texts:
I am currently working on a project, where I need to calculate the current in a circuit. The setup is as follows:

Allegro ACS758 Hall effect current sensor (ACS758LCB-050B-PFF-T), primary sampled current -50 to 50 A, sensitivity 40 mV/A
Analog Devices LTC1968 true RMS-to-DC convertor
Analog Devices LTC2420 20-bit ADC convertor

The current sensor outputs 0V for -50A, 1/2Vcc for 0A and Vcc for +50A. The measured current is the phase current of a BLDC motor and that is why a RMS-to-DC convertor was used before outputing the data to the ADC.

I now need to calculate the current value from the ADC output and I am unsure whether I am doing it correctly. So if you could please review my thinking and tell me if I am right or not, I will be very grateful.

The output of the current sensor is 0 - 5V, the output of the RMS-to-DC convertor is also 0 - 5V. But the datasheet of the ADC states:

I am using Vref = 5 V, so in my case the input voltage range is limited to -0.3V to 5.3V, thus the range is 5.6V and the calculation for voltage per point (vpp) is:

$$vpp = \frac{5.6}{2^{20}-1}$$

Taking it the other way around, I have calculated points per volt (ppv) as:

$$ppv = \frac{2^{20}-1}{5.6}$$

Therefore -0.3V would be then represented by 0 points and 5.3 V would be represented by ppv*5.3 = 992401.34 points. Assuming linearity over the whole range, I could now calculate all the points in between and the current from that.

Am I correct?

Thank you for your time.

EDIT:
old schematic:

EDIT2 (new schematic)

If I understood everything correctly, then this should now be a working example. The Hall sensor will output 0.5 - 4.5V, I will run this through a circuit, that would limit this to 1.5 - 3.5 V and this would be the input to IN1 of the RMS convertor. IN2 would be at a potential of 2.5V and thus the condition of max. peak input swing of the RMS convertor is satisfied. But I am not sure of the output of the LTC1968. Is it possible to do as I did in this schematic? Connecting the output return pin to a voltage of 1.5V, so that the output pin will output a voltage of 0.5V with respect to ground (-1V with respect to the return pin) for -50A through the circuit and 2.5V for +50A through the circuit. And a 2.5V reference voltage for the ADC. I hope I understood it right now. Thanks.


texts: Prototype Options For Medium Current Application

texts:
I'm looking for the best option to develop a medium current (approx 1-2 amps) prototype board.

Should I be using perfboard, Vero/stripboard or etching a custom board? Or are there any other options available?

Thanks


texts: Will this "off delay" circuit work if a continuous trigger is applied to pin 2?

texts: This is an off delay circuit using a 555 timer. I want to know if this can be used even if the trigger signal is continuous. If, not what modification is needed?


texts: Evaluating junction temperature from thermal imaging data

texts:
I have a SOD-123F diode through which a current of ~1A flows, creating a forward voltage drop of around 300mV. The datasheet does not specify Rjc but gives Rja = 200 C/W and Rjl = 70 C/W for a 10cm x 10cm copper pad area (!). I only have 12 mil traces going to and from this diode, so I am far from this ideal heatsink scenario.

From thermal imaging data I have a top-side casing temperature of 65C (~40C elevation).

What can I do to evaluate the junction temperature ?

Since I do not have access to Rjc, I thought I could evaluate a worst case scenario with Rjc = Rja = 200 C/W (since in reality Rja > Rjc) and assuming ambient to be 65C instead of 25C:

Tj = Rja * P + 25C = 200C/W * 1A * 300mV + 65C = 125C

Which is just on the 125C limit allowed by the datasheet. There should be some margin in there since I used Rja > Rjc.

Any other thoughts ?


texts: Connecting KSZ8863RLL to a MAC using RMII

texts:
(Edited to ask further question about the MDIO/MDC pins.)

I'm adding a Lantronix xPico 250 to an embedded deivce to provide WiFi access. The device has an ARM based SOM which includes a PHY and there is also an external RJ45. The three are connected using a Microchip KSZ8663RLL 3-port switch.
The SOM's PHY is capacitively coupled to one of the PHYs on the switch, and the external RJ45 is connected to the other.  These can communicate with each other no problem.  The Lantronix xPico 250 supports an RMII interface so this is connected to the RMII port on the switch.
The RMII pins on the switch and the Lantronix are direcly mapped to each other by pin name. i.e. TX -> TX, RX -> RX.

It doesn't work though. I can access the xPico 250 wirelessly and accessing its internal webpages can see that the status of its ethernet link (eth0) is down. I don't have much else to go an at the moment.

I've checked the clock. The Lantronix xPico 250 expects a reference clock as an input which the switch is providing.

I've done some Googling and am aware that RMII isn't designed to work between two MACs.  The datasheet for the Microchip switch refers to the RMII interface supporting both MAC and PHY modes but doesn't explain how to configure this. Every example reference design I've seen on the internet has it set up as a MAC. How can I be sure the switch is set up as an RMII PHY?

If it is actually a MAC and I'm connecting MAC to MAC, do I need to swap the signals round (ie. RX -> TX, TX -> RX etc)

Here's a schematic:

Additional queestion about MDIO/MDC..
I have left the MDIO and MDC pins not connected/floating on the Lantronix. On reference designs the Lantronix has been connected to a PHY and they've been used. Is it possible that this is causing a problem? Should they generally be pulled up/down if not used?


texts: How does a servo hold its position without drawing too much current?

texts: In a standard DC motor if you supply a voltage and stop it from rotating i.e. applying a heavy load, it will draw a lot of current. How is this not the case with a Servo? How does it hold its position and resist changes in its position without drawing a lot of current?


texts: Can I switch two 12v sources with 5 pin relay?

texts:
I'm installing a stereo in an RV and would like to maintain default behavior of having the stereo receive power on vehicle accessory power/ignition, but also be controlled by a switch in the RV for use when the vehicle is not in use. These are the requirements:

When the RV switch is OFF, the stereo turns on and off with vehicle accessory power.
When the RV switch is ON, the stereo remains powered regardless of vehicle operation.
The source of power when the vehicle is running does not matter, but it must utilize the RV batteries when it isn't.

Would there be any problems with utilizing a ~30A 5 pin relay to achieve this? The stereo utilizes an external amp, so it will be drawing very little power.


texts: BJT or MOSFET switch for led indicator problem

texts:
New to the site, and indeed fairly to electronics. I'm having a bit of trouble with this circuit I've made. It is an led indicator type circuit.

The problem I'm having is that there is not enough power getting to the external load. Am I right in thinking that this is due to resistance of the transistor (losing about about 0.7V?).

I thought I'd try a MOSFET instead because I'd heard that they were lower power, but it seems there will always be a problem since no current can flow from gate to source, and the pulldown resistor gives the same problem.

Am I missing a really simple trick or am I trying to get something for nothing?


texts: How does a CRC check work between a microcontroller and EEPROM?

texts:
I have communication between an EEPROM and a microprocessor over SPI and I want to take care of data integrity.
Could you please confirm my below understanding?
I have a data which I want to write  in the  EEPROM along with a CRC code.
Before writing in EEPROM I will use a CRC16 polynomial to generate a CRC code and append it to the data and send if over SPI to the EEPROM.
When I read the EEPROM after system reset or tun time again over SPI from the microcontroller the data along with the CRC code are read (data+crc) and it is divided by same CRC16 polynomial to check with remainder zero? If zero data is good else not.
Could you please confirm if my above understanding is correct?
I just have to implement data integrity for one memory block and for that I'm doing dual CRC check for single memory block by implementing redundant block.


texts: How can I model a flyback transformer on PSPICE / Multisim?

texts:
I need to simulate a flyback transformer, this one specifically. I have not used any models not provided in the regular PSPICE or Multisim before. I checked the manufacturer website and no models were provided (besides some for 3D models).

Any suggestions are appreciated.


texts:
According to http://www.st.com/web/catalog/mmc/FM141/SC1169/SS1031/LN775/PF216846,

All STM32F1xx-series MCUs (and up) "offer standard communication interfaces (up to two I2Cs, three SPIs, one HDMI CEC, up to three USARTs and 2 UARTS)".

Is there a possibility to use more than one SPI line at same time to construct some kind of custom high-speed bus?

Thanks.


texts: I can't seem to find what type of transistor this is based on the markings. It's broken, so I need to replace it. It is in a Chrysler Jeep radio from 1995. The letters are "CBRP".  Thanks.


texts: Multiple switching power supplies sharing the same(v-) reference

texts:
I need multiple 5v switching power supplies to power around 12,000 WS2812 digital Leds. I also need a MCU, which will be powered by a 12v supply through a DC bulk converter.

The goal is to have every led and the MCU have the same reference ground(v-) so the MCU can properly send digital signal to the LEDs. What is the proper way to do it? Can I simply connect the V- of each power supply together?


texts: Output table equivalent to state diagram?

texts:
I have the following state diagram to which I am supposed to construct an output table for. I have the answer, but I do not understand how they derived this output table?
If someone could explain one of the lines in the table to me, just to clear it up, that would be great!

Here is the question:

Construct a state and output table equivalent to the state diagram below. Note that the diagram is drawn with the convention that the state does not change except for input conditions that are explicitly shown:

Here is the table:

An example for me is: For row B, why is the are the transitions B,B,B,D,D? And the output Z1=1, Z2 = 0?

Another example question for me is, for S=C, the diagram shows it transitioning to G's state which is 10, why then is G not filled in for 10 in the table???


texts:
According to my textbook, abca with 2 ohm resistor is independent. A second loop with 3 ohm resistor and the current source is independent. The third loop, with 2 ohm resistor in parallel with 3 ohm resistor is also independent.

Now the definition of an independent loop is a loop that contains a branch that is not part of any other independent loop.

Let's take the first loop, abca with 2 ohm resistor. Say the unique branch is 2 ohm resistor. now bc with parallel resistors 3 and 2 ohm is also said to be independant. but the latter contains the 2 ohm resistor, meaning 2 ohm resistor is not unique to a loop after all. Same goes for the current source and 3 ohm resistor loop, 3 ohm is also not unique.

