texts: SC16IS752 not responding to SPI communication

texts:
I am trying to expand the number of UART ports I have available on a nRF52832 microcontroller using an SC16IS752 attached by SPI. However I don't manage to get responses back from the SC16IS752.

When I set CS to a low level SC16IS752 raises the MISO line to a high level. It stays at that level until after CS went high again. So I'm always continuously reading 0xFF on the SPI MISO line. It kind of looks like SC16IS752 is not seeing any clock signal on CLK. However I can measure the CLK signal of 4 MHz is present..

Any idea what else could result in this behaviour of the SC16IS752?


texts:
I am not sure PCB identification is on-topic for this site, please let me know if it isn't.
My wife found this PCB in her bag. She thought I had given it to her, but I do not recall that at all. Does anyone know what it could be from or for?

It is around 31 by 37 mm in size. On on side it has four pushbuttons and a small blue led, which blinks at different frequencies when different buttons are pushed. On the side it has what looks like a micro-USB connector.
On the other side it has two small IC's, one with 14 legs and H3-100 written on it, the other has ATMLH434, 16CM Y, 4W2601B, and a search brings up some shopping sites with little information, but there are IC's with the same first line that seem to be eeprom chips.
The PCB itself says 215BHS-1.
Does anyone have any idea what this could be? Thanks!


texts:
I need to measure a 4-port device (a directional coupler) using a 2-port VNA.  This answer covers the basics, and this document goes into more detail.

My problem is that I'm not sure how to perform the "matrix renormalization" step on page 10 of the NPL document.  What calculations are required to convert the six raw VNA measurements (for example, the transmission measurement between ports 1 and 3 of the DUT), and the measured (complex) reflection parameters of the loads attached to the DUT ports, into the normalized 4 x 4 matrix?


texts: Implementing Modbus RTU on a UART device

texts:
I have a particle counter HPMA115S0 which has a UART communication interface. I bought a TTL UART to RS485 Converter Module to make it work with a PLC over Modbus RTU protocol.

I usually work with devices that have RS485 serial communication standard but those devices have all the information I need to make them work over a Modbus serial communication protocol (PLC as a master) such as the ID and the baud rate and the registers' addresses which contain the data to request.

However, with HPMA115S0 I don't know what the ID would be, what is the register address of the measurement value and so on. So can I make this device with UART communication to work over Modbus serial protocol by using the UART to RS485 converter?


texts: How does connecting base and emitter help in this switching application of transistor

texts:
As far as I know, to use transistor as switch we only need to apply voltage on the base to turn the transistor on. When this voltage is removed the transistor switches off. The idea is to make the base emitter junction conduct. All we need here is a base resistor to control base current.

However, in here the author is connecting a second resistor calling it R2 and giving value 10 times that of base resistor. Here is the picture:

It says "Resistor R2 is not essential to this circuit but is generally used for stability and to insure that the transistor switch is completely turned off. This resistor insures that the base of the transistor does not go slightly negative which would cause a very small amount of collector current to flow."

Questions are:

What does author mean by stability, we are using transistor as a switch here after all.
How does R2 help to maintain this so called stability
How does one turn off this transistor? By applying 12V to R1?
Why in the world would the base go ever slightly negative which I assume is <0V, as it explains near end of paragraph?


texts: What did I do wrong? Inverting amplifier 1:1 ratio

texts: I'm getting a non inverted output. The resistors I used were two 100ohm 1/4watts. Signal was 4v peak to peak 600hz.


texts: Can you please tell me a scenario where i2c probe gives the slave address but i2c read command fails..


texts: How to uniquely identify USB HID class device?

texts:
I would like to identify a USB keyboard uniquely(something equivalent to unique mac-id for the Ethernet cards) on a computer. Does the USB HID profile has a support for such identification ? If so what is the field called ?
I understand that VID and PID uniquely identify a make of keyboard from a vendor, but I am looking forward to identifying each keyboard separately.

PS : Asking the question on Elex SE, since I would have to implement this USB profile on  AVR32.


texts:
I want to replace physical keyboard with raspberry touchscreen.
Is there any IC that can make contact between any PIN, like keyboard does?
Keyboard is connect to GAL22V10, but I don't wanna mess with that.


texts: Is possible to compile and programme ATtiny10 with AVR CrossPack?

texts:
For my next project, I would like to use ATtiny10, but I have computer only with Mac, so I cannot use AVR Studio. Can I use AVR CrossPack for programming this microcontroller?

I found this article about programming ATtiny10 (it is a year old text). The author is saying it is not possible to programm ATtiny with avr-gcc nor avr-as and avrdude cannot work with TPI.

So what (and how) can I use?


texts:
I'm trying to develop some sort of a one-time switch.
Let's say when a criminal opens a switch - transistor opens and alarm sets on. I want it to continue working once switch is closed again.
I believe there are some special "clever" components for this purpose but can I achieve it by adding only simple stuff like transistors/capacitors/diodes/etc.?


texts: What happens to remaining 12 segments in 8086

texts: 8086 can access DS, CS, SS, ES which takes max size of 4*64KB. Then what happens to remaining 12*64KB. How is it utilized.


texts:
Brief sum up (you can go directly to the end if you already read the sum up in the other question)

For a home project I'm making a controller to drive a two-direction 230V motor. For those unfamiliar with this, it is a motor with two windings; when you power one of them the motor turns clockwise, when you power the second it turns counterclockwise.

Excluding the power earth, the motor consequently has three wires. The neutral is always connected to the mains N, while the other two get connected to the L 230V wire when the motor should be turned. Only one winding should be connected to the L at a time, the other is left unconnected.

For this project, space is very critical; please keep this in mind when replying.

Now, in this project I need to monitor the voltage on the two wires, in order to see whether a command is sent, and to monitor the current flowing in the motor, in order to understand when it finished the movement. This question is about the first problem. You can read about the second here.

END OF THE SUM UP

So, now I need to detect whether the 230V is present on the two contacts. The circuit must be insulated from the 230V.

What I thought of was the following circuit:

simulate this circuit – Schematic created using CircuitLab

(I'm not sure about the 100k, I have to get the schematic of a former project I did, and the 1N4007 are instead their SMD alternatives. The PC817 are optocouplers, and I draw them as LED since the other part of them is not meaningful for this topic).

I put 3 0805 resistors in series to comply with the power and voltage ratings, but I preferred to share them with the LED/Diode because, well, space.

Do you think this is ok? Do you have any improvement or problems which can arise in your opinion?

EDIT: Ok, I made some measurements following the first answer. And these are the results. It took me a while since I had to buy 100:1 probes.

The scope measured these voltages on the two terminals. I'll call terminal 1 the one with the full 230V (which is the "direct connection" on the motor) and terminal 2 the one with the square wave (which is where the capacitor was put).

Please note that the two scales are not equal; the square wave is 10 times more magnified than the sine.

I then modeled the two waves as a sine wave at 50 Hz (with a bit of phase shift) and a square wave with slow transients (values are taken roughly). This is the comparison between the two waves and the corresponding modeled values

The I tried to estimate the current in the diodes. I set a voltage drop of 2.5V on the two diodes series, then checked which was the smallest between the two (and, of course, I discarded the positive values) and then got the current in the diodes knowing that the resistor is 100k. This is the plot of the currents.

I think the "activation" current will be at least 500uA (and, after all, it can be modified changing the pull-up value on the digital side of the opto-coupler). Since the two values are so different, I think there should be no problems detecting only the main "wave"


texts: Clamp diode to a solenoid activated by a raspbery pi, how do I choose it?

texts:
I need to activate a solenoid using a raspberry Pi, to do that I'm using a TIP121 to drive the current and a 12V power supply to power the solenoid. I also put a clamping diode (1N4001) but I'm not sure if it's the right one.

Here is the schematic, I couldn't change diode's value on the schematic, so ignore this value.

simulate this circuit – Schematic created using CircuitLab

Is the 1N4001 enough or I need another one?
It it's not the right one, how do I choose/calculate the right diode (I googled but I didn't find anything useful).


texts:
I want to buy some 0402 SMD capacitors (well some is about 1 to 10k).

I always use the method of use the cheapest part for the given specs approach. But today I noticed something odd:

I was comparing these two parts on digikey:

Partno.         Price/piece   Price for 10k
-------------------------------------------
490-10777-2-ND  0,00317€      31,68€
399-8942-2-ND   0,08236€      823,63€

The top one is from a company called murata (never heard of them) and the bottom one is from KEMET (which I know of).
But looking at the specs given, there is  absolutely no justification for the much higher price:

I know there might be some other parameters which might come in to play which are not listed by digikey.

But really 10 times the price for some capacitors? What is the justification ? Is it because of the brand-name? If so, why should I care?


texts: What should the single-ended impedance be for LVDS?

texts:
For LVDS, it seems like the traces are usually specified as 100 ohm differential impedance.  What should the single end impedance be from each trace to ground?

I'm looking at PCB impedance calculators, for example the nice list here: https://www.fedevel.com/welldoneblog/2011/08/pcb-impedance-calculator-single-ended-differential-pair/

Using http://www.skottanselektronik.com/impcalc_en.html, I can put in er=3.66 and w=0.30 t=0.035 h=0.17 s=0.7 (all in mm) and I get Z0=50.52 ohm, Zdiff=100.1 ohm.  Is this correct for LVDS?

(This is supposed to match the OSHPark 4-layer stackup)

It seems that by adjusting w (width) and s (spacing), different combination of Z0 and Zdiff can be obtained; Zdiff seems to be < 2*Z0, and approaches 2*Z0 as s gets large.  At closer spacing Zdiff can be much less than 2*Z0, for example w=0.17 s=0.10 produces Z0=69 ohm and Zdiff=100 ohm.  Is this also okay for LVDS?  Is it better than 50/100?

This is my first time dealing with LVDS, sorry if this is too basic a question but I couldn't easily find an answer anywhere.  The part I'm using supports LVDS1.8 per IEEE 1596.3-1996, if that helps.


texts: Fourier transform of the components of bandpass signals

texts:
I'm referring to a book called Communication Systems by Simon Haykin, 3rd Ed.

