texts: Strange effect of adding resistor to the circuit

texts:
Here is the circuit:

And this is the simulation settings:

Because D1N4468 is 13V Zener diode, the temperature coefficient is positive and so the breakdown voltage should increase as temperature increases. Here is the result of simulation for the breakdown region:

The curves with the label triangle and square correspond to the maximum and minimum temperature respectively. So why this happens? Weirdly if we remove the resistor, the curves would be as we expected and the breakdown voltage increases with temperature.

It seems that at some point curves intersect and then continue. This didn't happen when there was a resistor.

There is another question related to this. Is it true that for all Zener diodes breakdown voltage increases as temperature increases? I know there are there are two possible mechanisms for pn junction breakdown. Zener effect dominates in low voltages with negative temperature coefficient while avalanche dominates in high voltages with positive temperature coefficient. So I think for low voltage Zener diode TC should be negative and TC be positive for high voltage Zener diode but I don't know whether it's true or not.


texts: Auto-protecting power sources with no voltage drop

texts:
In a circuit I have three possible power sources: (a) USB with 5V (500mA max), (b) 7.4V+ via a buck converter (3A max) and (c) a direct pin to the 5V rail in the cicuit, 3A max.

The problem is now when source (c) is connected I'd like to disconnect the buck converter (as I fear there might be some problems when it is powered with 5V in reverse direction and open-loop at its input) with a diode or MOSFET, but at 3A the voltage dropt at the diode is too high (the microcontroller needs 4.5V at least). Using different sources or a different microcontroller is not possible.

So how could I do this then? Is it that of a problem when there is about 2.5V at the buck converter in reverse mode, which happens when I use a MOSFET as diode (gate to ground, source to 5V rail and drain to the converter), or can I "disconnect" it complete without voltage drop when there is a power source connected to pin (b) and nothing to pin (c)? I am not really experienced with MOSFETS sadly :/
It should be possible to tune the converter to more than 5V at least, I think up to 5.5V max.

Also, do I need some kind of protection for the USB-connection? Like also disconnecting it with a MOSFET when there is another source connected? Or can the internal diode of those USB-hubs handle my situation?

Thanks for your help.

UPDATE

Oh I totally forgot to mention that I will be using a LT2596 buck converter with the following setup, but with 5V+ setup (or without the two resistors at the top when I choose the 5V fixed version):


texts: DPI interface for Raspberry pi including backlight driver

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I am designing a DPI interface for my Raspberry Pi ZeroW.
I believe the screen I have is exactly the same as the Pimoroni Hyperpixel 4.0 Square, just without the chunky interface PCB:
https://shop.pimoroni.com/products/hyperpixel-4-square?variant=30138251444307
I have the hyper pixel and it works great and my interface will be almost the same as it but in a different form factor and with some additional circuits incorporated (that are currently on I2C breakouts).
The main part I am struggling with is driving the LED Backlight. This is all the info I currently have on the backlight but am awaiting more from the manufacturer and will update if/when they get me something:

If I have a separate 12.8V power supply, would the following work to "boost" the PWM output from the Pi to the LED's?  If not, what is the best approach if I already have the right power lines?

What is the best/easiest way to boost the 5V from the pi to 12.8V so I don't need this external power supply?  I am using EasyEDA and have tried using boost converter chips but the circuits seem overly complex.  On the back of the hyperpixel, what looks like the LED driver circuit is quite efficient in terms of space and component size (red circle below):

Although the actual DPI part is relatively straightforward (following Raspberry Pi's DPI guide, and common sense just matching the pins up), the hyperpixel seems to have a bunch of resistors near the header (blue circle in image above) which roughly seem to align with the RGB pins. Are these just general purpose resistors for protection or something?  And is it recommended to use these for DPI?  Is there a way to calculate their values?

Thanks in advance!
Current circuit:


texts: Connection of EZ430-RF2500 development tool with PIC18f877

texts: I want to conect the ez430-rf2500 development tool with PIC16f877 throught uart, do I have to use a max232 chip in order to be able to communicate between those two MCUs or it can be done without it.


texts:
I am trying to design a simple 2 bit ALU which can perform addition, OR and XOR. Here's the picture of my design in multisim.

Problem with my design is i'm not understanding the purpose of select lines here. I refereed my note for that. I've something like below for arithmetic circuit design, concerning my note

I'm not sure whether i applied those strategy or not.


texts: Fixing power supply interference issue (?)

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I am working on a project that involves controlling WS2812B led strips using a Teensy 4.0 microcontroller. I got everything working during the testing phase, but now, after transitioning from breadboards to prototyping boards, I'm having some issue with power delivery to the microcontroller. I do not have any electrical engineering background, so this might be a total newbie question, forgive me please ;)

I created a quick sketch of how the power supply is setup right now, to give you a general idea of what we're working with.

Running it like this results in glitched visualizations of the data sent to the matrix: (later you'll see what it is supposed to look like)

Of course, I have already tried a bunch of different things to fix it, following the "try random things until it works"-solution finding pattern.

I noticed that, when powering the microcontroller using its USB port with my laptop, while disconnecting the 5v line between the power supply and the microcontroller, but leaving the ground line between the two connected; the interference/noise/glitching (whatever you call this) will go away. (as long as the USB cable is lying on the table near the 5v and ground wires from the power supply (this seems like magic to me, but maybe this information will help you))

So I continued reading and trying stuff out. I tried looping the positive wire (between the microcontroller and powersupply) through a ferrite (probably) core. This, in itself does not improve much. However, when I press my fingers on the metal USB-input-port-casing and some pins on the microcontroller, then the interference disappears again!.

I am stuck with this problem. Like I said, I do not have a background with electrical engineering, and this is my first bigger project I'm working on. If the problem is super obvious to you, please PLEASE let me know. Otherwise, I would also appreciate material to read up on or general pointers that can get me thinking in the right direction.

In any case, thanks a lot for reading this far!


texts: Strange behaviour observed while SMPS testing:

texts:
I was doing load regulation test for the converter NB679GD. The converter supports input voltage from 5.5 V to 28V and produces a regulated output of 5V. Load is varied from 0.01A to 8A.

The test was performed for three different input voltages- 6V, 7.5V and 8.5V. For 6V input, the output voltage increases initially ( ofcourse within regulation limits) but decreases at higher loads ( above 5.5A). Whereas for 7.5V and 8.5V inputs, output voltage increases monotonously as loading increases.

Why is the trend different for low input voltage? Is there a theory behind this or a random occurrence?


texts: Reduce load cell creep and drift programatically

texts:
I am trying to build a weigh scale and have read through the parameters that affect its reading in the long run. My question is can we reduce the Creep and drift of the load cell by compensation programmatically?
If so..How can I achieve it?
Thanks in advance


texts:
I am looking for loading a 15W BLDC motor with another BLDC machine, sort of like a master slave configuration. I'm not exactly sure how the slave BLDC machine windings should be connected. One idea was to short the windings together. Another is to connect resistors to the slave machine's terminals, operated as a generator, as loads. But in what configuration, star or delta? Can potentiometers be used? Any help will be greatly appreciated.

[OLD TEXT]
I have a 15W Hurst brushless dc motor, whose rated torque is 0.07Nm, rated speed 2054 rpm (~215 rad/sec). I am looking for a simple method of exerting 0.07N.m load at rated speed, without having to purchase a magnetic brake (they're expensive). One idea I had was to attach an adjustable coupling of a specific weight to the shaft (radius ~ 0.004m). The coupling, having a certain mass and inertia, will exert a specific amount of load on the shaft at a certain angular speed (supposedly). Since the coupling is a hollow cylinder, the inertia can be given by

Inertia = mass \times radius^2 [kg.m^2]

Then the torque can be calculated as

Torque = speed \times mass \times radius^2 [N.m]

Edit: This formula for calculating torque is wrong as pointed out in comments

However, I suspect that its not that simple. The formula can be altogether wrong. With this formulas, for a coupling inner radius of 0.004 m, speed of 2100 rpm, I get around 20 kg of mass for the coupling, which is huge!!!

Can you please provide your inputs on this matter (Edit: How to best load the motor without a magnetic brake)?


texts: altium designer - Could not find port 'PA0' on model 'tm4c1294_01' for pin 'PA0'

texts:
I am designing my very first PCB. I need a PCB with a cortex M4 core in a qtf package. I tried to follow this tutorial: https://www.youtube.com/watch?v=0n6k6GYu_V0&index=2&list=LLwe2piHB5wGY6Mycs0n3TZg

But get the following error when compiling at the end:

[Error] tm4c1294ncpdt.SchLib    Compiler    tm4c1294xl_01: Could not find port 'PA0' on model 'tm4c1294_01' for pin 'PA0'

Where did I do the error and/or how can I solve it?

Here you have a preview of the schematic and footprint I made.


texts: Why does this simple circuit oscillate? (Ekasi oscillator)

texts:
Why does an Ekasi oscillator oscillate?

From my research, I learned that when this is first plugged in, the capacitor is charging, so the LED doesn't shine.
When the capacitor reaches 12v, then the current switches to the top loop (which is possible because the voltage of the battery equals to the breakdown voltage of the flipped transistor). Note, because we are using its breakdown voltage, the base doesn't need to be connected.

As for its oscillation, I read that when the current goes through the top loop (and the LED is shining), the capacitor begins to discharge. So, because the voltage across the capacitor goes down, the current stops flowing to the top loop and goes back to the capacitor to recharge it (so the LED stops shining). This repeats, creating an oscillation/blinking LED light.

My question is: why would the capacitor discharge after it reaches 12V? What causes it to begin to discharge? Is it because when it's fully charged, no current is flowing towards it, "preventing" it from discharging? So it's free to begin discharging, but as soon as it does, then it begins to slowly recharge once again, creating this repetition? Sorry if it's a bad question folks, I just recently got into electricity! :)

Here's the schematic:

simulate this circuit – Schematic created using CircuitLab

Edit: Added resistor to circuit.


texts: Hydraulic pressure sensor for biological sample

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I need to filtrate blood sample (About 2 ml). I have a tube (roughly 0,5 inches of internal diameter) attached to the filter cassette inlet. The cassette is plugged to vacuum pump. I would like to measure the pressure before filter. The easiest thing is to use some small sensor plus Arduino. What sensors can be used for that? Most common I see water piping sensor but it`s too big for my sistem.

