texts: Are DC link capacitors suitable for use with AC?

texts: In looking for high-value (33uF) film capacitors for use with AC, I've come across a number of "DC link" capacitors. Can they be used with AC assuming their DC voltage rating exceeds the AC RMS and/or P-P?


texts: Why do I get these odd foot prints from JLCPCB - 0602 and 1206

texts:
Why do I get these foot prints from JLCPCB?
The parts are regular 0602 and 1206 and capacitors.
I'm using KiCad 5.1.7. No external libraries. Everything is default.

My GerbView:


texts: Why is my body the path of least resistance during a shock?

texts:
I must say that electricity is hard to grasp conceptually. Just when it makes sense, you think hard about it and it all becomes confusing.

When someone says electricity takes the path of least resistance, it never made much sense. Consider you have a light bulb and one of the wires connecting to it is bare and the bulb is on. If I touch the bare wire, I will get a shock and it will travel through my body to the ground. I can understand this if I cut the bare wire and connected myself in series with the bulb. There is no where for the electricity to go. But when I touch the wire, I am in parallel with the bulb. The bare wire has less resistance so shouldn't the electricity bypass my body and go straight to the ground terminal? There's less resistance to get there as opposed to going through my body which is very resistant.

What is so special about ground (the floor) that electricity goes to it. How can it possibly complete the circuit?


texts: Any equivalent load circuit when an animal is connected to a current injector?

texts:
When the human body (chest, arm, etc) or an animal (limbs, belly, tail, etc) is connected to a circuit, I think this acts as a load.

For instance, people simply model the connection between the AED (automated external defibrillator) and the human like this.

Are there models to simply a human or an animal (mice, for instance) as a circuit?
Like the dry human skin mostly acts as a resistor with a parallel pF capacitor.


texts: How do I find open circuit voltage in this circuit?

texts: I need to find IR4 along with UR4 using Thévenin's theorem. That means I need to remove resistor R4 and find open circuit voltage. I tried to simplify the circuit by using the fact that on U is formed voltage divider, but I don't know how to proceed next. Could you show me any efficient method how to find Ui?


texts: Senseo & Raspberry PI soldering circuit board

texts:
I am kinda new to the whole hardware stuff and as an amateur I am working on a little project. I would like to connect my senseo machine to my Raspberry Pi. I've got a senseo HD7810 and a Raspberry Pi 2B.

I've found an online tutorial, but unfortunatly the tutorial is written for another senseo machine. Now I am kinda lost on wich places I should solder the wires.

I've attached a picture of my circuit board. The most left red button is the button for 1 cup of coffee. The middle button is the power switch and the most right button is the 2 cups button.

I'm not quitte sure if I am allowed to post a link directly to the tutorial, so I will just type the instructions:

"Solder your wires to the points on the Senseo board like shown above. As you can see all the white wires are wired to the "bridge" on top of the board. This is the ground and we'll be extending it to the ground of the Pi.

The coloured wires are connected to the other end or positive side of each I/O element. In my case black is soldered to the LED, orange is soldered to the "1-cup" button, red is soldered to the on-off button en green is soldered to the "2-cups" button. Don't wory about the colours, but you should remember or mark down which wires you use for the different I/O elements."

The circuit board used in the tutorial:


texts:
I am planning to build a project around https://www.sparkfun.com/products/12650 to take an ECG while I am on a roller-coaster (not for medical purposes, just for fun).
The following points are (additional) requirements:

To capture the data, I need to write them onto an SD card or some other memory device.
The device should support wifi so I can have a live feed on my mobile phone. So one possibility would be an ESP 32 or ESP 8266.
Another great addition would be an acceleration sensor......
Because this should be useable on a roller-coaster, a power bank for mobile phones (except for very small ones) and a stationary power source are both not useable. The power source (maybe a battery?) should last about 12 hours. If this is possible with a small power bank, I will use one of these, because I can ignore the protections against discharging and such problems completely. So that decision depends on the energy consumption of the build and the possibility to use an USB cable for connecting the two.
The whole device can not take up a lot of space (it should fit below my shirt or so, to not fly around freely, I will 3D print a casing).

I experimented with ESP and raspberry pi before, so I know how to program and connect additional devices to them, but I never tried to build a "portable" device at all (only built stationary so far) and never used something from SparkFun's "ecosystem" before.
To come to a conclusion, it would be great, if you can help me finding the right parts for that project. If you have a better ECG solution, I am not bound to this item linked at the top.
I am waiting for your answers and hoping, that you can help me


texts: Impedance matching resistors for digital output

texts:
My circuit has to emit an S/PDIF digital audio stream over an RCA connector. According to the specs (from Wikipedia) the signal should have an output impedance of 75Ω and a peak-peak voltage of 0.5V.
I've found a schematic for a TTL to COAX converter:

but it's meant to work with 5V digital output, while my device (MAX II CPLD) works at 3.3V. So I'm trying to adapt this schematic for 3.3V by changing the resistor values.
As far as I understand the base circuit, including the input device, should look like this:

simulate this circuit – Schematic created using CircuitLab
I have to compute Rx and Ry so that I can properly set up a voltage divider from 3.3 to 0.5V, and make a current of (0.5V / 75Ω =) 6.67mA flow from my device to the load. But I'm struggling in setting up the system of equations.
So far I came up with this one for the voltage dividing:
$${1 \over {{1 \over R_y} + {1 \over 75}}} = 0.18R_x$$
And this one for the currents:
$${3.3 \over {R_x + {75R_y \over R_y + 75}}} = {{0.5 \over R_y} + 6.67mA}$$
But when "developing" them they become really long. So I'm not sure if the approach is actually right or if I just did some steps wrong.
I'd also like to know the total current, to check if it's below the maximum source current of the CPLD.


texts: How to model MOSFET as a switch on LTSpice

texts: I am trying to use MOSFET as a switch on my circuit. I hope someone can help me model it!


texts: Auto Voltage Selection between 12V and 5V for Irrigation Controller

texts:
Background
I am working on a hobby project, it will be a general purpose open source irrigation controller.
I haven't built the PCB yet but I want to power the board either through the USB port for small valves and through 12V to 24V for larger ones. Here is a block diagram of what I have in mind.

I am sharing the whole power section of the PCB so that the reader gets a better idea of the system.

To select between these voltages I thought of using a circuit I usually use to select between VBUS and a single cell Lion/Lipo battery. The spice simulation gives an acceptable result as seen below. The green line is the voltage at Source of the PMOS and the blue line at the Drain.

Question
However I am unsure if this is the "good" way of doing it, since VCC will also power the valves . Which are inductive loads. I will be using the circuit below to drive the Valves albeit with different components. I don't have any previous experience designing motor drivers.

I would very much appreciate it if you could point out any errors I may have in my line of thinking.


texts: LTSpice AC Simulation giving unexpected output

texts:
I am currently working through AoE, 3rd Ed., and am on Exercise 3.7 (pg. 180). I am trying to find the -3dB point of the circuit pictured, and I am using LTSpice to check my answer.

LTSpice says the -3dB cutoff is ~882kHz. This does not agree with the answer I got on paper, which is ~398kHz. Can anyone point me in the right direction?
For reference, my quick math is:

Z(C2||R2 @ 398kHz) = ~24.2k
Voltage divider with Rser, V(out)/V(in) = 24.2k/34.2k =~ 0.7079 = -3dB


texts: Question about ESD wristband and lightning

texts:
as far as I know all ESD wristband's ground connection has an 1M ohm resistor built in for safety. So what would happen if I am working on lab wearing ESD wristband which is connected to the home electrical earth and at that moment lightning strikes nearby or on electrical earth line? Will I get hurt? Or will it be safe because of that 1M Resistor?
Thanks.


texts: I would like to use my homemade battery charger, rated 15VDC 7A, to charge a 25Ah lead acid battery. Would there be an easy way to limit the charging current to 2.5A (Ah/10)?


texts: Will this attempt at building a four transistor multiplexer work?

texts:
Ordinarily I think most people would build a multiplexer out of a NOT gate, two AND gates, and an OR gate, which would involve seven transistors, wouldn't it? I want to see if I can do a multiplexer with just four transistors. I've got three bit inputs, A, B, and Ua; and one bit output Out. I want Out to take the value of A if Ua is high, and I want Out to take the value of B if Ua is low.

I don't know how to create an image of a circuit diagram, so I'm going to have to just explain it. In addition to the three input bits and the one output bit mentioned, I have one input bit Vcc, which is a high voltage, and output bit Gnd, which is just ground, three transistors, Toa, Tob, Taa, and Tab, and a resistor Res. All transistors are the type where the base activates them if it is high except Tab; Tab's base activates that transistor when it is low.

I connect Vcc to both the collector of Toa and the collector of Tob. I connect A to the collector of Taa. I connect B to the collector of Tab. I connect Ua to both the base of Taa and the base of Tab. I connect the emitter of Taa to the base of Toa. I connect the emitter of Tab to the base of Tob. Then, I connect together the emitter of Toa, the emitter of Tob, the resister Res, and Out. Finally, I connect Res to Gnd.

If anyone cares to make a circuit diagram of this, that would be much appreciated. I have a diagram drawn in Notepad right here, but I suspect that if I tried to copy that into my article for posting it would get garbled.

All that said, would this work? I realize that the outputs of Taa and Tab (which are the emitters of those two transistors) are not getting amplified, but the output of the OR gate (made up of transistors Toa and Tob) is getting amplified, isn't it? So isn't that okay? If anybody has any input on this description, I would really like to hear it.


texts: Taking this as an example - if a strand of hair gets in say in cpu socket of a PC or any other slot of device, what would be the consequences, rather the symptoms if the hair gets in between those pins:


texts: stretching ns analog pulses for digital conversion

texts:
Problem statement

in one of my design i need to stretch narrow 10 ns pulses coming from photo diode after TIA stage, if i have to measure the pulse amplitude i have to stretch it at least by a factor of 100, in this search i have found a approach in which the circuit was using a capacitor after its feedback path, but i have not understood how exactly the circuit works, but when i tried to replicate it, no pulse stretch was happening, here below is the circuit and kindly suggest few modifications to the circuit or suggest an approach for the analog pulse stretch

circuit

Opamp is a high slewrate 3000V/us and high BW of  100M as BW = 0.35/risetime and slewrate = 2* pi * BW * Vpp, so for my 10ns input the opamp would do the job.

pulse output is just zero !

