texts: Commanding a 12V DC motor with high power (~20A)

texts:
I'd like to control a 12V DC motor but it has very high power, around 20A.

I was looking for H-bridges but they all support only low power (around 1A)

Do I have to build my own H-bridge with high power MOSFETs?

I just need a high power H-bridge.


texts: Delaying a 5 volt power off with an RC circuit

texts:
I have a microcontroller that needs to be able to survive a power outage just long enough to shoot an email telling me that the power is out. I figured the best way of doing this would be a resistor capacitor circuit, like the one below that I made that works well, that keeps the LED lit for a second after pulling the plug.

Ideally, I'd like to have something like this for my microcontroller! I just need to be able to keep it up a few seconds after the power goes out! (it instantly detects an outage)

I just have no clue what size resistor or capacitor I need, or if this is the right circuit type for the job.

specs:

Input Voltage: 5.15V

Minimum Voltage: 4V

Current draw:  600mA

Time needed: 5s minimum

I've run across many calculations, but I don't even know enough to say if I'm plugging in the right variables.


texts: Understanding startup circuit in this power supply

texts:
This design is from  a TI App Note: http://www.ti.com/tool/PMP10195

I want to understand the behavior of the circuit around Q3 and Q4. As far as I understand Q3 is turned on first for the VIN and and ULVO pins. Then when U1 is turned ON it activates Q4 and consequently turns Q3 off?


texts:
The problem is that when I heat an underfill chip to reflow it, the solder tends to boil and come out of the sides causing shorts and other problems.

Does anyone know how to prevent that and why it actually occurs?


texts: Solving a circuit with node voltage method

texts:
I have the following circuit:

Knowns:

Iz = 80 mA

R1 = 100 Ohms
R2 = 150 Ohms
R3 = 220 Ohms
R4 = 330 Ohms
R5 = 100 Ohms

As I understand Gi stand for the current source internal conductivity, but provided only the current Iz how can I calculate it? My guess is I need to know the resistance of the whole circuit...
How to calculate the resistance of this whole circuit, I tried simplifying but as it seems to me there is nothing to simplify
How to solve it using node voltage method, preferably if you can elaborate step by step so I understand it

If anyone helped it would be greatly appreciated!


texts:
I am looking for a small, low power buzzer for my circuit. The components I found in the market do not fit my requirements. The piezo buzzers are too big (min diameter 9mm) while the electromagnetic one consume too much power.

Is there any other type of buzzer I can use? What is used in wristwatches?


texts: Compatibilty between GPRS and LTE modules and networks

texts:
I summerized the question for ease as follows:

Lets say we have an LTE module under the coverage of an old base
station like 2G with GPRS. Will the LTE module work?
Lets say we have a GPRS module under the coverage of a newer base
station like 4G with LTE. Will the GPRS module work?


texts:
I am designing an adjustable power supply. Input voltage is 12V from adapter, and the output should be ranging from 0.5V to 12V.

I'm planning to use LM2575, but apparently its minimum output voltage is 1.23 based on datasheet. My concept is instead of using potentiometer to adjust feedback voltage from the LM2575, I use DAC MAX522 to create feedback-like voltage (this is possible right?).

Here is my current schematic

The question is:

is there any recommendation about the DC-DC step down regulator with minimum output 0.5V?
To avoid wasting resource, will this schematic works?

Thanks in advance


texts: Can I use a 220V incadescent bulb to drain a 12V battery?

texts:
I'm about to replace the batteries of my UPS. For safety, I'd like to drain the old batteries completely before disposing, but I don't have a large 12v load at my disposal.

Can I wire it to a 220V incadescent bulb (a.k.a. a 'lamp') to drain it?


texts:
I've been learning about phase-shift oscillators and put together this design:

I built it and it seems to work pretty well, you can see the exact values I used, and design here: [1]. But the design I used seems different from a lot of those I've seen online. Most designs put the capacitors in series for example:

I found that harder to understand which is why I went for my design. Is there any reason this design is more common? Is it because my design will result is more losses over the in series resistors?

[1] https://41j.com/blog/2014/12/phase-shift-oscillator/


texts: Instantaneous voltage drop acrossed resistors in series

texts: When two resistors with equal resistances are wired in series the voltage across each resistor is equal to half the voltage of the power supply. Is this also the case the instant the power supply is turned on? At the instaneous moment when the electric current has just reached the first resistor in series is the voltage across that resistor equal to half the voltage of the battery or all the voltage of the battery? In the case of the former being true, how is the current "aware" of the second resistor in the circuit before encountering it? In the case of the later, how does the circuit eventually reach equilibrium?


texts: Can a system with a response Y(x) = ax + c be called linear?

texts:
I made a DC-DC converter its  ideal transfer function is:
$$  V_0(D) = DV_i  $$

I took measurements of its response and then made a linear regression, I got this result:

$$ V_0(D) = 0.98DV_i -0.42 $$

Quite similar to the expected value. Now, can I say that the system has a linear response?

strictly speaking, the system response should be zero when the input is zero, but in this case, if D = 0:

$$ V_0 = -0.42 $$

What would be the correct way to refer at the response of this system?


texts:
I was reading some posts about how light can damage a camera by heating it up its internal components?
Link: Can camera sensors be damaged by light?

If I shine a 150-lumen flashlight at a monitor or webcam constantly for 5 minutes will it result in damage? A simple explanation of why or why not would be very helpful. Will it cause overheating?

How does the magnifying glass effect apply to this

Thank you for helping me understand.


texts: Do I need a dummy load for a GPS satellite signal generator?

texts:
I'm in the process of applying for an FCC experimental certificate so I can be legal when I purchase a satellite generator.

I found a used (calibrated) generator on eBay and want to know if I need a dummy load on the RF outputs that aren't being used. The is one on the front limited to -110 dBm and the one on the back is labeled CAL/MON and is always on and transmitted at -48 dBm.

I understand those signal levels are VERY LOW. Do I still need a dummy load on the unused port?


texts: How to isolate the car ground with MCU ground?

texts:
I know optocoupler does the job of isolation very well. How to isolate supply ground?

If car battery is supplying the power to the MCU, then the ground will be common always and it defeats the purpose of having optocoupler for sensing voltage.

Is there any way to isolate supply ground, should be as cheap as possible or if not possible what to do?

Here is the circuit :


texts:
If we look, for instance, at a Lightning cable, its connector is shaped like "—", with receptacle being "=". Apparently, this construction contributes to durability, to the ease of use, and lowers production costs.

USB C, on the other hand, opted for a connector shaped like "=" and receptacle like "≡". This is more likely to break from pressure and more prone to accumulating dust. What is the reasoning behind this choice?


texts: What "external" source can change a General Purpose Working Register if no interrupts are enabled?

texts:
I have a 8-bit ATmega processor (from the 48/88/168 family) and encounter a strange behavior: after a brown-out reset, sometimes (around 20%-30%) it fails to start after a short brown-out. It always starts correctly after a longer power-down.

I narrowed down the problem to the part of the startup which is generated by the compiler and has the role of clearing the RAM:

;CLEAR SRAM
    LDI  R24,LOW(__CLEAR_SRAM_SIZE)
    LDI  R25,HIGH(__CLEAR_SRAM_SIZE)
    LDI  R26,LOW(__SRAM_START)
    LDI  R27,HIGH(__SRAM_START)
__CLEAR_SRAM:
    ST   X+,R30
    SBIW R24,1
    BRNE __CLEAR_SRAM

This code segment does the following: it counts down the word in R24,R25, meanwhile incrementing the X Register (R26,R27) and writing R30 (which is zero) to the location pointed by the X Register. This clears the RAM until R24,R25 reaches zero. However, the code is stuck in this loop. Whenever I halt the progam, it stops on one of the last 3 lines in the above code, with seemingly random values in R24 and R25. Interestingly, if I run it step by step, it correctly decrements R24, and when it reaches zero, it correctly sets R24 to 0xFF and decrements R25. When I set both to a very small number they correctly reach zero and the loop is exited correctly, but only when running it step-by step. It seems that something writes some values into R24 or R25, but I have interrupts disabled, and I even set breakpoints to the interrupt registers to make sure and they are never triggered.

When this test is running (stuck in the loop) the power is stable, so there is no brownout while in this loop.

The watchdog is disabled while we are in this loop.

Does anyone have any ideas what to look for?


texts: Why isn't the saturation current of a photodiode the same as its short circuit current?

texts:
The formula I see everywhere is:

$$
I_{sat} = \frac{V_{bias}}{R_L}
$$

But this seems incomplete for the following reason:

The larger the resistance is the smaller the saturation current, it stands to reason then that if it was zero, we would have the greatest current the device can physically produce, but if you see the short circuit current of any photodiode like this one (second table in the data sheet) it will be very low, microamperes in this case, instead of microamperes as one would expect.

How then can I calculate the highest saturation current of a photodiode and how is it different from the saturation current?


texts:
I was reading this article on how to detect hazards.
I have some questions which I couldn't find answers for:

Say I have a circuit where t_pd=t_cd for each gate and t_pd is equal for all gates.

Plus, each path from input to output has only one gate. It's clear that there are no hazards here, but what if the K map was something like this:
 x/y     00 01 11 10
  z

  0      1  0  0  1

  1      0  0  1  0

There are adjacent zeroes which means a 0 hazard.

Hazard fluctuations occur when different paths from the input to output have different delays, but that doesn't make sense. Why?

Consider my example in question 1 above: We said it has no hazards, but now change t_pd for only one path and there could be a hazard. However the K map in both cases is the same, which is a contradiction.


texts:
In the figure below, an RLC circuit, the author in the book says, that the resonant circuit sees Rs and RL to be parallel so he combined them (R total = the parallel sum of Rs and RL), is it right that is the current (Is ≠ IL ) so
The two components are parallel?


texts: How to remove degradation in voltage gain when replacing the original \$R_L\$ with a small value resistor?

texts:
For the following common-emitter amplifier, the original \$R_L = 4.7\space kΩ\$. When I replace it with a small value resistor (\$100\spaceΩ\$), the voltage gain will drop. Is there any way to drive the new low-impedance load without causing the degradation in the voltage gain?

Circuit Diagram

SetUp Details

\$
\space \space \space \space \space \space \space \space R_G=600\space Ω \\
\space \space \space \space \space \space \space \space R_1=82\space kΩ \\
\space \space \space \space \space \space \space \space R_2=15\space kΩ \\
\space \space \space \space \space \space \space \space R_C=4.7\space kΩ\\
\space \space \space \space \space \space \space \space R_E=910\space Ω \\
\space \space \space \space \space \space \space \space R_L=4.7\space kΩ
\$

Thank you for your help.


texts: Turning a microcontroller on with a flip flop

texts:
I'm working on debugging a circuit that I've built and am trying to wrap my head around an issue.

I have the following circuit (74LCV is an inverting flip flop and the NCP1400 is a boost converter):

The goal is to be able to turn on and off the load (an 8051 based uC) by pressing both switches. When the uC turns on, it sets PWR high, and then when the switches are pressed again, pin 4 of the flip flop goes low, turning off the boost regulator and uC.