Everything upper 1 kPa causes cells death. Pressure range must be rougly 0-750 Pa


texts: Single pole triple throw analog passthrough

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I have a circuit that will simulate a device.
The device in question normally communicates by adding/removing resistance from a generated signal, the source of the signal will then measure the voltage difference and interpret that as a message.
In order to simulate it, I need to be able to route the incoming analog signal (1kHz square wave, V1 in below schematic) to different points in the circuit or make it NC.
I tried looking for multiplexers, but those I found weren't able to pass the analog signal through.
I couldn't find any single-pole triple-throw relays anywhere.
What type of component can I use in place of U1 below to achieve this behavior?

simulate this circuit – Schematic created using CircuitLab
V1 is a PWM signal with a +/- 12V amplitude. It's a control signal which won't be carrying a lot of current (maximum 5nA).
I would like to be able to control U1 with a 5V control signal (an arduino or something to that effect)
This is what the "mechanical" counterpart would be:


texts: What will be the simple SPI sequence to transmit packet with cc1101

texts:
I'm trying to mimic behavior of my weather sensor with esphome and cc1101.
rtl_433 detects it as:
https://github.com/merbanan/rtl_433/blob/master/src/devices/infactory.c
What should be put on cc1101 SPI to send similar packet?


texts: Altium Designer PCB editor text too small

texts:
I have this annoying issue with Altium where the text of the net names on pads, vias and tracks in the PCB editor (and in pcblibs) is way too small. I looked all over the defaults, tried resetting everything to the defaults, but no luck. I use version 20.0.10 (and hate it)
Does anyone know how I can make the text bigger?


texts: Two different LED types: diode test on two different multimeters shows just "1"

texts:
I have two multimeters - granted, they're both the super cheap DT830B types, but slightly different models and one is straight from the packaging.

I also have two bags of LEDs - bright red and bright blue (from Aliexpress). They did not have a great indication of forward voltage, saying something like "1.8V - 3.4V" for both, clearly unhelpful (3.3V "popped" the first one I tried: I'm guessing that range is for across their range of LED colours).

With either meter and either LED, in diode test mode, all I get is a solid "1" displayed. In all cases, the LED lights dimly, but no reading. On the newer one, the display briefly displays a number (~1000-~1700) before returning to, "1".

I'm pretty baffled. These are standard 5mm LEDs as best I can tell, other than being called "ultra bright".  Since the documentation around them is flaky, I really wanted to set the voltage/current correctly, rather than assuming 20mA, for instance.

What's going on here - crap/broken multimeters? Crap/broken LEDs? Misunderstanding? Thanks!


texts: Is a parallel capacitor needed in this application?

texts:
As it can be seen in below schematics, I have a transformer connected to mains 220V and converts to 9V, which then connects to a bridge rectifier and voltage regulator through AC1 and AC2 labels.

This is a TRIAC control project and I am using the signal labeled SYNC to let the microcontroller know about the zero-crossing points.

I am carrying AC1 and AC2 to the bridge rectifer from an another board through some breakaway connectors and a PCB, which in total is about 8 cm long trace per signal.

Do I need to put a small valued (about 100nF) capacitor across AC1 and AC2? If so,where should I place this capacitor on the PCB, closer to the bridge rectifer or the transformer? How to calculate the voltage rating of the capacitor? What is the value of the capacitor needed?

What would be the purpose of this capacitor, in detail?

Edit:

I have not given a lot of details about R1 and C1 in the second schematic. I will try to give more information with this edit.

I am using D1 to isolate the filtered (DC) voltage so that I can have a zero-crossing detection signal. I wanted to have a 100 Hz, where my line frequency is 50 Hz. That's why I've taken the signal after the bridge rectifier.

Here are some scope-screen-shots of various configurations.

Secondary of the transformer*:

R1 is populated, 7805 sourcing ~10mA
R1 is populated, 7805 sourcing ~75mA
R1 is not populated, 7805 sourcing ~75mA

Output of the bridge rectifier*:

R1 is populated, 7805 sourcing ~10mA
R1 is populated, 7805 sourcing ~75mA
R1 is not populated, 7805 sourcing ~75mA

Input of 7805*:

R1 is populated, 7805 sourcing ~10mA
R1 is populated, 7805 sourcing ~75mA
R1 is not populated, 7805 sourcing ~75mA

Signal labeled SYNC_In - R1 is populated, 7805 sourcing ~10mA

As you can see, in the scope-shot captioned Output of the bridge rectifier - R1 is not populated, 7805 sourcing ~75mA, voltage never goes down enough to create a SYNC_In signal.

**:Image captions are from left to right and are listed below the related images. Clicking on the image caption will open up bigger resolution image in the same tab.*


texts: Why are old digital ICs families still so "popular"?

texts: Why is it so? The basic 74 series, the 4000, are such poor ICs compared to the newest families (by the 74: AUC, AUP, ALVC...), which only have advantages over the oldest one: lower power consumption, lower propagation delay...


texts: Antenna Attenuation, Gain and RSSI calculation

texts:
I am using a RAK7258 LoRa gateway operating at EU-868MHz. I am looking to have the gateway and the antenna on each side of a wall (gateway inside, antenna outside) and receive some packets from some sensors I have outside.
I would need about 1m to 1.5m (3.2ft. to 4.8ft.) cable between RAK and Antenna. I tried calculating the gain and getting an RSSI value and would love some advice; Be pointed in the right direction :)
I did the calculations with 1.5m to estimate a worse case scenario.
Thanks a lot, I really appreciate the help. I have just updated my calculations, from some values for attenuation in small coax cables I found on Table 1 on the data-alliance site U.FL Cables Coax Types Compared: 1.13mm, 1.32mm, 1.37mm, RG174, RG178.

Any suggestions on cables or extenders would really be welcome. The RAK uses UFL connector and my outdoor 9 dBi antenna has an N type Female connector. I wouldn't mind terminating the cables myself.


texts:
I'm trying to create a system to detect when a set of lights trigger in drag racing to the thousandth of a second. However, all my attempts at finding cameras for a raspberry pi or arduino aren't quite fast enough. Is there a camera out there capable of this, or another way to do this perhaps using some other component?

The process of detection is fairly simple. There are two sets of lights and I want to detect when the first triggers, and when the second triggers (while the first is still on.)


texts: Voltage regulator selction based on Junction−to−Ambient thermal resisatnce

texts:
Thermal resistance, Junction−to−Ambient (\$ϕ_{JA}\$) of NCP1117 voltage regulator is 160 °C/W and thermal resistance of AMS1117 voltage regulator is 90 °C/W. Remaining specifications are almost same for both regulators. Which of them is preferable?

What is the role of thermal resistance while choosing a voltage-regulator?


texts: How to burn arduino mega 2560 bootloader?

texts:
I have my new Arduino Mega 2560 and I might have overwritten the bootloader when uploading another program through AVR studio.

I really need advice and instruction of how to burn it using AVR Studio 4 and AVR ISP external programmer.

I have tried to do everything mentioned on the Arduino website but it was not a successful attempt.


texts:
Where did the following transfer function come from?

\$H(s) = -H_o\frac{\frac{\omega_o}{Q}s}{s^2 +\frac{\omega_o}{Q}s + \omega_o^2}\$

\$H_o\$ is the gain at resonant frequency.

I'm told it describes a "classical resonant circuit response" and so I guessed it might somehow be derived from the laplacian of a damped driven oscillator or something of the sort. It appears very generalized. I'm using it to build a multi negative feedback band pass filter.

The original equation appears in this derivation as well as the design:

http://eet.etec.wwu.edu/hardyc/project/docs/Filter%20Design/Multiple%20Feedback%20Bandpass.pdf

For instance, in the link I posted, the transfer function for the filter ends up being:

\$H(s) = - \frac{\frac{s}{R_1C}}{s^2 + \frac{2}{R_3C}s + \frac{1+R_1/R_2}{R_1R_2C^2}}\$

from which they deduce based on its similar form to the original equation I posted what \$\omega_0\$, \$Q\$ and other variables are.


texts: Does anyone have any examples or suggestions utilizing Atmel's ATMEGA2560 and external interrupt's?

texts:
I am trying to utilize an ATMEGA2560 and it's interrupt.  I have some code that must execute until a button is pressed at which time I need the code to stop and wait for another button press to continue.

Is anyone familiar with this type of circuit and the interrupts?

Here is what I am currently referencing for the ATMEGA2560 interrupts.


texts: Under-clocking an 10gb Ethernet SFP+ module

texts:
The Xilinx device on the Picozed board is a version of the Zynq 7030. The 7030 in general has a GTX transceiver, which in principle is rated to 12.5Gb/s SERDES with the relevant line coding for 10gig Ethernet.

Unfortunately, the specific chip on the Picozed has its GTX transceiver down rated to a reduced 6.6Gb/s.

Is it possible to use a reduced line rate with off the shelf 10gig Ethernet networking hardware (modules and switches)?

Without knowing enough about the precise tech, at first glance, I can't see a problem in principle with the TX side since it would result in a reduced implicit clock frequency. On the RX side it seems more problematic: the other end would need to either realise or be told to transmit at a reduced rate.

Is this something that can be made to work?


texts: What fuse to select for a 240W power supply

texts:
I have a 12Volt 20Amp 240Watt regulated power supply to use for a table top pinball game - comprising of solenoids (2@ 12V 8A peak), some LEDs and a micro controller. The unit has an internal fuse but I also need a fuse for the AC IEC socket (which has an on-off switch and separate fuse) on the back of the cabinet, and also one for the main wall plug.

If fuses are rated approx 125% of the normal operating current:

(240W/240V) * 1.25 = 1.25A

Would a 3A fuse be fine for both the socket and the wall plug, or should I use a different combination?


texts: Use a Zener diode to turn on a transistor?

texts:
I am building a circuit that charges a mobile phone.

I am using the IC Chip MP1583DN that has been configured to give a nice 5.30v out.

i want to add protection so only a maximum Vout voltage  does not exceed 5.40v.

The IC Chip has a pin called EN, if this pin is pulled low it will shut the chip down.

i was thinking i could use a zener diode connected to theVout  5.30v and when voltage goes near 5.40v the zener diode turns on a transistor. That transistor connects ground to EN pin of the IC Chip and turn the chip off and save the mobile phone from any damage

would this work ? if so what value zener or transistor would be best to use ?


texts:
How does R4 prevent the output voltage drifting towards one of the supply rails to the op amp? I understand that R4 has to have a high resistance but I do not know why?