EDIT1:
primarily i forgot to mention that my 10ns pulses will repeat at a rate of 1Hz-50Khz, so just after some small modifications, i came with below circuit where i increased the gain and obtained pretty decent results, kindly provide your valuable comments

Results

PS: i was using TINA from TI as simulator in above case


texts: How to add holes in package and create elongated plated holes EAGLE

texts: I need to create this package on EAGLE but I've problems with this elongated plated holes on sides. How I can do that?


texts: Setting up the "Basic Bipolar Output Operation" connection on a DAC08 chip

texts:
I have an 8-bit waveform description coming from an FPGA into the DAC, and I want to read the analog output on an oscilloscope. I figured I should implement this setup found in page 11 of the data sheet, but I am not sure how to do so.

What I am uncertain about is the 10V between the two 10k resistors. Is it just that the node voltage will always be 10V? Or should a 10V source be connected there?


texts: Multi-layer Via-in-pad with 0.5mm Pitch BGA in KiCad

texts:
I am working on a 4 layer board with an 81 pin 0.5mm pitch BGA which effectively requires via-in-pad for dropping down to other layers. Decoupling must be done on the bottom as there is no space for components on same side as the BGA for several of the VDD/GND pairs.
The pad diameter specified for the BGA package is 0.23mm (0.05 around pad, NSMD) so ideally the via should have a 0.23mm annular ring to perfectly match the pad and should be filled/capped to effectively replace the pad of the footprint to prevent wicking the solder from the balls.
An example of the required interconnect in my stack up for decoupling of power pairs is illustrated here:
BGA__________VDD__________GND________
            (   )        (   )
TOP -------  | |  ------  | |  ------
GROUND ----  | |  --------| |--------
3V3 ---------| |--------  | |  ------
BOTTOM ----  | |  ------  | |  ------
             [ ]___CAP____[ ]

In general what would be the cheapest/best option for achieving this at the required sizes?
For KiCad specifically, how can I represent this in Pcbnew so that I can generate files for fabrication?
Research leads me to believe that drill size limitations make stacked microvias seem like the best choice but this doesn't appear to be an option (DRC gives "Micro Via: incorrect layer pairs (not adjacent)"). Should I be using "blind" vias that go from top to bottom?


texts:
There are numerous MCU platforms and once somebody has gotten used to one, they are generally reluctant to switch to another platform.

My question is: If one started using a MCU for general purpose tasks today, how would one go about choosing one? What are the unique selling points of the different platforms?


texts:
I have a general question about reference clocks for ethernet PHYs.

The PHYs I have seen so far require an external clock source like a xtal or other singleended clock (in addition to the clk lines used by the data transmission protocols).
I assume that this reference is used for the external communication lines and internal computations.

Now I have seen some different implementations of the clock of which some are just free running generators or XTALs and others are synchronous with the internal MCU clock. And also i saw an application note which describes a pair of PHYs using the same clock which is recovered from the network using a LMK05318.

Its clear that for any serious communication, synchronization is needed. But in which way is the PHYs external reference involved, since free running clocks also work and therefore why do some applications need a synchronous clock between multiple PHYs or the MCU (the MII already has its own clk)?

My current assumption is that using a reference from the MCU is just because its already there. And sync between multiple PHYs or over network is needed for very time precision critical applications to which a free running impl could not sync itself precisely enough to.

I hope my question is clear enough. Thanks in advance


texts: Looking for some references for embedded telecom board

texts:
I am involved with an embedded software development for telecom industry. I have zero experience before with such embedded hardware devices.

I got a network processor board, which is featured in switching pipeline engines. Besides the board, there is also an accessory board called "piggy" (seems for ethernet connetion), and another serial line connection.

I am completely lost about these boards and serial line connections. what they are used for? I tried to use google to find some useful introduction or materials but failed. Can anyone point out what this piggy board is used for? Any good references or books that explain about this?


texts:
This is the vhdl code and it need more, can you help me?
library IEEE;
use IEEE.std_logic_1164.all;
entity divider is
 port( s, clk, reset: in std_logic;
 input1, input2 : in std_logic_vector (7 downto 0);
 quotient, reminder : out std_logic_vector(7 downto 0));
end divider;
architecture behavior of divider is
signal a :  std_logic_vector (7 downto 0);
signal b :  std_logic_vector (7 downto 0);
signal r :  std_logic_vector (7 downto 0);
signal q :  std_logic_vector (7 downto 0);
signal c :  integer range 0 to 7;
begin


texts: In a ideal transformer we assumed that there is no resistance in windings.   Then why there is no infinite current in windings?


texts: How to start reverse engineering a circuit?

texts:
I have an old controller card from a pc which had to control some stepper engines. But there are several problems with it:

The pc isn't working anymore, and I have no access to the program which controlled the card because of a hard disk failure;
I have no manuals at the moment for the devices which has been controlled, because it is custom made.

But after the circuit consists only of 8 ICs and 6 capacitors and every wire on the pcb is shown clearly, I want to try to reverse-engineer the card, because we want to use the controlled devices again.

Thus, my idea how to solve the problem is:

Use eagle to draw the board and the devices;
Simulate it;
Try to figure out what happens if I play around with the input.

Is this a useful approach? If no, what can I do else?

Problem with this is that there are two programmable ICs on this board (P8255A), and I do not have the internal programming. Thus my second question is: Is there a possibility to get the programming of these ICs out?

Edit: What I may have not completely stated is that I am not able to simply get the datasheet for the stepper motors, there is still a controller between the stepper motors and my card, and all the stepper motors are built into a spectrometer where I have no access to...

Edit 2: Some Images:
Front:

Back:


texts:
Why higher frequency processors use more power?

A higher frequency processor would solve the task in less time, thus increasing idle time and thus reducing power consumption.

This would compensate the fact that it uses more power.

What's wrong in my reasoning?


texts: Effect of bias resistor value on common-mode rejection in a differential or instrumentation amplifier

texts:
In the below schematics a source is coupled to a differential amplifier.

Rb is a bias resistor for bias currents to flow:

Since in instrumentation amplifiers it is a remedy to add resistors for bias currents to find a return path(See the middle in this link.).

So basically I wanted to see the effect of this resistor value on common mode voltage rejection in a simulation. So I simulated the above schematics in LTspice for Rb = 1 Ohm and Rb = 47k resistors. Source is a 50mV DC and the common mode voltage is 50Hz interference.  Here are the results for Vo1-Vo2:

For Rb = 1 Ohm:

For Rb = 47k 0hm:

As you see above in Rb = 1 Ohm case the distortion/common mode is rejected much more than in Rb = 47k case.

On the other hand the manufacturers recommend 10k to 100k resistor for Rb. I couldn't get the logic behind if it is causing more distortion why wouldn't we just ground the negative side or use a very low resistance? And what makes 10k very recommended?


texts: Software based Caller ID project- Problem with getting caller ID signal

texts:
Nowadays, I am trying to make a Caller ID project without using Caller ID ICs. Firstly, I have done a lot of research in Google to get information of phone lines and their electrical properties.

I have found and done:

In my country Caller ID data is FSK modulated. And the name of the
standard is Bell 202. In this standard there are two different
frequency which are 1200 and 2200. As you know these frequecies are
using to digitalize the data(1 and 0).
Secondly, I write a C# program that demodulates any arbitrary FSK
modulated signal. This program uses the Goertzel Algorithm and it
fits like a glove for DTMF decoding and FSK demodulation. Basically,
its output gives you the dominant frequecy in your reference
frequecies(1200 and 2200 in our case) for your input signal.

Here are some screenshots from code and output result.

Input:

Output:

I will add the running code here later. The file link I have added the end of the page may not seen a non-dangerous file for some people like me:)

I think the first part of project done. But the real problem comes with second part for me. I do not have enough practical electronic skills and measurement tools(ossiloscope, common components etc.) to get phone line signal into computer. I look google and see that phone line has very high voltage -48Vrms to -52Vrms. I want to make a circuit that get the digitalized phone line signal to send it to the computer in the place of my arbitrary input. I found some application notes in Caller ID ICs datasheets and there are some circuitry and I think some of them is very appropriate for me. In this point I need to get some assistance to realize this circuit and project.

Here are some circuit that I think it is proper for my project.

What is the output of the circuit in the red rectangle? Is it an appropriate signal for an MCU like Arduino or a for a PC?

What about that circuit? According to this paper. RX signal is 1.2V DC biased and 400mv p-p signal and it propably carries our data we want, right?

PS:I am adding the link of the code and screenshots for people intersted in.

http://www.filedropper.com/goertzelalgorithm


texts: What is the lowest capacitor voltage rating that is safe to use?

texts:
I'm using a few Case R tantalum capacitors (10uF 6.3V) as bulk decoupling on the 3.3V power of a 100mbps Ethernet phy. I am also using 0.1uF ceramics closer to the pins.

As usual, I'm terribly pushed for space on the PCB, and so I would like to replace them with 0603 size caps. The problem is that they're only rated for 4V. Normally I would always rate my capacitors for twice the voltage that they're ever going to see.
Is it likely to be a problem if I use a 4V capacitor on a regulated 3.3V line?


texts: Having trouble setting up a data call via AT Commands and using the wifi chip as a hotspot

texts:
I have a WiFi chip embedded on an evaluation board which also has an application processor which runs A-grade Linux, in addition to a modem processor.
I want to set it as a hotspot via hostapd which I was able to do, and I also see the network showing up in network manager on a client, but I can't connect to it.
I realized the issue was the SIM card not being configured to use the network data. So I ran the following commands in an application processor in ADB shell to set up the data call:
AT+COPS?
+COPS: 0,0,”T-Mobile USA”

AT+CGREG?
+CGREG: 1,1  // network is registered

AT+CGDCONT=1,”IP”,”epc.tmobile.com”

AT+CGATT=1 //Perform a GPRS Attach

AT+CGACT=1,1  //Activate the PDP context

Now that the PDP context is enabled, how do I go about actually using the network data so it could be used on the host as well as by the clients trying to connect to the hotspot?
Following are the logs related to hostapd:
// logs collected while running hostapd_cli

1608235787.411050: wlan0: AP-ENABLED
1608235787.411111: wlan0: Setup of interface done.
1608235787.411717: RTM_NEWLINK: ifi_index=14 ifname=wlan0 operstate=6 linkmode=0 ifi_family=0 ifi_flags=0x11043 ([UP][RUNNING][LOWER_UP])
1608235787.413187: RTM_NEWLINK: ifi_index=14 ifname=wlan0 wext ifi_family=0 ifi_flags=0x11043 ([UP][RUNNING][LOWER_UP])
1608235787.414836: nl80211: Event message available
1608235787.415597: nl80211: Drv Event 88 (NL80211_CMD_CH_SWITCH_NOTIFY) received for wlan0
1608235787.416785: nl80211: Channel switch event
1608235787.417761: wlan0: Event CH_SWITCH (38) received
1608235787.417845: 1608235787.417849: wlan0: IEEE 802.11 driver had channel switch: freq=5745, ht=1, vht_ch=0x0, offset=1, width=3 (80 MHz), cf1=5775, cf2=0
1608235787.420730: wlan0: CTRL-EVENT-CHANNEL-SWITCH freq=5745 ht_enabled=1 ch_offset=1 ch_width=80 MHz cf1=5775 cf2=0 dfs=0
1608235787.421290: wlan0: AP-CSA-FINISHED freq=5745 dfs=0
1608235787.421989: nl80211: Event message available
1608235787.425177: nl80211: Drv Event 103 (NL80211_CMD_VENDOR) received for wlan0

