texts: Modelling heat transfer from Power LED to metal bar

texts:
I'm playing around with workplace illumination and have developed a 20 V –> 38 V PWM'able constant current source to drive my power LEDs (max power about 64W). So far, so good. However, I've nearly thermally killed one LED by fixing it on a significantly undersized heat sink ("luckily", the wire contacts unsoldered themselves just in time, stopping the process).

Now, I'm considering cooling options. Wanting to avoid active cooling (i.e. the humming of a fan), I was considering the "lazy" way out (dimension far from final, I don't have a heatsink candidate yet):

I'd like to mount the 19 x 19 mm LED directly onto an aluminum bar or profile. Now, I'm already playing around with thermal simulation software, but that seems over the top (and so far, it mostly crashes, plus I have a lot of theory to catch up on). So:

Is there a well-known analytic model for heat distribution when attaching a constant-power heat source to a piece of metal?

if not, is there a go-to simulation software? So far, I'm playing with Elmer.

Is simulation the way to go here, at all, or is passive cooling damned for 60W LEDs?

Data (from LED datasheet):

Junction-Case Thermal Resistance 0.8 K/W
19x19 mm
max rated power 64.2 W
continuous power I'm planning to use: 36.6 V · 0.72 A = 26.352 W


texts: Why Offset nulling circuit not working in Proteus simulation?

texts:
I tried simulating the offset nulling circuit for LM741 in Proteus but it does not work:

The inputs are grounded and the rail voltages are +15V and -15V. Potentiometer is connected to the  nulling terminals(pin1 and 5) while the wiper is connected to - 15V.
The output is saturated to +14V no matter what adjustment I made in potentiometer. Whats wrong with my circuit?


texts: Problem Switching Relay with Transistor from Microcontroller

texts:
This is my first time posting here, so hopefully I'm doing it correctly.

I've build a circuit which uses a USB-connected FTDI-UMFT240XA.
http://www.ftdichip.com/Support/Documents/DataSheets/Modules/DS_UMFT240XA.pdf

Basically I'm sending 1-byte packets of information to the controller, which are then used to turn on and off transistors, which then will turn on and off relays. I am using the DATA I/O pins to send the logic signals to the transistors.

The problem I'm having is that when I switch the relay on and off via the circuit multiple times, I find that every once in a while, the microcontroller just shuts off. This only seems to happen when I introduce the relay into the circuit. I can switch LEDs on and off without a problem.

I have tried both NPN and N-Channel MOSFET transistors and both yield the same behavior. I have it hooked up as follows:

Gate (or base) of transistor hooked up to digital logic signal (DATA 0, a 3.3V signal)
Source (or emitter) of transistor hooked up to ground
Drain (or collector) of transistor hooked up to the relay in parallel with a flyback diode, both of which connect to positive voltage (+5V)

The gate also has a 1M pull-down resistor hooked to ground.

At first I thought perhaps the USB bus was not able to supply enough power to the circuit, and was therefor being shut off, however this does not seem to be the case, as I have removed the two solder jumpers on the chip and connected an external power supply (using a 5v and 3.3v regulator in place of the USB power, as described in the self-powered configuration in the above pdf)

The ONLY way I seem to be able to avoid this dying of the microcontroller is by connecting the DATA 0 to the gate with a diode, rather than a straight wire or a resistor. The problem with this is that upon connecting the circuit like this, it takes a long time for the voltage on the gate to drop far enough to turn the transistor back off. (about 5-7 seconds).

Am I missing something here? Am I using one of these components incorrectly?

EDIT:

I don't have a schematic, but here's a look at the breadboard with some labeling.


texts: Which microcontroller has good linux supported simulator?

texts:
I am looking for a good microcontroller to learn electronics.

EDIT

I want develop on linux, and I wish there is a good linux supported simulator.

I want use C language.


texts: What's wrong with my Verilog multiplexer?

texts:
I created a 2-way 4-bit multiplexer:

module mux2(c, x, y, m);
  input c;
  input [3:0] x;
  input [3:0] y;
  output [9:0] m;

  assign m[3:0] = (~c & x) | (c & y);
  assign m[9:4] = 0;
endmodule

I instantiated it from my top-level module:

module top(SW, LEDR);
  input [9:0] SW;
  output [9:0] LEDR;

  mux2 mymux(SW[9], SW[3:0], SW[7:4], LEDR[9:0]);
endmodule

I did a functional simulation in Altera Quartus Prime Lite on a Cyclone V 5CSEMA5F31C6 (having imported assignments from DE1_SoC.qsf) and got this unexpected waveform:

As expected, the output M follows X when C is low; however, M does not follow Y when C is high. Instead, it seems to have a combination of X and Y values.

Here is an expanded version of the previous waveform:

I assume I'm instantiated mux2 incorrectly but don't see what I did wrong.


texts: Connecting and disconnecting the power supply

texts:
I have learned that powering a chip without ground is quite dangerous and might cause permanent damage to the chip or the board in general. I have also seen that happening many times in non isolated DC to DC step down converters and some microcontrollers as well.

How can I prevent that from happening? Assuming I have a board with a non isolated switching regulator and a microcontroller that is connected through a UART to a USB to serial cable or to another board. How can I prevent the current flow if the ground disconnects first or the positive line connected before ground?


texts: Audio playback information when pressing buttons (school project)

texts:
My son is making a display (about A1 sized card) about space for school and I am trying to find out a simple way to add some buttons, that when pressed plays an audio recording with info about different topics. So multiple buttons spread over the display and each buttons plays a specific recording.

My first thought was those little devices in greetings cards that play sounds when opened. But they may be a bit too quiet? They can't be too big as it has to be attached the the card display.

Is there anything that is small, capable of playing back different messages based on which button is pressed?


texts: ATMega328P - faulty ADC behavoir - update

texts:
BLUF: What causes the ADC2 to work perfectly while ADC3 charges towards a value of 328 (1.6V) on ATMEGA328P?

I use an ATMega328P for one of my current projects and had an issue with the ADC.

\$A_{VCC}\$ is connected as in the datasheet with a 100nF capacitor and a 10uH inductor.

My project reads frequently ADC2 and ADC3 to calculate some outputs.
When I tested it, ADC2 was reading the same voltage as I could measure with a multimeter. But ADC3 showed semi-random values (at least it appeared to me at the time).
After some measurements and flashing some code which just outputs the ADC2 values to Serial I figured out that ADC2 was working perfectly.
Then I did the same with ADC3 and what appeared to be semi-random values was actually the charging curve of a capacitor (which btw. was completely independent to the actual voltage on the ADC3 pin).

Update

After I changed the inductor it was working. After a couple of tests, it went bad again. Meanwhile, I checked everything again, including the points mentioned in the comments.

All negative:

The connection of the pin is Ok
there is 0V on ADC3 Pin
The inductor is OK
100nF cap is OK

I even changed the ATMEGA and the same happened again, it was working for some time, and then went bad...

Below the shematics:

As for the code:

void setup() {
    analogReference(DEFAULT);
    Serial.begin(9600);
}

void loop() {
    Serial.println(analogRead(A3));
    delay(100);
}

This results in the following data beeing plotted:

void setup() {
    analogReference(DEFAULT);
    Serial.begin(9600);
}

void loop() {
    for (uint8_t i = 0; i < 50; i++) {
        Serial.println(analogRead(A2));
        delay(100);
    }
    for (uint8_t i = 0; i < 50; i++) {
        Serial.println(analogRead(A3));
        delay(100);
    }
}

This results in the following data beeing plotted:

Either way the ADC2 result runs towards a value of 328 (equals 1.6V), which I cannot measure anywhere in my circuit...

Update
I changed now all parts twice. The inductor, both capacitor and the ATMEGA. From time to time it's working, from time to time not.


texts:
Even though there are questions about ESD protection for i2c bus already in this forum, I wanted to ask how to suppress the clamping voltage of a TVS diode to a safe level. As an example, the following plot shows the clamping voltage of RClamp0582BQ.

Let's say a microcontroller's SCL, SDA pins are connected to a sensor over wires. Then one wants to protect the chips against an ESD strike caused by human contact. In the circuit below, the TVS diodes clamp the fast transient. The 100 ohm resistors slow down the short current and dissipate power to reduce the stress on the TVS diodes. However, How does one suppress the clamping voltage further ?

(1) an additional ~1k ohm series resistor  (as in the image above)
If the device is powered off the impedance of the SCL and SDA pins should be already high, so 1k ohm would not help that much, right?

(2) a ~20pF capacitor
Would it be good to place such small bypass capacitor next to the I/O pins? Since the capacitance should not exceed 400pF, it might be difficult to use a higher value, when there are many slave devices. But I'm not sure if 20pF or something similar is useful.


texts: Replace amplifier IC with a class D amplifier (AN7133N with TPA3116 board)

texts:
Today I received this nice 90's Panasonic RX-CT900 boombox in the mail.

The specs claims it is 2x60W PMPO (PMPO b**llsh*t throw-of- a-cliff specification) but in fact it is just 2x5.5W RMS (Panasonic AN7133N IC). The amplifier is described in the service manual (right click with mouse and open in another tab to view/zoom it full size):

Sound is pretty good however when you crank up the volume is starts clipping (this is an amp problem - not a speaker problem), especially when using the XBS function.
Edit 11/13/2020: Discovered it is actually a speaker problem: foam rot!
What I want to try is to replace the amplifier IC with a modern, more efficient, more power and better specs one. I have many of these small OEP50Wx2 boards, they are pretty good (used many - excellent sound quality) however Class D (Texas Instruments TPA3116 IC):

The question is, to you specialists, is this a stupid idea, does somebody tried such thing already (for example replacing obsolete IC) or can do this without problems.
What I want to do is to create an adapter socket (on the main-board) that allows me to plug-in (with compatible pin arrangement) the new amplifier module (and to easily switch back when it is no success or for other reasons - don't want to stress the solder connections too much).
In the service manual they specify a 15V input, which is perfect for the module because it outputs only 25W max (in theory). Because a class-D amplifier is more efficient (and consumes less current and more power at volumes) I think this a could be a great improvement in sound quality or is this just a crazy idea? I know the speakers maybe don't match the output power however I have some heavier replacements and test speakers (max 100W) that can be used to test the new setup (speakers are detachable) first.
Before I try, what do you think, possible or a source of many problems? Here is the full schematic of the mainboard (right click with mouse and open in another tab to view/zoom it full size):

Notice:

If this is possible it could be a great method to replace obsolete
IC's with modern tech to keep devices away from the landfill;
The pictures of schematics are assembled of pdfs with separated pages (can contain some allignment errors).


texts:
Why is it not possible to measure the internal potential difference in a p-n diode across the depletion region externally when no external voltage is applied to the diode ?

