texts: Transformer hum - DC offset? Does this cause transformer breakdown?

texts:
I have an integrated amplifier that I like, but it hums - it's an Arcam A22 and contains a big toroidal transformer. It sits on the desk right next to my monitor and I can't live with it. I just swapped in another amp and now I can hear that one hum too - it's one I built myself and is based on LM3886, it also contains a biggish toroidal transformer, Farnell-branded so hopefully not garbage. Not because it needed a huge one, because I had one handy.

There's also an autoformer, a big 2KVA industrial looking thing cast in epoxy, which we use to run a U.S. KitchenAid from Australian 240V socket. It hums too.

Forums discussing transformer hum in amplifiers tend to be populated by audiophiles so I am a little skeptical of the suggestion that it's down to DC offset. I can't find a definite answer one way or another here - possibly I don't know the right terms to search for.

Is this right? Could the problem with three humming transformers be that the house supply has DC offset? Is checking it as simple as measuring a wall socket on a DC range?

And could this DC offset, in causing the transformers to hum, be accelerating the aging of these transformers making them more likely to hum even if the DC is gone?


texts: Drawing with a triangular aperture in Gerber

texts:
So, I`d like to output a rounded equilateral triangle in Gerber format.

The first method I tried was to pick a large triangular aperture (%ADD11P,8X3*%, that is) and draw a small closed arc, a.k.a. circle, with it:

%FSLAX26Y26*%
%MOMM*%
G01*
%LPD*%
%ADD10C,1*%
%ADD11P,8X3*%
D11*
X00000000Y00000000D02*
G03*
G75*
I01000000J01000000D01*
M02*

However, the reference Gerber viewer throws a rather peculiar error while trying to interpret that file:

Arc with a non-circular aperture found. This is invalid.

Okay, I thought, but I can still approximate a circle with lines, right? Let`s try drawing a line:

%FSLAX26Y26*%
%MOMM*%
G01*
%LPD*%
%ADD10C,1*%
%ADD11P,8X3*%
D11*
X00000000Y00000000D02*
X11000000Y07000000D01*
M02*

And again, the reference app doesn`t seem to like what I`m trying to do:

Draw with an invalid aperture 11 emulated. Review resulting image.

And only if I correct my aperture definition to become a diamond instead of a triangle (%ADD11P,8X4*%) no errors get thrown.

Am I doing something wrong? Is drawing arcs or lines with triangular apertures documented as incorrect in the standard somewhere?

Naturally, I know I can compute 3 points and draw 3 segments between them using a circle and then fill the interior with a polygon, but I`d really like to avoid that. The task this one is a part of implies drawing multiple triangles with different orientations which can easily be set using the aperture angle parameter.

…Well, preliminary solution found:

%FSLAX26Y26*%
%MOMM*%
G01*
%LPD*%
%AM_my_own_triangle*
$5=$1*
$6=$2x$1*
$7=0.8660254x$5*
4,1,3,$5,0,-0.5x($5+$6),$7,-0.5x($5+$6),-$7,$5,0,$3+$4*
4,1,3,$5,0,-0.5x($5+$6),$7,-0.5x($5+$6),-$7,$5,0,$3+$4+120*
4,1,3,$5,0,-0.5x($5+$6),$7,-0.5x($5+$6),-$7,$5,0,$3+$4+240*
1,1,$6,$5,0,$3+$4*
1,1,$6,$5,0,$3+$4+120*
1,1,$6,$5,0,$3+$4+240*%
%ADD10_my_own_triangle,100x0.1x0x0*%
D10*X00000000Y00000000D03*
M02*

Here I make extensive use of the so-called Aperture Macro definitions. AMs can be rotated independently, see $3+$4+*, and support variables in arithmetic expressions.

This seems to be it, so if in a week`s time nothing less inelegant appears in answers, I`m going to answer the question myself.


texts: What does impedance control on a PCB mean

texts: I understand that when the electrical length is less than 1/10 of the trace length I would have to go in for impedance matching. A PCB impedance is controlled by its stack up. THat is thickness of prepreg, copper etc. So when a factory says it does impedance control , does it mean that they do that kind of a stack up? What does it mean when a factory says they will not do impedance control? Is it that they cannot do that stackup? If so , sticking to a normal 4 layer board stack is sufficient? What is th main FR4 specification that determines the impedance? Because right now I have a boards which has a stack up for 4 layers with thickness of each layer. DO I have to send this stack up to every PCB house and ask if they do this? How do I build these boards?


texts:
For example in a double side board I'm using one layer as gnd and the other layer as power, and then I route the whole circuit inside the planes.

Is that ok? Because I saw that usually both sides are ground. But its easies to me to work one plane as power and the other as ground.


texts:
I'd like to use this LED, but its package is just listed as 'MiniLED' in the datasheet.  Is that a standard package, or just a Vishay term?

Is there an equivalent part already in Eagle 6?  If not, I don't quite understand the  dimensions in the datasheet well enough to create the part myself.

http://www.vishay.com/docs/81233/vlmosy21.pdf


texts: Capacitive pen input sensors on screen edge

texts:
I've got a couple Kobo Touch devices in my possession. I've recently started hacking on the software. I'd love to enable stylus input by putting a Wacom or similar tablet behind the screen, but I don't think physics would permit.

Would it be feasible for a homemade solution to place capacitive or inductive sensors around the edge of the 4"x6" screen and get fast, accurate pen sensing? (~0.1 mm, ~60 samples/second)


texts:
Apologies if this is really obvious, but I'm struggling to understand the datasheet of the FL5150MX IC.

I think my confusion may stem from the integrated shunt regulator.

Under the 'Recommend Operating Conditions' section it states 'Ishunt=5 mA'.

Is that the current for this IC when operated at the typical 17V?

Datasheet


texts: Does C-1602A-1YN LCD use the HD44780 controller?

texts: I am new to using PIC microcontrollers and electronics in general. I have been reading a tutorial on how to interface a PIC with a HD44780 compliant LCD. As I have been shopping for a LCD I have been finding it difficult to tell whether a LCD uses the HD44780 interface after reading its datasheet. The specific device in question is the C-1602A-1YN from Tinsharp.  Please let me know whether this uses the interface, and where in the datasheet this information can be found.


texts: Do I need a balance charger if i use a Protection Circuit Module for Li-ion batteries?

texts:
I'm looking into making a battery pack for a portable speaker system.

If I use one of these:

http://www.ebay.com/itm/1-x-4S1P-14-8V-18650-Holder-Case-Battery-w-Li-ion-PCM-Protection-Circuit-Module-/151545904114?pt=LH_DefaultDomain_0&hash=item2348d6fbf2

or these:

http://www.ebay.com/itm/A-4A-PCM-Protection-Circuit-Module-for-14-4V-14-8V-4S-Li-ion-Li-Po-Battery-SM389-/221166587306?pt=LH_DefaultDomain_0&hash=item337e8e4daa

do I still need a balance charger? or can I just use a simple wall wart?


texts: Will this circuit work for smoothing out DC adapter output?

texts:
I have a battery driven touch activated kitchen faucet.  I am trying to convert it to DC adapter operated one to save on batteries.  First thing I tried is just hooking up a 9V 2.5A DC adapter.   It kind of worked but the faucet would turn on and off erratically without being touched.  I figure that electronics are sensitive to fluctuations that are not present when battery operated.

Am I right by thinking that the erratic behavior is due to fluctuations or is it likely due to something completely different?
If it is due to fluctuations, would the following circuit smooth them out?
If yes, what specific diode do I need to make this work?
Is this a common problem?  I did a conversion like this for some battery powered motion sensor lights and they work but once a month they need some kind of a "reset" to work again.  Could that be also related?

simulate this circuit – Schematic created using CircuitLab

Note: as you can tell I'm a complete beginner at this.  I kind of just googled stuff and figured out things in circuit simulator, but I have no idea what I'm doing so I would not be surprised if I'm on completely the wrong track in trying to accomplish this.


texts: I have a lot of threads stretched vertically. I want to detect the touch them. So that you can then play them like a guitar for example). What is the easiest way to do it (detect touch, not to make a guitar)? What kind of sensors could you recommend for that?


texts:
I am looking for a device (preferably in a small form factor) that can provide feedback for the user even after the power has been removed from the PCB (No, I don't want a battery powered solution.). (This device would need to be soldered onto the PCB.)

Basically, I am trying to replace a status feedback LED with something that continues to give feedback (holds its state) even after the PCB is no longer powered.
So, for example, I have a board with a bipolar LED: red for error, green for OK. I want something, that can visually indicate that an error has occurred (eg. over voltage) even after the PCB is no longer connected to the power supply and thus the LED isn't able to stay on any longer to indicate the error by being red.

I have some bistable (latching) mechanical solution in mind. Like a bistable (latching) relay with a state feedback, just without the power coil.

So basically I am looking for a latching mechanical LED... :D

Are there such feedback components on the market?
Do you know what they are called, how I can search for them?
Do you know some specific device mabey to get me started in my search?


texts: How can I tell how much juice a LiPo battery still has in it?

texts:
Suppose I have a circuit that draws its power from a LiPo Battery.
I would like to know how much power the battery still has in it.
Ideally a circuit of power level to voltage will be best .. this way I can connect the output of that circuit to a ADC input in my Arduino.


texts: Where does the Maximum Emitter-Base Voltage come from?

texts:
The datasheet for a BD679 transistor lists amongst the absolute maximum ratings that the "Emitter Base Voltage" has a maximum of 5v.

This figure confuses me - my mental model of a (BJT) transistor has the path from the base to the emitter equivalent to that of a diode and the potential difference is irrelevant - it is the current that controls the gate.

I have searched for this term and among the results get ones like this which appear to be talking about a different property of the transistor.

The notation ('Emitter Base Voltage' as opposed to 'Base Emitter Voltage') makes me think this might be referring to the maximum 'negative voltage' that could be placed across the Base-Emitter, instead of the maximum in normal operation. Is this correct?

If not, what is this figure, and what causes this junction to have such a low maximum compared with the rest of the device?


texts:
I have following situation:

Solarpanel with 20 W, 2 12V lead-acid batteries, the solar panel is charing the batteries. I measure the current coming from the panel with a ACS712 in a 3 minute interval.

The output then looks as following:

Amp;Date
1.08699;"2015-05-07 12:42:33"
1.09222;"2015-05-07 12:45:33"
1.00338;"2015-05-07 12:48:32"
0.984217;"2015-05-07 12:51:32"
1.06783;"2015-05-07 12:54:33"
1.01557;"2015-05-07 12:57:33"
0.386719;"2015-05-07 13:00:32"

I want to calculate the total ampere hours of a day.
I had the followin in mind:

As the ACS712 is very noisy, I set all values below 0.10 amps to 0.
I square every value, then sum it, then divide by the amount of values I have for each day.
Then I multiply by the amount of seconds that have passed between start and end.

