlal oscillator with out damped oscillations

texts:
I am trying to designthe rc phase shift oscillator .I designedfor 1khz frequency using BJT. But when i try to convert the same circuit by changing the R and C values fot 90 khz  I am getting the damped sinusoidal oscillation. Can some one please say what was the issue and also wether can we generate 90khz signal with RC phase shift oscillator.

And can some one suggest what is the easiest way to design the RC phase shift oscillator for higher frequency ranges above 100 khz.


texts:
Can I further minimize this boolean expression
A'BC+AB'C+ ABC'
As I guess It can't be  further minimized


texts: Half-wave diode rectifier - is textbook wrong?

texts:
I've noticed that in all resources on diodes and rectifiers, they show the output voltage as the positive half-wave of the input signal. However, that seems wrong.

I understand that there's a voltage drop across the diode, and if the total voltage is below this level, the diode is closed. Therefore, it'd only seem logical, if the diode didn't open right away, but only after the input wave reaches this voltage.

Here's my illustration - first, input. Second, my idea of output. Third - output as shown in textbooks.

If I am wrong, how is it possible that there's no "flat area" in the output signal, when the input is below the diode's opening level?


texts: Faster IO on ARM Cortex-M3 (Sam3x8e) than PIO_SODR and PIO_CODR?

texts:
I have a very simple C program that toggles a pin on a Cortex-M3 board (SAM3X8E) with a 84MHz clock speed.  I built this using Atmel Studio 6.1.

#include <asf.h>

int main (void)
{
    board_init();
    PIOB->PIO_PER = PIO_PB27;  //Enable PIO
    PIOB->PIO_OER = PIO_PB27;  //Set to OUTPUT
    PIOB->PIO_PUDR = PIO_PB27; //Disable the pull up resistor

    while(1) {
        PIOB->PIO_SODR = PIO_PB27; //Enable output
        PIOB->PIO_CODR = PIO_PB27; //Disable output
    }
}

Now when I load this onto the board, and hook up an oscilloscope up to the pin, I see the signal pulsating at about 700kHz.  I would have thought that the speed of the cycle would have been much quicker with this minimalistic code.

Is it possible to get a GPIO frequency higher than a MHz using this setup? Is it my build environment that is not producing optimal code?  Is it possible to get faster GPIO using another technique?


texts: Serial capacitors in electronic ballast of a fluorescent lamp

texts:
Recently I repaired one broken electronic ballast of a linear 30W fluorescent lamp. Now it seems to be working as expected, but I had to make some changes to it and I'd like to ask if you see any hidden problems I can get into due to those changes.

Here is the diagram. It is not exactly my diagram, but very similar and I hope fully usable here:

On left side you can see power source (230VAC, 1:1 transformer, diode rectifier). Look at those two (red) electrolytic capacitors in series. I assume they are charged to 162 volt only (Vpeak is 325V, so each cap gets 162 V only). The original caps were rated 15uF 250V, and I needed to replace one of them. I wasn't able to obtain the same for a good price, so I replaced only one of them with a 22 uF 250V. So now I have one old 15uF, and one new 22uF. (I cannot put there two 22uF, because they're too big. One old small 15uF and one new bigger 22uF can fit there.) My question is simple: What did I cause by this? Will there be problems?

Those caps are surrounded by a lot of diodes. I expect that normally the potentials around and between those caps are -162V, 0V, +162V. When I replaced one of them by a different one, I probably moved the center potential out of ideal zero. Does it matter here? (The capacitors are never 100% ideal, so I hope the ideal zero potential isn't required here.) I am affraid I don't understand how this strange rectifier actually work. According to the diagram, It seems to me that now one of the transistors work with the higher voltage, and the other one with a bit lower voltage. Or am I wrong? Maybe those two capacitors are discharged in parallel thanks to those diodes so it doesn't matter whether they ar absolutely the same or not. (Vpeak on both transistors is 325V, but when mains voltage goes down the transistors are powered from capacitors, and each of those capacitors have probably got a different charging voltage. This is all too compliceted to me...)

Note that the reason why there are two strange capacitors instead of one 400V one is probably just the space. Two smaller 250V caps can fit into restricted space, one big 400V cap woudn't fit there. Here is the real photo:

My second question: I also had to make one more change: The 0R5 resistors on emitters of each transistor are now 0R56. I am affraid I don't understand what I caused by this, if it's dangerous change or not. (Again, I wasn't able to obtain the pretty same resistors as were the originals.)