Steven here https://electronics.stackexchange.com/a/33235 does not elaborate on why the potential difference cannot be measured.


texts:
This is my second time changing my mobile because I forgot it all the night on the charger.
I know there is an IC or circuit inside my phone that will disconnect the charger once the battery is fully charged,

So I brought my Multimeter and put my Lumia 520 under testing for 1 hour to see if there is anything I can build my charger on, and calculated everything; time, temperature of my mobile and my room, voltages and Amps.
and this is the result

In the beginning I was disappointed, I thought the voltage of my charger would drop down when my phone was closer to full charge. It took two minutes to charge my mobile only 1% and there was no change in temperature (just 3 celsius from 61% to 100%). But after full charge the temperature increased from 20 to 25, in twelve minutes.

I found something interesting when my battery is fully charged after 100%, the voltage changed from 5.39V to 5.50. My voltmeter is not that sensitive and I am sure its 4.50V. Anyway that little change will make a big difference.

I connected my charger to Arduino and made it stop the charger when the battery is full.

Some people said it's not necessary to do that, others say that heat will not have any effect on my battery or on my mobile!

From what I know the IC in the phone can't stop the charger completely, So that will damage the battery after extended use!

In the same time IC will be over heated if you let it do its job for a long time!

I am completely confused, I read some research about Lithium battery there is no recommended "specific point" to keep you battery on, or charging it at specific point, some research said 35, other 45, and the weirdest one was 80!

Can someone tell me if i am wrong or explain this to me!


texts: LTSpice: Pass/Fail in Error Log if Voltage < Constant Reference

texts:
I am looking for a way to have LTSpice report a "Pass" or "Fail" ("1" or "0") in the error log if a measured voltage drops below a preset constant reference value.

I have a model I made of a transmission line and I would like LTSpice to be able to identify when the amplitude of the signal being transmitted over the simulated cable drops below the receiver's detection threshold. Is there a method to do this in LTSpice, perhaps using the CROSS command? I have been trying to solve this for some time but have not had any success as of yet.

EDIT: To clarify, I would like to have a variable labeled "test_result" that would be set to "1" if the signal does not drop below the threshold, and would be set to "0" if it does, and the value of "test_result" should be shown in the LTSpice error log.


texts: Do high+variable refresh rate (small) displays exist (i.e. of type OLED)?

texts:
Here's my conundrum - I'd like a portable display that can be driven at both variable and high refresh rates > 80 Hz (for some visual perception experiments). Does anyone know if this tech exists / if it's possible with OLEDs?

A lot of datasheets don't seem to be clear about this, and - truthfully, I'm not very well versed in how this stuff works / what the bottlenecks are. I know there are displays, display-driver ICs, and that the refresh rate is typically dictated by the number of rows (I think?).

All of the ones I've seen that have been clear about this have been <= 60Hz, and I'm not sure if that's just due to the clockspeed, or the physical properties OLEDs themselves.
I would buy some displays to play around with, but it seems like this could quickly become an expensive mistake (on my budget).


texts: Capacitor constant power charge, constant current discharge curve

texts:
I have an (ideal) capacitor that is simultaneously being charged through a DC/DC boost converter (assumed constant power \$P_{in}\$) and discharged through a linear regulator (assumed constant current \$I_{out}\$).
I would like to analytically find the relation between time \$t\$ and the energy stored on the capacitor \$E(t)\$.

I tried to approach it through the energy/power equation with capacitor voltage \$v_c\$:

\$E(t)=\int_{0}^{t}\big[P_{in}-v_c(\tau)\cdot I_{out}\big] \, d\tau + E(0)\$

Clearly, \$v_c(t)\$ is not independent of \$E\$ and I'm currently lacking the right approach to solving this integral.
Obviously the same thing happens when writing the equation in terms of voltage.

Would highly appreciate a solution or pointers in the right direction.


texts: Problem simulating 2-bit counter with OrCAD

texts:
I used OrCAD Capture to create a 2-bit counter using two D-type Flip-Flops (DFFs).
Here is the schematic:

My problem is that I get no output when I try to simulate it. I know for sure that V3, the input clock, is working.
Here the simulation result:

Is there anything in particular I need to do in Orcad Capture when doing analog and digital simulation together?


texts: ModelSim does not run until "$stop" command after editing my testbench

texts:
I keep running into this issue where my code stops running before the "@stop" command. This only occurs whenever I add code in Libero and then go back to ModelSim. When I go to simulate in ModelSim, my new code is showing up, however it is stopping early.
The only way I have been able to fix this so far is by creating an entirely new testbench each time which is very annoying when I should be able to just edit my existing one.
I've attached a screenshot from ModelSim so you can see what is going on.
Thanks for the help!


texts: What kilogram is doing in volt unit definition?

texts:
My question is inspired by this: Why do farads multiplied by ohms produce a result that has a unit of seconds?

I want to ask what kilogram is doing in this equation:

$$\mathrm{V = \frac{kg \cdot m^2}{A \cdot s^3}}$$


texts: Timing Issues with Optically Isolated Data Signal

texts:
I have been working on a system that requires data transmission between two devices powered by separate supplies. I have based my design on the MIDI-hardware Spec, as I'm comfortable working with that configuration and have successfully implemented it in other areas.

However, I am experiencing some strange timing issues with this latest design, and can't seem to track down the problem. The screenshot below shows the Data Input (blue) and Isolated output (red). The transmission frequency has been slowed from 200kHz to 30kHz to try and assist debugging:

The high(1) and low(0) levels are as I expected, but I can't figure out where the timing issue or 'lag' is coming from. The falling part of the signal is always delayed by around 25uS.

I'm using an ACPL-247 opto-isolator. But I think the problem is more likely in the 2N3904 part of the circuit, as I've not encountered this problem in previous uses of the same opto-isolator IC. Example Circuit Below:

Thanks for reading, any advice or pointers to relevant literature will be greatly appreciated!


texts: reducing the effect of a parasitic capacitor!

texts: According to my text book, the second figure says that the noise current returns to their source without flowing through z1, how is that possible? if the noise returns why doesn't signal/ original current also return without flowing through z1?


texts: ESP8266 ICSP design: which circuit design guidelines to avoid fails/damages?

texts:
I'm working on a project which is all on breadboard right now. I'm close to final version, so I'm planning to design PCB for the release (not commercial use, just for some friends of mine).

The microcontroller is an ESP8266-12E, and I want to be able to program it after it has been soldered to PCB (so ICSP). To achieve that, I planned a pin-strip to expose:

RX
TX
GPIO0
GPIO2 (not sure about that, some schematic don't use it)
GPIO15
CHPD
VCC
GND

according with programmer schematics you can found online (eg. this or this).

This is how 'programming relevant' pins are used in my project:

RX and TX pins are used for a GPS module connection.
GPIO2 used as 'debug serial'
GPIO0 used as output
GPIO15 not used

I never worked with ICSP so I'm quite confused about some points:

Resistors in programmers schematics (like the second link I post): should I put them on the programmer board (which will be then connected to pin-strip with a cable to program) or should be placed into the PCB?
Are there any other PCB/schematic design guidelines I must to know to safe perform an In-Circuit-Programming procedure without damage other PCB device/IC or the microcontroller? (eg. pull-up/down, decoupling, etc)


texts: How can a 74LS76 JK Flip Flop's outputs Q and Q-bar not be fully complementary?

texts:
I have a 74LS76 JK flip flop hooked up as follows:

You think that should be easy. But look at my scope traces of Q above and Q-bar below:

how the heck can a JK flip flop's output Q and Q-bar be not completely complementary?
Here is Q above against the CLK below if it helps figuring that one out.

Even if this is falling edge triggered, this should not happen!
Clock is 4 MHz.
More scope traces requested in comments:
Here is both probes in Q:

here is !Q against CLK:

Q against (Q AND !Q)  (AND - 74HC08)

!Q against (Q AND !Q)

CLK against (Q AND !Q)

So you can see, this is real, not an issue with the scope. It's also a fairly isolated test so not much could go wrong. The wiring checked and double checked.

pin 1 = CLK
pin 2 = H
pin 3 = H
pin 4 = H
pin 5 = H (Vcc)
pin 6 = pin 1
pin 7 = H
pin 8 = pin 3
pin 9 = pin12
pin 10 = NC (2Q)
pin 11 = NC (2!Q)
pin 12 = RCO of 74LS161 #2 - or H for same test on JK FF #2 of same chip
pin 13 = GND (L)
pin 14 = NC (1!Q)
pin 15 = NC (1Q)
pin 16 = H

bypass cap 100nF riding between pin 5 and 13
This is read from the wiring, not from the schematics.
Here is the chip, I am in Brazil, and so I'm stuck with what I'm getting here.

I don't think that ground bounces are the issue since I check my power rails with the scope too and it is just too reproducible with this chip.
UPDATE:
I would have to get another '76, which I will try. Meanwhile I tried the '74 and it is almost working with that, except the high stage that is supposed to toggle when the ripple-carry-output of the '161 is high and the next clock pulse comes, that isn't working right. It would toggle too early. I had to make a poor man's AND gate with resistor diode and that would mess things up anyway. If I use a real AND gate then I'm going to have switching delays again.
I guess I haven't paid attention to that previously, I need to trigger that on the falling edge of the RCO, so maybe I need to get a falling edge triggered JK ff anyway. Let's figure this out:

74LS76 - DUAL J-K FLIP-FLOPS WITH PRESET AND CLEAR
74LS78 - DUAL J-K FLIP-FLOPS WITH PRESET, COMMON CLOCK, AND COMMON
CLEAR
74LS112 - DUAL NEGATIVE EDGE TRIGGERED J-K FLIP-FLOPS WITH
PRESET AND CLEAR

I'll run now before the store closes here.
BACKGROUND ONLY: I have a 16-bit counter, 74LS161, it runs at 4 MHz now but I want to get it to work with 16 MHz. The counter value becomes RAM addresses, and for that application I found that glitching is a major problem. So I moved from async 74LS393 with 74HC4040 to 4 74LS161 counters.
For the correct derivation / switching of the counter values to become the RAM addresses, I require bit 0 (LSB of low byte) and bit 8 (LSB of high byte) to exist in both straight and inverted form. But, if I use an inverter to invert this bit, then the follow-up address selection logic glitches because of the delay of the inverted LSB.
I thought I had a solution by running the LSB as a parallel JK flip flop which would be clocked by the same clock, or an prior inverted clock, depending on whether the JK ff is rising vs. falling edge triggered. Here is a piece of the schematics using the 74LS78 JK flip flops:

sorry for the vertical arrangement and low resolution. Anyway, right now what matters is just the JK flip flop.
If I use the 74LS78 I have it glitching on the high stage, in such a way that Q and Q-bar flip over even just by me putting the scope probe in one or the other, and if both are tied as inputs to the following AND gate(s), they end up rapidly flipping around.
Now I gave up on the 74LS78 and used the '76 instead. With the problem as initially stated.


texts: What are methods to mitigate or reduce brown out resets?

texts:
How can I prevent or reduce the effects of low voltage causing the Arduino to reset?  What would be the best proactive or reactive methods to deal with brown out resets?