Here is the schematic which is puzzling me:

The link to the CircuitLab schematic:

https://www.circuitlab.com/circuit/x66cq6/basic-frequency-control-circuit/


texts:
I was doing this project for a kid - an ultrasonic buzzer that alerts you when an object is within 1.7 meters in front of you. We are using an HC-SR04.
I set up a 555 in an astable multivibrator configuration that produces a 10Hz rectangular wave (T = 100ms.)
Now the way this ultrasonic transducer works is realtime generation of a asymmetric PWM, what I mean to say is it does not wait for the ultrasonic echo and then generate a PWM and send it to the ECHO pin. So if there is no object detected, it will send back a 38ms PWM.
For 1.7 meters, the PWM width is 10ms, anything above 10ms is empty space (until you reach there.)
Here is how the wave at TRIGGER AND ECHO look

All I would want to achieve is let 15, 18, 5 ms pass through but the 38ms PWM should be blocked. What should be the approach I should take?


texts: Calculating Signal Loss (dB) Through Vias

texts:
Does anyone have any useful calculations or links to material covering good ways to calculate signal loss through vias?

What would be perfect is a graph with typical loss in dB over the range 1GHz to 10Ghz+

I'm calculating the total signal loss of some 10G SerDes traces, in order to work out the required pre-emphasis.


texts:
This may not be in the right location, so tell me and I'll move it.

I am a recent EE grad and I was hired to build a system that exists on a SoC with a simple 32-bit processor. The system basically monitors several external devices and performs some DSP on it, and then is supposed to send the results using a WiFi device (in my case I have the ESP8266 using UDP) to an email server for logging/notification.

I have been trying to find a library that I can use, but my uC can only program in C and I have it set up for UDP, and everything is in C++ using some other protocol, or something else completely.

I am great at DSP, decent at SoC's and uC's, but when it come to this email server communication thing I am at a loss.

I have successfully configured everything for the sensors, the datapath, the DSP, and connected the system to my WiFi via UDP, but I have yet to figure out how to send data to any servers.

Could someone help me understand how I should go about this?

I have looked into some simple SMTP commands such as HELO, MAIL, RCPT, DATA, etc.  but I cannot understand how I actually should implement them in my code.

When I send out the WiFi data via UDP what type of data do I send and how do I format it?  Do I need to send any other kind of flags?  How should I expect the response?  I also know the data has to be transformed into base 64 which is confusing me further.

I am also not super familiar with UDP to begin with, I have been using libraries that are part of the SoC's default library to connect to my WiFi.

I know these may either seem like obvious or stupid questions but it is were I no longer have any knowledge, and everything I find online doesn't make sense, or doesn't attempt to explain it, just gives a pre-made solution

I have found the RFC2821 but it doesn't get any clearer.

I know that's a lot but any help at all would be a lifesaver!


texts: Understanding specs of PNP transistor for replacement

texts:
I want to replace an ON Semicondutor BC557 PNP transistor with a Multicomp BC557 PNP transistor. It is just for general switching of LEDs. But the specs look different although they are same mode.

Why are voltages from Omsemi transistor are negative while those of Multicomp transistor are positive?

Can I still replace it with that one?


texts: Why is there an extra resistor on the opamp in the LM399 datasheet?

texts:
While looking at the LM399 datasheet, I noticed on the portable calibrator application there is a 5k resistor between the output of the opamp and the noninverting input. It looks like it forms a voltage divider with the 200k resistor, but I cannot figure out why they have that in there?

LM399 - Datasheet


texts: How do you solve Thevenin equivalent for circuits with variable resistors?

texts: I have this circuit and I have to solve the Thevenin equivalent across the terminals A and B. How do I solve for RTh in terms of the variables present in the circuit?


texts: Designing a bluetooth 4 low energy device - what needs to be taken into account for future FCC and CE certifications

texts:
We are designing a BT4LE device based on Nordic chipset with chip antenna.

The question is how can we understand is it required to put the chipset into an RF shield or not?

I've seen some BT4LE device designs which were CE certified and contained no RF shield. At the same time I heard opinions that the shield is required for FCC certification. Is there anybody who can help and explain how the decision should be made?


texts: Can Mq4 sensor be used for smoke detection?

texts:
I wanted to ask if Mq4 can be used for fire smoke detection?

I read it have small sensitivity to smoke in the data sheet, but I wanted to know what is the least value in ppm for it to detect smoke ?

MQ-4 datasheet
http://www.geeetech.com/Documents/MQ-4%20Datasheet.pdf

Thanks in advance.


texts: use RFID ( or what else? ) for a broad distance measurement in 1-2 meter wide area

texts:
Let's suppose we have a suitcase containing some RFID tagged objects. With a reader contained in the same box, I periodically poll the content in order to check if something is removed from the suitcase. Removed means at a distance, lets'say, >1 m. Is that strategy possible with RFID?
Any idea on how to achive that otherwise?
Problem is we have to indentify precisely a set of items contained in the suitcase, and understand when one of these is removed from the case, even by is id, then returned.

ADDITION
Suit case must contain all what we need for the tracking. We can't rely on triangulation infrastructures in place.
As a semplification, is acceptable to have the suitcase partitioned: would in this case an NFC antennas matrix help?

EDIT
I'm a programmer, not an electronic engineer so I'm definitely ignorant. If there is some obvious solution to track items in a suit case, in term on when a specific item is extracted (  not stolen, so not gone at undefinitely far distance ) , any idea are welcome. Solution based on RF signal based seems IMHO a little too weak, but if you say it will work, I will try.
Maybe some matrix of NFC receiver would work? Is there some solution I can buy for try?
Surprisingly my googling on the topic did not produce satisfying results.


texts:
I have the following circuit.

The transistor is working in saturation mode. It means both p-n-junctions are forward-biased. Thus, there are two diffusion currents in transistor (electrons move from the emitter and from the collector into the base, the currents of holes from base into the emitter and collector are fewer because of the fewer concentration of impurity in the base). So I expected, that the emitter current and the collector current had been equal. But it is not that in the computer model. The collector current is much greater than the emitter current. Why? Can you explain, please. I have no idea.


texts: How to measure AC current in a wire without direct contact with the wire?

texts: I am building a power monitor project, and I want to measure the current flowing through the 230V mains supply to my house non-intrusively. I am aware of AC current clamps/transformers. I also came across hall effect current sensors like WCS1500. I've also thought about making my own current clamp. I'm not sure which is the cheap and efficent way to do this.


texts: Speed control for high power DC brushed motor

texts:
I am going to drive and bi-directionally control the speed of some 12V/24V, 100W to 300W DC brushed motors.

I have some experience in controlling small DC motors (6V/9V/12V, 0.5A to 2A) with PWM signal from an Arduino and a L298N dual H-Bridge Shield. However, for the relatively high power DC brushed motors that I am preparing to drive, I have no such experience and am wondering what methods and chips should I use.

PWM is the method of choice when controlling speed for small current motors. Is this still the method of choice for higher power DC brushed motors ?

For 100W to 300W motors, the operating current may be as high as 10A to 25A, and may get even higher if once the motor is stalled. The L298N dual H-Bridge could not be used in such a high current environment. Assuming that the maximum current is below 100A if the motor is stalled, What chips and circuit should I use in these cases ?

Could I use PWM signal to switch a "solid state relay" / "optical coupler" to control the speed of these higher power DC motors ?

How could I handle the case that the motor is overloaded and is stalled, and the current gets much higher to impose danger ?


texts: I'm studying digital electronics where the components ALU and multiplexer appear. To me the ALU seems like a multiplexer but it's not specifically mentioned that this is the case. Is it so, or why not?


texts:
The question:

Design an automaton that receives inputs X0, X1 and produces outputs Z0, Z1.

Z0 is 1 If the last two bits of X0 are the complement of the last two received on X1.
Z1 is 1 If in the last two bits of X0 and X1 there is an even number of 1

Example:

X0 0 0 1 1 0 0 1 1 0
X1 0 1 0 0 1 1 1 1 0
Z0 - 0 1 1 1 1 0 0 0
Z1 - 0 1 1 1 1 0 1 1

I have problem to solve this type of question. I'm tried many times to solve this type of problem but I couldn't.
This is not homework, it's a question from my last exam.


texts: Mysterious Trace in Battery Fuel Gauge Datasheet

texts:
I'm using a lipo battery in a project, and I want to include a sophisticated battery fuel gauge in my design.  I have a battery input stage with a TI BQ24072 charge management IC and a linear down-regulator to 3.3v.

For the fuel gauge, I've chosen the TI BQ27421-g1 as I've had good luck with their battery charging IC.  The typical application circuit is shown below:

I'm a little confused about the function of the SRX pin.  The datasheet only has about 2 sentences about it.  To make things more confusing, this diagram on page 20 says that it should be shorted to the BAT pin (sorry if the pin names are tough to read):

Here are my questions:

Am I mis-reading the diagram on page 20?
If I am reading the diagram on page 20 correctly, then how does the coulomb counter even work?
If I don't understand the diagram on page 20, then how should the SRX pin be hooked up?


texts: Microwave Oven: Switching Magnetron (Transformer) with SSR

texts:
I've got a used microwave oven and want to improve it with a digital user interface.

Is it ok to switch the magnetron (more precisely: the transformer from 230V 50Hz to some kV followed by a diode and a capacitor) using an SSR (solid state relais), or should I use a mechanical relais?

One more burning question: Is it ok to use phase cutting to regulate the microwave power or will this lead to problems with the transformer, the rectifier or the magnetron?

Thanks
  Hansi


texts:
I want to make a water level indicator but, instead of all LEDs lighting at 100% (for example) I want the top one only to light and the rest turn off

at 0% all LEDs off
at 25% the first LED on
at 50% the first LED of and the second on
at 75% the second and first LED s off and the third on
at 100% only the fourth LED  on.

I tried this circuit but it did not work with water.


texts: Are pads from the EAGLE "testpad"-library printed?

texts:
just a quick question.
Are EAGLE "testpad"-library printed or seperatly bought and mounted?

E.g. "testpad / PTR1"

TEST PIN
Footprint: B1,27 (Version 1)
TEST PAD
3D Package: B1,27 (Version 2)
TEST PAD


texts: Using a bypass capacitor with a no-neutral smart light switch on two lamps in series?

texts:
I am considering purchasing a smart light switch which does not require a neutral wire and instead works with a bypass capacitor parallel to the load lamp. This switch would control two lamps in series, however, and it will not be easy to install the capacitor such that it is connected to the one side of the first lamp and the second side of the second lamp. Can I use two capacitors (of double value each?) each connected parallel to each of the two laps?
Instead of this:

This:


texts: Reasons to use a voltage divider and regulator?

texts:
If I have a circuit that requires 2V, I can use a voltage divider to get me the 2V from the 3V battery. I have been told that it is a good idea then to run that through a 2V regulator. This seems like overkill to me.