So according to the definition, why are these three loops independant?


texts: Diode rating for a UPS project with extra battery

texts:
I am planning to add an additional 12volt deep cycle battery to my APC UPS but I dont want to use the charging circuit built into the UPS. I think that if I throw in a Diode between the external battery and the UPS system it would accomplish my goal (and add an external charger). My question is about the rating of the diode that I should purchase. I am thinking that during a power failure, the load will be about 600watts. Would a 50V 5Amp diode be appropriate? What could I use that would be good for this applications?
Thanks in advance for your replies, thoughts and suggestions.


texts: How to calculate parasitic capacitance in a trace?

texts:
I am given the equation for parasitic-capacitance as:

\$ C = \dfrac{\epsilon_r \cdot \epsilon_0 \cdot L \cdot W }{ d }\$

I am also told my trace is to be 1000 micrometers long (1mm) and 45nm wide. The spacing between traces is 45nm as well (and the thickness of the metal layer is 45nm). A second coplanar trace is 100 micrometers long (.1mm).
I am not sure what I am plugging into the equation. I understand that the adjacent trace will distort the signal on my original trace with noise, especially at high power or high frequency, which I assume is the point, but I need to calculate the actual capacitance. I don't mind doing the math, but I need to know what goes where in the equation.


texts:
I've spent a few hours reading about the basics of RF directional couplers, but I am still having trouble understanding just the very basics of what a coupler does. To start with, I've had difficulty finding a good, simple explanation of what directional coupling is. I read through Radio Electronics, but the section on directional couplers doesn't give an overview of what it means to "couple."

Could someone offer a simple explanation of what "coupling" is and what a directional coupler actually does?


texts:
I am designing a circuit, which can use either 5V from USB, or some higher voltage (7-12V) from a battery. If both power sources are connected at the same time, I want some kind of electrical switch, that would disconnect the battery and power the circuit just from the 5V USB. But the circuit still has to work, when only one of the sources is present. I tried to design a switch using two mosfets, but I was not able to figure out a working circuit.

Can such a circuit be build by only using two mosfets? Also, do not worry about the voltage regulation, that is taken care of.


texts:
Here it is written:

  Some references use the negative temperature coefficient (NTC) a to describe the sensitivity of a thermistor alpha = -B/T².

and here it is

  The B constant expresses a degree of thermistor sensitivity (change rate of its resistance) to temperature changes.

Which is common now?


texts:
Why are radiated emissions standards for consumer electronics different from industrial?

Source:??


texts: Nonzero initial conditions for a circuit solved using superposition theorem?

texts:
Suppose I have a linear circuit with 3 voltage sources Vin1, Vin2, and Vin3 in it, and one voltage of interest Vout. It's common practice to solve it using the superposition theorem, so this will lead to a set of 3 equations:
$$V_{out,1}=f_1(V_{in1})$$
$$V_{out,2}=f_2(V_{in2})$$
$$V_{out,3}=f_3(V_{in3})$$
Then
$$V_{out}=V_{out,1}+V_{out,2}+V_{out,3}$$
However, it seems each of the equations individually must have their own initial conditions, and naturally (in my case anyway) only the initial conditions relating to the total circuit are known - not their breakdown into each "layer".

What I mean is that I know
$$V_{out}(t=0)=V_0 \neq 0$$ and $$\frac{dV_{out}}{dt}(t=0)=0$$
But neither
$$V_{out,1}(t=0)$$
$$V_{out,2}(t=0)$$
$$V_{out,3}(t=0)$$
nor
$$\frac{dV_{out,1}}{dt}(t=0)$$
$$\frac{dV_{out,2}}{dt}(t=0)$$
$$\frac{dV_{out,3}}{dt}(t=0)$$
(example of 2nd order system)

Is there a relationship between what I do not know (the initial conditions of the subcircuits) and what I do know (the initial conditions of the total circuit)?


texts: systemverilog same function, different simulation

texts:
I am actually seeking the root cause why the simulator calculates different results for these signal prova1 and prova2 as in my opinion those are representing the very same function

Signal declaration is:

logic [12:0] sub_ton;
logic [11:0] sub_ton_neg;
logic prova1;
logic prova2;

Here simulation results:


texts: Brushless Motors kv rating and testing methods/procedures

texts:
I’m very interested in testing Brushless motors and Prop sizes.

I have been involved with ASTM ASHTO and other testing methods.

What procedures/standards are used for testing brushless motors for the purpose of manufacturing?

I want to learn to use these procedures and I don’t know where to find them.  Thanks.


texts:
I am designing an LED power supply unit, using off-the-shelf constant current drivers (Phillips Xitanium). The system will include a 0-10v dimmer, and I need to connect the Xitanium to both 120v for input, the low-voltage output to the LEDs and the 0-10v from the dimmer (which also takes 120v input to control shut-off of the line voltage). My supply unit will be constructed from 1/16" aluminum sheet metal.

In an earlier design I put a standard 4X4X1.5 junction box inside my power supply unit, but that makes it much larger than I need. I have less than 8 18W wires to connect typically, so this seems like real overkill. The Xitanium drivers are only 3X4X1.1 inches, so it would be great if I can keep the 120v connections the same depth (1.25" deep) and not take up too much space for the 120v connections. This will make it much easier for me to size the box for my needs. Ultimately I will want to get UL approval for this unit. The circuit for hooking up the drivers is trivial, I just want to be sure my physical design is correct.

My questions are:

Do I need to encase the 120v separately from the low-voltage wiring if it is all the same gauge wire, and it is all inside my metal case?

If I do need to keep the 120v connections separate from the low-voltage wires inside the box, then can I use a smaller metal box that I build inside the unit? How big does it need to be? Does this follow the NEC 3.12 guidelines of so much volume per wire?


texts: Double Sideband Suppressed Carrier modulator List

texts: I am using ring modulator for DSB-SC  am modulation in a transmitter circuit. Can anyone please tell me about more DSB SC modulator for am modulation? I want to know which one to use where?


texts:
I want output to equal "11111111" on the first rising edge of the clock but it only happens on the second rising edge when I test the code with ModelSim. The code might look weird as a simplification of a more complex design where I have the same kind of problem.

code:

library ieee;
use ieee.std_logic_1164.all;
entity delay is
port(
clock : in STD_LOGIC;
output : out STD_LOGIC_VECTOR(7 downto 0) := "00000000"
);
end delay;
architecture behavioral of delay is
signal debug : STD_LOGIC_VECTOR(3 downto 0);
begin
process(clock)
begin
if rising_edge(clock) then
    debug <= "0000";
    case debug is
        when "0000" => output <= "11111111";
        when others => output <= "00000000";
    end case;
end if;
end process;
end behavioral;

testbench:

library ieee;
use ieee.std_logic_1164.all;
entity eentestbench is
end eentestbench;
architecture behavioral of eentestbench is
signal clock : STD_LOGIC := '0';
signal result: STD_LOGIC_VECTOR(7 downto 0) := "00000000";
component delay
port(
    clock : in STD_LOGIC;
    output : out STD_LOGIC_VECTOR(7 downto 0)
);
end component;
begin
uut : delay port map(
clock => clock,
output => result
);
stim_process: process
begin
clock <= '0';
wait for 1 ns;
clock <= '1';
wait for 1 ns;
end process;
end behavioral;


texts:
Am working on an arduino project where am controlling a motor through a I/O pin turning it ON and OFF, circuit below:

Now am trying to make a PCB out of this circuit, to do so i wanted to switch these two THT components to SMT, alternatives as below:

Diode is 1N4001, the alternative is S1-A.
The MOSFET is RFP30N06LE, alternative is PMV15UNEAR.

My question is am not sure if i made the right choice for alternatives, is there something else i can go for? or are these good choices?

Note: The RFP30N06LE MOSFET has an alternative called RF1S30N06LESM stated on the datasheet but i could not find any footprints for it and it not shown on the datasheet only thing said is it is TO-263AB package and am not sure if there is a generic size for this, also the drain pin for it seems to be pretty much the same size as the package and am not sure how to even route it so i chose to go with an alternative something am familiar with.

Thank you very much for reading!

EDIT

Thank you all for I apologies if my question was too vague, The circuit works with no issues so am not really trying to troubleshoot anything.
Am simply trying to turn ON and OFF a motor by sending a signal through one of the I/O pins of the Arduino board, The motor am using is a simple 3-5V motor. Below is the schematic for this circuit if it is needed.

The diode am using on this bread board setup is 1N4001
The MOSFET am using on this bread board setup is RFP30N06LE

My question is really can i use S1-A instead of the 1N4001 diode and PMV15UNEAR instead of the RFP30N06LE MOSFET, if not is there any better SMT choice for them?

Please let me know if this does not answer your questions or make my question clear am really new to this community.

Thanks


texts:
I have a international Power Sources Model PUP110-40-S power supply, I think its somewhat generic, that provides +/-12VDC,+/-5VDC.

The unit has failed, and I am attempting to replace it with an ATX PC power supply.

There is a diagram, on the bottom of the Power supply that tells you the voltages on each pin. 2 pins say DC Com. I don't understand what that means.

I can tell you Pin 1, Pin6, which are both labeled DC Com, are not internally wired as common. I'm not sure if I should jumper them together or what.


texts: How to determine the max current my USB Charger can safely supply

texts:
I have bought a 5 Volts 2 Amps USB Wall Charger off of Aliexpress for about $1.70. Let's call it cheap charger. It looks a lot like this one (stock image):

I want to use this USB charger as a power supply for my project. Said project includes 30x WS2812 (incl. 5050 LED) and an ESP8266. This setup will draw something like 1,3 A of current at 5 Volts when the LEDs are on full brightness.

When charging a phone, the charger will heat up slightly. But powering the mentioned components will heat it up even further (from how hot it feels). This leads me to not trust the rating anymore (the 5V 2A is written on the back of it). This is reinforced when using another 5V 2A USB Charger, that came with a tablet. Let's call this one regular charger. This one only slightly heats up.

Question: Is there a way for me to determine what current my charger can safely supply?

Please keep in mind, that I don't have extensive tooling. I only have a digital multimeter and another (bigger) power supply. The USB connector cable that I also bought there ($0.16) doesn't have wires for D+/D-. So measuring the resistance is more or less impractical.

To differentiate against other questions:

Best way to test a USB wall charger for output current talks about negotiations between devices. I do get at least the 1 A of current but want to know if my supply can provide that steadily.
The answer to Properly testing a USB power supply says "[some USB chargers from eBay/Aliexpress] tend to outright lie about their specifications." Which I believe is true for my charger. Do I really have to replace it?

After the suggestion by @Jogitech I tested the cheap charger and it maxed out at around 1.5 A. The multimeter shows a voltage of around 4,1 V at this point. The LEDs started flickering so I stopped there.

I also tested the regular charger, that came with a tablet (this one is also rated 5V 2A). Using this one, I was able to draw the full 2 A of current while the multimeter still showed 5 V.

Conclusion: Like @user2497 said in the comments, I will be looking for a new power supply, that can actually power the circuit without the constant fear of breaking.


texts: What are some important properties for classification of signals? (P300 speller project)

texts:
I'm trying to detect p300 in signals by using classification methods. each signals is 700 ms (sampling rate : fs=1000) long and p300 should happen somewhere between 200-400 ms. Signals are detected from 64 different channels.
The properties I have used so far are:

In time domain:

variance
(mean in 200:400 ms)- (mean in elsewhere)
correlation of different channels
the time when the signal is at its maximum amount
mean of the whole signal
(maximum in 200:400)-(maximum elsewhere)
the number of data with a value between 7 and 8, 6 and 8, 5 and 8

In frequency domain:

mean frequency
mode frequency
median frequency

What other properties do you suggest I use ?