Edit: is there a reactive way to programmatically know if there has been a brown out?


texts:
We have a brushless motor with the following characteristics (Slow(8T)):

For that motor, we are developing an electronic speed controller using the hall sensors. The microcontroller is an atmega328p and we are generating a PWM frequency of 8kHz in the low MOSFETs with a 6-step commutation.
The problem is that this configuration generates high currents (4 A in the source and 10 A in each phase) and in a short time of motor operation, the MOSFETS start to heat up.
I would like to know if the problem is in the design of the controller, the frequency of the PWM, or something that we are not considering to improve the performance of the controller.
Here is the schematic:

How can I improve the design of my electronic speed controller?


texts: Why is my crystal oscillator not working with KSZ8999 switch?

texts:
I am using KSZ8999 ethernet switch from Micrel and I have problem with 25 MHz external oscillator. There is constant 2,1 VDC on output pin which is VDD for the switch, so crystal is not oscillating.
There should be no problem with crystal, because I tried to connect it to other design and it worked fine. I also tried using different values of load capacitors but with no result. There is also no short circuit between VDD and crystal pin.
Can you please help me find out, what could cause this problem? Thank you for your answers.

R15 is now 510k, R16 is 0R, C41 and C42 is 15p. Crystal MPN is now GC2500081. Sorry for the weird schematic symbol, it was downloaded this way.


texts: How can I get touchscreen (HID) data into Windows 7?

texts: We have a hardware design in progress that is taking touch screen inputs and passing them along via I2C to an FPGA. The FPGA translates the I2C data to PCIe. The PCIe passes the touchscreen data to the processor. I am wondering how to get Windows to recognize this PCIe interface and deal with it like a HID. (Human Interface Device) It appears HIDs are typically USB. Can PCIe be recognized and used with Windows? Would this require a custom Windows driver? I have seen I2C to USB pSoCs that convert I2C to USB. We are trying to use the FPGA as a central point for simplifying and consolodating I/O but the tradeoff of simplifying the layout and parts may be overcome by the software development effort for custom PCIe drivers.


texts: I just started network theory and stuck to this problem, in book it is written that an ideal transformer supplies constant power, so I randomly assume a question as shown in figure and try to find current in secondary side but I got two different answers for same current calculation, so where I'm going wrong and how to calculate current in this case correctly?


texts:
Imagine there's an electromagnetic wave propagating in vacuum with a frequency \$f\$ and wavelength \$\lambda\$. Its speed is \$c\approx3\cdot10^8{{m}\over{s}}=f\cdot\lambda\$.

Now, the wave has to travel through a material with relative permittivity and permability \$\epsilon_r\$ and \$\mu_r\$. The speed of the wave will change in the new material, the new speed is$$v={{c}\over{\sqrt{\epsilon_r\cdot\mu_r}}}=f^{'}\cdot\lambda^{'}$$

There are three possibilities to fulfill the equation:

The frequency changes.
The wavelength changes.
Both the frequency and the wavelength change.

My guess is that one of these two properties is more "fundamental" than the other and remains unchanged. Is that assumption correct, and if it is, which is the fundamental property?


texts: Help finding a freescale MC68LK331CPV27 datasheet

texts:
I'm looking for an old cpu datasheet which seems to have disappeared from existence.  It is for a freescale MC68LK331CPV27.

I've ran out of stock on an old cpu and the replacement (MC68LK332ACAG16) is supposed to be pin compatible but it isn't working.

I'm hoping there's a guru out there who knows where I can dig deeper in finding this item.

Thanks


texts: What is the correct terminology usage regarding "downconversion" and "correlation"?

texts:
I've recently taken a digital communications course.
To provide some background to my question: In passband, it was explained that the incoming signal r(t) is "split" into different channels, and correlated with known reference signals, or basis functions. This is illustrated below (from Digital Communications by Bernard Sklar)

I think I understand above theory, and how you utilize orthogonality of basis functions to express signals as a linear combination, then introduce things as signal space, etc. However, I also see many referring to the mixer operations in the above pictures as "downconversion" - instead of "correlation". A less mathematical representation, and more practical, is the following picture (article source):

The article, source of picture above, describes the first RF mixer as a downconversion to IF - which I agree with because we are not interested yet in decomposing the signal into orthogonal components by correlation. However, the article also refers to the two later IF mixers as the "second downconversion". And this is the heart of the issue, perhaps I am being picky, but to me, it would be much more descriptive to refer to that operation as the "correlation" than "downconversion". Granted, down-conversion is a side-effect since we are multiplying two sinusoids, but really what we're after is to "extract" the I and Q components by using correlation. Would you agree?
Fundamentally, in light of above rant, my question is: How would you define the following operations in a communication system, especially in relation to each other: Downconversion and correlation. Or perhaps they are used interchangeably?


texts:
i have to build a kind of dress that can unserstand the blend angles of neck, shoulder, elbow, wrist. i thought the best is to use arduino lillypad and some flex sensors.

i've saw this: http://sensorwiki.org/doku.php/sensors/flexion

but i'm still confused on what kind of sensors could fit best in my project.

for example the sensor in the neck sould be a little more accurate that the one in the shoulder and i don't know if i need a different sensor or i can use different offset via software. then i heard that some flex sensors are going to get broken if they are misuring more than 90° (but.. is it true?) and in my project elbow is blended kind of everytime more than 90°.

can someone give me some advice?


texts: Minimum power rail voltages for given input voltage range (inverting op-amp)

texts:
Recently I've been looking at single-ended to differential converters. An engineer designed an SE/DE converter with +7 and -4V supply rails. It got me thinking as to why he chose such odd values for the rails.
The first stage of the converter is a standard inverting op-amp, with the non-inverting input set to 1.67V. The single-ended input voltage range is +/-5V - I thought this would be a problem for the inverting stage, since it would have an input voltage lower than its supply voltage. I then realised (after an embarrassingly long time) that due to the feedback of the inverting amp, the op-amp's input doesn't actually go below the supply. I then wanted to know how low the supply voltage could be, before damage would occur. The circuit its as follows:

simulate this circuit – Schematic created using CircuitLab
This is what I came up with :

So this, I believe, gives you the minimum power rails required so that the output doesn't saturate; in simulation this works. Does it also tell me the minimum power rails needed, to ensure the inputs don't go above/below the power rails?
I'm sorry I keep asking questions recently, it's just great to have such a vast knowledge base to ask questions to!
Thanks in advance, and sorry for the rambling, I hope it makes sense!


texts: Figure out the Resistance Value With Known Device Specs

texts:
I'm learning electronics and trying to find the right resistor value for my device: a Eachine Rotg01 Receiver.

The specs

Working Current     200mA/5V
Power Supply        5V(by smart phone)

I don't want to fry my receiver so I was  hoping to get some confirmation that my math is correct. Let's say I want to use a 9 volt battery as my power supply. From the specs, I am assuming 5V is the voltage drop so V = 9-5 = 4. Plugging this into Ohms Law 4 = R*.2 So that would work out ot a resistor of 20 ohms. Is this right ?

I'm not sure if 5V is the voltage drop of the device. I tried measuring with my multimeter, but got OL. Any help is much appreciated.


texts:
I need to select LED/LEDs for a light source in my project. The requirement is that the light source should approximately be able to project light beam of 1.5m diameter on a surface, from a distance of 1.5m. The incident light should have lux equal to 1500.
How do I go about selecting the LEDs for this application? What factors should be considered?


texts: Static Discharge on Metal Enclosure for Tablet causes restarts

texts:
The setup I currently have is a Aluminum enclosure for an Android Tablet. Inside the enclosure, a shielded USB cable is routed into the micro USB port and out through a small opening. This cable is then plugged into a 5V charging port on a power supply.

If I tie the enclosure to earth ground, have USB plugged in and shock the enclosure with a Piezoelectric igniter crystal (to emulate an ESD shock), it causes the tablet to reboot between every couple shocks. With USB disconnected, shocking the enclosure does not cause restarts.
I've also tried placing a 1M ohm resistor between the enclosure and ground but that doesnt help either.

The one thing I also noticed after tearing the tablet apart is that DC ground is tied to chassis ground (shield) internally. Is there anything that can be done to help suppress the shocks and not affect the USB circuitry which is most likely causing the restarts?


texts:
What are the general guidelines for handling a cryptographic keys?

I know that saving them in plaintext is generally frowned upon, does this hold for true uCs where no user code is run?


texts: Understanding surface and volume polarization charges

texts:
Can someone please give me an intuition of this formulae?
I am unable to visualize the formulae in equation 5.26.

Specific question - How does a dielectric when kept in an external electric field gives rise to both surface and volume charge density?

My take: In dielectrics, electrons are bound to the nucleus and hence cannot penetrate the outer surface of the dielectric at any cost.
When a dielectric material is placed in an external electric field, positive charges (nuclei?) tend to drift from their equilibrium position in the direction of the applied external field, while negative charges (electrons?) tend to drift in the opposite direction thus creating an electric dipole.

Now since these charges which drift either way cannot penetrate the outer surface of the dielectric they are bound to get accumulated at  the outer surfaces thus generating surface charge density.

What I am having trouble understanding is the process of volume charge generation within the dielectric.
Won't there be equal positive and equal negative charges inside the volume?


texts: I came across this IC and it is an IC i need, but i would like to controll a heavier AC load with it, 220V 1A but this particular device is for low volatage levels. Is there high load alternative for this IC or a tool that will help me search through the alternatives in future


texts:
There are countless projects online that start with "harvest the stepper motor out of an old CDROM drive." Many of these projects look super fun, but I don't have a pile of old CDROM drives around gathering dust.

