texts: Programmed-current mode and hystereis control for DC converters

texts:
Could anyone please advise if the following understandings of DC converters are correct?
(1) The output of buck/boost/buck-boost converter should be regarded as voltage source, i.e. it can give a constant voltage regardless of the loading.
(2) A converter operating under programmed-current mode is a current source. That means it can give a constant current regardless of the loading.
(3) A converter operating under current hysteresis control is a current source - giving a constant current regardless of the loading.
If the above three notions are true:
(4) Consider a buck/boost/buck-boost converter operating under programmed-current mode. Should it be a current source or a voltage source?
(5) Similarly, consider a buck/boost/buck-boost converter operating under hysteresis current mode. Should it be a current source or a voltage source?
Thank you.


texts: Select appropriate bandwidth for sensor (MEMS gyroscope)

texts:
Short question: how to select the correct bandwidth for a sensor?

Some further details. I'm working with an ADIS16260 (rate gyro) placed upon an industrial vehicle. This sensor has both an analog filter on the front-end and a digital filter. I need to set their parameters.

I'm asking a rule-of-thumb to set them. What empirical measures I might take? I don't have a mathematical model of the equipment. It's quite heavy, so movements are slow, but I still need to determine the order of magnitude of the bandwidth.


texts:
I want to detect the rotation speed of an impeller (fan wheel). Imagine a fan without a motor submerged in a liquid. This device is used for visual indication of liquid flow. I want to detect the rotation form the outside without modification of the device, therefore the only choice is optical.
The fan wheel is behind around 1mm of plexiglass, is black color, and is submerged in red liquid which is transparent. Also its rather higher speed, but not as fast as a regular fan (maybe up to 100rpm).
Is there any SMD sensor that could be used for this project? I was thinking of a color sensor, to detect the black fan blades, but i'm unsure if they are fast enough.


texts: Where does the sum current of the three currents flow?

texts:
In the following star and delta connections, if each individual current enters via Phases R, Y and B, where does the sum of the three currents (that is Ia+Ib+Ic) flow after meeting at the common point of the three phases?

Moreover, in such types of connections, across which terminals is a load connected to these types of systems to draw current/power for its operation?


texts:
Can an OR gate be implemented using 4 CMOS transistors? The circuit would have two n-type transistors in parallel in the pull-up network, and two p-type transistors in series for the pull-down network. Every implementation I've seen uses 6 transistors, with the output of a NOR circuit used as the input to an inverter circuit.

EDIT
Added diagram created with Logisim. The boxes represent input pins, and the circle is an output pin. My knowledge of electronics is very limited, so I'm sorry I can't produce a detailed schematic. I'm a CS guy.


texts: On the fly digitizing audio from analog audio jack

texts:
If I am correct, I believe that all normal audio jacks (like the ones you have to your PC, traveling to your speakers) are analog.

Is there a way (perhaps with a high speed ADC) to convert it to digital on the fly?
I am considering a project with Arduino (perhaps) where you capture audio in digital form and store it in an SD card.

Then of course, this will be just a sequence of bits. So is my project bound to failure because of the heavy volume of data? Or perhaps the information won't even make sense because it won't be equivalent with any audio format? Or essentially, it will be a WAV file (without the header)?

Finally, is there something like an analog to digital encoded (MP3 or whatever) hardware encoder?


texts:
I think one day soon, if not already now, somewhere, there will be Multimeters that have touchscreens and are software configurable with Apps that allow you to add most anything to your meter like an O-Scope, function generator, logic analyzer, etc. and a way to configure inputs and outputs and test sequences to use for specific testing circumstances.  And if your repairing a certain type of device you can upload your test sequence so that others can follow your process and steps with things like "put the leads on this component press test" and it compares the results to your pass/fail requirements along with pictures and so on, so  you can do this on site. Companies can send out the complete steps to troubleshoot their gear that are downloaded and put into your meter so that all you have to do is follow along to find the problem.  With that in mind, is there a particular development board and software out there that can handle something like this? I think the touchscreen part is out there but I need something that has specs like  National Instruments multifunction PCI card that is built onto the development board, or an add on board, or could someone smarter than me make something like this ASAP?

Thanks Russ


texts:
I am trying to return a string.

String getBinary(String str) {

  String message = str;
  message.toLowerCase();
  int length = message.length();
  String binaryNumber = "";

  for(int i = 0; i <= length; i++) {

    char c = message.charAt(i);
    int letter = ;
    Serial.println(letter);

    binaryNumber = binaryNumber + String(c, BIN) + " ";

  }

  return binaryNumber;

}

But I get this error:

binary_telegraph.cpp: In function ‘String getBinary(String)’:
binary_telegraph.cpp:53:18: error: expected primary-expression before ‘;’ token

Any suggestions?


texts: Solar Charge Controller Function Details

texts:
I am planning to make this Solar Charge Controller:

I would like to understand the way the components work to switch from charging to dumping and vice versa at set points. Note that the 555 timer is not being used as a timer, but is being used for its internal components.


texts: Should I select components based on peak current, RMS current, or average current?

texts: I am designing a SEPIC supply around an LT3757. The MOSFET will have ~6.5A pulses with a strange ramping pattern (see image), but the RMS current is only 3.38A and the average current is 2.60A. Assuming 50% over-rating, which rating should I be looking for in a suitable FET? Also, does this apply for resistors, inductors and capacitors, or are there other specifications to look out for?


texts: How best to power more than one Arduino board as part of a single project

texts:
I'm working on some little projects that'll involve more than one Arduino (right now two of them, an Uno R2 and a Mega R3) along with some other 5V items that may themselves draw a few amps.

Rather than have multiple external power supplies, I'd like to have one 5V supply for the whole project, feeding all the Arduinos (which won't directly draw that much power) and the high-power part as well. (Alternatively, I would be willing to create a 12V->5V regulated supply just for the Arduinos - the base supply has a few buses to work with - since the high-power 5V line may sag a bit under its load (a long LED strip)... or just feed 12V to the wall adapter inputs of the Arduinos instead.)

All that said, if you have a nicely regulated 5VDC supply to work with already, how best to feed that to a few Arduinos? What happens if you then plug one of the powered Arduinos into a computer? Will this direct power supply and the USB power be in conflict?

(Note: My understanding from this related topic is that if you power an Arduino via the external adapter AND plug the USB into a computer, the external adapter still does all the powering. However, if you are feeding 5VDC regulated to the Arduino some other way (e.g. Vin) then I'm not sure how that'll work... assuming that's not Just A Bad Idea.)


texts: Small DC motor in parallel - what battery to use for powering the circuit

texts:
I am very new to the word of electrical circuits.
As I finally decide to learn about electricity and componants, I bought this kit to start in a fun way:

The motor according to the seller is a DC 1.5-3V and 24000 rpm. So a single AA 1.5V battery should be enough for this motor.
I connected 4 motors in parallel to have more torque in the system but I cannot figure out what battery voltage should be the best for this circuit. As the motor is 3V rated, the 4 motors are connected in parallel it should only need a 3V power source to run (i.e. 2 AA 1.5v batteries.)
The 4 motors are connected in parallel with the power source and there is no other component in the circuit.
When I use 2 AA 1.5V batteries the motors run for a very short period and slow and stop, and when I use x4 AA 1.5 batteries the motors run but the wire starts heating a lot.
What is happening here? How do I work out the right voltage for this circuit
I have been searching the answer on this forum for 3 days but I'm still not sure.
Here is the picture of my setup:
As you see on the picture, the wires were so hot that the case with 4 AA batteries melt and the yellow connector moved away...


texts: ADC value (4000 to 20000) to (0-400) milibar conversion

texts:
I am getting full scale ADC value from 4000 to 20000. I am trying to convert o 0-400 mbar pressure, as I am ultimately measuring height of a tank.

I have a equation to measure the Height of Liquid.

Pressure Eq.

\$ L = \dfrac{P}{ \rho \cdot g} \$

\$ \rho = \rho_{0} \cdot SG \$

\$ SG = 1.033 \text{ (Specific Gravity of Milk)} \$

\$ \rho_{0} = 1  \text{ (Density of fresh water)} \$

\$ \rho = 1.033 \$

\$ P = \text{ADC Coutn To MiliBar Or Bar Value} \$

But how can I convert the ADC value to Milibar or Bar value?


texts:
I need some info on efficiency of power supplies. Imagin a power supply with 91% efficiency that can provide a maximum of 800watts.

Does the rated 91% efficeincy is for all loads that going out from this source? I mean if it is providing 500W, the efficiency is still 91% or less or higher? is there a formula between load amount and efficiency?

Thanks.


texts:
I've been given the circuit below.

For \$t>0\$ the switch is closed.

I'm asked to find the charging time for the capacitor, but I'm not so sure how it is charged through which resistors?

I looked up the answer, and it says that the charging time is given by:

\$\tau=(R_1+R_2)\cdot C\$

They justify this by saying you can form a Thevenin circuit with the 1mA source and the \$R_1\$ resistor. Then \$R_1\$ and \$R_2\$ are in series.

But that seems very non-intuitive to me, and it just comes out of nowhere. It's almost as if you have to know, that you can do that.

Can anyone show me another way of solving this problem, cause this solution just seems like some sort of cheap trick.


texts: daisy chain ethernet: performing arbitration on an FPGA

texts:
EDIT:

After discussions in the comments, I've realised that the only way to do this for full-duplex is to use a switching IC.

Also, I mean simplex, not half-duplex for option 1. That is, the FPGA is only receiving packets, not sending them.

I've been looking to implement ethernet in a daisy-chain configuration on my board.

Hard requirements:

1000BASE-T
low cost
latency through board < 8us

Nice to have requirements:

full duplex
as few IO pins to the FPGA as possible

Options after a bit of research:

Link for full size pic

Option 4 was the first thing I thought of, but is the worst at meeting my specs. Options 1 or (ideally) 2 would meet my requirements, as long as I get the implementation right.

Can the RGMII interface be used in this way? I guess is the first question. If not, then I'll probably have to go with option 1 and call it a day.

I'm quite sure that option 1 would work, however I would really like full duplex. It's not hugely necessary, but a very good nice-to-have. Are there any suggestions as to how to handle the arbitration re option 2? Is it possible to do something like that using the FPGA?

Option 3 is out purely because multiple boards are going to be daisy chained and the diodes attenuate the data lines too much.

I'm also not really looking at switch ICs due to cost. If it's possible to find one below $5 or so then it's within budget and probably considerable, but I doubt that's the case.