Are there any advantages to this? Is it better to drop the divider and just use the regulator?


texts:
I am trying to solve a numerical where the Speed of a DC motor operating at 15V was measured to be 2000 rad/sec. Now a PWM signal is applied to the same motor to get a speed of 400 rad/sec. If the voltage amplitude of the PWM signal is 5V, then what should be the value of duty cycle?
I know the formula of duty cycle is
D=Vout/Vin
D=duty cycle
Vin=15V
Vout=5V
therefore the duty cycle is =5/15
i.e 1/3
therefore duty cycle in percentage is 33.33%
is my calculation right or whether I have to consider the speed of motor at 15V(2000 rad/sec) and at 5V(400 rad/sec)? If yes then how?
this the exact question


texts: Current limiting resistors for preventing shorts at power supply turn-on

texts:
In a text it mentions about a power supply that the filter cap will act as a short at initial turn-on. Below I showed these points as A and B:

In this case, the diode will have a surge current Is. And the text says this Is current should be limited by a resistor between the transformer and each diode.

But in practice isn't transform's winding enough to limit this current? What is the typical value for this resistor lets say for a 24V power supply? Im asking because I dont see any such series resistors in examples. Im wondering is it fine to neglect it.


texts: Compensate frequency dependency of an Ammeter

texts:
In order to measure voltage with an Ammeter, the current through the impedance of the Ammeter is measured and the voltage is determined indirectly. In the circuit below the impedance of the Ammeter is \$ R_2 + L_1 \$. The resistor \$ R_1 \$ is there to limit the error in current for a temperature dependent \$ R_2 \$.

Now I want to compensate the frequency dependency of this circuit. For that \$ C_1 \$ is added in parallel to \$ R_1 \$, which I want to calculate.

$$
\frac{\underline{V}_1}{\underline{V}_m}=\frac{R_1||\underline{X}_c}{R_2+\underline{X}_L}+1=\frac{\frac{R_1}{1+iwR_1C}}{R_2+iwL}+1=\frac{R_1}{R_2+iwR_1R_2C+iwL-w^2R_1CL}+1
$$

If all the terms holding a \$ w \$ cancel out, I actually would get a frequency independent circuit.

$$
iwR_1R_2C+iwL=w^2R_1CL
$$

But that seems like an impossible task. How could two complex numbers add up to a real one? What am I doing wrong?

simulate this circuit – Schematic created using CircuitLab


texts:
I'm using a photodiode module, model: coaxial InGaAs, Gtel.

I set it in reverse bias with 5V and tested it with a laser but it doesn't give any output voltage. Unfortunately I don't know the laser wavelength. The resistor in this circuit is 5k.

I have 3 of these modules but none of them worked.


texts: Output voltage approximation in Wheatstone bridge

texts:
When I calculate the potential difference in the above circuit, I find:

v1 = Ug*(ΔR+R)/(2R+ΔR)

v2 = Ug*(R)/(2R+ΔR)

Uo = ΔU = v1-v2

ΔU = Ug*[ΔR/(2R+ΔR)]

But it is always approximated to:

ΔU = Ug*ΔR/2R

Another example of this kind of approximation can be found here.

What makes this approximation mathematically valid?
Is it the derivative?
If we ignore ΔR and not ignore and plot the expressions we see that they get so close for small values of ΔR:

I just cannot show it mathematically.


texts:
I have a CD4021BE set up very similarly to the Arduino ShiftIn Tutorial (the main difference being that I don't currently have 8 buttons so have just connected PI-5 to PI-7 to ground with a resistor, I get the same misbehaviour if these are left floating).

All of the values that I'm getting are being shifted up 1 bit, so with 5 buttons connected to PI-1 to 4 and PI-8), pressing the one connected to PI-1 gives me the value 00000010, pressing PI-2 gives me 00000100 and PI-8 just gives me 00000000.

I have my data pin connected to Q8, which as far as I can see in the Datasheet is the right place. Just to see what happened I connected it to Q6 and get 00001000 from PI-1 and so on.

I got 5 of these chips when I ordered them and have tested 3 so far and all perform in the same way, which really just suggests that I'm doing something stupid.

This is the code I'm currently using:

#define CLK 10
#define LATCH 9
#define DATA 8

int data;

void setup() {
  Serial.begin(9600);
  pinMode(DATA, INPUT);
  pinMode(CLK, OUTPUT);
  pinMode(LATCH, OUTPUT);
  Serial.println("Begin...");
}

void loop() {
  digitalWrite(LATCH, HIGH);

  digitalWrite(LATCH, LOW);

  data = shiftIn(DATA, CLK, MSBFIRST);

  Serial.println(data, BIN);

  delay(500);
}

CLK is connected to CLOCK on the chip, and LATCH is PARALLEL/SERIAL CONTROL.

Why is this happening?


texts: Use of frequency multipliers for a signal with DC component

texts: Is there a frequency multiplier (say frequency doubler) that can deal with a signal with DC component? (so 0 hz is still 0 hz, while 1 hz becomes 2 hz, etc.)


texts: Estimating the schematic of a black box using the measured impedance curve

texts:
I need to estimate/predict the circuit design of a black box using the measured impedance at the output of this box. The only hint I have is that the circuit inside the box is a demodulator. Is it possible to estimate the schematic of the black box? Is there any smart method to find the connections inside the box? Should I measure other things which could make the estimation process easier?

Any help will be appreciated (tutorials, literature, videos, etc...).


texts:
I would like a circuit that detects current imbalance between two conductors.  The currents are normally equal and opposite in direction, but can vary in time (or reverse direction).  Neither conductor is very close to ground.

This is pretty similar to GFCI device, except in my case the imbalances of interest are in the microamps, and the current is up to 100 milliamps.  Also, current can spike up or down (while staying balanced) over tens of microseconds.

How do GFCI devices usually work?  Are they based on transformers and relays, or semiconductors?  Would it be possible to modify that circuit to make it more sensitive (and faster)?  Is there a different approach that would work?


texts: How much ground current vs. neutral wire current?

texts:
This is a follow-on question to an earlier question of mine; I think it deserves its own question, though.

I am trying to learn as much as I can about how current in a power grid (transmission and distribution) returns to the substations, power plants etc.

In researching this, I came across the claim that in Minnesota in 1995, 59% of the power returns from the consumer to the substation through the ground rather than the neutral wire. On the face of it, I find this number hard to believe, and am looking for an explanation.

The source was given as "Hendrickson, R.C., Mike Michaud and Alvin Bierbaum. 1995. Survey to Determine the Age and Condition of Electric Distribution Facilities in Minnesota: Report 1: Analysis of Overhead Distribution Feeder Testing Data. Minnesota Public Utilities Commission. May 18, 1995" but this does not appear to be available online.

I can think of a few potential explanations:

Is SWER widely used in Minnesota? I found some mention in passing that SWER is used somewhere in the upper Midwest, but not where, specifically.
Three-phase distribution systems out of perfect balance without a neutral wire would also cause ground current.

Are there any other explanations?


texts: Relay flashes during reset but not on power up

texts:
I have the following pcb design working based on a previous question. When I plug the circuit all works as expected, the relay does not get energized but when I press the reset button the relay flash very fast 3 or 4 times and gets closed as expected, It works but .. how can I avoid this situation?

My original design was :

I have tried R10 with values 1K, 10K and 47K with same result.

EDIT: Reset schematic


texts: Why is there audible noise in the inductor of a boost converter?

texts:
I have implemented a boost converter (120V to 400V). I was testing it by driving a single phase induction motor. When the boost output voltage increased to 200 volts that time you run the motor through VFD. Then I can hear audible nose in the inductor. The motor is drawing current normaly.

I feel it is very dangerous when there is audible noise in the inductor. The noise increased while I was changing the speed of the motor.

Can you tell me why this noise is happening and how I can remove it? Is that noise dangerous for my circuit?

Schamatic of Converter


texts: What kind of a sensor does a arcade punch (boxing) machine have?

texts:
I am working on a project, where I have to measure the pressure exerted by a punch. I am trying to understand how an arcade machine works, and see if I could replicate the same mechanism in my project.
Additionally, I would like for the sensor to be in the punch-bag itself, which is different from an arcade machine. (They have the sensor directly on the back of the machine.)


texts: What are my options to measure oxygen concentration in a high temperature wood burner flue gas?

texts:
I'd like to measure oxygen concentration in flue gas from my wood burner.

Lambda sensors are suitable but, even if relatively cheap, they need a control unit to keep working temperature and other parameters under control, and that increases the price significantly. I found the project Lambda check that is priced at around 300 euro. The sensor and control unit by themselves are about 180 euro on third party websites.

What are my other options to measure the oxygen concentration?

It has to be assumed soot will need to be periodically burned out and the operating temperature should exceed 500°C.


texts: Can anyone explain that what kind of sound a piezo can and cannot produce when compared to A speaker. Can it just play notes? Is there some quality reduction in piezo buzzer?


texts: How to control and power 25 x 25 nichrome wire matrix

texts:
I would like to control and power a 40x40mm size array of 25 x 25 small heating elements which should function just like a visual display of LEDs, but switching  heating elements on/off instead. I am thinking of using tiny strips (<2mm square) of 28-30 AWG nichrome wire. And I would like to use an Arduino to drive the matrix of wires. Each nichrome strip needs to reach temperatures between 30°C to 45°C in the air. Power source can be 1 x Li-Ion Polymer battery OR  2 x Li-Ion 18650 (2300mAh) cells.

but need the following advice:

Would SMD themistors be suitable instead of resistive nichrome wire?
Can I provide the Nichrome wires with sufficient current through using a multiplexor? or must I use relays to power them directly?
How does cooling nichrome wire (drawing heat via conduction to lower temperature) compare to less resistive wires? does this require less or more power?
What are some suitable multiplex shields or other methods of controlling them with an arduino?
Would Nichrome sheet be able to be chemically etched just like laminated copper boards?

Thank you!


texts: Phase Detector for PLL: Operation and Realization

texts:
I have some doubts about the realization and the operation of a phase detector for a PLL. My reference book is "The Design of CMOS Radio-Frequency Integrated Circuits" (Thomas H. Lee).

The basic scheme of a PLL is this one:

Its aim is that of generating a signal which has the same frequency and, more precisely, the same instantaneous phase, of a reference input signal.

The Phase Detector is defined as a component whose output is a signal whose amplitude is proportional to the difference of phases of its input signals. The simplest way to realize it is that of using an analog multiplier, i.e. a mixer:

where \$\ S_i (t)\$ and \$\ S_f (t)\$ are the input and output signal of the PLL, both put at the input terminals of the Phase Detector.

The output of a mixer contains a term proportional to \$ cos(\phi)\$ and a term which contains \$ \omega \$, and the last one is deleted through a filter (not shown in the scheme) in order to get only a signal proportional to the cosine of the phase difference.