And when a client tries to connect to the network, I see the following logs indicating the STA is connected but really it hasn't.
1608235887.930244: WPA: EAPOL-Key MIC using HMAC-SHA1
1608235887.930828: WPA: 3c:22:fb:cf:ba:cd WPA_PTK entering state PTKINITDONE
1608235887.931168: wpa_driver_nl80211_set_key: ifindex=14 (wlan0) alg=3 addr=0x81262238 key_idx=0 set_tx=1 seq_len=0 key_len=16 key_flag=0x2c
1608235887.931816: nl80211: NEW_KEY
1608235887.931930: nl80211: KEY_DATA - hexdump(len=16): [REMOVED]
1608235887.932539:    addr=3c:22:fb:cf:ba:cd
1608235887.932603:    pairwise key
1608235887.996702: wlan0: AP-STA-CONNECTED 3c:22:fb:cf:ba:cd
1608235887.997799: nl80211: Set STA flags - ifname=wlan0 addr=3c:22:fb:cf:ba:cd total_flags=0x61 flags_or=0x1 flags_and=0xffffffff authorized=1
1608235887.998796: 1608235887.998802: wlan0: STA 3c:22:fb:cf:ba:cd IEEE 802.1X: authorizing port
1608235887.999008: 1608235887.999012: wlan0: STA 3c:22:fb:cf:ba:cd WPA: pairwise key handshake completed (RSN)
1608235888.000782: nl80211: Event message available
1608235888.000909: nl80211: Drv Event 103 (NL80211_CMD_VENDOR) received for wlan0
1608235888.001635: nl80211: Vendor event: wiphy=0 vendor_id=0x1374 subcmd=101
1608235888.001663: nl80211: Vendor data - hexdump(len=24): 0c 00 05 00 02 00 00 00 01 00 00 00 0a 00 04 00 ff ff ff ff ff ff 00 00


texts:
This is an exam question. Our professor has some generator of tests and out of the blue this beast came. We couldn't ask for the clarification, being an exam question, but from what I can see it relies on diff amplifiers, something I've forgotten, mostly. It's also completely different from other exam questions, SO if someone could give me some miraculous tip that simplifies this.

The question is to find the transfer function \$\frac{V_{output}}{V_{-IN}}\$, if +IN is grounded.The final answer is -50.


texts: Extend number of PWM pins on an arduino?

texts:
How do I extend the number of PWM pins on an Arduino without using software solutions, I need 32 to drive 32 mosfets?

Thanks!


texts: Simplifying a circuit to measure current

texts:
So I'm to calculate the current in the places I put the ammeters in (yeah, I reckon one of them is turned around :)):

And while I can calculate such things for series or parallel circuits, I was taught I should first try to simplify the circuit and do it with Ohm's law and supplementary resistance. So I did something like that (which is my only idea):

And, regretfully, the results in the simulator are different. Then, how can I evaluate the 3 Ohm resistor (the one being "vertical" in the first picture) to somehow simplify the circuit and be able to calculate it? Could you please help? :)


texts: STM32F4 - Digital Signal Processing ( DSP )

texts:
At this website, I have read that STM32F4 microcontrollers have DSP instructions. To quote:

  It also implements a full set of DSP instructions

I am beginning to learn embedded C programming with CooCox CoIDE and STM32F4 Discovery board.

My question is: How do I make use of DSP instructions, when I am writing code in C? Do I need to include some special libraries / functions?


texts: To which voltage rail should I connect pull-up resistors?

texts:
I designed a circuit which have some components with different voltage ratings.
There is an ESP8266 which should connect to 3.3V.

There are more components such as PCF8574 (Multiplexer which is reading active-low buttons), DS1307 (RTC), 24L08 (eeprom), ... which should connect to 5V.

There are some pull-up resistors needed in this circuit. Pullup for I2C bus, PCF8574's interrupt, buttons, reset and program pins of ESP8266, ...

My Question is: To which voltage rail should I connect these pull-ups? For example, PCF8574 is connected to 5V and its I2C bus is connected to ESP8266 which is 3.3V tolerant. How should I determine its rail?

I2C bus is not my problem. I just want to know: Is it important which rail to pull up to?

Another example to clarify: Can I use 5V to pull up ESP8266's reset pin and calculate a suitable value for its resistor?

Is this really important which rail?


texts: Can I share source code/software from Microchip through my website?

texts: I've done some projects including bootloader for PIC microcontrollers. But all these are done by modifying official microchip codes. Also want to share official drivers and softwares. I want to share this open. Is this possible? Is there any legal problems by doing this?


texts: How to drive power MOSFET by logic level signal without inverting phase?

texts:
I struggle yet another day with very simple problem (circuit).
This challenge seems to be very common, but nowhere I can find a complete solution:

I have a heavy load (12v / 1 Ohm peltier = 12A max) which I need to drive using microcontroller (5v Arduino to be specific).

I was able to get an IRFZ44N N-channel power MOSFET, which is rated 49A Vds so hopefully can handle that load.
The thing is that its Vgs = 10V (the voltage to turn it fully on).

Here is the circuit I came up with until now, based on 2-stage voltage level shifter (as suggested here):

Simulation shows phase shift between input vin and vdrain anyway, even if there is no phase shift between vin and vgate (which is very mysterious for a noob like me):

Can you please help me understand this or help me coming up with a complete solution? I did spend lots of time trying to Google it and nowhere I can find one without inverting PWN phase (even here at stack-exchange).

And this must be extremely simple right?

In case you ask: I have my reasons to keep it non-inverted (long story short - I do not want the situation that load is on when micro-controller is off as they have separate power supplies). Even thou - I still want to understand the problem and find a solution.


texts: Phase lock loop frequency of reference signal

texts: I am writing a Matlab code for phase locked loop and up to now I assumed that frequency of input signal is given (known) and I choose frequency of my VCO close or exactly the same as reference signal. However I am wondering what if I do not know the reference signal frequency, how can I approach the problem in that case?  How can I choose the frequency of VCO?


texts: Problems with Ring Oscillator using CMOS inverters in Cadence

texts:
I'm using Cadence Virtuoso 6.1.6 and am trying to design a ring oscillator using CMOS inverters. I have looked at other questions that have been asked on this forum, but I wasn't able to find any that were designed using Cadence.

A little background - I have been tasked with making a "VCO" using "sgfet" CMOS transistors. These "sgfet" transistors are very similar to regular CMOS transistors. The only difference is that these transistors are cylindrical as opposed to having a width and length. But their behaviour is exactly the same as regular CMOS transistors.

I strung three inverters together to create the ring oscillator as follows -

The capacitors I used between the inverters are both 10nF (I'm not sure if these are necessary or not).

Once I ran the simulation, I get the following output -

Why am I not able to get an undamped output? I have tried almost everything I can. Please help!


texts: Can I transmit data over RJ12 to a PC from a PLC?

texts:
I have a Click PLC which has two RJ12 ports. I have successfully programmed it using C# and nModBus as a slave, but now I want to test the PLC as a master and the PC as a slave and noticed my laptop has a female RJ12 port, and was thinking is there a way I could transmit data across RJ12 to my PC from the PLC (e.g. PLC as master telling PC slave to read some data). Is this possible, and if so, where do I begin to communicate through RJ12?

If it's not possible, then here's this. If I use two adapters, one to convert RJ12 to Serial DB9 and another from DB9 to USB to connect to my computer, should I be able to communicate through the serial port on my laptop, or will two adapters cause some conflictions?

Thanks in advance stack!


texts: High-side pMOSFET does not switch to ground

texts:
This is the schematic in its basic form. It's an nMOSFET that gets driven by a pin of an Atmega328p, this nMOSFET on his turn, drives a big pMOSFET. The source is connected to a voltage regulator (9V6), the drain is connected to the backlight of an RGB screen. The Atmega generates a PWM-signal (100kHz, duty-cycle is variable) so one can change the brightness of the screen.

However, when looking at the drain, I noticed that the OFF-part doens't go to ground and there's lots of ringing.

The ringing I could damp by adding a snubber network to the drain of the pMOSFET. But the OFF-part still doesn't go to ground and there is still a sudden peak in voltage that I could not remove. It seems something is pulling the voltage back high.

How comes that there is still a DC component in the OFF-part of the PWM?

How can I remove that part so it goes to ground?

The only other question I found, is this one: High side mosfet source voltage does not switch back to ground
So I added a parallel RC network at the output.

Measuring now, it goes down to ground, but there is still a peak present in the signal.

Can I clean this up further?


texts: What is the correct current in the datasheet for the LED-Matrix?

texts:
If I understood correctly the maximum DC Forward Current for one LED is 30mA (Page 2). So if I wanted to drive an entire column (5 LEDs) I would need 5 times the forward current. If I don't take the maximum but something like 20mA it would result in 100mA per column. Is that correct? Basically I'm wondering if the 30mA is for one LED or for a column.

Datasheet


texts: Passive harmonic filter: Why Immensely Hot and Humming

texts:
I encountered a passive harmonic filter, PHF with highly non linear loads, i.e. variable frequency drive, VFD (most of the time running 50Hz) serving an induction motor.

I believe that it is a commonly used resonant shunt filter to eliminate the 5th harmonic.

The enclosure housing the PHF has a ventilation fan, but still always (the reason why I am writing here) very HOT! Up to the extent that the contactors, wires have melted/discolorated/burnt mark etc

I suspect of the over saturation of the 3 phase transformer (V_phase2phase=415V), I believe acts as an isolation transformer-cum-line reactor. The capacitors are still in good condition (not bulging of the caps), but the winding insulation of the transformer is discoloured.

Any help to do further diagnostic is welcomed. I will conduct a harmonic assessment with a Fluke power analyser next week.


texts: When do I connect to negative terminal or ground?

texts:
Easy question (or at least I think).  I've installed a siren in my vehicle which calls to pull power direct from the 12 volt battery.  I currently have the circuit completed by connecting to the negative terminal on the battery.  I've been told that sometimes it is best to connect to a grounding point on the vehicle like the frame.

Is this necessary for my situation or ever?