Also re < 8us latency through board: I calculated this spec based on system requirements, and I think it's possible since a 125 Mhz clock has a period of 8ns, so 8us is 1000 clk cycles of RGMII, plus a latency of 1.5us through each PHY, seems like enough for options 1 - 3. option 4 goes through the FPGA which makes things a bit more complicated (latency through TEMAC, etc), although I can't imagine even the temac latency is too long.


texts: Purpose of negative bias reference generator

texts:
I am working on a redesign and there is a negative bias generator on the ADC in the circuit. (not the circuit below) I am pretty sure that the small negative voltage instead of ground is there to ensure readings are correct when the input to the ADC is close to zero (or ground) but I am not sure I fully understand. Can someone explain the purpose of the negative bias generator more clearly? Also will the negative reference on the ground pin affect anything else in the circuit? For example do I need to compensate for the offset at the output at all?

NOTE: The circuit below is not the circuit I am working on. just an example that I found using the negative bias.


texts: Building a full adder with NPN BJT transistors

texts:
So I'm trying to wire up a full adder just with NPN BJT transistors (I know there is a 74XX283 4-bit binary full adder, but I want to do it just with transistors if possible for my own learning).

The full adder I'm trying to build looks like the following with logic gate symbols:

Image from Wikipedia

I use a NAND, OR and AND gate to build the XOR gate:

Image from Wikipedia

Right now my current circuit looks like this:

simulate this circuit – Schematic created using CircuitLab

Schematic notes:

BC 548A NPN transistor datasheet
LED with built-in resistor 5mm 5V (L-7113ID-5V) datasheet
All those 1k resistors you see going to ground are pull down resistors, so I get a more cleaner signal, but I'm not sure if they are required or optional or where and when exactly I need them.

But the circuit does not work as intended:

A B CIn | Sum COut
------------------
0 0 0   | 0   0   (Both LEDs are clearly off)
0 0 1   | 1   0   (A clear one the LED glows; the other is off)
0 1 0   | 1/2 0   (The LED just glows like half; the other is off)
1 0 0   | 1/2 0   (The LED just glows like half; the other is off)
1 1 0   | 0   1/2 (The LED just glows like half; the other is off)
1 0 1   | 0   1/8 (The LED just barely glows; the other is off)
0 1 1   | 0   1/8 (The LED just barely glows; the other is off)
1 1 1   | 1   1   (Both LEDs only glow half)

The expected behaviour would be:

A B CIn | Sum COut
------------------
0 0 0   | 0   0
0 0 1   | 1   0
0 1 0   | 1   0
1 0 0   | 1   0
1 1 0   | 0   1
1 0 1   | 0   1
0 1 1   | 0   1
1 1 1   | 1   1

I have tried to remove, change or add some pull down resistors on the gate outputs, but the above circuit is the best attempt I have right now. I have also changed out all components and the breadboard I use, just to make sure it isn't some component that is dead. I already have double/triple checked all resistors and connections, so that I don't just have a misplaced wire or wrong resistor.

I also tried to use a multimeter to find the error, but that just confused me more. But if I have to I can also check stuff with the multimeter if necessary.

So I'm at the end with my knowledge here how to fix my circuit design and get a clear on and off output?

I don't know if I use wrong resistor values, I don't use the transistors correctly or if my design is wrong from the start.


texts:
I'm designing a circuit to use a P mosfet as a high side switch. The supply will be either 12v or 24v. The circuit is being designed for 8 amps max current draw. Does this circuit look exceptable?

EDIT: I've revised the circuit. The PWM will be no more than 1khz. D29 has now been changed to 12v to protect the fet. D30 is simply a freewheeling diode. R120 is there to pull to ground for when the controller is booting. I lowered R121 to 4.7K from 10K to increase the allowable PWM speed. All good now?

EDIT: The PWM signal will be 5v


texts: Placement of damping resistors, closer to driver or load?

texts: I'm connecting an FPGA and MCU and currently optimizing the placement. Does it matter if it's randomly placed? Should I place it like a series terminating resistor and strictly place it close to the driver(source)?


texts: Can a 9v battery be substituted with an array of LiIon 3.7v?

texts:
I use some audio devices (mixers and effect boxes) that literally drains out my 9v cells (specially the rechargeable).
I'm thinking on doing arrays of LiIon batteries (rated at 3.7v-4000mAh each), but not sure the amount of batteries in series will 'mimic' the behavior of a common 9V.
Could it be a 2 cell series array = rated at 7.4 V ?? which I'm thinking this may suck-up more power and reduce the performance of batteries)
or it Could be a 3 cell array = 11.1v!! ?? I'm affraid this could fry my circuits the second I plug it in.

Any comments, are really appreciated.


texts: High voltage input/Low voltage, low current power supply

texts: Most of the times, metering devices are low power devices powered from high voltages inputs. Let's say I have 600V three phase, what would be a good approach to get 5V/50mA or 12V/100mA from this system to power a control circuit? Off the top of my head I would use a flyback converter with some 1500V rated transistor. Or maybe two switch flyback? A 60 Hz transformer would be big, I think. Has anyone had this kind of experience?


texts: Does the motor speed change with the fully automatic star(wye)/delta starter?

texts:
At no load, I connected a 380V motor to start in the star connection for 5 seconds and thereafter change to the delta connection.
I understand that torque will change since the current will change as well. In fact, the torque should increase as the connection changes from star(wye) to delta... But what about speed?

When I look at it, it seems as though the motor actually rotates faster when the starter switches to delta. However, I've been told that speed remains the same.

I do not have access to a tachometer to test it myself, so it's hard to tell. Does speed increase as well or does it remain the same?


texts: Why does the voltage of the photodiode "bounce"?

texts:
I have setup a BPW-21 photodiode as shown below:

The photo-diode is activated by an oscillating laser beam. I expected to get a clean +5V to 0V transition at point A when the laser beam falls on the photodiode and a 0V to +5V transition when the laser moves off the photodiode. However what I actually get on the oscilloscope are multiple 0V to +5V transitions lasting for few hundred microseconds before settling to the expected voltages. Some example traces are below:

My question: Why is the voltage at point-A "bouncing"? What is happening in the photo-diode to make the voltage bounce between + to +5V before settling on the expected value? Any ideas

Abhishek


texts:
I was reading the LPDDR2 spec today out of curiosity. While browsing the spec I became curious about "how might one hypothetically design a minimal working LPDDR2 PHY on paper/for simulation, perhaps to release as an open source design?"

According to this answer, the internals of how LPDDR2 works are confidential. Additionally, according to this article, most SoC designers today use a (LP)DDR PHY IP. So schematics of memory chips and PHY internals are unlikely to be found online. However, I imagine there are people browsing EE.SE who would know about designing PHYs, and that some design techniques are not specific to (LP)DDR PHYs apply anyway.

Does there exist literature on how a memory PHY of might be designed at the schematic level (including simulation and DRC), or general techniques on how to design a (LP)DDR PHY?

If no to the above question, I'll reduce the scope to my immediate questions about LPDDR2, using the spec as a reference.

LPDDR2 specifics that all logic level I/O is relative to a V_ref (page 160), and that the memory controller generate voltages relative to V_ref to indicate high or low, even if V_ref is out of spec. What is the rationale (analog behavior) behind this design decision? How would a PHY generate these voltages (a simple summing amplifier?)?
LPDDR2 requires that supply voltages always obey certain requirements (page 26), such as voltage rails always being no more than 100mV within each other. What analog behavior within a LPDDR memory would require this behavior, even during the power-up phase, when voltages are likely to be erratic? Would circuitry inside the controller or memory chip be able to enforce these requirements?
Can the voltage-level generation/regulation circuitry as described in the above two bullet points be analyzed/created using pencil and paper approximations, or are the analog effects required to meet the conditions too precise to be reasonably analyzed on paper (thus, requiring a simulator)?


texts: Switching a transistor with audio output

texts:
I am wondering how can an audio signal be used to switch a transistor, if the voltage is too low? I am trying to switch some LEDs with the output of an amplifier, but it seems that the audio voltage is too low for the transistor to turn on.

I have the output of the amplifier going to the base of a BC549 transistor, the collector connected to the negative of the LEDs, and the emitter connected to ground. There's a 100K Ohm resistor each from the collector and emitter to base. The positive of the LEDs is connected to 5V, which the amplifier is also running off.

When I put some music through the amplifier, I have to turn the volume up to probably 90% of the amp's power for it to switch the LEDs.

So does anyone know how I can boost the voltage of the audio to the transistor?


texts: Small battery for multiple small charges

texts:
What are small batteries that can put up with lots of small charges?

I get that you can't have everything in a design, so I get that it will be heavy or expensive.

Imagine a RC car with some photo-voltaic cells. Car would have irregular exposure to light and could charge such battery.


texts: May I connect two open collector outputs in parallel

texts:
May I connect two open collectors like this in parallel?

simulate this circuit – Schematic created using CircuitLab


texts:
I'm trying to design an audio input card that only need to support TRS format.
I was hoping to use TRS + 1 switch (to indicate if a plug is inserted) but because of mechanical constraints all I could find was CUI SJ5-43502PM TRRS which is a TRRS jack.
On my schematic, I have the jack wired as below.

Pins 1 (TIP) and 2 (RING) for left and right
Pin 3 (RING) used as a switch to indicate a plug is inserted (signal is fed to an FPGA)
Pin 4 (SLEEVE) as a GND which is also tied to chassis GND.

-When nothing is inserted, pin 3 will be pulled high to indicate a plug is not present.
-When a TRS plug is inserted, pins 1, 2 and 4 will act as a normal TRS jack and pin 3 will be pulled low to indicate a plug is present.
So I think the wiring works for TRS plug.

However I'm not sure what happens if a user accidently plugs in a TRRS plug.
-If a CTIA TRRS plug is inserted, GND of the plug will pull pin 3 low to indicate a plug is inserted. However pin 4 will pull down MIC of the plug. Is this okay? What happens if there's an MIC bias voltage from an audio source?
-If an OMTP TRRS plug is inserted, GND of the plug will make contact with pin 4 which is also GND. However MIC will make contact with pin 3 of the jack which is tied to an FPGA. If there's an MIC bias voltage from an audio source then pin 3 will not be pulled down or even worse could damage the FPGA.