The fact is that the ballast seems to work perfectly now, and the tube nicely shines. :-)

Epilog: I still hope that thanks to those diodes, the two electrolytic caps are always discharged together in parallel, so it actually doesn't matter whether they are the same type or not.


texts: I know basic gates but not their structure

texts:
I know everything except the structure of logic gates. Recently a HighOrderThinkingSkill question asked the gate from structure where I was totally stumped please help me:

simulate this circuit – Schematic created using CircuitLab

where A and B are input and :
$$1\to>5V\\0\to<1V$$

How to find and be prepared for future questions?

The answer key says it's an AND gate, but I don't understand why.


texts: Theory/equation for wiring a irregularly shaped LED matrix for row/column selection

texts:
I have a large (~90) LED matrix I am whipping up. However, rather than being the traditional easy square shape, its in an odd heart shape.

The reason this is a problem, if I just use horizontal rows and vertical columns, I "waste" a lot of pins on rows/columns with only a few LEDs (like at the tip of the heart), and dont have enough pins on my current equpiment to address them all.

So the question is, how do you go about combining the LEDs such that you maintain ~10 per pin, without overlapping any rows or columns (my first attempt was simply to combine the smaller rows together, which cause them to intersect with multiple columns at a time).

I feel like this is a linear algebra problem, though I took that class 10 years ago (and failed it)...


texts:
We are developing a shipboard system which needs to be connected in a IT network (Unearthed neutral). In order to comply with this scheme we need to avoid negative-grounded, as all the metal enclosures and cable shielding needs to be grounded to create a protective earth and prevent electric shocks. (With the only exception of some capacitors of EMI filters).
We are using isolated power supplies and differential signals for most communications, however some signals or the antenna connection are only possible using coaxial cable.
I have serious doubts about the coaxial connexions as those usually use the shield as negative/reference for the signal.
How can two systems or an antenna in a ship be connected using coaxial cable and not introducing direct or indirect connections between supply lines and earth?


texts:
I have to measure potentiometer sensor value in a noisy environment (car). The sensor is about 3 meters from my main processor board, my idea was to simply use this sensor as voltage divider and read on the Analog input of microcontroler the value.

My main problem (perhaps not !) is to send my clean 3.3 V on the potentiometer, I am afraid to get ESD/EMI or whatever on the 3.3 V lines along the wire and get back to my card where microcontroler and other sensitive component are.

So how could  I isolate the 3.3 V? Can any DC/DC converter do the job ?


texts: I have a simple circuit with a relay with a SSR. I am getting leakage measured using a multimeter of ~4v. Is there a way to eliminate the leak?

texts:
I have a simple circuit. My computer controls an SSR via a 3v dc signal. The load is from a VAC transformer transmitting 10v ac. When "off" I am measuring ~3v coming from the SSR using a multimeter. I have no (literally no) good experience with electricity so I hope I'm using the right terms.

This is for biological research. The end goal is that I can deliver a 1 sec, 5v shock (just enough to be uncomfortable) to a fish upon signal from the computer. What I do not want is for the poor fish to be mildly shocked continuously for the duration of a session.

Is there a way to get rid of the leakage? I don't know if a elctromagnetic switch will work because I might not have enough voltage coming from my computer output to drive it.


texts:
I'm making a simple LED circuit. I have a 6V power source, and a LED with 2 forward voltage and that requires 18mA. I calculated the resistance by dividing the voltage with the required amps (6-2 / 0.018). This gave me 222, which I rounded to 220 Ohms. Now I have a 220 Ohms resistor.

Now I have a 6 volt battery, 220 Ohms resistor, and a LED. Now I can calculate the current. So I divided the total volt (6v) with the total resistance (220 Ohms). But this gave me 6v / 220 Ohms = 27mA. 27mA does not equal 18mA, which the LED needs to work.

With my understanding, these two numbers should equal. What am I doing wrong?


texts: What happens if you put two coils in parallel

texts:
I want to build an LC-Filter from a tutorial I found (German language, if anyone is interested, I'll add a link).

In that tutorial, a 330uH Coil with a max amp of 1A is used.
I have some 330uH coils lying around, but they've only 450mA.

The consumer device will draw up to 700mA.
Is it possible, to put the coils in parallel, like in that schematic?