It says that a band-pass signal \$s(t)\$ with mid-band frequency \$f_c\$ and bandwidth \$2W\$ can be represented as follows:
$$
s(t) = s_I(t)\cos(2\pi f_c t) - s_Q\sin(2\pi f_c t)
$$
where \$s_I(t)\$ is the in-phase component of \$s(t)\$, and \$s_Q(t)\$ is the quadrature-phase component of \$s(t)\$. Following this, it says that the Fourier transform of \$s_I(t)\$ is related to that of \$s(t)\$ by
$$
S_I(f) = \left\{\begin{matrix}
S(f-f_c) + S(f+f_c), &  -W\leq f\leq W \\
0, & \text{elsewhere}
\end{matrix}\right.
$$
Similarly for \$s_Q(t)\$,
$$
S_Q(f) = \left\{\begin{matrix}
j[S(f-f_c) - S(f+f_c)], &  -W\leq f\leq W \\
0, & \text{elsewhere}
\end{matrix}\right.
$$

I can't understand how the relations between \$S_I(f)\$ and \$S(f)\$, and \$S_Q(f)\$ and \$S(f)\$ are being derived.


texts: Cascade connection of TS3USB221 USB multiplexers

texts:
I need to design some kind of selector logic in order to route USB signals to three different selectable sinks. For this purpose I decided to use TS3USB221 1:2 USB multiplexer from TI. It turned out that I need 3 levels of TS3USB221 connected in series. The datasheet of the TS3USB221 is available here: TS3USB221 datasheet

Initially I do not understand different ON resistance values such as ON_state resistance, ON-state resistance match between channels and ON-state resistance flatness.
I also do not understand input (ON) capacitance. Is it between D+ and D- or between each of them and GND.
Without understanding this I am not really able to derive the equivalent electrical circuit of the trace when using 3 stage multiplexer.

The second question is how does multiplexer influence reflections on USB trace. We are using USB 2.0, and I USB traces are shorter than 5cm, so maybe the transmission line effects are still negligible  (?).

Here is the frequency response of the TS3USB221:

As can be seen, by putting three of this devices in series, -3db point will be moved from about 650 MHz to about 400 MHz.

How could I combine all of the available data in order to be able to say if this is going to work.

Thanx!


texts: Photodiode operational amplifier's strange temperature behaviour

texts:
I have two identical circuits (see attached schematic for example) residing on one PCB. Each circuit amplifies the signal from a silicon pin photodiode VEMD5080X01 . The diodes are sitting in a black enclousure without the possibility of light entering that enclousure. The whole arrangement is placed inside a temperature chamber for a temperature cylce (almost 24 h) from 25 °C up to 70 °C down to -30 °C and back to 25 °C again (black curve in the diagrams). Both "DIFF" signals (see circuit at Cf8) are sampled and logged by an 12 bit ADC with 2.9 V reference -> q = 700 uV). The red curve is the signal from circuit1 and the green one from circuit2 (both identical as already stated). What seems strange to me is that the circuitry seems to behave strongly different. The red curve is dropping down from 140 mV when temperature goes up and the green one is  rising slightly with temperature.
Has anyone have a clue if that is related to some instable operating point of the OPAmps used, or even a condition which is out of specification fot that particular OPAmp AD8692?
I'd appreciate any hint in order to track down the reason of that behaviour.

Additional information:
EDIT1: @jonk, thanks for the hint I'll calculate that. According to reverse bias: No It is not reversed biased. I guess for the sake of dynamic range they gave up linearity and decided not to reverse bias. (I am not the initial "designer" of that circuit and have little to none design documentation for that.
@Tony Stewart EE75, thanks first of all for your hints.

"Unbalanced source.." do you mean that I should AC-terminate each differential signal "PD1" and "PD2" to GND?
"Open circuit voltage.." that I have noticed as well. Signal "Diff" at the end of the chain is drifting in the order of same magnitude as the -3 mV/K would suggest. Should I consider the PD as beeing in open circuit conditions with that much of resistance connected (high impedance amplifier inputs)?
"The PD's capacitance.." So it is, but how would it be linked to the behaviour observerd?

Will consider your suggestions (need time foor that) though it means changing much of the circuit. First of all I need to understand them first.
EDIT2: @jonk, the PD is operated with almost 0 V across it, in order to minimize dark current and noise. That's what I was able to investigate. I still need to look for some web ressources to support that statement.
EDIT3: Further thoughts: 200 digits signal correspond to approx. 80 pA current (calculating back through the amplifier chain), which indeed could be dark current. Imagine that the PD is not held at 0 V because the OPamps (TIA) contribute to a Voltage by having certain input offset voltages. Now, if the resulting voltage across the PD is positive I will get current flow in the corresponding direction. But if the resulting voltage is negative the current will also reverse. Is that reasonable?


texts: How can I add a stable DC voltage and a DC pulse train together?

texts:
For a project I am working on I need to take a DC voltage source, around 12V, with at least 1A of current, and I need to add it to a generated DC pulse train which will be from -4 to 4V and will be very low current, say less than 20 mA. So I need the output to be from 8V to 16V DC pulse and I need the current to be from 0.98 to 1.02A.

Someone told me about a summer, but you can imagine googling "summer" does not bring up much that is not related to the season of summer. Googling voltage summer tends to bring up summing amplifiers using op-amps which only handle very small current. And remember I do not want any current or voltage gain. I have my two inputs and I want to simply sum their voltage and currents together.

Does anyone have any ideas for how to accomplish this? Any help would really be appreciated.

In case you are wondering, my 12V, 1A voltage source will be a switching converter from mains supply (110V, 60Hz to 12V DC)

My -4V to 4V pulse train will be from an op amp output setup as a comparator.

Thank you for any help you can give.


texts:
I am trying to program a PIC18F4550 to control a 3 Phase BLDC motor.

I have doubts about how to make the program, since I have seen many examples that what they do is use the TIMER to generate the 3 shifted PWM signals.

And I don't know why the PWM module that this PIC has is not used to do this process.

Is it not possible to generate 3 shifted signals with the PIC18F4550?


texts:
I have been working with the LM2907 as I have been designing a few circuits around it. This has lead to me wanting to understand more of its inner workings and build up a breadboard model of the internal circuit. The reason for not just using the chip is I need to display the relative key functions.

The Ouestion

Is there possible errors in the below schematic? Specifically:

Charge Pump
The use of Q2 to charge the 22nF which is in the external area
My choice of C1, being electrolytic

Below is the schematic referring to the question:

How I believe it should work:

The comparator (IC1A) would turn the input frequency into the correct "pulse" to the Charge Pump.

The Charge pump is based off of a single stage charge pump model. I placed Q2 so as to charge C2 as would the LM2907 do.

After this it would go to the OP-AMP, aside LM741 is used but could be any, which will control the output resistor Q1 with feedback to the Inverting input from the emitter.

Reference Schematics

These are images from the datasheet. The first is the circuit to which the above is meant to mimic in operation(less components for visibility).


texts: Cortex M0 - ADR "cannot represent THUMB_ADD relocation in this object file format"

texts:
When attempting to use the ADR instruction in an assembly program, the assembler chokes with the error "cannot represent THUMB_ADD relocation in this object file format"
I'm referring to the official ARM docs at http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0497a/BABEDJGG.html
If I try the label example on that page (e.g ADR R1, TextMessage) I get the above error. If I attempt the other form which uses an offset from the PC, (e.g ADR R3, [PC,#996]), I get the error found ',', expected: ']', which suggests a malformed instruction. I'm using the GNU ARM assembler (through System Workbench if that's at all relevant).
I'm just trying to load the address of a variable/constant (defined using either .set or .equ directives) into a register for later use.
I tried looking up the error in question and found a whopping six results, none of which gave any insight into the cause. Suffice to say, the error doesn't mean much to me so I'm not sure how to proceed.


texts: Capacitor with pulsating dc voltage source/current

texts: When an A.C voltage source in series with the DC voltage source are applied to a capacitor in series with a resistor they say that capacitor will block Dc and will let AC pass to the resistor. I am not understating it. By using super position theorem the statement can be proved but i am not getting the concept. Since the voltage/current across the capacitor is now pulsating Dc in this case then how the capacitor is blocking DC while letting AC passing through the resistor? How and why a capacitor makes a pulsating DC input to an AC output across the resistor ?


texts: Problems connecting an Arduino Uno to a Commodore 64 Joystick port

texts:
I have made up a DB9 connector, which is the connector that fits the Commodore 64's joystick port. A small program on the Arduino sends HIGH signals to pins 1,2,3 and 4 of the connector. Another small program on the Commodore 64 reads the state of the joystick port (joystick port #1) and prints it out. However, the Commodore 64 is not registering the signal changes on the port pins. What am I doing wrong?
Is the problem due to the Arduino being unable to supply enough current, and if so, how do I fix that?
Thank you.


texts: What thermic insulation to use on a heat wire?

texts:
I have a thin nichrome wire that will be heated up to approx 100 degrees C, inside an enclosure. Since this wire needs to follow a specific path I would like to attach it somehow at some points along that path. Now my question is what material I could use to wrap the wire at those points as to limit the amount of heat dissipated through direct contact at those points.

When looking on the internet I found plenty of insulation materials that can resist high temperatures, but their main purpose is to insulate the electricity going through the wire, not the heat radiated from it. I would need a material that blocks as much heat as possible so the outside would be as cool as possible. This to avoid having all the heat from the wire transferred through the attachments into the plastic of the enclosure, which could melt the plastic at the attachment point. Maybe ceramic can be used for this?

What I was thinking about doing was put some insulation around the wire above the attachment point and clamp the insulated wire to the attachment point. If I were to clamp the wire directly, using bolts and nuts for instance, the heat transfer from the wire through those bolts and nuts would heat up the plastic way too much and it would start getting soft.

Since I am 3d printing my enclosure I can use plastic that can withstand 80 degrees (printing with PETG), which is clearly not enough for this case. Even using nylons I can only go up to 110, which is too close to the wire temperature.


texts: Is there a way to use a depletion mode MOSFET "inverse"?

texts:
I aquired some surplus led strips and I want to make a certain control circuit for it. I took another goal of using only the components I have laying around. I found a nice reclaimed power MOSFET to switch the LEDs in the parts bin. I designed the circuit and went around to test the aforementioned MOSFET if it still works. Turns out it's a depletion mode MOSFET, not a regular one.

Is there any way to use it in "inverse" so I do not have to flip the whole logic(I spent some 5 hours designing it)? I guess I could put an inverter before it, but I thought maybe there's a more clever way.