Thanks in advanced!


texts:
I am in the process of designing a PCB for a solder kit that receives
NeoPixel type LEDs, the ones with the short head:

Now, there seem to be different pinouts:

Ordered on Amazon.de as WS2811 LED Chip:

(DIN, GND, +5V, DOUT|

This pinout I figured out myself. With several batches I got the
same pinout. (The datasheet for these actually had different
pinouts in different locations, and so I fried a few at first.)
WS2812D-F5:

(DIN, GND, +5V, DOUT|

This pinout is in the datasheet WS2812D-F5-15MA-C1规格
书_18031509334119.pdf available on the Worldsemi’s web site.
SparkFun LED - RGB Addressable, PTH, 5mm Clear:

(DIN, +5V, GND, DOUT|

See the datasheet COM-12877.pdf on the SparkFun web site.
Regular NeoPixels (long head), distributed by Adafruit as
NeoPixel Diffused 8mm Through-Hole LED:

(DIN, +5V, GND, DOUT|

See the picture 1734-04.jpg on the Adafruit web site.

Maybe someone can shed some light on this: Is there any system so
that I can know when ordering which pinout I will get?

Update

I did a little bit more digging, which may answer the question. There
seem to be two large manufacturs of the NeoPixel type THT LEDs with
short head:

Worldsemi Co. Limited, making the WS2812D-F5 mentioned above:

(DIN, GND, +5V, DOUT|

Shenzhen LED Color Opto electronic Co.ltd, making the SK6812D5
(datasheet) and the APA106:

(DIN, +5V, GND, DOUT|

My take is that it’s best to order from vendors that clearly state the
model number. Interesting is also the WikiLEDia list of chips
sorted by manufacturer.


texts:
Well, it's taken me weeks to think of a new absurd question but here I am at last. You're welcome!

I'm looking at using a small, adjustable, switching buck regulator (likely a LM2574) for a very basic supply:

120V AC in --> stepdown transformer --> bridge rectifier --> switching regulator.

This will be used in a commercial product. I've amazingly not designed with one of these before. While I don't think for this product we need to technically be concerned about EMI, I'm curious if a little bitty switching regulator like this generates all that much noise? I'd rather not add cost with upstream filtering if it's not needed.


texts: Writing to parallel port with minimum latency

texts:
I want to use a parallel port to control some stepper motors (many of them). So far I've got it connected to a little test board with LEDs and I've written a C program in Linux to set the pins using outb or outl calls. Because I want to use all 12 output pins I'm setting both the data byte and the control byte. (Actually, more than 12 pins would be nice, but 12 will have to do.)

This all works and the LEDs light up as expected, but it's a bit too slow for my needs. A loop with 1,000,000 iterations that call outb twice (data and control byte) takes ~3.9 seconds. If I replace that with a single outl call that takes ~3.6 seconds, so it looks like each outl takes about 3.6 us. From what I read it should work in about 1 us or even less. The question is: how do I make it faster?

The machine is an AMD Sempron with an on-board parallel port. There are 3 settings for the port in BIOS: "Bi-directional", "ECP" and "EPP". ECP gives the numbers above. Bi-directional is slightly slower and EPP is much slower (running exactly the same code). Is there something special I need to do in code to take advantage of the faster modes? Is it a limitation of the hardware so maybe a dedicated PCI IO card would be faster? Do I need to use DMA (which I think requires a kernel-mode driver)?

Alternatively, is there some add-on device out there like a parallel port, but with more pins and/or lower latency for setting all the pins? (I don't need to change one pin at a time.)

Edit (more details):

I want to control 1,000 stepper motors in total. The original design was to have 5 Arduinos controlling 200 motors each using logic gates to address each motor in sequence. A 6th Arduino would be the "master" controller, sending data to the other 5. However, an Arduino doesn't have enough memory to store all the data I want to send, so that's where a PC came in. Once a PC was involved it seemed much simpler if I could cut out the Arduinos entirely and use 2 (maybe 4) parallel ports to control the motors directly, probably under RTLinux (though the test above was done on regular Linux). I don't think I'd need a 1 us timer resolution as such. I was thinking of a timer firing every 1500-2000 uS and each time sending signals to all 1000 motors, one by one (500 or 250 per parallel port). The parallel port speed seems to be the limitation here.

I understand that there are dedicated stepper motor controllers, but buying 1000 of them gets expensive. Is there something that can control many of them? Ideally I'd like to keep as much of the work as possible on the PC, because it's just so much easier to program and debug.


texts: How do I direct input/output to correct circuit module. (2 bit calculator circuit)

texts:
I am designing a 2-bit four function calculator. With separate modules for division, multiplication and add/subtract.

Subtraction is performed by adding 2’s complement to input. So I have 3 modules.
These modules are gate based i.e. only AND,OR, NOT,XOR etc are used.
I am using a 7-segment display to display output that means I also have a 7447 decoder.

I designed these three modules separately. i.e. on three isolated breadboards.
In that phase I had separate decoders and 7-segments for each module

Now the circuit is complete and I have to merge the 3 modules in the following way.

There will be 4 inputs ( 2 numbers of 2-bits each) a0,a1, b0,b1.
A selection of function (add,subt,multiply,divide).
Output should be on 7-seg display

For a single module, I’d happily connect inputs, and outputs will go to decoder, and we have our nice 7 seg display powered up.

But how do I do this with 3 modules in a way that only the selected module gets the input and the output from only the selected module goes to decoder (and hence 7 segment display)?
This diagram, I believe will help clarify the scenario.


texts: Testing paradigms for consumer electronics

texts:
I am brand new to EE/ECE (my background is software) and I am curious about how real-world electronics testing takes place.

In software, there are many different types of tests that a piece of code should be run through to make sure it's of high quality and that it is functional/correct:

Code reviews (manual process)
Static analysis (basically automated tools that scan your code and tell you if it stinks or not)
Unit tests (small tests that are quick to run which test flow through a particular "path" in the code; essentially tests a single function/method)
Integration tests (test a particular unit of code integrating against some other unit of code, or, say, a mocked database)
Functional tests (an end user - either a human being or an automated process - actually using the software and checking for correctness at the top/system-level)
Performance tests (the software might be functional, but perhaps its slow or consumes too much memory, etc.)
Security tests (the software might be functional and fast/efficient, but perhaps its not secure and will be easily hacked)
Smoke tests (basically a subset of functional tests that can be used to make a quick go/no go decision as to whether the software is functioning correclty)
And many more!

I'm wondering what the testing equivalences are in EE-land, and what they look like. I would imagine that the unit testing counterpart would be testing all the individual parts/components (making sure the LEDs light up, that the motors spin, etc.). I would also imagine that the integration testing counterpart would be testing each individual subsystem assembly for correctness. But beyond that:

What different types of tests are typical in EE-land? How are they conducted?
What about non-functional tests? Like making sure the device works under particular humidity or temperature ranges, etc.?
Is functional testing performed on each final device, or is cherry picking/spot checking employed? If I have 10,000 units of a prroduct/device, I would imagine it would be timely/costly to conduct full bore tests on each one...


texts:
I have the following Driver IC for a stepper motor:

http://www.ti.com/lit/ds/symlink/drv8825.pdf

When the motor is running, I cannot hear the switching from the current chopping in the motor windings, but when I stop the motor (no more STEP inputs are coming in the driver), i can hear the switching frequency at a random, audible frequency. The Driver should provide 30khz constant switching frequency.

I tried also to switch from mixed decay to slow decay and fast decay, the problem remains the same. I use 1/4 Step Mode.

Can anyone suggest me, what I could do against it? The only thing that works so far is to disable the motor, but then there is no holding torque and that can lead to a drift over time.

I measured with the oscilloscope the switching behaviour when the motor stops, different cases can occur at random:

This one is non aduible:

This one is adubile:

There are alot of other audible and non-audible cases aswell, where always the audible cases have a constant switching frequency.


texts: Why is an aluminum track not performing as a voltage divider?

texts:
I have an arm that moves along a track. I need to know its location. My idea was to have a wiper on the arm that acts as the output of a voltage divider. The voltage could then be sent to the microcontroller and be converted into the location.

Just to test things out, I attached two ends of a piece of aluminum foil to a battery. My idea was that the aluminum foil has some relatively consistent resistance across it, thus the center should provide half the voltage.

I could not get a reading on my multimeter. I then coiled nichrome wire around a rod and used the same divider method as above and it worked. Why is this?


texts:
Recently I went shopping for more electrical components and on my list was solder wire. I bought one reel of solder wire from an indigenous company called Oswal. It is a 60/40 tin:lead solder wire. The thing that I did not notice was that the label said 'Resin Cored', Rosin cored I know but what is this resin cored solder wire? Googling for answers I found none which detailed it. I searched for Resin which is:

In polymer chemistry and materials science, resin is a "solid or highly viscous substance," which are typically convertible into polymers. Such viscous substances can be plant-derived or synthetic in origin. They are often mixtures of organic compounds.

Now I used this wire to solder a few things and it behaves just like a Rosin core solder wire. So my question: Is this resin core different from Rosin core or is it just a rebranded version?
There is one place I found similar wire being sold, if it helps: Resin core solder wire


texts: I would like to know if it is possible to visually identify circled components of old G5 Apple Motherboard. Keyword search of the number written on the component is not useful in identification of the part.


texts: How can I use the voltage generated from inductive kickback?

texts:
I'm designing a circuit that requires a high voltage pulse in order to fire a spark plug. I'm thinking of using an inductor to provide this pulse (via inductive kickback), but I'm struggling to figure out how to actually make it work without destroying my power supply.
I understand that spark plugs in a car are fired in a similar way using an ignition coil (which is actually like a transformer, so the high voltage side is isolated from the low voltage side). However, I haven't been able to figure out how the battery is protected from the massive voltage spike. From what I can tell, a flyback diode on the primary also prevents spikes on the secondary, so it seems near impossible to actually get a spike.
My design doesn't use a transformer as it seemed like there was no difference in using an inductor vs a transformer. So, I am currently designing the circuit with an inductor although I could change it to a transformer if that's the only way to do it. The circuit looks like this:

I'm simulating the spark plug as a high resistance (100GOhm) element. The 1.4 kOhm resistor is being used to tune the output voltage, as my understanding is that the output voltage is given by V=I*R where I is the current through the inductor before switching, and R is the resistance of the RL circuit. The 1 Ohm resistor is being used to limit the current through the resistor.
This circuit does technically do what I want it to do. It produces a very high voltage (I think about 7 kV) spike when the switch is opened. However, the switch is the real problem. If I use a solid state switch (MOSFET, SSR, etc.), there would be major issues with the voltage rating of the switches as it is going to be very hard to find a switch that is ok with 7 kV being dropped over it. The easier alternative is using a relay, but I need to prevent the relay contacts from sparking. The only way I know to prevent this issue is to use a flyback diode, but that will also reduce the voltage produced by the inductor so the spark plug is unlikely to fire.
The only solution I've come up with is to use a PPTC resettable fuse to block high currents (as anything greater than (5 V/1 Ohm =) 5 A would be unusual in the above circuit), but that would also rely on the fuse being rated for very high voltages. Are there any better ways of doing this? How do cars do this without having a huge potential difference between the positive terminal of the battery and the positive terminal of the inductor in the ignition coil?


texts: Upper and lower dimmensions in schematics

texts:
What is the difference between upper and lower dimmensions in schematics?