For a better understanding, what exactly will happen if I do this?

simulate this circuit – Schematic created using CircuitLab


texts: I have a outdoor WiFi connection, each module has a 5dBi antenna, today I extended with a 16dBi directional external antenna. before it was -65dBm the received signal level now it's -83dBm, I'm a bit confused I waited to increase the value, like -30dBm? Is it a better value?


texts: Input and Output Impedances of Differential Amplifier

texts:
I have this circuit that is used to convert an incoming analog differential input signal to a single ended signal. The differential input is connected at IN+, IN- and the output is taken from OUT.

I want to calculate input and output impedance's of this differential amplifier. How can I calculate it? Will it change if the power supply of the circuit is changed.

Edit:
Simplified the circuit image for clarity.


texts: What causes the 'knee' in higher order filter magnitude response?

texts:
I'm studying the unity-gain Sallen-Key low pass filter

I can't find any material explaining the rise in knee of the magnitude response at/after the cut-off frequency, other than that the Q factor (and ratio of capacitors) affects this

Is this a type of resonance between the two capacitors?


texts: How to justify that op-amp 1 has negative feedback?

texts:
Op-amp 1 is topmost in the schematic below. I used the ideal amplifier method (using A until the end and then lim A->infinity) and also the virtual short method.

But I don't know if that's enough to prove negative feedback?

simulate this circuit – Schematic created using CircuitLab


texts: Bulk Capacitance inrush current limiting solutions

texts:
Usually in DC input motor controllers a relay is placed in series with the power supply ( Vbat+) a resistor is connected in parallel with it. This resistor is said to be a precharge resistor for the bulk capacitance (ex: 4700uF at 48v ).

I want to eliminate the relay from this circuit , and i want to know what are my options for limiting inrush current for the bulk capacitors , which as i understand stabilized the dc link from switching and supplies peak current for motor.

My question is:

1- can i use an NTC alone and have the same performance if yes how is the selection is made ?

2- should i place a mosfet in parallel with this NTC that opens after the capacitors are charged ?

simulate this circuit – Schematic created using CircuitLab

3-is there any recommended alternative ?


texts: How to get the gain in db against frequency curve for this parallel LC circuit in pspice?

texts:
simulate this circuit – Schematic created using CircuitLab

I have been trying to get the frequency response (magnitude of Vout/Vin on y axis and frequency on the x axis)for the circuit shown below, however I am unable to get this. Please could someone help/instruct on how to get the frequency response for this circuit ?, and where exactly do I measure Vout and Vin ?. I have been taking Vout as the voltage across C1 and Vin near the source.
Also I cannot add a AC voltage source for this circuit in pspice.


texts:
Hi I'm designing one application which have rf communication over the 868 Mhz.
i'm using Telit's LE70-868 Module it support the wake on radio feature. but i have configure as per its datasheet but it not working.


texts: Signal Noise in Bluetooth Adapter when Using SLA Battery

texts:
I've been working on a custom Bluetooth speaker for a while and I recently upgraded the amplifier and battery in it. I started out with a limefuel USB battery and a hand-wired audio circuit based around a TDA1517P which was 12 volts and required a boost converter. That was fine, but it was not loud enough for me, so I upgraded to a 25 watt amplifier chip from amazon and I also upgraded to a 12 volt SLA battery. I'm still using the same Bluetooth adapter, which is an Esinkin W29-ESK001. The adapter requires 5 volts, and it worked perfectly fine with no issues on the USB battery. However, now that I'm using a 12 volt battery I have to use some sort of regulator circuit.

I wired up a LM7805 according to many circuit diagrams I found on the internet and it was outputting 5 volts just fine. I connected it to the Bluetooth adapter and attempted to play some music. There was quite a bit of high pitched beeps when connecting to the adapter, and when I started playing music there was many more of the same thing. It almost sounds like you can hear the Bluetooth chip processing the audio signal.

I assumed the LM7805 was just too noisy, which I then looked up, and it turns out linear voltage regulators are actually quieter than switching power supplies, but I went ahead and ordered a buck converter anyways to see if that would solve it. Still no luck with that once I got it wired in; I was hearing the same exact beeps/blips I was hearing before.

Now I'm at a loss as to what to try. I've seen some mentions of ground loop isolation, but I'm inclined to believe that's not the problem as the setup worked perfectly fine with the USB battery. I'm under the assumption that the SLA battery is introducing noise into the power for the Bluetooth adapter, and that I might need some sort of filtering, but I'm certainly not an electrical engineer and I don't own an oscilloscope so I can't really test that theory. I know that the amplifier isn't creating the noise because if I plug the 3.5 mm jack straight into my phone it's crystal clear. I assume I need maybe a low pass or high pass filter to put on the 5 volt line going to the Bluetooth adapter, but I'd thought I'd ask the community what they thought before I wasted my time with that.