EDIT: test rig:


texts: How do I model a simple metastable flip-flop in ngspice?

texts:
Problem

I'm trying to simulate the simplest possible model for a flip-flop: two inverters connected in a circle. I'm using ngspice 31 on Arch Linux. I based my model on the CMOS SOI Inverter example (https://sourceforge.net/p/ngspice/ngspice/ci/master/tree/examples/soi/). Here is what I came up with:

SOI Flip-flop

.include ./bsim4soi/nmos4p0.mod
.include ./bsim4soi/pmos4p0.mod
.option TEMP=27C

Vpower VD 0 1.5
Vgnd VS 0 0

MN0 X Y VS VS N1 W=10u L=0.18u Pd=11u Ps=11u
MP0 X Y VD VS P1 W=20u L=0.18u Pd=11u Ps=11u
MN1 Y X VS VS N1 W=10u L=0.18u Pd=11u Ps=11u
MP1 Y X VD VS P1 W=20u L=0.18u Pd=11u Ps=11u

.ic V(X)=0 V(Y)=0
*.ic V(X)=1.5 V(Y)=1.5
*.ic V(X)=1.5 V(Y)=0
*.ic V(X)=0 V(Y)=1.5

.tran 2ps 2ns

.control
  run
  plot X Y
.endc

.END

This should correspond to this schematic:

simulate this circuit – Schematic created using CircuitLab

I want to see how this circuit behaves under different initial conditions for the gate voltages, especially metastable ones. (I know I could use NAND gates instead of inverters to make this into an actual RS flip-flop and produce metastable states with input pulses, but I'd like to use this simplest model if possible.)

Results

The stable initial conditions yield stable results as expected:

X = 1.5 V, Y = 0 V:

X = 0 V, Y = 1.5 V:

One of the metastable starting conditions also looks fine, with an initial metastable period and a stable outcome:

X = 1.5 V, Y = 1.5 V:

The other metastable starting condition, however, produces this:

X = 0 V, Y = 0 V:

This looks different, because the voltage overshoots to 1.6 V. A longer simulation time show that it takes about 2 us to settle to 1.5 V:

Now this is still fine, I didn't expect both cases to look the same. My problem is that the values change drastically when I change the simulation step size.

From 2 ps to 0.2 ps:

To 0.02 ps:

So a resolution of 0.2 ps increases the overshoot to 2.6 V, and a resolution of 0.02 ps seems to push both gate voltages to 3.75 V.

I experimented with the uic option for .tran and with .nodeset, but as far as I can tell from section 15.2 of the ngspice manual, the way I did it should be the right one.

Question

I am wondering what the issue here is. Is this naive simulation model, using only initial conditions, somehow inconsistent or wrong? How can a change of simulation resolution produce such different results? Or is this just not a suitable problem for a simulation because of the non-well-behaved nature of metastable states?


texts:
I want to drive a power ignition IGBT (IRGB14C40L), and for this a driver MC33153 has been chosen. I have several questions about my supposed schematics, shown below:

0) This design will (allegedly) drive an automotive spark plug;

1) MC33153 datasheet tells us, that it's better to use separate turn-on (R1) and turn-off (R2) resistors, later one with diode (D1). For resistor values my calculations are based on IGBT datasheet: it tells that maximum peak current through Gate should not exceed 10 mA. So to be on the safe side R1 should be 1.5k Ohm. But how to choose D1?

2) How to choose value and type of C1 decoupling capacitor? I guess it should be physically located as close to Vcc and Vee pins as possible?

3) Datasheet of IGBT shows an internal resistor about 20k, which connects Gate to Emitter. I guess because of this, I don't need an external one to keep Gate low in case of floating input, am I right?


texts: Higher brightness LED with bigger resistor to save battery life

texts:
I need to run three LEDs for indoor indication purposes and want them to be around 500 - 1000 MCD. I will run them off batteries and I'm wondering if there is anything I can do to increase battery Life since I don't want them to be that Bright anyway.

They will be wired in parallel and need to be constantly lit when powered on. Series Circuit is not an option because I can't fit a higher voltage battery. 3-4AAA is the most I can fit inside. I also want to keep the Circuit as simple as possible.

I have some options for leds that are rated at Everything from 1000 - 15000 MCD. They are all rated at around 2-3.6V and 20mA.

Is it better to choose a brighter LED and run them at maybe 1-5mA or so to get the wanted brightness by adding bigger resistors or should I use a more appropriate LED for the wanted brightness with smaller resistors? They are all rated at 20mA.

I know that resistors waste energy but I'm not concerned with that as long as the energy wasted by the resistors is smaller than the energy saved by running the LEDs at lower currents. Unless it will get really hot because it's inside a box.


texts: Single regulator to power mixed signal PCB?

texts:
I have a codec (ADC & DAC) with both analog and digital power and ground connections (upper half is analog, lower half is digital). By placing the device package in such a way that all digital traces are routed under its center and all analog traces are routed above its center I should get a proper layout. My question is how can I power the entire board using a single regulator? Placing it on either parts of the board (above the analog ground part or above the digital ground part) would cause power traces leading to the analog section to cross digital ground or vica versa.

What is the best practice here?


texts:
I am using an mtk3333 to read gps coords. I set nmea messages to only output gll data. The problem is that I am receiving the GLL packets but in this format:

$GNGLL,,,,,004912.869,V,N*6D

GLL packets format should look something like this:

So I am not receiving coordinates. And even the time doesnt make sense. I assume that's why the status field has a "V" for invalid data.
Any idea as to why this could be happenning ?


texts: What value pull up resistors does the MPU9250 use?

texts:
Looking at the datasheet

On page 32, the datasheet says "The MPU-9250 always operates as a slave device when communicating to the system processor, which thus
acts as the master. SDA and SCL lines typically need pull-up resistors to VDD. The maximum bus speed is
400 kHz."

There's no information about what value pull up resistors to use. Doing a quick search on google for mpu9250 schematics I see this schematic

It uses 10k resistors as pull ups. My question is whether this is accurate, and more importantly can I settle for 4.7k resistors since those are what I have lying around?


texts: I need 3 opams for a circuit. One for amplification, one for level shifting and one for sharpening badly shaped pulses, For the last part(pulse sharpening) I want to use a comparator/schmitt trigger. Can I just use LM324 for all since it has 4 opams inside or I need another IC?


texts: Using ENC28J60 to communicate over the internet

texts:
I've read that we can interface a microcontroller to the ethernet using ENC28J60 ethernet interface chip, but can I use the same to interface the controller with the internet? I've googled about it for over a month and i felt that there is no single proper explanation which covers all parts of this concept.

I got to know how to interface the ENC28J60 with the controller through SPI, and how to configure ENC28J60 IC, but then I ran into something called as a "TCP/IP" stack. Now this is supposed to be a set of internet protocols. But all I want to do is a simple webserver so isn't UDP/IP and ARP enough to do this?? why will I need TCP?


texts: how to calculate the feed back capacitor

texts:
i have narrow pulse of width 10ns repeating at 20us rate to be processed coming from a photo diode, so i have used a very high GBWP opamp like below,as my interest is to work at 100Mhz as pulse is 10ns, i have managed to get a pole at 100MHz using 1K resistor and 1.6p capacitor in the first stage while having a gain of 1K

simulate this circuit – Schematic created using CircuitLab

but when it comes to the second stage my gain curve is flat when i use a 100femto capacitor and also 1.6p, with a different phase response here

one can see that first graph is a 100fF response and second is a 1.6p response,

  how to calculate the feedback capacitor of the second stage,

when i observe the pulse response, the 100fF response is  quite sharp while the 1.6p response quite expanded pulse output

  why a 100fF is a better suit here

  more importantly is a 100f capacitor, how practical it is on a PCB board


texts: What technology should I use for tracking small boats venturing upto 50km in the sea?

texts:
2017 south India was struck by a cyclone Okhi which took many small fishermen's life. I'm an electrical engineering student and want to do a project regarding tracking these boats and implement an emergency beacon system. Current I'm considering LoRa but I'm highly sceptical about it's range. What are the other cost effective options to track a boat within 50km from the shore. I'm aware of the EPIRB but that thing is costly and I cost is a primary concern for me. Any help would be appreciated.
Thanks in advance.


texts: A question about instantiating a module with a parameter in systemverilog

texts:
I'm now writing a testbench. In my testbench, I want to read the length of a text file and pass it to another module while instantiating. The idea is like this:

module TB();
integer text_len;

ABC #(.text_len(text_len)) ABC_1(//some input/output arguments here);

task read_text(output integer text_len);
//read text file and get the text length
endtask

initial
begin
read_text(text_len);
end

endmodule

When I compile it using Questasim, it keeps saying the expression for a parameter actual associated with the parameter name text_len for the module instance ABC_1 must be constant.
Does anyone know how to deal with it?


texts: Portable battery charger: how can I recharge the batteries without direct connection to my home electricity?

texts: I'm working on a smart watering system for few flowerpots I have in my balcony. My main problem is that I don't have electricity output there, so I'm trying to think of a way to power my Arduino with 12 V somehow. I thought of using 12 V battery and a solar panel, but since I have indirect sun most of the day, and small solar panels are expensive, I dropped the idea. I hoped for some advice, how can I recharge the batteries without direct connection to my home electricity?


texts: Potential difference between two points on ground

texts:
I noticed that when I stick digital multimeter's probes in the ground near my house it shows potential difference about 0.01-0.21 V what looks pretty high. If probes are close it's smaller when farther it's higher. It could look as a "step potential" BUT I made multiple trials in multiple random positions dozens feet away from each other and behavior was the same. If it was step potential indeed it would have been noticeable only in one place that is close to grounded object.

Any explanations?


texts: If I have a system with a response time of T milliseconds, how fast should I run a digital PID loop ie what is the minimum frequency that the lop should be?


texts: Why is it necessary to use a voltage limiter at the output port of a Schmitt trigger? How are switching thresholds determined in various types of Schmitt triggers?


texts: Duplicate RX in uart (two devices listening one of which is data-logging)

texts:
I am not too familial with UART yet, and was wondering if I could some how duplicate the stream of information going to a microcontroller from a GPS. My application will be using a msp430g2553 microconltroler to communicate with a GPS module while data-logging with (OpenLog).