The blue signal in these pictures contains p300, and the other doesn't:


texts: How to derive cutoff frequency equations from the transfer function

texts:
I am working on a problem from the textbook Electric Circuits 10th edition

simulate this circuit – Schematic created using CircuitLab

I am trying to figure out first how to go from the transfer function to the magnitude. It's almost as if the denominator gets a \$ w^2 \$ out of nowhere. Then, I can't seem to figure out how to move from the magnitude in order to solve for the cutoff frequencies.

\$ H(s)=\frac{\frac{R}{L}\times s}{s^2+(\frac{R+R_i}{L})s+\frac{1}{LC}} \$ - using voltage divider

\$ |H(jw)|=\frac{\frac{R}{L}w}{\sqrt{(\frac{1}{LC}-w^2)^2+(w\frac{R+R_1}{L})^2}}\$

We can find the cutoff frequencies:

\$\frac{R}{R_1+R}(\frac{1}{\sqrt{(2)}}) = \frac{\frac{R}{L}w}{\sqrt{(\frac{1}{LC}-w^2)^2+(w\frac{R+R_1}{L})^2}}\$

The cutoff frequencies are then defined as:

\$wc_1 = -\frac{R+R_1}{2L}+\sqrt{(\frac{R+R_1}{2L})^2+\frac{1}{LC}}\$

\$wc_2 = \frac{R+R_1}{2L}+\sqrt{(\frac{R+R_1}{2L})^2+\frac{1}{LC}}\$


texts:
I've been googling for about two weeks now and I still can't seem to get my I2C working. I've used this (what seems to be complete) tutorial. I followed the Master Write and Master Read examples to try and read from my sensor. I've referenced the I2C_MASTER.zip and I2C_SLAVE.zip from the Microchip site, and my I2C still does not work. Can I get some tips?

More information:

SDA, SCL hooked up to PIC18F's SDA1/SCL1, configured for open-drain and wired to supply voltage
Tried different approaches with IdleI2C1() and EEAckPolling1(address) with no progress
Followed the Microchip example of checking the collision bit, but still doesn't work
Using i2c.h from the XC8 Compiler
SSP1ADD is set to 19, but maybe it's not right? I have my clock running at 8 Mhz with the internal oscillator, and got that value using Fclock = Fosc / (( SSPxADD + 1 ) * 4), where Fclock is 100 kHz and Fosc is 8 Mhz
I do not have an oscilloscope to view signals

Does anyone know of any libraries I can easily use for reading and writing without worrying about Ack/Nack signals?

Here's the relevant code:

void init()
{
    CloseI2C1();
    OpenI2C1(MASTER,SLEW_OFF);
    SSP1ADD = 19;

    getEEPROM();
}

void getEEPROM()
{
    static signed char status,data;
    IdleI2C1();
    StartI2C1();
    while(SSPCON2bits.SEN);
    do{
        status = WriteI2C1(MLX_EEPROM_WRITE);// Signal to EEPROM start point
        if(status == -1)
        {
            data = SSPBUF;
            SSPCON1bits.WCOL = 0;
        }
    }while(status!=0);
    IdleI2C1();
    do{
        status = WriteI2C1(0x00);// Signal to EEPROM start point
        if(status == -1)
        {
            data = SSPBUF;
            SSPCON1bits.WCOL = 0;
        }
    }while(status!=0);
    IdleI2C1();
    RestartI2C();
    do{
        status = WriteI2C1(MLX_EEPROM_READ);// Signal to EEPROM start point
        if(status == -1)
        {
            data = SSPBUF;
            SSPCON1bits.WCOL = 0;
        }
    }while(status!=0);
    IdleI2C1();
    getsI2C1(eepromData,255);
    /* // supposed to be the same as getsI2C1
    for(i = 0; i < 256; i++)
    {
        eepromData[i] = ReadI2C1();
        IdleI2C1();
    }
   */
    NotAckI2C();
    while ( SSPCON2bits.ACKEN );
    StopI2C();
    while ( SSPCON2bits.PEN );
}


texts:
I have two Arduino Mega 2560 boards, both gives errors when trying to upload sketches (I bought the second board thinking its a fault with the first one, but same thing happen with the new board).

The new board started to fail after a day! The boards worked perfectly in the first few (~10) uploads. I can't imagine how this happen, but it's like the board is dying with time! The same sketch, which could be easily uploaded previously, can't be uploaded now.

If you ask me what happens, It starts uploading and gets stucked at about 95% of the progress. (please see the following image)

I found this is the exact issue mentioned in this thread. I found several other posts too regarding this matter so I hope I'm not the only one to face this. But unfortunately, still I couldn't find any working solution.

Can anyone please suggest me a proper workaround? At least, will downgrading the Arduino IDE will work, permanently?

Arduino IDE version, 1.0.1


texts: Why can't I redefine the ground for this ideal opamp circuit?

texts:
I have the following circuit with an ideal opamp and \$R_1=R_2=...=R\$

with \$U_{out}=-2U_{in}\$.
If I now naivly redefine the ground like this

the behaviour of the circuit changes to \$U_{out}=-U_{in}\$
Why can't I redefine the ground like this?
(I'm aware that those circuits aren't super useful. This is just an example to analyze a circuit. I'm just a little confused that I can't choose an abitrary net as ground for this schematic.)


texts:
This is my first time to use PIR (HC-SR501 ) . It's in repeat trigger model. But when I test the output of the PIR , it gives always HIGH .

I rotate sensitivity adjustment and time delay adjustment randomly to see any changes occur. I even cover the sensor with cloth so that It get's no infrared . still it gives high.
I changed my sensor and bought a new one. This shows the same problem too.
arduino code :

int PIC_IN = 10;
int LED = 13;

void setup()
   {
  Serial.begin(9600);
   pinMode(PIC_IN, INPUT);

  digitalWrite(LED, LOW);
   }

void loop()
{
  int val = digitalRead(PIC_IN);
   if (val == HIGH)
   {
  Serial.println("Moton detected");
  digitalWrite(LED, HIGH);
   }
else
   {
    Serial.println("...........");
  digitalWrite(LED, LOW);
    }
  }

here is the link for PIR  Datasheet.

What I am doing wrong ? I have no clue why it's not working.


texts: Insight on analog and digital Lock-in amplifiers operation principle?

texts:
As far as my knowledge goes:

  in the analog case, the discrimination of the, low S/N ratio, signal is done by (demodulation) comparing it to local oscillator with almost identical frequency and then passing it through low pass filter. So it must be that, if the input signal is: \$\sin(a)\$ and the reference signal is: \$\sin(b)\$ (almost equal), are multiplied and integrated, long enough, the result will be: \$\frac{(sin(a+b)+sin(a-b) + phase)}{2}\$, and after the filter only the low frequency component will be left, i.e.: \$\sin(a-b)\$.

Question:

More complete view in the operation principles (of both the digital and analog amplifiers) and the stages of signal processing would be greatly appreciated.


texts: calculating voltage or current for a plain transistor (no resistor)

texts:
the short version of my question is this:  how do you know what the current through a transistor will be if there are no resistors?
I am reading mostly the second edition of the Art of Electronics, and I've read and reread chapters 1-7 over the past couple of years, plus a lot of supplemental things like the Kuphaldt Lessons in Electric Circuits.  Most everything is making sense, but I find that when I'm trying to see how a circuit works by reading the schematic, I get really thrown if I have a transistor (bjt or fet) with no resistor to help determine what the current will be for a given voltage drop, e.g.  Is there a standard rough calculation for this?
The authors actually mention this in part of the discussion, where they say something like "what happens when the emitter resistance approaches zero?" and they introduce the intrinsic emitter resistance.  But if I try to use that alone for calculations, I get something very different from what it says in a simulation on EveryCircuit, e.g.  That modeling app seems to attribute by default a 1-ohm resistance to each terminal of a bjt, but I haven't seen that elsewhere.  Any guidance would be much appreciated!
Well, it took while -- I'm pretty sure my question was inspired by this diagram and by the FET Q1, which the authors state functions pretty much as a current source and biases D1 and R2 (?).  I assume that the purpose is to regulate the current and therefore the zener voltage, correct?  Thanks for the answers on this -- I have been rereading the transistor chapters and realize I was just confused about which element establishes current.


texts:
I noticed that if I set IF bandwidth low, the measures done with a vector analyzer are better (with higher SNR) but it is slower.

Precisely, what does it happen when I change it? Can you explain me simply what it represents?


texts: How bad is it to momentarily overload a transformer?

texts:
I have an espresso machine from the US running on a transformer in the UK.  Inside the machine there is a grinder, a pump, and some heating elements.  The machine is labeled 120VAC 1150W.

I have it connected to a hefty 1000W wound transformer (this is not a travel transformer!).  It seems to work fine.  Here is the label from the transformer:

I've connected up an ammeter to the mains side and when both heating elements kick in, it momentarily draws 1050W.  If I run the grinder at the same time, it draws 1220W total.  Running the pump, grinder, and all the heating elements draws up to just under 1250W.  The heating elements are only one for a minute or two and then it drops down to about 50W.  Even when you are trying to shoot continuous shots of espresso, the machine is not heating all the time.
The transformer gets warm as they normally do but definitely not hot, certainly not too hot to hold or touch.  The transformer's 6A fuse never blows which makes sense because that's 1500W at 6A.
My question is, if this transformer is rated at 1000W, generally how bad is it to momentarily go over this rating?  I'm guessing there is always some leeway in the ratings and that it's probably rated at 1000W for continuous use so my momentary 1250W draws are probably fine and given it's fused even at 6A.  It all seems fine, should I be worried?


texts: Reverse polarity protecion on an electronic load

texts:
I want to add reverse polarity protection on my electronic load which will be capable of sinking 20A and with a max. voltage of 50V (max. power is limited to 250W). Because I want to go with low input voltages for e.g. testing batteries, a typical solution like a PFET at the positive load input terminal is not a solution because of the V_GS_th of the PFET.

Diodes are also not suitable because of the high current and the related power dissipation.

I came across the solution of Spehro Pefhany which is shown in the picture.

I got one question about it:
My electronic load input terminals (Vx) are going to be floating (no connection to mains earth because of a transformer). The metal case is going to be connected to mains earth.

Is there a possibility to screw anything up, if some strange connections are made?

E.g. connect the negative load input terminal to the case and attach there the positive terminal of my DUT. Now I connect the negative terminal of my DUT (which is mains earth referenced) to the positive load input terminal. That would short out Q2 and the current would flow through the body diode of Q1.
Is this the only case which could cause problems?