The result is the charging current for that day, I think. Is this a viable approach to this problem, or should I skip the squaring part?


texts: Calculate highest modulating frequency for T.V. system

texts:
Calculate the highest modulating frequency for following data:

Case:
Alternate black and white dots for equal vertical and horizontal resolution.The no. of scanning lines are 250.Interlace ratio is 1:1 picture repetition rate is 50/second aspect ratio 12:9.Vertical retrace time 10% of frame delay.Horizontal retrace period is 20% of line period.Resolution factor is 80%.

Above question asked by my professor.I solved it.

My ans:

resolution factor=80%=o.8=kell factor

Vr=Na*k=250*0.8=200

Hr=Na*k*aspect ratio
  =250*0.8*(12/9)
  =266.66 pixels or line
  equivalent 267 pixels

There is 250 lines/frame there is 50 frames/second

So,
250*50=12,500 total lines

So time required is,

1/12,500=80 micro second

Retrace period is 20% of total time,

So, 80 micro second*20%
    =16 micro second

So,trace time = 80-16=64 micro second

1 horizontal line=267 pixel
2 pixel=1 cycle

So,

1 cycle=267/2=133.5=133 cycle (equivalent)

For 133 cycle required 64 micro second,So for 1 cycle

=64*10^-6/133
=0.48 micro second

So,

fmax=1/Tmin=10/0.48 micro second=2.08 mhz

But sir told me there is some small mistake in my solution but I didn't get whats wrong in above solution.

So is there anybody who can help me with this ?

Thank you.


texts: What is the significance of primary and secondary flats in wafers?

texts:
I am confused about how the orientation of primary and secondary flats represents the crystal orientation of the semiconductor. I looked at this site mentioned in this answer:

  The primary flat has a specific crystal orientation relative to the wafer surface; major flat.

Is the "specific crystal orientation" the same for all wafers? What is "major flat"?

  Secondary flat Indicates the crystal orientation and doping of the wafer.

How does it do that? For example what does a 45° angle between primary and secondary flats represent? Is there an actual physical correspondence between flat angles and crystal orientation? Or is it just by convention?


texts: Using a BeagleBone board as a serial terminal server

texts:
I am trying to use a BeagleBone Green Wireless board as a serial terminal server.

That is, connect USB-UART cables to the USB ports to control other serial devices when I log into it over the internet

I currently have one USB-serial cable connected at /dev/ttyUSB0, which is then connected to a serial device in which I wish to control. From the terminal inside the BeagleBone, I use the screen command to communicate with the serial device as follows sudo screen /dev/ttyUSB0 115200

On attempting this, the communication is extremely slow, taking about 20 seconds or so to get responses. Is there anything I can do to solve this, or is this the limit with suing USB 1.1 on the BeagleBone device?


texts: Is the current flow through the diode carried out by both holes and electrons?

texts:
Consider a pn junction diode is forward biased. And assume the voltage applied to the diode is enough such that the depletion region is disappeared.

In this circumstance if we zoom inside the diode, can we say the following for the electric current through the diode?:

The current in p part of the diode is carried by the holes; and the current in the n part is carried by the electrons?

If so, does that mean the speed of the current flow is different at p and n parts?

edit: Is the resistance at p and n parts of the diode different in forward mode?


texts: How does random memory access of RAM work?

texts:
HDD works in a partly sequential manner. However, RAM is known for random memory access, allowing equal speed of memory access for every location at every time.
So, what makes RAM so special? How does random memory access work? (I know that DRAM is not exactly random access, and works in burst. I am not sure what this means also.)


texts: Programming ATMega328 from arduino with separated power supply

texts:
I actually need to update the code on a project who use an ATMega328. I'm using an arduino as a SPI programmer.

So, I need TX/RX and RESET pins to program the external ATMega328.

My problem is, the actual ATMega328 run on an other power supply than the programmer. Is it a problem ? Should I use optocouplers to connect the two circuit for the programming ?

I can replace the power supply by the +5V/GND of the arduino, but I'm just wondering as this could be really easier for me.


texts: ZigBee end-device could not connect to Coordinator

texts:
I'm using Atmel's ATMEGA256RFR2 (link) for Zigbee (802.15.4).

I needed to redesign the antenna part because with the previous design it did not produce good range.

Here is my other (answered) question about the redesign: link.

Now, after assembling the board I have stuck because there is no link between this end-device and the coordinator.

Parts:

Microcontroller: Atmel ATMEGA256RFR2,
Balun: Johanson 2450BM15A0015,
Antenna: Johanson 2450AT18A100E.

Schematics:

Microcontroller:

Antenna:

Layout:

N$27 wire is matched to 50 Ohm impedance, and design recommendations from the antenna's datasheet has also been considered.

The bad:

With the previous schematics and layout this end-device and coordinator could find each other but the link quality was wrong. (You can find the previous schematics and layout in the other question I've linked)

Now I have these questions:

Is the new schematics have some trivial problem compared to the previous one?
Can I somehow test the sanity of the RFN and RFP pins of the chip?
What would worth trying to make this end-device find the coordinator (possibly without replacing the whole board)?


texts:
What are the main advantage of using 3 phase 4 wire supply over 3 phase 3 wire?
What is difference between both?
I have seen a energy meter using 3 phase 4 wire power supply and i am not getting why it is required.


texts: The different of Load Series and Parallel with Transistor in Switching Circuit and Amplifier Circuit

texts:
I'm so curious, What is the different of putting load series or parallel with resistor like below circuit

the circuit will be used just for switching circuit with VCC higher than the input
Is there any correlation with current flow through the load? which is better for the switching?

if i use the circuit for the amplifier (of course there will be a Voltage Divider Biasing circuit and Resistor and capacitor in emitter), which is better?

thank you


texts: Derivation of the compensating resistor in integrator with DC gain control

texts:
Hi all in EE stackchange,
I wonder how the compensating resistor (\$R_3\$) in integrator with DC gain control equals \$R_3 = R_1 || R_2\$, which is to offset effect by the input bias current. I was trying to derive it by same way in Razavi's textbook but I can’t reach the result of compensating resistor \$R_3=R_1 || R_2\$ (As depicted in below Figure) It would be very appreciated if someone let me understand this. Thank you in advance!


texts:
I am having some trouble dealing with xbee s2 sleep mode. Hope you all can give me some help.

The following is my setup:
The network composes of one coordinator and several end devices, all in transparent mode The coordinator is connected to X-CTU and a computer and receives all the messages.

End devices are connected to another MCU(MSP430), MCU wakes up xbee periodically(8 seconds, 16 seconds, 48 seconds etc), writes a short message (11 bytes) to xbee through UART, then immediately asserts sleep_rq pin of xbee.

Here is the problem:
if I set the wakeup interval at 8 seconds, then all messages from the same end device will come in two messages batch at roughly 16 seconds interval instead of one message every 8 seconds.
If I set the wakeup interval at 48 seconds, then again, all message still tend come in two messages batch roughly every 96 seconds, plus the last two bytes of the second message constantly get lost.

The SN, SP on both coordinator and end devices are set properly. The RO is at default value 3.

If I don't assert sleep_rq pin of xbee and keep xbee awake all the time, then no matter what the interval between two messages is, all the messages come in one by one at defined interval.

I believe this has something to do with packetization but I could figure out the exact problem.

Edit: I believe at certain conditions, when sleep_rq is asserted, message up to certain length will be retained in the transmit buffer of xbee until xbee being waken up next time. I am wondering if there is any way to force xbee to send out everything before entering into sleep. One way of doing this is to write enough dummy byte to fill up the entire transmission buffer(84 byte in transparent mode without encryption). But this is really a waste of limited throughput of xbee network. So I hope someone can come up with something better.

This is driving me crazy. Some one please direct me to some relevant literature.

Thanks in advance,
ZL


texts: How can I identify lead-free solder if it's unpackaged?

texts: Is there a test to determine whether solder is leaded or lead-free? Perhaps conductivity/resistance?


texts: Dark sensor circuit by using two transistors

texts:
Could you please help me by checking whether this circuit diagram is correct for connection digram.

Kindly ignore resistor R2 330 R (as it is not included in the connection diagram)

Actually I am a beginner in the electronics.


texts:
I have built an FPGA based DDS (fc=200MHz.  out: 0-50 or 0-80 MHz) . I have a decent DAC output  wave and now trying to build an appropriate filter for it ( Fig-1 ). The filter works rather fine but there are 3-4 strange noises there ( I have another question here that I think the solution for each one may help in solving the other one) .

I say "strange" because according to Nyquist diagram , the image wave should be at a higher frequency but my noises are in lower parts of the band. For example at 20 MHz, we should see the image frequencies at fc-f = 200MHz-20MHz=180 MHz. This noise is easily removed by a low pass filter but I have these noises also:

1- Fig-2 50-60 Hz (this may be due to main line  but this is 7 volts pk-pk !!!)   .

All the upper frequencies drive on it

2- Fig-3     130-140 Hz . I can't guess where this has come.

All the upper frequencies drive on it.

3- Fig-4  Around 50 KHz:  this one has steps between cycles  and  I have never seen anything like that before .

All the upper frequencies drive on it

The main frequency ( in this example 20 MHz) drives on to of all of them ( 4- Fig-5  ). This causes that the main frequency jumps up and down on the oscope screen

Settings:

1-  These noises are just seen in higher frequencies ( > 5 MHz)

2-  When putting the oscope probe on 10x, their amplitude is reduced ( not too much. just a bit) but the output shows step distortions.

3-  Probe's barrel clasp is connected to the ground ( with many decoupling capacitors ).

4- tried the same configuration with dedicated DDSs ( AD9850 , AD9833) and the same noises arise at freq > 5MHz.

Edition: results with an analog Oscillosciope added at the end ( Fig 7-9 )

Fig-1 The filter:

Fig-2: 50-60 Hz:

Fig-3:  130-140 Hz

Fig-4  50KHz

Fig-5  Main frequency

Fig-6 Up jumping main frequency:

Fig 7- analog oscilloscope: low frequency:

Fig -8 analog  oscilloscope: main frequency:

Fig-9  analog  oscilloscope: Jitter like behavior seen at fx10 setting:


texts: Instrumentation Amplifier - how to use it correctly

texts:
I am trying to perform some measurements based on a special technique used to detect corrosion in rebars of concrete bloc. The idea is to measure the potential difference between an electrode and the rebar:

I tried it with a conventional voltmeter. It worked just fine. The potential difference lies between 0V and 1V.

Now, I want to do it with a micro controller. My idea was then to connect the two inputs (electrode and rebar potential) to the input of an instrumentation amplifier and then to read the output with an ADC input of the micro controller.