The issue that I've been having is that in the off setting (pin 4 low), the PWR pin is held at about half the battery voltage, which prevents me from turning the device on.

My best guess is that because the uC no longer has a valid ground reference to the battery (the MOSFET is not conducting), the PWR pin is being held in an indeterminate state because of a small current flow through the uC. Is this correct?

What can I do to allow the uC to be turned on/off by pressing both buttons while avoiding issues with debouncing.


texts: basic RF transission in noisy environment

texts:
I built a little quadcopter, and I need to transmit some data to it in a max. 4-5 meters range.
The transmitter needs to transmit in a quarter of a sphere (the quadcopter will newer be "behind" the transmitter, neither under it); the quadcopter will only receive signals in half of a sphere: under and all around it's body.

I built a working communication system based on the RF modules in the picture below. But when the 4 DC motors of the quadcopter start, the electromagnetic noise blocks the communication. The motors are about 6 cm away from the receiver, which is surrounded by them.

My questions:

1) each motor has a capacitor between its terminals, and I read that two additional capacitors, one from each terminal to the motor's case, would help; is that true? I also read "but only if the motor's case is well grounded" (I didn't rellay understand that, does it mean I have to connect the case direcly to ground?
2) I had a couple of cheap 433MHz transmitters/receivers around (I don't mean "transceivers": each module can do only one thing, TX or RX) and I decided to try using them. But many people says they're garbage: I don't mind if that's true in general, but is it possible to use them in my case whit a quite good reliability?
3) I had trouble understanding the antenna I should use. At this very moment I have two identical quarter wavelength straight 6mm copper wire antennas, one on the quadcopter and one on the ground. Are there best antenna types for this kind of transmission? I can have what I whant on ground, but the quadcopter needs a lightweight antenna.

Those are my actualRF modules


texts: Can I charge capacitors in series with voltage higher than the rated voltage of 1 of the capacitors?

texts:
I am making a coil gun. I have just ordered some 330uF 200v 105c Radial Electrolytic Capacitor.

I will be using the charging circuit from a disposable camera. I know that two of the same caps in series have double the voltage rating but half the capacitance. I haven't received my caps or camera, but my question is if the charging circuit charges at 300v (which I think it does but I will test when I get the camera) and I have 200v rated caps if I make 2 sets of 2 caps in series then put those to sets in parallel can I charge it at 300v?  If I understand this right then my total capacitance would be 330uF and my voltage would be at 400v.

Thanks


texts: Designing a hybrid RF ampilifier with tube and transistors

texts:
I have an 807 vacuum tube and I want to design a RF power amplifier with it.
Since I have only one tube so I want to use transistors for the rest of the power amplifier circuit.
The 807 tube will be used in the final stage and transistors will be used in the pre-amp stages.
I do not have any previous experience in tube based amplifier design, but I have done transistor amplifiers. The output power needs to be 10-20 W. I have a QRP CW transmitter that produces about 800mW on 40m. I am planning to use this tube amplifier with that transmitter.
807 tube datasheet


texts: pt100 RTD transmitters not working - two in a row - am I doing something wrong?

texts:
I just tried to use two different ones of these RTD transmitters with a pt100 probe (3 wire) with no success.
I am connecting the transmitter directly to a 4-20mA input on a PLC, as shown in the following circuit diagram.  Using 24VDC supply.
However, the unit always flows around 32mA through the current loop, no matter what temperature the probe is, or whether the probe is even connected.  This exact same thing has happened with two of these transmitters. I assumed the first one was bad, but then when the second one did the same thing, I started to wonder what I had done wrong.
Any advice appreciated.
Diagram:


texts: What are some quick, cheap hacks for determining the source of EMI in my house?

texts:
TL;DR - Without dumping a bunch of money, is there a quick MacGuyver-y way to help diagnose what's causing the EMI in my house?
Longer -
I have the curse that I'm a little too technical to be helped here by dummies.com, but not sophisticated enough to have or use the tools I imagine most of you would recommend.
Several times per day - sometimes hours without issue, sometimes firing once every 5 seconds - the wifi blips for a few seconds.  I've caught command line ping dropping packets for about 2-5 seconds, on computers throughout the house.  Notably, we realized the baby monitor also cuts out for just a few seconds at the exact same time ping goes down.
So it would appear my house is regularly awash in brief bursts of EMI, that's causing connectivity issues (especially a problem with video conferencing in the current covid-19 lockdown world).  But I have no idea what to buy or rent to help me triangulate where this is coming from or what it could be.  I have some dim memory that magic things can be managed with an oscilloscope and simple length of metal plugged into it operating as an antenna.
How can I find EMI?
(Meta - if there's a better place besides electronics.stackexchange.com for this please leave a comment)
UPDATE (for more information, as requested in comments)
The Baby monitor and its receiver is an Infant Optics DXR-8, audio and video over 2.4ghz wireless (NOT wifi / tcp-ip, but some point-to-point proprietary).  In fact, shielded twisted pair cat5 appears undisrupted  (but not a fix for everything getting disrupted in our wifi world).  The wifi is 5ghz AC + 2.4 ghz N (both ranges/protocols impacted).  To my knowledge, I'm not particularly close to any unusual EM sources - e.g. airport, military base, transformers - though I guess you never truly know.  It is relatively dense population (single family residences every 35 feet) - I'm wondering if a neighbor has one of these "weaponized" routers that disables other people's wifi, but need some kind of proof before I go pounding on doors. All of this aside, to keep the question within format for stackexchange, assume generic American residential suburbia, and let's see if we can dream up a gimmick that works generally.  Anything further peculiar to my immediate situation I can answer in comments.


texts: FFT Bin Problem with external 24 Bit ADC(FFT bins changing with time)

texts:
Currently I am working on one project that includes 24 Bit external MCP3919 and MCP3914 ADCs and Tiva C series 32 Bit MCU. I am trying to calculate harmonic values of input signal.

I am using CMSIS DSP Library in Code Composer Studio. FFT functions are working great I have no problem with implementation of these functions. I tested them with internal generated sin signal and modulated it. Results are expected.

ADC_Output : 3255 Hz
FFT_Size : 64 point
Window_Size : 2*FFT_Size

I have a problem that when I read real world signal from signal generator, my FFT bins are changing with time in n*50Hz signals. When I increase the input signal to 50.9 Hz there is no problem. It is same with 150Hz, 250Hz, 350Hz. It seems like there is fixed frequency error related with 50Hz.

For example : FFT functions work great with
50.9 Hz signal instead of 50Hz (1*0.9Hz)
152.7 Hz signal instead of 150 Hz ( 3*0.9Hz)
254.5 Hz signal instead of 250 Hz (5*0.9Hz)

I am sharing my FFT Bin graphs

                       **Fig1 : 50.0 Hz and 250.0Hz**

                    **Fig2 : 50.9 Hz and 254.5Hz**

As a result, with frequency changing FFT bins are true. I need your experiences with this issue.

Thanks in advance

dredg


texts: Battery removal circuit via interruption

texts: I am designing to detect battery removal with minimum current. I tried some designs that I expect interrupt when battery removal, but the port of my MCU was floating.  If I design like circuit in the attachment, Can I detect battery removal by interruption? still the port of mcu would be floating instead of grounding? Or do you have any suggestion design?


texts: MOSFET Drain-to-Source Leakage Current over voltage and temperature

texts:
I'd like to know what's the characteristic curve of Idss in N-Channel MOSFET transistors over different Vds values at high temperature. As I've checked datasheets (like Fairchild's 2N7000 or FDC637BNZ), the Idss parameter is normally specified for Vds voltages very close to BVdss (breakdown voltage). It is clearly stated that current will increase considerably at higher temperatures, but the effect of Vds is not mentioned. I've also read some application notes (like NXP's AN211A or Fairchild's AN-9010) and they do not provide much information about it either.

I have this design where I need to keep Idss within the range of the low µA @ 100°C (the lower, the better), and I've thought I could get away with a transistor that has a much larger BVdss than the working voltage (e.g., BVdss=100V, working voltage=3.3V), but it's unclear if that would be of any effect.

The question is: is the Idss parameter solely dependent of temperature, or the Vds/BVdss ratio would play a role with it?


texts: If you have a BMS, will current be limited at some points to a DC motor and affect performance?

texts:
I am part of a group in a senior design project. We are designing an electric bicycle. Our professor proposed an issue to us and we are having trouble figuring it out, as we can't really seem to find any information on this.

We have a 10s5p battery pack using Lithium Ion 3.6V nominal rating cells. So 10 in series for 5 parallel connections. Each is rated at 2.6Ah.

The question the professor posed is when the BMS is balancing the parallel packs, is there a point where there's such a huge difference between let's say parallel pack 1 and 2, that pack 2 is disabled, and then suddenly there isn't enough current available for the motor?

Is this situation possible, and how can we avoid this? We noticed on https://www.orionbms.com/manuals/utility_o2/param_balancing_description.html it says a BMS can be programmed for such a small difference such as 10mV, wouldn't it be such a short time between balancing this wouldn't be an issue?


texts: Why is my DC motor making a rattling scraping sound?

texts: The DC motor on my hob extractor fan is making a rattling and scraping sound when I switch it on. I know it is coming from just the motor because I have tried running the motor on its own. What could be causing this sound? How can it be fixed? Thanks!


texts: How to cut or remove the unwanted waveform?

texts:
I want to remove unwanted signal at particular time from the input signal. But I am not sure how to start this. I used capacitors to reduce the unwanted signal. It worked OK, but not well.