Any suggestions as to what I should try? Thanks!

EDIT: Added some images of the setup.

The first image is the buck converter. It gets 12 volts from the battery and supplies 5 volts to the Bluetooth adapter and to a USB socket so I can charge my phone (note that in my tests, I did not have my phone charging.)

The second image is of the bare PCB of the Bluetooth adapter, which is in the back. I moved the tactile switch which initiates the Bluetooth connection so that I could press it more easily and it works just fine. To the left you can see the USB socket, and a LED voltage display which connects directly to the battery (note that in my tests, I tried unplugging this to see if the noise would stop and it did not.)

Not pictured is the battery, because it would get in the way as there's not much space in my enclosure. The battery is an Expert Power EXP1270. Also not pictured is my amplifier chip. I tried to add the picture but Stack Exchange informed me that I do not have enough reputation.


texts: ASUS Laptop A/C Power Supply Output Doubled

texts:
My laptop power supply is rated for output to 19.5v, 7.7A.
However, it's kicking out 41.5v. Strange thing is that before I measured this voltage, I have been using it to power on my laptop and it works fine. There's a problem, however; I've been trying to understand why my battery doesn't hold a charge. I have it plugged in and it charges (according to my battery manager) up to 84% and never higher than that. The status also reads to be "plugged in, charging." When I disconnect the power cable, the machine shuts down and cannot be restarted with only the battery. I have to plug it back in to get it to restart.
Why would it do that and can I fix it? Is it still safe to use to power up the laptop, which requires a 19.5 VAC power supply even if it's kicking out so much more voltage?


texts: RMS calculation in cheap microcontroller

texts:
I normally see that RMS calculation is done using some kind of DSP or more high end microcontroller. I'm using this microcontroller and I would like to know if it could do RMS.

I need to read 60 Hz current from a current transformer through an op-amp as shown below. I don't have values in the drawing because I'm just illustrating the concept. I've heard that one can use an external precision rectifier to sense the peak and calculate RMS from that. In my case I have the signal with a DC shift, and I think that doing RMS would be more robust against noise compared to just sensing the peak.

Any suggestions?


texts: Can anyone tell the real life examples of electronic filters? Why do we need them ? Whey do we need certain range of frequencies while others are rejected ? Sorry i am new in electronics so please do not mind.


texts:
I'm trying to connect an optical encoder (Bourns EN series) to AVR microcontroller, and a few things are not clear for me from the datasheet.

At first, datasheet says that the maximum supply current is 26mA, but do I have to limit current (i.e. by putting resistor on VCC) or this means it just drains not more than 26mA and can be directly connected to +5V?

And a second question: do I need to put any pull-up resistors on Channels A/B, or I can just connect them directly to AVR pins?


texts: BJT audio amplifier for 8 ohms 0.025 watts speaker

texts: I have to analyze an amplifier circuit for 8 ohms, 0.025 watts speaker and don't understand how it works. What is the working principle of the components? What configurations are used? In which stage does the amplification take place? What biasing are used and why?


texts: IRFZ34N doesn´t switch on when a NE555 timer pulse is applied

texts:
simulate this circuit – Schematic created using CircuitLab

I have the above circuit in my breadboard. The problem in a nutshell is that when the NE555 timer is switching at 50kHz in astable mode the IRFZ34N seems not to be able to follow the circuit switching. Instead, it gives me the following signal:

The signal in yellow is probing mosfet drain and the the pink one is the 555 output.

My thoughts on why it´s not working have to do with gate-source capacitance not being able to discharge completely for another cycle, or maybe some stray inductance causing the voltage to become negative. Anyway I´m not sure these are the problems and do not know how to solve this issue either.

I have not added any pull down resistor once I think the 555 timer already pulls the output to ground when off, not leaving the output floating

EDIT: I got back to the bench and probed the drain voltage again, unfortunately the pictures I´ve taken are over 2MB which means I cannot upload them. Anyway I´m gonna explain what I visualized:

The same 555 timer switching, but now the resistor R1(drain resistor) has been changed a couple of times and I could see it plays a really importante role in the mosfet switching speed. The greater it was, the slower the drain voltage would reach 15V as the gate signal had been switched to 0V.

I´ve made some tests with $R_1=33k\small{\Omega}$, $R_1=2.2k\small{\Omega}$ and $R_1=33\small{\Omega}$.