To do so, I used the INA118.

I left the Rg input unconnected to have a unity gain.

V+ = 5V
V- = GND (therefore "single supply operation")
Vo = ADC input (with 100nF capacitor to GND)
Ref = GND

I also connected two resistors of 1MOhm between Vin-,+ and GND.

Now the problem is that I have nothing on the output of the INA118. More precisely I have 30mV always; even when I short-circuit Vin+ and Vin-.

What is wrong with my circuit?

Should I add an offset voltage to the inputs of the INA118?
I have read that:
"With single supply operation, V+ and V– must be both
0.98V above ground for linear operation. "

Or is it that the input bias current is too low?

Thank you

Image of the circuit:


texts: I2C Pulldown and Pullup...is it possible?

texts:
I am using a PIC18F2550 to control a H Bridge, and I am using several input signals, such as RS-232, I2C and Analog 0-5V to make the final PWM output for the H bridge.
I have a problem with PCB space, so I am joining all the input signals in 4 pins, since they will never be used together: Vcc, GND, S1 and S2.
S1 will be RS-232 Tx connected to the I2C SDA, and S2 will be RS-232 Rx connected to the I2C SCL and the Analog input. This way, since the user will select which kind of control he wants before using the system, I can save some space. Just to make it clear: The user will select one kind of input (RS-232 for example), and all the other inputs connected to this PIC pin will become a disabled input pin so to not interfere with the communication.

Since I have an analog input (were if the user send 0V the PWM will be 0% and 5V it will be 100%), I wanted to add a pulldown 100K resistor to make it safer in case there is nothing connected, because this is an analog control, so in case the connection is lost, the analog pin could read some voltage and the motor could go nuts. But since I have a I2C connection in the same pin, is this possible? I think it isnt because the I2C needs a pullup, and this will make a voltage divider, right?

Does anyone have a better idea, about a way to make it read 0V in case there is nothing connected in the analog mode, and still have the option to use the pins for I2C or maybe SPI in the future too?
Thanks!


texts: Choosing a transistor and resistor for PIC input pin protection from Car Power

texts:
Further to my previous question,
Using a PIC to perform switch on and timed shutdowns in automotive environment

I've been pointed at zener diodes and voltage dividers, but I'm now confused by the PICs builtin weak pull-up resistors (and if I check the datasheet, values are TBD... I assume something like 10k?)

So the PIC input pin protection circuit I think I have understood is this:

But using weak pullups, I think I could do this:

But all this does is swap a resistor to a transistor.

Update

Further to comment from @PJC50, I now think the circuit utilising the PIC's pullup resistors would look like this:

It's now clear why I should do this and how it reduces component count.

How do I choose a resistor and transistor that are suitable?

Is the voltage divider circuit correct?
Is the circuit that uses the weak pullups correct? (i think not)
Why would I use pullups over normal voltage divider?

So my new circuit looks like this:

Update 2:

I've tested the circuit with pull ups, and I think I'm getting closer to real solution, any further comment/critique welcome!


texts: Raw data acquisition from a capacitive touch screen

texts:
I'm trying to integrate an existing PCAP touch screen into an experimental project I'm working on. For it to work the way I want, I need access to the raw data from the touch-screen nodes instead of what the controller would normally output, post-filtering and finger detection etc.

I've found an example of someone achieving a similar result using the official Raspberry Pi 7" screen :
Example using the official RPI 7" screen

That shows exactly the sort of raw output I would be looking to obtain. In that case however, the controller just happens to already have a separate I2C output and the controller chip in question is documented and provides the raw data, in addition to the filtered.

Ideally for a prototype I need to use something at least 24-28". I had a Hanns G 28" touch screen lying around, so after taking it to pieces I discovered it's using a SiS9250 + SiS9202 + Lenovo(HST)_28"_V02 controller. These chips are ganged together to handle the large format. The particular chips don't seem to have any datasheets or reference available so I'm guessing they're proprietary for OEMs, and this appears to be the case for all the larger size screens I've looked at. The touch controller board has 3 FPC (70pin) connectors, so I would guess there are 70 driving electrodes and 140 sensing based on the configuration of the chips on the board. Their site mentions a high driving voltage of 30V but that's about the limit of the technical details.

I have an RPI 3 and some microcontrollers lying around and was hoping to get something wired up using one of them.

The two approaches I could think of would be:

Use a controller which exposes this raw data, assuming that the controller provides some sort of I2C / GPIO capability alongside the processed touch data.
This would be a preferred option, as this process could run independently from the existing OS/driver applications requiring touch support.
Ignore the controller completely, connect up 3 FPC 70pin connectors, using either the R.PI or MCU drive (30V ?) through the drive electrodes sequentially and then read the voltage from each column, possibly through a bunch of analog multiplexers as we'd have 140 inputs. Assuming the effect of the capacitance on the nodes is interpreted as a voltage change (range) on the inputs.

If anyone has any ideas how to go about this or has attempted something similar, any suggestions on the way forward would be hugely appreciated!


texts:
SBC like Raspberry have the 40 pin header which contains a I2C master. This is a accessible via /dev/i2c-0.
I would like to achieve the same thing on my linux laptop (ubuntu) using the FT232H chip. I can interface the FT232H using the pyftdi package, however it would be great if I could use the exact same thing on any linux machine that has a free usb port.
When I plug the device on my laptop(linux), I can only see that the UART is mounted to /dev/ttyUSB0. Anybody an idea how to 'mount' the I2C function of FT232H on /dev/i2c-0 (or /dev/i2c-1, -2, -3, ..)?
I don't know where to start looking, so any help is very welcome.
Thanks.


texts: What is the proper way to ground this DC circuit?

texts:
I have 3 components: dual +/- power supply, linear voltage regulator, and pre-amplifier. They are to be mounted in a aluminum box. The PSU is powered by a 24V DC bench supply. I am confused on where to ground each component with regards to the "common" ground of the PSU. The pre-amp is processing signal data, where as the LVR is simply stepping +12V down to +9V.

My first thought is to connect the PSU "common", the GND of the pre-amp, and GND of LVR to a star ground mounted on the chassis. I don't want to damage the PSU so I was hoping to get advice from more knowledgeable folks. Thank you!


texts: What is this transformer, is it package only without coil or complete transformer?

texts:
I did a simulation on TI Power Bench for a isolated power supply,
There I got transformer spec in BOM,
Core=Wurth Elektronik , CoilFormer=Wurth Elektronik
Core=150-2340 , CoilFormer=070-4477
Core Type = ER14.5
Core Material = TP4A
Turns Ratio(Nps) = 5:2
Is this available purchase/ready to buy or Wurth Elektronik would custom made for this spec with ?
edited
Ti does not provide no inductance of the coil
ti web bench parameters

Vin min 7.9V
Vin max 8V
Vout 5V
Isolated yes
Iout 1A
temperature 30 Celsius


texts: Why do dc motors have the magnets on the sides and the coils rotating in the middle? Why isn't it the opposite? The magnets rotating in the middle and the the coils static on the sides. Wouldn't it be better to rotate the magnets that are free of wires while the coils need to be connected to wires?


texts: If one node is transmitting a message to more than one node and if one of the receiver node failed to receive the message, then how does the transmitter node know which node has failed to receive the message?


texts: What does it mean when a resistor symbol in a schematic has a value of zero or "NO-POP"

texts: Two questions in one. I'm looking at a schematic with two resistor symbols (unrelated to each other), with one having a value of zero and the other having a value of "NO-POP". What do these mean? If I had to implement their circuits, what components would I use?


texts: Is it possible to read erased flash memory?

texts:
In hard disks, a "quick format" does nothing to the actual data on the disk - just clears the FAT (file allocation table), which then appears as a "blank disk" to the user. Therefore, it is fairly easy to ignore the FAT and read that data. Although it is tricky to read specific data, as there are no indicators to where a particular file begins and ends. Some format commands even save a backup of the FAT table, and restoring this backup manifests as the "unformat" feature.

A long-format of a hard disk does reset most of the data, which would seem to eliminate the possibility of reading said data - except for a characteristic inherent to magnetic storage media: hysteresis. When a bit is set or cleared on a hard disk, the process is not 100.00% accurate, as the media exhibits hysteresis. So some small amount of residual magnetism remains from the previous operation, and certain software tools can be used to scan areas of the disk (many times) to read that fraction of a percent of latent magnetization and "recover" this overwritten data.

But how do today's solid-state non-volatile memories fare? Thumb drives, SSD's, NAND Flash? The only relevant information I could find about their security and vulnerability is in this Wikipedia article which states:

  In addition, deleted files on SSDs can remain for an indefinite period of time before being overwritten by fresh data; erasure or shred techniques or software that work well on magnetic hard disk drives have no effect on SSDs, compromising security and forensic examination.

Wait, what? These seem to be two completely different statements - the first implying that long-formats are never done and Flash therefore is always susceptible to my first paragraph's vulnerability. This can't be, correct? As I can "long format" a thumb drive or SSD, or instruct a uC to overwrite every block of a NAND Flash. And since wear-leveling places blocks somewhat randomly, I'd assume which blocks get overwritten to be rather random as well. So perhaps not all of a file would be overwritten in time, but some of it seems highly likely.

It also states that erasure or shred techniques do not work on Flash which I find hard to believe. As long as every allocation unit were overwritten, that would make any data completely un-recoverable, correct?

How this applies to EE.SX: Imagine a NAND Flash with several crypto key pairs on it. If the chassis is opened, the device is erased, so nobody can "get" the keys. But is an "erase" enough?

That said, are nonvolatile flash memories susceptible to any type of data recovery technique? Is there any electrical field hysteresis to leverage for recovering overwritten data?


texts: What PCB thickness is this USB connector targeted for?

texts:
The following USB Type C connector has lead lengths of 1.6 mm:
https://adam-tech.com/downloader.php?p=USB-C31-S-RA-CS1A-BK-SS-TR.pdf

What's a good PCB thickness for this connector? Also, why are there so few USB Type C connectors made for 1.6 mm thick PCBs?


texts: How to wire up a street light to change lights in specific states (digital circuit)

texts:
This is the final project for the only electronics course in my career. I have never taken any other electronics course and I'm seriously at a lost here. I need to score 100 here to pass the course.

I need to create a synchronous counter that will control a streetlight with 4 sides. The South-North side has 4 lights (an extra green one to steer left) while every other has 3.

The cycle lasts 14 seconds.

I have the counter made, but I have no idea how to actually make it turn on/off the lights at the specified times.

Problem instructions are as follow:

  "The first green light of S-N and the one from N-S must light up for 5 seconds,
  meanwhile, the red lights from E-W and W-E must be on as well.

  After these 5 seconds, the yellow lights for both S-N and N-S turn on for 2 seconds.