So far I have assumed that those are simply maximum and minimum values specified by the tolerance. Is my assumption correct?

Edit 1:

There is also a statement bellow the datasheet that tolerances are +/- 0.15mm which is inaccurate in the case of 3.60/3.20 (or 2.90/2.50).

A relevant schematics here:


texts: How is this current source be transformed into a voltage source?

texts:
Can someone explain how is the current source on the left side below is transformed into a voltage source?:

I thought a current source is shown with resistor in parallel. I'm not used to see the conductance G with a current source. How can the circuit on the right side can be derived from the one on left side step by step?

Edit:

I tried to plug 1/R1 to G1 and this is what I reached:

Where am I wrong?


texts: Sziklai Darlington Transistor Configuration

texts:
I'm building a infrared 38khz emitter and I would like to use 4 or 5 LED in multiples directions.

I found this article, where in the end it shows a Sziklai Darlington schematic and dont use resistors. I'm not sure if it is OK.

Based on the article, I made this example considering 2 LED emitters. I also included R2 and R3 to limit the current on LEDs.

It's not clear to me the current flow.

How do I calculate (or check) if it will work as I expect?

Do I need base resistors on T2 and T3?

It can be calculated with tipical values.


texts:
I have a tri-phase generator which outputs AC voltage waveforms (\$R\$, \$S\$ and \$T\$) with 120o phase shift between them. I want to rectify these voltages and obtain a single DC voltage.

I designed the circuit below, but I'm not sure whether it will work or not.

a) Would this circuit work? (Importatant, please don't skip.)
b) What are the alternative/better circuits for this purpose?


texts: How feasible would it be to use capacitive detector through 5 mm thick glass with a gap between PCB and glass?

texts:
I'm researching for a project that would need to have some sort of touch detection through a 5 mm thick glass table.

Would it be feasible to use a PCB with appropriate patterns and a mTouch/QTouch/capSense microcontroller with it on one side of the glass and expect it to be able to detect touch on the other side of the glass if there is gap between the PCB and the glass? I'm thinking of having SMD LEDs on the side of the PCB close to glass. Ideas to fill the gap are welcome too.

I did do some research on this and I've seen that some people here have managed to have gapless sensors work through glass, but I'm not sure how this would work with the gap in it.


texts: Help me correct this circuit with N mosfet

texts:
I am trying to build a protection for my circuit in case someone attached batteries or any power supply in reverse even if the other supply is normally attached.

As you can see I have 2 power supplies. Is it safe enough to protect the both power supplies and protect my circuit too.

Can anyone illustrate if i am doing wrong .

I simulated this circuit on LTSPICE and it shows correct. I am not sure what
 would you say about it.

Should I keep the common GNDs connected together?.


texts: How to visually tell the difference between axial inductors and common resistors?

texts: Is there a simple way to tell axial inductors and resistors apart in through-hole type PCBs? I do find the color code on both very confusing. Is there an obvious difference that I am missing? As a beginner, I might just be overlooking something very simple.


texts:
Usually Google guides me to http://www.alldatasheet.com/ or a similar site when I'm looking for a datasheet, but no such luck this time. The XC prefix reminds me of Xicor, but after being directed by Google to the Intersil site I couldn't find it there either.
Does anyone have a datasheet for the XC34064P?


texts: Different microcontrollers can communicate?

texts: Can different microcontrollers communicate with each other? Are there any small chip that can communicate with 89C5131A-UM? And how do I know what frequency does the 89C5131A-UM communicate? I have read the datasheet but could not find it.


texts:
As a follow-on to the question "Using forward voltage drop of diodes with linear regulator" I am looking into designing PMOS voltage regulators.
General Topology
A common problem with the intuitive solution seems to be strong oscillations of the output:

(See the question "Stability problem in unity-gain opAmp". Some of my questions may have been answered there but I am not sure I understand those answers correctly. Hence this question.)
As I understand the issue arises solely due to the use of positive feedback. My understanding is that the Barkhausen criterion requires multiples of 380° phase shifts for oscillations - which in purely resistive circuits only appears with positive feedback. Right?
In this lecture by Vahe Caliskan from Motorola, the following circuit is presented for LDO PMOS linear regulation:

I have a feeling that this is faulty: It seems to me that the switch is open when the scaled output is already larger than the reference voltage.
It looks to me that the inputs of the amplifier should be reversed. Correct?
Power dissipation and gain in the loop
My understanding is that one of the differences between linear regulators and PWM regulators is that the series element of linear regulators dissipates P_loss=I*(Vin-Vout) while the series element with PWM dissipates very little power.
What does the power dissipation of the PMOS in the above (corrected) circuit look like?

P_loss = I*(Vin-Vout), or
P_loss = R_on*I² ?

I imagine the answer depends on how the PMOS gate is drive in response to small perturbations of the output voltage from the reference voltage: If it is driven in a quasi-on-off fashion, loss is more like in the PWM case while if it is driven in the ohmic region in response to smll perturbations the loss is similar to "ordinary" linear regulator case.
Is it right then to assume that using large gain in the feedback loop of the PMOS voltage regulator, a quasi-PWM regulator is obtained?
Minor points

Generally FET regulator circuits are presented with JFETs. Does this mean that enhanced MOSFETs or even Power MOSFETS cannot be used? How does their use affect the cuircuit behaviour?
Everything above assumes that Vout drives a resistive load. How do (partly or purely) capacitive loads change the stability of the circuit? What can be done to improve the stability range?


texts:
What's the name of connector which can be used here?

I know that I can always solder it to PCB, but I was looking for more "elegant" solution, and I remember seeing these connectors before on PCB's but I don't know how to search for them (under which name):


texts: Home made USB charger based around LM2596: Smoothing caps

texts:
I'm embarking on building a home made mains USB charger based around an LM2596 DC:DC converter. I had a couple of Newbie questions.

Can I connect 5 or 6 USB plugs to the output of the LM2596 (assuming it's set at 5v and I respect the aggregate current limit of the devices I'm trying to charge).
If I feed the output of the bridge rectifier into the LM2596, do I have to be particularly fussy about the smoothing cap value? (do I even need a smoothing cap)


texts: What are common ways that modern processors handle data hazards with asynchronous registers

texts:
I'm trying to design a processor in VHDL. While the base instruction set is done, I'm having trouble building on top of it.

Specifically, I'm implementing control and status registers (CSRs), which allows the system to be controlled to a greater degree.

These CSRs do not need an instruction to be altered, they can change based on the state of the machine.  This comes with a set of data hazards that I have been trying to solve. There are not many existing resources that offer solutions to these hazards.

Rules:
All instructions which associate with these registers are atomic instructions which are meant to swap the CSR value with a general purpose value.

Hazard 1: RAW
The register is read from, and the CSR are read from on one clock cycle of the pipeline. On the next clock cycle, the values are written. During this time, the CSR may have changed.

Hazard 2: interrupt WAW
Something in the processor triggers an interrupt, And changes a whole bunch of registers at once. In the pipeline, however, there is an instruction which writes to a CSR which has been modified.  This corrupts the register.

What are some common ways to remedy these hazards?


texts: How to shift down a square wave at 0 - 5 V?

texts:
I have a square wave that oscillates at 500 Hz from 12 to 14 V. I would like it to oscillate at the same frequency from 0 to 5 V, so I could use to trigger i.e. a switch. Is there any circuit to do this (shift down the signal)?

It goes from 12 V (low level) to 14 V (high level). I would like it to shift it down so it will go from 0 V (low level) to 5 V (or higher from 5 V... I don't mind).


texts: Phase voltage vs main voltage in three phase system

texts:
My question is from my book : A frequency converter is connected to three-phase network (400 V, 50 Hz). How much phase current it pulls from the grid during normal operation (785 W).

the correct answer is : I=875/√3/400=1,26 A .

How I know if I should use the main voltage or the phase voltage to get the correct answer?

How you know that 400 V is a phase voltage and we have to use the main voltage in our equation?

Thanks


texts: Turning a torch on or off using a single mini-switch

texts: I need a circuit to turn on and off a torch, as given in the figure. The circuit must turn the output on when I press the mini-switch once, and turn the output off when I press the mini-switch again.


texts: Are there two band contributions to diffusion current at the PN (diode) junction?

texts:
My question (I hope) is a simple one.  Are there two components of diffusion current (valence band AND conduction band) contributing to the generation of the PN junction voltage?  If so, do those components stay exclusively within their respective bands across the junction and throughout?

Or is it like this:

Or are BOTH pictured paths involved?  Can anyone refer me to a source that DOES go into that sort of detail in terms of current in both bands?
Also, at the interface between the diode and the conductors attached to them, do valence and conduction bands both participate in electron current to and from their respective conductors, since the valence and conduction bands of conductors overlap?  Or is this pictured the ONLY transport to and from the semiconductors?

All the sources I've seen start by mentioning that N-doped silicon creates extra electrons in the conduction band in the N-type, and P-doped silicon creates extra holes in the valence band in the P-type.  Then they make no further mention of bands when discussing diffusion and drift current and treat both types as black boxes.  But perhaps they do in the language of crossing the junction and filling holes.  Here are two examples:
https://www.youtube.com/watch?v=7ukDKVHnac4&feature=youtu.be&t=158
More accurate picture of diffusion current (amended):
https://www.youtube.com/watch?v=btOIDQeMrMg&feature=youtu.be&list=PLfYdTiQCV_p711DywXAh53wL3xI7S55lg&t=192


texts:
I'm already having trouble understanding Q-point of a transistor. I have been assigned to draw Q point as follows:

Calculate and draw a graph of Q point , VCE(cutoff) , Ic(sat) if IB = 100uA,
200uA, 300uA, 400uA, 500uA, 600uA and β = 150

Note: The values in the diagram will be replaced if mentioned in the question.

The problem is that when base current is 400(micro Amp) it gives -3.2 V VCE and negative values for other proceeding base current values. How should I plot it in the graph? Before plotting the graph I want to know if it is even possible to have negative VCE. If yes then how will current flow towards ground as it's at high potential now?