What would happen if I connect a mains earth referenced power supply to my load terminals in a normal way (positive to positive and negative to negative)? That would connect the negative floating input terminal to mains earth and would bridge the isolation. Could this be a problem?


texts:
I have a 120VAC, 0.01 amp motorized ball valve that I need to plug into a control box. A pcb inside the box turns the valve on and off. The valve is shipped with an attached 2-wire cable that ends in bare leads. The system is designed to handle multiple 120VAC components inside the box, so I can't switch to a lower voltage DC valve.

I'm looking for a safe, panel-mount connector to attach to the valve's bare leads.

I've previously used barrel power connectors I had available, but these are only rated to around 30V. I've looked at IEC 320-C7 type plugs, which have a great panel mount female connector, but I can only find IEC 320-C7 cables that are pre-assembled. I'd prefer to solder the valve's leads onto a plug end, like with a barrel or audio connector, instead of attaching it to another set of leads.

I think it would be dangerous to run 120vac through the barrel power connectors (only rated to 30V), correct?

Is there a better type of connector to do this? Or do I need to solder or crimp the valve's bare leads to an IEC 320-C7 plug?

Edit: After researching IEC 320-C7 cables more, I think they're only available with factory terminated cable. Here's a link to a DIY site for making your own, but I need something that isn't hacked. I think I'll use Anderson Power Pole Connectors (as recommended below) or JST SM connectors.


texts: What happens if a 12V Thermo-Electric cooler / Peltier Module is supplied with 17-18v?

texts:
I'd like to connect a thermo-electric cooler to a power source that's actually being run from a solar panel to a 12V battery, and I'd like to tap the cooler module onto the leads for the solar panel before they reach the charge controller on the battery, as the current won't then flow back up through the charge controller (There's a diode), and I only want the thermo-electric cooler to be powered and functioning when there is input from the solar panel.

If I do this, however, I'll be tying the 12V peltier module / thermo-electric cooler to a 17V-18V peak voltage source, and I'm not sure if that will damage it or not.

Could this damage the unit? How so?


texts:
I have an homework assignement that gives me an headache, I have a circuit with a 2000W heater with a all or nothing regulation using a thermostat
The heater is running 1/2 hour then stop for 1h from 6pm to 6am next day, so I calculated the duty cycle ratio (Time powered/(Time [s] powered + Time not powered) <=> (830)/((830)+(9*60)) which is 0.31.
I need to calculate the mean instant power of that circuit, I went to the conclusion that this value would be nominal power * duty cycle ratio but I'm not sure at all of that
Am I right with my calculation?


texts: Missing component on the Usb to RS485 converter

texts:
I have a Usb to RS485 converter that was dead on arrival. I opened it up to see if I could fix it to find out that it was missing a component on the top left corner. This is a very common converter. Can someone who has the same device tell me what the missing component is?

Thank you!


texts: Is 128KHz oscillator in ATmega same as Watch Dog Oscillator?

texts:
Where is the 128KHz oscillator located in ATmega328p?

I am unable to find it on the ATmel data sheet ,Is it same as watch dog timer Oscillator?

I am attaching the clock section from the ATmel Datasheet below,There is no block labelled as 128KHz Oscillator?


texts: How do I calculate the cutoff frequency of a low pass rc circuit?

texts:
I want to calculate the cutoff frequency for a specific filter, but I can't find any formula for that.

I know the formula for the cutoff frequency of a low pass filter:

$$f_c=\frac{1}{2\pi RC}$$

But how is that derived in the first place? I don't have a regular low pass filter, but something similar that I want to calculate the cutoff frequency of.


texts: How to find out the spec of an unmarked li-ion battery

texts:
I have got some li-ion batteries which I don't know anything about and there is nothing written on them. Can you advise some testing methods to find out about their specifications and charging data so I can safely charge and use them for my own circuits?

Some of them are 18650 size and others are flat square shaped.

You are right to advise me to be on the safe side and get rid of them. But right now I am more curious to solve the puzzle than caring about the economic side. I have the device for two of them and can put the batteries in and charge. So I think I can find about the max voltage, and may be other data.


texts: NL17SZ74 D-Flip Flop circuit doesn't work!

texts:
I've been having trouble with what should be a really simple Momentary-to-Latch D flip flop switch circuit.

Basically:

I want the momentary switch PUSH to set the CP (Clock Pulse) Pin Low and on toggle SYSPWR pin high and low
BMOUT = supply = 5V
R107 is to act as a pulldown so there is no undefined behaviour on the pin
R106 and C109 are a RC filter so there is no bouncing on the CP pin on low-to-high transition

What's Happening, when pressing the PUSH button:

D and !Q pin is staying high
Q pin is staying low

Ideas:

need a resistor between D and !Q pin
need a pullup on Q pin

Can anyone tell me why this isn't working?
Here is the datasheet and truth table:


texts: Identification of Pin1 on LAN8720A 24SQFN package

texts:
can anybody help me identify which is pin 1 please?  - which corner and side is pin 1?
I find the data sheet and the actual picture confusing between the Datasheet
and the device


texts:
To sum up my question, can a digital dimmer switch be controlled with a ESP8266 WiFi switch? I don't fully understand how a digital dimmer works and I doubt that just switching the power through a relay would work?  Below is my question in more detail.

I am looking to control a Lutron Dimmer setup in a 3-way configuration without a traveler wire. My thought is there must be a way to do this with a couple Shelly 1s (UL) and direct through HTTP in case my HA box ever goes down. My question is can this Lutron switch be controlled with a Shelly one as it is a push button switch with dimmer? Thanks in advance.

Shelly 1

Lutron MACL-153M


texts: Optimize heat sink design - connect cooling pad on PCB backside by vias

texts:
In one of my current projects I'm using an MC7805 in a D2PAK package to generate my logic supply of 5 V from an available 24 VDC supply. The current required by the circuit is 250 mA. This results in a dissipated power of the MC7805 of:

\$P=(24\ V-5\ V)*230\ mA=4.37\ W \$

The PCB has to be assembled into a small plastic housing with the MC7805 inside. The arrangement is like this:

So heatsinks like for example these are not possible. Also the housing itself has a quite small volume and would heat up.

My first try to solve this thermal issue was to add vias to the pad and make an exposed pad on the other side of the PCB. Like this I want to dissipate the heat on the outside of the housing. Apparently this was not good enough as the thermal overload protection of the MC7805 kicked in after a about a minute.

So I added a small heatsink to the exposed pad at the backside of the PCB and now it seems to be working (the heat sink is still getting pretty hot!).

Besides my trial-and-error approach I would like to understand this thermal design a bit better and optimize it (as of now I cannot say what would be the temperature of the junction, and therefore I don't know how reliable this would be).

I already read a couple of other questions, but so far I'm still not completely clear (even thinking of power as current, temperature as voltage and resistors as thermal resistance, thermal design has always puzzled me...)_

So regarding this design I would have a couple of questions:

When using vias, the plating of the via is conducting the heat, while the air in the via hole is more or less isolating. So if not filled with solder, you want maximize the copper area of the vias in order to minimize the thermal resistance top to bottom layer. As I kept the solder stop mask open, the vias should be covered with solderpaste and getting filled while re-flow soldering. To minimize the thermal resistance between top and bottom layer I assume it would be best to have as much 'hole' area as possible. Is this assumption right?
Is there a 'not incredible complicated' way to calculate the thermal resistance between junction and bottom pad?
If not, can I somehow measure this thermal resistance (with a temperature sensor?
As the top pad and the D2PAK housing will also dissipate some heat. Can I (following the resistor analogy) put these in parallel? How would the thermal resistor network for this system look like?

I would like to further optimize this thermal design.

I cannot increase the size of the housing and PCB.

I cannot add a fan.

I cannot increase the size of the top layer pad.

I have already increased the size of the bottom pad to the maximum possible of 20 mm x 20 mm (above picture mentions both pads as 15 mm x 15 mm.

Do you see any further things I could optimize?


texts: power supply oscillates when loaded with instrumentation amp

texts:
I've been working on an instrumentation amplifier for a PWL ECG signal in LTSPICE. It should be able to filter out the common mode noise. I Also need to design a power supply. Both the power supply and the instrumentation amp work on their own. That is to say when the power supply is loaded only with a resistor and the amp is powered by ideal voltage sources. When connected however, it seems like the common mode noise is being picked up on the power lines and ends up in the output wave packet of the amp. (I should mention that the I've been playing around with the values for the components in the power supply so they're not final by any means.) Why exactly is this happening and how can I fix it?
If any more details are needed I'll be more then happy to provide.

 schematic

 signal


texts: Why was a resistor and capacitor used in this IR receiver circuit

texts: The circuit shows an IR receiver whose output pin is interfaced with a PIC. Can you explain why a resistor and capacitor were used and why those values were picked.


texts: Can I screw up my board by guessing which RS232 pins are which?

texts:
I have a Raspberry Pi that I want to hook up to a serial (RS232) cable. I've found and read some information about this, so I know what pins on my RPi are Rx/Tx/3.3V/Gnd...

Now the cable I'm hooking it up to has a standard RS232 connector on one end, the other end is just four female header connectors. I do not know which if the 4 connectors is which Pin for the RS232.

Will I cause any trouble if I "guess" which pin on the RPi should be connected to which of the header connectors? I'm thinking it just won't work right until I get the combination right, but I'd hate to screw up the board because I guessed wrong.

The cable has been around for a while, there's no documentation or anything. It has HAURTIAN E164535 and I bunch of other stuff printed on it, but when I searched for that it just showed a standard RS232-RS232 cable, not what I have. Also I can't seem to find this "HAURTIAN" company to check for documentation there.


texts: Calculate gauge of wire with voltage and current

texts:
I would like to figure out these two things:

X gauge of wire needed dependent on the current needed, and the length.
X max length of wire dependent on the current, and the gauge.


texts: Solar tracker using photodiode: circuit design

texts:
My aim is to differentiate between two different levels of illuminance. I would like to know when one photodiode is in shadow and other in direct sunlight. So I don't really need the level of lux but the difference in lux.

I have come across circuits like this, but instead, I would like to have this in differential mode utilizing both the photodiode in one amplifier. Also, I will be reading the output on Arduino so if possible I would like to avoid the amplifier prefer doing taking the difference in digital. But I guess directly reading across the diode won't be a good idea either as the voltage range is very small (0-0.5 V) and so the ADC resolution won't be good.

So, overall, I am trying to find a schematic for either:

A direct ADC of each photodiode with sufficient resolution so that I can take difference digitally.

Or

A differential amplifier with range suitable for ADC.

Sorry if you feel I haven't tried enough on my own. In that case please just leave a guide point and I will try to design the circuit.