I have read that you should not just simply have 1 sender and 2 receivers,
https://learn.sparkfun.com/tutorials/serial-communication

Any suggestions/advice will be appreciated.


texts: How to compare brightness of different color LEDs (not RGB)?

texts:
I wonder - let's assume one would build some user interface using green, yellow and red or just any other available colored LED (not RGB LED) - what would be the proper (aka best) way to compare the brightness of LEDs in order to choose "equally bright" LEDs regardless of the color in respect of sensitivity to different colors by the human eye - based on thetechnical specification given for an average LED such as milliCandela, Wavelength, etc.? In particular, I am aware that two LEDs of the same mcd are in theory supposed to be equally bright - however, you rarely get different colored LEDs of exactly the same milliCandela value, so expressed differently; if there is a green LED of 45 mcd and a red LED of 23 mcd, is dimming the green LED to 50% duty cycle enough to make them equally bright? (I suppose not, but then how..?)

Thanks!


texts:
Say a person touches the live wire as shown in the first attachment, the current will flow through him and dissipates into the ground as shown in the second attachment right? the fault current through a person does not really “return” to the source as drawn in pencil correct? Also is it possible that the return current is less than the outgoing current? 2/3A vs 1/3A , assuming that the resistance of a person is 10 ohms .
Much appreciated!

Sorry the second picture was not able to be attached , it just shows current dissipating into the ground in ring shaped waves propagating away from a grounding rod in the earth


texts: How do I calculate phase margin for a feedback amplifier

texts:
I'm learning analog design and can't seem to get a firm grasp on the concept of phase margin and wanted to ask a few questons:

First Part: I understand that Phase margin is the difference between the phase at unity gain and 180

Question 1: If I have an inverting amplifier, my output phase starts at 180.  When the phase remains 180 up to the 3dB frequency, is my phase margin now the distance from 0deg?
Question 2: Is there an equation to calculate the phase margin?  What happens when I have negative phase shift, am I now comparing to -180deg?

Second Part: I followed this video from Linear.com, and I used the following circuit with the LT1212 op-amp to run an open loop analysis:

simulate this circuit – Schematic created using CircuitLab

Running this in LTSpice shows two different 0dB crossing in the bode plot (1MHz [55deg] and downward slope, 7MHz [-86deg] and upward slope).  Am I right to assume this circuit would be unstable?


texts: Differential Equation of a LC Low Pass Filter

texts:
I'm trying to learn about different applications of RLC circuits and have been presented with a weird looking circuit...

I've only ever dealt with circuits that can be modeled with a 2nd-order differential equation, so I'm unsure how to approach this. I've researched the circuit and found this article on low pass filters comprised of LC components. This is a lot different than the RC low pass filters I've studied.

Is the circuit above a low pass filter as well? Does the resistor merely a load resistance or does it influence the behavior of the following LC components? The values aren't provided in the graphic, but C1 and C2 have different capacitance values. The article shows the capacitors both being equal to C/2.

How would I relate the output voltage y(t) to the input voltage x(t) using a differential equation? I tried to create a differential equation using mesh analysis but quickly got mixed and couldn't figure out how to manipulate the equations I got into a differential equation. This article shows a similar circuit being solved but I'm confused by how everything relates.

Here's what I've done thus far...

EDIT: I think I figured it out...


texts: LVTTL Buffer IC output logic when input is high and not connected to supply voltage

texts:
To buffer a LVTTL signal to FPGA I am using this TI buffer SN74ALVCH16827DGGR.The buffer IC is placed on a FMC based IO card mated to a ZYNQ mother card. The problem I am facing here is when an input signal is applied to the buffer IC, there is an output signal even when there is no power supply to this IC. The output enable signals are connected to PCB GND.
I want to avoid this as it may damage the FPGA. Can someone suggest me with a solution?
Schematic for reference


texts:
I have a question regarding Xilinx Vivado. I don't really know how to explain it, but I'll give it a try and hopefully you will know what I mean.
In Vivado, you can instantiate primitives for example an IDDR. I need 15 IDDRs, is it enough when I instantiate one? The instantiation looks like this:
  IBUFDS_inst : IBUFDS
   generic map (
      DIFF_TERM => FALSE, -- Differential Termination
      IBUF_LOW_PWR => TRUE, -- Low power (TRUE) vs. performance (FALSE) setting for referenced I/O standards
      IOSTANDARD => "DEFAULT")
   port map (
      O => O,  -- Buffer output
      I => DIN1P,  -- Diff_p buffer input (connect directly to top-level port)
      IB => DIN1N -- Diff_n buffer input (connect directly to top-level port)
   );

But I also need IDDRs for DIN2P, DIN2N till DIN15P,DIN15N. Do I have to instantiate this component 15 times?


texts:
I'm working on a project in which I must send audio over RF such that remote speakers can pick up the signal around a house/apartment. The goal is to broadcast music from a single device somewhere in the house to multiple speakers without the overhead/limitations/tedium of Bluetooth/WiFi. My current approach is as follows:

Input mono audio from 3.5mm barrel audio jack to transmitter
Create 200KHz triangle wave using ADA4851 op amps
Modulate audio using triangle wave, resulting in 200kHz PWM
Transmit PWM using FS1000A 433MHz RF transmitter module
On one or more remote devices, receive RF signal using MX-RM-5V receiver module
Use BU4S584G2 inverter to produce complementary PWM signal
Use 2x FAN73932 gate drivers to drive MOSFET H-bridge using the complementary PWM signals
Filter the H-bridge output using LC low-pass and connect speaker to its output

My main issue at the moment is that I didn't realize the RF modules have such a slow datarate: only around 4-10kbps. So, I need a new RF module with the following characteristics:

Cheap (can't justify using xBees, plus I don't know if xBees can emulate a wire, or if they must use a serial protocol)
Data rate at least 2Mbps (minimum pulse width must allow for wide PWM range)
Range of at least 100ft indoors to reach a whole house
Only need one-way broadcast in a star network

I'm open to other options, too. I chose PWM so I could use the digital RF modules without needing to encode/decode a binary audio stream. I would rather avoid the hassle of programming microcontrollers at either end. Please offer any suggestions you may have, but my particular interest is finding an equivalent (but faster) RF link.

Thank you, all!


texts: Is half stepping possible by powering the two consecutive coils?

texts: I have some stepper motors with a step angle of 1.8 degrees and I am wondering if it is possible that powering the coils next to each would it get the spindle to go to midpoint between the two coils? So for example power coil 3 and 4 to get it to go between both points(so step angle between 0.9 degrees) or will it keep moving very slightly? I only ask as the stepper motors are at college and its the weekend so can't test it.


texts: Linear voltage controlled resistor divider

texts:
I'm working on an audio amplifier project and I'm trying sort out the solutions to certain problems.

The problem that I most need to get solved is that I want to digitally control certain operations within the amplifier via a digitally controlled resistor and/or resistor divider.

I would need a voltage controlled resistor that is both as linear and noiseless as possible and it would need to function on voltages as high as 600v at 100ma with a resistance ranging from near nothing to multiple megaohms.

The only thing I can remotely think of is octocouplers but I know little about them other then they are inherently non-linear. I've heard that they can be linearized through certain techniques but I just don't know anything about the subject.
The linearity and noise factor are paramount here, it might even be worth it to use a mechanical solution to control a trimmer.
Does anyone have any ideas?

The resistors that I need to control are circled in red.
I intend for the CVS to be adjustable from 10v to near 600v and the CCS to be adjustable from 1ma  to 100ma, possibly more. The intention is to be able to manually shift the load line operating point and accept a wide range of tube types reaching up to high voltage tubes such as the 300b, which I would want to be controlled digitally and with safety measures so I don't shoot 350v and 70ma into a 6SL7 or something.


texts: How do I charge a lithium-ion battery from a solar cell

texts: Let's say I have a lithium-ion battery like the this one. and let's also say that I have a solar cell like one of the following this or this. i know that charging a lithium io battery is tricky and ideally involves ramping up the voltage at larger amperage followed by a flat voltage and lower amperage If I'm not super concerned with performance, is it possible to simplify the process and trickle charge the battery over a longer period of time? Also, if the voltage output of the solar cell is less than optimal, would that effect the performance of the battery?


texts: Does connecting neutral to chassis (bootleg ground) rise chassis potential to main's voltage with respect to ground?

texts:
I know that bootleg ground is dangerous and should never be done, I am just using it as an example for my question, I probably have a fundamental misunderstanding about current flow and voltage, because, by my reasoning, the chassis of an appliance, if connected to neutral wire while the appliance is turned on (so, hot wire is connected to the neutral wire inside of appliance circuit) should have the same voltage on it as the hot wire. See this picture:

The reason I think that, is because neutral wire and hot wire are only different when they are not connected, once they are connected, both hot wire and neutral wire become the same wire, right? So, voltage on the part of the wire that we previously called neutral should become the same as on the hot wire with respect to ground, right? And since appliance's chassis is connected to the same wire, shouldn't voltage on the chassis rise to hot voltage with respect to ground, if not why? Touching the chassis with bootleg ground should provide an alternative path for current through the person to the ground, so why doesn't this happen?
If ground and neutral are bonded at main panel, why aren't all grounded device chassis energized? - This question seems to be actually the same as the one I have, because I also don't understand why chassis of appliances does not have voltage in a TN-C-S system where ground wire and neutral are bonded at the service panel, don't they become the same wire if they are bonded?
To summarize: If neutral wire and hot wire are connected through a load, don't they become the same continuous wire which should have mains voltage on it with respect to ground? In a TN-C-S system don't ground wire and neutral become the same wire if they are bonded at the service panel?
Edit 1: changed the picture per comments.
Answer:
I revisited Ohm's law and understood the answer to my question. My problem was that I was mixing the fact of something being grounded directly causing the effect of everything being in the below (neutral) part of the circuit at 0V relative to each other. When in fact I should be thinking of everything on the ground as resistors connected in parallel to the neutral, the voltage drops at the radiator making it close to 0 for everything else, a person touching neutral is like a resistor in parallel to resistance of neutral.


texts: Using a piezo disc as an input and output device to ATtiny85

texts:
I am working on an art installation and plan to use a number of these small circuits to make sounds, to sense sound/vibration and also to move the device (using a triangle wave output).

This link gives examples of input and output using the piezo. I have crudely mashed the circuits together into one. Would this work? Or do I need some more components, eg diode protection on the output.