Please let me know solution asap.

Thank You.


texts:
How a CAN transceiver detects the 5 successive high or low bits and inserting the opposite bit as stuff bit ?
what is the logic behind the bit stuffing process?.

I am sure that, it's not handled in CAN driver software side.


texts:
Is it practical to use Xbee for extending the wifi range of my home router?  I thought of the following steps:

Providing the router output to an Xbee transmitting unit.
Transmit signals to the next Xbee.
Re-transmit the Wifi signals.

I would like to do it as my next academic project.


texts: The starting torque of an induction motor increases with increasing rotor resistance. However, we know that, with increasing rotor resistance, rotor current will reduce, and hence rotor flux will reduce. How does the torque increase then?


texts:
We got a bulk of stepper motors, you can see specs on the following image:

I'm doing some work on my school laboratory, and they want me to test this motors to see which ones work and which ones doesn't. As of now, I have used a Arduino micro and an Easy Driver(Allegro A3967), just STP and DIR signals, after 10 motors, the driver died, I found a short between A- signal and V+.

Reading the complete datasheet I have now realized that we are not suppose to "hot swap" the motors, we have to turn off the unit and swap, but that is slow and does not work for me, so now I connected a Relay to an arduino output (Darlington Driver), that Relay turns ON and OFF the easy driver board, (Opening and closing V+ Line), after 60 motors, again the driver died, again short from 1 output terminal to V+.

My next move is to put some schotky diodes to clip transient voltages on the A+, A-, B+ and B- terminals and see how the board responds.

My question is: Do you have any idea how to make a Hot swappable driver for a stepper motor?, Do you know any IC that can do that? Do I have any more options? is this really possible?


texts: Advantages of filtering signals using analog or digital methods?

texts: In my understanding, it seems that there are, broadly speaking, two primary ways in which signals are filtered for analysis by computers, which are software-side filters and hardware-side filters (generally of the RC op-amp variety). What though is the advantage of using the RC op-amp setup though for, say, low and high pass filters when there is always tradeoff between the amount of attenuation and integrity of the signal when using a hardware filter like an RC op-amp setup. Whereas a digital, code-applied filter would function almost exactly like the brick-wall that is the filter ideal for low and high pass filters. But that seems a little too cut-and-dry to me, is there some benefit to using one over the other (or both together)? Maybe for notch filters I could see analog active filters working better precisely for their imperfect attenuation, but that's all I can think of off the top of my head.


texts:
I'm looking for a way to limit the speed of some wheelchair motors in order to gain better control when using them in my RC device.

Currently the motors are very sharp and don't ramp up to speed, which makes it difficult to make delicate movements.

As such I thought that reducing the input voltage would help; but I wanted to do this in a way that I could adjust the amount of speed limiting. E.g. 12V slow speed - 24V max speed (and anywhere in between).

As such, I thought some sort of Voltage Regulator/Variable resistor would be appropriate, but I'm concerned when it comes to the Amperage value and need a bit of guidance - or to be honest - told if this is the correct way of thinking or not.

I've sort of drawn out a (very basic) sketch of the proposed wiring diagram for your consideration.

Any help with this would be much appreciated.

Thanks

[Update]

Thanks for all the replies - I thought it best to update the post.

The motor controller I'm using is from a Company called Cytron: Cytron 30A Bi-directional Dual Channel DC Motor Driver Controller. Link: enter link description here.

Whilst I do have full control over the speed of the device, it's the granularity and sharpness I'm looking to smooth out - as well as add a variable speed limiter that allows me to select a maximum speed so that if I were to loose concentration and pushed the joystick to top speed, it would max out at 3Mph for an indoor environment or full speed outside.


texts: SIMPLE digital control over 555 timer frequency and PWM?

texts: I'm looking to create a sound generator with only simple ICs and components. I believe the 555 timer IC is a good candidate to be at the core of it, but I cannot for the life of me find out how best to control frequency and PWM digitally, and without complex devices like digital potentiometers. I've tried working with different configurations of ladder networks, but nothing is giving me the results I need. Could someone more knowledgeable than me with 555 timers and simpler component networks (i'm far too used to my fancy digital stuff, ha) help me out on this one? I'd like to get a square wave frequency out with 10-90% variable duty cycle and frequency from around 50 to a few thousand hertz. Would appreciate any help from a veteran in this stuff to point me the right way. Thanks!


texts:
I am using Avalanche Photodiodes and I was told that they use a much higher voltage then standard photodiodes and I was wondering if I need a High Voltage PCB to drive them? I am currently just using Ardunios but I'm guessing that I will need something better?

I am using 8 FirstSensor AD500-9-8015 avalanche photoiodes.

Also if I was using photomultipliers would I need a different PCB to run these to get the optimum output?


texts: What makes PC SDRAM so much more expensive than the same capacity in a chip?

texts:
I'm picking a SDRAM IC for a custom embedded board and was surprised by the low prices. Was expecting orders of magnitude similar to PC ram of the same capacity.

For example H5TC8G63AMR-PBA chip costs almost 4 times less than this Corsair Vengeance 8GB (1x8GB) DDR3 1600 MHz (PC3 12800).

Digging into the datasheet [page 4] for the RAM on chip it states that it its configuration is 512M x 16 and the speed isn't clear from the name.

Is the speed the main reason for the difference?
Are there other factors (like a need for a PCB) that multiply the price?


texts: I am trying to build this amplifier. Looking at the diagram, am pretty sure how it works, but is there a way I can modify this variable resistor with some fixed ones?


texts: Sizing Photovolatic cells based on solar load

texts:
I'm designing a Photovolatic system to power up a certain electrical load (around 1000 Watts). I've just finished my solar calculations determining the optimum tilt angle and the optimum surface azimuth angle for optimum solar energy input over the year.

I picked a MITSUBISHI PV module with the following specifications:

  Maximum power rating: 225 Wp
  Maximum power voltage: 31.2 volt
  Module efficiency: 15%
  Aperture efficiency: 16.7%
  Dimensions: 1625 x 1019 x 46 mm
  Cell type: Monocrystalline

I come from a mechanical engineering background, I need help in the next design stages.

Do I use average yearly solar irradiance or maximum irradiance over the year to size the PV system?
Do I design the system based on module efficiency or maximum power rating?


texts: ICM-20948 with DMP can't find its own compass

texts:
I am interfacing to the Invensense ICM-20948 9-DOF IMU chip using an ESP8266, and a 1.8V level shifter & regulator, which works fine.
I am trying to get quaternions from the internal DMP using full 9-axis sensor fusion, as according to the datasheet the ICM has an AK09916 magnetometer on board, which should allow for drift-free rotations.
The "library" for that chip I am using is an ESP8266-adjusted version of this one from GitHub, however the relevant code in there is actually from Invensense's official code.
The problem that I am facing is, that I cannot get the ICM to work with its own internal magnetometer.
I tried every magnetometer option that the library has to offer, as well as all official I²C addresses of the magnetometer, but every time the Invensense library returns an error when trying to init the compass and the mag data is always 32767 on all axis, so no valid data. Reading the gyro and accelerometer, as well as quaternions using the DMP and 6-axis fusion works.
Has anyone worked with the ICM before, and knows why this happens, and what I could try to troubleshoot this further?
I have also ran an I²C scanner, and I found two devices, one on 0x68 (the IMU chip) and one on 0xE8 (Don't know what that is). I tried 0xE8 as the magnetometer address for the ICM, but still get that same error.
Any help is much appreciated.
Update 1: I've changed from 0x68 to 0x69 by pulling AD0 HIGH, and now it detects the mag but it's stuck at "[4915.049805,-4915.049805,-4915.049805]"


texts:
just got this http://www.robotshop.com/en/rs-775-motor-7000rpm-12v-7613oz-in.html

I hook it up to 12VDC power source for a test ; the motor doesn't run without a push and I read 4V, 0.46A on my source. As soon as I remove contact with DC motor, I read 12V on my source.

Does someone have an idea what could be wrong ?


texts: Switching Boost Converter only works while probing with o'scope?

texts:
/See Edit below/: Why was the collector drive current not sufficient?

I'm trying to improve a 4S LiPo (14.4V nominal) to 19V/3.5A boost converter based on the MC34063 PWM switch controller. I initially built it once with a Schottky diode for the catch diode, and a IRLB8701 N-channel for the switching transistor.

Now I'm trying to do synchronous switching based on the IRS2183 MOSFET driver, and two IRLB8701 N-channels for both ends of the switching. (One assmption is that the high-side 8701 built-in body diode will provide some amount of forward conduction even before the built-in cross-conduction delay of the 2183 kicks in and pulls the gate of that thing higher.)

The problem I'm seeing is that when turning on, the circuit doesn't switch -- it just sits there at 13.8V output with 14.3V input.

As soon as I probe pin DRV_C (or the connected resistor R3 on the connected side) of U1 with my o'scope, it starts switching like a champ, and outputs a buttery-smooth 19V into my 200 mA test load (a 100 Ohm 5W resistor)

Why would this be?

My guess is that perhaps there is no initial charge to boost the gate drive of the high-side N-channel -- but the forward body diode of that device should (and does) provide enough conduction to output voltage, and the voltage sensor of the 34063 should sense "low voltage" no matter what, so I feel this guess is poor.

Here's the schematic:

And here's the actual board, in case it helps someone (I know this is kind-of hard to read as-is; red is top layer; blue is bottom layer.)

Also, I'm somewhat considering hacking a 22 pF capacitor and 10 MOhm resistor between GND and DRV_C, and hoping that makes it work without the scope, and then calling it good :-/
Better proposals highly appreciated :-)

Edit: I solved the problem, and this question is now: Why was that a problem?

Thinking about why adding capacitance to DRV_C would help, the main thing it would do is add current to the DRV_C pin. That pin, inside the MC34063, drives the base of a second transistor, which I'm using to pull the input to the 2183 to low. My theory was that 14V over 4.7 kOhm means 2.5 mA into the base of that transistor, and with a hFE of between 20 and 100, that should be plenty to drive the logic-level input to low. Aparently, that's not the case.

Changing the 4.7 kOhm R3 to a 1 kOhm resistor solved the problem. However, it also makes the converter less efficient, especially at lower current draw, as there's now appreciable loss through this resistor, in addition to the 2.2 kOhm pull-up for the logic input on the 2183. The capacitor might actually be the better solution !?


texts: Placement and values for ferrite bead/capacitor ESD protection / transient suppression filter

texts:
I've been researching but found it difficult to find a clear answer on this. I need to add ESD protection to my circuit, in this Texas Instruments video it talks about combining a TVS diode with a FBC (ferrite bead/capacitor) filter to maximize ESD protection, which to me seems like the best approach. I am wondering about placement and values for the filter. I will be powering a 3.3V ADC and MCU from a 5V AC adapter as shown in the schematic. Would the best placement of the FBC filter be right at the start of the circuit at the output of the AC adapter? I saw mention of using them at other places in the circuit and I think I saw using multiple FBC ESD filters mentioned. To me it seems like just one at the start of the circuit should work well but that's just my unknowing guess.