What are the stats on these ubiquitous CDROM steppers, so I can find an equivalent one to order? Or if anyone already has a favorite model they use for these projects, I'd love to hear it.


texts: Can someone explain what this line means in the code for a D Flip Flop written in Verilog

texts:
module dflipflop (data  ,clk  , reset ,q);// Code for Asynchronous Positive Edge triggered D flip flop
input data, clk, reset ;
output q;
reg q;
 always @ ( posedge clk or negedge reset)
  if (~reset) begin //what does this block of code mean
    q <= 1'b0 // particularly this line
  end  else begin
    q <= data; // and this one
end//
endmodule

I am new to learning Verilog and I have to learn the codes for the various types of flip-flops. However, I haven't been able to understand this one entirely and what it means.
For instance, as the D flip-flop is positive edge triggered, hence we write posedge clock and it has an asynchronous reset input apart from the normal D input.
But what I do not understand is the use of '<=' operator in the highlighted lines and what is being done there. Does it mean q is being assigned a value less than zero? What does data variable refer to in the other line and what exactly does the line mean as well?


texts:
Why is the efficiency of rectifers not 100% even when ideal switches are used for its modelling? In conducting state, the voltage across switches is 0, and during blocking state, the current is 0. So power loss in the switches must be 0. Where does the lost power go?
Assuming ideal switches without snubber circuits.


texts:
I would like to ask if a mosfet transistor has lower power consumption compared with bjt transistor.

For example a mos transistor has a subthreshold regime where power consumption is very low, but a bjt hasn't got this regime.


texts: Any way to use N-channel mosfet in P-channel configuration?

texts:
In my application, I need the HIGH signal to turn a device OFF and vice versa. Clearly, this is P-mosfet configuration. However, I only N-mosfet on hand.
Is there any clever way to utilize N-mosfet to turn a device OFF when signal is HIGH ?
In other words, given a switch (N-channel mosfet) , is there any way to turn a motor ON when signal is LOW & vice versa ?

Credit:vishay.com


texts: Solar powered water pump - need some advice

texts:
I am completely new to elecrical engineering, but I want to give it a shot and am really interested in learning more details about how all of it works. I've had an advanced physics course in high school, but that's about it, so please bear with me while I'm trying to get into it.

Now onto my "test project", which will be my first electrical engineering project after building a electromechanical motor in high school.

I want to create a battery powered water pump, which can be charged by a solar panel (think about it as a portable garden hose). My idea is that the solar panel charges the battery, and the battery powers the pump.

Here are my questions:

What special requirements do pump, battery and solar panel have? I
found a 12V 20000mAh battery, and a 12V solar panel. Also, I found a
water pump that needs 12V of power to work. Are there any more
requirements for the components to work as I want them to?
How do I switch the battery from charging to actually powering the hose? Can it do both?
How do I detect (and/or display) the current charge of the battery?

Thanks for your help! If I am missing anything, please let me know.


texts: how to isolate coupled noise source in parasitic capacitance in high voltage pcb design?

texts:
I'm new designing a high/medium voltage (V <=10kV) with low voltage and low current (10mA). There will be only a few HV relays. Their coils will be triggered by LV.

I have read some literature about this subject. I have known that noise could be coupled to the parasitic capacitance at the insulation: "If noise couples through parasitic capacitance on the board or in the insulation, it can easily propagate to very sensitive areas of the board".

So, it could be bad news if this capacitor discharges its own charge and starts having continuity between 2 isolated points where should be isolation.

How could I avoid these capacitor effects? How can I stop the noise running through Capacitance between 2 isolated (or potential different) points?


texts:
I work in a laboratory, and we are performing experiments on a cycle ergometer, during which we would like to deliver magnetic stimulations during cycling exercise.
To do so, we need to know the angle of the crank, in order to standardise the angle at which we are stimulating.
We have sensors on the crank which give us the waves showed in the image. What I would like to do is convert this into the actual crank angle (i.e. between 0-360 degrees). This should look something like a triangle with a verticle drop when the angle passes from 360 to 0 degrees. Would anyone know if there is a calculation that I can perform in the software in order to convert to the actual angle? If we placed a goniometer around the crank, such that we could see the which value in the image is associated with a specific angle, perhaps this could take us towards a solution?
Many thanks in advance


texts: Where is the ground/earth used in the Sparkfun Logic Level Converter

texts:
I am studying the Sparkfun Logic Level converter and the basic aim of this is to understand how these BSS138 transistors are used in logic level conversion. I have used transistors before in driving high current motors with MCU's i.e. small time h-bridge configurations. Now I want to use them to make my own logic level converters.

So went to the SparkFun GitHub repo and downloaded the eagle files. Something just does not add up in the schematics for me and I seek clarification around this.

Lets look at how the BSS138 is wired up:

The first thing that strikes me as odd is that I cannot see a earth/ground connection here seems like the low voltage side is connected to the Gate and Source while the High voltage side is connected to the Source.

However there is a clearly defined GND on both the HV and LV side of the board designs and on the schematic? See below:

I must be missing something fundamental here.I can even see how current wuld flow without the BSS138 having some sort of grounding.


texts: How to measure the total current consumption in a system

texts:
I recently designed a system based on toradex iris carrier board. Application was simply using a UART channel to interact with other systems. There are 10 digital IR sensors are used and interfaced with GPIOs. As they are digital, so when they get activated, it gives 3.3v and when low, it shows 0v. Based on this data and algorithm, a final data is send to UART and ethernet. So a UART port and ethernet is also used. This is about working of the application.

Now we need to use UPS which can give it a power backup upto 20-30mins. UPS comes in different ratings like: 1KVA or 3KVA. I am facing few problem in selecting the proper rating as I do not have much knowledge about it. I started searching and found out that, lets say 1KVA UPS can hold a load of 0.8Kw (given that power factor is 0.8). That means 800W. We have 220V mains power supply here, so it can give upto  3.6A current.

Is this current sufficient for the system. I searched alot and summed up all the current consumption in my system:

Toradex    3A ( Datasheets say it can take upto 6A but I will not be using all the components like display, sd cad, hdmi port. So assuming 2A)

Sensors    50mA * 10 = 0.5A

Led, Coupler, Diode  = 0.5A

If I roughly calculate the total current, then it comes out to be 4A-5A which I think is too high for this kind of application. So I want to know how exactly everyone calculate the total current and then how to select the UPS to provide it a backup


texts: PCB design software with ability to use PCB 'components'

texts:
IS there any PCB design software where I can design & route common part of design (like DCDC with support circuitry), and make it some kind of 'component' - so that I can always drop it to my new project, and it will appear already routed.

There might be needed several occurrences, and if I update component - it must update all it's instances on the board/schematics.

What can you suggest (at the moment I am using Eagle - I know it's possible to use some kind of macros to do this once, without ability to edit it later)? Both free and commercial software is considered.


texts: Analyzing 4-pin data port to determine protocol

texts:
I have a Solar controller for my pool, it controls the pump and actuator for routing water onto the roof to heat it up, when required. The controller knows the pool and roof temperatures, as well as the state of the pump and actuator. All of which I'd like to monitor.

The controller has a 4-pin port labelled "Data". I would like to interface to this port to monitor the controller and pool parameters, if possible. I contacted the manufacturer but they responded with a generic "this port isn't supported for end users" kind of thing, as I expected they would. I have searched around, of course, but nobody has documented this port.

I would like to determine if this 4-pin data port speaks a standard protocol that I could potentially connect to.

This "Data" port has 4 pins labelled: "BK", "W", "R", "BL". (See photo)

I assume these labels are abbreviations for Black, White, Red, Blue.

Based on that, I've made an assumption that "BK" is Ground.

With a multimeter I have probed pairs of pins to determine:

BK <-> W     +5V
BK <-> R     0V
BK <-> BL    +5V

I borrowed a Saleae Logic Analyzer from a friend and wired up its probes to analyze the port output. Again, assuming BK was Ground. The analysis revealed chatter on the W pin, although all the other pins revealed no activity. See the two screen shots below, one showing the full analysis (i.e. zoomed out) and the other showing the zoomed in detail of one of the spikes.

Saleae Logic has a bunch of protocol analyzers built in, and I tried the ones that makes sense with these set of pins, but haven't been able to make any useful sense out of any of them.

I was wondering if this port could simply be a USB port. The latest Logic contains a USB 1.1 analyzer, but it did not recognise anything useful from the probe.

Any suggestions on what kind of port it could be or recommended steps to continue the reverse engineering process would be great.


texts:
I understand how a current higher than what the LED is rated for can burn out an LED, but how does something equivalent happen with voltage?

If the correct current is on an LED but the voltage is too high, what causes it to burn out?

I just don't see what effect voltage has on the LED.


texts:
I find lately that this connector type would come in very useful for the projects I make. but I have no idea what the connector is called, could someone please point me in the direction of its name, maybe I can buy a strip to cut to size?

Thanks


texts: STM32 - several PWM signals with different multiplied frequencies

texts: Is it possible using STM32 F to generate several PWM signals with one timer, but each channel has different frequency (multiplied of two) of PWM? All signals must be synchronized, so I need to use only one timer. Each channel should have different duty cycle.


texts: pic16f628a successfully programmed but not working

texts:
I want to blink led with pic16f628a using pickit2
I generated the hex file and successfully write it,
according to code, RB are input, but when I put led between RB0,1,2,3.. and ground it turn on. all the pin turn on the led, I'm using 5 volt output

code :

#include<htc.h>

// Config word
__CONFIG(FOSC_HS & WDTE_OFF & PWRTE_ON & CP_OFF);

// Define LED pin
#define LED  RA1

#define _XTAL_FREQ   8000000

void main()
{
    TRISA1 = 0;                // Make RA1 pin output
        TRISB = 1;
        LED    = 0;                // Make RA1 low

    while(1)
    {
        __delay_ms(500);       // Half sec delay
        LED = 0;               // LED off
        __delay_ms(500);       // Half sec delay
        LED = 1;               // LED on
    }
}

scheme :


texts:
I am performing SI analysis for the GTX transceiver interface. the FPGA that I am using is Xilinx Kintex-7 FPGA. I have received a reference SI analysis report done by customer which has eye width, height extra details.
Can someone please help me out in understanding how is the minimum eye height other values obtained are decided that their within the specification.
I will be following SATA 3.0 protocol. My signal rate is 6GB/s.
Attached is the values obtained from SI report.


texts: What are the different types of solder used for?

texts: How do I know when to use lead, flux-core, lead-free, or any other kind of solder out there? Do you have any tips on solder gauge for specific applications?


texts:
I have a quick question as to why my LM833N is behaving as such.