The objective is to create a small circuit with the minimum of parts that can be experimented with as a cell in a kind of physical automaton.


texts: HX711 noise, but only in a specific environment

texts:
I'm working on a small project at my farm to automate vegetable weighting. The system consists of an STM32 MCU, some additional ICs (matrix decoder, parallel-serial converter for some push-buttons etc.), an LCD screen (HD44780 compatible) and finally, an HX711 ADC to interface a load cell. Everything is supplied by a single 12V PSU (switch mode), followed by a 3.3V and 5V regulator module (switch mode). The system was designed on two PCBs. Everything would be installed in a custom-designed, quite large sheet metal housing.
I'd be really glad to have your opinion about two things:

The first question is about noise. When I'm using the system on a test bench, the readings of the HX711 are rock stable. The final measurements are converted using a basic linear regression to get a calibrated values in decagrams. I'm using a 5 measurement long buffer for averaging (when successive measurements do not exceed a threshold value), but even without that I get stable values.
But when I assemble the system in the housing (same PSU, cables, and other components), the variance increases a lot, which means jumps of roughly 5 decagrams. I tried to introduce some noise when using the system on the bench to reproduce the issue (WiFi enabled mobile, high voltage lines etc.) but nothing seems to disturb the measurements there, only when it's outside in the metal housing.
Has anyone already faced a similar problem? What can be the issue?
The only visible difference is that on the bench, the load cell is fixed to a plank, but when I assemble the system, it has direct contact with (screwed on) the metal housing. No other electronics is touching the housing, just the body of the load cell (I couldn't find any connection between the body the cell and the wires of it with a multimeter).
Is it possible that the housing introduces the noise to the load cell or to the ADC? I'll try to do a test measurement with the load cell "floating" on its wire or with another load cell, just to see if it has any effect, but I can visit only next week, so I thought of asking this in order to get some additional ideas.

I'm just a hobbyist, and since I mentioned the housing as a possible cause of the noise, I have a question that most likely to be a basic one. Like I mentioned, all electrical components are separated from the housing, only the load cell and the push-buttons are touching it. Since there are some push-buttons, the PCB is (theoretically) protected by a debouncer IC, which has ESD protection.
But should the housing itself be connected anywhere (eg.: earth) considering the safety of the user, furthermore the safety and proper function of the system?

Thank you very much for your help in advance!


texts:
As in the picture , how can I determine ki , kp , kd
I tried (using provided data) by finding ζ and ωn
But I end up with third order transfer function could not subsitute my results to find PID parameters (ki kp kd ) values


texts: Converting a circuit from Multisim into a PCB

texts:
I drew this metal detector circuit in Multisim.  How can I make a PCB board from it?

Is there an option in Multisim to convert it to PCB or do I need another program?


texts: CBC-MAC implementation optimised for 8-bit MCUs

texts:
Does anyone know if there's an CBC-MAC implementation designed/optimised for 8-bit (8051-based) MCUs? I was hoping to find one in the AVR-Crypto Lib but there doesn't seem to be one. CBC-MAC for 8-bit MCUs seems to be hardly ever mentioned in the scene.

Thanks


texts: I am experimenting with the arm cortex A8, it has a bunch of LCD outputs I first thought I could just convert LCD to a HDMI signal, but can't seem to find any thing of an use, any help would be greatly appreciated.


texts: How can I determine the quality of an accelerometer? Is there a standard measure, such as the SNR, or set of measures? What makes one accelerometer better than another; the accuracy of its sampling rate, and "noise" of its x,y,z samples?


texts:
Is there a logical way to count number of most significant zeros?

For example

5 leading zeros                    5
00000100 -> combinational logic -> 00000101
1 leading zero                     1
01000000 -> combinational logic -> 00000001
0 leading zeros                    0
11111000 -> combinational logic -> 00000000

Edit: Using gates


texts: Force sensor reading values Raspberry Pi

texts:
I have this force sensor:
http://www.robofun.ro/docs/2010-10-26-DataSheet-FSR400-Layout2.pdf

I need to connect it to a digitial pin of a Raspberry Pi. In order to do that I want to use a polarized capacitor of 1μF measuring the frequency of the capacitor discharges.

However I don't know exactly How can I connect the pieces, is the following scheme ok? If yes, what vlue should R2 take?

Thank you!

simulate this circuit – Schematic created using CircuitLab


texts: Simulate press on a rubber button infrared remote control with a Raspberry Pi

texts:
I'm stuck.
I'm trying to use a Raspberry Pi to simulate a button press on an infrared remote control that uses conductive rubber buttons in order to control/automate a toy with Python.
Really grateful if someone could explain if it is possible to solder a wire from the Rasberry Pi gpio and do the above or any other method that might work. Please point me where I should document myself more.
With my basic knowledge, I understand that the rubber button when pressed completes that specific button circuit, so I was wondering if I could just send a signal in the continuation of the circuit (where the contacts would have meet) to simulate that circuit.
I think it goes to the integrated chip on the back side where it is modulated into the infrared code.
Or maybe just send some data directly to the chip?
Another idea was to cut the infrared LED from the remote and attach it to the Pi, then brute force the the command codes with Python.
How do people hack these basic remotes?


texts: How to take a raspberry pi project and get it mass produced

texts:
I was wondering how can I take my project that I have done with a raspberry pi and convert it to a PCB for mass production.

My project is an e paper display that is attached to the raspberry pi in order to generate a menu for a user to interact with. The project was designed so I could give my employees a way to log data easier.

The issue is that the raspberry pi is not available on 123d circuit design for the PCBs. Is there another low power computer I can base this off of? Or is there a way to create your own raspberry pi based board for mass distribution?

I have seen the raspberry pi compute modules but I cannot find a connector for them in 123d.

I am a complete newbie to designing PCB so any advice would really help?


texts:
We have a problem with the DC motor driver DRV8835 that we have soldered to the black PCB attached below (4). Prior to this driver, we were using L293D h-bridges to run these DC motors and never experienced an issue. We changed the drivers from L293D to DRV8835 and the motors not only overheated but also drew twice as much current. With the old board (3) four motors (not loaded) were drawing ~0.2A and with the new one (black PCB) it is drawing ~0.5A. We never had this issue with the old PCB and L293D drivers. We are using ESP32s microcontroller and the schematic of the new board is given below (5).
Before designing the PCB we set up a circuit on a breadboard (6) and everything was working fine. The motors got slightly warmer with DRV8835 on the breadboard but they were running at the same speeds comparing with L293D. Are there any suggestions to this problem that we can try implementing? We are working on robotics but we don’t come from an electronics background so any suggestions are appreciated.
Thanks!


texts: PIC18F SPI SDI line affecting/distorting data from slave device?

texts:
I have a PIC18F14K22 connected to a flash memory chip (Winbond W25Q80BV) via SPI and am having trouble reading the output from the chip. Specifically, the flash data output becomes distorted when I connect its output line to the SDI PIC pin. If I just watch the flash output from a logic analyzer, I can verify the correct output is being produced. My thought is that possibly the SDI line (RB4) is not in High-Z mode, but I explicitly am setting it as an input:
TRISBbits.RB4 = 1;    // RB4/SDI is an input

Note that I can use this SPI port successfully with another chip (not a memory chip, something else).

I have tried pulling the line high and low to bias in either direction. However, the line DOES change level, just not quickly enough or maybe is not strong enough to produce the correct signal.

Here is a demonstration from the logic analyzer of when the SO signal looks correct (not connected to PIC SDI) and then after I connect it, the incorrect signal: http://imgur.com/Nbhg6FJ,gonA2H5#0

Any ideas?


texts: Is it OK for traces to come off SMD pads at the corners?

texts:
I'm working on a PCB and have found it very convenient to connect adjacent passive components by running traces between them diagonally, as shown below:

Is this bad for any reason?


texts: Please help me identify the SMD component in the picture (or help me fix my Wacom)

texts:
Could anyone help me identify what type of SMD component the one in the red circle is? The label seems to be ID but I can't really tell very well because it's so small. My guess is that it's a diode but I could be wrong so I'm looking for another person's opinion. It appears to be the first component connected to the 5V input of the USB port. I tried checking its resistance in both directions but it seems to be open except when there is power where I can measure -2.4 Mohms in one direction.

The device is my Wacom Intuos 5 graphics tablet which doesn't work via USB but works via wireless sans battery charging. I tried using a cable to temporarily jumper that component and it worked so the component is surely broken. I think I'll be able to repair this myself if I can identify what it is.

I'm just a hobbyist so I need some expert advise. You think it would be safe to just solder in a jumper and bypass this component? If it's a diode, would any common diode be ok (even non-SMD)?

Thanks in advance! I'd save a lot of money if I can get this to work instead of buying a new one so any help would be very much appreciated!


texts: How to safely demonstrate backfeeding AC

texts:
I'm looking to setup a basic demo of backfeeding AC and how it effects some AV equipment. My idea was to wire up an extension cord with a three prong if on one end and a simple single gang outlet on the other. This is US equipment. Then wire an AC transformer to the circuit. Plugin the piece of equipment and slowly increase the voltage coming from the transformer to demonstrate how it effects the equipment. Max voltage would be about 70 volts. Is this even a proper demonstration of what backfed AC is? Would this just not do anything? Will I burn my house down? Or explode?

Why?

I work for a cable company. In this area we have a lot of old houses. Old people. And old TVs. When we have a customer who is experiencing tiling or other abnormal behavior and all RF issues have been addressed, we check each outlet (inhouse cable line) for AC or foreign vtage before it hits the splitter. To test we take the (-) lead from our meters, ground it out and test the center conductor of the coax. There isn't supposed to be any AC. Some trace energy is fine. But we find lines with anywhere from 2 - 70 VAC. We ground out the line in question and no more issues.

The sitters seem to act as a weak capacitor building up stray AC until it causes an issue.

If we have time we check all outlets with an outlet bug to make sure they're properly grounded and wired. Its usually either a broken ground wire, a two wire circuit with three prong outlets, or older TVs and VCRs that are backfeeding.

What I want to demonstrate is how it looks with various amounts of VAC. I have the test board with the coax all setup that's easy. Originally I was going to take a variable AC transformer and wire it to a coax line Hooke up to a splitter and thus the test RF network. Thinking about it again I still feel like that is my best option. But it'd be hard to get real-time readings of VAC POST splitter. So then I wondered about my above question. Why not just wire up a single circuit I can plug in, and send vtage to the outlet itself. I guess that wouldn't be the same though....

Basically I don't know enough about VAC to know if I plug something into an active outlet and somehow send energy back in the other direction if I'd cause a glitch in the Matrix or worse! :)


texts: Is full wave rectifier better than half wave one?

texts:
I am curious if there are practical differences between a DC power supply based on a half wave rectifier or a full wave rectifier.