  After this, the red lights for S-N and N-S turn on
  and the 2nd green light of S-N will turn on for 2 seconds to allow traffic coming from the south to steer to the west.
  This is the only instance where 2 lights of the same side are lit up simultaneously.

  While the 2nd green light from S-N is on, every other Red light must be on as well.

  After the 2nd green light from S-N turns down, the red light of S-N and N-S will stay on, and the green lights of W-E and E-W will turn on for 3 seconds.

  After these 3 seconds, the yellow lights will turn on (while the green ones will turn off) for 2 seconds

  and then the red ones will turn on, starting the cycle anew.

  Total duration is 14 seconds".

This is SERIOUSLY driving me crazy because I see no way in which I could say "From 1 to 5 stay ON and then turn OFF", I cannot think of a single way of setting up logic gates so that they're only outputting 1 to the lights when
they're 0001, 0010, 0011, 0100 and 0101. Because if I make logic to output 1 when you have that, then literally every other binary code except from 0 and 15 will output one. I.e the lights will never turn off.

Note that this is entirely digital, using Digital Works. The solution cannot have any component that is not included in the program and should, in fact, only include Flip flops, LEDs, logic gates and of course the wires.

EDIT: Thank you for your help and tips. I managed to do it.
For reference, here is the completed and working circuit:


texts:
from MOS theory we know that, in case of a P substrate, a Gate-Bulk voltage higher than a certain threshold value creates an inversion layer, in this case made of negative charges. This is also described in wikipedia (https://en.m.wikipedia.org/wiki/MOSFET).

But we always consider as threshold voltage that between Gate and Source, and this seems in contrast with the previous description. The answer cannot be (as someone told me) "Source and Bulk terminals are often connected together", there is a deeper analysis.

For instance, let's consider a pass transistor circuit made with a N-channel MOSFET (enter link description here).

The input signal is sent on the drain and the output signal is taken at the Source. Its maximum value is VDD - Vthreshold since from that value, the Vgs voltage would be lower than Vthreshold, as we know from theory. From this analysis we understand that the voltage that switches on a NMOSFET is that between Gate and Source. And here the Source is not connected to Bulk, which is at GND. This does not agree with MOS theory.

So, which is the voltage that switches on a NMOSFET?


texts: How does this 433Mhz garage remote control work without an antenna?

texts:
I have a 433 Mhz garage remote control that works very well even from 30 to 50 meters and it has no antenna!

How is it possible that it works so well without an antenna?

Also, given the picture of the PCB, is it a "superregenerative" or a "superheterodyne" module? I was told the latter was better in terms of range.

PCB of the remote control:

Here with the case:

PS: As a comparison, I'm struggling since days with these transmitter and receiver modules based on FS1000A and even with 17.3cm long antennas, the range I get is really poor, only a few meters... (maybe I was just unlucky with this production batch):


texts: Using WiFi adapter to capture different wireless traffic

texts: I wish to be able to read wireless traffic sent from my wireless keyboard. At first I thought I could just buy some board like Arduino, plug in a module like nRF24L01+ and use this combo. Since I'm not good at all with electronics, I'd rather find another solution and, eventually, I thought that I already have a transceiver for wireless comunication: my laptop's WiFi adapter. As I said I don't know much about electronics so I wonder if it's actually possible to write, let's say, a linux device driver for my adapter in order to make it able to capture and process wireless communication other than WiFi. Is there some electronic impediment? Is this just a software problem or maybe my WiFi adaptare firmware won't allow me to read anything except from WiFi traffic?


texts:
I want to build a signal generator using a ATmega 328P on an Arduino. Which way would be better. Using one of the timers (8bit or 16bit) built in to generate a PWM and then low-pass filter it, or using a R2R ladder system?

I care more about harmonics than frequency, but I'm hoping for about 10kHz or above.

Thanks for your advice.


texts:
I would like to know which inverter function is correct for BLDC motor model simulation.
I want to create mathematical model of this scheme:

where BLDC motor model is created based on "http://webfiles.portal.chalmers.se/et/MSc/BaldurssonStefanMSc.pdf".
I have seen several proposition of inverter functions. First one is from earlier link:

But it gives currents signals other than ideal (4 levels instead of 3):

Other source:
"https://www.youtube.com/watch?v=l60p4G7Bdi0&t=3s"
Shows another inverter function which gives currents signals more similar to ideal (3 levels)

I would like to know which version is correct and why.
Simulation was runned for:
R=12.5
L=0.91
Ke=0.01
J=0.005
Kt=0.01
Kf=0.0000000138
p=2
TL=0
Vs=6


texts:
I have 4 opamps which need +12 V and -12 V supply voltage. I have 2-layer PCB and want to keep it that way; the bottom layer is dedicated for GND of course. To keep noise/EMI as low as possible, +12V and -12V should be routed close to each others to each opamp. But that would mean quite a few passes to bottom layer and back to top layer and breaking GND layer.

So what should I aim at:

Keeping +12 V and -12 V on top layer as much as possible: More solid
GND layer but bigger space between them +12 V and -12 V.
Routing +12 V and -12 V as close together as possible: Break GND layer
more but smaller space between +12 V and -12 V.


texts: What would be the lightest batteries to run a 12v/12.5A skillet for 2 hours?

texts:
I like to go camping and use various gas stoves to do my cooking. I was curious with the current (no pun intended) state of battery technology, how heavy, bulky, and what sort of wiring it would take to cook via battery.

I found an electic skillet designed for RVs online, and its specs are 12v, 12.5amps, 150 watts.

What would be the lightest combination of batteries (motorcycle, car, AAs (NiMH, Lithim, Alkaline)) that would be required to satisfy this, and how should they be wired.

I had read that AA's although they may be rated to ~2000+ mAh, can't consistently put out more than .5 A.  So my thoughts were 25 in parallel to get 13 amps, then those 25 in series with another 7 sets of 25 to get up to 12v.
In theory that would provide the necessary amps and volts, for as much as 5 hours, but I'm sure there's more to it than that, and I'm not sure if a 12v motorcycle battery would be far smaller and lighter and still satisfy the requirement. And all of my calculations might be way off.

Thanks


texts:
I am creating a circuit which is controlling a solenoid valve and I was wondering what is a safe distance to keep this circuit from the solenoid valve. Circuit includes an ESP module and some other deep components like resistor capacitor and some TIP122 transistor.
I am planning to keep the solenoid valve within 5 millimetres of the circuitry and the solenoid valve takes around half an ampere current and is controlled by a 12 volt DC.
Would the electromagnetic radiation from the solenoid cause any harm to any of the components or ESP microcontroller?


texts: Why is there a 'zeta' in zeta converter?

texts: Why is the zeta converter called so? What is the significance of the Greek letter '\$\zeta\$' in it?


texts: Capacitor notation number multiplied by number in circuit diagram (22x16)

texts:
On circuit diagrams, I sometimes see the notations for the capacitors like C57, 22x16, or C40, 10x10

What is 22x16 (10x10)? (it's not the physical dimensions).


texts:
This App Note states:

To have the maximum ADC conversion precision, it is preferable that
the ADC dynamic range matches the maximum amplitude of the signal.
Assume that the signal to be converted varies between 0 V to 2.5 V and
that VAREF is equal to 3.3 V. The maximum signal value converted by
the ADC is 3102 (2.5 V) as shown in Figure 9. In this case, there are
993 unused transitions (4095 – 3102 = 993). This implies a loss in the
converted signal accuracy especially if the ADC lineaty performance is
not ideal.

In my case I'm using a SAR ADC to measure RMS of sine wave. The ADC VREF is 3.3V coming from the same power supply of the microcontroller. The mid point of the input signal is set to 1.65V using the circuit below.

With 1.65V being the mid point, my RMS measurements have around 7% error.
When I use 1.25V as the midpoint as below, the error is reduced to ~1%.
The point is that I was expecting the error to increase with 1.25V mid point since the unused ADC translation range increased as my VREF remained to be 3.3V. Why is this?


texts: Need help with gaining some basic intuition regarding transmission line traveling weaves?

texts:
I always thought about current traveling through a wire much the same way marvels would travel inside a hula-hoop (all moving at the same time from one end to the other).

In this simple scenario, there is only one voltage source (only one differential of potential) that is fixed (never moves) and electrons flow in and out from that immovable voltage source.

But now, I have discovered that this is not always the case, particularly in the case of fast voltage pulses which cause traveling voltage waves. I discovered this after watching a YouTube video that talks about transmission lines. In the video, the narrator talks about what happens when a voltage pulse is sent through a transmission line (https://youtu.be/I9m2w4DgeVk?t=4m5s). The three illustrations below are excerpts from the video and show what happens (according to the video) when a battery is briefly connected to a transmission line.

The last illustration shows what I think is the infamous voltage traveling wave speeding along the transmission line.

So here are a couple of questions that are driving me crazy:

How many waves are traveling on a traveling wave? One or two? I am going to guess two (one positive wave lacking electrons and one negative wave with excess electrons).
What is physically occurring inside of these traveling waves? If I was able to get extremely close to these waves would I see one wave as a traveling bundle of excess electrons and the other wave as a traveling bundle of lack of electrons?
Assuming that point 1 and 2 make any sense, how come if the transmission line is short-circuited at the end there is a reflection of the traveling waves? Why doesn’t the wave with the excess electrons deposit the excess of electrons in the wave with lack of electrons and call it a done deal? Why must they bounce around?

At this point it should be evident that I have no idea what I am talking about! So what I am looking for is to gain some basic intuition regarding what is going on here!

Thank you very much for your help.


texts: Discharging capacitors on a computer motherboard for safety

texts:
A daycare in my city has taken a donation of desktop and laptop computers for the older children to take apart.

I am concerned that the various capacitors would present a shock hazard for the children, and have volunteered to discharge them.

The original plan was to unplug the computer, hold the power button to discharge the PSU output capacitors, then cut off an ATX cable and short the rails to ground, which should take care of the electrolytic filter capacitors on the motherboard.

Would this create a floating potential that could cause a shock if someone were to be touching the case and something else that was properly grounded?

Also, would there be a good way to discharge the PSU input capacitors?


texts: Typical (cell-phone quality) audio modules and formats

texts:
My question is twofold :-)

What are typical audio modules that I can use in a lo-fi electrical application to playback some simple music (of about 1 minute)? Think of cellphone speaker quality.

What is the digital format of this audio? I spoke with an electrical engineer and he mentioned PCM A-Law. which sounds reasonable due to the small usage. Are there any other formats available? Another tip I got was MIDI, but I think that using a wavetable limits the music capability but makes it easier.