I'm not an audio circuit expert so I'm not sure if my reasoning about how TRRS works is correct.
Will above wiring work for both TRRS plugs? If not, is there a way to make sure CUI SJ5-43502PM TRRS would accommodate both TRS and TRRS (CTIA and OMTP)?
My design only needs to support TRS (unbalanced audio) but I want to make sure nothing bad happens when a TRRS is connected.
Any comments or feedback would be appreciated.
Thank you!


texts: Linker error using Atmel Studio with C++ project

texts:
I have created a simple C++ project using Studio 7.0.1006. Then using "Add Class", I added a simple class called CGPIO.

To this class I added a public method called Initialize. The code compiles and runs until I add the following code to main.cpp to instantiate a CGPIO object: CGPIO* pGPIO = new CGPIO().

Compiling that program results in an "undefined reference to '_sbrk'" error. A more involved program generated undefined reference to several other routine (e.g. _exit, _close, _read, etc.).

I have tried playing with linker settings - specifically Do not use standard files and Do not use default libraries. Selecting Do not use default libraries, the _sbrk error goes away, but a undefined reference to __libc_init_array shows up.

I could not find much information on C++ programs for the SAMDxx series. Is there an good working example to start from? Do I need to add a different library to the Linker settings?


texts:
I am currently designing an electromagnetic accelerator meant to accelerate a spherical nickel-plated NdFeB (neodymium) projectile along a circular tube, in a similar manner to a particle accelerator. The projectile is to be accelerated by a series of eight solenoids positioned along the tube.

The dimensions of the solenoids and the predicted dimensions of the tube (the details of the tubing have yet to be finalized) suggest that there is likely to be a gap of 2-3 millimeters between the solenoids and the tube.

I know that placing an iron, or any material with µ>1, core within a solenoid increases the strength of the magnetic field produced by the solenoid. My question is if I place a ring of iron, approximately 2-3mm in thickness, 32-33mm in diameter, in this gap between the solenoid and the tube, will it increase the strength of the magnetic field generated by the solenoid as in an iron core?

Additionally, should such a design increase the strength of the solenoid's magnetic field, are there any other materials, which are generally not unreasonably difficult to acquire, that would be more effective in such a role?


texts:
My instructor in electrical circuits has given me the following creative problem:

Construct a communication chain, that follows the drawing below:

The input is an AM signal, \$V_{send}=V_1\cdot cos(2\pi f_1t)+V_2\cdot cos(2\pi f_2t)\$
The chain consists of:
\$V_{send}\$ \$\rightarrow\$ An amplifier  \$\rightarrow\$ Transmitter antenna \$\rightarrow\$ Transmission through air with distance \$d\$ \$\rightarrow\$  Receiving antenna \$\rightarrow\$ An amplifier \$\rightarrow\$ \$V_{rec}\$
Plot the frequency spectrum of \$V_{rec}\$.

Okay, for this I have some questions.

I plan to use the HA-8089 antenna as my transmission antenna, but  can I also use it as my receiving antenna, or do I need another antenna for that?
Are the amplitudes and frequencies in \$V_{send}\$ (by those I mean \$V_1\$,\$V_2\$,\$f_1\$,\$f_2\$) dependent of what antenna or amplifier I use, or can I choose the values as I like?
When the signal travels through the air, it gets damped. To calculate the dampening I intend to use this formula: \$F=20log(d)+20log(f)+32.44−Gtx−Grx\$. Where \$f\$ is the frequency and \$Gtx\$, \$Grx\$ are the gains for the  transmitting and receiving antenna. But what frequency should I use? \$f_1\$, \$f_2\$, or a combination of the two?
And lastly: When I have the amplifier gains, the antenna gains and the signal dampening, how do I then combine all that information to calculate the received signal, \$V_{rec}\$? Would it just be: \$V_{rec}=(V_{send}\cdot G_{amp} \cdot G_{trans} -dampening) \cdot G_{rec} \cdot G_{amp}\$?

I know that was a lot of questions, but I need some help now, cause I haven't been able to find an answer.
Datasheet for antenna: http://www.professionalwireless.com/wp-content/uploads/2016/03/S8089-Helical-Brochure.pdf


texts: Should the Gauge of wire be consistent for DC

texts:
I'm looking at an ATX Power Supply with 2 rails each with a specification of 12 volts @ 20 Amps.  That should be a maximum of 240 watts (per rail). The modular plugs/cables that plug into the power supply are less than 20 gauge (probaby 16 or 18).

I have some devices that uses ~10 watts at ~1.0 amp at 12 vdc.  These devices do not have a power supply or male power plug that can plug them directly into the power supply I have to create my own.

I want to purchase these custom plugs that use 20 gauge wire to plug into the devices.  I would hack off the end of the modular cables provided with the power supply and connect the wires from modular cables to these plugs.

How do I calculate the maximum number of devices I can plug into the power supply (using just these two rails) with these custom plugs?  And is the limitation based on the 20 gauge plugs?


texts: How do I generate a high frequency sine wave using a PLL? 900 to 950 MHz

texts: I know of a few ways to generate a sine wave; Op-amps, 555, LC, crystals, or microcontrollers. But none of those would really work for a frequency as high as 900 MHz. I have heard of phase lock loops, but I don't know how to use one. What's the highest factor I could multiply my reference frequency by and still have it end up with the expected output frequency, and how do I divide the frequency leaving the VCO? Is a VCO part of the PLL or are they separate components? Will my output be a sine wave if my reference frequency is a sine wave, or do these only output square waves?


texts: Connect two embedded devices with USB host with Ethernet?

texts:
I need to connect two microprocessors that only have USB host, not OTG or client.

Obviously I would like to connect them as directly and quickly (ie 10's of Mbit up to 100) as possible.  A USB to serial to USB bridge is simply not fast enough.  Also Prolific's PL-25A1 looks ideal but is specific for windows whereas both of my platforms are running linux.

My current thought is to implement a USB to Ethernet to USB solution.  For example if I used an SMSC LAN9512 then I would get my ethernet connection.  The LAN9512 has built in MAC and PHY.

My question is how much of a physical interface do I need to implement?

Similar to TI's AN-1519 as referenced in this exchange.
can I get away with some 33nF caps?

Thanks in advance!


texts: What's the minimum amount of transistors I need to operate a stepper motor?

texts:
I would like to know the minimum amount of transistors to operate a stepper motor.Could I pilote it with one transistor or I need one transistor for every coil?

Thanks in advance!

Edit: the minimum number N of transistors I should connect to ports to drive the stepper motor.
For example, if I have 4 coils, I think I should have 4 bjt to drive my motor .

My question is actually: does exist a stepper motor with 4 coils that could I drive with only one of these bjt like this?

(I know this last circuit is for dc motor but somebody told me I could drive a stepper motor with this same circuit.... is that true?)


texts: I have a bunch of wall warts of widely varying DC output voltages.  I find that they almost invariably show a no-load (or low-load) DC voltage considerably higher than their stated rating.  I'm wondering about what physics is causing that.  I assume that a load much closer to their rated max current will bring the voltage much closer to the rated voltage.  I guess the moral of this question is "Always use a voltage regulator capable of encompassing the no-load condition".  Any tips on their use that will not damage the electronics they're intended to drive?  Thanks.


texts:
I have AVR that needs to drive 12V 1A motor.
I always used NPN BJTs (2N2222), but reading the datasheet says the MAX is 1A (which means I cannot use it here).
Instead, I willing to use MOSFET. I have several N-Channel IRFZ44N.

Reading the datasheet says Vgs(th) is 2-4V, and I am driving it from the AVR (5V), should be fine, right?
N-channel MOSFET needs to be on the low-side, right? means Source to GND, Drain to motor.
Do I need resistors on the Drain, Source paths?
Gate current - the AVR will drive max of 20mA 5V on the gate to switch the FET on, do I need resistor between the AVR pin and the Gate pin? I don't want to overload the AVR, and I cannot find the current the FET pull.
Do I need pull-down resistor on the AVR pin - Gate path, connected to GND?

I never used FET transistors, so I had may some newbie questions (and this is after reading the datasheet for several times and spending hours online reading about FET)

On one of the sites I saw this basic diagram for N-channel MOSFET:

Is the diagram will be accurate for connecting my AVR to the Motor? I mean, no resistors at all (only the pull-down one)? won't it overload the AVR?

Thanks.


texts: Electrical switch/relay that will stay on once triggered (regardless of future inputs)

texts:
I am looking for an electrical device that will allow for me to take an input (that will change from high to low to high again) and have it trigger an output (turn high when my input is low) but stay at this high state regardless of any future inputs.

Does something like this exist? Sorry if this is a duplicate, I just don't know what terminology to search with.

Thank you in advance,

Julia


texts:
I've got to analyze an electronic metronome schematic and I'm having trouble understanding how the oscillator in this schematic really works.

I believe it's a Wien oscillator with variable output wave frequency.
Diodes in negative feedback loop are used for amplitude stabilization and output should be a half-wave rectified sine wave (only positive half-waves because of the opamp power supply) if I'm not mistaken.

But I'm wondering what do resistors R15 and R16 in parallel with capacitor C7 do? Are they just used as a voltage reference, or are they used for something else?

I assume that variable resistors are used to set frequency of the oscillator. Do I use Barkhausen equation to calculate the frequency based on the resistance of variable resistors, or is there an easier way to do it?


texts:
I’m a noob, would appreciate any help with the following:

THE PROBLEM
We live on a mountain in North Carolina. When the temperature drops well below freezing, the well head freezes resulting in loss of water and broken pipes. I installed pipe heater tape which worked well for several years, but the tape burnt out and well head froze again. Many $$$ to repair.

THE QUESTION
Build a circuit that will:
1.  The easy part… turn heater on when thermocouple is closed, turn heater off when thermocouple is open.
2.  The hard part… when heater is OFF, monitor the circuit so that if the heater is open, an alarm will sound.

The problem is that if the heater fails (burns out) at 3 am, you don’t know about it until too late. After 4 days of head scratching, I came up with the attached circuit using several relays. I’m not sure this will work, I think the heater will still run when K2 is fired, and the alarm will be on anytime the thermocouple is open.… All commercial products are designed to thermostatically control a heater.
Looking at some circuits on Stack, it seems the best approach is a small current across the heater when it is off, then sound alarm when open is detected??