EDIT

The reason I want to use photodiodes and not LDR is the nonlinearity of variation of the resistance with lux. In my experiment with LDR I first measure the resistance at ambient (~50k ohm) and then threw a flash on it for a few seconds, but when I removed it I found that resistance does not go back to the same value (stays around 10k ohm for minutes). It is kind of a Hysteresis non linearity with LDR. While for photodiode I felt that readings were consistent. Please try to take this too in consideration.

EDIT 2
So, considering the solutions suggested below and keeping in mind the time and components availability constraints I finally implemented the LDR and baffle mechanism. It worked out all well and so I wanted to share this video with you all Solar tracker-Light follower. Thanks a lot.


texts: Why is there difference between the "ideal scenario" and the "ideal simulation" for this isolation transformer model?

texts:
The illustration below shows how an isolation transformer is protecting from electrocution by not letting the current to loop through the earth at the secondary side. Neglecting the parasitic capacitances and assuming ideal conditions the current induced at secondary will loop as shown in red and not through the human(I believe "ideally" without any parasitics there will be no current passing through the human):

When I tried to simulate this again with ideal conditions where there is no parasitic capacitance ect, I observe the line voltage at one of the secondary terminals as shown below:

Then I first connected 1k Rhuman to bottom terminal and there is a tiny current passing through the Rhuman:

Later I connected 1k Rhuman to the upper terminal and there is a no current passing through the Rhuman:

My question is why I am observing voltage and tiny current between the secondary terminal and the earth in my simulation even though there are no parasitic capacitances?


texts: Why do Lithium Ion batteries self discharge?

texts:
I've seen some questions about loss of capacity due to internal resistance and oxidation of plates. I've also learned that these batteries have protection circuits.

But I'm curious about Self discharge, the phenomenon of charging a Lithium Ion battery to 100% and leaving it unused, only to return months later to find it has not preserved a full charge and requires topping up.

Is self discharge over time attributable to the chemistry of the battery? Is it the overhead of the protection circuitry? Or is it more complicated than that or some combination of the two? What is the mechanism behind self discharging Lithium ion batteries?


texts: CD4053B Supply Voltage Ambigious in Datasheet

texts:
I'm designing an analog voltage switcher based on the CD4053 and +-15V rails. By accident, I ordered the HEF4053 which clearly states that Vdd-Vee may not exceed 18V.
Now I'm looking at the TI CD4053B datasheet where it states:
Supply Voltage (V+ to V-, Voltages Referenced to VSS Terminal): Max 20V.
The question is: Can I run a CD4053 from Vee=-15V and Vdd=15V?


texts: Are MOV-based surge protectors designed differently for different appliances (drawing different amperages)?

texts:
I have come a cross a line of MOV-based surge protector that supposedly differ by the amperage of the appliance they are designed to protect. For example one protects "LCD and plasma monitors" and the other "dishwashers and washing machines". They specifically boast different amperage ranges as the difference (as opposed to features such as timers meant to protect mechanical compressors).

However it is my understanding than MOV-based surge protectors work by clamping voltage, not amperage so I am assuming it is a marketing ploy. Am I correct in my assumption?


texts:
I have an LED lamp that I want to control with my Arduino.  It has 6 bright white LEDs (on a PCB) connected to a 6v battery pack.  These all appear to be running in series and connected directly to the battery pack with no resistors in sight anywhere which doesn't make a whole lot of sense to me because of the voltage drop between LEDs (assuming 3V) but it works and is bright.  Only 2 wires come off the PCB.

My question is, how can I connect and control this with my Arduino Mega 2560.  My understanding of the Arduino is that each pin can only output 40ma which is by far short of the required amount if each LED uses 20ma.

Do I have to connect an external power source?  If so, how would I go about doing this and could I also power the Arduino with the same power source?

PS. I'm new at all this so please excuse any ignorance.


texts: Inquiry regarding digital toggle switches

texts:
Does there exist a toggle switch (both IRL and in LTSpice) that can take two, mutually exclusive, digital input signals which can toggle it between on and off states?
By mutually exclusive, I mean these two input signals will never be the same/equal.


texts: Does Xilinx/Vivado have something like Altera LPM?

texts:
A few years ago I used the Library of Parameterized Modules from Altera (now Intel). I am now using Xilinx/Vivado, and I can't seem to find any equivalent.

For example, I used to instantiate counters left, right, and center. I find it hard to believe that Vivado doesn't have this facility... but I can't find it!

Am I missing something here?


texts: Finding exact breakpoint location in long wire

texts: How can I find the exact location of breakpoint in my long transmission line? Please help with the methods.


texts:
I have a PIC development board which has few on board led's. I am programming MCU so that it can blink 3 led's in a parallel manner. I have made the following code:

void led1() //blink led1 with delay of 700ms
{
  LED1 = 1;
  Delayms(700);
  LED1 = 0;
  Delayms(700);
}
void led2() //blink led2 with delay of 1200ms
{
  LED2 = 1;
  Delayms(1200);
  LED2 = 0;
  Delayms(1200);
}
void led3()  //blink led3 with delay of 2000ms
{
  LED3 = 1;
  Delayms(2000);
  LED3 = 0;
  Delayms(2000);
}

void main()
{
  //******//
  /** code to blink led's in parallel **/
  //*****//
}

What logic should I write to blink led's in paralledl manner. I know embedded can only do one task at a time but there has to some coding solution for it. I don't want to use FreeRTOS for simple applications. I want them to blink at the same time. Like 1st one blinking with the delay of 700ms, at the same time, 2nd blinking with delay of 1200ms and at the same time 3rd blinking with delay of 2secs. All 3 parallely


texts:
How easy compare dimensions and footprints for different size SMT components.

I mean how compare footprints of 0603 with 0402 size components.

For example. I want to know is there possible to use 0402 component on footprint 0603. Or some another parts.

In which software or web servises I can do it?


texts: Assembly Jump Question (PC Offsets) - MSP430

texts:
So im still trying to understand basic computer architecture, and have been writing a little bit of assembly for the MSP430 (basic LED/Switches stuff).

I've been browsing the instruction set, and things are starting to make more sense.

However for example a JNE/JNZ (Jump if Not Equal/Jump is Not Zero). I understand these are checking the status bits (that were maybe set from a CMP function).

However the operation looks like this(Grabbed from the instruction set):

if Z = 0: PC + 2*offset -> PC
if Z = 1: execute following instruction

So if Z is 0, go to the next instruction...makes sense. But I don't understand the PC + 2*offset -> PC, I think im maybe confused on the PC itself. The user guide doesn't go into a HUGE detail about it. The PC presumably points to the NEXT instruction to be executed?

When it says it points to im guessing it's holding whatever is next? (Like maybe it's holding a MOV #020h,R9 or something? which would convert to some binary opcode + source and destination binary bits (thats a total of 16 bits? (I could be wrong here)

However I do not understand the PC + 2*offset part, offset of what? I think that's the part that gets me. But I think the whole "process" of whats happening is still confusing, I understand WHAT is being written and where but maybe not "how". (im getting there though!)

Edit: I think perhaps Im forgetting also that something like MOV @020h,R9 is actually 3 separate 16 bit words (I Think.....which would be 3 different PC counts) (since the registers are 16 bits large).

Edit2: Here is an Example from the MSP430 book: (Keep in mind I do understand "What" it's doing, but not why? and I don't understand the offset part

DelayLoop: ;
inc.w R4 ; Increment loop counter
cmp.w #DELAYLOOPS ,R4 ; Compare with maximum value
jne DelayLoop ; Repeat loop if not equal


texts: How fair is comparing a pair of long wires with a capacitor?

texts:
Long ago I was reading an explanation why twisted pair is batter than just a pair of wires. That text was discussing long distances - miles or dozens of miles. It said that two wires in parallel acted like a capacitor, so whenever the sender wanted to send a pulse and raised the voltage that long "capacitor" would take some time to charge and so the receiver would see slowly rising voltage instead of a pulse and when the pulse ended at the sender side by quickly lowering voltage the "capacitor" would continue discharging and so the receiver would see slow decrease in voltage. So transmitting short pulses was just impossible - pulses had so be impractically long.

How fair is such explanation and comparing a long pair of wires with a capacitor?


texts:
I read somewhere that bad VHDL code can lead to FPGA damage.

Is it even possible to damage a FPGA with VHDL code?
What kind of conditions would cause this and what are the worst case scenarios?


texts: When to "wind-your-own" vs "scavenge" a transformer?

texts:
I often see answers for one-off designs including the advice, "Just wind a transformer...."  Like it's no big deal.  Did I miss a class in which they handed out a sheet listing the formulas for core size, composition, geometry; wire gauge and insulation; and winding style as a function of voltage, power, frequency, duty cycle, and load application?

But I also frequently see people scavenging and reverse-engineering the pins on flyback transformers from CRTs.

So I'm deducing that there's an envelope inside which one realistically hand-winds a custom transformer, and outside of which it would be difficult/wasteful/dangerous to do so.  What are the parameters of that envelope, and why?


texts: How to generate assembly schematic file in Altium

texts: I need some help in generating assembly schematic file like the one below (first image). I managed to create something similar to it (second image), but I couldn't add those component names, values and descriptions beside them. I am using Altium Designer version 17.


texts:
After etching a PCB I discovered a big spot across some of the traces - probably from a finger. I transferred the PCB layout from a transparent film.

What would be the best way to remove "finger" and others from both the PCB and the film before etching without destroying them?


texts: How do I decide which method to use in circuit analysis?

texts:
I'm an Electrical Engineering student, and circuit analysis can be really confusing to me. I sort of understand the concepts of solving circuits, but I don't really know when to use which method. Are there any simple rules on choosing which method I should use for solving circuits? Node-voltage analysis? Superposition? Mesh analysis? Just use reduced linear equation system (or whatever it's called in English)?

Should I just calculate how many equations each method will take and pick the one with least equations?

Also, how do I know if I should use Thevenin's / Norton's generator to substitute a network?

Please note that this is not really for practical purposes - I'm studying for an exam, but all the assignments in my textbook are categorized by methods, so I know which one to use. However, in the exam that info is not given to students.

Thanks.


texts: Picking correct level of resistance for a voltage divider

texts:
I want to measure my DC voltage source (aka batteries), vs my known Dc voltage from my DC-DC regulator.  To do this I'll need a voltage divider.  I can calculate the resistances I need - but what I'm not sure about is the over all level of resistance I should go for.

If the voltage divider resistance is to low, I'll be burning current for no effect.  If it's excessively high.... is there any downside if the current is near zero?  Should I just got for 100K ohms and leave it there?