Thanks in advance! :-)


texts: No output for C++ GPIO code for Beaglebone Black

texts:
Could anyone tell what could possibly be wrong in the following C++ code for enabling and setting pin no 49 (p9_23). I am directly checking the output on multimeter.
#include <string>
#include <fstream>
#include <sstream>
#include <iostream>

using std::ofstream;
using namespace std;

#define gpio_path "/sys/class/gpio/"

enum GPIO_DIRECTION {INPUT, OUTPUT};
enum GPIO_SETVALUE {LOW=0, HIGH=1};

class GPIO {
  private:
    int number, i;
    string gpio_dir, name;
    string filename, a, c, j, b, path, dir, val, value, high, low, input, output;

  public:
    GPIO(int number);
    virtual int setdirection(GPIO_DIRECTION dir);
    virtual int setpin(GPIO_SETVALUE val);
    virtual int writein(string filename, string  value);
    virtual int  write(string filename, int  value);
    virtual ~GPIO();
};

GPIO::GPIO(int number) {
  this->number = number;
  std::ostringstream s;
  s << "gpio" << number;
  //again converting stream to string
  this->name=string(s.str());
  j=string(gpio_path);
  this->path=j + this->name;
  write("j/export", this->number);
}

int GPIO::setdirection(GPIO_DIRECTION dir) {
  switch(dir) {
  case INPUT:
    return this->writein("path/direction", "in");
    break;
  case OUTPUT:
    return this->writein("path/direction", "out");
    break;
  }
  return -1;
}

int GPIO::setpin(GPIO_SETVALUE val) {
  switch(val) {
  case HIGH:
    return this->writein("path/value", "1");
    break;
  case LOW:
    return this->writein("path/value", "0");
    break;
  }
  return -1;
}

int  GPIO::write(string filename, int value) {
  ofstream ds;
  ds.open(filename.c_str());
  ds<<value;
  ds.close();
  return 0;
}