Help appreciated in advance…


texts:
What is the correct name for those little jumper cables, with a small socket each end, designed to go between header pins on PCBs. A bit like these, but singles

http://www.ebay.co.uk/itm/5-Pcs-30cm-Length-3-Pins-PCB-Board-Jumper-Wire-Cable-Connecters-/121208591808?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item1c389855c0


texts:
I built a driver for a pulsed laser. This required a low voltage DC source to provide a bias current through the laser and also a high voltage DC source to drive an avalanche transistor to make the pulses for the laser. The original design (which works fine) uses a 3 Volt AC to DC wall transformer plus a voltage regulator for the bias current and a separate 15 Volt AC to AC wall transformer plus a voltage multiplier circuit to get the ~65 Volts for the transistor.

I'm trying to simplify the design so that I can power the whole thing with just one wall transformer. I chose a 9 volt AC to AC transformer. I connected the output of the transformer to a 5-stage cascade multiplier circuit to get the high voltage and I also connected the transformer output to a bridge rectifier, smoothing capacitor and voltage regulator for the low voltage laser bias current.

Here's the problem (I think): One input terminal of the cascade multiplier also serves as the negative terminal of the voltage multiplier (i.e. ground). That means that the negative output of the bridge rectifier (ground) is also connected to one of the bridge's AC inputs. I'm a high school physics teacher, not an EE, but I'm pretty sure this is bad. The rectifier gets hot and I'm not getting the high voltage I need from the multiplier.

What would be a better way to do get both the low voltage (6 Volts 25 mA is plenty) and the high voltage (65 Volts at very low current) from a single wall transformer?


texts:
I am working on a VGA driver for a PIC 24F microcontroller. I have set all B and C ports for OUTPUT with TRISB = 0 and TRISC = 0. After scoping I noticed that one of my pins always stays high after it is set only once, while the other pins react correctly.

More specific, PORTCbits.RC3 = 0 and PORTCbits.RC3 = 1 works perfectly fine, PORTCbits.RC4 = 1 works but stays high after the first toggle, and PORTCbits.RC4 = 0 does nothing.

The processor I am using is a PIC 24FJ64GA004, if this is relevant. All ports are configured in the same way via the tris registers and cleared beforehand.

Sorry if this question is not general enough, this is my first time asking something on this site.


texts: How does baud rate affect power consumtion on a Xbee module?

texts:
How do baud rates affect power consumption on Xbee wireless modules?
For example: What would be more power efficent: Sending a packet with lower baud rate or with one, twice greater than the first, but thus saving time and being able to set the controller connected with the xbee module(and the Xbee itself) in sleep mode faster.


texts:
I am trying to make home automation system. Basically it consists of lights and fans connected through a relay to an arduino which is connected to internet. I have to switch them on and off by an application if no one is present in the house which is known by placing IR sensors.
So i want sensors,arduino,relay.

How to simulate the circuit working in virtual environment as it is costly to buy hardware and program? Is there any tool to do so?


texts: Do 5 pin soldering stations/irons have standardized pin outs and specs

texts:
I need to replace the iron for my soldering station for which the manual provides no specs on the 5 pins nor replacement specs.  Are soldering stations/irons that use 5 pins standardized?  I mean can I just buy any 5 pin iron and expect it to work with my station?
If not, given I can get no more support/specs for my station how can I determine which iron would be compatible.
this post show possible pinouts Why do heaters vary widely in resistance even though they have similar power requirements?
per comment below is pic of pinouts.  It is numbered clockwise 1-5 from the register
Mine is no longer sold. This one is still being sold and looks nearly identical and has same make number.  Zeny is probably just a seller brand. https://www.amazon.com/dp/B07S4GPM66/


texts: Arduino Mega (ATMega2560) UART does not send

texts:
I set up Atmel Studio on a Windows PC using this tutorial. Afterwards I proceeded to implement a UART. But it didn't work (no signal measurable with oscilloscope). So I just copied a simple UART example from the
ATMega2560 datasheet Section 22.5 and 22.6.

#define FOSC 16000000
#define BAUD 9600
#define MYUBRR FOSC/16/BAUD-1
#define F_CPU 16000000
#include <avr/io.h>
#include <util/delay.h>

void USART_Init(unsigned int ubrr);
void USART_Transmit(unsigned char data);

int main(void)
{
    USART_Init(MYUBRR);

    while(1)
    {
        USART_Transmit('A');
    }
}

void USART_Init(unsigned int ubrr)
{
    UBRR0H = (unsigned char) (ubrr>>8);
    UBRR0L = (unsigned char) ubrr;

    UCSR0B = (1<<RXEN0)|(1<<TXEN0);

    UCSR0C = (1<<USBS0) | (3<<UCSZ00);
}

void USART_Transmit(unsigned char data)
{
    while(!(UCSR0A & (1<<UDRE0)))

    UDR0 = data;

}

But even this example does not work. I took an oscilloscope and connected it to the TX0 pin and a ground pin, but no signal was received. When I removed the USART_Init function, the character A was sent over UART but of course with a wrong baud rate. Did I forget about something?

Does anyone have an idea/hint? Is something wrong with my question?


texts:
In my device I'm using a "capacitance multiplier" to filter DC-DC output voltage. That's my schematic:

In Multisim simulation I've achieved necessary output parameters, but when I soldered my PCB and measured the output voltage I've got huge mismatch.

According to simulation, when the output load is 10MOhm (approx. multimeter resistance) voltage comes about 4.4 volts. When I measure open output I got 3.7 volts.
To estimate loading caracteristics I connected 10 Ohm resistor and got 2.6 volts instead of 3.8 in model.
What reasons could cause that mismatch?


texts: Laser driver configuration with 5MHz modulation and current monitoring

texts: I have a huge task in front of me and I am actually lost. I want to drive this laser diode. I've worked with laser dirvers before and I used LM317 for simple circuits. This time I'd like to safely drive this laser with 5 Mhz modulation up to 150 mA and I also want to control the amout of current I apply with a variable resistor and monitor this current and the current laser uses with an LCD screen. This will be connected to a butterfly laser mount. I'll need a TEC Controller too but I think I can handle that. So basically what I want will look like this and the completed system will look like this. My question is, what is the best configuration for such a laser driver system? I know there are similar questions but I did not understand what to do with those to modify them for my system.


texts: Avoiding EMI with crammed radio PCB design

texts:
This is the PCB I'm almost ready to put into production. In the picture, the parts are laid on a 1.27mm grid. Every component and track has at least 10mil clearance. The smallest track size is 10mil. Ground is 13mil with 11mil clearance but I'll turn that large space on the board into a ground plane so that each ground track is substantially greater than 13mil. The thick tracks are between 0.7mm and 0.9mm in size and both have a 12mil clearance.

The parts in boxes are as follows:

The circuit in red box is the transmitter
The circuit in purple box is the receiver detector
The circuit in turquoise box is the receiver amplifier

In order for me to effectively use the circuit board space (instead of creating a big gap of nothing in the middle), I arranged the components so that the opamp is located more in the middle instead of to the right.

Now here is where I might have a problem which I'm hoping for an easy solution for without having to redo my layout.

If you look at the light green wire (shown in all three boxes), you'll see the connection starts at the opamp output and runs to an IC via a jumper block which is an xor input (I didn't show the part number). I also added a capacitor with a test point so that I can test my radio setup with a speaker.

In the end, the speaker will be disconnected and the jumper block will be closed so that the light green track will become live. This will be the main wire for all incoming wireless data. The speed of the data is adjustable and is estimated to be roughly 11kbps, but not more than 115200kbps.

The frequencies of the transmitters and receivers are expected to be between 300Mhz and 500Mhz.

Because the wire is within 2cm of the transmitter and receiver oscillators, would my setup be a candidate for EMI (to the point where one signal from an oscillator will jump to another wire)? If so, I would consider increasing the clearance for the wires but by how much? and if there is any other way I can reduce EMI without requiring substantially more circuit board space, let me know.


texts: 2 DC motors connected in parallel to H-bridge move with different speed

texts:
First of, since I come from web programming world, I'm pretty new into electronics and maybe some of the things I'm doing are wrong or could be done better, so any hint is highly appreciated.

I'm building a robot/crawler with 4 wheels. Each wheel is directly connected to a 6V 210RPM Motor DC with encoders.

I have a dual-way motor driver with 2 H-bridges

The driver is powered from an LiPo 2S battery 7.4 V

2 right motors are connected in parallel to one H-bridge and 2 left motors to the second H-bridge of the driver.

I'm controlling the motors through an arduino UNO by sending PWM signals to the PWMs of the driver.

Since the motors have encoders, I could read the rotations of one encoder from each side (one from left and one from right) and adjust dynamically the PWM for the other side, by taking the slower side as a master and the faster one as a slave, to force them move in sync.

The problem I have is that the motors which are connected in parallel move with different speed, although they receive the same voltage / PWM signal. Also their specs are identical.

I understand that mechanically they are not identical and different factors can affect their performance, but how to solve this problem? Is it possible?

Here are my ideas:

Does it make sense to read the encoder values from both motors connected in parallel? I think not, because if I'd try to lower/increase the PWM - both would be affected and the faster motor would still be faster.
Maybe attaching a resistor to the faster motor and trying to find a good value for the faster motor to slow it down up to the moment when it rotates in sync with the other one. But then this would work only if their speed difference is also proportional.
Last idea is to match them by the least speed difference and to connect in parallel those pairs which are closest to each other.

Maybe there are other proper ways to solve the problem which I have no idea of. But from the big amount of similar projects I found in internet, I guess they have a solution for this. Or maybe nobody cares that the front wheel of the right side would rotate slower than the back wheel from the same side?


texts: How to measure the temperature of a thin wire using a infrared (IR) thermometer?

texts: I got a laser thermometer to measure the temperature of a wire for my science fair. However, when I attempted to measure the wire, it was too thin and I just measured whatever was behind it. How can I measure the temperature of only the wire?


texts:
Hi
I want my circuit to be able to switch on and off several 230V AC circuits. I was wondering if relays are my only option. It starts to get a bit expensive if you need a few. Originally I was going to use a 5V dc relay to switch the devices on and off


texts: How to reconfigure resistor value from a working circuit

texts:
So, I'm not much of a circuit expert, but I did get to study some theory and practice in college. The thing is, that it wasn't enough. Now that I'm trying to build a circuit (that I finally finish up) it ends up working half way.

What am I trying to do? A simple three-band led color organ. Yes, it sounds absurd to post it up here, but the circuit is not my problem, it's the results. As stated before, I still lack of knowledge to handle myself with this.