I mean I have a few small DC power supply units which should give 12V 0.1A each. They all have a transformer 240V->18V, then 1 diode or 4 diodes, then 78L12 (0.1A regulator) and one or two capacitors (typically 220uF or 470uF).

My question is if the power supply can give a good quality DC voltage with just a half wave rectifier (a single diode) when a 470uF capacitor and 78L12 is added, or if bridge rectifier (4 diodes) is better.

I also have one old 12V 0.2A power supply based on a Zener diode instead of 7812 regulator. It also has 18V going to just a single diode, then 33R resistor which limits current to 0.2 Amp, then Zener diode parallel with a 1000uF capacitor. Again: Would it be better to have 4 diodes there, or is the half wave rectification good enough here thanks to the 1000uF capacitor?

(All my power supplies work well, I am just curious "why" and "how" these things work.)

Update:

I found two more interesting information:

Capacitor should be approximately 500 uF for each .1 Amper of output (or more). This applies to full wave rectifier. Since I saw the same values in half wave rectifiers, it isn't enough and they are bad design.
4-diode rectification cannot be used when we want to have a combined 5V/12V output (or any other two voltages) with a simple transformer, because it can't provide a common ground for two different circuits. (A more complicated real example: I have got a power supply with four output wires from transformer -7/0/+7/+18 Volt. Then it uses 2-diode rectification to get full wave 7V output, and 1-diode rectification to get half wave 18V output. The 18V line can't be "upgraded" to 4-diode rectification here.)


texts:
By using the open loop transfer function for a control system, how would you then sketch the Nyquist plot by hand?

I'm aware you'd substitute any \$s\$ term for \$j\omega\$ and then rationalise the denominator by moving the \$j\$ terms to the numerator. But from this point forward I am unable to get to the point where I can plot the rough shape of the Nyquist plot. Any break down of the steps would be greatly appreciated.


texts: Press and hold the reset button to reset AVR!

texts: I connected a tactile switch to the AVR reset button according to the circuit below. every time I press the button the AVR resets itself but my question is: Is there a way to make this button acts after let's say 3 seconds? I mean press the button and hold it for 3 seconds and then the AVR resets itself. (some kind of resistor-capacitor circuitry)


texts:
I'm having some complications when I'm trying to control 16 Relays using 2 595, these relays control loads connected to 5V, 12V and 220V. There are 8 loads at 220V using the 8 LSB from my SPI communication with the 595.

Everything works great as long i have connected 5V and 12V to the relays, when i connect 220V relays turn on and off randomly, sometimes they work just right, as I change the registers. Using an oscilloscope I've seen some noise in VCC (5V), but I've been unable to eliminate it.

I've tried:
 -Connecting different power supplies to my arduino and to the relay module. I'm using a pc power source for 5V and 12V.
 -Changing Serial freq.
 -Using a low pass filter at latch. To avoid a noise induced data storage.

I'm using there relays:
SainSmart 8-Channel Relay Module

I'm completely out of ideas, so any kind of insight will be appreciated.

Regards

Edit

Here is my circuit schematic, i've checked that everything works except when i connect my relays to 220V

Edit2

This is the schematic i've found:

As you can see and I had forgot to mention relays are drive by pulling 595 pins to ground.


texts: Phase lag of an ISO124 isolation amplifier?

texts:
I want to use an ISO124 isolation amplifier. The input frequency will be about 100Hz. I'm trying to figure out what the phase delay will be from the input to the output and i'm not having any luck. I can't seem to find anything in the data sheet (or i just don't know where to look).

From the data sheet how can the phase delay of a 100Hz input signal be figured out?

OPA124 data sheet


texts: Why connecting this sensor output to pin 22b, the voltage at this point become half? For example, if we disconnect this sensor from the circuit board, the voltage at this point is about 6volt but when we connect the sensor to the circuit board, the voltage at this point become 3volt?


texts: what jtag for arm freescale IMX35 for debug?

texts:
We currently run Linux in a Freescale imx35 processor.
We have coded several applications, but never done any debug.

What hardware should i use?
can i run breakpoints and watch variables and registers in run time?
What pins should I use for this purpose??
Our code cross compiled with gcc.
I suppose we should use OCD.


texts: Negative value for saturation mode voltage of MOSFET

texts: I want confirmation of whether a MOSFET is in saturation or not. I have calculated the condition using the formula \$V_{GS}-V_{tn}\$, and my answer is a negative value. Does it matter if the value is negative? If yes, what is the value actually showing?


texts:
A close person got hit by a car and died a few years ago. The persons iPhone flew trough the air. The police was not able to turn it on and mentioned that it would be impossible to collect data from it. (Which might would have helped to solve the case). Back then iPhones had the status "quite damn save". One had to invest a lot of effort into reading the encrypted data from the hardware.

I recently found out that this iPhone is still lying around. I got concerned that the LiPo might catch fire. Therefor I have put the iPhone somewhere save. That was when I noticed that after years of electrical engineering at university and some advances made in iPhone penetration, I might be able to collect some data from it.

What is the current situation? I assume NSA would be able to read some data from it. Since it is already an old phone, would I be able to do so? The iPhone was heavily damaged due to the impact. Which parts would need to be intact? Is it enough if the flash is alright? I have another iPhone 5 which I could use to solder in the flash drive. But I remember something like there is a hardware encryption key in many parts of an iPhone. Thats why I fear transplanting the flash would not work, since it would stay encrypted.

I have the password and everything from the original owner. Therefor I would not have to crack that. But I suppose it's not just a little soldering work. What would have to be done to make it work?

(I don't want to talk about if I should do this. It is already too late to change something. Case is closed. It is more about the technical aspects. And of course I would be thankful if some clarifying facts arise.)


texts: How to determinate a reasonable clock frequency for a MCU?

texts:
Currently my datalogger is running at 12Mhz, and sleeps 90% of the time. When it's active its mostly blocked by I/O like SD-card or UART.

I suspect the system would still work at 6 Mhz, but how do you know whats reasonable? I can decrease the clock untill weird bugs starting to occur, but that seems too fuzzy. I can count all assembly instructions and calculate the value, but thats too exact (and way too much work).

So are there some rules of the thumb to make a reasonable estimation?


texts: Can I continue to generate a netlist despite ERC errors?

texts:
I am a KICAD newbie and have stumbled upon a few problems. I have about 119 ErrType(2) warnings and one ErrType(3) warning all essentially saying that the wires are not properly connected to their components. This is true(?) for some cases:

However, i encounter the same problem even after "fixing" some of the issues.

Can I simply continue on to generate a netlist ignoring these "warnings" and will KICAD understand the connections between components? Or are these warnings severe and if so how should I fix them?


texts: Why does an op-amp in this simulation not produce a large voltage swing?

texts:
One circuit I have seen used many times is an op-amp and a current sense resistor to implement overcurrent protection. I have seen this circuit implement both an overcurrent protection that turns off the circuit and something more along the lines of a constant current circuit.

I am interested in overcurrent detection, not trying to implement a constant current circuit. I constructed this circuit in LTspice to try and better understand how this works. I based this off my understanding from reading reference circuits and application notes from supplie

V1 is an AC voltage source so the current in the circuit varies over time. R1 is the load and R2 is the current detection resistor. V2 is my reference voltage. I am expecting that when the current in R1 is above 1 amp the voltage of the LM308 swings high.

I had to add some feedback via R5 because LTSpice would never actually produce a simulation otherwise. I am expecting comparator behavior from this circuit, not a proportional output.

V3 is there just to run the op amp. R3 is the "load" of the op-amp, which is basically just there to source the output of the op-amp back to ground for simulation purposes. The op-amp I used is an LM308, this appears to be the single version of the extremely LM348 I see in many circuits.

Here is the simulation of the circuit

The red line is the voltage coming out of R4 and driving the op-amp. The green line is the reference voltage from V2. The blue line is the output of the op-amp which is basically constant. Why is this happening? Is there some additional components I am missing which are commonly omitted from reference material?


texts: Calculation for IC lifetime for supply voltage overvoltage

texts:
What calculation can be used to calculate the lifetime of an embedded processor (<28nm process) when subject to a slight overvoltage?
The supply rail in question is for analog portions of the circuit (Clock PLL and SerDes receive).
0.87 to 0.93V - Recommended operating voltage
0.945V -absolute maximum
0.938V - voltage measured during manufacturing test.
The supply voltage has been set high - 0.923V centred and using 0.1% resistors but remote sense of core voltage has added unaccounted 6mV. Rework unwanted outcome, I need to explore lifetime implications of this overvoltage.
I tried searching google and stack exchange for clues but all I can find is the temperature effects on IC lifetime.


texts:
Disclaimer: I am not sure if this is the right place to ask this.

I am trying to create an sdram controller for the numato mimas v2 fpga. The board contains an LPDDR module (either the Micron MT46H32M16LF or the Winbond W949D6CBHX6E, which operates the same way). The clock is transmitted using the differential pair ck, ck_n. In the constraints file for my design, the signals are defined as DIFF_MOBILE_DDR (while most other signals are defined as MOBILE_DDR: they don't seem to cause troubles).

My first try was to set ck to the clock, and ck_n to not(clock). However, I get the following error message in Xilinx ISE:

  The I/O component "ck" has an illegal IOSTANDARD value.  The
     IOB component is configured to use single-ended signaling and can not use
     differential IOSTANDARD value DIFF_MOBILE_DDR.  Two ways to rectify this
     issue are: 1) Change the IOSTANDARD value to a single-ended standard. 2)
     Correct the I/O connectivity by instantiating a differential I/O buffer.

(and a similar message for ck_n)

My guess is that I have to use a differential I/O buffer. How can I do this is Xilinx ISE?

Googling didn't lead to much. A related question which seems to suggest that there is some HDL from a library that does what I want, but I still have no idea which one.


texts: Laptop surface vibrating when rubbing over it

texts:
Because my previous HP laptop adapter stopped working, I got a new one. But if I use this one, I feel a kind of vibration when I rub over my laptop's surface. I don't have this if I work on battery, and I also didn't have this with my old adapter. It doesn't vibrate from itself, only when I rub over it.

What is this? And can it damage me, my laptop, or any devices I plug in (like USBs)?

My new adapter is not grounded, but my previous one was. Might this be the reason?


texts: Efficiency of Antennas vs operating frequency

texts:
I have refereed a document from TI which mentions that antenna efficiency decreases as frequency is further decreased.

Although 136 - 240 MHz has highest range for equal power, the efficiency of antennae at that frequency is not acceptable.