int GPIO::writein(string filename, string value) {
  ofstream ls;
  ls.open(filename.c_str());
  ls << value;
  ls.close();
  return 0;
}
```


texts:
I am not a specialist in electronics. I'm just a programmer. I ask this question just for fun.

My question: How the frequency for a design of a digital circuit is chosen?

Is the frequency chosen "before-hand" before doing actual design, "as the last choice" after the circuit is already designed, or "in-middle" adjusting it several times during design?

What if it turns out that different parts of a big circuit require different optimal frequencies? Isn't it a reason for redesign of some parts of the circuit?

Could you describe the stages of choosing frequency during design?

How it has happened that many of "Core" series CPUs had lesser frequency than Pentium-4 having indeed greater speed?

I've also heard that lesser frequency leads to lesser power consumption. But aren't Core CPU having lesser frequency having nevertheless not lesser number of logical gates changing their state per second? Isn't the number of gates changing their state not frequency the factor which defines power consumption?


texts: Is it possible to create power factor compensation for a single power supply?

texts:
A 24V 150W power supply's power ratings is marked on its surface as follows:

In this case as you can read the cos phi is 0.45.

I know that the utility which provides power to the systems wants to supply low current so by compensation the current going into the system is lowered. And if I'm not wrong they use capacitors to reduce the power factor for inductive loads in industry.

But back to this power supply's case. If we think this power supply as our system and if we want to bring the power factor from 0.45 to around 0.9 or close to unity, is there a way to do that?


texts: How to attain a topping charge for a lead-acid battery?

texts:
Charging a lead-acid battery involves three stages: CC, CV, and Float.  I have a charge controller which charges my battery at CC to the float voltage.  I would like to add a device that would charge it via CV to full charge.  (See Lead Acid Battery Charger Design Factors for description of stages.)

For example, I could attach something that would charge it, keeping it at 14.6V until the current goes down to .1A, and turn off.  When this device would turn off, the charge controller would kick in, and keep it at 13.7V Float stage.

However, I cannot find a device that would do that:

1) Charge controllers that have a "Absorbtion" 14.6V stage typically have it timed,
    say for 10 minutes, and then turn off regardless of the current.
2) Charge controllers that I can program to rise to 14.6V indefinitely, have no way
    to tell me when their current goes low enough (other than through an LCD display).
2a) I can attach a timer to turn off such a controller after giving it enough time to
    reach .1A current; however, since my system if powered by solar panels, it might
    not reach .1A within that time frame on a cloudy day.
3) I can use a CC / CV power module to output 14.6V; however, that will not measure
    the voltage of the battery, nor determine when the battery is fully charged.
4) I have bought several commercial chargers, such as ElProg Pulsar, capable of doing
    such a charging; however, all of them require at least pushing a START button to
    initiate the charge.

I have consulted with my dad, who's an electrician; however, all options have gave are either very power-consuming (e.g. involving PLC), or are not available at 12V.

I am open to buying a commercial product that would do this, if it is too complicated to make by myself.  Please give some advice.


texts: CD4052 multiplexer with different input voltages

texts:
I've been working on designing a PCB for my indoor garden and i'm facing a problem i dont understand.
In my design i use a multiplexer (cd4052), to choose which sense resistor my current sensing chip (ina219) is reading.
I have 4 different sense resistors,

12V in
5V (right after a linear regulator)
12V out LEDS 1
12V out LEDS 2

After receiving and soldering everything correctly (i guess), i end up measuring 11.3V where it should be 5V.
So i've soldered a 2nd PCB with only some components, the 5V output is correct until i solder the CD4052...

MP_0, MP_1 and MP_2 are linked to a resistor on the 12V routes
MP_3 is linked to a resistor on the 5V route

I may have missunderstood things about the CD4052 documentation but i'm stuck anyway.
Thanks for reading/helping !


texts: reading EEPROM at startup only versus reading everytime from EEPROM

texts: I have an AVR code where I store data in EEPROM, this data is actually some settings and USER phone numbers. These are quite often accessed. So I planned to read all the values at start-up to memory at the start-up. and then use only those values instead of reading them from EEPROM whenever required. This method is OK but it uses a lot of data memory. So now my plan is to read from EEPROM whenever I need to use that variable. Is this OK, will it affect the EEPROM???


texts: 3 PCB Design Question about Length Matching, Trace Position and Signal on Layer

texts:
About a year ago I designed a PCB with a processor and RAM (400MHz and 133MHz speed respectively). I did not know about length matching and it did not work properly. I then redesigned the board with length matched traces and it worked.

Now I have 3 questions.

I am designing a PCB with an MCU and there will be JTAG, SPI, I2C and USB. Do they need length matching? (SPI should not need in my perspective but others might need).
Since it is 4 layer would that be a problem if I pass traces below crystals (12MHz and 32.768kHz)? Would that trace affect crystals performance?
I dedicated one layer to power from a Li-Po battery because there will be a huge amount of current draw. But I also need this layer for use with traces of some GPIO pins. Would that create problem?


texts: Using audio instrument cable for 1MHz transmission

texts:
I'd like to transmit digital data together with an audio signal along an instrument cable.

In more detail, I'd like to send MIDI data and the audio signal of a guitar on a single cable. The rationale is that audio cable is ubiquitous and saves me the trouble to find the specific kind I need whenever it breaks.

The original idea I had was to simply send the MIDI data raw along the cable, but its low bitrate (32 kbauds) makes it dangerously close to the audible range, and in my experience even though the data in and of itself is not audible, it produces whines whenever evenly spaced packets are sent (as in CC messages).

I then thought of producing a 1Mhz carrier that would be modulated by the MIDI signal, that would then be decoded at the receiving end: this solution is supposed to solve the bleed into the audio signal.

I now find two main issues in my idea: first and foremost, I have no idea whether the audio cable has enough bandwidth to let a 1Mhz signal through. I found this spec sheet that mentions some parameters, and according to this answer the resulting impedance is around 400Ω, which is a standard impedance in the audio industry, IIRC. I don't know how this affects the ability to transmit RF signals, though. Also the capacitance is specified for 10KHz, not 1MHz.

The second doubt I have is that the audio signal is low-voltage, high-impedance: could this be a problem when decoding downstream? Will a simple passive lowpass filter be able to eliminate the data carrier leaving the audio (relatively) intact?

Final note: I have zero experience in RF circuits. I have no idea if I would have to do stuff like terminating the connection or things like that, I am not really sure how important it is at 1MHz frequency.


texts:
I'm trying to create a passive RLC band-stop filter for my Sony EX71SL earphones, which has a nasty little spike in one treble frequency area.

I found a similar such filter on the likwitz website: http://www.linkwitzlab.com/reference_earphones.htm

But my output impedance is much lower and my frequency center point higher. I'm having trouble calculating the values I need for the filter to work with my devices/amps. I've played with online calculators, such as http://sim.okawa-denshi.jp/en/RLCbekeisan.htm but I still can't seem to generate a similar notch depth AND Q value at the same time.

Here are my devices and their output impedances:

Apogee Duet: 32ohms - iPhone 6: 3.18 ohms - C5 amp: 2.2 ohms - Sansa Fuze: ~1 ohm

Center frequency: 6,000hz

Cut: 7.8db

I was thinking I can use the 32 ohm for my calculations and simply add a 30 ohm adapter to my other two devices, thus essentially giving me roughly 32 ohms for each device when used.

He lists a Q value of 17, but I'm using EQ apps with lower values. I'm using a 7.2 Q value or 0.2 BW (bandwidth) if you want to convert it to that.

These result in a perfect reduction of the 6,000hz treble peak as found with a sine sweep.

Using the values on his site result in a different amount of reduction and whatnot if I plug them into the online calculator.

Can someone tell me what values I would need to use to achieve a 7.8 or rounded to 8.0db reduction at 6,000hz with a 7.2 Q if my output impedance is 32 ohms, and would it matter if the output is off by 1 ohm on each device? How much would that effect the shape?

I'm starting to understand some of the equations, but I can't seem to isolate the exact relationships and what I need to do to arrive at these values even just putting in values on the online calculator and trying to tweak them.

Any help would be greatly appreciated.

Amplification shouldn't be an issue either. The C5 seems to easily drive these earphones well past iphone levels and much louder than I'd ever use.

I'd love to understand this all, so any detailed responses would be great.


texts:
I was looking through chemistry textbooks to find out how to determine how much current a galvanic cell should generate and what affects that current value. However, I did not find anything: textbooks just talk about the EMF of a cell.

I wanted to know what determines how much current a cell generates. Certainly, the amount of electrons produced externally contributes to the current produced by the cell. However, what about internally? Batteries have internal resistance. Is that true of cells too (it should be because batteries are made up of many cells)? What determines amount of internal resistance: does the type of electrolyte(s) affect it. If a cell uses a weak electrolyte (like acetic or carbonic acid) will it cause more internal resistance then if something like sulfuric acid (strong electrolyte) is used?

What if a cell used weak electrolyte as the cathode electrolyte and the strong electrolyte was the anode electrolyte, will that cause more internal resistance due to there being less ions in the cathode compartment as not all of the electrolyte has been dissociated into ions (thus, the cathode cation cannot be reduced)?


texts: Does order matter in a center tapped transformer's windings?

texts:
I have a center tapped 20-0-20 transformer whose wire colors on the secondary are notated as follows:
c || c -------- blue
c || c
c || c
c || c -------- green
c || c -------- blue
c || c
c || c
c || c -------- green

With a volt meter I have identified which wires connect to one of the windings and which connect to the other winding. However, I don't know which pair of wires is the top winding (in the diagram) and which is the bottom. Looking at the diagram, I want to connect the two middle-most wires so that current flows from top to bottom, but I might accidentally connect the two outermost wires so that current flows from middle to bottom then top to middle. Would that actually be any different than connecting the two middle wires?
Of course current will flow in the same direction in both windings.


texts:
I overwrote by mistake ST-Link programming pins PA13 and PA14. Now I cannot reprogram my chip.

How could I fix the problem?

Datasheet


texts:
Based on my research so far, I've concluded that a relatively low-cost, yet reasonably reliable way to control operation (on/off) a motorized water pump, is a well spec'd EM-relay with flyback diode. I might also put in an opto-coupler for isolation, if that improves safety. The whole thing would be assembled on a general-purpose phenolic veroboard, with point-to-point connectors.

Given the pump motor's specs, I wanted help checking if the selected relay  would fit the bill, or should I look for another.

The pump's specs (the relevant parts):

Self-priming 1.0HP mono-block pump
Operating voltage: 220VAC +/- 6%, single-phase 50Hz
kW / HP: 0.75 / 1.00
Current: 5A
Cap. run: 20uF 440V

The operating characteristics are about 100 on/off cycles per month, with each "on"-cycle being about 60mins long. AC power quality is not that great, with voltage fluctuating 10-12% around 220V, and line frequency fluctuating by 6-7% (as told by a local friend, who is knowledgeable in power electronics).

The EM-relay specs:

General-Purpose 1Pole Heavy Load SPST-NO Power Relay
Coil Voltage: 12V
Coil Resistance: 185 Ohm
Contact current: 25A
Switching voltage: 250VAC
Life:
  Resistive-Load: 100 x 10^3 operations
  Motor-Load: Min. 200 x 10^3 operations, given
                     (250VAC inrush 80A, cosφ=0.7, cut off 20A, cosφ=0.9)

Does that sound good enough ? The above mentioned relay has 3 variants -- Standard, High Isolation, High Current. For the moment, only 'Standard' one is readily available. Would that suffice ? Just curious, what might be the other 2 variants good for.

A surprising observations was that the EM-relay has longer life with motor-load, than resistive-load. Is that normal ?

Also, the readily available part is a "PCB mount" relay. Is that acceptable, or should I really try to hunt for the socket-mount / tab-terminal kinds ?

Finally, is it fair to assume that I do not need any kind of "snubber circuitry". PS, I understand very little of "snubber" though, but it has appeared few times in the material I've read so far.

Edit:
Signs of aging, and some carelessness. Had asked this question exactly a year back, when I had just began working with relays, and forgot all about Russell's excellent answer. It does cover many of the questions I re-asked here. Thought of linking this together.


texts: Possible measures to make power supplies safe

texts:
I'm looking for a list of ways that mains-powered ELV power supplies with touchable terminals can be made safe in the case of transformer failure with primary and secondary coils becoming connected within the transformer.

One method I'm aware of is a feedback control circuit that isolates the input to the transformer in the case of excessive voltage across the secondary winding, that in part uses an opto-isolator, as described here. However I'm not certain what failure conditions within the transformer that this method can/cannot protect against.

I'm primarily concerned with conformance with CE marking and other EU requirements but non-EU regulations and beyond would be a bonus. I'd like multiple options as I'd rather have overkill (no pun intended) than potentially mediocre protection. Cost is an issue but I'd like to know the options so appropriate optimisations can be made.

Last but not least, references to reputable sources are important.


texts: Digital signal in my circuit is too noisy

texts:
I have a very simple digital circuit which I built with 74LS chips. Basically, the Q output of a JK flip flop is fed into a chip in another prototype board through a connector about 30 cm long (the only one I could find ).
The problem is that the signal at the end is too noisy, as I checked disconnecting the cable and probing with my oscilloscope the signal diretcly from the JK flip flop.
Is there any way to reduce the noise ?


texts:
I'm replacing a fluorescent ceiling light with an LED fixture. I removed the entire chassis, ballast, etc, and now I'm just left with the hot/neutral cabling (no ground wire available).