When $R_1=33k\small{\Omega}$, as the 555 pulse reached $0V$ the drain voltage reached about $10V$ within 2 microseconds.

Similarly, the outcome for $R_1=2.2k\small{\Omega}$ was $800ns$ to reach $15V$ and about $200ns$ for $R_1=33\small{\Omega}$.

From this data, what role does the drain resistor play in this switching? How does it affect the mosfet rise and fall time?


texts: Using Timer0 overflow to gate Timer1 on PIC12F1822

texts:
I am trying to use TMR1 to count TMR0 overflows. To do this I am using TMR1 with gate enabled, and using TMR0 overflow as the gate source.

Using MPLAB SIM, I can see that TMR0 is counting and overflowing. The TMROIF bit in INTCON is being set correctly.

TMR1 counts correctly without the gate enabled, and stops when I enable the gate control - so far so good.

However, TMR0 overflowing does not seem to be triggering the gate. The T1GVAL bit of T1GCON is never set.

I am running TMR1 at Fosc and I have the gate running not in toggle mode or single pulse mode...
TMR0 is running at instruction clock / 256, although I presume that this doesn't matter...

Here are my config bits:

__CONFIG _CONFIG1, _FOSC_INTOSC & _WDTE_OFF & _PWRTE_OFF & _MCLRE_ON & _CP_OFF & _CPD_OFF & _BOREN_OFF & _CLKOUTEN_OFF & _IESO_OFF & _FCMEN_OFF</code>
__CONFIG _CONFIG2, _WRT_OFF & _PLLEN_OFF & _STVREN_OFF & _BORV_19 & _LVP_OFF

and here are the relevant lines where I configure TMR1

banksel T1CON
movlw   b'01000001' ; source = Fosc, prescale 1:1, LP osc - no, Timer on
movwf   T1CON

banksel T1GCON
movlw   b'11000001' ; gate enabled, active high, toggle no, pulse mode no, source TMR0
movwf   T1GCON


texts: Can superimposed (combined) wireless signals create a health hazard?

texts:
Not to sound all tin-foil-hat-like but I'm learning about wireless signals and am trying to understand it better. So my question is:

When multiple wireless signals are transmitted at the same time on different frequencies, they end up getting superimposed or combined together to create the field that travels through the air. So if I had two signals at different frequencies whose amplitudes varied between 1 and 0, the combined signal in the air could have an amplitude greater than any signal by itself (In this case, the signal in the air could have an amplitude greater than 1).

Wouldn't that mean if you had a lot of normally harmless wireless devices (say cell phones or wifi routers) in a given area that you could create a region that is no longer safe since each small harmless signal has combined to create a higher powered dangerous one?

Update to add more context:

Outside of even standing waves, if I look at an image like the one linked below, I see points where the red, blue, and green waves are all positive and close to their peaks creating a combined amplitude of around 2.5 times that of any wave by itself. While I can certainly see some waves canceling out because they are negative when another is positive, with the hundreds or thousands of wireless devices saturating an area, wouldn't we still have some decent amount summing to create a much higher level of energy transmission? Or is it simply the power transmitted by these devices is just so low that even with say a thousand devices summing together, it's irrelevant?

link


texts: Is it possible to repeatedly use a schottky diode at its surge current without damage

texts:
I've been working on a circuit with an inductive load and a MOSFET, but I'm having trouble finding a suitable freewheeling diode. If I choose a diode with a maximum surge current higher than the maximum current through the load, would it be dangerous (for the component and/or for me) to frequently switch the MOSFET on and off? (Minimum of a few seconds between switchings)

I believe the biggest issue is that I don't know how long the inductive voltage spike will last, so I can't properly estimate how long the diode will be powered at max surge current.

As I understand it, it's a temperature thing. As long as I keep the temperature under the maximum rated temperature everything should be fine. (When the temperature starts getting worrisome, give it some time to cool off before using it again.)


texts: PSOC 5 LP negative input on adc delta sigma in differential mode

texts:
I want to use an adc sigma with negative voltage input, I am using this psoc : CY8CKIT-059 PSoC® 5LP.
It's a bit unclear in the ADC config because the Input range Under the input options says : +-6.144V, but in the graph on the right Under input range show an ADC range between VDDA -250mV and VSSA +100 mV.
So my question is: Can I put a negative input on the adc sigma in differential mode?


texts:
I found oscillators with from 10ppm up to 50ppm and more, but how I can calulate maximum jitter of this oscillators?