Now, I have the following questions:

1) The book says that the best choice is that of realizing a PLL which perform the lock condition with a phase difference equal to \$ \phi = 90°\$ in order to maximize the phase detector gain, whose expression is:

But, how can I decide at which angle does the PLL stabilize and perform the lock? I think that in theory the previous PLL may generate an output signal with any value of phase difference with respect to the input signal and I do not understand how can we decide it: it seems to be a casual number. In fact, the following stage is a VCO, whose output signal's frequency is proportional to the voltage signal applied to it.

Therefore, it is sufficient for the output of the Phase Detector to be constant, in order to have a stable oscillation frequency of the VCO. So, it seems to me that the loop may stabilize with any casual value of the phase difference: the only important thing is that it must be constant in time.

2) My book proposes other types of Phase Detectors for the situation in which one of its input signal is a square wave (while the other one is a sine wave).

I do not understand if the square wave is an approximation of a sine wave (and in that case I do not understand why approximate only 1 of them in this wave) or if it is properly chosen to be a square wave (and in this case I do not understand in which sense the PLL may synchronize it with the other sine wave, since they are different waveforms).


texts: Is it possible to build non-linear resistor using linear potentiometer

texts:
I have CAT4101 constant current LED driver and I need to control LED current. My idea is to use microcontroller and digital potentiometer (MCP41010) to control the current.
While the potentiometer I have is linear (resistance is proportional to the digital code), LED current is not linear due to CAT4101 characteristics:

LED Current    RSET
[mA]           [Ohm]
100            4990
200            2490
300            1690
400            1270
500            1050
600            866
700            768
800            680
900            604
1000           549

Its datasheet says that it maintains constant voltage on the Rset pin and LED current is approximately 400 times the Rset pin current.

Is is possible to "invent" some circuit based on linear digital potentiometer that will change its resistance in non-linear way and allow linear LED current control?


texts: I'm calculating the power consumption of each module on my board. For USB2.0 port, I know when it is working , the power consumption is 5V * 500mA = 2500mW. However, I'm not sure how to estimate its sleep power consumption, I mean when an usb-stick is plugged in but no read/write operation on it, can someone give me a suggestion about it? Another question is if the USB port is empty and nothing is plugged in it, does the power consumption of USB port equal zero?


texts: Cropping of OV2640 full resolution, understanding the registers

texts:
I'm working with a k210 chip on a sipeed maix go, and I'm trying to process UXGA pictures. The chip can't handle having more than QVGA pictures in memory, so I want to only retrieve a "crop" of the full resolution at a time.

To do so, I'm trying to use the registers described in the datasheet.
The thing is I don't understand how the registers relate to each other, and I'm getting a lot of "sensor timeouts", "green images" and other things of the sort.

I've identified the following registers as being relevant: HSIZE, VSIZE, XOFFL, YOFFL, VHYX, TEST, ZMOW, ZMOH, ZMHH, SIZEL, HSIZE8, VSIZE8, COM1, COM7, HREFST, HREFEND, VSTRT, VEND and REG32.

Can someone help me understand how this registers work and how to use them to achieve the desired objective?

The maix go is a bit more complex than the camera, It has it's own "firmware". There are 3 alternatives for the firmware, which can be found here: github.com/sipeed. Two are C and one is a micropython implementation(MaixPy). I'm trying to modify MaixPy's source code ov2640 interface implementation. I've tried using windowing but I think I must change the other registers in order for it to work. The interface is here: ov2640.c. I'm messing with "svga_config".

Also, here are

maixpy's docs: maixpy.sipeed.com
k210 page: kendryte.com
And sipeed maix go page: seeedstudio.com.

Basically, sipeed took the chip and put it into "usable" boards.


texts: Line - Line voltage with different phase angles, amplitudes and frequencies?

texts:
I know that the mathematical equation for the calculation of Line - Line voltage with same frequency, same Phase angle, same Voltage of 3 lines from the same generator.

now, i want to know having different properties of Line - Line Voltage.

what are the mathematical techniques use for this example problem.

  if,

  L1 — 100V, 50Hz, 30 degree phase angle,

  L2 — 230v, 60Hz , 120 degree phase angle,

 (I think it is not practically workout, just assume those are individual generators connected to same neutral )

now,

  what is the line to line voltage of L1 & L2 ?


texts: Wiring a Potentiometer for a positive voltage

texts:
I am attempting to make my own adjustable voltage supply that provides a positive voltage (anywhere from 0 to +200 VDC).

The sections I have devised so far are able to provide 450 VDC, however I need an exclusively positive voltage and one that is 200 VDC or less (voltage going to the load will be 0-200 VDC).

Unfortunately, I'm not too experienced with wiring potentiometers for this kind of a situation. To my knowledge, this is how a potentiometer would usually be included into a circuit (please note that while this diagram uses a motor, I will not be using one in my set up):

If I wanted to only have a positive voltage going to my load, should I simply ground the negative lead shown in the picture?

P.S. If people are curious about the load, it is simply a grid bias for a thyratron, nothing terribly advanced that requires anything beyond 0-200 V.


texts: Drive stepper motor with potentiometer in Siemens PLC

texts:
It is difficult for me to drive a stepper motor with potentiometer (position stepper motor with position potentiometer).
I've done program, to see the value from potentiometer with NORM_X.
I am using CPU 1214C DC/DC/DC with program TIA V14.
How can I match the potentiometer value with the stepper motor position?
Would it be better with PID 3step? But, how?


texts: High voltage transmission, transformers and Ohm's law

texts:
I have difficulties with understanding high voltage transmission and transformers working process. Particularly with this expression: "the higher the transmission line voltage, the smaller the current".

I will try to explain:

The first case - we have usual line transmission, without transformers:

Here is all straightforward: we have circuit, with

R = 50 Ω;
V = 1000 v;
I = 20 A

Everything is clear and understandable.

Now, the second case - we have high voltage line transmission with transformers:

Two trasformers was added: step up and step down. Why it was done? I know the answer, it is wrote everywhere on the internet - it was done, to decrease current in transmission line, in order to reduce losses, caused by high current. Voltage have increased, but power should stay the same, therefore current should be decrease, the formula P = I*V, Joule-Lenz law... etc. It's all clear.

But! Now we are have potential difference 10 000 volt in our transmission line. Resistance stays the same. Apply Ohm's law and get:

\$I = \frac {10000v}{20 Ω} = 500 A\$

500 amperes instead of 20 amperes in the first scheme. I understand, that it can't be the truth, because then there would not high voltage lines existence. But where I made error?

Edit1:

I have found good discussion on this topic here. They working on this question thoroughly. Look there, if you are interested in the detailed answer too (first three pages needed to read).

Edit2:

Can anyone explain this moment:

We are turn on generator (AC source)
It starts produce AC current
This action affects step up transformer by the magnetic field on its primary coil and step up transformer start works too, generating current on its secondary coil.
Then current goes to the high voltage line
After high voltage line, it comes to the step down transformer
Step down transformer starts work too
And only now is the turn of ‘Load’.

What I think - ‘Load’ is passive entity, it is take what it is given. How it can dictate and regulate magnitude of current which pass through high voltage line? 'Load' just sits on its place and waits what current will be on the step down transformer and uses, what has come. It can't sucks current, how it want. Furthermore, even if ‘Load’ turned off, circuit will closed and will work. Right?

In the first case (without transformers), we are not having closed circuit, before ‘Load’ is turned on. But in the second case we have closed circuit without 'Load'.

Second question: how ‘Load’ can determines and affects to the current in the high voltage line, when it is passive entity (in my opinion)? Is the current in the high voltage line depends from the load after step down transformer?

Found answer to the second question here. Very good article.


texts: What is the use of the unused Data pins of a LCD

texts:
I've a 16 pin LCD. The whole display (16x2) can be driven just using only half of the data pins (D4 - D7) of the LCD. Other 4 data pins (D0 - D3) can be neglected.

I need to know why then the LCDs come with eight data pins. Of course, there should be some reason(achieve faster update rates etc...)

Can someone show me the reason..
(This is just for my knowledge)

Thanks!


texts: Problem with Bluetooth read range for arduino project

texts:
I have been working on an Arduino project for a door entry system in my business office but have encountered a problem.

I have a group of 8 working in my office but we have a room which only 3 members are allowed to enter. To stop unauthorised entry I have installed an Arduino door sensor with Bluetooth Low Energy (BLE) to the door which will always ring if the door is opened. The only way to stop the alarm from activating is for the 3 members to have their BLE fobs with them when they open the door.

The drawback I have found is that if I increase the read range of the sensor it picks up fobs which are nowhere near the door and the alarm never sounds. When I limit the read range to around 5 to 6 feet the fobs do not get read when they are put in handbags or wallets.

So I need a technology which can have a very short read range so it does not pick up fobs far from the door. I also need it to have a powerful signal within that desired 6 feet or less read range. The power of the signal should not be affected by being put in pockets, handbags etc.

It’s also important for mobile phones not to block the signals seeing as all my employees have them.

The technology should not rely on line of sight either because the fobs will be concealed in bags and wallets most of the time. Your advice will be most welcome and appreciated.


texts: 24volt to 5volt pulse conversion without affecting frequency

texts:
im a newbie . id really appreciate if you could help me out on this issue.

i have a 24v operated pulse generator that i want fed into the arduino working at 5v. how do i change the voltage level without changing the frequency of the pulses.

These pulses are from an open collector output of 24VDC .maximum frequency of 5khz.
will a voltage divider work??or is optocoupler recommended ?

thank you in advance for your help!


texts: I need a circuit for a linear integrator using a capacitance multiplier

texts:
There are various circuit topologies for capacitance multipliers using op-amps.  I need to implement a linear integrator where it would be advantageous to reduce the size of the integrating capacitor by (say) a factor of ten.

Are there any topologies for this?


texts: How does a magnetic ballast (large inductor) stabilize a negative resistive circuit (such as a fluorescent light)?

texts:
When reading about fluorescent lights, I noted many sources stating that a large inductor (the magnetic ballast) in series with a negative resistor (the light, in this case) will stabilize it by blocking large AC currents.  (Sources that say this include: [Reactive_ballasts] or [Fluorescent lights])

However, the impedance of a negative resistor in series with an inductor is $$\frac1{j\omega L+R},$$ where R is negative, leading to an unstable pole.  What am I missing?  Are the sources wrong, or am I misreading them?  If so, how does a magnetic ballast actually stabilize the light?


texts: PWM module and inrush current from motor

texts:
I'm trying to setup a power feed for a milling machine using an old DeWalt drill motor.

I've got a 13.8v 20A power supply and a Kemo M195 20A PWM module.

My concern is the inrush current from the motor, Using a clamp on meter I get peaks of around 22-24A on starting. Is around 5A running with no load.