Schematics:

This is part of a kit, but we all know it can be done at home. So, after hours of work and soldering I finished up my circuit. Pardon its bulkiness, I still haven't been able to optimize space use. This is the finished circuit:

As you can see, there's wiring all over the board, but those are to V+ and GND on left and right, respectively. LEDs are Red, Green, Blue as encircled in this image:

My problem is the following: When I energize my circuit, all the LEDs light up for a fraction of a second, then, only the red LEDs stay on and one very dim green one. This makes me know that all the circuit is well soldered and connected, hence all emitting light sources work. But why don't they stay on? Red LEDs have 4.3V from resistance to V+, Greens have 4.6V, and Blues have 4.9V.

Another thing, this little friend here (encircled in red) Overheated and melted the plastic next to it almost to the wire core (if I hadn't noticed, who knows..)

The resistor is 47ohm, as shown in the schematic, and I think this should be changed, but I'm not sure.

Transistors are 2N3904 to match up 2222A, source is 12V DC 500mA (but real output is 15.2V). The circuit creator stated that circuit works well from 9 to 15V and consumes 25mA tops. I also energized the circuit with 11V battery source, but it still has the same issue; Red LEDs on only (a bit dimmer) and the 47ohm resistor heating up. What's the problem with this circuit? How do I change/reconfigure my resistor (if that's the problem)?


texts: How to add two output expressions to calculate the third expression in Cadence icfb 5?

texts: I am trying to calculate the average propagation time carry_TP from carry_TPHL and carry_TPLH which I already got the expression from the calculator tool and works well. Now how do I make the third output expression for carry_TP = (carry_TPHL+carrt_TPLH)/2? What I have tried (shown in image) isn't working for me. I am using the cadence icfb version 5.


texts: What are the DC motor wires in the picture for?

texts: I'm given a DC motor without any specs. But it is not pwm thats I'm sure. The point is there are 3 wires brown, red-black. red-white. I cant find out how to power the motor and which wire is gnd or plus.


texts: Average Inductor Current in RL Charging Circuit

texts: Here's a switching circuit. The input Vs is a 24V rectangular pulse at 20kHz frequency with 75% duty cycle. Since the time constant L/R is very much greater than the pulse width, we expect the inductor current to be a triangular wave (i.e. integral of a rectangular wave) at a certain DC offset which is the average current. My problem is, how do you find the average inductor current assuming Vbatt is 13.8V? (Please ignore questions b and c.)


texts: Current return path when using an AC coupled transimpedance amplifier

texts:
Is a current return path a good (or reasonable) design practice with an AC-coupled transimpedance amplifier?

Horowitz & Hill states that "you must provide a return to ground for the (very small) input current" and an article at analog.com on common design errors highlights this as a common design error.

It is not clear to me if a current return path is also required with an ac-coupled transimpedance amplifier.  When I look at Horowitz & Hill, the ac-coupled transimpedance amplifier section of the circuit shown in Figure 8.87 does not have a current return path after the blocking capacitor.  It could have been omitted for clarity because the figure shows the ac-coupled as an optional configuration.

FWIW, I am not designing a circuit.  I am trying to understand some unusual behavior in some equipment and my working theory is that the blocking capacitor is building up a charge over time (as indicated in the analog.com article).

I have included a circuit diagram (revised to show the recommended resistor from the lower plate of C1 to ground).

[


texts: Is there any reason for the wires in a PCI-e and CPU power cables to be separate?

texts:
These are the connectors they are for:

So as you can see, the PCI-e connector uses either 3x12v + 3xground or 3x12v + 5xground wires in the cable. I've red that optionally some of the wires can be used for some sort of regulation signaling but nobody really uses this functionality and as far as the power supplies and graphics cards are concerned, its fine if they are just 12v and ground.

For the 8P CPU connector, its always just 4x12v and 4xground as far as I know.

Now the reason I'm asking is because I've built some 8P CPU connector -> 2x 8P PCIe adapters which work well and I'm looking to build a whole bunch more.

What I want to do is to not bother with all the separate wires and just use a pair of 15AWG wires for the cable which I then split up for the separate pins in the connectors. The max current would be 25A which both the connectors and wires are able to carry.

From the PSU's that I've opened, I've seen that the 12v and ground wires all get soldered together anyways so there shouldn't be a reason why this would be bad.

Before I go ahead and do it, do you guys know of any reasons to keep the wires separate?


texts: Problem with Xilinx SDK - Failed to Scan JTAG Chain

texts:
I am having an issue with running a simple Hello World program on the Trenz TE0720-01 board with a Zync 7020 FPGA. I have been following the tutorial to setup and run the Hello World program given here.

I have no problem up until I have to program the FPGA, which it then gives me the error,

"Program FPGA failed. Reason: Failed to Scan JTAG Chain. Unknown error."

I am using a standard USB A-Male to Mini-B cable to connect the board to the host computer.
I am also running on Windows 7.

How can I fix this error and get my FPGA to program?


texts: Buying Low Volume Populated PCBs and Handling Passive PNs

texts:
New to Eagle PCB design. I plan on making a custom Beaglebone Black Wireless PCB, and so have pulled down the Eagle files. I'm a student and have a student license. This project will be too difficult to assemble myself, because of the large BGA component and so forth, so I plan on purchasing the boards assembled. In order for the fab. house to know what parts to put on it, they will need a BOM.

My question is this:

How come none of the passives in the Eagle files has manufacturers or manufacturer part numbers? Am I to take it the fab. house can populate generics from Panasonic or something? If so that's great, but it seems like a lot of work to put on the fab house to source this? If not, how would you recommend going about this?

Thanks for the insights


texts: Driving a 74HC245 in one direction with 3.3V when Vcc is 5V

texts:
I have a 5V device that accepts parallel data in. That data is buffered by a 74HC245 IC (TI datasheet, NXP datasheet) where the Dir pin is hard wired to drive in one direction. I can't change/modify this device hardware-wise.

To date I have been driving this device using an ATMega328P, running at 5V, with no problems.

I now have to switch to a 3.3V microcontroller for other reasons out of my control.

I am hoping that I don't have to add logic level adjustment circuitry in-between the microcontroller PCB and the device being controlled. Reading the datasheet of the 74HC245, the input high threshold is 2.4V(typ.) to 3.15V when Vcc is 4.5V. Being that the 74HC245 IC is supplied by 5V, I am concerned that 3.3V logic out of the microcontroller is going to be right on the limit.

Will I be able to get away without any logic level adjustment circuitry?


texts:
I have LT1302CN8-5#PBF, fixed 5V DC/DC boost converter.

I have built the same circuit as shown in the following datasheet document. (https://www.analog.com/media/en/technical-documentation/data-sheets/lt1302.pdf)

The first problem is low power efficiency. I use the DC electronic load device to test this circuit, and the best efficiency I got was only 64 percent when (Vin = 3.794V and Iin = 0.151A) and (Vout = 5.0194 and Iout = 0.073A).

The second problem is that my target output is 5V and 300mA, but if I set the current output to be 300mA, the voltage will drop below 3V.

The testing results are far worse than what I read from the datasheet document and from the simulation I did with LtSpice, which shows I can get 5V and 500mA.

What could cause this issue?

Components I used:

100uF : ESH107M450AN2AA
(https://www.mouser.com/datasheet/2/212/KEM_A4005_ESH-1101279.pdf)
10uH : RLB0608-100KL
(https://www.bourns.com/docs/Product-Datasheets/rlb.pdf)
Diode : 1N5818 (https://www.diodes.com/assets/Datasheets/ds23001.pdf)
0.1uF : ceramic disc capacitor, unknown product number.
0.01uF : ceramic disc capacitor, unknown product number.
20K ohm : Unknow product number.
Input voltage : 3.8V
Input current : maximum possible is 5A.

Thank you for your help.


texts: How to calculate instruction cycles on pic?

texts:
I want to know how much instruction cycles are each line of a program, is there a way to do that?

It's important to me because i'm having a problem with the oscillator (or might be something else) doesn't seem be as fast as i want.

The pic in question a a PIC32MX470F512L.

I'm using the following config with MCC:

I made a simple program which only toggles a pin that i will see with an oscilloscope:

#include "mcc_generated_files/mcc.h"

/*
                         Main application
 */
int main(void)
{
    // initialize the device
    SYSTEM_Initialize();

    while (1)
    {
        // Add your application code
        IO_RG0_Toggle();
    }

    return -1;
}

On the oscilloscope it toggles every ~13.8us.

This seems to be super slow.

Note: Using the timer with 1ms calculated period and alternating the signal of the port with the timer callback it alternates every 1ms.

But if i set the timer period to 8us the value goes to 16us:


texts: PIC16F SSPADD Causing SCL To Go Low Early

texts:
I am not able to communicate with my RTC (PCF8563). I am trying to communicate with it using a PIC16F876 over the I2C bus. The code below is all I am doing in my main(). I am unable to receive an ACK from the RTC. For some reason, when I set SSPADD it creates an additional START condition which is throwing off everything. I am positive it is the SSPADD , as a step through and removing it shows. Can anyone explain this? I have, by sending two START conditions, had it stop and recognize the correct address. In that situation SDA remains HIGH. If I set SSPADD before I enable SEN it will not send anything. Both pins are connected to +5V through a 2.2kohm resistor (also experimented with 10kohm).

TRISC = 0b00011000; //RC3-RC4 INPUTS
SSPM3 = 1; //set as I2C master
SSPM2 = 0;
SSPM1 = 0;
SSPM0 = 0;
SMP = 1; //disable slew rate control (running at 100khz)
SSPEN = 1; //enable serial port

SEN = 1; //create START condition
SSPADD = 0x09; //set baud rate to 100khz
SSPBUF = 0xA2; //buffer in number

Screenshot from logic analyzer: SCL on top, SDA on bottom:


texts: Replacing resistors with equivalent resistor

texts:
This is somewhat a homework assignment, but please bear with me. Given the following schematic, I want to know the overall resistance when measured from node A to node B.

simulate this circuit – Schematic created using CircuitLab

First of all, I'm not sure whether the order of calculations is important. Here's what I did: R3 and R4 are in series, so they add up to 500 Ohm. R2 is in parallel to those two, so (1/500+1/500)^-1 = 250 Ohm. Now I add R1 and my previous result because they are in series and thus get 1250 Ohm.