With an online calculator I've found with 40Mhz and 50ppm this value:
2.500e-12s Max - Min Period (sec), so 0.0025ns
Can I assume that this is Max. Jitter time?


texts: What grade of fibre is used in optical fibre displays?

texts:
Optical Fibre displays such as Fibre Optic Trees probably isn't going to use cable designed for 10GBase-ER.

So what grade of fibre is used in these displays? Clearly, it can't be terribly expensive.  What are the limitations of this type of fibre?


texts:
I have the question "For the circuit shown"

Find the value of the supply voltage V.

I know that the equation for voltage is V = IR.

However, I am not sure what the values for I and R should be ?


texts: Redrawing a diode circuit in a clearer way

texts:
I'm trying to redraw the circuit with nodal voltage circuit in a better way. Is my drawing right? Can I make it simpler?

Redrawn as:


texts: Full wave rectifier with inductor filter

texts:
The capacitor-only bridge rectifier can't remove the ripple under heavy load and for a linear lab power supply I need to have an output without any ripple under load. after simulating the bridge rectifier circuit under 1A load I ended up with this;

Ripple without an inductor:

Ripple with an inductor:

The transformer is 24/1A and diodes are schottky.

Considering it's going to pass trough a linear regulator which will reduce the ripple to some degree and with such low power transformer, do I really need to reduce the ripple to almost nothing by adding an inductor? or is it better to have the inductor there regardless of the transformer power?


texts: On AVR-GCC, how can I find out what statically initialized variable is using up my RAM?

texts: The variable does not show up on the MAP file so it is hard to track it down. I'd rather not have to manually search though all the source code looking for static initializers.


texts: Is a gate resistor needed on a 2n7000 mosfet when driven by a 4543 BCD for multiplexed led display?

texts:
I have a multiplexed common-anode LED display (7-segment) that is using a 4543 BCD with segment outputs connected directly to the gate of 2n7000 n-channel mosfets (no gate resistor).  Mosfets are switched on/off around 320x per second (320hz) due to multiplexing of the displays.  One digit is lit at a time.  The segment load (to light the led) being switched to ground by the mosfets is only around 10mA.  5v logic levels are used.  PCB traces between 4543 outputs & mosfet gates are probably longer than ideal (several inches in length).  The displays are working fine with this setup, I've not seen any issues.

My question is.. am I okay without a resistor on the mosfet gate?

Reading up on the subject I've found a mixed bag of opinions.  Everything from how it's good practice to always have a gate resistor to it not being needed if it's a small signal mosfet with low gate capacitance, switching a small load, and being driven by something with limited current to supply the gate.  The 2n7000 has a Ciss of 50pf, the 4543 can supply a max of 2.5-3mA per output, the load being switched is about 10mA.  So that would seem to fit the bill.  But I've also seen discussion of parasitic oscillation, ringing, EMF, etc that can happen without a gate resistor & wanted to get a better idea of things.

...

UPDATING WITH SOME PICS

Oscilloscope probe at the mosfet gate:

Comparing to waveforms here it doesn't seem bad?
http://www.richieburnett.co.uk/temp/gdt/gdt2.html

More pictures..

Red arrow on the waveform that's "zoomed in" on in the 2 pictures following this one.


texts: How to discharge a capacitor being charge by an op-amp?

texts:
I've only shown a very small part of the circuit (if the rest of the circuit matters I can show the rest - diodes are used to maintain the charge acorss the capacitor).
Background:
The capacitor is constantly getting charged by the op-amp, i.e. the capacitor is initially at 0v, and keeps getting charged (without losing its charge) up to a peak value and it stays at the peak voltage. The peak value is determined by the power supply of the op-amp (In my case this is 15v).
Problem:
What I've been trying to do (without much success) is find a way to discharge the capacitor to 0v (ground it, or just really close to ground) really quickly, and allow it to get charged up again, similar to a relaxation oscillator.
What I've Tried:
I've tried using a UJT, PUT, SCR, and interesting transistor combinations. I can always seem to ground the capacitor really quickly once it reaches a certain voltage, but I as do, it doesn't charge up again (I think it's because I also end up grounding the op-amp, but I'm not too sure). I can show them if need be.
Please help:
It would be great if there was a way to discharge the capacitor once it reaches a certain voltage, and once it has been fully discharged, allow the op-amp to continue to charge it up again. Is this actually possible to achieve with this setup? Or is it inherently not possible? I'm hoping to try and find solutions using purely analogue components (transistors, capacitors etc)
Thank you!
Edit:
Full Circuit (Simplified a bit)