Could the inrush damage the PWM module?


texts: How to generate a -5V to +5V sine wave from one DC supply?

texts:
I need to generate a -5V to +5V sine wave, the only supply I can use is one battery upto 12v. I need to be able to adjust the frequency with a potentiometer. Output current needs to be a minimum of 100mA. Two bonus features would be to be able to adjust the amplitude and offset with two additional pots. Frequency range needed is around 60-600Hz

I have tried to do some research on my own but am struggling with the correct terminology as I'm only a hobbyist with little experience in analog electronics.

I don't expect someone to come up with a complete design for me (but that would be a bonus of course!) but just to help with a starting point, some terminology that I am lacking or some reference sources.


texts:
I am trying to drive a motor/lamp (10 Amp Max). The voltage across the load will be controlled via an N-Mosfet. I started building the mosfet drive part and I'm kinda stuck.

simulate this circuit – Schematic created using CircuitLab

The FET heats up when barely 1-2 Amps are flowing through. I never faced a problem when used these same FETs on an H bridge configuration driven by DRV8701P with the same amount of heat sinks. Also tried making Totem Pole driver using BJTs, same issue. Changed FETs several times.

Also, some of my FETs went bad, dont know why. Their drain and source terminals shorted out. On some, all of the three terminals shorted out. I have changed around 8-10 FETs on this. Any help is highly appreciated. Thanks!


texts: What is this device? (8+2 pin + string + label = "Test")

texts:
I found this trackable but it does not say in the description what is actually is. Out of curiosity I opened it and only found 4 resistors soldered to the pins labeled 1, 4, 5 and 7. The other pins are not connected. Can you identify it from the photos? I would like to learn more about it.

The scale is in centimeters.


texts: Using a 5A power supply for an LED Strip rated for 3A per color

texts:
I bought a kit off ebay that came with an SMD 5050 RGB LED strip, an IR controller and a 3A PSU. Long story short, I have a second srip on its own and instead of buying the same PSU, I'm wondering if I can use a higher amperage PSU (5A) to power the strip so it can be brigher essentially. The ebay item is here.

What I'm sceptic about is that (while not listed on the ebay page specifically) the strip is rated for 2A each colour, and the IR controller is also rated for <2A each colour.

In my mind this makes sense as when using all colours, the 5A is distributed across the three colours using ~1.6A each. Sweet. But what happens when I run just a single colour, say blue? Does the 5A all go into that single colour potentially frying stuff or does the excess get grounded or is it even pulled from the wall at all?


texts: Programming pattern to generate VGA signal with micro-controller?

texts:
I want to generate VGA signal with micro-controller (like TI Tiva ARM which runs at 90/120Mhz speed).

I'm not sure how to make accurate timings with micro-controller. Which programming pattern I need to use?

Do I need any inline assembler code? How to wisely use interrupts?

Would be great if anybody show some pseudo code how to generate VGA signal.

I successfully generated VGA signal with FPGA. But I just can't figure out how to do it with MCU.


texts: I have some PCB and on it this chip. I'm trying to figure out what it is. I've searched all over the google, SMD codebooks, datasheet websites and I haven't even found a similar thing


texts: What are the optimal conditions to maximize Peltier cooling performance and duration?

texts:
Hi first time poster here, I got a few peltier plates just last week and have been doing some research surrounding their polarity reversal and the limits of what they can do. However I still have a couple questions:

My peltier plate only stays cool for about a minute or so then begins to heat up, I'm not sure if this is supposed to happen or maybe I should lower the voltage I'm using?
What would the optimal circumstances be to maximize cooling performance? Is there an specific voltage or condition that would allow a for the highest yielding cooling effect?
Lastly, I was wondering is there any way to orientate the conductors to have the hot and cold plates be on the same side?

Any suggestions for these?


texts: Proper shielding techniques for chassis grounded equipment located 30 feet apart

texts:
I am just hoping to get some best practices out of this discussion:

I have two pieces of equipment that are located about 30 feet apart and bolted to a metal frame (chassis ground). They interface with each other through two cables - one carries high frequency (280Mhz) differential pair digital signals and the other carries analog voltage rails.

In designing shielding for the two cables, I had always thought that the shielding should be connected to ground on the power supply side and left floating on the other side to prevent ground loops. To which my colleague replied that I was now creating an antenna that could be used to inject noise back into my system. Thinking about this further, I realized that the shielding on USB cables is connected on both sides, so am I wrong? Or is there a trade off point between low and high frequency lines?

Thanks!


texts: What is the practical difference between Peltiers of different rated current, e.g., TEC1-12706 vs TEC1-12703?

texts:
I'm no expert, but from playing with Peltier modules I understand that, for a constant temperature difference between the two sides, they behave almost as a resistive load, with an almost linear relationship between input voltage and consumed current.
So, assume I have power supply flexibility to run the things at any voltage I like. That means I can make them consume any amount of current I like, below the max. So a TEC1-12706 is rated for max 6 amps, and a TEC1-12703 is rated for max 3 amps. But if I run a 12706 and 12703 at different low voltages so as to make them each consume the same total watts, will they perform differently?
From what I understand, when you run an individual Peltier module at any lower voltage than its maximum voltage, two differences are:

It is more efficient, in that it produces a lower ratio of waste heat compared to the useful heat pumped thru it.
It can only sustain a smaller temperature difference between the two sides.

Do I understand those two points correctly?
If so, still I can't understand what current rating of Peltier I should choose. There must be a difference, otherwise they wouldn't bother to make all the different ones.
Basically, in practice, assuming I have complete choice of input voltage, when are higher-current modules better, and when are lower-current modules better?


texts: Hidden Wire Detector, Oscilloscope Measurement

texts:
We have a hidden wiring detector device

I used 2SC1815 transistors and the value of R was 1K0. My antenna was made of 300 mm length copper wire with diameter 0.3 mm. I've measured its inductance - it is about 2 uH.

When we connect the oscilloscope to the base of the transistor, and put the earth on the emitter, we get an oscillogram with a cut off top.
She cuts about 0.47 volts
Why is that? What's the matter?


texts: How to choose the correct N channel Enhancement MOSFETs?

texts:
Having little to no experience on MOSFETS i am having trouble part sourcing the correct one, one that will work for my applications.

But before i go with the terms let me show the circuit first

simulate this circuit – Schematic created using CircuitLab

I am creating a inverted LED indicator, the initial plan was to use a 3904 instead of MOSFET, but notice R3 before the switch, the switch that i have may OFTEN HAVE a 11.3k contact resistance when closed meaning the led will remain on even if switch is closed.

Following the recommendation of a previous question and my own reading the net, I already know that i will be using a N-channel enhancement MOSFET. So i went to digikey to source possible candidates. There i was presented with filters that are way over me.

Here are the filters, Please correct me if weather i am right or wrong:

Drain to Source Voltage (Vdss) - I guess this filter means that the maximum voltage in the drain and source, basically the maximum voltage the mosfet can function.

Current - Continuous Drain (Id) @ 25°C - The maximum continuous current that the mosfet can handle. but on the choices there are some letters in parenthesis that are odd to me. e.g. 115mA*(tc)* or 115mA*(tj)* or 115mA*(ta)* . What are these ta tc tj.

Drive Voltage (Max Rds On, Min Rds On) - The voltage in the gate for the mosfet to turn on, since the mosfet act like a variable resistor the max Rds On is giving out the maximum resistance and min rds on is giving the smallest possible resistance e.g. 1.8,2.5 at below 1.8volts the mosfets is at maximum resistance and at 2.5v it is at minimum resistance

Rds On (Max) @ Id, Vgs  - im a litle bit confused on this one i think this is supposed to be maximum resistance the mosfet but the values are in milli range e.g. 22mOhm @ 6.5A 4.5v

Vgs(th) (Max) @ Id - ???

Gate Charge (Qg) (Max) @ Vgs - ???

Vgs (Max) - ???

Input Capacitance (Ciss) (Max) @ Vds - ???

are there filters that i should not mind ?


texts: Non Inverting Summing Amplifier - Ripple Gain

texts:
I've created the following non-inverting summing amp.

This seems to sum flat DC fine although if I add ripple, the ripple get amplified, surely this should only add the ripple.

Why is the ripple being multiplied?


texts: How DC offset affects the spectrum of a single pulse

texts:
I know that in the magnitude spectrum of a single square DC pulse (0-8V) the lobes are zero at frequencies $$\frac{1}{t},\frac{2}{t},\frac{3}{t},...etc. $$ where t=pulse duration.

If the square pulse goes from -2V to 6V, is the formula for the zero points of the spectrum still the same, ie. $$\frac{n}{t}$$ where n=1,2,3... etc. and t=pulse duration?

What is the difference?


texts:
I want to specify a square cutout in my PCB, to fit a sensor module.

The cutout must be very tight, that is it should only be 100μm wider than the sensor on all sides, as it is used to hold the sensor.

But as to my knowledge, the manufacturer cannot make sharp edges because the cutout is made by milling, so the corners will be round.

My corners don't need to be sharp, only the cutout dimensions need to be correct.
So how is the correct way of during this? Should I just define a hole in each corner?


texts: How can I measure a voltage between two conductive surfaces that are completely isolated?

texts:
I am in the middle of diagnosing an issue where the case of my battery box (steel) is floating at a potential of 120V relative to the negative terminal of the battery (350V). I've started removing connections but in this process i've been probing a lot.. The battery is completely isolated by several layers from the box. It's modular so i've removed one of the modules and placed it 2 meteres away, on top of two wooden blocks and a towel on a bench.
How is it possible I can measure a solid voltage (In this case, roughly 10V) between a battery terminal and the battery box which is 2 meteres and multiple insulators away? I then started probing random metal surfaces in the area and all showed a voltage, what is happening here? How is the multimeter showing a solid voltage when there is no current path?


texts: Any advantage to series connecting small 12V chargers?

texts:
My scenario is this:  I have a 36V golf cart which has six 6V FLA batteries in series.  I have a large 36V 21A charger but it is too heavy and awkward to take with me in the cart.  Outside the clubhouse, they have courtesy outlets where members can charge their carts for free.  For fear of damaging the large 36V 21A charger, I leave it at home.  However, I have some small and very light 12V chargers that I sometimes use at home to charge the 36V bank without breaking any series connections.  So that tells me they have electrical isolation from each other since they "float" relative to a common ground.  For example, imagine the batteries are numbered 1 thru 6.  The negative of charger 1 will connect to the negative of battery 2 and the positive of charger 2 will connect to the positive of battery 3 but the negative of battery 2 and the positive of battery 3 are jumpered together in the 36V string.