Any time I try to power the amplifer with 9V or over nothing happens, its just a flat line on its output like its turned off or something.

simulate this circuit – Schematic created using CircuitLab

This is whats happening when Input 9.58V


texts: Connection between metal enclosure and 0V in industrial system?

texts:
I have been testing an industrial system. I have developed a test device to properly test this industrial system. I am currently finalizing the test device and have put it in an enclosure to EMC proof it from external sources.

When probing around the industrial system with my multimeter I discovered that in the industrial system the 0V is connected to the EARTH(enclosure) via a 200k resistance. I don't know where the connection occurs, but I was a little surprised.

It does not seem to make sense cause this way, you loose the EMC proofing, right? Since the test device is also connected to the 0V it also looses its EMC proofing... The industrial systems' main components are a AC Drive, PLC and Power Supply. But I would suggest these components are designed to act as floating components if not EARTHed by the user.

Since I'm not the designer of the Industrial system and due to company rules, I can't go in depth on its workings and function. Though I am surprised that the EARTH connects to 0V.

Maybe an experienced engineer can enlighten me with some information on EARTHING, 0V reference points and EMC in industrial systems?


texts:
I want to build a 7 Rows x 15 Columns keyboard from scratch, thus I have started from the theoretical design of the matrix. The classic way should be to assign directly the Rows and Columns to (7+15) I/O of a microcontroller and also connect 7X15 diodes to every each switch in order to prevent the "ghost" effect.

Yet, I redesigned a matrix using multiplexers - demultiplexers as follows:

Just to keep it simple, let's say that I have a 8x4 matrix, the columns connected to a demultiplexer and the rows connected to a multiplexer. That should work with the pseudocode:

for each output of the demux:
    for each input of the mux:
        check if a individual button has been pressed, else \\
        send HIGH due to pull up resistors

Since in every each loop only one switch can be inspected and there is not any physical connection to other switches, I think I could prevent the "ghost effect" without the need for any diode component.

Also, for a 15x7 matrix, instead of using (15+7) pins, I could use a 16:4 demux and a 8:3 mux, thus only 4+3 = 7 pins.

Please, tell me your opinion, or point any flaws of the design.


texts: What kind of transistor do I use for switching high voltage with a microcontroller?

texts:
I am working on a project with Nixie tubes which require a high voltage supply. I have some "indicator dot" tubes that require 90V DC, and I want to turn them on/off using a microcontroller control line.

I am thinking a transistor is the right tool for this, but I am not familiar enough with the different types to know what will work (BJT vs MOSFET, NPN vs PNP, high-side vs low-side switching).

simulate this circuit – Schematic created using CircuitLab

Please forgive this schematic. It is probably wrong; it is merely indicative of what I want to accomplish.. that is the question I am asking. What is the right way to do this, and what type of transistor should I use? Specific part numbers would also be appreciated.

To be clear, I don't need to amplify any voltages, I already have the voltage supply I need for the 90V line.


texts: Calculating the MOSFET gate resistor for an H-bridge driver

texts:
I'm designing a DC motor driver using Allegro's A3941K driver. The block schematic shows a gate resistor for the MOSFETs. The A3941 gate structures are as below,

The GHx voltage would be a maximum of 18V? Knowing the current that should flow into the gate would help me calculate the value of the resistance. I found this app note from Microchip on Driving Power MOSFETs in High-Current, Switch Mode Regulators. Using the equations from there and the data from the MOSFET datasheet, I calculate the Ig = Qg/t(rise time) = 10nC/58nS = ~172mA. Hence, the gate resistor Rg = 18/172mA = ~105ohms. Is this the correct line of thinking?
The switching frequency is 20KHz and the MOSFET used is BSC100N06LS3.


texts:
I live in an area that gets hit by storms once or twice a year and the power would go out for a day or two each time. It doesn't justify buying a generator, but it's a nuisance not to be able to charge phones and tablets. So I thought it'd be fun to build a 5V battery bank for this purpose. My requirements are:

I want to leave it plugged to the wall outlet all the time so it'll be charged when the power goes out.
It doesn't have to be lightweight.
It doesn't "leak" when not being used.

My questions are:

What's the ideal battery for this application? I heard Li-ion batteries can be finicky and since I don't need the mobility, would lead-acid batteries be a good choice?
If I use 3 cells of lead-acid batteries, it'd be ~6.4v. Is it OK to feed that to the cell phone, or is it better to run it through a regulator?
If I run it through the regulator, would it draw some current even if it doesn't have a load. I.e. is it going to have a leak?

Thanks!


texts: Solenoids pulling more than rated current (6VDC, 300mA)

texts:
I'm building a musical instrument using thirty JF-0530B solenoids, rated 6VDC and 300mA. But I've discovered when I power them directly with 6VDC they draw ~1.5A, because they only have a resistance of ~4 Ω (they all do, except for three that appear to be shorted/bad).

(The values above are as measured with my multimeter, like so – just to make sure I didn't mess something up here.)

My concern is that I'm going to damage the MIDI decoder board, which switches the solenoids via ULN2803 chips (Darlington arrays with embedded flyback diodes) that are only rated up to 500mA per output.

The odd thing is, before discovering all this I tested the solenoids with the decoder – and not only does it work at 6VDC, it works at 12VDC when the solenoid pulls nearly 3A! (I just used the wrong supply.) Maybe I just got lucky here because the solenoids are only powered for a fraction of a second.

I'm not familiar with solenoids, but isn't 4 Ω a low resistance for a 300mA-rated solenoid? Did I get a bad batch or do I misunderstand how to use them? I'm trying to ask vendors for the resistance of the 12VDC version of this solenoid (which I'm thinking of using instead) but no success yet. I've seen this thread (among others) but that seems to have boiled down to misuse of equipment. Another forum suggested I was seeing inrush current, but this seems to apply only to AC solenoids.

Thanks in advance for any thoughts!

Midi decoder board


texts:
I have a battery for a robot hoover (aka vacuum cleaner) (Ni-MH) that seems to be on the blink (very low run time). I'm trying to understand how it works in case I can do anything to fix it or if I should get a new one.

The battery is this one:
http://www.alibaba.com/product-detail/Ni-MH-14-4v-sc-rechargeable_1528323749.html

You can see two pairs of contacts on the top -- one set is clearly for the power, and I can measure the expected 14-15V with a DMM. The other is possibly a temperature sensor so that the thing knows when it's charged up. But it's a bit strange -- at room temperature, I measured a resistance of 7.8kOhm across this pair, and as a test, I put it in the fridge for an hour and it came out at 11.8kOhm. Does anyone know what kind of sensor this might be?

The other question I have is how the robot knows when the battery has run down and it needs to go back to its dock for a charge?


texts: Need help with terminology so that I can source a din rail version of this part

texts:
Im looking for a 12 VDC power supply that has the ability to switch to a battery when ac power is lost in addition to having some type of AC status function such as an open collector. This part does everything I need but I would prefer one that can mount on a DIN rail. Can anyone suggest one or help me with some better search keywords.

https://www.meanwell.com/webapp/product/search.aspx?prod=PSC-60&mws=E8F3D2F026E800B6

Similar to https://www.meanwell-web.com/en-gb/ac-dc-industrial-din-rail-power-supply-output-dr--ups40 but they only make this model in 24v

The only things im finding that are close with "DIN rail UPS", and "DIN rail power supply with battery backup" are devices meant for industrial automation that typically cost ALOT more.


texts: Eclipse and OpenOCD works only, if I program the MCU on Discovery board

texts:
I'd like to program and debug an STM32F030 MCU with Eclipse, OpenOCD and ST-link. I have an STM32F4 Discovery board that includes an ST-link debugger.

Programming the STM32F4 MCU on the discovery board works very well. I use Eclipse, OpenOCD and the ST-link (ST-link is actually on the board). With this IDE configuration I believe I should be able to program other STM microcontrollers that are on a different PCBs (Of course after I connected them each other and turned off the jumpers to select the target)

My problem is: I'd like to program an STM32F030 MCU. When I connect this MCU to the ST-link, "STM32 ST-link Utility" says that the connection is fine, so I guess, I should be able to program it. But when I try to program it, Eclipse always shows the same error message: "Quit (Expected signal SIGINT when the program is resumed) - Exception condition detected on fd 0 - error detected on stdin"

Probably the problem is with the settings of my IDE, but I have no idea what it could be. How is it possible, that I can program the MCU of the discovery board but I can't do the same thing with another MCU?

Do you have any idea?


texts: How do I estimate the transmission distance of a 50 watt 2m radio?

texts:
Can anyone point me to a reference for calculating (estimating) the transmission distance of a 50-watt, 2-meter radio? The transmitting antenna will probably be 5-7 meters above ground. Probably the same height for the receiving antenna.

Thanks!


texts: Why do we need voltage stabilizion in bridge measuring system with ratiometric connection?

texts:
i found in many weight scale reference designs that they use either low noise linear regulator or voltage reference for voltage stabilization.

Why do we use them if ratiometric design cancel the change of adc output caused by excitation voltage change?

Can i connect ratiometric weight-scale system to 3.7 V Lipo battery without any stabilizer and be sure that results wouldn't be affected by battery voltage drop due to discharging?

Many thanks,
Matija


texts: Can an ATX PSU power a USB port directly?

texts:
I'm going to build a benchtop PSU from an ATX PSU, and I would like to add a USB charging port on it. It should be able to power an Arduino or charge my (non-Apple) phone. (I know Apple devices require additional circuits, but I don't own any so I don't bother with that.)

Since USB uses +5V I could directly connect the +5V of the female USB connector to +5V on the ATX, and USB GND to ATX +0V, leaving the data lines unconnected.

Is this a good idea? Does this allow devices to draw as much current as they need (like a USB phone charger), or are they limited to 500 mA (official USB max current) or even only 100 mA (USB initial max current)?


texts: Occupancy detector using the MQ-135 gas sensor

texts:
Is it doable to make an occupancy detector using the MQ-135 gas sensor (datasheet) for a small room by checking if the current CO2 value is (significantly) larger than the base value?

Apart from connecting 5V and GND, you would connect the analog pin to Arduino as input and to GND with a 20kΩ resistor.

I understand that it needs 48 hours to burn in before a first use, and 10 minutes after re-use, during which time the device would be and remain in that room.

Wouldn't it be possible to use a digitalRead() on Arduino to establish the average base value after those 10 minutes, during for instance 20 minutes, and then alerting if the current value is, say, 10% higher? The percentage could be empirically established.

Being right most of the time would be good enough.

I see no such projects online, so I assume I'm clearly missing something. Especially since occupancy detecting is a tricky subject.