What causes this effect?


texts: Help Identifying a Capacitor (R1C 332 and KDP 109)

texts:
I've been looking through the various posts on capacitors and doing some research on identifying capacitors and haven't found anything that quite fits my situation. I have a very small ceramic capacitor from the power supply side of a subwoofer amp that I believe may be dead as some of the nearby components are also not reading correct values.
This capacitor has two sets of markings, one on either side. The following is what I've been able to make out for how small it is: R1C 332 and KDP 109
From what I've read 109 might be 10000000000 pF, but also 332 might be 3300pF.
I've also read that 1C = 16V, but maybe R1C means 0.16V since R can mean a decimal?
I'm not really finding much on KDP (although that D looks a little off)
Also, there doesn't seem to be much in the way of a polarity on this capacitor, other than tracing the circuit it came from to find the ground is there a way to tell by looking at it which way the capacitor is polarized?
Thanks for any help!


texts: Altium Black Squares From Footprint Ultra librarian

texts:
I have made a PCB on alitum designer and have generated gerber and NC drill files and Zipped it up and put into the osh park website that allows you to view what you are submitting.

However as you can see I have this black squares on my board which should be surface mount jst connectors of which I got the footprint from ultra librarian. (Example https://app.ultralibrarian.com/details/2676f7bd-d30e-11e9-b85e-0ad2c9526b44/JST/S3B-PH-SM4-TB-LF--SN-?uid=624fab468b7bbd88&exports=AltiumDesigner)
But when I am looking at my PCB on altium I see nothing wrong.

Will this effect my board when it is manufactured?
If anyone has any advice or know why it is doing this please let me know.
Cheers,


texts: How to design 1T-1C DRAM circuit in spice design tools, such as LTSPICE?

texts: I have been trying to design a DRAM cell using the LTSPICE MODEL tool. The DRAM that I want to design is of 2nd GENERATION, i.e, 1t-1c dram cell. But whenever I design digit line it states the line is floating. How to design it? Also how to precharge DRAM's digit line?


texts: I need help with project ideas that include the construction of an AD converter and....?

texts:
Disclaimer: Somewhat homework related. I apologize if this question is not challenging enough or not considered productive, but I need some direction for my final lab project. My partner and I decided to construct a AD converter using MOSFETs, a 555 timer and the other required components for our final project. Here is the link to the project description.  However, it is not enough, the school project is a sparkler and I want a roman candle. I would like to do something SPECTACULAR with it (within 2-3 week deadline).

I have yanked a single point load cell out of a digital scale, I am going to take the track and motor out of an old printer (maybe create a miniature CNC router table or etch-a-sketch), I have several TV's stripped down and just picked up an older computer full of fun stuff to tear out!!

Are they any ideas for interesting AD converter uses? It seems like they are mainly used for measurement conversion. I would really like to focus in the direction of automation, robotics, or CNC positioning. They would be the most beneficial for my experiment. I would like to do more than count on a seven segment display with a pot. Lame.

Any input would be much appreciated. Thanks for reading!


texts: Why is mains power sometimes 110V and other times 120V?

texts:
(The same question can apply to locations with 220/240V mains, if I am not mistaken.)

Frequently I see mixed ratings indicating that something is suitable for 110, 115, 118 or 120V (in the US). I've always referred to mains power as 120V but with the understanding that it varies because of:

Different means of generation (number of phases, etc.)
Line losses and imperfect conditions

When designing something, should one always test using the lowest expected voltage (110)? What reasons are there for the differences in mains voltage?


texts: Four layer PCB stackup with thick prepreg layer: how is it useful?

texts:
I've been working on a four layer board with 100Ω differential pairs. Prototypes were built, impedance was measured, things were fine. But then as I tried to move the production to a different facility, I discovered that some PCB fabs use a much thicker prepreg layer (dielectric between top layer and inner 1 copper).

If you look at specs from MacroFab (https://s3.amazonaws.com/mfprodpublic/datasheets/MacroFab+Stackup+Report.pdf), they use a 0.23mm prepreg layer. OSHPark has an even thinner 0.17mm (6.7mil) prepreg (http://docs.oshpark.com/services/four-layer/). I've seen similar numbers in standard stackups from Chinese manufacturers as well.

But then I encountered a local fab that specified 0.36mm, and looking around I saw that the Eurocircuits standard 4 layer build has a 0.36mm (14mil) prepreg  layer (http://www.eurocircuits.com/images/stories/ec09/ec-std-buildups-0-8-layers-english-4-2010-v2.pdf).

I am puzzled as to how this kind of stackup can be useful.

Assuming 0.1524mm (6mil) trace separation, 35µm copper, with a 0.23mm prepreg, I calculated 0.233mm width for 100Ω differential pair (differential microstrip) traces. That's about 9mil, and it's perfectly fine.

But again with a 0.36mm prepreg (same 6mil trace separation) I end up with my differential pair traces having to be 0.32mm wide -- 12.6mil! That seems too wide to be useful, you can't route those traces to 0.5mm pitch ICs. And things get even worse if you need 90Ω (USB).

So, what am I missing? From this point of view, the thick-prepreg stackups of some manufacturers are useless. But they exist (and in fact are standard!) for some reason. How do people use them?


texts: Microchip PIC24F & Android device: Which can be host device?

texts:
I work on a project where I want to connect PIC24F (Accessory Development Kit for Android www.microchip.com/android) and Samsung Galaxy S2 that I updated from android 2.3.3 to android version 2.3.4.
I loaded firmware to the PIC24F and Demo app to Galaxy.
When I connect devices my galaxy still says: "Device not connected".

Does Samsung Galaxy S2 can be a host for PIC24F or is this hardware-dependent?

Does anybody know if it is possible for PIC24F to act as a host instead of android device?


texts:
Greetings.
I have this problem. I have a telephone that requires 3 AAA cells. I installed 3 AAA dry cells. it works good. LCD display is very sharp and bright.
But then i thought. one day that the dry cells will surely get over and I will have to buy new ones. So instead of replacing new dry cells what if i install rechargeable ones. So i opted to buy 3 AAA NiMH cells.

I had always known that dry cells are rated at 1.5 volts whereas NiMH cells are 1.2 volts. I had understood that it doesn't make much difference.

After installing the NiMH AAA cells the lcd display was about 20% dimmer than previously seen. It clicked me that 3 NiMH cells will lead to a loss of 0.9volts in total. thats like 1 volt drop.

So i have few questions here.

Was my idea bad ?
If we compare 6 Dry cells vs 6 NiMH cells then there is a voltage difference of whopping 1.8 volts.
dry cells  1.5v x 6 = 9v
NiMH cells 1.2v x 6 = 7.2v

Which means we need to consider atleast one more NiMH cell, isnt it. So 7 NiMH cells will be somewhat at par with 6 Dry cells. (there would be still a difference of 0.6 volts.

Am i right with all these ideas?

So how do i solve the dim lcd in my telephone.
i am still short of 0.9 volts.

can i simply add one more NiMH cell in series. I would have to engineer a slot for it in the phone.


texts: Will ADC readings disrupt my analog control loops?

texts:
I have two separate analog control loops for battery charger circuit - one for voltage regulation and one for constant current mode.

I want to read voltage that comes to opamp via resistor divider and current value that comes from differential amplifier to microcontroller via ADC.

Should i buffer these voltages to read them via ADC? How do i decide?

Microcontroller i'm using is LPC1343.


texts: Why does a weakened 9V battery show lower voltage but a weakened 1.5V battery doesn't?

texts:
This is a curiosity question.  The batteries tested were Duracell coppertop alkaline batteries.

Recently, my bass guitar was acting weird and it was caused by a weak 9V battery.  I checked the voltage and it was like 6.5V or something crazy low.  Now, if I check a C 1.5V battery when it's weak, its voltage is relatively high.  I think I measured the weak C at 1.42V.

I forgot to check the 9V while under load and I wasn't able to measure the voltages of the C battery under load b/c all the devices I could find needed the cover closed for it to work.

In any case, why does a 9V drop that much when it's weak but a 1.5V doesn't?


texts:
I am trying to understand how to modify the circuit below to output ~180V at 4mA minimum for a multiplexed nixie design.

LT1308A Datasheet - Circuit on Page 17

Voltage:
The 1:12 transformer is being replaced with a 1:10 coupled inductor, which should drop the voltage right off the bat. Modifying the resistors connected to the FB pin for a specific voltage should allow the IC to regulate the output voltage by changing its duty cycle, though only within a certain range. It appears the upper right portion of the circuit is a voltage multiplier, so could that be modified to drop the voltage?

Current:
I don't know how to go about modifying the current capabilities. My guess would be that it bottlenecks somewhere, since other 'Typical Application' circuits in the datasheet can handle much higher current loads. Is this output possible with the circuit?

David Forbes' nixie watch uses one of these ICs in his schematic, though it is the B variant. There are several forums in which he says one of these can output up to 4mA, but I don't know how to achieve this output.


texts: gate current direction during turn-ON of P-channel mosfet

texts:
In a lecture, my instructor told us that mosfets  have various capacitances associated  with them. eg for a switching application the important ones are- Gate-source cap, Drain-source cap, and Gate-Drain cap.

Now he said that during turn-ON of a mosfet a current flows through gate of the mosfet that charges all these 3 capacitances. The capacitance of these capacitors determine the turn-ON time of a mosfet. He gave the example of a N-channel mosfet.

While I was applying same concepts to a P-channel mosfet, I came across a doubt. In case of a P-channel mosfet, does gate-source cap. and all above caps. charge or discharge during turn-ON of a P-channel mosfet. It seems to me that caps. should discharge during turn-ON and should charge during turn-OFF.

Specifically, I'm driving a P-channel mosfet as High-side switch via a open collector output pulled up to 5V. So I need to know this.
After searching through many docs on google and many books, I still have this doubt uncleared as all have examples of N-channel mosfet not a P-channel one.

Can anyone clear this doubt or provide any references or links?

The circuit is similar to this,

but components are different. If required, the mosfet I'm using is IRF9392.

Update1 on 2012-07-09 :

"This circuit will switch off slowly due to Resistive turn off gate drive. OK in most on/off cases - but not at smps frequencies.
D3 not obviously useful."

In above schematic ckt. why D3 is not useful after adding a D2 schottky(Anode to Gate) and D1 zener(Anode to Gate) in parallel, physically and electrically close to Q2?

Why will turn-off be still slow(even with diode D3)? Is it due to resistor R4 or increase in gate-source capacitance due to zener and schottky?