So of course I can just continue charging the batteries this way by just bringing the chargers with me to the golf course and connecting them this way (3 chargers connected to 3 subbanks simultaneously), however I was wondering what might happen if instead of connecting them as previous described, what might happen if I series connect the chargers into one 36V charger and then charge the golf cart bank with only 2 connection points?  Assuming it will even work, would there be any advantage to doing that?  To me it seems like a recipe for problems.  Would it suffice just to preset the chargers in the same mode and then fire them all up simultaneously?  For example, set them all to 12A AGM mode.


texts: What's the name of this nice spring contact?

texts:
Ah, it is really a beauty isn't it (see picture below)? Around the package you see some spring contacts, really, really nice. I have some ESP8266MOD modules and like to use these spring contacts before soldering anything on the pins.

What is/are the name of this/these contact(s)?

Update 04/12/2018:

@bitsmack came up with the idea that these springs could be test-loops and search on it and found this picture:

He could be right!


texts: Difference between current transformers and power transformers

texts:
In a current transformer, the primary current causes a magnetic field in the core, which in turn generates a current in the secondary. Fine.

How come then that a power transformer outputs a voltage, and not a current? Isn't it the same principle?


texts: Help for VR sensor signal conditioning (variable reluctance signal conditioning)

texts:
im trying create a CDI/TCI unit for my Suzuki Bandit GSF400. i need some help for VR sensor signal conditioning section.

this is the disc that generate the pulse signal.

i have found this image from Megasquirt Support Forum. and actually this is the same signal that generate in my bike also.

the first signal is the processed signal, and the second one is generated by the VR sensor.

i need a help to create a circuit to process the VR sensor signal to the above signal.

i believe this processing is not done by using zero crossing detector circuit, because the signal disc teeth sizes are efferent.


texts: How is current flowing through this P-Channel Mosfet?

texts:
I am probably being stupid and should probably go to bed but how is current flowing in this circuit below?

From my understanding, a P-Channel Mosfet allows current to flow when its gate terminal is at a lower potential than its source terminal. Of course a certain threshold must be met to fully "turn on" the channel but regardless. What I don't understand with this circuit is how the capacitor is able to charge. As can be seen from the graphs, the VGS starts at 0V. VGS = 0V means that the gate and source are at the same potential, thus from the earlier criterion, current should not flow. However, it does flow and charges the capacitor to the source voltage. Wtf is going on here?


texts: Ideal voltage source connected with ideal Inductor

texts:
We have an ideal inductor with the dc source in figure A.

When switch is closed we get equal and opposite voltage across the inductor against the source voltage and a constant rate of rise of current given by di/dt = V/L. This constant rate of rise/change in current will also produce the rising magnetic field (shown in green colour).

Suppose some how we reverse the battery instantly, shown in figure B. That reversed battery will cause the reversed rise of current (shown in figure B in brown colour). But at the same time the magnetic field (which was caused by the current when battery was not reversed) is collapsing and is inducing the voltage and current opposite to the reversed current.

My question is will there be no reversed current flowing as long as the magnetic field is collapsing as that collapsing magnetic field is causing the current in the opposite direction of the reversed current.

Plus there will also be electric and magnetic field produced by the reversed voltage.

How will these two collapsing and rising magnetic field are going to interact with each other ?


texts: Noise margin calculation for schmitt and non-schmitt input signals

texts:
The noise margin is defined as:

Noise Margin High = VOH - VIH

Noise Margin Low =  VIL   - VOL

Is the noise margin calculated the same way for schmitt and non-schmitt buffers? If so then why?

This question is within context of input output buffers of ASICs.


texts: How do I know the input current of a LED driver?

texts:
I want to driver 3 power LEDs and depending on the solution I choose I find something strange.

If I have this situation :

I want 330 mA flowing in my LEDs. I choose a 10 V DC-DC converter. The forward voltage of the LEDs is 3 V. I set the current through the resistor with the remaining 1 V by choosing R = 3 ohms.
330 mA under 10 V equals to 275 mA under 12 V, so the input current of the DC-DC converter is 275 mA. So far so good.

Now let's consider this situation, where I use this LED driver : http://www.ti.com/lit/ds/symlink/tl4242-q1.pdf
and choose its resistor so that it outputs a constant 330 mA :

I want to know the input current of the DC-DC converter. To do so I need to know the output current of the DC-DC, which is the input current of the LED driver.
In the datasheet they say the LED driver consumes around 12 mA when its output voltage is 6.6 V. First : How does this value change when the output voltage changes ? Why don't they give that information ?
Finally if the output current of the DC-DC converter is 12 mA, then the input current of the DC-DC converter is 10 mA.

In the first situation the system draws 275 mA, in the second situation is draws 10 mA.

Is there something I am doing wrong ?

Thanks.


texts:
So I just started tinkering with circuits online using circuits.io

First I made this circuit using 1.5v battery to power two LEDs which was insufficient and wouldn't glow.

Then I removed and added a 9v battery without a resistor which was over-sufficient for the LEDs.

Lastly, I added both of them (9v+1.5v) and that seems to power the LEDs sufficiently

I thought that in the last case they both would be overkill for the LEDs but that didn't happen. Don't the voltages get coupled when supplied in series?

*Doing something like this practically is a bad idea but I wanted to know theoretically so experimented this.

Edit : The much preffered schematic


texts: GUI for writing HDL and viewing simulation?

texts:
I am a software developer and I'd like to code for FPGAs. Prior to buying an FPGA I thought it might be better to obtain a simulator where I could practice my HDL and see whether I can get the hang of it all.

What would be the best GUI for writing VHDL and being able to see what the code would actually do if it were flashed to an FPGA?

If the simulator could allow me to drag & drop common library components that would be great.

Any other advice regarding this is most-welcome.


texts: Looking for component/s to split 24v to all of 12v, 5v, 3.3v

texts:
I'm still learning and messing with electrical engineering so please keep answers easy to understand.

I'm looking for a component or set of components that I can use to split a 24v power line into multiple power lines at 12v, 5v & 3v. also what these components called. are they just called dc-dc-converters?


texts: sensing current noninvasively using hall effect sensors

texts:
I am trying to sense if DC current increases in a wire when the load changes. I do not care about the value of the current, I only want to know if it increases (motor at idle vs motor running). I cannot modify the wiring of this motor, so I need to do it noninvasively.
I purchased a few analog hall-effect chips, hoping that if the chip was against the wire it would detect the change in magnetic field, but perhaps I need to brush up on my physics! I am seeing no change whatsoever when measuring the output when the chip is taped to the wire. I tried multiple orientations of the chip, as I know they are sensitive to poles, still nothing.
As a sanity check, I used an actual magnet, and the chip responds as I would expect.
I am using these (from digikey):
part number: Texas Instruments DRV5053VAQLPG
TI Chip
Can someone tell me if I am close here, or lead me in the right direction? Thanks in advance!


texts: When is it appropriate to mount components at a 45 degree angle?

texts: I've seen some PCB's with components mounted at multiples of 45 degrees (45, 135, etc.) I recently discovered my PCB program (gEDA PCB) supports these, though it isn't a GUI function and you have to run a command. When is it appropriate to mount at these angles? And what about angles of 30 degrees and 60 degrees, or arbitrary angles?


texts:
simulate this circuit – Schematic created using CircuitLab

I'm having an analog project where I have to amplify a weak signal coming out of a photo transistor. I used LM741CN OpAmp for this and found out that nothing comes out as the output when connected to a RS232. So I tried creating a basic inverting amplifier using this IC and the oscilloscope showed the same input signal like waveform as the output signal. I tried with another LM741CN IC and it gave the same result. Addition to that, the IC seems to be heating up a lot. Then I tried a non inverting amplifier but that didn't work too. Same input signal as the output. I tried 4 other 741CN ICs I bought from the shop the same day and all not working. (I assumed that it's not possible for 6 chips to be burnt like that) One of my friends had a LM741CP IC and I plugged into the same proto board with the same pin configuration and it worked.

So my question is are these LM741CN and LM741CP different? Do these last letters N and P mean anything like p type or n type?

EDIT: Here I've added the circuit diagram I used to create the inverting amplifier. The project description was to create a background. My problem is about the difference between LM741CN and LM741CP. Since I couldn't make the circuit with 6 741CN ICs, I used LM386 and it worked. Was just wondering why CN didn't work when CP did.


texts:
I want to use the following MAX3485 chip: https://datasheet.lcsc.com/szlcsc/2006181334_UMW-Youtai-Semiconductor-Co-Ltd-MAX3485ESA_C668204.pdf
I do not speak any chinese, but my question is more in a general sense: does an MAX3485 chip need additional pull-up and pull-down resistors for lines A and B?
This and some other datasheets have figures about the topology where there are no pull-up and pull-down resistors. But at the end of this datasheet, and I have also seen that on the internet when I was searching for this, line A is pulled to VCC with a 10k resistor and B is pulled to ground with a 10k resistor (the 10k I have seen in the internet not in the datasheet).
What is the purpose of those resistors and when are they necessary?


texts:
I have an Arduino Uno and I'm trying to use it to provide data for 1200 WS2812B leds. When I tried to provide data for them, the Arduino IDE says "Sketch uses 5086 bytes (15%) of program storage space. Maximum is 32256 bytes.
Global variables use 1952 bytes (95%) of dynamic memory, leaving 96 bytes for local variables. Maximum is 2048 bytes.
Low memory available, stability problems may occur."

What does dynamic memory mean and how do I make more space for it. Also, I'm going to eventually switch the Arduino with a Raspberry Pi for wireless control of the leds. Will the Raspberry Pi have more dynamic memory?


texts:
I'm doing an FPGA design using a T2080 MPC interfacing to an Altera Cyclone V FPGA. The goal is to use my FPGA to pump 2 other FPGAs on the same board.

I need to create a scheme that allows the Cyclone FPGA to pull data from an address in the processor memory using DMA. I know that the PCIe interface between the 2 devices works. I can read and write registers inside the FPGA via the T2080.

I've also created some control/data registers inside the FPGA that will house the address of the data on the MPC and some other info.