By seeing the below image you may understand my problem:

The above image is output of the hall sensor.
Before the on & off time of single wave, there is a small square wave.
How to remove that small square?
I used capacitors but I don't know how to use the capacitor to remove or reduce the extra wave (1ms of square wave).
I need to measure the RPM of motor using the hall sensor. In order to measure, I used a hall sensor to capture the frequency. But the hall sensor output is not good.


texts: STM32F0 (master) writing multiple bytes by I2C to MCP4728 (slave) using StdPeriphLibrary

texts:
void I2C_Config(void) {
    I2C_InitTypeDef I2C_InitStructure;

I2C_StructInit(&I2C_InitStructure);
I2C_InitStructure.I2C_Timing = (PRESC << 28) | (SCLDEL << 20)
        | (SDADEL << 16) | (SCLH << 8) | SCLL;      // 100kHz
I2C_InitStructure.I2C_Mode = I2C_Mode_I2C;      // I2C mode
I2C_InitStructure.I2C_Ack = I2C_Ack_Enable; // enable acknowledge when reading (can be changed later on)
I2C_InitStructure.I2C_AcknowledgedAddress = I2C_AcknowledgedAddress_7bit; // set address length to 7 bit addresses
I2C_Init(I2C_PERIPH, &I2C_InitStructure);       // init I2C peripheral
I2C_Cmd(I2C_PERIPH, ENABLE);

}

void I2C_HW_tx(uint8_t i2cAddr, uint8_t *dataTx, uint8_t length,
        uint8_t stopOrNotWhenSent) {

if (stopOrNotWhenSent == STOP_WHEN_SENT) {
    I2C_TransferHandling(I2C_PERIPH, i2cAddr, 1, I2C_Reload_Mode,
    I2C_Generate_Start_Write);
    PRINTF("\nI2C_tx - 1\n");
    while (I2C_GetFlagStatus(I2C_PERIPH, I2C_FLAG_TXIS) == RESET)
        ;
    PRINTF("\nI2C_tx - 2\n");
    for (uint8_t i = 0; i < length - 1; i++) {
        I2C_SendData(I2C_PERIPH, *(dataTx + i));
        while (I2C_GetFlagStatus(I2C_PERIPH, I2C_FLAG_TCR) == RESET)
            ;
        PRINTF("\nI2C_tx - 3\n");
    }
    I2C_AutoEndCmd(I2C_PERIPH, ENABLE);
    while (I2C_GetFlagStatus(I2C_PERIPH, I2C_FLAG_TXIS) == RESET)
        ;
    I2C_SendData(I2C_PERIPH, *(dataTx + length - 1));
    I2C_ReloadCmd(I2C_PERIPH, DISABLE);
} else {
    I2C_TransferHandling(I2C_PERIPH, i2cAddr, length, I2C_SoftEnd_Mode,
    I2C_Generate_Start_Write);
    PRINTF("\nI2C_tx - 1\n");
    while (I2C_GetFlagStatus(I2C_PERIPH, I2C_FLAG_TXIS) == RESET)
        ;
    PRINTF("\nI2C_tx - 2\n");
    for (uint8_t i = 0; i < length; i++) {
        I2C_SendData(I2C_PERIPH, *(dataTx + i));
        while (I2C_GetFlagStatus(I2C_PERIPH, I2C_FLAG_TC) == RESET)
            ;
        PRINTF("\nI2C_tx - 3\n");
    }
}
if (stopOrNotWhenSent == STOP_WHEN_SENT) {
    while (I2C_GetFlagStatus(I2C_PERIPH, I2C_FLAG_STOPF) == RESET)
        ;
    I2C_ClearFlag(I2C_PERIPH, I2C_FLAG_STOPF);
}
PRINTF("\nI2C_tx - 4\n");

}

void I2C_HW_rx(uint8_t i2cAddr, uint8_t *dataRx, uint8_t length) {

PRINTF("\nI2C_rx - 1\n");
I2C_TransferHandling(I2C_PERIPH, i2cAddr, length, I2C_AutoEnd_Mode,
I2C_Generate_Start_Read);

for (uint8_t i = 0; i < length; i++) {
    while (I2C_GetFlagStatus(I2C_PERIPH, I2C_FLAG_RXNE) == RESET)
        ;
    PRINTF("\nI2C_rx - 2\n");
    *(dataRx + i) = I2C_ReceiveData(I2C_PERIPH);
}
while (I2C_GetFlagStatus(I2C_PERIPH, I2C_FLAG_STOPF) == RESET)
    ;
PRINTF("\nI2C_rx - 3\n");
I2C_ClearFlag(I2C_PERIPH, I2C_FLAG_STOPF);

}

I read bytes from MCP4728 using I2C_HW_rx with success.
The problem is with I2C_HW_tx - it halts when trying to send:

uint8_t dataTx[8];
for (uint8_t i = 0; i < 4; i++) {
    *(dataTx + i * 2) =
            FASTWRITE
                    | (((channelData->powerMode << 4)
                            | (channelData->dacValue >> 8)) & 0x3F);
    *(dataTx + i * 2 + 1) = channelData->dacValue & 0xFF;
    if (i < 3) {
        channelData++;
    }
}
I2C_HW_tx(DEVICE_CODE | (mcp4728WholeData[mcp4728Id].currI2CAddr << 1),
        dataTx, 8, STOP_WHEN_SENT);

}

So my question to You - how to send multiple bytes by STM32F0 (master) to I2C bus, using StdPeriphLibrary? I was searching in Google, but the few examples with StdPeriphLibrary for STM32F0 are with sending I2Caddr, register and value (three bytes), but I need to send for example I2Caddr and ten bytes.


texts: I see that a PCB requires certification even if it incorporates a certified RF module, so EMC tests for spurious emissions will still be needed. Is FCC-approval needed if a Raspberry Pi is shipped/sold with a USB WiFi dongle? So how is modular integration actually defined? Are EMC tests for spurious emissions needed when a USB WiFi dongle is connected to a Raspberry Pi? Or is it that FCC doesn't consider integration via USB isn't considered to be "


texts: How to configure an ARM GPIO port (STR9) to an alternate function?

texts:
Because I am new to programming on microcontrollers coming from the C++ world, I have been studying on getting code running on a microcontroller board to work with many inputs and outputs.

For the first project I am working on an ARM9 chip (STR912FAW44) with Rowley Crossworks for ARM to program my board. I understand that I have to setup port 7.3 to output mode to drive a LED. I also understand that the GPIO port has multiple modes on this pin, defaulting to GP Input. I also know the alternate output 1 configuration is GP Output.

Now the manual for the chip says:

  There are up to 80 GPIO pins available on 10 I/O ports for 128-pin and 144-ball devices, and
  up to 40 GPIO pins on 5 I/O ports for 80-pin devices. Each and every GPIO pin by default
  (during and just after a reset condition) is in high-impedance input mode, and some GPIO
  pins are additionally routed to certain peripheral function inputs. CPU firmware may initialize GPIO pins to have alternate input or output functions as listed in Table 8.

This sounds wonderful. The question is how can I get the port to accept a different function?

I have sample code for a similar, but different board where the LED (easiest to test) is on port 9, but this does not work when adjusted to port 7 as I expected.

Here is the sample:

void
ctl_board_init(void)
{
  // leds are connected to GPIO9.0-GPIO9.3
  SCU_PCGR1 |= SCU_PCGR1_GPIO9_MASK; // turn on GPIO9
  SCU_PRR1 |= SCU_PRR1_RST_GPIO9_MASK;
  GPIO9_DIR = 0x01; // select output direction
}

void
ctl_board_on_button_pressed(CTL_ISR_FN_t buttonFn)
{
}

void
ctl_board_set_leds(unsigned v)
{
  *((&GPIO9_DATA)+(0x01<<2)) = v ? 0x01 : 0;
}

The macros come from header files, but can anyone help me find reference to which bits I should set to drive GPIO port 7.3 as output?


texts: Components to record ultrasonic sound? Up to 200kHz

texts:
For a personal project, I’m trying to record ultrasonic sound. I would like to find the best way to record from 20kHz to 200kHz.

As I found from Wikipedia, animals can hear up to 200kHz.

As I prefer to design my own board, the best component I have found is this Knowles SPH0641LU4H-1.

But the range is from 50Hz to 80kHz...

What is the best configurations/components to record ultrasonic sound?


texts: What is the highest possible optical output power of an SLED?

texts:
I am inquiring about this because I'm looking for a suitably high-power, large bandwidth light source for a fibre optic communication system I am designing.
The distance the data will be required to travel is 45km and the light source needs to transmit data at a bandwidth of 12MHz, and at a data rate of 12Mbps. Ideally, I want to use a light source with a central wavelength of >1300nm. The catch is that I have to use multi-mode fibre and laser diodes are out of the question too.
What kind of output power out of any potential light source should I be looking for here?


texts: MCP4131: How to know what value resistors to use on the multiplexed SPI IO?

texts:
There are two aspects here. The first question is related to R1 below:

The datasheet says: "R1 must be sized to ensure VIL and VIH of the devices are met" but gives no formula. So first question:

(1) How does one determine value of R1?

The datasheet gives maximum SPI SCK frequency for this device as 10MHz for 5V supply as given in Tables 1-1 and 1-2. However, for the read operation on the device where the SDI/SDO are multiplexed, the idea is different because:

The point 2 under the Table above says that the max SCK can be increased by using a pull up resistor. About these things I am wondering the following:

(2) Why is max SCK frequency lower for multiplexed SDI/SDO read operation only?
(3) If I connect a pull-up resistor it will certainly form a voltage divider with the R1 in the first picture. How do I determine the value of both of these resistors then?

Finally, since the Table 1-1 and 1-2 give SCK Input Frequency for voltage 1.8V to 2.7V as 1MHz rather than 10MHz which applies to 2.7V to 5.5V.

(4) Why is the max SCK lowered at lower supply voltage?


texts: Where can I find how to use those rf transmitter/receiver

texts:
I bought those rf trans/receiver (GWB T400)

I figured out that the sck, miso and mosi are for the spi communication.
Gnd and 3v3 are pretty clear as well but I’m not sure what rst and cs are for.
I don’t know where to look for to learn how to use it with my arduino either.
Any help would be greatly appreciated.


texts: What is a safe max rated current percentage for a 1A, 5V positive voltage regulator like a 7805?

texts:
I have a simple circuit comprised of seven 5V relays and eight 5mm LEDs, if the supply is 5V, it will draw a max of 660mA DC.

I was planning to use a 7805 positive voltage regulator rated for 1A, so at worst conditions, it will be working at 66% of it's max current rating.

Is this an acceptable percentage considering that the circuit will be mounted inside a metal chassis so I can bolt the regulator to it to heat sink and ground the circuit?

I usually de-rate all my parts to about twice the currents and voltages they will ever see so 66% seems reasonable but I've read how tricky current ratings are because of proper heat sinking and temperature rise factors.

Is 66% still safe or should I look at one of those high-current circuits using a transistor that appear on datasheets, or look for a 1.5A regulator?

Thanks in advance for any input!


texts: Is it possible to figure out the specifications of an electronics piece without datasheet?

texts: I'm brand new on the "electrical engineering" scene with my Arduino and I have a question about random electronics. I've been taking apart some old phones, salvaging LEDs, motors and speakers, mostly just for fun. If I were to use these pieces in my own projects is it possible to figure out their specs knowing little to nothing about them? If so, what tools would I need and how would I go about it? What do I need to know to safely integrate them into my own circuits?


texts: Calculating SMD resistor temperature rise

texts:
I am interested in knowing the actual power dissipation of an SMD resistor at a 70C ambient temperature. I am looking at a 10kOhm 2512 1Watt resitor RMCF2512JT10K0.

from the electrical specifications section of the datasheet, the resistor is rated 1W at 70C:

now from the derating curve, it seems that this power rating is referring to a 155C operational temperature limit:

we can conclude that 1W of power would rise the resistor's temperature by 155-70=85C and that the thermal resistance between the resistor and ambient is 85C/W. This can be used to estimate the temperature rise of the resistor while dissipating a specific power.

So far so good until we compare the above calculations with the temperature rise curve:

My question is

How can we explain the last curve (and table) where 100% power dissipated by RMCF2512 will cause 150C temperature rise!
The description of the test done is also ambiguous.