Is it not precise enough? If the value would fluctuate between 100 and 150 if the room is empty, it might not be possible to adequately compare with somebody actually being in the room.

Any other fundamental issues?


texts: 3.3V input to 5V output for motor control

texts:
I wanted to connect my DC motor to raspberry PI and control it with PWM pin. Problem is that gpio pins are 3.3V in PI and I have pololu 10:1 DC motor which I would like to run on 5V(to make it faster).
How can I convert those 3.3V to 5V for motor? Can I just simply connect PWM and GND pins to motor to steer it?


texts:
From what I've read the speed is controlled based on the supplied power voltage, or using delay on arduino code, how about the torque, is there a way to make the servo motor change the torque ? like torque(0) it goes lose and any eternal force can turn the motor, torque(max value) to apply max torque to achieve the needed angle?
Edit 1:
I'm planning to use one of those KRS-2552RHV ICS
Edit 2 : I've done a little research after reading the comments and it seems like I will need to create a different controller or motor driver circuit to be able to change the speed using pulse width modulation, that way the speed will be controlled with pulses and the torque would be controlled with the intensity of the current


texts: Wait make the STM32L073RZ freeze in stopmode

texts:
With my STM32 I'm trying to configure a deepSleep mode and use RTC to generate interruption (actually each 30 seconds).

When my STM start, this one configure the RTC and directly go in Stop mode. After 30 seconds the board is waking up and use Serial to configure LoRa Radio module RN2483 with the Serial communication and also use I2C to read and write some datas. But for the configuration of the RN2483, we need to wait response (it take around 3 seconds).

After that the STM go in deepSleep mode again. This is a loop. If this periode between two deepsleep take too much time (due to wait or printf for example) the next deepSleep will be bad configured and the STM never wake up again and the power consumption is high.

Does anyone have any idea ?

Maybe I need to check some deepsleep registers or something like that ?

EDIT:
This is a picture of my state machine

For the DeepSleep configuration this is my script below

void STM32_DeepSleep(void){
    //Clear bits
    EXTI->PR &= 0xFF840000;
    //Enter in stopmode
    HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON | PWR_CR_CWUF | PWR_CR_ULP | PWR_CR_FWU , PWR_STOPENTRY_WFI);
}

After some researches the problem is coming from __WFI() function. Due to a long time before, the __WFI() freeze. Maybe a watchdog inside the STM32 make the script freeze ?


texts: How many large format LiFePO4 cells can be connected in series?

texts:
Is there any real reason why I couldn't connect 320 LiFePO4 cells in series (for a nominal 960Vdc)?

Or is there some limitations within the pouches inside the cells?

Like to see your thoughts!


texts: Is slow charging a Lithium Polymer battery any better for it?

texts:
I have a lot of LiPo packs, from 1000mAh to 20000mAh.

We are usually told that a "Normal" charge rate is 1C (IE 1A per 1000mAh capacity) and that fast charging (3, 4, 5c +) is bad for them.

But is slow / trickle charging (0.1c, 0.5c etc) BETTER for the pack than charging at 1C? is it worse? or a waste of time, IE the same.


texts: How do i measure current in 10uA till 10A range in steps of 10uA?

texts:
I'm planning to build a circuit that measures the current from uA till 10A DC Line. Initially I thought of using HECT, but it is having better accuracy in higher current range. so I'm figuring  out if i can use the sense resistor to measure lower current(but again burden resistor is trade off here) and HECT for higher current. I need automatic switching here. because the output is fed to DAQ. Suggest me the methodology. I'm also trying in the Internet.
Thanks.


texts:
I am very confused with the following scenario. I am using a PIC microcontroller, and I am transmitting a continuous sequence of messages. According to CAN protocol I need to give some time before I transmit the next message.

To solve this problem I started checking for the Tx buffer is full or free before transmitting. But my only problem is I can't continuously be in the while loop checking for the flag as there can be a possibility the bus is not available, and it can never come out of the while loop. How do I avoid this tricky situation? The microcontroller I am using is in the dsPIC family.


texts:
How much distance I have to create on a PCB between a coated conductor and an uncoated component pin with a voltage difference of 200V?
From different websites and calculators I can only get the information how much distance is needed between two coated conductors or two uncoated pins, but not a mixture of both.


texts: howto align mount holes in 2 pcb the right way?

texts:
I'm tring to make some sort of shield board (it's not an arduino):

first board was made in orcad, I have source files gerbers and so on...
I'm making a 2nd board in eagle.

When trying to align the 2 boards mount holes and connectors I am having some trouble.

I tried exporting pdfs of each board and importing into gimp and inkscape, but the boards get rezised and im afraid it doesnt work.

Sometimes I get huge files and computer crashes...

I would apreciate ideas on how I could align the boards. What would be the right way to do this?


texts: What is the value of x-ray inspection of an assembled PCB?

texts: I've heard discussion of x-ray inspection of assembled PCBs. I understand this to be useful for things like BGAs, where there's no other way to inspect all the solder joints under the package. Is it useful for other situations? Can it provide helpful information about visible solder joints? Other things? Or is xray inspection typically limited to boards or components with particular parameters? And if so limited, what are those parameters?


texts:
First post on this site, sorry if it's too basic.

I'm learning to interface with a particular chip which has a GPIO pin. I'm using the GPIO for input with a pullup resistor and a switch between the pin and ground, really simple.

Due to an implementation detail, that pin needs to be high or floating (i.e. not grounded) at power on time. The firmware on the chip doesn't start if the pin is grounded.

I was thinking something along the lines of a delay with a capacitor and transistor in series with the switch but that's where I'm a bit rusty.

Appreciate any guidance. Thanks!


texts:
I'm putting together this circuit, but am not clear how to wire up the part with the diode. This is what I have so far, but it doesn't seem right (how does the solenoid get power?).

Components are:

5V Solenoid
1N4001 Diode (between the transistor collector and solenoid power?)
NPN Bipolar Transistor
2.2KOhm resistor (between output from the Pi and the transistor base)
Raspberry Pi Zero
LM2596 Converter (so I can power the RPi with the same source as the solenoid)


texts: If an electron has 0 electric potential after passing through a resistor, how does it flow to the other terminal

texts: If an electrical circuit only contains 1 resistor, and electron's potential difference (voltage) before and after passing through a resistor is equal to the e.m.f, how does the electron have potential energy after passing through the resistor to flow to the positive terminal of the battery?


texts: How to tell CCS debugger where to start?

texts:
I am just starting with MSP430 and Code Composer Studio (CCS).

I want to make a pure-assembly project. At the moment, I have a "hello world" program that does nothing but light an LED on the MSP430F5529 Launchpad.

However, when I run this program in the debugger, execution begins at address 0x0000 instead of at my designated entry point, called RESET (0x10000). I can see that PC is intially set to 0x0000. If I manually set it in the watch window to RESET, the program runs as expected.

I have declared RESET to be global, and I have set the linker option to make RESET the entry point.

I'm guessing I have a problem with either debugger settings or the (boot)loader, but I could be totally on the wrong track.

            .cdecls C,LIST,"msp430.h"       ; Include device header file
    ;-------------------------------------------------------------------------------
            .text                           ; Assemble into program memory
            .retain                         ; Override ELF conditional linking
                                            ; and retain current section
            .retainrefs                     ; Additionally retain any sections
                                            ; that have references to current
                                            ; section
;-------------------------------------------------------------------------------
            .global RESET
RESET       mov.w   #__STACK_END,SP         ; Initialize stackpointer
StopWDT     mov.w   #WDTPW|WDTHOLD,&WDTCTL  ; Stop watchdog timer

;-------------------------------------------------------------------------------
                                            ; Main loop here
            bis.b #01h, &P1DIR
            bis.b #01h, &P1OUT
;-------------------------------------------------------------------------------
;           Stack Pointer definition
;-------------------------------------------------------------------------------
            .global __STACK_END
            .sect   .stack

;-------------------------------------------------------------------------------
;           Interrupt Vectors
;-------------------------------------------------------------------------------
            .sect   ".reset"                ; MSP430 RESET Vector
            .short  RESET


texts: Determining DC Motor Characteristics From Datasheet

texts:
I am working on a project to design a brushless DC motor that is designed to act as a replacement for an existing brushed PM DC motor from a handheld drill (supplied by an 18v 3A/hr battery).

I am trying to determine the characteristics of the existing motor. The datasheet lists the following:

Voltage:       18 v
Max Power:     300 W
Stall Torque:  63 Nm
No-load Speed: 300 / 600 / 1700   RPM, depending on gear

I believe the gear ratio for gear 1 (300 rpm) to be 76:1.  Making the rotor speed 23,000 RPM.

I have carried out testing to determine the motor constant Ke and believe it to be 0.0036.  My issue is with this Ke, to deliver the stall torque the motor would have to be supplied with 200+ amps
(from T=I*Ke)

By assuming the maximum power point occurs at half no-load speed & half stall torque, this gives:
$$\ \frac{\text{Stall Torque}}{2}  \cdot\ \frac{\text{No-load Speed (rads/sec)}}{\text{2}} =\text{Max Power}$$
$$\ \frac{63}{2} \cdot\ \frac{300 \cdot\ 2\pi}{\;2  \;\;\cdot\ 60} = 494 \;W $$

Which is more than listed on the datasheet.

Basically, I can't understand how the motor produces the torque / output power listed on the datasheet.  Is it possible the datasheet lists theoretical maximums that the actual drill will never achieve, or am I not considering certain factors?

Also, how do you determine where on the torque / speed curve a motor should be designed to operate, especially when that motor will have a variable load?


texts:
I am getting a small pick and place machine with a reflow oven. I am wondering how can I reflow two-sided PCBs.
I have read many methods on the Internet like use two soldering pastes with different reflow temperature, using roaster oven, etc. I am not sure what the right method is.
How can I professionally reflow two-sided PCBs?


texts: led resistor calculation, and resistor wattage?

texts:
I know this has been asked time and time again but bear with me as I am struggling to understand,
so say I have this simple circuit here

with 120v (dc for simplicity) as the input voltage
and I have an led that runs on 3.4v and max 20ma
ohms law states I=V/R so R=V/I, so R=120v/0.02a = 6000 ohms or 6k
is this correct? how do I know the voltage drop across the resistor is correct,
and what about power dissipated by the resistor?
also, Is there an easy way to calculate everything at once?


texts: Why does iSim give a different result than hardware

texts:
I am working on a MIPS CPU for an FPGA - this is mostly a personal project to understand FPGA's.

I have a 5 stage pipeline CPU implementation working correctly when run on iSim, however when I run it directly on the hardware (Spartan 6) I get a different result.