The math is easy.  But picking the right target?  That's hard.


texts: What is a full rectangular output characteristic for a power supply?

texts:
From what I understand, a rectangular output characteristic of a power supply refers to the fact that the maximum power is achieved when Vmax and Imax occur simultaneously. Kepco has a power supply that claims "full rectangular output characteristic." Is this because this is not a common quality? That is, do most power supplies not meet this criteria?

If so, what physical or design limitations prevent a power supply from achieving a rectangular output characteristic?

Here's a link to the product: http://www.kepcopower.com/klr.htm


texts: Controlling a Brushed Motor with DC Voltage to Avoid EMI (no speed control needed)

texts:
I have a fairly simple project coming up. My task is to design a system which powers and controls a Pan and Tilt positioner for a camera. It has some weird and unavoidable requirements/constraints:

No telemetry allowed in the Pan and Tilt positioner. Power must go
straight from a control box, through a wire, directly to motors.
PWM or AC should be avoided. The Pan and Tilt conductors will have to be in
the same Minikevlar cable assembly as some low-voltage analog
signals, and PWM would likely be too noisy.
As the title suggests, speed control is not a requirement.

The Pan and Tilt will likely contain 24V brushed motors for both axes. My initial approach would be to use a switch joystick to open/close a circuit for each motor in forward and reverse, and supply it via a 24V+ DC power supply (I say 24V+ because I will be accounting for Vdrop). I would also need a current limiting device of some sort to protect the motor when it reaches end-stops.
My second idea would be to use PWM anyway, and if it causes interference in the sensitive low voltage signals in the cable, I could keep changing the PWM frequency until I find something that works (while driving the motor properly, of course). However, if I keep the PWM duty cycle at 100%, I feel like it defeats the purpose.
What are your thoughts, and how would you approach this? I'm assuming my solutions are missing something important because my experience with electronics is not quite as extensive as I want it to be.


texts: Alright, I should probably know this, but I don't.  For a school project, I need to be able to charge a 12v battery from an alternator.  What I am stuck on is the method of how batteries (generally speaking) are charged.  Is it just plain old voltage going into the battery?  Or is it something more?


texts:
I am trying to recover the use of an old cordless drill by replacing the Ni-Cad batteries with Li-ion. I have removed the 10 x 1.2V Ni-Cad cells that were wired in series with 4 x 3.7V 4200mAh high drain Li-ion cells wired in series.

The original charger arrangement is through a transformer and a protection circuit built into a charging adaptor that fits on the battery pack (you have to remove the battery pack from the drill in order to fit the charging adaptor). The output of the adaptor is 15.5Vdc to 15.7Vdc at 500mA. I have charged the battery pack once and stopped when the battery pack voltage reached 15V. The drill appears to work well - there is plenty of torque but I'm not certain that the speed of the drill is as fast as it was previously.

Now the question: am I likely to cause any damage to the batteries by charging them in series (as opposed to using a balanced charger in parallel) and do you have any tips to get the best out of these cells i.e. what voltage to charge to, for how long, when to top charge during periods of non-use, etc.


texts:
I have this long cable which is carrying two differential voltage signals (around 300kHz maximum frequency) through a very "noisy" environment. I need to acquire this signal through a differential op amp (PGA204) and I was thinking about putting a filter at the input of the instrumentation OP AMP.

I found this nice filter:

(Image from: Analog Devices Tutorial MT-070 - In-Amp Input RFI Protection)

But I cannot deeply understand the purpose of the two different filters (DM and CM). From what I know, a common-mode noise is a noise present in both lines with the same "polarity", while a differential-mode noise is a noise which is complementary in respect to the ground in the two lines.

What I see in the schematic are three LP filters, two of them (R1 C1 and R2 C2) filter the signal in the two lines independently, with respect to the ground, while the third one (R1 R2 C3) filters the whole differential signal. But aren't we just adding poles to filter the input signals? I mean, if I set the cutoff frequency of the two CM filters to a certain value, these two filters will just filter the signal within the range set. In the same way, the differential filter will just filter the input signal within the range set.

How exactly do these two filters work together?
How can they act on different kinds of noise if they are just LP filters?

Thank you


texts:
I am looking at using small lengths of single colour 12v LED strip (2835) in a project, maybe just 1 or two sections i.e. 3 or 6 LED's. I have tried single 2 pin LED's and they aren't bright enough.
My question is if I wanted to use say a 12 V 500 mA wall wart, would it damage/blow the pieces of strip because the current was way over the top. Or would the strip just pull what it needed and the built in strip resistors handle the overcurrent?


texts: How to choose the right ferrite bead for an LDO

texts:
I'm trying to design a custom board that will include the FGPMMOPA6H GPS.

Looking at the Adafruit integration of this GPS, I can see a ferrite bead on the output of the LDO (MIC5225-3.3). See below:

I agree with the use of an LDO to get a clean power supply for the GPS, but I don't know how to choose a "good" ferrite bead on its output.

I'm not very familiar with the use of ferrite beads, so a little help would be highly appreciated!


texts: Non-sinusoidal waveforms: relationship (resistance, capacitance)\$\xrightarrow{\text{affects}}\$ (amplitude, frequency)

texts:
During the laboratory we have analyzed the following two non-sinusoidal generators:

square-wave generator

triangular-wave generator

Sadly we didn't have enough time to complete the last task.

My question: What is the relationship between the values of resistance/capacitance, and the amplitude/frequency of the generated waveforms? (e.g. inverting input wave of square-wave generator).

$$\Big(\text{resistance, capacitance}\Big) \xrightarrow{\text{affects}} \Big(\text{amplitude, frequency}\Big)$$

Is there any general rule-of-thumb to follow for the two above circuits? For example that increasing/decreasing the capacitance increases/decreases the amplitudes of all waveforms?


texts: Simulating pad button press with GPIO rPI3

texts:
So, i have very limited knowledge when it comes to electrical components. I have a decent amount of programming experience however.

I am trying to simulate a button press (big middle button in linked picture below). However, nothing seems to happen when i change the GPIO to high or low. I have checked with a multimeter and it is changing voltage but i guess thats not enough?

If i ground the other (top part) of the button, it does trigger the button but this happens even if the rpi is off (and ofc regardless of gpio setting). The lower part of the button is attached to a leg on some chip and the top seems to be connected to the battery (3v watch battery)

Any help is greatly appreciated.

What ive tried:

Soldering jumper between leg on chip and the other side of the button works like normal.
Soldering either point to gpio (only 1) has no effect. (Regardless of gpio settings)
Soldering chip leg to gpio and other to ground makes the button always trigger, even when rpi is off and regardless of gpio settings.

https://i.postimg.cc/CLdnP4GX/20190807-231615.jpg


texts: How exactly averaging is performed in the diode sensor based power meter?

texts: I was just wondering how the power averaging works in the diode sensor based power meter. Can you please enlighten me? Thank you.


texts:
It's a long story. Please bear with me as I try to describe what I intend to accomplish.

I've got a Raspberry-PI controlled Lego Technics (pre-Mindstorms era stuff) construction.
It uses a couple of 1980's Lego motors, that are normally be powered by 3 C-size 1.5V batteries in series: Effectively some 4V to 4.5V.

The motors appear to be just that: No fancy electronics, overload protection, rectifier circuity, at all. (There may be an internal capacitor in parallel, like in the newer 9V Lego motors, but that would be just about it.) The battery-box only contains a mechanical switch with neutral, left and right positions. Single 2 wire lead from battery-box to motor. (Polarity gets reversed to change direction of motor.)

I'm not directly switching the power to the motors from the PiFace. I found a relay with 2 inputs (cutoff and polarity) which mimics the behavior from the mechanical switch on the battery-box and which completely isolates the "controlling" circuitry from the "controlled" circuitry. (I know I'm not using the proper terminology for relays, but I hope I'm clear.)

It made sense for me to use that, to make sure the rather delicate Pi/PiFace doesn't get sprayed with electric noise from the motors, when the polarity reverses.

The entire setup is now working, using the original battery-boxes, to power the motors.
As they eat batteries at an alarming rate I'm interested in powering these motors with a 5V feed from the power-supply that currently feeds the Raspberry-Pi and PiFace that control the Lego motors.

The PSU is actually a normal 450W computer PSU, where one of the 5V leads is brought outside the case to feed the hobby-project. The computer itself is always on (drawing abotu 250W), so there is no issue with using an unloaded or severely under-loaded switching PSU.

My days of analog electronics are 25 years behind me. I was never any good at it either. (I'm a digital guy.)

Even so I'm quite certain I better not wire this up "as is".  (I do know enough to know when I need a bit of help.)

Will 5V straight from the PSU fry the motor? I guess some sort of voltage (and maybe current) limiting circuit is desired. (I don't have any spare motors, so this really worries me.)
Will the induction of the motor-coils cause stability issues with the PSU when suddenly reversing polarity to the motor. I can, in software, introduce a "not-powered" period, between reversing the polarity if needed, but how long should that period be?
If a limiting circuit (1st point) is used how will that affect point 2?

Has someone tried something like this before? Any guidance will be appreciated.


texts: I2C multiple masters, one master has internal pull up, do I need external pull up?

texts: I use 2 MCUs as 2 I2C Masters connect with 1 Slave F-Ram to Read/Write data frequency. One MCU has internal 12k Ohm pull up resistors on SDA & SCL. So do I need external pull up resistors?


texts: lt1076 buck boost converter outputting voltage that is too low

texts:
I am using this buck boost converter from the lt1706 datasheet:

It should take 10 to 40V and output 5V and 2A. But when I proto boarded it it only outputs 2.2V and I really need the 5. I am giving it 16VDC.

Here are the exact parts I used:

RL-2444 Renco 0942 100uH inductor
lt1076ct switching regulator
mbr 340 1410 Schottky diode
200uF capacitor
560uF capacitor
0.01uF capacitor
2.7k resistor
2.21k resistor
2.8k resistor

I'm not sure if one of my parts are wrong, I'm pretty sure everything is connected properly. Any suggestions?


texts: Automatic LED emergency lamp circuit with overcharge protection for 12v lead-acid battery

texts:
I am a newbie in the field of electronics.So please  help me with my questions. I am trying to implement this circuit below.

I have a 9-0-9 centre tapped transformer. Then how to change the circuit for a fullwave rectification. And I want to use a 12v battery. Will this circuit be sufficient for 12v battery for sure?

Requirement summary:

Charge 12V lead acid battery. Low charging rate is acceptable.
Maintain 12V lead acid battery at correct "float" voltage when charged.
Automatically turn on an output (light, LED strip etc) when input power is removed.
Utilise available 9-0-9Volt output transformer.


texts: I have to design a 150 Ampere, 1.5 mH Inductor for a power supply project assigned to me, and off-the-shelf components are to be used. My instructor is insistent on using a transformer Bobbin to wind the conductor around, however wants me to optimize the design to standard bobbins available commercially. My question is, what is the "standard size" per se? Is there a chart, a la wire gauge chart, available for it? I've tried Google but sofar haven't found anything useful. Any help is appreciated.


texts: What is the proportion of the strength signals between wired and wireless mouse/keyboard?

texts:
I understand that the PSU of a desktop PC is creating noise (ripples and ringing) at frequencies that propagate along the cable of the mouse and the keyboard, and radiate those signals through them. The frequencies may be beyond 100 Mhz.