I wanted to verify that the power was off before I started getting too touchy with wires, so I grabbed my multimeter to measure the AC voltage. With the light switch on I measure 120VAC, but with the light switch off I measured about 60VAC. I then flipped the circuit breaker off for the circuit that the light is on, and it measured about 0VAC.

Would 60VAC ever be normal for a switch being "off"? This is an older house, no idea about the quality of the wiring, and I noticed that there is an old doorbell transformer in the basement, if that could possibly explain anything


texts: Transimpedance Amplifier (TIA) - How to shunt high current spikes?

texts:
I am working on the design of a high-bandwidth transimpedance amplifier (TIA) to detect a relatively weak optical signal (100μW) but also be able to withstand short pulse, high power optical signals (>10W peak, 100ns long). The aim is to achieve a 50MHz bandwidth with a transimpedance gain of 5kΩ. I wish to use the FGA21 photodiode and the OPA657 Op-Amp to achieve this, key specifications include:

Gain Bandwidth Product: GBW = 1.6GHz
Photodiode Capacitance: C_d > 100pF

To limit the effect of input capacitance and push the bandwidth out I am using the bootstrapped architecture described by Hobbs. The SPICE model of this circuit is illustrated in the figure below:

Simulations suggest that this can achieve the required gain and bandwidth. However, I need to extend this design further so that it can shunt the ~10A pulse generated in an efficient manner. My thought is to use a Zener diode between the inverting and non-inverting op-amp inputs to regulate the differential voltage and provide a low impedance path for the current spike to ground. For this I require a Zener capable of handling high currents and that has low capacitance (as any capacitance >5pF will limit my TIA bandwidth), which is a big ask.

So I am wondering if there alternative methods to shunt high currents with minimal capacitance or is there a way to increase the maximum power dissipation of Zener diodes?


texts:
I need to activate a 5V relay with the 3V3 GPIO of an ESP8266.

However the GPIO pin to be used has an additional function as a boot mode select pin for which it must be high at startup, therefore the signal controlling the relay should be high when not activated, and low to activate it.

I was thinking about a P-Channel MOSFET acting as a switch, but any solution with minimum components is welcome.


texts: Determining voltage and current changes to make components compatible with the voltage source

texts:
Brand new to electricity & hobby electronics here, and I just watched this video on calculating the resistor needed for an LED, and I had a basic question about that process that I (surprisingly) could not find an answer to.

In that video, the setup is very simple:

9V battery
LED rated at 9V and 20mA

Hence the author explains that you need a resistor rated at:

R = (V2 - V1) / I
  = 9V - 3V / 20mA
  = 6V / 20mA
  = 300 ohms

Math is simple, and makes sense. Well, mostly...

However the battery is outputting/supplying (giving off?) 9V of voltage. And a cursory Google search yielded that the avergae 9V battery outputs/supplies (gives off) ~5mA of current. So to me, in my newbie/dummy brain:

The battery is providing us with 9V @ 5mA
The LED requires 3V @ 20mA
This means we need to lower the voltage by 6V (9V - 6V = 3V); and
It also means we need to raise the current by 15mA (5mA + 15mA = 20mA)

My assertion: So by lowering the supplied voltage from 9V -> 3V and by raising the supplied current from 5mA -> 20mA, we are providing the LED with the correct voltage and current that it needs to operate successfully & safely.

So to me, the problem here is:

  How do we "convert" the outputted/supplied voltage & current to the required voltage & current of the component (in our case, an LED; but could be anything I guess, a buzzer, a motor, etc.)?

So my question here is: am I correct in asserting that the way you decide how to wire any component to a voltage source (9V battery in this case) is by deciding on the required adjustments to both voltage and current? Or do we just care about voltage? And why?! (For example, are there some cases where we care about making supplied voltage equal to required voltage, other cases where we only care about making supplied current equal to required current, and maybe other cases where we care about both?)

So if you really read between the lines of my question, I'm looking for the strategy on determining what "supporting components" (resistors, transistors, capacitors, etc.) need to be added to make a voltage source "compatible" with some other IO component (LED, pushbutton, buzzer, motor, etc.).


texts: In what situation,we should consider the balanced bridge when we calculate the equivalent capacity?

texts:
Question: Find the value of the equivalent capacitance between \$a\$ and \$b\$

Solution:Because of the balanced bridge,so the circuit become

So \$C_{ab}=30 \mu //[(4\mu // 6\mu)+((6\mu // 9\mu))]=5\mu\$

Honestly,when i see there is a \$\Delta\$ circuit ,i will want to transform it to \$Y\$ circuit,i won't think about the "balanced bridged".so i want to ask :

In what situation,we should consider the balanced bridged?i don't need to consider the balanced bridged when there are only two capacitors which they are parallel connected to each others.but why should i need to consider the balance bridged in this circuit?

2.Why will we ignore the \$5 \mu \$ capacitor,not the \$4 \mu \$ capacitor?


texts: Can I "duplicate" a stereo signal to 5 channels? Are there any impedance issues?

texts:
A friend of mine has an old 5.1 audio system. The amplifier of the system has 5 cables as inputs to be connected to the audio source.
My friend actually uses some cable splitters to send the stereo channel to each one of the 5 channels (yes, it's crazy, but please read on). He asked me if I can design and develop a PCB to avoid all that cables.

His idea was a PCB with 1 3.5mm jack "in" and 5 3.5mm jack "out":

Audio source ---- SPLITTER PCB --┳-- AMPLI IN 1
(PC/MP3/..)                      |-- AMPLI IN 2
                                 ...

Are there any impedance-related issues with a so simple design?


texts: Is it possible to multiplex SIM cards using a CPLD?

texts:
I am building a hobby project using a GSM module and would like to be able to switch between multiple SIM cards, in case one stops working or I have poor reception on one provider (the project will be quite inaccessible once deployed).

Would there be any issues doing this with a CPLD? I can supply the SIM cards with 3V always. I was thinking I could switch them on / off with MOSFETs and just multiplex the CLK, IO and RST connections for each SIM.

Would it be easy/possible given that the IO line needs to be bi-directional?

Would the propagation delay of the CLK be an issue at all?

Anything else that might prevent this from working?

I don't have any experience with CPLDs


texts: Is it possible to create an external electric field using a toroid?

texts:
I would like to create a directional, "external" electric field.

For example, a solenoid creates an "external" magnetic field in one direction(coming out of the ends of the solenoid). I would like to do the same with an electric field.

This diagram below shows how a toroid could create an external electric field:

Electric fields are only generated from changing magnetic fields, so by applying an alternating current to the toroid, I change the magnetic field inside the toroid, which should create an electric field.

Is this possible to create a reasonably strong electric field with a toroid? (Stronger than say, the E field from just current flowing through a wire).


texts: How to make Quartus II find the Altera DE2 board?

texts:
I use Quartus II web edition and using that driver my computer can find the card:

And the card appears in the device manager so it indeed looks correct so far.

But when I start Quartus Programmer to download my logic to the board, the hardware part of the interface is blank where I expect to see my card:

What can be done? The instructions I have are available here.

Can you help me?

Update

I reinstalled the drivers, reinstalled Quartus II different versions many times, reset the board, tried both the Quartus version from the CD and from the internet, I see many other people have the same problem with the same board, thank you Altera for making us lose valuable time wasting our time on faulty software. Why can't it work? From the command-line I can run a tool named jtagconfig that actually seems to find the board but this is from the command line:

Update 2

I reinstalled and ran the program this time with admin privileges and antivirus turned off and then it worked. The DE2 board appears in my Quartus Programmer and I can download the logic to the board.


texts: On our board we use 74AC244-SO buffer to isolate microcontroller pins from outer world, buffer is shown on the picture below. Just for the purpose of test I've simple SPST switch attached between one of the inputs - AUTO_NAV and 3V3. When switch is closed I see 3V3 on corresponding output pin MCU_AUTO_NAV, but when switch is open I see MCU_AUTO_NAV voltage jumping low and high. When I try to attach scope to the input AUTO_NAV - problem dissapears. What can be the problem? Can it be that this buffer is very sensitive, so wires to the switch pick up EMI? MCU_AUTO_NAV is connected to the microcontroller (STM32F4) input pin with 40K internal pulldown.


texts: Delta Sigma DAC-like switching of a mains AC load

texts:
I'm helping out in a project to convert an electric rice cooker into a sous vide cooker with a PID control. For those unaware, this is a precision-controlled water bath at "low" temperatures (setpoint at between 50 and 80 degrees Celsius).

The AC load is switched by means of a TRIAC, triggered by a TRIAC optocoupler with zero crossing detection (MOC3063).

I'm sensing temperature using 7 NTCs, distributed in various points of the cooker, all connected to a TI LMP90079 A/D converter. This part has a few fixed sample rates, and the one I'm thinking of using is 6.71 Hz. Actually, due to differences in the crystal frequency and the use of a calibration mode available in the part, there may be a very slight (~0.2%) discrepancy to this nominal rate. Since I sample 7 channels at a time, my sampling rate is divided by 7, so it's approximately 0.959 Hz, which is the rate at which I run my PID loop.

My initial plan for actuating the rice cooker's heating element was to generate a 1 Hz PWM wave that is input to the TRIAC optocoupler. The duty cycle would be given by the controller output obtained from the PID loop. Each time the PID loop is run, I would update the duty cycle.

At this point, it occurred to me that I could feed the controller output to a delta-sigma modulator, but first resampling the controller output signal to a frequency of 120 Hz (since I'm using a TRIAC optocoupler with zero-crossing and there are 120 semicycles in a 60 Hz mains waveform.) The output of the delta-sigma modulator would be used to actuate the TRIAC, synchronized to the zero-crossings of the mains waveform.

A sigma-delta modulator requires a low pass filter to be applied to the output of the modulator, but my reasoning is that the physical system itself serves as a low-pass filter: The rice cooker has a capacity of 4.5 liters/1.2 US gallons of water, and a 700 W heating element, which means I need at least 27 seconds to heat the contents of the cooker by 1 degree Celsius.

So here's what I'm wondering:

Is this idea fundamentally sound?
What's the equivalent number of bits of this DAC? For the 1 Hz PWM waveform solution that I was previously going with, I reckon accuracy is ~7 bits since I can choose between 0 to 120 semicycles for each 1-second period, and log_2 120 ~ 7. As for the sigma-delta DAC, according to this Maxim application note, using a second order modulator with 128x oversampling (120/0.959 ~ 125 so that's close), I should expect a 90-95 dB SNR, which works out to ~15-16 bits of resolution. Is this correct?
That said, should I expect to see any kind of real-world improvement if I used this sigma-delta DAC, compared to the original 1 Hz PWM waveform solution?
Is a second order sigma-delta modulator a good choice? The ADC that's reading out data from the NTCs has a 16-bit ENOB and noise free resolution at the choice of PGA gain and sampling rate that I'm going to use. From my calculation above, I'm getting out the same resolution from the DAC using a second-order modulator, so anything above that would be overkill, in my understanding.
There is no integer oversampling factor that takes me from the 0.959 Hz sampling rate to a 120 Hz sampling rate exactly. So say I get to a 119.8 Hz rate; then there will be a beat frequency of 0.2 Hz between the mains waveform and my waveform. What effect will this have on the accuracy of the conversion process?

I'm aware that I could use a non-zero-crossing TRIAC optocoupler to perform phase control of the AC waveform, but I'm doing this as an intellectual exercise, so I'd like to pretend that solution is not available.


texts: What determines the maximum discharge rate of a battery and how can I create a high current power supply from batteries?

texts:
I am looking for ways to make a mobile power supply for 10 units of MG996R servo motors, each of which can draw up to around 800 mA to 1 A and operate between 4.8 V to 7.2 V.

I have 12 Eneloop AA batteries (BK-3MCCA8BA), and from Panasonic Eneloop BK-3MCC (4th gen) - where I can find maximum discharge current?, I gathered that each of my Eneloop AA battery can discharge up to 6 A, which means that I should be able to power up to 6 MG996R's with a 4 or 6 AA battery pack.

This appears to agree with my setup where I am trying to control the 10 servo motors using the Adafruit 16-channel 12-bit PWM driver with a 1000 uF capacitor.

Once I begin to control over 5 servo motors, I get jitters, which I assume is due to the insufficient current.

However, I also read at How do I determine the maximum amp output of a battery pack? that I can model the batteries as a Thevenin-equivalent circuit, where the current is V_Th/R_Th. If I had 4 1.2 V AA batteries in series and assumed an individual internal resistance of 100 mOhms, I should be getting 4.8 V/ 0.4 ohms= 12 A.

This current should be sufficient for 10 of my servo motors? However, this is not the case.

What am I missing here? Also, could I put 2 packs of 6 AA battery holders in parallel to provide sufficient current?


texts: How does a FinFET reduce subthreshold swing comparing to a regular MOSFET?

texts:
I get that a lower subthreshold swing means there is a smaller current when the transistor is off and that's one of the reasons that finFET is preffered to MOSFET. But I don't understand how it does that.
I've been googling it and all I find is complicated advanced papers on improve finFETs and things like that.
Can you explain this or refer me to a place I can read about it in simple words?


texts: What is the definition of a complementary filter?

texts:
This appears to be a general classification of observers, but I can't find it in the index of my applicable texts:

Mathematical Methods and Algorithims for Signal Processing (Moon and Stirling)

Applied Optimal Estimation (Gelb)

If someone can provide a reference to classification of observer, that would be great.

Also, I'm not allowed to create and "estimation" tag, can someone with 300 reputation do that for me? Is there another applicable tag?


texts: Which one of these shielded scenarios is correct?

texts:
I have a system were both the signal generated and the sensing equipment is sharing the same ground.

Which one of these shield terminations scenarios is correct? (if any). I searched the internet for about 2 hours and could not find a clear definite answer.


texts: Generate electric spark with Arduino (high voltage boost converter)

texts:
Suppose I have an Arduino Uno or a similar board. I would like to have it create an electric spark over a spark gap as reliably as possible when instructed to do so.