  The resistor surface generated temperature variation after applied rated voltage

Did they apply the rated voltage to the resistor (200V to 75K 1Watt resistor => only 0.53Watts)?

What is the meaning of that last table (surface temperature)!?


texts: Is there a way to make a drill hole only up to half depth of the PCB in Eagle?

texts:
I need to solder a through hole ZigBee as though it were an SMD part.

The other side of the board is a touch pad so there should not be any solder or components on it.

I think it is better if I can make plated half-drilled (one side drilled) holes.

Is there a way to create such holes in Eagle?

As in this photo:


texts:
In my upcoming project, I am working with a Microcontroller called the Microchip PIC32MX695F512H and a Wifi Module called the Microchip MRF24WB0MA. Since I am new to electrical engineering, I've pretty much just been copying what I learned out of the data sheets on their websites and an already made schematic utilizing these two parts (the links are below). There are pictures I put as well that are down below.

Although all seems to be going well, I am having a few difficulties. On pin 7 of the Wifi Module (RESET), each schematic seems to be connected to different wires with different resistor types. One is connected to +3.3V with a 4.7k resistor, and the other is connected to ground with a 100k resistor. One other thing is that although on one of the schematics, pins 33, 34, and 35 all have a 4.7k resistor, only pin 33 has a 4.7k resistor on the other schematics.

I'm really sorry if these are newby questions, but I just recently got in the field of electrical engineering and need an answer DESPERATELY! Thank you!

Links:
       Wifi Module Data Sheet: http://ww1.microchip.com/downloads/en/DeviceDoc/70632C.pdf
       Schematic that is already made: http://ww1.microchip.com/downloads/en/DeviceDoc/70678A.pdf


texts: Converting karnaugh maps to Boolean expressions

texts:
My professor briefly mentioned that there are ways of "taking 0's" and "taking 1's" from a K-map that allow you to form the logical expressions differently (e.g. NAND-NAND, AND-OR, NOR-NOR, etc.). Can anyone explain this, or direct me towards a discussion on this topic? The only method I can seem to find is minterm vs maxterm solutions.

Here is my current understanding:

For minterm solutions, we make groups of 1's in powers of 2. For each grouping, invert if the unchanged variable is a 0, and do nothing if it's 1. Each variable in the group is ANDed together, and this forms a product of sum of products with the other groupings (if any)- the result is AND-OR logic.

For maxterm solutions, we make groups of 0's in powers of 2. For each grouping, invert if the unchanged variable is a 1, and do nothing if it's 0. Each variable in the group is ORed together, and this forms a product of sums with the other groupings (if any)- the result is also AND-OR logic.

I'm not sure what I'm missing.


texts: Can you bridge off of a 240 V Breaker Box that connects to an Intermatic Timer?

texts:
I have an Intermatic T104 Timer drawing power from a Homeline Breaker Box
for a home swimming pool. I'm wondering whether it would be considered safe to use the knockout in the timer enclosure to bridge from the 240 V coming from the breaker box into an Arduino Uno reading data from a pressure transducer.

That is, 240 Volts from the breaker box into the timer, and then tap from the timer into an Arduino Uno. The only load on the Arduino side would be a pressure transducer and a wireless WiFi shield, and I could connect to a common ground in the timer.

Thank you.


texts:
I am using an A7-100T FPGA development board used for a project. Up to this point, I have only been doing simulations on Vivado with simulated clocks or when I have been using the board, I have not had to create any clock signals due to only having basic combinational logic designs.
What is the simplest way to create clock signals? I have read tutorials and watched videos and it seems you have to create an IP package and use the HDL code as a component within the top-level file on the design?
I need to produce two clock signals at the same frequency with one of them having a 90-degree phase shift.


texts: Transistor module and its maximum allowable power dissipation

texts:
I have a question regarding the selection of transistor modules. These modules often have a parallel diode. When calculating the losses and thus the expected heat development, I am not sure how these diodes have to be considered. The maximum allowed power dissipation is (according to this Infineon application note, page 12 equation 2):

I know that both the transistor and the diode has a thermal resistance. Still, I don't see how it affects the temperature rise since, e.g. in a buck-boost converter, the diode and transistor in the module will never conduct at the same time.


texts: I'm looking to allow two cartridges to be inserted into a slot that normally only accepts one (more specifically, Nintendo 64 cartridges). I can't just toggle the power lines to each cartridges because of backfeeding. What sort of device would I need to use to switch a large number of lines from one cartridge to another (an N-pole single throw relay)? In this case, there isn't much power passing through the lines, but in a more general sense what component would one need to actuate multiple switches in a near-simultaneous timeframe?


texts: Compilers and MSB identification for Data types

texts:
I would like to know two things that is making my head quite confusing these days.

If i allocate an int in C18 compiler I know it will take two bytes and, if I initialize a pointer to the variable, say:

int x,*xptr;
xptr = &x;

then I have to access *xptr for first byte and *xptr+1 for the second byte?

Well, what factor determines that which one is MSB and LSB?


texts: High Current DC LEDS Strips with Aluminium Plate... is grounding advisable?

texts:
I'm in the process of planing to make a rather large LED light panel that uses 24v 130w in total. The LED PSU Driver is rated up to 150w and comes with 3 inputs (earth, neutral and live) and 2 outputs positive and negative.

The LED strips that I'm using have fairly decent PCB copper thickness but to help dissipate the heat I've decided to use a large 5mm thick aluminium plate which hopefully will prolong the life span of the LED brightness.

A simple diagram can be found below:

The question(s):

Is it advisable to earth the aluminium plate using a wire attached to the plate back to the chassis of the PSU?
Or is there an alternative option or is it not required?

Extra Information:

Meanwell 150W 24v CLG-15024A datasheet

CLG-15024A Schematic

Picture of the LED STRIPS

Looking at the LED strip it seems to have SMD Resistor with label 121 (120ohms, I think) on the +24v and -24v which then reduces the voltage by half to 12v which is then split between 6 leds in series resulting in 2 volts each.


texts:
I am working on a project involving several stepper motors, I have chosen the L298N as the driver - and my system supply is a switching power supply 12V 15A.

My question is, how can I connect the 12V 15A supply to the L298N? I do understand the wiring and schematics but do not understand the power input to the driver itself.

I considered a buck converter but because I have 6x L298N's, I am struggling to understand how I can connect the 6x L298N's with 12V 15A Supply. It is clear 12V input is fine but 15A isn't? Any guidance would be appreciated.

The data sheets are here if needed:
https://www.sparkfun.com/datasheets/Robotics/L298_H_Bridge.pdf
https://docs-emea.rs-online.com/webdocs/157a/0900766b8157a734.pdf


texts: How do non contact voltage detectors work on open circuits

texts:
I’ve seen how people use non contact voltage detectors to check whether or not a socket’s live wire has power. Non contact voltage detectors take advantage of capacitive coupling that occurs in AC in order to figure out if there is power or not.

Now, what people usually do is simply stick the detector into one side of the socket (the live side). This part completely confuses me, how is it possible to detect if there is power if the circuit is open? There is no connection from live to neutral which would close the circuit and allow current to flow.

Another thing that doesn’t make too much sense to me is that why does it only detect the live wire and not the neutral? When people insert the detector into the neutral side of the socket the detector doesn’t light up. The neutral wire is a must for current to flow, why doesn’t it also detect it?

Any help is greatly appreciated.


texts: Help implementing a synchronous circuit in Logisim

texts:
I am trying to implement the following circuit in Logisim, yet all I get is y=0. Any idea what might be the problem? As the original circuit seems to be correctly implemented I would guess that the problem in my implementation perhaps stems from leaving the R,S,EN of the DFFs open. Or it could be with the MUXs. I am not sure. This is my first attempt trying to implement something synchronous.

Here's what I drew in Logisim:

What should I add for you to be able to indicate what might be wrong with what I drew?


texts:
I have a quick noob question about current flow through a hall effect sensor.

Does the current flowing from one end of the sensor to the other purely depend on the load's draw from the power source? Or is it also affected by the voltage output?

In other words does the current draw stay static regardless of the output voltage changing? Tell me if I'm thinking about this the wrong way, I'm quite confused.

I'm specifically trying to figure out how to calculate what will happen to voltage and amperage when I put a resistor on the sensor output.

This is the diagram I have been looking at if it helps:

Thanks for your time!


texts: Constant DC Load Stability and Bandwidth slewrate

texts:
For this circuit, how do I know if the rise edge was limited by slew rate or bandwidth? What's the effect of R2 and C2 on bandwidth?

-3db of this circuit in simulation is 649 kHz, I know in this circuit, R1 and gate capacitance, R2//C2 , will affect bandwidth, but it doesn't add up with 2πfc formula.

NE5534 has 10 MHz bandwidth, and 13 V/µs slewrate.

I was trying to decrease C2 and R2, rising time shortened, but it comes with stability issue, with overshoot and gain peaking, how can I break the loop in order to see its bode plot? Also any idea on how to increase raising time will be appreciated.

DC load Schematic

Frequency phase analysis

DC load Chart


texts: Migrating from C18 to XC8 ADC Conversion Issue

texts:
I'm working with Pic18f6622 and migrating my program into XC8 compiler. Before I'm using the C18 compiler ADC conversion was working just fine, but in new compiler ADC returns me 11 bits value and the expected value is far more different. Maybe the timing is not enough to allow ADC to work healthy, but I couldn't be sure.
EDIT #I'm using external 10Mhz crystal#

The "analogval" value returns as 077C, but should be 01DB or close to this. By the way I'm reading PT100 value. I'm sharing the snippet below:

#include <xc.h>
#pragma config OSC = HSPLL, WDT = OFF, WDTPS = 512, BOREN = SBORDIS, BORV = 2, PWRT = ON, LVP = OFF,  MCLRE = OFF

unsigned int analogval;

void AnalogReader(void) {
  while( ADCON0bits.GO != 0 ) continue;

  analogval = ADRESH;
  analogval <<= 8;
  analogval += ADRESL;

  ADCON0 = 0x10; // select first AN0 to AN4
  ADCON0bits.ADON = 1;
  ADCON0bits.GO = 1;
}

void InitDevice(void) {
  TRISA = 0b00111111;
  TRISB = 0b00000000;
  TRISD = 0b00000000;
  TRISF = 0b00111111; // F0~F3 analog input

  // an0 an1 an2 *an3-NC* an4 an5 an6 an7 an8 analog, internal vref+ vref-
  ADCON1 = 0b00000110;
  ADCON2 = 0b10110010; // right justified, 16 tad acquisition, fosc/32
  ADCON0 = 0b00000001; // enable adc

  INTCON2 = 0b11111000; /// pull-up disabled

  RCONbits.IPEN = 0;  // interrupt priority not used
  INTCONbits.INT0IE = 1; // int0 interrupt enabled
  INTCONbits.PEIE = 1; // peripheral interrupts enabled
  INTCONbits.GIE = 0; // interrupts disabled
}

void InitTimeBase(void) {
  T3CON = 0x00;
  T1CON = 0x00;
  CCP1CON = 0b00001011; // Compare mode(RC2 OUTPUT): reset TMR1, set CCP1IF