I am also looking for general values for the bead and capacitor. Most beads I looked at have a resistance of about 20-200 ohms at 100MHz. What size bead and capacitor would be ideal for ESD transient suppression? Should the capacitor be smaller value, or larger which could also double as a bulk supply decoupler for the circuit? Does the capacitor type matter? I've seen many mentions of the filter used but values have not been described. Thanks very much for any help.


texts: How to demodulate an overmodulated signal?

texts: Say I have an overmodulated signal like the example above. When you demodulate this you will get distortion. Is it possible to somehow demodulate this?


texts:
My application for the USB5744 is a simple USB 2.0 HUB with a 3 ft cable soldered to the board. The HUB and the devices connected work without issue unless the board temperature is reduced below 15ºC. Since the USB5744i and all components on the board are rated to -40ºC I am at a loss to why the device is no longer being recognized by the computer when cooling the board slightly.

I have confirmed with localized cooling that the USB5744 is the point of failure unless cooling degrades the signal. This issue is present on several boards. The data traces on the board are 0.3" each with a  ESD protection diode (TPD2EUSB30ADRTR) close to the cable solder pads.

I looked at the signals but I'm new to highspeed diff signals. See pic.
What can i do to resolve this issue? What tests can i preform to diagnose this?

3/20 Update:

The impedance of the transmission lines was controlled by the board design. Trace width of 11 mils, trace spacing of 8 mils, dielectric spacing between top layer and ground plane of 9.8 mils, creating an impedance of ~90 ohms.

As for coupling, there is no AC coupling in my measurement and no DC coupling on my board. I am not terminating the shield on my board and shield is terminated at host side (computer).

The measurement of my signal improved when i moved my probe returns to the board instead of the supply's return (green signal now the same height as yellow) but the signal is still switching into the negative (related to ground).

Localized cooling and heating doesn't seem to affect the measured signals but cooling still shuts off the chip or prevents communication to the host. I'm starting to suspect the IC or solder joints...

3/20 2nd UPDATE:

I have yet to verify the quality of the soldering but the assembly of the board was done by a reputable board-house (IPC-610 cert) and looks good with the naked eye.

Looking into some helpful responses, I realized the scope I'm using needed 50 Ohm probes... changing the probes cleaned up the measured signals and was able to capture the eye diagram. The eye diagram was measure with a differential probe across +D and -D. Other images are measure using board ground pad/via closest to measurement point. Confirmed that localized cooling does not degrade the eye diagram measurements but problem still exists.

3/21 UPDATE:

Apologies if I missed unanswered questions, I am a first time poster and have limited test equipment for high speed signals. My original intent was to create a USB3.0 HUB but the USB3.0 connections kept dropping out (mostly after HUB) and any large data transfers would drop the host's connection. When disconnecting the USB3.0 lines to only use USB2.0 speeds, the device works and transfers data at 300Mbps through a USB to Ethernet adapter.

The board was made with the recommended footprint with a ground pad and has 16 vias (4x4 grid) for the ground/thermal pad.

I captured the signal of one side of the oscillator (only have one 50 Ohm probe..) and the frequency does not change over temperature. Im unsure how to measure phase margin of the oscillator but I added the captured signal below.

The 3 first images are all measured from my USB HUB input port closest to the IC when connected directly to a laptop without test software or test patterns. I do not know if the signals are from Host or from HUB but i assume it is normal idle communication between the two. Funding to resolve the issue is limited but appropriate all support from these responses (Special thanks to Ali Chen).

Is there any method of improving the stability without a respin of the board? What type of USB protocol analyzer is recommended?

FINAL UPDATE:

After testing everything signal related, I put an oscope to the 5v, 3.3v, and 1.2v bus voltages and noticed the 1.2v bus has a 800mV ripple... changing the output cap of the regulator to 100uF reduced the ripple to 50mV and now the board operates at -20C!

Case Solved!

Signal Images Updated:


texts:
My question is with reference to this question - ESD protection using a capacitor

I am unable to grasp the relation between charge, voltage, and capacitance, although I can understand all these terms in individual context.

When they come together and get related in this ESD question, I have poor clarity.

Voltage or potential difference between any two points, is the work required to move a charge from one point to another.

However, electric charge is defined as the force that it experiences when placed in an electromagnetic field.

And capacitance, is the ability of an object to store charge.

So, when the accepted answer, states that, when something can have high voltage but low charge, how is it possible and how can I understand it intuitively?

I just want to understand this concept of charge, voltage, and capacitance more intuitively. An analogy would be better.

How is the capacitance value of our body taken as 100pF?


texts:
I can't wrap my head around how the capacitor gets discharged in UJT relaxation oscillator. I understand when \$ V_E \$ reaches or exceeds a threshold (say \$ V_{ON} \$), current flows from emitter to \$ B_1 \$. But \$ V_S \$ supply the circuit with a constant DC voltage and eventually after an \$ \tau = RC \$, the capacitor locks in a charged up state with voltage of \$ V_{ON} \$, as \$ V_E \$ also holds onto a constant \$ V_{ON} \$ passing current from emitter to base.
The capacitor has no where to discharge the current unless \$ V_{S} \$ is removed and only then can the capacitor supply voltage to the UJT instead of \$ V_{S} \$.
I've read a few tutorials which all sum up, without much explanation, that once the capacitor charges up to a threshold voltage, it discharges through the UJT. And once the capacitor gets fully discharged it gets charged up again and the cycle goes on producing a pulsed waveform out of the base.  I do not see how the capacitor can discharge unless \$ V_{S} \$ is taken out.


texts: Using kirchhoff's voltage law with current sources

texts:
This is a follow up question of this question. Summarized: The question is solved there good, however I wish to solve the problem the using Kirchhoff laws.

Kirchhoff's voltage/mesh law is nice as it gives a good method to solve passive networks. It just boils down to defining a (linearly independent) meshes, and solving the equations that come from these meshes; probably using some easy matrix algebra.

However I wonder how to handle this in the following schematic

simulate this circuit – Schematic created using CircuitLab

There can be three meshes easily "identified" (of course there are many more just take the obvious ones), and for the calculations let's name the loop currents \$I_a, I_b, I_c\$ from left to right, and let's assume all loop currents are counter clockwise. (Can't seem to draw those in the schematic..).

Now the to calculate the loops starting with the 8V voltage source:
$$ 8 - I_aR_1 - 3 + (I_a- I_b)\cdot X = 0 $$
$$ (I_a- I_b)\cdot X - (I_b - I_c) \cdot R_2 = 0$$
$$ -(I_c - I_b) \cdot R_2 - I_c \cdot Y = 0$$

However as you can see I putted "X" and "Y" for the current sources - as I can't really see what a current source does with the voltage in a mesh. At first I would simply remove them from the equations (Ideal current source doesn't provide / remove voltage right?). And then add some extra equations:
$$ I_a -I_b = 3 A$$
$$I_c = 1.25A$$

But can anyone do this? How to add current sources in the equations?
Similar question: how would one add other passive components like inductors/capacitors (diodes?) to kirchhoff's laws? Or can I no longer use this law then?


texts: Keeping a TVS diode biased continuously?

texts:
Quick question: Does operating a TVS at or above its "rated" (1 mA) voltage damage the device over time, as long as it doesn't get appreciably warm?

Background:
I'm driving some pretty hungry motors with a 4-cell LiPo battery. This battery is nominally at 14.8V, and fully charged at 16.8V (but pretty quickly down to 16.4V again.)

Now, the motors generate some pretty hefty noise on the power line, even though they're already enclosed in servo controllers with some filtering. Oscilloscope says about +/- 3V. There is also some risk that these motors will be back-driven when the device is turned off, and thus generate voltage, and they may be back-driven faster than the motors normally move, and thus generate more than the 16V I normally put in.

So, to soak up some of this noise, I've put some pretty beefy ceramic capacitors on the power line. Additionally, I'm putting a 5 kW TVS diode across the power, to clamp if voltage goes too high. When I used an 18V TVS clamp, it actually didn't do much in this case, because the noise I see is 13V - 19V, and at 19V, that 18V device doesn't really have a lot of conductivity.

Here's where the question comes in: I'm currently using a 16V clamp. I believe the 16V number is the approximate "1 mA" voltage, above which it starts to conduct more. Given that the battery starts out at 16.8V and stays above 16V for some time, is this continual operation right on the border of real conduction damaging for the diode? Even when the battery is fresh, the clamp doesn't conduct enough current to get hot, just luke warm at worst.

I'm guessing this is actually alright and I can look forward to years of trouble-free service, but if there's some wear-out phenomenon at work here, that would be foolish...


texts: What is the most convenient way to make/buy step 66V DC down to 12V DC?

texts:
There is a big battery that I have which has 64-67 volts, and I need constant 12 DC volts from it.

I tried ebay, but the best buck converter that I found had limit of 55 volts. My local electronic parts store doesn't offer what I want either.

I have some basic skills in soldering, I have some resistors, diodes and MOSFETS, I know how this all work separately, buy is there a way for me to make a converter that I need? Or where to get one?

Update:

For instance, can I use transformer-type of this-other-pulsing-type 220 AC - DC 12 converter, but with 66V DC input?

Update:

Can TPS2490DGS help me with it? I don't understand english well, but from what I can tell from the datasheet, this thing can control two external MOSFETs providing nice custom current and voltage outputs. But how to use it? It has 10 pins...

Update: The max current on the output I need is 4A.


texts:
I have a raspberry pi trying to drive an intercom system.

The intercom has a 12V output which when connected to ground opens the door.

What I want to do is have the raspberry pi 3V GPIO switch drive the optocoupler and this will ground the intercom opening the door, like below.

simulate this circuit – Schematic created using CircuitLab

The issue I have is not enough current is passing through the transistor side of the optocoupler to the emitter, with R1 being 150ohm, only 15mA passes through.

The optocoupler I'm using is:
http://www.cel.com/pdf/datasheets/ps2501.pdf

I'm assuming I'm using the wrong optocoupler or its something to do with the CTR, but I'm at a loss as to interpret what the issue is.


texts:
I'm working with the DRV103 PWM driver chip; this chip generates an initial long pulse followed by PWM and is useful for driving coils/solenoids. The problem is, this chip operates at 8-32V, while the solenoids I'm driving with it operate at 48V.