Update2 on 2012-07-14:

Is a gate to source zener, like D1 zener(Anode to Gate) required, even with a flyback diode across an inductive load(instead of resistor R3) connected to drain of Q2?


texts:
Does anyone know what voltages TI Launchpad's I2C and SPI run at?

I think it is 3V3 from a comment on a post, but can't be sure.


texts: How does one obtain connectors for game controllers to put on a PCB if e.g our design takes input from a PS1 Dual-Shock controller?

texts:
It is quite possible that one decides to design a device that can take input from a (wired) game controller like the NES, SNES, PS1, PS2 controllers which are going to have their own protocol. For a PS2 dual shock controller, designing something that can decode the protocol is a project in itself.

However, always there is a problem of where to get a connector for the "consolve side" of the controller connection. When the game console was manufactuered, they put in a connector on the front. However, if I want my own design project to take input from e.g a PS2 dual shock controller, how do I get the "female" connetor that shall go onto the PCB? Any ideas?

One possibility is to design a connector and print it using a 3D printer, that however is a project in itself and it still needs to be considered how the metal contacts will be put in.


texts: Serial communication between STM32F4 and PC -USART-

texts:
The question I will ask now is not about how to solve something, I am currently able to make the connection as it will be mentioned below, but my problem is I really did not understand WHY ? Thanks in advance.

Hey, I am trying to connect my STM32F4-DISC board to PC via USART. It is a very common and basic example like sending a string to PC COM port which is covered by lots of tutorials on the web. But my question is,

I first used this product and directly connected to my board's RX TX pins and I was able to get data  but all the data was a mess.(Not random, always same but some characters I have never seen before.)

I think there was nothing wrong with connections because when I disconnect the jumper which connects the Rx of converter and Tx of DISC board, there was nothing ongoing even that messed up characters.

After lots of thinking about "what is wrong? is it code?( It could not be because only 3 lines of code and all examples writes the same thing) ", I found a little device which has a chip on it( I can't read what is the model or manufacturer) and one side is D sub 9 male and other side has 4 jumpers come out of that named as Rx,Tx,GND and 3.3V. Then I also used it and created a connection like this:

PC --USB ENTRANCE-- DIGITUS USB to serial adaptor -- D SUB 9 ENTRANCE -- THE IC I MENTIONED ABOVE -- JUMPERS -- STM32F4

After this setup I was able to see the correct text on the screen and everything worked well.

I researched about why this could be but did not understand. The digitus product itself looks like the only necessity to connect my board to PC but It does not work alone.

I wonder what is the real case?


texts: Solving Clipper Circuit containing battery and resistance in series

texts:
I have learned to solve clipper circuit with and with out battery in parallel to the output node. But have no idea what to do if a resistance also connected with it in series.
There is nothing said about it in my book. How can I solve this circuit?

simulate this circuit – Schematic created using CircuitLab

A general procedure for solving this type of problem will be helpful.


texts:
In an ideal operational amplifier, I understand that the inputs draw no current (due to infinite impedance). So, in the example below, the value of Vp would equal the value of the EMF (because there is no voltage drop across the resistance), which is 1V.
Unless I'm mistaken, the definition of voltage at a particular point is the amount of electric-potential energy per coulomb of charge. I'm wondering how exactly the electric-potential energy from the EMF gets "transferred" (for lack of a better of term) across the resistor and to another section of the wire if there is no movement of electrons?
Also, since there is no current, then what's the purpose of the 8.9kΩ resistor if there is no voltage drop?

Image Source: http://raise.spd.louisville.edu/EE220/L13.html


texts: How can I make a small housing for LEDs?

texts:
I am trying to recreate  for a flight simulator game I play (DCS World). I have the software working now, but I am unsure how to build the actual panel itself.

I want all the lights to be flush in the panel, as in the picture, rather than typical dome LEDs popping off of a board.

A few friends have suggested making a small enclosure around each LED out of hazy plastic and making those sit flush behind the panel but I am unsure how to do this or if it is the best approach.

What would be the recommended approach and how do I go about doing it?


texts: As I was using this instruction movx a,@dptr . and I didnt udnerstand how a 16 bits number is being copied to the accumulator when the accumulator can only hold 8 bits ?


texts: What is the point of "software data protection" in a rewriteable ROM?

texts:
I've been considering trying to hack an old '98 era motherboard. The ROM(I presume for the BIOS) is a Winbond W29C020-70. In it's datasheet, there is a thing called "Software-protected Data Write". The gist of it is that 3 specific bytes must be written to certain addresses before the ROM will allow you to write to it.

The values and addresses that need to be written are documented in the datasheet, and I don't believe there is a way to change these magic values. So, using this feature for security doesn't seem likely. I can't really think of any other reason for this feature to exist.

What is the point in this kind of feature?


texts: How can I write an analog voltage on arduino?

texts:
My question reference's a problem I'm having with my eletronic solution. I'm using a CI LM3915N-1 to build a bargraph circuit, where I need to turn on a few LED's depending the voltage that my CI receives.
The problem is the arduino just write PWM and not analog voltage.
So how can I solve this? how can I convert the PWM to a analog voltage?

Here is a image of the Bargraph circuit:

To understand better what I want, is to imagine that at Signal Source will be an arduino sending AC signal.


texts: How much power can be supplied over Beaglebone Black's USB?

texts:
I'm using Beaglebone Black. How much power can I provide over USB to an external device?

I have read the specifications, and the information I found was 2 amps to the board should be good enough to power external device. What I don't know is how much power can be delivered to the external device? I could not find that in my research.


texts: How to Calculate the charge/discharge power of a battery?

texts:
I need to measure the discharge power of a battery in general.

At the end i want the maximum charge/discharge power as a function of the state of charge(SOC).
So i need a curve that looks like the figure that is displayed here.

I already calculated the power as a function of the SOC but i am not sure if my method is correct.

Lets assume we are looking at a lithium ion battery. I found two ways to calculate the power.
The first one was simply using the voltage curve as a function of state of charge for different C- Rates. Then multiplying the Current with the voltage and getting my power.
P(SOC) = U(SOC) * C-Rate.

The second method was using two graphs of a battery the voltage as a function of the SOC and the internal resistance as a function of a SOC and then P(SOC) = (U(SOC)^2)/R(SOC).


texts:
Have a few problems with my assignment.

Ive derived a truth table and come up with this :

Can someone verify if the above is correct?

Ive then got these 2 logic expressions :

Y = A'D' + C'D' + B'D'

Z = D+ B

What I want to know is (if the above is correct) Is it possible to implement the above circuit using fewer logic gates?


texts: DDR3 trace impedance - short traces but high impedance

texts:
I'm putting together a small PCB based around a Xilinx Zynq (the CLG225 one), because the DDR3 pads are all in a big block on one side of the device and because I've been designing for a 4 layer PCB, the traces have had to be routed with ~80ohm single ended impedances.

My question is this: With a single 16bit DDR3 chip ticking over at 400MHz (800Mbps), am I going to run into unacceptable signal integrity issues if all the traces are 80 ohms but are kept under 20mm? Or, are 20mm traces short enough to avoid any serious transmission line effects with DDR3-800 memory?

Most recomendations advise 40 ohm traces, but there just isn't enough room for tracks that wide (and no, I can't change the stackup, it's with OSH park and it's just for fun) All byte groups are length matched to <0.5mm of course and so are all the command and address lines, it's just that the impedance is twice the recommended value. There are unbroken planes beneath all signal lines.

This is not for a product, this is not really even a proof of concept, if I was to go to 8 layers, it'd be a cinch, but I just want to see if it can be done with a hobbyist only fab and I'd like to hear from someone more experienced in the field than me if it's even going to work in the first place.


texts: I am wondering about situation, where there is an ESD to specific part of circuit, conatining IC. As I know TVS diode has defined delay time - it will not protect immadiately. My question is - what is happening while this delay time? Is this high spike of voltage passed to IC? How is this possible, that IC survives it?


texts: Connect a 5mm led to a GPIO without transistor?

texts:
I am currently designing a circuit with a MSP430 MCU supposed to blink a LED (5mm round green). The circuit is a powered by a CR2 cell which the voltage will vary between 3V and 2V.

Assuming that I would choose the proper value of the limiting resistor between my GPIO and my LED, I am currently wondering if I can connect a 5mm led with a If=20mA and a Vf = 2V directly to my GPIO (with resistor of course) or if I absolutely need to use a transistor in between?

I suppose the MSP 430 will not be able to supply 20mA from its GPIO port?


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How can I identify a transistor PMOS, when I only know the printed label/legend in it "T9F"?
and the same to identify a zener or diode, when I only know the printed label/legend in it "2U90"?


texts: Making a pure R-2R resistor ladder DAC with adjustable offset

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I'm looking to make a DAC for my Arduino so that I can generate values spanning almost completely from 0V to the 5V supply. Because I won't have access to any +12V or -12V rails or anything, I'm afraid that I won't be able to incorporate any op-amps or other active components.

Fortunately, R-2R resistor network DAC's fit the bill almost perfectly...

simulate this circuit – Schematic created using CircuitLab

Fortunately, the thing I'm driving this with has high input-impedance, so this circuit works very well for my needs. However, I don't need the lower voltages in the range, so I was hoping to develop a resistor network which had an offset. So, for a network of n bits, instead of getting 2^n values within 0V-5V, maybe I could get 2^n values between, say, 1V-5V.

While googling around, I came across a priceless snippet on Wikipedia which read: "It is not necessary that each "rung" of the R-2R ladder use the same resistor values. It is only necessary that the 2R value matches the sum of the R value plus the Thévenin-equivalent resistance of the lower-significance rungs.". So, I figured that I might be able to add in a little voltage-divider to "lift" the ground that the main network is seeing:

simulate this circuit

Because the Thevenin resistance of the lower-left corner (the two 100-ohm resistors in the voltage divider plus the 150-ohm resistor) is still 200 ohms, I still get fairly linear voltages with increasing binary values.

However, this arrangement leaves two things to be desired. First, it requires that I know, beforehand, how much of a lift I'll want. It would be nice if I could have a potentiometer in there, somewhere, so that I could just dial in whatever lift I want.

Second, there's a limit to the amount of lift I can get. Even if I tweak the voltage divider to give me the full 5V feeding into the left side of the circuit, it looks like the most lift I can get is (5V/2^n).

Does anybody know of different ways of tweaking the circuit to solve either of these issues?