  CCPR1H = 0x03;
  CCPR1L = 0xE8; // 1000 increments(=instructions)
  // Instruction cycle: 1/(40Mhz/4) = 0.1us
  // 1000 instructions = 0.1ms = 10KHz

  TMR1H = 0x00;
  TMR1L = 0x00;

  T1CONbits.TMR1ON = 1; //start timer

  PIE1bits.CCP1IE = 1; // TMR1 interrupt enable bit
  INTCONbits.PEIE = 1; // Overflow interrupt enable bit
  INTCONbits.GIE = 0; //Global interrupt enable bit
}

void main(void) {
  InitDevice();
  InitTimeBase();

  delay_ms(2000);  // custom delay

  do {
    if (PIR1bits.CCP1IF) { //10kHz  --> 1000 instruction.
      PIR1bits.CCP1IF = 0;

      /*
       * Bunch of operations
      */

      if (slot == 0)
        AnalogReader();
      if (slot == 1)
        // OP
      if (slot == 2)
        // OP
      if (slot == 3)
        //OP

      slot++;
      if (slot == 100) // slot 0..99 : Enter a slot each 10ms.
        slot = 0;

      //-----------------------------
      counter++;
      if (counter == 10000) {
        counter = 0; // 1 sec
      }

      if (counter > 5000) { //0.5 sec
        PORTBbits.LED1 = 1;
      } else { //0.5 sec
        PORTBbits.LED1 = 0;
      }
    }
  } while (1);
}

I appreciate any help.


texts: I'm using ADS2006A version and I'm trying to plot an eye diagram. However, I need to import a .csv file into ADS first because I did the simulation in Matlab. While importing, it asks for pattern length and point/bit. I tried putting several values but did not manage to get the simulation that I want. Can I know what pattern length and point/bit refers to?


texts: Wiring of body terminal in a network of MOSFET switches

texts:
I am trying to design a set of switches in a cmos design.
The switches are supposed to control a number of capacitors and I want to implement them as single NMOS or PMOS transistors.

Based on my understanding I have done the following: Choosing PMOS for switches where the voltage signals switched are closest to VDD and NMOS for switching voltages closer to gnd, to enable optimal drive conditions and this way decrease Rds_on. All the switches are driven rail-to-rail.

I also think that I have to ensure that all the switches operate in the ohmic region.

But when it comes to wiring the body terminals I get a little bit confused. I have read that you should tie the body terminal to the source terminal/gnd in the case of NMOS. In my design, some of the switches are placed in between a PMOS sitting at the top and NMOS. In this case the source terminal is not connected to the lowest potential, should it then be wired to ground or the source terminal?

I have also heard that transistors in common design processes are symmetric devices. Does this mean that it does not matter if the drain and source terminal are swapped? Does the body potential influence this polarity?


texts: How do we model the behaviour of circuits on ultrashort time scales (< ns)?

texts:
The electric field has a finite propagation speed. How do we describe the behaviour of circuits on timescales before even changes in the electric field have reached the entire circuit?

Is this is a phenomenon that integrated circuit designers are concerned with? How do charge carriers flow in a wire on these time scales?

For example, imagine that we just connected a battery to the circuit below. Assuming that each LED is physically identically, would they all emit light at exactly the same time, not even an attosecond apart? Assume that we measure an arbitrary number of samples to average out any quantum mechanical timing randomness.

I am aware of parasitic elements and I know that these is a deep connection between relativity and electromagnetism. I am curious to know how these effects can be mathematically modelled and simulated.


texts: DC power supply by RF signal through a coax cable

texts: I want to power a circuit which is only connected by a coax cable. Now I was wondering whether it is possible to convert a RF signal sent over a coax cable into a DC signal to save any bias Tees. The rf signal should be in the ISM band. I found rf to dc converters used for energy harvesting (e.g. http://www.powercastco.com/wp-content/uploads/2016/12/P2110B-Datasheet-Rev-3.pdf) but the output power does not fit my needs. I need at least 2W (better more). Or maybe is there a chance with a classical rectifier from a power supply unit to get a nice dc from a rf (I am concerned because of the high frequency of approx 800-900 MHz)? Thanks in advanced. Any suggestions would be greatly appreciated.


texts: What determines the frequency of a ZVS driver

texts:
Schematic of ZVS driver

Output waveform of transformer

Determining frequency from time difference between peaks of output waveform at secondary coil of transformer
I was simulating a ZVS driver in LTspice and while the frequency of the output waveform matched up with f = 1 / (2π √LC) when the transformer had not been added yet. With L and C being the value of the inductor and capacitor at the output respectively. Taking C as 1µF and L as 4µH, f is equal to 79577Hz.
After adding the transformer, the frequency changed. By taking the time between the peaks of the waveform to be 17.592µs, and using the formula 1/T, you get 56844Hz as the frequency.
Hence my question:  What exactly causes this and how can I calculate the frequency properly?


texts: Ohm's law and the voltage drop across a resistor

texts:
I'm trying to wrap my head around Ohm's law and there are plenty of similar questions already asked in this forum. But I just still don't understand it. It's about calculating resistor values.

Let's say that I have an IC which has an input pin I want to control high. I am doing this by connecting 3.3v to the input pin and I want to limit the current flowing to the pin to 2mA.

So by the use of Ohm's law I have calculated that 3.3 / 0.002 = 1650. So I would need a 1.65 KOhm resistor right?

So what happens to the voltage now? Shouldn't the voltage going to the pin be lower too because of the resistor? How can it still be 3.3v?

How about this? The supply voltage is still 3.3v but I need to lower the voltage to half for the IC, with a current of 1mA. So my calculation is (3.3 / 2) / 0.001 = 1650. The resistor value is exactly the same  as before. 1.65 KOhm!

Can someone explain what I'm doing wrong? I feel really dumb right now.


texts:
I'm a software engineer, so please excuse my gross ignorance of this topic. We are trying to figure out why our DC-DC converters sometimes fail and stop outputting power after a month or so of runtime.

Please refer to the drawing. Below is also a quick textual description of the drawing.

We use a 48v/1A passive PoE power injector to introduce 48v into the system. As far as we can tell (measured by multimeter), it seems to provide stable output at different loads. We then split that power two-ways: one to a 5v/3A step-down and another to a 12v/2A step-down. The 5v converter powers a tablet PC (approx. 10W-nominal / 15W-max load) and the 12v converter powers a battery (approx. 15W-nominal / 22W max peak). Note, the battery has a custom designed charging controller to self-limit its power draw to < 2A. Also, I believe the converters are 95%+ efficient (if the supplier is telling the truth).

We've used DC-DC converters from different suppliers, some with even higher output load capacities, and we still experience intermittent failures. We seem to have about 1 failure out of 10 per month.

We've also tried using a diode between the battery and the 12v converter (to ensure voltage is not fed back into the 12v converter's input side from the battery). This did not seem to make any difference. I've also verified that the tablet PC is NOT feeding back-voltage to its converter.

So, my starting question:
Is there anything obviously/inherently wrong with the way we're doing this, or the components we're using? All I really know is the power-budget and that we need to stay well under it (like 80% or less of max).

If any of this is unclear, is there any other information/testing I can provide?

UPDATE #1:
Power cable length can be up to 100m, but we typically use less than 5m (copper Cat-5e or better).

UPDATE #2:
Specifications are hard to get about the actual components in datasheet format, but below's images of specifications is the best I can do for now.

UPDATE #3:
I've included photos of oscilloscope measurements on the 48v side, further below. I really have no clue how to properly use a this device, so I just connected the ground to the PoE/48v negative and the probe to the PoE/48v positive. I then just pushed the "auto" button on the scope.

First image is for the 12v converter...

The next images are for the 5v converter...

This is the oscilloscope reading on the 48v side, with no DC converters connected (no loads whatsoever), as a baseline:

This is the oscilloscope reading on the 48v side, with only the 5v DC converter connected (and its load, the tablet PC, connected):

And just for fun, this is the oscilloscope reading on the 48v side, with ANOTHER brand of 5v DC converter connected (with tablet load connected):


texts:
U10, U20 and U30 are the inital voltages across the capacitors. The question is: What is the voltage U3(in steady state) after the switch is closed?
So...
After a long time, I know the charges will balance themselves out.
I tried using charge conservation Q_before = Q_after and got (C1 * U10 + C2 * U20 + C3 * U30) for the LHS, but then I don't know how I should write the RHS.
Is there another/better way of solving these kind of problems? What's the best approach?
Thank you guys for any help.


texts: If the longest path that my digital signal must travel in a microprocessor is x cm. What would be the highest frequency of the clock signal for that chip?


texts: Connect / disconnect USB while external power source remains connected

texts:
I have some arduino mini pro collecting environment data, so they operate a long time collecting and I need to connect Gnd - Rx - Tx once in a while to transfer data to my PC, and then disconnect.

I have read some comments here and I know it can be dangerous for the circuit, but can't find a practical solution.

Is there any practical recomendation / recipe to do this ?

I am wondering:

Keep power source connected, then connect in order gnd - rx - tx using three cables, then disconnect in the oposite order.
Use a USB connection with gnd - rx - tx (no Vcc) to connect and disconnect.
Disconnect Vcc from the external power source, then connect gnd - tx - rx, then Vcc from external power source.
¿ Any recipe / recommendation ?

Thanks in advance.


texts: How to practically measure the resolution (PPR) of incremental rotary encoder?

texts: I have an incremental rotary encoder that I can't determine its model number thus I can't get its data sheet, How can I measure its resolution manually?


texts: Why do microwave ovens, with metal walls, not blow up?

texts:
Why does a microwave oven with metal (?) walls work fine, but if I (theoretically) put a metal spoon in it, "bad things" may happen?

Maybe these internal walls are not conductive?


texts: Transimpedance amplifier transfer function

texts:
I am learning analog design. I am trying to understand transimpedance amplifier using Op-Amp. Here is my transfer function.

My understanding is assuming Node Va as virtual group I got (Vout= -Iin*Rg) which means feedback is frequency independent (No impact because of input Capacitor C).
Here what is the purpose of adding a capacitor in feedback path for compensation(adding Zero) since feedback is frequency independent.
 How to find where to add zero and what value cap to be added? Can someone point to good reading book/website?

Please correct me if my derivation is wrong.


texts: Kicad footprint for right angle mount with 2 circular through holes

texts:
Currently I have created a footprint by using one large retangular pad + 2 through holes.

However the DRC picks this up as an error.

Is there a better or more correct way to do this? Or is the DRC in this case being overzealous?

Datasheet for the part: http://www.pemnet.com/fastening_products/pdf/smtradata.pdf


texts:
I'm interested in using some UV LEDs to light some projects.  Specifically, painting some designs on RC aircraft with florescent paint and illuminating them with UV light for night time visibility.  The LEDs I'm considering are 400-405nm, 5mm, 30mA.