Normally this would be simple amplification, but it's complicated by the fact that the DRV sinks rather than sourcing, with it's OUT pin pulled high to its supply voltage while 'off' and sinking low when 'on'. This means I have to change a  PWM supply that sinks from ~20V to GND to one that sinks from 48 to GND.

I've come up with this circuit, is there a way to do it with a single transistor/component? The output must be active when DRV_OUT is low, to preserve the initial long pulse, and the solenoid is expected to draw 600-700mA. The PCB this circuit will be on only has a single 48V input, which I've regulated down to power the DRV.

The resistor divider is there because the cheap transistors I've got in there can only tolerate up to 20V at the gate (but up to 60V drain-to-source). DRV_OUT has a pullup resistor not shown here.


texts:
In my A level physics I recently did an experiment to find what the optimum frequency to send a digital signal through a RG58/U Coaxial Cable is. My results are available on Dropbox. What I found was the noise ratio oscillated. There also appears to be a slight bell curve, with more noise in the middle frequencies than the outer frequencies.

I initially thought this may be due to standing waves, however my maths disproved this (might still be a valid theory though). We have some physicists in the Science department, but it'd be nice to hear some ideas from Electrical Engineers.

Any and all ideas welcome. It might be worth noting that I was conducting this experiment in KHz when coaxial cables usually work at much higher frequencies, does this make a difference?

What is causing the oscillation pattern?


texts: Reading Optocouplers datasheet: current transfer ratio (CTR)

texts:
So I am working with an optocoupler at the moment, and having trouble understanding what CTR value to use in my calculations.
The datasheet states 50% Min and 600% Max, which is a huge difference. Do we always take the minimum for our IC/IF equation? Or do we take it from a graph? Its not clear on this datasheet


texts: Why is the time constant 63.2% and not 50% or 70%?

texts:
I am studying about RC and RL circuits. Why is the time constant equal to 63.2% of the output voltage? Why is it defined as 63% and not any other value?

Does a circuit start working at 63% of output voltage? Why not at 50%?


texts: Interfacing TDC sensor (inductive pickup) to a microcontroller

texts:
I'm trying to do some diagnostics on a classic car (aircooled VW). In particular, I'd like to monitor a signal that flags the TDC (Top Dead Center) on every engine revolution.
The signal is available via a plug with 3 contacts, one of which is grounded (it appears to be the shield for the two other wires). This is the schematic representation of the plug from the Owner's Manual wiring diagrams:

According to this source, the signal is generated by a variable reluctance pickup sensor. Quoting from it:

Beginning in '74, a sensor was added behind the flywheel to detect TDC.
As far as I know, this sensor was a variable reluctance type of pickup.
The flywheel had a steel pin on its back side which swept past the pickup face to create the pulse.
The combination of the TDC sensor and the #1 plug wire pickup allowed the computer to accurately determine initial timing setting and even to observe timing advance with speed change.

In short, it should create some sort of pulse for every revolution of the engine.
For more context, this other source has got more detailed information around the sensor. There it's called an inductive pickup:

It's an inductive pickup that produces a signal when each of two dowels attached to the back of the flywheel pass the sensor and it's used for measuring the engine timing electronically.

As I've not come across such inductive pickup sensors before, I'm not quite certain what type of output is to be expected from the sensor plug. This article seems to indicate it should be a voltage (1 to 2 V), but without previous experience with these, I cannot be certain.
Update:
After some more research, I've found out about these ICs as possible candidates to do the signal conditioning:

MAX9926: Variable Reluctance Sensor Interfaces with
Differential Input and Adaptive Peak Threshold
LM1815: Adaptive Variable Reluctance Sensor Amplifier
NCV1124: Dual Variable−Reluctance Sensor Interface IC. With an application note - AND8149/D: Understanding and Using the NCV1124 VR Sensor Interface

Of the three, the MAX9926 seems to be the only one with differential input, which seems to be what my sensor provides. The other two seem to expect a ground-referenced input. Regardless of the functionality, unfortunately, the MAX9926 SMD packages seem too small to do manual soldering on a prototype
These ICs seem to be based on detection of zero crossing of the output signal. Information on such sensors seems to be mostly for modern cars, where the sensor is facing a toothed gear with a missing tooth at the TDC point. The output seems to be an AC waveform for these. On my sensor, there is only a dowel (tooth), so I'm guessing the output would not be AC, but rather a positive pulse-like type of waveform.
If I were to feed it as an input to a microcontroller, what sort of signal conditioning should be applied to it to be able to read it? Or could I use one of the signal conditioning ICs?


texts: I have two parallel lines intersecting a circle.  Is there a command that will break the drawing up into separate pieces (2) at the intersection points? I want to send up with what's in (3).


texts: Low Overhead Constant Current LED Driver

texts:
I have a 3V3 rail and want to run an LED with a Vf=3.1V at 10mA with a constant current source. I'm used to circuits like the one below but the problem is that I only have 200mV of overhead and discrete circuits I am familiar with count on the 0.7V Vbe, which would brown out the LED.
Can anyone provide a constant current circuit using cheap discrete parts that can provide 10mA with less than 200mV of overhead? I am familiar with specific LED drivers or circuits that use op amps but they seem like engineering overkill to turn on an LED.


texts: Placement of feedback line on DC DC converter, before or after cap? (and dropout problem with LT8390)

texts:
I am using an LT8390 DC to DC converter, I have a highly inductive load and it is causing dips. The dips are shown here (and about a 6V drop for 7ms):

I need to get rid of the dips, which I will increase the output capacitance from 100uF electrolytic to 1000uF.

The layout is such that I have moved the feedback line after the filter caps, thinking that this would keep the line more steady at the point I wanted it controlled at. I'm wondering if this could be part of my problem.

From a control stand point, where do I want to place the feedback line entry point in the circuit?
Pictured below are the schematics, is A or B better?

Entry point A with feedback line before filter capacitors:

Entry point B with feedback line after filter capacitors:

Edit, here is the section of the board that has the feedback trace, I have ran it directly to the output of the board, instead of before the output cap.


texts:
I'm working on a prototype that has a few fine pitch (0.5mm) components. I'm thinking about adding local fiducial marks for these components as an afterthought. My idea was to place them close to the components where there is space for them. However, I have read here that local fiducials should be part of the component landmark. Do local fiducials really have to be placed directly at the component to be useful for the pick and place machine? Are they usually part of the footprint?
An example for my naive approach looks like this:


texts: Buck boost inverter design with current mode

texts:
As a project, I should design inverting buck boost converter without using IC.    I designed somehow the converter but not optimized it yet since I have no proper drive.
I am planning to set output of PI controller then use comparator and flip flop to feed MOSFET.
First of all, I have not much information especially about control diagram therefore I am kindly requesting your help. Questions are:

How much should I reduce to voltage to make PI controller circuit work properly I tried like 5V Vref?

For the output of the opamp what should I expect to see since I will compare this with shunt resistor current at the source of MOSFET ?

I created somehow transfer equations but can not calculate the proper capasitor and resistance so I tried it first without capasitor to experience opamp bit. I supplied almost 4.6V and Vref is 5V as far as I tried like that  5-4.6 = 0.4 V * 5 = 2V should be output of the op amp but I see at output 7V.  Is there something I did wrong ?

I just simulate the output of the converter to play over it with following values.
Vref3 = 400VDC
Vref = 5V
Transfer function
V(in) = 200V
V(out) = 400V
V(s) / E(s) = Kp + Ki /s
Kp = Rf/Ri    Ki = 1 /C*Ri
Some points might be defined wrongly so let me know please.


texts:
I have two signal voltages
V1 ranging from 100mv to 600mV and
V2 ranging from 100mv to 600mv.
I want to implement a difference amplifier using this opamp 601 which is a single supply CMOS. My Vdd is 5V and Vss is 0V.
When V1>V2; I am getting an voltage 'X' as per the TF (V1-V2)*R2/R1
However when V2>V1; I am getting 0V. Where in I am actually supposed to get -ve 'X'

Please guide me here.

Am I supposed to use -Rail to Rail Voltage OpAmp ?
I'm using R1 and R2 = 5.6 KOhm. Therefore my gain in 1.Because, I just need the difference between the signals
Is it because of improper choice of resistors ?

Thank you


texts: Is there any good way to limit primary current on a low inductance transformer?

texts:
For a while, I used hand wind transformers to make high voltage (250v, then several stages of cockroft walton to 750-1000v) from ~12-24v at around 10khz and max 100ma on the primary side. But of course it's a lot of work to handwind transformers, and the end result is really far away from a compact design.
I need the high voltage to drive PMTs so it's fortunately very little current.
My goal is to make a transformer that uses max 2W of power, and I think I can get away whit just 1W. Due to this it doesn't matter if the transformer is lossy at a non loaded state, because it uses so little power.
One day, I found small smd transformers on aliexpress what's usually used in flash lamp circuits. It has a 1:25 turn ratio that would be perfect for my needs. But it's usually used in high current applications to charge a capacitor, for a couple of seconds. Because of this the primary has a 8.5 uH inductance which means I need to drive it several MHz if I want below 0.1 amp usage, so it gets impractical pretty fast.
Is there a good way to reduce the primary current in a way that I don't need to drive it that fast. Say drive it at 200kHz max, and add series resistor or inductor, or some current limiting feature. Can that work? Or is it simpler to just go another route, and make say a high voltage boost converter?


texts:
I have an inexpensive 2 inch diameter speaker.  The back is stamped with “8 ohm, 0.5 W”.  The measured DC resistance is 7.2 ohms.

Does the stamped “8 ohm” refer to the total impedance at some standard sine wave frequency, e.g., 1 kHz?  If so, does that mean that when driven at 1 kHz that the total impedance may be expressed as 7.2 + j0.8 ohms?

Thanks.


texts: How to handle RS-232 grounding when connecting multiple devices?

texts:
I need to connect multiple devices using RS232 in a ring where the TX of one device goes into the RX of the next device. I will use a copper cable for the physical layer.

I can't use RS485 that supports multidrop instead.

I don't know how to handle grounding.

I don't know if I need some other components (comm boards, etc..)


texts:
What do VDDA and VSSA mean? Are they for a separate analog power supply? What is an analog power supply in this context? How does it differ to a digital power supply? Which one is better to use and in which situation?
For reference I'm trying to incorporate the STM32F103C8 to my first digital schematic and I'm not sure what those pin-outs are. But regardless to my specific situation, I'd like to understand the concept in general, hence the generic questions.


texts:
If I have 90 VDC 3.5 A, and I want to reduce to 12 volt, in excellent efficient the amps will be around 25 A.

Can I use a 12 V L7812 regulator?