Is this way of calculating correct? If I, for example, first calculate R2 and R3 in parallel, and then in series with R4, I get a completely different result, which confuses me a lot.


texts:
This is an abbreviated version of WS2812 LED control routine. I have removed all the no-ops for the sake of readability here. Can someone explain the role of the branch instruction (brne) towards the end of the routine?

 asm volatile(
    "       ldi   %0,8  \n\t"
    "loop%=:            \n\t"
    "       out   %2,%3 \n\t"    //  '1' [01] '0' [01] - re  "       sbrs  %1,7  \n\t"    //  '1' [03] '0' [02]
    "       out   %2,%4 \n\t"    //  '1' [--] '0' [03] - fe-low
    "       lsl   %1    \n\t"    //  '1' [04] '0' [04]  "       out   %2,%4 \n\t"    //  '1' [+1] '0' [+1] - fe-high
    "       dec   %0    \n\t"    //  '1' [+2] '0' [+2]
    "       brne  loop%=\n\t"    //  '1' [+3] '0' [+4]
    :   "=&d" (ctr)
    :   "r" (curbyte), "I" (_SFR_IO_ADDR(ws2812_PORTREG)), "r" (maskhi), "r" (masklo)
    );


texts: Electrolytic capacitor at negative voltage regulator input

texts:
I'm trying to use a L7912 to output -12 V DC. The datasheet says to use a 2.2 uF tantalum capacitor on the input for stability. Further it says if an aluminum electrolytic cap is used, to have it at least ten times the size. The closest I could find was a 47 uF electrolytic cap. Without the cap the regulator works fine. If I put the cap in, (C2, + at the ground side, because it's negative voltage) the regulator seems to let the unregulated voltage through (higher, ripply).

What am I doing wrong?

simulate this circuit – Schematic created using CircuitLab

datasheet


texts:
Consider the following

simulate this circuit – Schematic created using CircuitLab

$$ H(s)  = \frac{sR_2C_1}{1+s(R_1+R_2)C_1}$$
$$ f_z = \frac{1}{2\pi R_2C_1} $$
$$ f_p = \frac{1}{2\pi (R_1+R_2)C_1} $$

I simulated the circuit in LTSPICE with \$R_1=R_2=795\$ and \$C_1=1nF\$ which should give me a \$f_z = 200kHz\$ and \$f_p = 100kHz\$.

Here is the AC anaylsis of the simulation.

Question: Given that there is a zero at the origin with a certain frequency - what should I see at that frequency ?

Additional information to add some clarity:
I am reading this book about Linear Circuits and it says the following

$$ H(s)  = \frac{sR_2C_1}{1+s(R_1+R_2)C_1} = \frac{\frac{s}{w_{z0}}}{1+\frac{s}{w_{p1}}} $$

where \$ w_{z0} = \frac{1}{R_2C_1} \$ and \$ w_{p1}= \frac{1}{(R_1+R_2)C_1} \$

I believe the intent of this form is to visually be able to extract certain information about the system. I am confused on the significance of the \$w_{z0} \$ and what it means.

Traditionally I have seen forms such as $$ H(s) = \frac{1+\frac{s}{w_z}}{1+\frac{s}{w_p}}$$ and I know that you have a flat line (magnitude plot)  until the wz and then you have an +20db/dec line and then a -20db/dec at the wp. But this zero at the origin is messing me up.


texts: Multiple voltage level on multiple rail using ORing PMIC

texts:
I have two voltage rail that i would like to have 4 different voltage levels 0v, 5v, V1, V2. where V1 and V2 are anywhere from 6v to 60v. The two voltage rail can have any of the voltage at any time.

So far I have come up of two schematic design, both i some uncertainties with.

First off the PMIC i am using is the LM7602 Which is a must have in my application because of Over voltage, Under Voltage, Reverse voltage, Over Current protections

how 0v and 5v on both rail is handled is: Not in the schematics are two 5v PMIC with basically the same feautures as the LM6202. So to create 5v, the 5v PMIC is enable and the raile chosen will have its LM76202 is turned to shutdown giving the rail 5v. 0 is kinda opposite of 5v where the 5v pmic is disable and the rail chosen is also disabled (there are two 5v PMIC, one for each rail)

V1 and V2 are user plugged voltage assumed to be 6v to 60v (and is protected by UVLO,OVP,RVP). On the left schematic basically there can be a max of 2 LM76202 enable at a given time and each rail has 2 LM76202 which are connetected to V1 and V2. depending on what the rail is set two v1 or v2 can be enabled. Now my problem with this is it seems to be a waste of IC since only a max of 2 can be used at any given time and this IC does not come cheap (5$) making 3pieces of this board is already 60$ on that ic alone.

The schematics on the right seems to be a more economical option by using 2 P channel mosfet like FDS8935 to switch the loads to other rail. The disadvantage of this is, one im not confident if the circuit is correctly made, and two, the rail will have to share the current limit of the other rail.

Is there any better way to achieve the multiple voltage on 2 rails that i require? My voltage range for V1 and V2 are 6-60v at max 2A. The 5v is set to 500mA each rail.


texts: Could use some help on what should be a simple LED wiring scenario

texts:
First off, I'm new here - found this site while researching to figure out why my circuit isn't working as I expected.  I appreciate any help you can provide...

The picture is the wiring diagram for the headlight circuit on a custom car I built (http://www.britishv8.org/MG/RobFicalora.htm).  I'm trying to add a bi-color LED (using 2 legs of an RGB LED) where green will indicate low beams on & blue will indicate high beams on.  The LED is a common cathode LED.

Instead, what I'm getting is green when headlights are turned on; both blue & green when I flip to high beams; both blue & green when I flip back to low beams; LED off when I turn the lights off.  The headlights themselves work properly and the low beam turns off when high beams are turned on.

Two questions:

Ignoring the LED wiring for a moment, note the headlight wiring & relays 2 & 3 in particular.  While troubleshooting, I noted that the wires between pins 87 and the headlight bulbs show +12V.  When I designed the circuit, I was thinking of those wires as "grounds" -- being passed through the relays when energized.  In retrospect, it makes sense they'd have 12V on them because the headlights natually connect the + & - sides.  Is there anything wrong with how I've designed that circuit?
Do you see what would cause the LED's not to work properly?

NOTE:  I didn't draw in the resistors, but I do have them wired & soldered to the LED legs.  Both the blue & green sides of the LED work properly outside of this circuit simply connected directly to the battery.

UPDATE ---------------------------------------------------

Ok, i'm not getting very far very fast.  I tried the capacitor with no luck.  And, I'm getting confused by the fact that pins 86 & 87 have 12V on them when the headlights are off (which makes sense given 85/86 is a coil so 85 passes thru to 86 & since the headlight has a filament ("A") which connects the 12V source to the "ground" side that goes to 87.  Not sure if one of those is causing a problem?  I've included a simplified diagram of just the low beam headlight wiring below for easier reference...

Oh, and headlights are standard automotive halogen bulbs (not HID bulbs).


texts:
I am a PHP programmer with basic knowledge of c/c++ and electronics. But i have keen interest in robotics and AI.

What are the basic things that i
need to learn before switching to
the robotics ?
What languages are
used to write the code and how is
that code transferred to the chips ?
What are the basic components that i
need to know ?

I would like to learn about the both hardware components and the programming part. (Are these different streams?)


texts:
I wanted to experiment a Smartphone Fast Charger. My source would 5V 25A, and output would be in 4 channels, all in parallel. Would that be safe to charge a smartphone?

If no, what can I use to bring down the ampere in one channel? Say, I'll be lowering the ampere down to 3.1A - like most fast charger does.


texts:
Currently working on a project requiring me to detect fog, and measure the amount of fog. It doesn't have to be accurate but it has to give a sense of how foggy it is.

The device (probably Raspberry PI or Arduino) will be placed on street lightning poles. I am currently thinking about using an Optical Fog Sensor as it doesn't require me to have anything on the other side of the sensor with e.g. light scattering techniques.

Is this a good option for my purpose or do you have any other recommendations?

Thanks in advance.


texts:
I'm trying to put together a boost converter to take a 11-14.4v input and boost it to ~17v with a max current of 2A.

Most of my designs (made either by calculations done by me or a calculator tool from the web, all of which have actually given me different values) work fine at low loads (~100-150 mA), but the voltage drops off quite quickly as I increase the load and I just get a small ripple followed by a flat voltage somewhere below 12v after about 300mA upwards.

I've made the circuit physically once, but now I am using LTspice to simulate it.

I'll be using a 100KHz switching frequency (LM2585T-ADJ) and the online calculators I've used have said to use:
Min 64uH inductor with 38% duty cycle (http://www.coilcraft.com/apps/selector/selector_2.cfm)
Min 6.28uH inductor with 15-35% duty cycle(https://learn.adafruit.com/diy-boost-calc/the-calculator)

EDIT:
Good point about the schematics, don't know why I didn't include them straight away.


texts: Inexplicable curve shape of short circuit current measurement on synchronous machine

texts:
I'm doing some experiments on a synchronous machine with follwing data:

nominal power: 5kVA
nominal stator voltage: 380V phase-phase
nominal stator current: 7.6A
nominal frequency: 50Hz / nominal speed 1500min-1 -> 2 pole pairs
connection stator coils: Wye
excitation circuit connected to 1kW controllable D.C. power supply
an external DC machine connected via the shaft drives the generator

Now I start up the generator with no-load until it reaches 1500min-1 and turn on the excitation current to get nominal voltage at the stator terminals. Then I suddenly close a short circuit with a switch at the terminals an measure the resulting current in each phase. (Circuit sketch below)

This is the result I get (1st is stator voltage between one phase and N, last 3 are the stator currents):

I'm wondering about the "strange" curve of the currents, which should in my opinion look like a sine wave. Once I saw a simillar form namely when a transformer is saturated. But my measurements look the same even when I'm doing the test with no-load voltage of 25V before the short circuit switch is closed. At this point the generator should definitely not be in saturation.
My question is now: why do I have this unexpected short circuit current curve? Perhaps somebody had a simillar issue.
Greetings!


texts: Help needed finding laptop FFC keyboard connector

texts:
I have a Thinkpad T440 keyboard that I'd like to convert to a USB keyboard. I've been looking for an FFC connector for it and it's been difficult finding it. It has 32 pins and 0.5mm pin pitch. The problem is that the cable is not straight, it has notches at the end (not tabs). Also, the notch on one side is 1mm deep and on the other side only about 0.6mm:

Here are a couple of images of the board connector, from an iFixit guide:

https://d3nevzfk7ii3be.cloudfront.net/igi/SRVjdRpMgGfAyEAP.huge
https://d3nevzfk7ii3be.cloudfront.net/igi/sTQR3J2d2XNhXos5.huge

In the schematic the connector shows up as JAE_FL10S032HA1, but I haven't been able to find anything about it, except for Lenovo schematic references. I haven't found any 32 pin FFC connectors from JAE.