Can this amount of UV light cause sunburn or eye damage?  What safety considerations should I take into account?


texts: Potentiometer output voltage for inverting amplifier and non-inverting

texts: When setting the voltage input to 2V from potentiometer, why does it increase to 2.55V after the Vout of potentiometer is disconnected for an inverting amplifier? And remains the same voltage of 2V for an non-inverting amplifier?


texts:
I'm poking around on eBay for some capacitors to use in circuits which I'm working on and see that they have a rated voltage.

After some quick research, I found that going over the rated voltage of a component can cause harm and/or destroy it.

Does the same happen if I go under it?

My circuit runs on a 1.5V battery and the cheap (xD) capacitors I was looking at have a rating of 50V and 16V. Will this affect my circuit in anyway, as I am running like 58.5V less through them?


texts: Low side MOSFET switch disconnecting charging

texts:
I have a problem with the design of low side MOSFET switch, that would be implemented in my electrical system to disconnect PV panels from a battery. This switch would be controlled by Controlling PCB.

Unfortunately, I don't know how to do it, my controlling circuit has to be on battery ground potential. How am I supposed to do it? Can I do it as simple as that?:

I don't think so, because I don't see the return path of the current, that would charge gate capacitance.


texts: Oil on stator windings, commutator, and armiture

texts:
So I took apart a circular saw, it was bone dry, pure metal to metal contact between the stator/commutator/armature.

However a refrigerator compressor seems to be different. It sucks oil from the bottom of the casing and sprays it all over the motor body getting the stator winding/commutator/armiture wet. Video can be seen here at the 3:25 mark: https://www.youtube.com/watch?v=3n8Kby6kgXc

In general, is it safe to put oil on stator windings/commutator/armiture, to help lube the contact surfaces? Reason I ask is I put a dab of oil in the circular saw between the armature and commutator and it started smelling really bad when turned on. How does it affect the life of the tool?


texts:
I'm heating a ferronickel wire, and I need a reliable measurement of temperature, I was using a thermocouple to do this measurement but the wire  is cooled when it's touched by the thermocouple so now I want to estimate the temperature by  the change  of the wire resistance , I'm using the four-wire method to measure so it should be good enough.

Now I need to find 't' from this equation

RT = R20 [ 1 + alfa (t-20)]

I found the resistivity  of the ferronickel to be:

0.86 ohm  mm2/m at ºC

Which is quite accurate, but I can't find alfa


texts: What are the factors that significantly affect the life span of a DC motor?

texts:
I'm currently planning to run a DC motor continuously on solar power. So I would like to know which things I should be very careful about for optimum lifespan of the motor. I found the following two, and would like to know what other factors do:

Voltage
Current Source


texts: Are SMD microcontrollers less affected by noise than DIPs?

texts:
Are SMD packages of microcontrollers (to be more exact : AVR mega series) less affected by noise rather than DIP packages?
Or the opposite is true?

By noise I mean anything that can disrupt the performance of the microcontroller.


texts: 1980's Transistor ID & Silkscreen (German Automotive)

texts:
From the circuit board of a 1985 Volkswagen engine control unit...

I can't find the device itself based on the markings. Does the silkscreen help?


texts: MOSFET push pull gate driver: Too high base voltage?

texts:
I'm trying to create a MOSFET push-pull gate driver using discrete components.

I already made a simpler one to drive most MOSFETs from 3.3 V using two NPN transistors. One to increase the voltage (saturate the MOSFET), the other to invert the high/low state.

Now I read a lot more about MOSFETs, so I want to avoid the slow switching problem and maybe, if necessary, the ringing problem.

After I finally understand that I totally need a proper MOSFET gate driver I read many articles about this. The following one is very interesting as it describes various setups.

With microcontrollers, especially the ones with 3.3 V, and very low current per pin I chose the one in figure 4.

http://tahmidmc.blogspot.it/2012/12/low-side-mosfet-drive-circuits-and_23.html

Trying to recreate the circuit, I encountered a problem:

The position of the push-pull transistors. The next link talks about how to place them correctly avoiding a short circuit.

http://www.talkingelectronics.com/projects/MOSFET/MOSFET.html

So I modified the schematic.

Looking at other similar schematics, articles and diagrams I found that the base resistors on the push/pull node could be just one.

So I modified the schematic.

After each component put on the breadboard I measured everything, checking the datasheet.

It works. I can't test it with an oscilloscope because I don't have one. It toggles a small LED strip on and off and there is no voltage drop...

BUT:

At the base between the first transistor and the push/pull node's base, as you can see in the schematic, I measured 12 V. Isn't the BC547's & BC557's maximum base voltage 6 V?
Why is it INVERTED? The MOSFET is an RFP70N06.

Here is the schematic:

simulate this circuit – Schematic created using CircuitLab

Extra notes:

All the resistors should be OK apart from the R3 & R5 ...it depends on how fast you want to switch. Over 100 kHz R3 should be around 500 ohm and R5 5 ohm; at least I read so...

Datasheets: BC547, BC557, and RFP70N06.


texts: Charging ultracapacitors separately and using them in series for regen braking system

texts:
I am a mechanical engineer therefore please correct me if there is anything that I got wrong. I am working on a regenerative braking system for an IC motorcycle and I am looking for the best way to improve its performance. The current theoretical system uses a 48V, 2kW BLDC motor and a bank of ultracapacitors. The problem is quite complex since the voltage produced by the motor/generator depends on the angular velocity which drops with the speed of the vehicle. Charging the ultracapacitors up to 48V would therefore require either braking at high velocities or a DC/DC converter. There is also another issue of controlling the braking force of the motor which is beyond my understanding of electrical engineering and mechatronics.I think that breaking torque is related to current? Should I control current for smooth breaking?

Looking for a simpler solution I had an idea of having a bank of ultracapacitors which could be electronically modified by changing the number of cells connected in series. At low speeds, the electronic system would charge low number of ultracapacitors connected in series at once, monitoring the voltage and switching between different units until the bank is fully charged taking advantage of low speed braking. If more braking power is required or the velocity of the vehicle is higher, the system would connect larger number of units in series to increase the overall voltage of the bank. Once the harvested energy is used to power the vehicle, the power and torque of the motor could be controlled by modifying the number of ultracapacitors in series. Obviously, the complexity of the system means that a number of monitoring devices would be required to prevent overcharging of single cells and to switch between the ultracapacitors at the right time. Would my proposed cap switching system be more complex than a DCDC converter?How many steps would I need for reasonable smoothness?

I understand that I am quite likely over-complicating things for myself therefore if there is a simpler way please let me know.


texts: How to understand initialization and stack checking of ARM assembly language

texts:
I am trying to understand How bad a 'void main(void)' is from the following link:
tech notes. But I have difficulties in understanding two assembly languages examples, the first one is shown below:

int main(void)
{
 return 42;
}

|main|:
       mov ip,sp
       stmfd sp!,{rfp, fp, ip, lr, pc}
       sub fp,ip,#4
       cmps sp,sl
       bllt |x$stack_overflow|
       bl   |__main|
       mov r0,#42
       ldmdb fp,{rfp,fp,sp,pc}^

I have found some explanations from ARM v7-M Architecture Application Level Reference Manual. so I know that stmfd is like PUSH here. But I still have many questions.

Why do we call the first six instructions the initialization and stack checking?
What do ip, rfp, fp, and sl mean?
Why does it sub 4?
What is bllt? I just find bl in reference manual
Where does 'x$stack_overflow' come from?
Why does it use ldmdb?

If you can give me a tutorial or reference manual about ARM assembly languages, I will be very happy. Because I think there is another more difficult assembly language example from that link.


texts: Can we use 3.3V voltage divider circuit from 5V voltage regulator for (800ma load and 3.3v)?

texts:
I am using (lm2576) 5.0v regulator from 12v battery 2-amps for my raspberry pi. I want to use 3 LDR and 5 proximity IR sensor for my mini project. For all sensor I need only 3.3V voltage. It is sufficient to use 3.3V voltage divider circuit from lm2576-5.0 v reg or else I have to use 3.3 voltage regulator so that I can convert 5v(lm2576) to 3.3v(lm1117/lm3940)

I got 3.3v reg-lm3940 I connected through lm2576 but both regulator getting heat too much and inductor got fire


texts: My microcontroller (ATMEGA328) only has one UART. Is it possible to effectively create, say, 8 UARTs with one 8-bit shift register (like a SN74HC595)? The theory would be to send 1 bit from each "virtual uart" at a time to the corresponding bits of the register... Is this doable?


texts: Re-usability of a used "pencil" (AA, or AAA) battery

texts: If, when tested with my multi-meter, a used 1.5 "pencil" battery is now showing, say 1.2 V and is therefore no longer suitable for the original purpose, can it still have value for some circuit for which a 1.2 V battery would suffice or should it just be discarded? If the former, is it common to re-use such batteries, whether singly or in combination with other similarly "spent" ones? or am I missing something here?


texts:
I'm getting into electronics (so my terminology may be a little wonky in places), and I'm trying to create a simple setup using a Raspberry Pi 4B, a GPIO extension board, a HC-SR04 sonar sensor, and an LED.
To wire up the sonar, the kit I'm using supplies this diagram:

Most of this makes sense, except for the need for the resistors, and the connection of Echo to GND.
Despite the sensor running using 5V, I'm guessing R2 is to protect GPIO24, since it takes 3v3?
My main question is about R1 and R3, and why Echo is connected to ground at all. My first thought was that this would cause the signal sent from Echo to be lost to ground, but then I realized that the total resistance going to ground is higher than that of the direct path to GPIO24, so most of the electricity will travel along the lower resistance path to the GPIO pin, and some will go to ground.
Is this simply "bleeding off" extra voltage into ground?


texts: Grounding conductor has a non-zero voltage (i.e. with respect to "true" ground). Why?

texts:
We're building a new house and I'm not confident with the skills of the electrician who installed the receptacles. In our country, residential structures are supplied with 240 V, 60 Hz (single phase).

Here's what I currently know:
1. Hot and neutral conductors may have been switched (he used the same color of wires for both so there's really no way of knowing which is which when installing a receptacle)
2. Grounding conductor is connected to a ground rod.
2. Grounding conductor is not yet bonded with the neutral conductor
3. At the receptacle, voltage across the hot and neutral conductors are 240V, as expected.
4. However, voltage across either hot and neutral and ground hovers around half of the line-to-neutral voltage, at about 120V.