The test program I have is simple:

load 0x128 into reg[1]
nop*
load 0x160 into reg[2]
nop*
add reg[1] to reg[2]
assert "finished" flag

when I run this in iSim, I get the correct result in reg[2] (0x288) however, when I run the program on the FPGA I get the result 0x3b0 - it appears that the final instruction is running multiple tiems

The nop instructions are present to force a cache miss during execution, and this is what causes the problem - without these the result is correct.

What I think is happening is that I assert a "stall" flag at the positive edge of the clock cycle - and something else that runs at the positive edge relies on the presence/absence of this flag. iSim by chance runs correctly (due to the arbitrary order in which it executes the simulation of always blocks) however the FPGA fails as the stall change is not available until the negative edge.

I have already scoured my verilog implementation to find where this is - and am still looking. My question is: how can I force iSim to expose this error?


texts: Equivalent model of my (real) transformer

texts:
I have created a transformer using a small cylinder (a tube) made of ferrite. The primary coil has \$N_{1}=5\$ turns of coil wire, while the secondary \$N_{2}=50\$ turns. According to a recent question of mine, a real transformer has an equivalent circuit like the following:

Where:

\$L_{P}\$ is the primary leakage inductance
\$R_{P}\$ is the primary copper loss
\$R_{C}\$ is the core losses due to eddy currents and hysteresis
\$L_{M}\$ is the magnetization inductance
\$L_{S}\$ is the secondary leakage inductance
\$R_{S}\$ is the secondary copper loss

(taken from here)

My question is how can I determine each quantity in the above circuit, using \$N_{1}, N_{2}\$? If any additional information is needed please let me know (plus how can I calculate them, if it is not obvious). I don't seek to create an 100% precise model, just a circuit that works correctly (for example with an AC voltage source connected to the primary coil and a capacitor connected to the secondary coil the circuit must work like a band-pass filter).


texts: What is the voltage drop across the 10 ohm resistor?

texts:
What is the voltage drop (V1) across the 10 ohm resistor?
Can I use voltage division to get V1?
Like V1 = (20 V x 10 Ω) / (10 Ω + 4 Ω)
But when I use nodal analysis and mesh analysis I get a different answer (12.30 V).
Which one should I use?
Or have I understood the voltage division method incorrectly?


texts:
I have been trying to use LTspice XVII with a model from Dr Lynn Fuller https://people.rit.edu/lffeee/CD4007_SPICE_MODEL.pdf.

However I get the error messages
Unknown model type "level" -- ignored
Fatal Error: Unknown SPICE device type "Ï" in "ï»¿"

Here's the model (I've tried changing LEVEL=7 to 8)

.MODEL CD4007_Nchan (LEVEL=7
+VERSION=3.1 CAPMOD=2 MOBMOD=1
+TOX=4E-8 XJ=2.9E-7 NCH=4E15 NSUB=5.33E15 XT=8.66E-8
+VTH0=1.4 U0= 1300 WINT=2.0E-7 LINT=1E-7
+NGATE=5E20 RSH=300 JS=3.23E-8 JSW=3.23E-8 CJ=6.8E-8 MJ=0.5 PB=0.95
+CJSW=1.26E-10 MJSW=0.5 PBSW=0.95 PCLM=5
+CGSO=3.4E-10 CGDO=3.4E-10 CGBO=5.75E-10)


texts: How to use arduino and P-channel & N-channel MOSFET to control voltage to PT2264 address pins

texts:
Im looking to control a PT2264 RF transmitter module from an arduino so that I can transmit to different receivers. To do this I need to supply either +12v or 0v to the various address pins of the PT2264 IC depending on which receiver I am addressing. The code will be done in a way so that both mosfets are not saturated at the same time (ie avoid a dead short). I believe the current draw from the PT2262 to be minimal. My proposed solution is this:

PT2262 datasheet: (http://pdf1.alldatasheet.com/datasheet-pdf/view/35122/PTC/PT2262.html)

Would this work in its current form?

Could both mosfets be switched by a single arduino pin?

Many thanks for any feedback.

Joe


texts:
I'm stuck with this simple problem (please be aware that this is my first non trivial circuit!):

simulate this circuit – Schematic created using CircuitLab

Due to Kirchoff law (I chose clockwise as positive) I've written:
$$-i_1+i_0+i_2=0$$
$$i_4-i_5-i_0=0 $$

$$i_1-i_3-i_4=0$$
$$i_3-i_2+i_5=0$$
So I go on with $$i_1-i_2=i_4-i_5$$
$$i_1=i_3+i_4$$
Then, for tensions:
$$V_1+V_3+V_2=0$$
$$V_4+V_5+V_3=0$$
$$V_0+V_1+V_4=0$$

I obtain the system of equations:
$$i_3(R_1+R_2+R_3)+R_1 i_4+ R_2 i_5=0$$
$$i_3 R_3+ i_4R_4 + i_5 R_5=0$$
$$V_0+R_1 (i_3+i_4)+ R_4 i_4 =0$$

I've solved the problem, but trying some simulators I realize that the result is correct if all the resistors are of the same value, and completely wrong otherwise. What's the problem?
Thanks a lot for your precious help!


texts: Understanding 74LVC245 datasheet and current source/sink

texts:
I'm using a SN74LVC245A (datasheet) to shift 5V TTL down to 3.3V so I can read the signals with a Raspberry Pi.

However I am getting really weird results (a 60Hz input signal is picked up by the Pi at anything between 110Hz and 320Hz) and I'm really confused about how to read the datasheet to figure out whether I need pullup or pulldown resistors.

The datasheet says on page 4 the "high-level output current" is -24mA, and the "low-level output current" is 24mA.  So to me this means that when the device is outputting a high signal, it is able to sink 24mA of current (since outputting a negative amount of current suggests the current is going into the device instead.)  But then if you're outputting a positive voltage, isn't that sourcing current?  Why is the figure listed as a negative value?

Is anyone able to explain what these figures actually mean?  When I disconnect the 74LVC245 output from my GPIO pin, I still get weird signals from the floating input pin so I am assuming this means the 74LVC245 output is also floating in one state, but I don't know in which state it is (i.e. is it left floating on a high output signal or a low one?)  It doesn't really make sense to be floating on a high output signal since it's a level converter and the whole point is to maintain the correct 'high' voltage, so do I need pulldown resistors to handle the low output?  If so, why does the datasheet seem to suggest the chip can both source and sink current?  (In my mind, source current means the device can output a current with a positive voltage, while sinking current means the device takes in anything and connects it to GND, so perhaps that is where I am going wrong.)

Anyway I'm quite confused so any clarification would be much appreciated!


texts: Use RMS or peak value of current for transformer selection

texts:
I'm going to make 12V DC power source for my project, using a transformer (230V AC to 15V AC) and full wave bridge rectifier, followed by LM7812.
The load will be 200mA DC.

This is the simulation circuit:

It is a standard bridge rectifier circuit, nothing special.

This is the Vout and current through Rload:

Clean 12V and 200mA as expected.

It is known that capacitors in bridge rectifiers are charged by current spikes. This is the current through Rsense2:

Peaks are about 450mA high.

That is all perfectly OK, I understand it pretty well.
But there is one thing that is not clear to me. Do I have to select transformer that is capable of providing 200mA or 450mA?
Transformers specifications usually say:
Power rating: 3VA
Secondary voltage: 15V
Secondary current: 200mA
example: TR Z03.00/15

I know that I should not pick transformer on the edge of current rating and have some margin. But my question is whether to use RMS value (200mA) or peaks value (450mA) for the selection.


texts: Eye diagram measurement of a CLK using an Oscilliscope

texts:
I'm still a junior engineer and wondering how to perform eye diagram measurement of a CLK using an Oscilliscope?
My second question: Is the eye diagrams just using to measure CLKs, or one may also measure Data using eye diagram?
My third question: what are the benifits in the verification when using eye diagrams instead of normal timing diagrams?


texts: Calculating max power from an RMS Voltage Source

texts:
I have a question that asks me to calculate the maximum power output from a power supply that can be delivered to a load.

I know what the answer is (0.5W) but I am struggling to get too it. I tried converting the Voltage source \$V_{RMS}\$ to \$V_{Max}\$ by multiplying by \$\sqrt{2}\$ and then using this value to calculate \$I_{Max}\$ then by applying \$P_{Max}=I_{max}V_{Max}\$ I get a value of 4W which is wrong. I think I need to factor in the frequency \$F\$of the voltage source to calculate the power however I am unsure of the equation I need, without knowing time \$t\$. Is there a specific method or equation I should know about?

The load in the circuit diagram is used in the second part of the question, and I don't think it is needed in this first part.


texts: What kind of switch takes a 12v in sends it to one of two output wires?

texts:
I'm looking for a switch that I can use in my car.

A sensor sends a 12v signal through a wire, into a switch, and out via one of two wires.

For example, if the switch is set to position 1, the 12v will exit through wire 1. Switch position 2, exit via wire 2.

Here's a rough diagram, and my apologies for any incorrect terminology (first time doing anything electrical).


texts:
I would like to have a circuit that can be controlled by two variable resistors, and it should use the value of the "most-recently-changed" resistor. How can I find out when one of the variable resistors is changing in value? I would like to figure that out and then flip a latching relay such that it uses that resistor for the input. Is this feasible using a circuit without a micro-controller monitoring the two resistors? what would such a circuit look like?

scenario: imagine a lightbulb that is controlled via a three-way switch. Now imagine the switches replaced with dimmers - the most recently adjusted dimmer should be the one used to control the lightbulb, the other one exists simply to allow adjustment from a different physical location.


texts:
I have recently bought a dcp917S and hoped I finally found a wireless chime that I can tie into my apartment buildings bell system. Since I live for rent there I can't do any changes that are not reversible, nor anything that is destructive to the whole thing, nor things that afflicts other residents.

Details: There are 5 wires coming in. Wire one is ground. Wire 2 is AC power 25V. Wire 3 is going out to the door buzzer. Wire 4 is the bell and provides 20V AC when the button at the building is pressed and something else (pulse to short for my measurement equipment) when the button at my door is pressed. Wire 5 is the intercom wire.

Since mains is 230V+-23V @ 50Hz I assume the AC frequency also to be 50Hz.

Also nothing is default or normed since judging from the circuit board in my apartment it (the intercom system) was constructed in the 70s (hand drawn and cut circuit board with solder reinforced copper tracks)

The chime has 6 lines in 1,2 is the buzzer button 1 circuit (with 3V). 3,4 button 2. 5, 6 is power in to up to 12AC.