I was able to find some connectors that look promising, from Aces, with the 1mm deep notch on one side and 0.6mm deep notch on the other, but I can't find any place to buy them:

http://www.acesconn.com/series/51699-xxxxx-xxx/2216
http://www.acesconn.com/series/51580-xxxxx-xxx/2199
http://www.acesconn.com/series/51555-xxxxx-xxx/2193


texts:
When using the 8255 to glow an LED array using BSR mode, is it necessary to first set port c as an output port? Why?

In our lab, when I had not not set port C as output and directly used BSR mode to set and reset individual bits, only the 4 led's connected to the lower four bits of port C were responding. When I set port C as output, the desired output was obtained. But what is the need to set port C as output? When we are setting and resetting certain bits in port C, shouldn't port C automatically be taken as an output port?


texts:
I'm working on the power supply of a temperature controller which sends about 5kW of power maximum (230VAC 50Hz) into 3 sets of 12 heaters (actually, 3kW + 1kW + 1kW). I'm at the stage where I need to detect if any of those heaters burns out or shorts.
I am currently considering current monitoring with a software algorithm to detect that.

I have 3 RS232 lines available, and 3 analog inputs (0-10V or 0-20mA) total (unless I add something else but I'd rather not to).
That leaves me with 1 current monitor for the whole set, or one per heater set. Hence the specs of the current sensor: >21A full scale or >13A full scale, <100mA accuracy.
Non-invasive technique is required (intrinsically isolated). I don't trust chips like the Allegro ACS709 to be completely short-free over the entire lifetime (15years) because it may be isolated, but still within a very small package (but maybe I should?).

Clampmeters are very appealing because they're definitely non-invasive and they generally have good accuracy. I have found only one which has a RS232 interface though, and the datasheet is quite poor.

Any suggestions?


texts:
I am trying to make a fault analysis of a bunch of ceramic capacitors.

Short description of the application:

10 220 µF ceramic capacitors 1210 package are placed in parallel with a 3.6 V battery. A MCU wakes up periodically (maximum once per minute) and draws current (maximum peak 10-15 mA for a few milliseconds). Total time before going back to extremely low power sleep is 130 ms. The capacitors are supposed to hold enough energy to cover this without dropping below 1.6 V (minimum supply voltage for the MCU).

This is needed since the operating temperature is low, and the battery cannot deliver. The battery has enough time to recharge the capacitors while the MCU sleeps.

I am suspecting shorts in the capacitors. Because:

The battery has drained very quickly on some of my PCBs
From what I have read ceramic capacitors, especially in large packages, are sensitive to mechanical stress and can crack, causing shorts

To see this for myself I have attempted making cross sections, but I have a hard time understanding what I am seeing.

How I made the cross section:

Used a dremel to cut off the corner of the PCB where the capacitors are placed
Molded the cut off PCBs in epoxy glue to make handling easier
Used a diamond circular saw blade to make a cross section approximately in the middle of the capacitors (lengthwise)
Wet grinding and polishing down to 1 micron and then 1 µ lapping film

I repeated this on two PCBs.

There are 3 capacitors next to each other:

Here you can see a color difference between the capacitors, top right and bottom middle are darker in color. But as you can see, not in the same position.

I don't have enough rep to add all images. I will comment links to all the images. Would appreciate if someone could edit and add the images to the post.

The darker colored ones (top right, bottom middle) look like this close up.

Almost what I was expecting a ceramic capacitor to look like. At least you can see some kind of layering. But the layers are not solid as I expected.
Can this be damage caused by the grinding and polishing?

The distance between the layers is 2 µm.

The lighter colored ones look like this:

What is this?! Can e.g. high currents cause the layers to melt together like this? Or can this also be caused by my grinding and polishing?

Here we can see an air bubble in the solder. But the gap close to the bottom, can that be damage caused by mechanical stress?

I later tried grinding and polishing a bit further into the capacitors. It looks exactly the same. If the strange wavyness and/or the broken off layers had been caused by the grinding and polishing I expect that the characteristics would have changed. E.g., a wavy one now has broken off layers instead, and the other way around.

The exact capacitors used are Taiyo Yuden JMK325ABJ227MM-T


texts:
I have a pre-made motor controller which I want to re-purpose for a hobby project by pulling the MCU off and attaching to a custom control circuit (with a more powerful MCU, current sensors, etc). The MCU is a LQFP-48 7mm package (0.5mm pitch pins). It seems like attaching to standard SMT footprints is a reasonably common prototyping task, but I can't find any products designed to do this. What is the name of some kind of adapter/interposer/something which is designed to solder onto the PCB in place of the MCU, and how would I go about finding one of the right size?

I've found a similar product called 14 pin DIP to 14 pin SOIC/SOJ, but that's very generic and hard to search for more of. It's particularly hard to search for because there are a lot of products for going the other way (attaching a SMT IC to larger wires). Some pictures of similar products I found for reference:

Just a name and/or source for those little metal clips on the edges would be helpful too, so I can attach them to my own PCB.

Finding some kind of SMT 0.5mm-pitch header strip would work too (solder those to the existing PCB, and then to a PCB of my own on top), but I can't find any that small.

If anybody has other ways to achieve the same goal, I'm interested in suggestions there too. Some approaches I've already considered: Soldering wires directly to the pads is hard because they're tiny. Finding other places on the PCB to solder wires is kind of annoying because it's a lot of wires to attach, and some of the nets don't go very many other places. Getting a custom PCB with 0.5mm castellated edges made for cheap doesn't seem to be possible.


texts:
I'm working on a project requiring production of sinusoidal waves. Normally, from my understanding, a DAC can produce a waveform that alternates between a negative voltage and a positive voltage, but for my needs I need the DAC to produce a waveform that alternates between a zero voltage and a positive voltage.
Is this possible using a DAC, and if not how would I produce such a waveform?


texts: How to pull a normally floating pin to ground for 500ms when circuit powered on and circuit powered off

texts:
I need some help designing a circuit to pull a floating pin to ground for approx 500ms when the circuit is first powered on, then pulling it to ground again for another 500ms when powered is lost. The floating pin is the trigger for an RF transmitter circuit, pulling it to ground will transmit its code - I need a pulse when power is turned on and pulse when power is turned off. I've got a 5v power supply. I haven't done any electrical engineering work for over 20 years..

It seems from other related posts that a tried and trusted 555 timer might be the simplest solution, I can clearly see how I can get a slight delay, then a 500ms pull to ground using a couple of RC networks and transistor on the 555 output pin when turned on, but can I use the same 555 and a capacitor to pulse when the power is lost somehow? I don't mind if I have to have two 555 timers - or if there is a simpler or easier solution?


texts: Can I read out this 10V load cell with the 5V OpenScale board?

texts:
For a robotics project in which I want to build a kite flying robot I want to measure the pull force on the rope connected to the kite. To measure this pull force I bought this load cell (which measures up to 500kg) and to not make things too complicated I bought this Sparkfun OpenScale board which can be used to read out load cells using USB. Below you see an example image from the Sparkfun Website showing the OpenScale board connected to a load cell:

The load cell I bought hasn't been delivered yet (takes a month!) but in the description I now read:

  For the bridge voltage:Recommended 10 VDC (standard signal 12V 24V)

I'm not sure what the "bridge voltage" is but the OpenScale board is powered by USB, which I guess means it's 5 Volts.

Seeing the image above I suppose the load cell should be powered through the OpenScale board. But if the openScale board is 5 Volts and the load cell needs 10 Volts I guess that can become a problem. So I plugged in the OpenScale board into my computer (with USB), took out my multimeter and measured the voltage on the Load Cell connectors from the OpenScale board. To my surprise it doesn't give any voltage in any combination of the connectors.

So I now wonder about a couple things:

How can the load cell be powered through the OpenScale board if it does't give any voltage?
If the OpenScale board is indeed 5V and the load cell I bought indeed needs 10V, will this be a problem? Can I combine my load cell with the OpenScale board?
If the load cell cannot be powered by the OpenScale board, is it possible to power the load cell from an external power source and still read it out using the OpenScale board?

All tips are welcome!


texts: setting the frequency of a PWM on a STM32

texts:
I'm trying to write a function that takes a desired frequency of PWM and sets the timer based on this value:

void initTimer(unsigned int freq ){

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);

    TIM_TimeBaseInitTypeDef timerInitStructure;
    timerInitStructure.TIM_Prescaler = 1000;
    timerInitStructure.TIM_CounterMode = TIM_CounterMode_Up;
    timerInitStructure.TIM_Period = 1000;
    timerInitStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    timerInitStructure.TIM_RepetitionCounter = 0;
    TIM_TimeBaseInit(TIM3, &timerInitStructure);
    TIM_Cmd(TIM3, ENABLE);

    TIM_OCInitTypeDef outputChannelInit;
    outputChannelInit.TIM_OCMode = TIM_OCMode_PWM1;
    outputChannelInit.TIM_Pulse = 500;
    outputChannelInit.TIM_OutputState = TIM_OutputState_Enable;
    outputChannelInit.TIM_OCPolarity = TIM_OCPolarity_High;
    // the first channel
    TIM_OC1Init(TIM3, &outputChannelInit);
    TIM_OC1PreloadConfig(TIM3, TIM_OCPreload_Enable);
    GPIO_PinRemapConfig(GPIO_FullRemap_TIM3,ENABLE);

}

The code works fine and generates the expected PWM. My Problem is that I don't know how to calculate the value of the prescaler based on the given frequency. In the example above the values are fixed.

Any idea how may I do this? Thanks in advance!


texts:
I need to replace this capacitor on an Acer E5-571 Laptop motherboard.

I'm trying to work out the ratings.  I am no expert, but know enough to resolder a new capacitor.

From what I have worked out, this is 68uf, but what is the voltage?  Is that 25V, with a tolerance of 3% (the "H"), or does the H indicate something else?

Diameter is 8mm approx

If anyone could point me to an equivalent on ebay?


texts: Can an electromagnetic field be created in a non-metallic coil?

texts:
OK, so here's a simple one. When current flows through a wire, it produces a tiny magnetic field. If you bend the wire into a spiral, the fields of each loop merge together forming a field you can actually measure.

But does the conductor have to be metal, or would any conductive material work? E.g., would a plastic tube full of water still produce the same magnetic field? [Assuming the water has enough impurities to be considered a "conductor" to start with, which it usually does.]