Is there a reference design that someone could point me to that shows how to set up this transaction using VHDL? I'm a novice but I can figure things out if I have a good example to follow. Or if anyone has attempted this, please feel free to comment.


texts: Method to realize any function with 2 input NAND/NOR gate

texts:
I'm preparing for a competitive exam where often these type of questions are asked

Find the minimum number of 2 input NAND gates required to implement the function F(A, B, C, D) = AB + ACD + BC’ where literals and their complements are available

And I often end up with a non minimal realization. Though I think there can be some pattern behind such type of questions.
Is there a method to implement any given function with only 2[or n] input NAND gate?


texts: PCM270xC USB audio DAC, power modes and THD

texts:
I am designing a USB DAC for headphone use, and planing to use a TI PCM270xC IC.
There are two power modes: (USB) bus powered, and self powered.
What I'm trying to understand is how does the power choice influence the THD characteristics.
This is the info provided on the datasheet:

Does this mean that the THD is always lower when Self-Powered? If so why is the displayed RL value lower?
Thanks


texts: Trying to program an FPGA. (Altera Cyclone II)

texts:
I have got FPGA development board (Cyclone II EP2C20F484C7) and am trying to implement a simple counter program as shown below (and maybe link it to the LEDs).

module counter (clk, reset, enable, count);
input clk, reset, enable;
output [3:0] count;
reg [3:0] count;

always @ (posedge clk)
if (reset == 1'b1) begin
  count <= 0;
end else if ( enable == 1'b1) begin
  count <= count + 1'b1;
end

endmodule

I have simulated it on ModelSim and it works fine but complied and Synthesized it using Quatrus II for some reason the FPGA board isnt detected when I try to program it.

Any suggestions on changes I might have to make in the code above inorder to get the required output? Or is there something i am doing wrong here?


texts: Magnetic field of a coil composed of stacked coils

texts: Basically my question is that if you have a coil with N turns with its ends connected to a source of current (I), and you have another coil which is N number of single coils stacked on each other with the same current (I) passing through each of the coils, is the magnetic field strength inside both of the coils essentially the same?  This is assuming that everything else besides this factor is the same.


texts: Splitting a bidirectional bus into two unidirectional ones

texts:
I am trying to sniff on a custom SPI-like bus protocol, which uses a unified bidirectional data line instead of separate MISO/MOSI. To make sense of the communication, I need to split it up into unidirectional lines before feeding them to my logic analyzer. Otherwise I wouldn't be able to see which device is responsible for which part of the signal. Since my devices won't talk to each other unless the protocol is carried out correctly, it's obvious that the bus splitting device has to be transparent to the actual agents communicating.

I tried to construct a bus splitting device, but failed as described here. Since this question was maybe too specific and has not been answered, I want to ask more generally: Is there a bidirectional bus splitter that is able to split 3-wire SPI into four wire SPI? Where could I buy such a device? (This seems similar to this question, only that I'm not talking about two really different protocols, so the answer does not apply). In principle only getting one direction would also suffice, since I could just subtract it from the full signal in order to retrieve the other half. And I'm also only interested in the master side of the communication.

The NXP P82B96 Dual Directional Bus Buffer seems to be a good candidate. Although it's advertised for use with I2C, it seems to be agnostic to the actual protocol on the lines. (As it does not even differentiate between DATA and CLOCK line for I2C.)

  Splits I2C-bus signal into pairs of forward/reverse Tx/Rx, Ty/Ry signals for interface with opto-electrical isolators and similar devices that need unidirectional input and output signal paths.

As my devices operate on SPI mode 3 (polarity 1, idling on HIGH), the implementation of the receive pin should work:

  sense the voltage state of the I2C-bus pin Sx (or Sy) and transmit this state to the pinTx (Ty respectively), and
  sense the state of the pin Rx (Ry) and pull the I2C-bus pin LOW whenever Rx (Ry) is LOW.

But I am still puzzled on how this would actually work in sniffing this bidirectional bus. I could connect one device with the I2C line and grab its MOSI at Tx and MISO at Rx, but I would eventually have to connect both lines before feeding it to the other device, therefore making it impossible to separate the signals at my logic analyzer again. How can I connect the Tx/Rx for the slave while still being able to read them separately with a third device?

Edit: I now think this is actually not helping at all, since it leaves me with the same splitting issue as with out the device. I already have separate master and slave lines, I just don't know how to join them while still retrieving the separate directions.

I also stumbled upon the Bus Pirate. It seems like this is a device designed for sniffing on buses, but I don't think it can help me in my case. Is there a mode where I can use it as a bridge on a bidirectional line and grab unidirectional signals off of it simultaneously?

Edit: I found this Texas Instruments document on I2C isolation which seems related to the issue. This does supposedly split the bidirectional line to feed it to two unidirectional isolators. The question is: Does this work for my setup? It describes the I2C lines being open-drain, whereas my lines are open-collector and also I'm not entirely sure if I could just leave out the isolator part and grab the signals from the lines or if these would have to be also hooked up to some transistor or be pulled high.


texts:
I have a PIC18F27K40 and would like to use the hardware SPI module. Of course, it would not take too much code to write a SPI library myself, but if it exists already I prefer to not reinvent the wheel.

Before, I always used the legacy peripheral libraries (plib), but they haven't been updated for a long time, and pconfig.h does not contain the required #defines for my chip.

Is then the only way now to use the MPLAB Code Configurator? I don't have MPLAB installed and it seems a large overhead if it's only to generate some peripheral libraries. Is there no other way?


texts:
How to solve the above question?

I cannot apply Kirchoff's current equation because of the presence of the dependent voltage source

Also, I am not able to apply supernode because of the 2 kOhm resistor in series. How should I go about it? Please help.


texts:
I met this kind of snubber network in Switchmode Power Supply Handbook (by Keith Billings and Taylor Morey):

They were using it with BJTs, and the reason was to limit dv/dt to avoid secondary breakdown of the BJT. Now if I'm using MOSFET in a Flyback converter, is this snubber needed (I have clamp in the circuit)? As far as I know, MOSFETs do not have secondary breakdown, and with proper clamp circuit they can withstand the voltages.


texts: Using a published Watt-hour power curve for AA batteries, I get a theoretical battery life that's way lower than in practice

texts:
I'm doing something wrong mathematically. Can anyone spot my mistake?

I'm powering some laser sensors and an arduino with 8 AA batteries and a step-up box for the lasers. I calculated a theoretical battery life using some empirical Watt-hour findings for my batteries here: http://rightbattery.com/57-1-5v-aa-duracell-procell-alkaline-battery-tests/

Both I and the source website used a cutoff point of 1V per cell. My cutoff point was 8V.

I first used their Wh values and plotted them out as in the attached image. Then I found an exponential approximation, input a measured current draw, and got an answer for my theoretical Wh (see bottom right of image under "Dual laser test setup (no LCD, Xbee)".

Then I divided the Wh by Watts, which is the measured system voltage times the measured current and got 0.169 hours which is 10 minutes. I ran a test though, and it took 85 minutes to reach 8V, starting from 11.7 with 8 batteries. There seems to be some discrepancy.

The batteries lasted 8 times longer than predicted! But I was under the impression that for batteries in series, you don't add the mAh, since the current through each battery is the same, as described here:  Adding mAh when wiring battery cells in series?

So what gives?


texts: Why am I not dead after repeatedly touching a high-voltage source?

texts:
While playing with mosquito racket in my home, I unscrewed the racket and touched the 2 wires with my hands. I felt that my bones were dislocated, I got shocked, but I am not dead.

My calculations say that I should die:

the output voltage is 5 kV to 10 kV, my body resistance is approx. 50 kΩ, the current through my body is 0.1 A if 5 kV to 0.2 A if 10 kV.

According to the table at https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html I should die; I tried this many times but I am still alive.

I think my interpretation regarding current, voltage and my body resistance is wrong (if right I would be dead by now) - please tell me why I am not dead?


texts: How to Connect an External Signal to Digi-Key SmartFusion2 M2S010-MKR-KIT?

texts:
I am currently trying to configure my board to take an external square wave from a function generator, measure the time interval between rising and falling edges, then output the measurement on screen.
I am not sure how to add external signals to the board or how to monitor the output measurement. I've attached a picture of the board from Microsemi's website.

I am quite new to FPGA programming and all I have done with this board so far is simulate basic counters, filp-flops and blinked an LED on the board.
Thanks for the help!


texts:
I am using an ADS1115 as an analog to digital converter.
R2 and C2 are used as a low pass filter.  I have used two schottky diodes as voltage clippers to protect against over voltage. To avoid floating condition I have put a pull down resistor of 10K(R6.) I have modelled a resistive voltage sensor as a voltage divider.  I have used a 100K resistor to model the input impedance of the ADC .
The issue is because of the pull down resistor I am getting wrong analog voltage readings.
Any suggestions for modifications in circuit so that I can read proper analog values?


texts: Limiting output amperage on an arc furnace

texts: we have built an electrical arc furnace from a couple of old arc welders. We are outputting around 200 A at 30 volts. However, sometimes it will decide to draw more amps than what our 400 A rectifier can handle (which converts the AC output into DC for a more efficient arc). Is there a circuit or a device that would control the output so that it won't go above 200 A but maintain roughly the same voltage?


texts:
I am experimenting with an Intel Edison mini breakout board with pinout like here: http://fab-lab.eu/wp-content/uploads/2014/10/Edison_IO_LED.jpg

Now, I soldered header pins to plug the board into a breadboard. Unfortunately, the GPIO levels are only 1.8V.

What should I do to make a LED blink from here (on a breadboard ideally)?
What else can be done with 1.8V GPIO levels?

UPDATE: It works with a BC547

However, depending on the blink frequency, it seems that LED does not turn ON completely. Might it be because the base resistor is 0 ?


texts: Short Circuit Protection of High speed Data lines

texts:
I need to protection data lines of a PIC32 micro-controller (SPI and parallel) running at ~10 MHz, from shorting to ground/Vcc or mis-wiring.

I usually (in low speeds) use series resistors to limit current and it worked well, but of course this does not work now because of the speed.

I am thinking to use line buffer/inverter (something like 74LVC04) this will save the MCU but the buffer will get damaged.

I searched many logic families (ACT , HCT , LVC etc..), but none provide short circuit protection.

I there a better solution?

Edit After Comments: This is a development board for testing and validation, due to coding mistakes pins can be configured incorrectly . or mis-wired , connecting MCU output to target output instead of input.

Edit #2: A PTC (0603L004) might be a solution however it is slow !


texts:
I have read that the max input voltage for this IC is -7V and max output voltage is -15.6V. According to it's name, the output voltage should be max -5V.

I read this here.

But for 7805 IC, the max output voltage is +5V and input voltage is max 35V.
I don't understand why is there so much difference in voltages for both the ICs.

Also, if the max voltage for 7905 is -7V, can we get output if we supply 0V to it?


texts: Why does power go both to and from a power station?

texts:
It is common practice that wires in power lines send power both to and from a power station.  Suppose that, instead of forming a closed circuit between a substation and a consumer, both the substation and the consumer keep one end of the circuit grounded (see schematic).  The circuit should still operate as usual, or no?

In other words, why is it necessary that power lines be two-way?  Is it ever possible to use the ground to "complete" a circuit, either in AC or DC cases?

simulate this circuit – Schematic created using CircuitLab