It uses a diode pump to charge up the capacitor in steps.


texts: I am learning electronics and I want to make a , variable regulation source for a soldering iron, which works at 50W, how much  voltage and amps should have the output? For the soldering iron works correctly


texts: Utilizing a signal in the needed form to drive a load

texts:
At the output of an LM741 opAmp I have 16Vpp sine wave @ no load. I want to use this sine wave on an 8 ohms load with 1.5W power . Therefore I  need 3.5 Vrms and 0.43 Arms on the load. Now, if I directly connect the load to the output of the opAmp, the voltage on the load drops to 0 immediately, and I assume this results from the fact that max current output of opAmp is around 20mA so it is not enough obviously.

Also I want to be able to adjust the power on the speaker, i.e the amplitude of the incoming sine wave.

So, what is the best method to drive that load with adjustable levels of output voltage? I would appreciate if anyone supplies an answer not involving buy this regulator or buy this converter etc. (***)Rather I prefer things like building a transistor amplifier circuit etc. Anyway, I am also open to other advices.

*** : actually, I have to design all these steps for a project. That's why I ask the fundamental methods. I know how silly it seems not using a commercial IC. By the way, the output of the 741 is the direct source of the sine wave. It is a sine wave generator(wien bridge oscillator) actually. I wonder can I do the amplification part seperately from that 741 oscillator circuit.

p.s : don't think matters but the load is a speaker which will be driven at 1kHz.


texts:
I have an arduino board but the jumper pins are seperate from the board itself.
Q: How should I attach this? solder? glue?
I dont want to make a mess and have the solder drops touch each other pins.


texts:
I am trying to switch stw12nk90z N channel MOSFET as high side switch at 20khz frequency with Vds=30V, Rload=18ohm, and Vgs=24V (Rgate=100ohm, Rpull_down=1kohm). I am using TLP250 for level shifting and obviously, An isolated power supply for the gate signal.

Unfortunately, the voltage between the drain and source pin (represented by the graph in blue in the picture) was not square like the input (represented by the graph in red in the picture), it had the straight rise-up and down but had a curve like a sin wave at the top and not stable. I have also added the snubber and anti-parallel diode with the gate resistor but it didn't resolve the issue. Moreover, the MOSFET is also getting heated rapidly even at the current of 500mA.

This is testing for the prototype circuit. The real application will have Vds=600V with Id=5A.

Kindly let me know what's wrong with the circuit or strategy. I am using the following circuit (note that TLP250 is 8 pin IC, I have used this schematic just for the sake of reference), just skip the transistors.


texts: why In I2C the min fall time for Fast and Fast Plus mode is 20ns*(VDD/5.5)?


texts: 8 bit SPI Microcontorller interface with 16 bit SPI slave

texts:
I'm willing to use the Atmega328 microcontroller to control the AD9833 waveform generator through the SPI interface of the microcontroller; the only problem is that the AD9833 reads 16-bit data while the microcontroller's SPI is 8-bit based.

I have been told that the most intuitive solution to this (sending two consecutive bytes) doesn't work, ¿is this true?

If it is, ¿is there anyway I could interface the two devices in order to implement the communication?


texts:
I have several 3d printers. One of them keeps tripping the breaker for the room. I'm trying to debug (obviously will not use it regularly until I can determine what is wrong) but in the mean time I need to keep my other printers running.

A power strip's breaker isn't enough for it to trip, so it's drawing less than 15 amps when it spikes. It also draws 50 watts when just running normally. The breaker for the room is 20 amps, but I'm running an AC and various other appliances as well. The combination is what causes it to trip the 20 amp. It's absolutely not the AC causing it to trip. I have eliminated variables and it's one of the 3d printers for absolutely certain.

I'm guessing I need between a 3 and 5 amp resettable breaker, one that works for a single outlet only. 120V.

Where can I buy such a breaker?

Would be even nicer if I could switch between a few different preset values, ie, 3 amp, 4 amp, 5 amp, etc.