My question is: what is the proportion between the strength of the wired mouse/keyboard radiated signals (which radiate that > 100 Mhz noise signals) opposed to the strength of the signals that radiate from wireless (WiFi) mouse/keyboard?


texts: Audio circuit: single point PLUS ground plane

texts:
I'm currently designing my first audio PCB. I've read a ton of discussions and guides about audio grounding, so I've decided to use single point grounding (with the point being last filter capacitor minus).

However, one question arised in my head and I haven't found an answer. Is it beneficial to the circuit to make a fill on the PCB, connected with ground at the single point?

It seems logical to me, that a fill on the PCB would reduce noise and crosstalk between signal traces, while connecting this shielding plane to ground in single point would eliminate all current return problems which normal ground fill would cause. Ideally, no current would flow through this plane, as whole circuit itself is connected following the idea of single point.

On the other hand, it could make the ground noisier, as the ground plane is sort of an antenna.

A following question would be - if my conclusion is correct, should I connect the fill to quieter preamp ground (which is more sensitive) or noisier power amp ground (which wouldn't care too much if its ground would collect some noise)?

Edit: To clarify: this is not a debate between single point and plane grounding. Grounding of the circuit WILL be done via routing components to the single point only by 1mm traces!

The point is: is it beneficial to put a separate fill on the PCB and connect it to the circuit ground in the single point (not connecting any component to the fill)? Will it increase or decrease overall noise if there is a screen added?
Again - the fill will be connected to the ground at ONE POINT, no component connected to it.
This is the PCB without any pours:

This is what my idea of screening fill would look like, notice that both bottom and top fills are connected to anything only under C8 cap, components are still connected to their single points:


texts:
While studying inductors, I learned that it will take some time for current to reach it's rated value \$ I\$, and considered in "steady state".

Is the same applied for singular wires(not forming a loop/multiple turn loop)? In general, if a wire with low resistance and possibly low inductance had DC flowing, will it time a short duration of time to reach maximum current? Using this equation: \$ t = \frac {L}{R} \$.

From the equation above, that's the time it takes for current to reach \$ \frac {2}{3} \$ it's value?


texts: ripping audio cd gives different checksum. Real? fake? Underlying reason?

texts:
Today I was talking about ripping CDs with a colleague, and the fact that if you rip the same CD twice the md5sum is different. This is what I personally experienced, and I knew out of reading around, but I am not well informed about the underlying hardware reason for this. To be fair, I start to question even my experience, which could have been the result of a mistaken execution of the cd ripping program.

Do you know if this makes sense from the hardware/error correction point of view, and what is the underlying hardware reason for unreliability of audio cd data extraction?


texts:
I am using A7 module from Ai Thinker for GPRS and GPS. However, what I notice is that,

The A7 module does not lock GPS
When the GPS application on Android Phone shows 13 detected GPS satellites, the A7 module struggles to detect even 3. The best I have seen so far is 4 satellite. But it did not lock the GPS.

I took the module in open area and kept it ON for 15 to 20 mins without any luck.

I used commands like AT+GPS=1 and AT+AGPS=1 to enable GPS.
Am I missing something here.
Any help in this regards would be useful.


texts:
I'm just getting a start learning about electronics, and purchased a new oscilloscope -- a DreamSource Lab DScope U2P20 4, which uses the open-source DSView software 5.  I built a simple 555 timer from page 7 of the Engineers Mini-Notebook: 555 circuits 6, and I'm getting an unexpected result from the scope.  (Note: I added a 0.1uF ceramic capacitor between pins 1 and 8 due to noise from my power supply.)
My question is, is this an electronics problem (my circuit needs improvement), an oscilloscope software problem (rendering poorly), a hardware problem (I chose the wrong scope), or is it normal (an education problem on my end)?  What can I do to get better results / visualization of the data?
Here's what I'm seeing:

When I zoom in, I get the following:

Thanks much for helping a rookie learn!


texts: Voltage Reference Resistor Calculation (Shunt)

texts:
I am trying to design a circuit using this LM4040-5 Voltage Precision Reference for my DAC8554, but I can't for the life of me figure out how to properly calculate the resistor value to be applied. Right now the LM4040-5V (5V reference) is giving me voltages ranging between 4.77v to 5.11v. Obviously not very precise!

This is the basic schematic for the LM4040 via its datasheet, as well as the formula they suggest for calculating the Resistor value:

So for my particular design, VS == +12v, VR == +5v, but where/how can I obtain the values for IL (load) and IQ (operating current)?


texts: On guitar amps, what is the difference between the two "watts" figures?

texts:
Disclaimer: I know nothing about electronics or guitar amps.

(Actually, I do know one thing:  that "wattage" is synonymous with "volume" when speaking about guitar amps and since watts are measured on a logarithmic scale, a 100 watt amp is only twice as loud as a 10 watt amp...I think.)

I am very confused.

My question applies to any guitar amp, but as a random example, I will use the Fender Blues Junior III amp.

According to the product description on the official Fender website (and all product descriptions of this amp online), it has 15 watts:

But, according to the plate on the back of the amp itself, it has 180 watts:

How come there are two different watts numbers with guitar amps? What does each number represent, and how can they both simultaneously represent the amp's "wattage"?


texts: How to measure CO2, O2, NO2 and NO3 concentration in water?

texts: I am making a system to monitor the environment vectors in my fish tank. And I am looking for some methods to measure CO2, O2, NO2 and NO3 in the water. I found some information to measure CO2 with infrared absorbtion on a gas. But, I have not enough information to do it in the water. Are there any methods to measure their concentrations in water?


texts: CONTROL CIRCUIT : Question Regarding Voltage and Resistance

texts:
I was wondering, whether my explanation was correct or not. I checked with online sources and they say I was incorrect, but I cannot understand how I am incorrect.

As the resistance increases, doesn't the voltage increase proportionally?
So if the resistor value increase the voltage at POINT C will also increase??

Thanks!


texts: How to get started with Microchip's PIC12 family programming?

texts:
I would like to start programming PIC12F683 but I have no clue how to handle I/O. Where can I find specific syntax for specific controller?

I have tried to register on their forum, but I have't received e-mail (resent registration email multiple times, no luck).

I have found programming guide on their site - PIC12F6XX/16F6XX Memory Programming Specification - http://ww1.microchip.com/downloads/en/DeviceDoc/52053B.pdf
If required information is there, then I have some trouble to find what I want.

Might be there is related articles, step by step guides, videos?


texts: Switch mode power supply making for beginner

texts:
Hi I'm a beginner at designing smps circuits tbh its my first time and i don't wanna get into the headache of using pwms and octocouplers insteas i want a mosfet or ic that can regulate itself i.e having a fixed voltage output and adjusting its switching frequency automatically according to the load added I don't really care about what ever voltage it outputs I'll add multiple of them in series just to avoid the headache of using pwms
So can anyone help me with such mosfets effecient ones are preffered and i need around 24 volts 21-24 volts


texts: How do I add a circuit to disable this system during the night?

texts:
Key bits of circuit illustrated below:

buzzer (J1) activates at interval, triggered internally by IC pin 4
when solar panel low (not making 1.6v) triggers IC pin 7 via Q2, which triggers IC pin 2/3 High (3v) and light led
buzzer can be plugged in & out, when plugged in it activates the timed buzz intervals from the IC via Q3 and IC pin 8

I want to mod it so when at night the buzzer doesnt run

I want to use the solar circuit to trigger 'darkness'


texts: How can I find the slip speed of a slip ring induction motor without knowing the rotor speed (rated RPM)

texts:
The Rotor of a 4 pole, 50hz slip ring induction motor has a resistance of 5ohm per phase and inductance of 150mH per phase. Calculate the slip speed at which max torque occurs.

I have used Ns = 120f/p to find the synchronous speed, being 1500RPM, but I cannot calculate the Slip speed without knowing the rated RPM of the motor.

Is there a way to calculate this using the given information?

UPDATE:
I believe this is the answer.

ns = 120f/p
     = 120x50/4
     = 1500 rpm

fr = X/2piL
   = 5/(2pi x 0.150)
   = 5.3hz (or rpm?)

Slip% = fr/f
          = 5.3/50
          = 0.106

Slip speed = slip% x ns
                  = 0.106 x 1500
                  = 159rpm at 10.6% slip (0.106x100)


texts: How do I calculate the temperature rise in a copper conductor?

texts:
If I pass a current through a copper conductor, how can I calculate how hot the conductor will get?

For example, if I have a 7.2kW load powered by 240VAC, the current will be 30A. If I transmit this power to the load via a \$2.5mm^2\$ copper conductor, how do I calculate how hot this conductor will get?

UPDATE:

From the comments and answer from Olin and Jason, I've created the following graph showing Watts per foot of \$2.5mm^2\$ copper wire:

But how do I translate this into the the actual temperature rise. I understand that the missing variable is the rate of cooling, but I just need to get an idea of what the maximum safe current is that can be passed through copper cable of a given thickness.

Assuming a constant current, and that there is no cooling at all, how do I calculate the degrees of temperature rise per hour per Watt for the foot length of copper cable in question?


texts: Is there any way I can power my 120-220V AC motor from a battery

texts:
I am building a new robot, it's a little bit heavy, so it's hard to find a motor that can push it. I am thinking of a way to use machines at home (I have two options: Automatic hair drying machine and drill machine (I have 220v one)) to get the motor inside to move it.

The problem I am facing here is that I need to use battery. Can I hack the motor somehow to find a solution ( i though of using 5 batteries 24v in series, but it's not an option for me as it would make it very heavy ).


texts: Does noise match of an LNA mean minimum signal to noise ratio at output?

texts:
Does noise match of an LNA means minimum signal to noise ratio at output? According to definition it means minimizing relative contribution of noise power with respect to source.

If not why do we then do noise match at input of LNA.


texts: Can I use ATmega328 TX/RX pins to drive an R2R network and still use the serial port to program the MCU?

texts:
Background
I wanted to make a simple function generator with an ATmega328 and an R2R resistor network, similar to Jesper Hansen's Mini DDS (Direct Digital Synthesis).
To make the function generation firmware run fast enough, I believe I have to wire an entire PORT (all of its 8 output pins) on the ATmega328 to the R2R resistor network. This way I can write one full byte to the port with a single command, like so:
PORTD = B10101000;

On the ATmega328, I think PORT D is the only port I can use like that. ATmega328 pinout and port distribution is below.