What could cause this? It's my understanding that since the neutral conductor is already grounded at the transformer on the utility pole, even if the neutral conductor at the load side is not yet bonded with a grounding conductor, measuring the voltage across neutral and a grounding conductor should read a very small voltage (e.g. < 3V).


texts: Low Voltage Programming mode of PIC18F2550

texts:
I am confused with how the Low voltage programming mode works on PIC18F2550. I know that PGM pin is pulled high when device enters into programming mode, but can't find  in the datasheet about what happens to the MCLR pin in LVP mode and where does it connect with say, PICKit3, or is it kept at supply voltage in programming mode?
Also, some sources mention that PGM pin is being removed from LVP mode in some recent devices, instead a 32 bit sequence is sent to put the device in programming mode. I can't find which pin this sequence is sent through, MCLR or PGD?
Thanks for the help.


texts: Wiring an air conditioner blower motor in a Ford Mustang

texts:
I am having some wiring issues with my vehicle following a fender bender. Everything on my air conditioner works as expected except for the blower motor. I can confirm it is a new blower with issues receiving power.

I had the thought to wire the blower to the battery using a circuit to control the blower speed by limiting the current delivered to the motor. The motor is rated to a 20 amperes peak at 12 volts. Would obviously be running off a 12 volt lead acid battery capable of outputting several times the current required to kill the blower. I'm not having any luck finding a PWM designed the operate in the required ranges.

Basically my question is whether anyone has any recommendations on how to set up such a circuit.


texts:
I'm looking into designing a board for a robotics application that is going to be spinning very quickly, and am wondering if there is anything special to take into account. It's going to be in the ballpark of 6000rpm, with the edge of the board 50mm from the center. That's a constant acceleration of around 2000g, with shocks of a couple times that. If I shock mount the board, that would reduce the sudden acceleration but not the rotational one.

What should I do differently from normal PCB design? Would through hole be better than surface mount? Which way should I orient the board, so that the acceleration is parallel to the board (preferable) or perpendicular? Which way should I orient components? Would conformal coating or potting be a good idea? I'd prefer not to, both for repairability and because of the weight. At what kind of accelerations would the component internals themselves start to break?

Also, maybe this is the wrong place to ask this, but what's the best orientation for a lithium polymer pouch battery in this environment?


texts: Find the initial value of the signal from its Laplace transform?

texts:
Given

My answer:

.
,
Since there is an impulse at the origin, the initial value theorem cannot be applied. Is this conclusion correct?


texts: How to make a two channel mono mixer with in balance control into stereo output

texts:
I thought I wanted a circuit that was a basic pan control, but after mapping it out it isn't so standard after all.  The final design will have this exposed:  two mono inputs (left and right), one stereo output (left/right), one pan/balance control.  When the pan/balance control is set to 50%, one mono is 100% on one side, 0% on the other side.  The other mono does the same but on the other side.  As the knob is turned to one side, that side gets quieter and the other side louder until only the other side can be heard.  Here is a table of what I am looking for.  The question is how do I make a circuit to do this?

So some more info.  This circuit is going to be used with my high-end Amateur radio that has two bands (think radios) built into it.  These are the two inputs.  I will be using headphones and monitoring two different channels at one time.  When I need to focus on one band I want to be able to hear it on both ears.
I posted the same question in an Amateur Radio group and someone there said he will work on a circuit. I shared the design below with this person.  This person liked it and added a wise requirement:

I would prefer full isolation between the two inputs. A traditional balance control provides some amount of output from one radio TO the output of the other radio. I would be happier if a signal wasn’t going into the output of my expensive radio, just to be safe. It’s not hard to do.

So the gentleman on Facebook has come back and added a bit, first canceling what he said above and then bring up an interesting point about how it would sound:

Alright I was thinking about this more. The responder to your question on StackExchange is correct - you don't need to do any further isolation because of the "virtual ground" at the "-" input to the op-amp. I think the one remaining question is how to get a response that's more pleasing to the ear (logarithmic). A pair of linear pots are going to hard to use, especially if they're ganged together. If you keep them separate then you could use "audio" pots. But I think there might be a tricky way to get a near-logarithmic response from linear pots.

Is there such a thing as a dual logarithmic center-tap POT?


texts: Connecting Power Banks for USB dvices series

texts:
While I was trying to work out to rebuild the battery for my electric bike by replacing all 18650 cells, I saw a TV ad of the product called "MiniMax" which is a power bank for USB charging devices as well as jump start the cars with flat batteries (12V-13V).

Can I connect those "MiniMax" power bank thing series so that I can achieve 36V for my electric bike?
They are easy to charge and much cheaper than buying 60 of 18650.
Or I am totally wrong...

Thank you for your advice in advance.


texts: How do I model an over voltage spike on LTSpice? Any circuit example

texts: I am doing project, I am trying to simulate an overvoltage/under voltage protection controller on LTSpice. How do I create overvoltage/unudervoltage on a source? For example a transient voltage spike? Please Help.


texts: using inductor in series with a psc motor

texts:
I'm trying to reduce a PSC electro-motor rpm to about 80% to 90% of it's nominal speed. It is attached directly to a centrifugal fan and a mechanical approach is not possible. The ratings are: 450 W, 2.2 A , 220 VAC, 50 Hz, 700 rpm, winding insulation class B.

I tried placing a series 15 Ω 150 W resistance on the current path. And it worked fine but the resistance got too hot, adding a heat sink helped but didn't completely solved the problem.

I also tried using a dimmer circuit, and it caused a 15 degree Celsius temperature rise from the normal temperature (I think because of the added harmonics), which is 60 degrees in 23 degree environment (all skin temperature). Since the working environment of this fan is 45 degree Celsius and the insulation class is B, I think dimmer solution would fail.

I'm now thinking about placing a series inductance on the current path. But I haven't seen a single page about this approach on the internet and I don't know if this would work. Inductor in this size is not readily available and making it is a lot of work. I would like to know why this approach may not work.

I would also appreciate any other solution or idea which cost less than 10 to 20$.


texts:
As a second part of my bad question about voltage converters .

Well, I was asking about a regulator to get me from 220V AC/DC,  into 12V DC .
A regulator can't do that , but today I got the Apple charger for the iPhone , that takes my 220v into a 5v , and its very small.

I think if you take out the plastic you get a tiny transformer.

Is this a switching power supply ?

So , my question now is, what kind of transformer Apple uses in its iPhone chargers, is it some kind of regulator, or just a small transformer with coils ?

My needs are very small voltage conversion, from 220V AC (or DC with diodes), into about 12V-24V DC, with a very small current consumption (MCU), that is in one small enclosure box, and relatively cheap.

I was looking for it everywhere, but couldn't find such a small box to do that.

(By small I mean to be on a board, not more than 2-3 cm)


texts: I want to run 20A constant current and 4.2V on a load using a variable DC power supply rated same

texts:
I want to run 20A constant current and 4.2V on a load using a variable DC power supply rated as 20A, 30V. But because my power supply is a switching CC, Cv type, and it kept switching to CV at only 1.2A. I really want to run it at 20A and 4.2V (CC, CV) on the same load despite the change of resistance of the load.

I will really appreciate step by step instruction on how to achieve that, if using resistors etc. In more details, the load is a 3.75V, 1000mAh battery and this battery is designed to take this much load for only 3 minutes to recharge. Currently the battery is on the nominal voltage checked using a multimeter.


texts: How (do i need to?) do i balance cells during discharge?

texts:
i have a 4s4p 18650 lithium ion pack and i balance during charge (from 4 to 4.2V) down to ~5mv difference

on discharge i still see >100 mV difference at the end (2.5V). is it worth it to add a balancing circuit for discharge?

all cells are individually protected for under/over voltage.

where would i purchase such a board and how do i wire it with the main circuit?

ty for your time


texts: How many opamps does it take to find the peak amplitude of a signal?

texts:
I'm a beginner with EE and trying to find the peak amplitude of an electric guitar signal (0-300mV) using an Arduino's 0-5v ADC. I'm going to use the data to pulse lights in accordance with each strum of the guitar.

I've figured out so far that I need to use op-amps to:

Rectify the 0-300mv AC signal (full or half wave)
Amplify the signal to 0-5v
Use a voltage peak finder to locate the peak
Use a buffer to protect against impedance (not sure if I need this?)

I've found circuits that use op-amps to do all of these, and they work fine, however they are all independent of each other.

My Question: is how do I combine all of these together into one circuit and how many op-amps should I really need.  My approach initially was just to daisy chain everything, but I'm not sure that's the correct approach. Also, most of these use a buffer op-amp as the last step, do I really need one if I'm sending the signal into an ADC?


texts: 3 Watt LEDs in Series - Using constant voltage source

texts:
I have 20 x 3 Watt LEDs and have a 80W constant voltage (not constant current supply). I originally wired this up with 5 sets of series string of 4 LEDs from my 12V supply, however I have been told that I need to limit the current. I don't really want to change the supply and wondered if I could add a very low Ohm resistor to each string to regulate the current?

This is a schematic as it now is? If I added say a \$1\Omega\$ resistor before each of these LED strings would this do a good job in regulating the current?

Alternatively could I maybe use one of these on each string

http://www.ebay.co.uk/itm/DC-Buck-Step-Down-Converter-DC-5A-Regulator-Voltage-Current-Adjustable-DE-/321439418999?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item4ad7484a77


texts: From where is this thevenin equation derived?

texts:
The equation is:

\$I_{in} = \frac{V_{th} - V_{in}} { R_{th}}\$

This equation is from a one-port network.

Variables:

I = input current

Vth = thevenin voltage

Vin = input voltage

Rth = thevenin resistance


texts: How to create a safe UART communication protocol?

texts:
I was wondering how to create a safe UART/USB communication protocol. I need it for the communication between a microcontroller and a PC. I have ~10 commands and thought I'd use 10 separate acknowledge commands for each of them.

The exchange should go like this:

PC sends wake up command via UART
µC recognizes that the PC is connected and sends his command to the PC, eg. 0x01
PC does what it was asked to (some hardware stuff) and responds with ~0x01 when it's done (I negate the number to create a larger "distance" between the two numbers)
µC knows that it sent 0x01 and is expecting ~0x01 from the PC. If something other than ~0x01 comes back, the µC will know that something went wrong and will send a new request or an error message

The case that the µC sends 0x01, the PC understands 0x02 and sends ~0x02 back but the µC reads ~0x01 due to some noise  would be pretty bad.

How safe is that in terms of transmission, or how can I make this more secure?


texts: Is there any way to cap input voltage for an ADC?

texts:
I'm in the early learning stages of EE and I'm trying to understand the concepts of different things so I can then use these ideas in my own hobby projects.

One such concept that I'm struggling with is how to limit voltage to protect ADC. (in a similar way to a scope & its probes)

I understand how the ADC works and that anything above AREF on the ADC pin isn't good for the continued operation of the pins. I'm also happy with the concept of potential dividers to scale things down for AREF/ADC etc.

However, if the target voltage isn't known, how can I ensure that any voltage above AREF is capped to AREF before it hits the ADC pin?