My workshop only has one circuit, just how the building is set up. (rather each room has one circuit, I only have access to the room I pay for)


texts: I need help figuring out how to make a teg fan. I connected the thermos electric generator but my motor is not spinning. Which side of the teg do I put the thermal paste and cooller


texts:
I have problems with unlatching relay with relay..
Schematics below:

simulate this circuit – Schematic created using CircuitLab

The purpose for this is to light on car sidelights when car is unlocked, when pressing lock button it turn off sidelights. Car gives negative impulse for locking and/or unlocking.
 My problem - When Door unlock impulse is given then 1st relay latch himself on so the lights are on (OK, thats what i need), but when i give lock impulse it do not energies 2nd relay to turn off sidelights.
 What im doing wrong?


texts: Common base transistor with early effect

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I have a circuit regarding common base transistor. I must find Av(Voltage gain) Rin(input resistance) Rout(output resistance). Our teacher said you should analyze CE + RE + RS transistör circuit. And I have drawn figure 1, figure 1 is below

Also I tried to solve this problem by using source changing. I have drawn it like below

I have 10 circuit and one of them is CE + RE. I could solve it but unfortunately I couldn't solve including CE + RE + RS one. Do you have any trick point for me ? How can I solve this question ?
Thank you so much.


texts: Resonant frequency of piezo elements, and generating multiple tones

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In another question I posed, there were couple of "piezo sounder" parts suggested for the purpose of a compact but reasonably loud, alternative to electro-mechanical hooters.

Was trying to understand the various device characteristics that these "pieze sounders" have, and how I could use them to generate a sound-pattern (involving at-least 2 different frequencies), without sacrificing too much on the "loudness" aspect.

This is where I ran into "resonant frequency" of piezo elements, which is mentioned in all the data-sheets. So my question is, is this the frequency at which the device is loudest but it is still possible to generate tones at other frequencies, possibly with reduced loudness ? None of these data-sheets provide a graph of the loudness-vs-frequency characteristics for the device. So I am wondering if the piezo sounders with "resonant frequency" mentioned (but missing the graph), can produce sound at only one frequency ?

The two SE QnA's referred to:

Piezo buzzer characteristics
Multiple tones using piezo speaker


texts:
simulate this circuit – Schematic created using CircuitLab

70I am trying to make a circuit in which the switches will determine the outputs for the xor gate however when i used the switches it is giving me the opposite outputs. For example, a 1 & 1 should give a 0 but i am getting an output of 1.

I have attached a picture of my board.

Note the resistors connected to 5v and to switch are 470kohm and the resistor connected to led is 470 omhs.

note that for IC the VCC is on top right and grnd is on the bottom left. Also the top two pins from right after VCC are the inputs and the one below that is the output (HC86 gate).

Edit * I am not sure the schematic is correct as I was not given one to work with but I think this is essentially what I am trying to do.

simulate this circuit

Figure 3. Corrected schematic for OP to verify. [By @Transistor.]


texts: Simple circuit to sense current drop and apply current to a separate circuit? Trouble with backup dashcam triggering from taillight

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Sorry I have very little knowledge of EE but I feel like there must be a simple solution to this.  I purchased a mirror dashcam with backup camera function.  Backup camera is supposed to be triggered by reverse taillight.  Instructions say to connect red sensing wire to the hot wire of the taillight.  Thus the backup camera is triggered whenever the taillight comes on.  I did as instructed but the reverse cam comes on and stays on regardless of what gear the car is in.  I wondered if there was some voltage still in the wire, enough to keep the backup cam triggered.  In desperation I tried connecting to the ground wire (It's actually labeled GND).  Strangely now the backup cam feature engages when in drive but goes back to normal function when in reverse.  So is the wire sensing voltage in the GND when the taillight is off?  Is this how Ford taillights are designed to work?  Anyway since it works wrong connected to the wrong wire but it works Perfectly wrong, I was wondering if there was a way to setup a separate circuit that would do the inverse of whatever's going on with that GND wire.  Since the logic is reversed is there a way to reverse that back without affecting the taillight circuit?
The manual seems to describe a circuit for a completely different problem, but I can't make heads or tails of it:

The car is a 2003 Ford Escape, and the dashcam is a CHICOM V21 1080p Mirror Dash.  Their tech support is telling me to box it back up and get a full refund, but it's a great camera and would be a huge waste to return it.


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Consider the nMOS for simplicity, even in saturation, Ids grows with Vds because the depletion region around the drain grows too with Vds and then the effective length of the channel is shorter.

What i don't understand is that, why we consider the depletion region around the drain a good conductor ?

For example, usually we want to work with a Vgs higher than Vt so that the channel is 'filled of' electrons (0 < Vgs < Vt we have that the channel is made by a depletion region and we just have some leakage of current...! but we don't use the MOSFET in this region...)