The Problem
The problem I'm facing is that I also want to use the ATmega328 serial port for programming the board, but the serial port is also on PORT D (pins PD0 and PD1), thus creating a conflict.
Proposed Solution
After some research, I've decided that I could get away with the design below. The relevant part is circled in green.

With that circuit I think I'll be able to use the serial pins for programming the board and also, but not at the same time, drive the R2R network to produce a sine wave.
Considerations
The considerations I gathered so far, including contributions from comments, are the following:

R17 is required to protect whatever is connected to the RX line (e.g. MAX232 IC) when ATmega pin 2 is changed to an output to drive the R2R network. That will prevent a large current from being sourced by the MAX232 IC when the pin is driven low.

R17 value (1kΩ) will slow down RX line a bit (increase rise and fall times), but according to what I understood from this answer by Leon Heller - Resistors in series with Tx and Rx, it won't be enough to prevent serial communication (pending experiments to prove it).

I won't be able to use both functions at the same time, but that's ok, as I plan to switch between functions in the firmware.

RX and TX lines are linked to each other by a 50kΩ equivalent resistance, by R1, R2 and R3. That will create a 0.1mA current in and out of each pin, when they show different logic levels. I think that won't be a problem, but further experiments are required.

Questions
My questions are:

Will my circuit work? If not, why not?
Will this circuit burn or stress my ATmega or whatever I connect to the serial connector?
Is there a better way to do it using an ATmega328 and the R2R network?

I know there are a lot of ADC chips out there that would help me solve this problem easily and would make my miniDDS more precise, but I wanted to start out with these requirements.


texts: What's the output of ICs if only one source pin is connected ( Vcc or ground)

texts: Let's suppose I have an AND gate whose output is connected to an OR gate. The OR gate is powered normally but the AND gate is only connected to +5 volt and the ground is disconnected (or viceversa) . What is the input of the OR gate? Is it undetermined? It's in a hogh impedance state? Does it depend on the state of the AND inputs?


texts: What's the physics behind LEDs wearing out?

texts:
Short version: I'm thinking about running LEDs in a potential over-current setup, but with a PWM-based supply. Will the LEDs suffer an early death? Said otherwise, do LED die of overheating, or really because of the over-current?

Long version: My setup consists of the following parts, all coming from various low-cost Internet shops - so no datasheet or reliable spec is available for any.

One LED strip. Composed of 12 modules in parallel. Each module contains 4 components in series: one 39ohm resistor and 3 5630 white LEDs. My understanding is that it's supposed to be fed by a 12V DC supply. When doing so (with a bench power supply), each LED operating point is around 3.3V/52mA, for a total of 7.6W for the whole strip (when the resistors are considered).
One LED PWM driver. A small $1 module that can generate blink patterns or dims the LEDs via an 1.5kHz PWM (confirmed with an oscilloscope).
One crappy wall wart, specified at 12V, 1.5A, but which outputs ~17V when there's no load, and around 13.25V when feeding the LED strip, operating each LED around 3.6V/60mA.

I've failed to locate any datasheet for a 5630 LED that has that kind of operating point. In the 12V setup, each LED dissipates ~175mW, which seems an odd value. Assuming that they're really 1/4W LEDs (even if most 5630 appear to be 1/2W), the 3.6V/60mA operation point would still be under that, albeit marginally.

Back to the question: I'm trying to speculate how long these would live if I was to operate them at, say, 80% duty cycle - which would probably end up being at a voltage/current even a bit higher than the numbers above. Can anyone provide some background of the physics of LED wear?

Obviously, adding an ~1 ohm, 1 watt resistor in series would solve everything, but where would be the fun in doing that...


texts: Using parallel capacitor-diode pairs to limit current in an AC circuit

texts:
I want to limit current from an AC source using capacitors.  As I am using dielectric (polar) capacitors, I thought I could use 2 capacitors with opposite polarity in parallel with a diode in front of each capacitor to protect it from reverse bias damage (see circuit diagram for clarification). My thinking was that every time the source's polarity switches, the current will go through a different capacitor-diode pair, always with the capacitor's reactance limiting the source's current.
When attempting to do this in practice, no current moves at all, so I must be misunderstanding something very important.  Would any kind sage be interested in pointing out my error?  I'm a physicist who likes to tinker, so if this is something embarrassingly stupid, that I should have learned in AC 101, I apologize.
I'm mostly interested in understanding the general idea of why this won't work, but if you'd like details, the AC source is mains (120VAC, 60Hz), the capacitors are 22uF, 400V, the diodes are 5A, 1000V rated.


texts:
This black component becomes very warm and I have a feeling it is broken since it becomes very hot compared to the other two similar ones.

Can't find any part number or anything.


texts: Voltage Division when we have a capacitor and resistor in series

texts:
I don't understand a particular feature of voltage division. Consider the circuit below (we are trying to find Vo):

simulate this circuit – Schematic created using CircuitLab

Now, if the 10-KOhm resistor was not there, it would be obvious that the voltage across the capacitor would simply be the Source Voltage multiplied by the voltage divisor

Vo = 30 x (40/(40+20))

However, we have a 10-KOhm resistor here in the same branch where the capcitor is. I always understood voltage as "pressure", and whenever voltage meets a resistor, some of that pressure is lost forever (i.e. until the current flows back into the voltage source).

Thus, in this case I would be inclined to think that the 10-Ohm resistor "eats up" some of that voltage and thus the Voltage across the capacitor would not be found using the classic voltage divider.

Well, I am wrong apparently, since the solution to this circuit is indeed given by the voltage divider.

So how come the 10-KOhm resistor does not affect the voltage across the capacitor?


texts: Aren't UBEC's just packaged voltage regulators?

texts:
I'm working on a project where non-trivial currents (theoretical peak ~6A) are needed at several different voltages. Since this is battery-powered, I initially started looking at finding an appropriate switching voltage regulator. After looking into a couple different ICs, I found that the prices (including all of the additional components) were coming out around $15 to $20.

I then stumbled on BECs, which are widely used in the R/C market and seem to effectively be pre-packaged voltage regulators (i.e. including all of the additional components). Here's an example.

Although I'm not clear on what the name means (it stands for "battery elimination circuit"), it seems that a BEC would serve my purposes at a slightly lower cost and with a lot less work than creating the circuitry from scratch.

Is there any reason why a BEC wouldn't be a viable option for voltage regulation in a non-R/C application?


texts: Can GPIO connectors be used for the same purposes as PIC i/o ports

texts: I just studied learning micro controllers and try to understand difference between them and processors. I've read examples of how to use PIC micro controllers to switch on and off LEDs. However, then I found one board PC - https://www.olimex.com/Products/OLinuXino/A13/A13-OLinuXino/open-source-hardware . It's much powerful and I start to think if I can use this one board PC and manage i/o ports for working with LEDs. Do I understand right that 1) we can do it 2) we do it via GPIO connector which fulfil the same tasks as i/o ports in PIC?


texts: Advice regarding bluetooth microcontrollers

texts:
I am doing some research into a potential electronics project I would like to try out. What it involves is having a collection of small remote devices that communicate with a larger central device. The amount of communication would be minimal, and low volume and power usage is important. From my reading i think that using Bluetooth (the low energy usage version) might be a sensible choice.

I think the best choice would be some type of integrated system which has the BT chip as well as the micro-controller in one package. I have seen several of these systems online, though I admit I am unsure about what equipment I would need to start developing. Many of these systems seem to have "Dev Kits" however they are often quite expensive (compared to the unit cost of the chip itself) and what I am looking for is the bare minimum (ie. 2-3 chips, connection equipment, and compiler if needed).

A few that look promising are:
CC2540 Mini Development Kit
Nordic Semiconductor nRF8001 Development Kit

I have some limited experience using micro-controllers as I took a short course programming an Atmega128 in assembler. I would gladly hear any opinions or possibly alternatives.


texts: Significance of timing simulation for FPGA

texts:
I have started to wonder what is the significance of the timing simulation for FPGAs nowadays. I can easily justify what is the idea behind that by quoting some Xilinx materials:

  Performing a thorough timing simulation ensures that the finished design is free of defects that can easily be missed, such as the following:

  Post-synthesis and implementation functionality changes caused by the following:
  Synthesis attributes or constraints that can cause simulation/implementation mismatches, such as translate_off/translate_on or full_case/parallel case.
  UNISIM attributes applied in the UCF file or using synthesis attributes
  Differences between synthesis interpretation of language in different simulators
  Dual-port RAM collisions
  Missing or improperly applied timing constraints
  Operation of asynchronous paths

Howevery, I do not know any engineers or companies in my area that would perform timing simulations for FPGAs. They just assume that if the timing constraints are correct and there are no timing violations after the place and route, then everything is fine.

I can understand this approach as timing simulation can take a lot of time for complex designs and, to be honest, I have never heard or read any story that timing simulation for FPGA has helped in fixing some bug that wouldn't be a bug on the functional level of the design.

Can we just say that nowadays timing verification of the FPGA designs has been reduced to trusting outputs of the vendors tool chains?


texts: Coax Cable Wave Impedance, Capacitive Load

texts:
I am studying the behaviour of cables over frequency, especially what a source sees, and have 2 Questions, as I did some simulations in LtSpice. As a model for the cable I used the "Lossy Transmission Line", values are per meter. I did a frequency sweep from 1 Hz up to 500 MHz with an Amplitude of 1 V. The first plot shows the Impedance in Cartesian form, the second the absolute Value of Impedance and the third the Phase.
Image 1, "matched") : Cable is impedance matched with 50 Ohm.
My thoughts:
The source sees from DC to approximately 300 kHz 117 Ohm Real Component (as 2x50 Ohm + 10*1.7 Ohm = 117 Ohm) and a minimal Imaginary Component.
But why does the Real Component of the Impedance fall down to 100 Ohm at frequencies above 10 MHz ? Is it because the reactance of the capacitor starts to shorten, and as so the line Resistor gets also shortened?
Image 2, "open"): Load is High impedance, cable mismatched.
My thoughts:
Between frequencies of 100 Hz and 200 kHz, the source sees a Capacitor, because of phase shift of -90 Degrees with 1000 pF (=10m*100 pF/m = 1000 pF).
Lets take an example where the cursor is located, at a frequency of f=50 kHz. As $$
X_{C} = \frac{-1}{2\pi*f*C} =  \frac{-1}{2\pi 50 kHz*10*100 pF } = -3.153 k \Omega
$$
, this matches with the imaginary component at that frequency.
Starting at 3 Mhz, the source sees alternately a Resistive, slightly inductive, Resistive and finally a slightly capactive load. Did I understand that right, if not, what am I missing ?
Many thanks!