As I understand, the minimum voltage required for a spark to form is 3kV per mm of air between the electrodes, so the Arduino has to be able to output a voltage in that order, preferably up to about 10kV in this specific situation. Now, I know that inductors can be used to create something known as a boost converter, which is able to step up the voltage quite a bit:

Schematic from Wikipedia (License: Public domain)

My idea was to connect a digital pin as well as the ground to the "Supply" side, and have the "Load" side be two cables whose ends are spaced a few millimeters apart.

I assume this would fry the board quite quickly. How can I prevent that from happening? Is it even possible to achieve the required output voltage using just the Arduino? If it is, please help with the details for the circuit components I need.


texts:
As I have understood the concept of modems, modems translate digital signal to analog ones and in reverse.

Well and then I've read the definition of a modem (technical book):

  A modem converts digital direct current signals to digital alternating current signals and the other way around.

Well how does the word "analog" fit in there!? How can I get a picture of it? Can you explain a bit how "direct current" and "alternating current" fits in there?


texts: How can I lower voltage coming in to a kiln?

texts: I have a small firing kiln. It heats up to quickly for my ceramic pieces. I was wondering if I could reduce the voltage coming into it so it could heat up slower ? And if I could how could I go about doing it? I was thinking I could use a resistor, but I don't know how to apply it or if I could where would the resister to go ?


texts: Why is it preferred to transport lower current and higher voltages across the PCB?

texts: In case of modern PC, the CPU requires fairly lot of power. At nowadays the CPU uses +12V rails and converts this +12V to around +1V in voltage regulator module near the CPU itself. Why is it preferred to transport lower current and high voltages instead of lower voltages and higher current across the motherboard? Is it because of crosstalk?


texts: Doppler pings from MH370 Inmarsat : how was the data processed?

texts:
Published news reports indicate Inmarsat used something similar to 'doppler shift' to analyze pings from flight MH370, concluding the plane was traveling south not north.

Any normal radio receiver would loose minor frequency shift early on in the signal path.  So how did Inmarsat do the analysis after the fact?  I assume it involved minor arrival time differences between subsequent pings, and the presumed angles of the north and south flight tracks, but exactly what was the mechanism?

  Chris McLauglin, a senior vice-president at Inmarsat, told Sky News:
  “What we did two weeks ago was say it could be north or it could be
  south, and what we’ve done is refined that with the signals we got
  from other aircraft.


texts: Why does this MOSFET always turn on in saturation?

texts:
Consider the following case:

In Razavi's book, it says that this MOSFET will always turn on in saturation mode.(assuming Vgs is just greater than Vth) I'm trying to figure out why.
For Saturation:
$$V_{DS} > V_{GS} - V_{TH} $$
Simplifies to:
$$V_{out}>V_{in} - V_{TH}$$

How does this prove that it will turn on in saturation? I mean yes we could probably prove that with the small-signal model, but there is no small signal here.


texts: Potentiometer/trimpot range 503 vs 103 with a resistor in series

texts:
Small intro:
I'm adapting this NE555+CD4017 module to fit into a nice little box and I am switching out the plastic trimpot that came with the package for a metal one that can fit through wood.
The trouble is, only now I see that the trimpot that came with the module, was a 103 (plastic) instead of the 503 it should have been - as indicated on the diagram and pictures of the module.
I ordered a replacement 10k metal potentiometer because I based myself off the '103' indication on the actual module instead of the diagram... silly me.
It's only now that I notice the 10-50k difference because I was looking up how to wire them up again.

picture of diagram & components in question

Actual question:
Right now the LEDs get shifted really fast (because of the 103- 10k pot?) and I think it should be able to go a lot slower if I use the 503 - 50k pot).
If I put in some extra resistors, say 20k worth more in series with the 10k potentiometer, would the shifting of the LED lights go slower by default?
And if I just order a new metal 50k potentiometer I would probably have the whole range (slow-fast)?

Thanks in advance!


texts:
I don't know if this is the right place to ask but here it goes..

I have an Headphone amplifier connected to a wall plug and usually to my laptop's sound card, i connect my headphones to this amplifier and listen to music.

Sometimes i toy with the jack on my amplifier that goes in the laptop, if i put it against my body my headphones make noise, i assume its resistance noise, is there any danger if i put it in my mouth/tongue by mistake, is there a danger of me being electrocuted by a dumb thing?


texts: Not understanding NPN transistor in circuit

texts:
I'm sure an analog of this question has been asked before, but I've spent the last day researching this and I've decided it's time to reach out for some help.

I'm working my way through Electronics for Dummies, 3rd edition.  I'm practically finished with my Masters in Computer Science, and this has been the book that I've gravitated towards to break into the world of electronics.   There is a specific circuit in Chapter 10 involving a 9 volt battery, two LED's, an NPN transistor, and a voltage divider consisting of a 1 megaohm potentiometer, a 10k ohm resistor, and a 470 ohm resistor (I think the potentiometer counts as part of the voltage divider - please correct me if need be, I really want to learn.)

Even with the pot dialed all the way up (to 1 megaohm), the white light still shines super brightly.  I'm not sure if I've setup the circuit wrong - I followed the instructions and the illustrations in the book to the best of my abilities.  It's my understanding that the white light can shine, but that it should not be bright, and that it should not brighten until I dial the pot all the way down (to 0 ohms).

When the pot is dialed all the way down, the red LED does come on and shines with respect to the setting on the pot.  But I thought there shouldn't be any current flowing between the white LED and the base leg of the transistor (except for leakage?) until the voltage rises by about 0.6-0.7 volts?  The white light shining brightly with the pot at 1 megaohm has me concerned that I'm missing a major concept here.

I've checked my resistors with my multimeter, all correct there.  I checked continuity between the collector and emitter of the transistor, and there is none - so that should mean the transistor is fine, right?  Even the potentiometer is testing fine, from 0 to 1 megaohm.

Any comments or suggestions would be very welcome.  Apologies if this is extremely stupid (I have no idea) and thanks to everyone who reads this.

Edit: Answered by StainlessSteelRat below, I had the collector and base legs reversed.   Thanks again!  =D


texts: Are DDR3 SDRAM's DQL and DQU pins different?

texts: Obviously they are, but I am using the Allwinner A20 and alliance memories AS4C128M16D3B-12BCN 2GB, it has DQU1,2,3,4 etc pins, but the Allwinner A20 does not, it only has the DQL, no DQU.  This memory is fully supported by the Soc, but for some reason appears to be missing pins? Am I correct in thinking that DQU is just a continuation of DQL? from what the data sheet says, they are both data strobes. Any help appreciated as I am well and truly confused.


texts: Controlling Wemos D1 power with P-Channel MOSFET

texts:
[ Note: this is the continuation of another question, the first one being my attempt to implement the same idea using an N-channel MOSFET. Based on the answers I received there, I went out, bought a P-channel MOSFET, and found myself with even more questions than before :) ]

I am trying to implement something similar to this: https://youtu.be/nbMfb0dIvYc?t=4m27s

The idea is that the microcontroller (a Wemos D1 Mini in my case) is powered up by an external switch. As soon as it starts up, it sets up a MOSFET so that it can keep its power connection until it finishes whatever job it is set up to do. In the end, it "kills itself" by cutting of the power through the MOSFET.

So I bought a P-channel MOSFET (IRF9Z34N - probably not ideal with a Vgs(th) max of -4V, but it was the best through-hole part I was able to find). And I built the following circuit:

When I press the switch, the D1 powers up correctly, pulls the MOSFET gate pin low, and goes through all of its code. In the end, it pulls the gate pin high, powering itself off.

However, something is wrong. When powering itself off (after setting D5 to HIGH), I would have expected the gate voltage to go to +5V through the pull-up resistor. Instead, it stays at around 1.25V - enough to keep the MOSFET partially open, with enough current going through it to keep the MCU in some weird, not-alive-but-not-dead-either, state (the MCU doesn't receive enough current to keep running its code, but it receives enough to prevent it from fully resetting and starting over again when I press the switch).

Based on the suggestion received from Brian Drummond on my original question, I built a dual-MOSFET arrangement:

This seems to work - but it seems needlessly complicated, especially compared to the original schematic (see youtube video above, starting at 04:24).

So my question is: is there any way to "save" the original schematic? Can I implement this using just a P-channel MOSFET? If so, how?

If it helps, here is the schematic for the Wemos D1 Mini. Note that I am powering it through the 5V line, which then goes through a power regulator.


texts: How to tell when the stepper motor is done stepping?

texts: I am working on a project that requires mildly accurate positioning of the x and y axis. It involves an airsoft gun and it is basically a motion tracking turret. Because of the requirements for movement that could be tracked I determined that a stepper motor would probably be the best option. I have ran into a problem though while picking the motor and a driver or even if I am going to stay with the stepper motor idea. My question is how do I know when my stepper motor is done moving like is there a pin that goes low on most drivers saying that the motor is done moving? Or should I just move onto using a servo. I choose stepper motors because they were powerful and relatively cheap but I don't really understand how to control them. I understand the whole signal sending idea and I will be using the accel-libary with an arduino to control it but how do I know when to give the motor a new position. Also as a side note will a motor with a torque rating of .1416 in-pd's I will be using a .5pd airsoft gun and will mount it in the middle of it's center.


texts: Power Arduino from MicroSD host and more

texts:
There are a lot of cheap MicroSD port extender flex ribbons from China. These things extend the MicroSD port quite a lot. I thought it would be cool to adapt these to power an Arduino from a phones MicroSD port. This would solve my problem of having to deal with USB OTG power and would be a nicer solution as the USB port could still be used.

My question; does the MicroSD port need signalling before VDD is powered?

And additionally, would it be possible to communicate a signal over the data lines with Arduino, or would that be really hard? A very minimalistic signal would already be nice.

Lastly, what can I expect to be the amperage to be supplied? Looking at a datasheet from a typical MicroSD card I see it requires 100ma to operate, so I figure at least that.


texts: Multiple lights with button that turns one on at a time

texts:
I am an artist trying to make an installation but I'm not too familiar with electrical work.

I want to have multiple light bulbs wired to one button. Each time the button is pushed one light bulb comes on. There will be probably over fifty of these bulbs.

Could you provide some design hints about how do I accomplish this?

EDIT:

I've been told I need to be more specific so I will try with some additional background.

I have a certified electrician who can help me understand language and execution if needed.

I would be using either 40 watt, 60 watt, or 25 watt bulbs. The kind of light bulb simply needs to have that classic look and be relatively cheap, so I'm not concerned about how bright it is. Those are just bulbs within my price range (because I need a lot of them).

The goal is to have a large long arched trellis with light bulbs hanging/on the sides looking similar to string lights. these bulbs would respond to one button and every time the button is pushed a singular light comes on.

Edit** The bulbs would stay on. I'm willing to hear anything anyone has to offer regardless of price, no need


texts: Sometimes LCD display is initialized half white

texts:
Rarely right after the startup my LCD display shows half the screen completely white, the other half shows the software without problems. The main problem here is that to see this problem I have to initialize my hardware a lot of times, I don't have the exactly figures but maybe once every one hundred initializations. Once the display is initialized with the problem the software and the touchscreen work as expected. But I see a pattern that maybe can help me to understand what goes on when the problem happens.

The screen is always divided in half vertically with one half working and other in white. If this is a random bug, the screen would be white on diferent proportions horizontally or vertically;
The half section that does not show the software is always white. After a couple of tests I've noticed that the white color is the color when nothing is written on the pixel;
The bug is very rare. And even at this low probability, when this happens the problem is the same, half the screen on white color;

I am using a LPC1788 connected to a LVDS transmitter (DS90C383B) and then to my LCD (HDA700L-GHL - 7”, WVGA 800 X480 , TFT Color Graphics ,White LED Backlight).

Can someone give me some advice? Thanks


texts: 2nd order Sallen-Key Bandpass filter design in Matlab

texts:
I'm trying to design a Sallen-Key BPF within Matlab. With the documentation found on ti: http://www.ti.com/lit/ml/sloa088/sloa088.pdf, I studied and understood the basic.

As for the design: The center frequency of my BPF is 40kHz. Q-factor and gain at center frequency must be 1. So in matlab I've made:

Fm = 40000;
R1 = 10000
R2 = 10000
C = 10*10^-9

R = 1/(2*pi*Fm*C);

G = 1+(R2/R1);
Q = 1/(3-G);
Am = G/(3-G);

w = 2*pi*Fm;

B=[G*R*C*w 0 ]
A=[(R^2)*(C^2)*(w^2) R*C*w*(3-G) 1]
sys=tf(B,A)

bode(sys,opts);

The issue is that my resulting bodeplot is indeed showing a BPF behaviour, but not at the desired frequency. Furthermore.

Can someone explain this to me?
Thanks in advance


texts: Controlling 2-pole contactor using Arduino

texts:
I am working with Packard C230C contactor to develop own EVSE. For a simple start i just want to toggle contactor using Arduino. OpenEVSE is already doing it. Just want to know how do they do it and some circuit explanation.

Reference : OpenEVSE Setup


texts:
I want to use LoRa (SX1280) to locate devices by RSSI and TDOA.
I put two LoRa devices on the table (within one meter,) one for TX one for Rx, and the RSSI values change a lot.
Then I power off the TX device,the RSSI values of RX device also change a lot.
I don't know how the chip calculates the value,but I only want to get the received packet RSSI value.
How can I solve this problem?


texts: Why not just use two ADCs (say GPIB from digital multimeters) and use them to collect the data. Afterward, you can just emulate the LIA by empirically determining the phase offset between the signal and reference signal?