Or do I need to design for a maximum voltage, scale from that, and accept that anything over this may blow pins?


texts: How to use a 2n2222 transistor to pull a pin to ground?

texts:
I am trying to use a microcontroller (specifically attiny85) to "fake" a computer fan on a computer motherboard. For the computer to recognize a fan, the tachometer pin on the motherboard must be pulled low twice per revolution of the fan. Thus, I am generating a square wave of arbitrary frequency with the microcontroller and I want to use a transistor to pull the tach pin low whenever the microcontroller output is high. GND is shared by the microcontroller and the computer. The tach pin normally sits at approximately 2.5 v when not pulled down. I currently have the following circuit:

When this is hooked up, it seems to shutdown the microcontroller, and resets when I unhook any of the connections on the transistor. Can anyone tell me what I am doing wrong?


texts: I have a PCB layout as shown. My question is can I route the PCB between the copper pads? The purple colour is solder mask. From what I know solder mask is the green stuff on a PCB which covers the copper, determines where the copper is actually exposed. So once copper is removed on the board, it is coate with a solder mask which is then removed at certain places. Is it okay to route between these red copper balls?


texts:
As requested by Marcus, here is a short post about a piece of hardware I bought recently from Little Bird Electronics.

I recently bought an XBee Arduino Shield, and was a bit curious when I tried to use it the first time. When I connected it to my arduino, it seemed like it wasn't able to be pushed down enough onto the arduino, but now I'm starting to think that it's missing the black plastic bits on the pins on each side. This means that while the shield is connected to the arduino, if you press gently on either side of the shield on top of the either of the two rows of pins, you can actually rock the shield from side to side.

Here is a photo of it (sorry it's not a very good photo):


texts: Sinusoidal Waveform Induced on Long (~15m) Wire

texts:
I have about 72 of the following circuits on my board. The MOSFET and R2 comprise of the output stage and the pull up resistor is my input stage. The long length of wire in-between is the wire under test.

I've had this working for quite some time now and it works well. However, today I hooked up a wire harness of about 15 m in length - I wanted to see how much ringing was present. I noticed something else though - there was 1.3 MHz sinusoidal waveform present at the "Output Voltage" node. The peak to peak voltage was approximately 400mV(!). Here's the waveform in all it's glory:

When I measure the voltage at the MOSFET's drain, I get this:

The induced voltage seems to be gone when the MOSFET drives the line low. I then got another harness of about 4 m in length - the amplitude of the waveform was much reduced now - approximately 150mV but the frequency was the same. Twisting the wires reduced the amplitude (I forgot by how much. I will do the test again when I go back to work and post here) however, for us, twisting the wires isn't a solution. The harness is manufactured according to our customer's specs and if they dont' specify twisted wires, we can't have twisted wires!

My questions are:

What could be causing this? Are these voltages being induced from somewhere? The environment isn't noisy.
How can I ensure these voltages don't cause issues when my CPLD reads the voltage at the "Output Voltage" node.

NOTE: I know the o-scope screens don't show the frequency, I'm not sure why that is, but the frequency was a stable 1.3MHz. I remember this vividly.

How did I measure the signals?
I connected my probe ground clip to a ground point near the pull up resistor, R1 (it's not visible in the schematic). I then I connected my probe to the "Output Voltage" node. This is the measurement at the input side. To see what was happening at the MOSFET side, I again connected my probe near a ground point that was near the MOSFET and measured at the MOSFET's drain. As the rising/falling times aren't excessively high, I don't think this is a measurement error - ESPECIALLY because the waveform's amplitude was reduced when I got a shorter wire.


texts:
I often see those phrases in tutorials with microcontroller I/O. An example use is "set pin 3 high", or "set pin 5 low for 20 ms".

I also recall reading several different definitions on what that terminology means. Does the low in "set low" mean low impedance? Does it mean low logic level (0 volts)? Or does it mean low as in negative voltage? Or is there even a universal meaning for those phrases?


texts: How to perform a \$\dfrac{1}{s+a}\$ type integration in MATLAB?

texts:
Currently, I am integrating an ODE of the form \$\dot x = f(x,t)\$ in MATLAB using the function ode45

This is equivalent (in block diagram form) as passing \$\dot x\$ through an integrator \$\dfrac{1}{s}\$ to obtain \$x\$

However, now I wish to use an alternate integrator of the form: \$\dfrac{1}{s+a}\$

What is the best way to achieve this using MATLAB?


texts: How to find supply voltages in zener diode regulators

texts:
A simple Zener diode voltage regulator is under design. The design constraints are:
Supply voltage: Vs = 150 V
Zener voltage: Vz = 50 V
Zener current range: 5 mA≤ IZ ≤ 50 mA
(a) Determine the value of the regulator resistor, R, so that voltage regulation is maintained
for a load current in the range: 1 mA≤IL ≤ IL(max). What is the maximum load current, I(L.max)
(b) If the variable load of part a is replaced by a 2 kΩ resistor and the regulator is constructed
using the resistor R calculated in part (a), over what range of supply voltages will regulation be
maintained?


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at my work there are a network of identical devices each of which control some 50 location-guidance light units. These devices or controllers are all linked together and then to a main server/computer via Rs485. The Light modules are linked Together  in series via a bus/rail and to the controller pcb's one 12v output socket.  I am investigating regular malfunction of these lights ( lights get stuck), and was suggested that there is interference with other high power machinery cables or internet cables that confuses the system or the light modules.  When lights get stuck/freeze they either need to be unpluged from board to get workin again, or when this does not help all lights need disconnecting one from bus rail by one until a faulty light is found and system goess back to normal op. So by the looks of it the light modules go faulty after a certain time or a certainn  amont of interference current. The interference is possible in the rs485 as its run with loads of other cables to the location of the controllers, but not likely in the 12 v bus i think. The rs485 has a shield but its not connected to any points as all connectors are plastic and shield is not connected to any pins either. Would it be a possible solution to replace for metal hood on at least one end? Also some suggested on different thread that shield should connect to signal ground as that is normally connected to mains earth throug h device plug. Is that why all these connectors made of plastic? And the person who installed didn't know they have to connect shield to pin5?
Any help would be appreciated!

Edit:
Light module array on bus bar is in parallel connection not in series.

Shield of rs485 seems to have continuity to earth just not connected in db9 shells.. although I have not checked  each connector yet.
Signal Grnd has continuity to PE and extraneous parts of rail.
When things go wrong, not all controllers and their light arrays are affected.
Rail/bus is powered by controller (26.6V) which in turn is mains powered.


texts: 7408 quad-AND with diode latching: sporadic (and undesired) self-latching at power up

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As an introduction to electronics, I am still working my way through Charles Platt's Make: Electronics (2nd edition).
This issue is about Experiment 21: A Powerful Combination
In circuit on figure 4-107, a 7408 (quad-AND) is used to implement a simple switch based "password system". The different switches have to be pressed in a given sequence, each switch allowing to change the output of a AND gate to high, thus latching this AND and providing a high input to the sub-sequent AND gate.
(I suppose I am not allowed to post the circuit schematic from the book, as it might be copyrighted material?)
Minimal example
I have been having problems with the resulting circuit sometimes starting in the "unlocked" state, without having to first press the correct sequence of switch. By fault tracing with a voltmeter, it appeared that, sometimes, the different gates are latched in high-output at circuit startup.
Here is a minimal example showing the latching for a single AND gate:

And here is the corresponding schematic (my first, please be indulgent):

simulate this circuit – Schematic created using CircuitLab
About 1 in 5 times when applying 5V to the power bus, the low-power yellow led will light up, without having to first press the switch.
Questions

What could cause this undesired (and erratic) self-latching at startup?
Is there a design flaw in this circuit? (or is there an obvious wiring error in my attempt to build it?)
The book is using 74HC08, where I am using 74HCT08N. Can it lead to the problem?


texts:
I know that there are many similar topics here, but none of them answers my questions.
I have an 868MHz RF module (cc1120 + cc1190), the output power is around 27dBm. The module is with a castellated connector.
The module is mounted on a 4-layer PCB. 1) - signal + gnd, 2) - gnd, 3) - power supply, 4) - signal + gnd.
Connect the ground of the SMA connector to the digital ground on the PCB?
Both grounds are connected in the module. Is it better to separate the RF ground from the digital one as in the picture? Place the antenna ground on all 4 layers and connect them via Via?
Should the analog part be put on the bottom?
In the first version, I underestimated the signal strength and in the analog part of the PCB a demodulated signal from the RF module appeared on the differential amplifiers.


texts: 12v LED Turn on and Dimming based on either MAP signal, or RPM of Car

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I've got a simple 12v Red Led strip installed in my car, and i currently have it hooked upto a relay which turns it on when you unlock it from the key fob (the same as the interior / courtesy lighting) this was simple to do as everything was on the car already to create the circuit.

I would like to take this one step further and get the angry red LED's to turn on when I am driving angry. So using high revs, or high boost pressure (measuring the map sensor readings)

Would it be possible to use some kind of regulator or switch to control the LED's voltage based on a signal wire (either RPM, or MAP)

So my ideal would be, at 3,300 RPM I would turn on the LED's with 6v, then increasing to the full 12v at 4,000 RPM+ (its a diesel) or similar but measuring boost.

It might be a crazy idea, but I think it would be a fun project.
Does anyone have any ideas?

Oh and the LED's are not under the car (fast and furious style) as that is illegal in the UK. They are positioned behind the front grill, so the whole nose of the car behind the grill is illuminated red. Looks really angry.


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I'm currently a student and I am looking to start doing some side projects. I've thought of trying to detect a cell phone from a certain range (5 meters max).

Is this possible to do with a cell phone that is idle? From what I have been reading, it's easy to do while someone is talking on the phone, sending text messages, etc but haven't seen much while idle.

Im looking to do something like in this video:

https://www.youtube.com/watch?v=xW-hXU7MWnM


texts:
I am considering buying one of the hbridge drivers referenced in the below tutorial, but when I looked at the comments underneath the second hbridges sparkfun page, kickback diodes were referenced and how one of the drivers has internal diodes but the other doesn't. I will be working with motors no more than 8V and much less than 1 A of current. Which of these drivers should I use and should I use kickback diodes with it also?
http://itp.nyu.edu/physcomp/Labs/DCMotorControl


texts: Does the Black's equation work for immortal wires / interconnections (or only for mortal ones)?

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I'm trying to understand whether the Black's equation is only true for mortal wire / interconnections or it is also applicable to immortal wires (essentially when its \$jL\$ product is less than \$jL_{blech}\$ where \$j\$ and \$L\$ are the current density and the length of the wire, respectively). In other words, does the Black's equation give a correct Mean Time To Failure (MTTF) estimation for the wires which do not suffer from electromigration (e.i. the wires with the \$jL\$ product less than \$jL_{blech}\$)?

Thanks,


texts: LMB204BDC with CCS Flex 4x20 driver not displaying text

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I am trying to get an LMB204BDC LCD screen working with a PIC16F877a and the Flex 4x20 Driver (I'm programming in CCS BTW), however for some reason the text is not displayed. Before, I mistaked the datasheet for saying to attack a 5k ohm resistor from the contrast pin to +5v, so I did that and later realized it said from the contrast pin to v0, I connected a 3k ohm resistor and the first and third lines only have faint boxes, might I have damaged the display?

Thanks in advance.