Line 5 can alternatively also be used as reference to line 1 and 3 to detect button presses, though none can be higher than 12V ac and have to be high enough to the transformer voltage to be detected ... so that's out of question, I think.

(Official wiring)

My two problems are:

The new chime only accepts up 12V ac so I need to bring down the 25V provided to 12V ... since I only need a few mA I thought I can put two 1M ohm resistors  between the 25V AC line (line 2) and ground (line 1) and leach of one of it in parallel to run the wireless bell converter.
When one of the buttons is pressed I get between some volts and 20V (AC) on line 4 I need that to close a circuit on the chime. I thought of a capacitive dropper circuit (since it is low power and won't be unplugged I probably save the discharge resistor) with 10 µF or something to switch a transistor which closes the chime circuit.

Do I have any mistakes in my thoughts?
Any easier ways? (tend to do things "right through the knee into the eye" way)

Oh! And I need to fit it all into the (relative small) box of the buzzer so anything than some soldered components is out of question. (e.g. Circuit boards micro controllers, larger circuits, transformers, etc)

Thought I do it like this:


texts:
I'm looking to buy resistors for a Raspberry Pi project, but am getting conflicting information on which resistance to use for my LEDs.

I will have three LEDs. The voltage from the RPi GPIO pins is 3.3 V. At 20 mA current, the forward voltages are 1.85-2.5V, 2.2-2.5V, and 3.0-3.4V for the red, green, and blue LEDs, respectively.

Using this website, I calculated all of the resistors to be around 15-82 ohms, which seems low to me, especially considering this Adafruit starter kit comes with 560 ohm resistors for the (near-equivalent) LEDs...

Can someone please advise me or help explain the discrepancy? Also, these LEDs will not be in parallel or series; each will be attached to a different out pin on the RPi.


texts: Old laptop power brick > DIY current regulator > 20w COB LED - will it do what I think it will?

texts:
I have a salvaged 20W battery-powered work light: the housing and LED inside. Before the electronics and the original 7.4v dead battery got tossed, I hooked up a somewhat discharged 7.4v battery to it and measured 18.5v / 1.2A to the LED itself. (Yeah, I should have kept the electronics but I didn't.)

I have an old 21v charger supply from an old laptop. It puts out 2.5A.

If I make a current regulator with a LM317 and resisters (or some other fast/easy way) and put that regulator between the power brick and the LED, will this actually do what I think it will?

Will it let the LED have only the amps I 'set' with resisters (in my case I will set it at 1A) and vary the voltage as needed from an  minimum and the full 21v of the power brick?

^

THE PREVIOUS SENTENCE IS WHAT I THINK WILL HAPPEN.

I know this is a silly question to many who already know about these things. I DON'T already know about this and am not clearly understanding the things I am reading about it online - so I am asking here if I am understanding what these basic types of current regulators will do.


texts:
In the following circuit:

taken from: https://circuitdigest.com/tutorial/quartz-crystal-oscillator

How is the crystal powered to begin oscillation?

I understand the amplifier is required to prevent the oscillations decaying and that it is required to be inverting to counteract the 180 degree phase shift of the oscillator, however, to first get the oscillator oscillating a voltage must be applied to the crystal. If the initial state of the schmitt trigger output is low then how can the crystal start-up?


texts:
I'm developping for a pic32 plateform. My application consists to realise I²C communication between µC 8051 and PIC32. The 8051 is the master and the PIC32 is the slave. I have established a I²C communication between the two microcontrolers. My need is to affect 2 slave adress to the pic 32. Also I have succeed to to affect 2 address to the pic32 using this code

I2C_SLAVE_ADDRESS=0x40;
I2CSetSlaveAddress(I2C4, I2C_SLAVE_ADDRESS>>1, 0x10, I2C_USE_7BIT_ADDRESS);

So the pic32 can accept data from 8051 throw 0x60 and 0x40 address. So now, i want to determine which parameter in I²C protocol allow me to determine when data arrives from 0x60 and when from 0x40 because I have two different types of data to receive in the pic32.


texts:
After playing with Arduino and different kind of sensors for my garden, now I'm starting a new project for my free time.

I want to work with RF communications because I need a long range device for my application, about 2 Km distance.

The idea is to make only an identification of which unit is, as a long range RFID but without RFID.

I mean some devices/units are placed somewhere, and after a time, someone could move them to another place, so I want to know where they are, only reading information send by them via RF. I don't mind their real position (GPS) because I going to be able to see them where they are from my top window. I only want to know which of them are.

I'm reading about 315/434 MHz, but it seems not be able to get this distance without a high power consumption.
What about a lower frequency (150 MHz)? It is above the license frequency band for AM/FM radios.

I live in a village - I have a lot of terrain to play with my experiments and a line of sight over 2 Km.

EDIT:

The @Hoppo idea is just what I'm trying to do. Also it lets me to get "energy harvesting" because the idea is transmitters go with a small battery.

Also the transmitters have to be small enough and without antennas for not disturbing and avoid dogs play with them.

In receiver side, it doesn't matter if I need a larger antenna or more power. It will go connected directly to a PC or power source.

Moreover as @Hoppo says, I only want to send a 'ping', a message with an identifier and maybe battery level, so data rates could be lower than 9600bps.


texts: Can you continuously flash a high power LED bulb or will it break?

texts:
I want a bright flashing display light.  Imagine the sort of thing on a one armed bandit machine, that flashes a couple of times a second. And it would run for days on end.  So either one of these which are rated at 5W:-

or:-

but the former is preferred as it contains all the necessary current control and is very easily replaceable without soldering.

Are these suitable?  I'm concerned that as they run hot they'll be no different than an incandescent, suffering continuous thermal shock and mechanically breaking.  Is there a more suitable high power LED for flashing or might I just as well use a traditional filament bulb?

There's Strobing very high power LEDs but that seems to deal more with frequency than resilience. There are some other questions too but again they seem to deal with implementation issues.


texts:
I'm currently having trouble getting a product through EMC.
Radiated emissions were comfortably under the limit, but conducted are failing badly.

Here are the results:

The noise appears to be largely common mode, with the exception of the first few big spikes which are differential.
The first of the big spikes is at the SMPS switching frequency.  I'm guessing the next 3 are harmonics of that.

Here's a schematic of the relevant/noisy parts of the circuit (the rest of the cicuit appears to be very quiet.  The noise is only a problem when these parts are enabled):

Anyone have any ideas on how I might tackle this?

Update:

The cable is a pair of discrete un-shielded wires, ~2 meters long, connected to the 'BATT' input and GND.
The BATT input is the power supply input to the module, nominally 12V DC (vehicle battery).

The components (along with a micro and a few other bits) are all on the same PCB.
PCB is 4-layer with an ground plane on an internal layer.  Unused areas on top and bottom layers are GND filled.
The module enclosure is plastic/ABS.

The SIM900 is a GPRS module.  It was powered for the test and talking to the micro via UART, but not connected to a mobile network.

Edit
Added PCB Layout after comments requested layout


texts: Placement of decoupling capacitors when driving a load through a long cable?

texts:
Common knowledge is that decoupling capacitors have to be close to the device that's being decoupled and connected with as short as possible connections, to provide a low inductance path.
Does this still hold true if the device that's being decoupled is driving a load through a long cable (= inductance)? One would think, if the current has to travel all the way through the long cable to the load and back again, a few extra centimeters between the decoupling cap and the device driving the load won't make much difference anymore?
Take, for example, Rod Elliott's Project 113 Headphone amplifier:

The op amp (U1A/B) had its own decoupling cap, C1. Then we have C4 and C5 to decouple the output transistors Q1L and Q2L. Since these transistors are typically driving the headphone's speaker through a long lead, is the placement of these decoupling caps on the PCB still critical?


texts: I cant seem to properly solder a stranded wire to that cathode terminal. Checked the answer https://electronics.stackexchange.com/a/90605/35737 - fluxing it did not help and solder does not adhere to it. Perhaps I am not applying flux correctly. I just put on some tacky flux I have got, then touch the fluxed cathode with the hot iron and immediately touch the iron + cathode terminal with solder. it barely sticks to it. Afterwards I bring that copper knot over it and apply the iron + more solder to the assembly. It just comes off in small balls. Any hints ?


texts:
What are these components? They have lots of wiring.

The left (bigger) one has 2 pins and description

00846
R647 Y

The right (smaller) one has also 2 pins and description

94565
R652

What kind of components are these?

Possibly similar function component with 1R0 at the top (updated after the answer of Bimpelrekkie):


texts: A few questions about basic capacitor concepts

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So say you a typical setup like in this diagram.

How does current flow while the capacitors charge? To elaborate, what is the mechanic that makes capacitors mimic the functionality of a wire instead of acting like the gap in the wire that they are?
When the capacitor is fully charged, the left plate is positive and the right plate is negative right? So does that mean when you disconnect the battery the capacitor discharges in the opposite direction that the batteries current was in?


texts: Turning off external sensors with Arduino: MOSFET vs I/O pin

texts:
For a project, I made an environmental sensor system, consisting of an Arduino Pro Mini 5V (with ATmega328P microcontroller), a data logger module and three sensors.

To save power between data logs I used several techniques I read about online, including turning off the power to the sensors using a MOSFET (I used the IRLB8721PbF).

Recently, I started reading a bit more about MOSFET's and turning off external devices with Arduino's, and I  realized that since my sensors only use about 4mA, I could have used the a I/O pin (set to output) on the Arduino instead.

As I was curious to see if there were any difference in current draw between the two methods, I tested the current draw when using the MOSFET vs when using the I/O pin to turn the sensors on. When using the MOSFET, the current draw increased with 4 mA when the sensors are turned on, corresponding to the sensor draw. However (!) when using the I/O pin the current draw first shortly increased with 6 mA, after which it settled at a 4 mA increase. These differences would suggest that it is more power efficient to use a MOSFET, even with low current draw apllications.

Now my question is (1) why do I see this short spike to 6 mA increase in current draw when using the I/O pin to power on the sensors? (2) And is it more preferable to use a MOSFET even with low current draw applications and why?

Another thing related to this: I recently read that a resistor in series with the gate is necessary when using a MOSFET, however I have been using the MOSFET for my application without a resistor and I have had no problems whatsoever for more than 6 months and counting. (3) Could someone explain why it has been working fine for my application? Does it have something to do with the fact I use the MOSFET to switch a low current draw load? Or does it have something to do with the type of MOSFET I am using (the IRLB8721PbF).

Lot's of questions, I'm kinda new to electronics...

Thanks in advance for taking the time to answer!