Edit for Clarification: OP is talking about a simple electromagnetic coil, without regard to core material or application. Assuming Air Core, would a coil of water in pvc tubing, electrified, produce a measurable magnetic field?


texts:
When creating logic using a for loop, Verilog requires the loop index to be declared. I've seen examples where it's done with either "int" or "genvar" keywords.
For example:
// Using genvar:
for (genvar x = 0 ; x < some_value ; x++) begin
// do something with reference to x
end

// Using int:
for (int x = 0 ; x < some_value ; x++) begin
// do something with reference to x
end

When should I choose one over the other ?


texts:
I'm designing a home automation controller in college. The system is on 24V (relays and sensors). I'm using TI Cortex M3 MCU and i want to control it over USB. This picture of the system is currently draft.

I have some questions that I could not find any answers. The board needs 5V(3.3V LDO on there), so a 24V to 5V conversion needed.

Is there any problem that the whole system is on 24V ground?
If 1. problem. Do I need a isolated DC/DC converter?

The outputs externally wired and the inputs opto-isolated.


texts:
Does anyone here know of any cheap-ish handheld meters that are capable of measuring the voltage at specific audio frequencies?

I'm dealing with a few constant frequency signals on the same wire - and would love to be able to tell the voltage at specific frequencies.

The answer below is a great answer - and I guess I should have clarified slightly in asking the original question.

The frequencies are specific frequencies: i.e. 1560 Hz, 1620 Hz, 1680 Hz, 1850 Hz

I have thought of using a scopemeter with fft support, but haven't though of using a microcontroller with fft!  I'll have to look into that.

I've also looked into using bandpass filters, but the frequencies are so close together that the orders would be crazy high.


texts: Finding equivalent resistance for time constant in R-C circuit

texts:
Given the first order circuit above.  The switch has been closed for a long time and is opened at \$t=0\$.  Find the equation for the voltage \$vc(t)\$ across the capacitor after the switch has been opened.

I have determined that \$vc(0)=7.619 V\$, but cannot find the time constant.

Here is my work for attempting to get \$R_{th}\$.


texts:
We know V(rms) is the equivalent dc voltage for same power decipation. But in half wave rectifier case wikipedia says V(dc) =V(avg) and not V(rms) .
Why it is saying V(dc) =V(avg) and not V(dc) =V(rms)?

https://en.m.wikipedia.org/wiki/Rectifier


texts:
I need advice on a problem I'm having

I need a follower to transmit an AC signal into a low impedance load which is the cathode of a triode but I also need it to be an adjustable current source to the load.

Unfortunately normal current sources have gain, I need a unity gain current source so the AC signal is not amplified.

The ac signal voltage is about 20v and the DC voltage levels are from 0 to -300v and I have access to 300v apex opamps if needed but I'm a novice at circuit design so I'm not sure how I would design it.

Any ideas?

Edit: Sorry I think people are getting confused.

This is a more accurate depiction of what I want to do

Ignore the opamp.

The 1uf capacitor carries the audio signal.

The cathode presents an ultra low impedance so I need the source follower for a buffer.

I want the audio signal to pass through the follower untouched but I also want the follower to provide a constant current to the load.

Imagine the 150k resistor as the current source bias.
The problem is figuring out how to replace that fixed resistor with a variable current source bias.


texts: Can't get I2C to work on PIC32 ("skips" bytes/hangs)

texts:
I am working on a PIC32-MAXI-WEB development board from Olimex that I'd like to have communicating with an Invensense MPU-6050 6DOF accelerometer/gyro. By modifying an demo from Olimex I managed to get the pic communicating.

I started working on a project for which I created a new project(in IDE) as I did not need/want the FreeRTOS kernel that the demo is built on. However I can't make the same I2C code work there. I get some output, but not what I should get.

Helper functions from the Olimex DEMO:

BOOL StartTransfer( BOOL restart )
{
    I2C_STATUS  status;

    // Send the Start (or Restart) signal
    if(restart)
    {
        I2CRepeatStart(I2C2);
    }
    else
    {
        // Wait for the bus to be idle, then start the transfer
        while( !I2CBusIsIdle(I2C2) );

        if(I2CStart(I2C2) != I2C2)
        {
            DBPRINTF("Error: Bus collision during transfer Start\n");
            return FALSE;
        }
    }

    // Wait for the signal to complete
    do
    {

        status = I2CGetStatus(I2C2);

    } while ( !(status & I2C_START) );

    return TRUE;
}

BOOL TransmitOneByte( UINT8 data )
{
    // Wait for the transmitter to be ready
    while(!I2CTransmitterIsReady(I2C2));

    // Transmit the byte
    if(I2CSendByte(I2C2, data) == I2C_MASTER_BUS_COLLISION)
    {
        DBPRINTF("Error: I2C Master Bus Collision\n");
        return FALSE;
    }

    // Wait for the transmission to finish
    while(!I2CTransmissionHasCompleted(I2C2));

    return TRUE;
}

void StopTransfer( void )
{
    I2C_STATUS  status;

    // Send the Stop signal
    I2CStop(I2C2);

    // Wait for the signal to complete
    do
    {
        status = I2CGetStatus(I2C2);

    } while ( !(status & I2C_STOP) );
}

My code:

int I2C_CLOCK_SPEED = 400000;

int actualClock;

// Configure Various I2C Options
I2CConfigure(I2C2, 0);

// Set Desired Operation Frequency
actualClock = I2CSetFrequency(I2C2, GetPeripheralClock(), I2C_CLOCK_SPEED);
if ( abs(actualClock-I2C_CLOCK_SPEED) > I2C_CLOCK_SPEED/10 ) {
    return -1;
}

// Enable the module
I2CEnable(I2C2, TRUE);

BYTE ADDR = 0x68<<1;

BIT WRITE = 0;
BIT READ = 1;

BYTE tmp;

StartTransfer(FALSE); // Read power management register

TransmitOneByte(ADDR|WRITE);
TransmitOneByte(0x75);

StartTransfer(TRUE);

TransmitOneByte(ADDR |READ);
I2CReceiverEnable(I2C2, TRUE);
while(!I2CReceivedDataIsAvailable(I2C2));
I2CAcknowledgeByte(I2C2, FALSE);
tmp = I2CGetByte(I2C2);

StopTransfer();

With a logic analyzer I can see that it seems to drop the address and send just the second byte of the three. It also fails to send the stop bit/return the bus to idle:

It should not be a hardware problem as the original demo works. I am using the xc32 compiler and MPLAB X IDE.


texts: I have constructed my circuit as shown in the picture. I am using raspberry pi to generate PWM to the transistor base and an MCP3008 to convert the anolog signals from the receiver. However, both the transmitter and receiver are not working at as intended. When probed with oscilloscope, the transmitter showed a constant 2VDC. The receiver showed a messy/unorganised/running millivolt analog signal (I'm not sure how to describe it). Sorry for the missing pictures of oscilloscope


texts: What are some of the real life example of the so called "tracking and regulation" problem in control theory?

texts:
Given a plant, we need to design a controller that takes in an input r and then ensure that steady state error between the output and input goes to zero while the system remains stable.

What is a realistic engineering system that this model and control technique is attempting to address?


texts:
Forgive the ignorance here, electricity is a weak point of mine and I'm trying to wrap my head around it all.
I'm trying to find out how many Ah exist in an old lead acid battery. I hooked up an inverter (500W) and a power strip with x3 150W lightbulbs (So 450W total) and hooked up a rPi to monitor the voltage. That setup ran for about ~7hrs (I know its not good to run these batteries to zero but its for science!).
I'm getting caught up between AC watts and DC watts, and possibly approaching this whole problem wrong. Using this calculator, 3 phase AC, 3150 Watts, 110V, with power factor of 1 yeilds ~16A, where as DC, 3150 Watts, 12V yeilds ~262A. So did I pull 16 amps or 262 amps out of this thing? Not trying to be super precise but rather that life this 200Ah battery still has.
Thanks for any feedback!
Edit 1
Inverter Link
Edit 2
Here is the graph of the voltage over time, any idea what in the world its doing in the second half?


texts: Connect multiple bipolar PSUs to one torroidal transformer with center tapped secondary winding

texts:
I'm currently starting my ventures into building a modular synthesizer in eurorack format and am currently using a single power supply like this with a 12V AC wall wart:

Source:
http://musicfromouterspace.com/analogsynth_new/WALLWARTSUPPLY/WALLWARTSUPPLY.php
As I will need another supply very soon and already ordered new rails for a bigger case I was thinking about using four of these supplies to be on the safe side (for an around 250 hp sized case, 10mA per hp as an estimate I found and also being reflected by the dimensions of commercially available case/supply combinations). The voltage regulators have a maximum output current of 1.5A, using four of them and splitting the modules on the different supplies would run each of them at around 250hp * 10mA/hp / 4 = 625mA. I think three would be enough as well, but using four would be easier for me to mount the power busses around the case.
The boards I created for the PSUs can also be used for a different kind of power supply:

Source:
http://musicfromouterspace.com/analogsynth_new/POWERSUPPLY2009/POWERSUPPLY2009.php
As I don't need the voltage regulation option I would stick to the 7812/7912 regulators.
Now my question is whether I can wire all four supplies safely to the same transformer? The 12V AC wall warts are quite expensive, especially if they have a high enough power rating (with the simple half bridge rectifier in the first PSU design I can only get half of the power out of them) I was looking at a transformer with ratings like 120 VA with 2x 12 V secondary each supplying up to 5A.
Here is a quick sketch of what I intended to do (only with two PSUs):


texts: Is it correct to say that the current through a resistor is PTAT(proportional to absolute temperature) if it increase when the temperature increases?


texts: What is the meaning of Angular Velocity Vector 100Hz of BNO055?

texts:
I am using an Arduino Nano with BNO055 Adafruit library.

The I2C speed is 400 kHz.

The Adafruit BNO055 Absolute Orientation Sensor mentions Angular Velocity Vector (100 Hz).

What does this 100 Hz mean?

Is it outputting angular velocity 16bit complete packets at 100 Hz speed? (Means 100 × 16-bit packets per second?)

Or is it the bit rate of outputting angular velocity 16-bit packet? (16b × 100/s = 1600 bps?)

How many Angular Velocity Vector frames actually I can get for 400 kHz I2C per second?


texts:
I want to implement a very simple delay function with more or less this look:

void delay(float seconds){
 int i;
 for(i=0; i<seconds*5000000; i++);
}

It is just based on the clock cycles (doing some tests I have assumed that 5000000 cycles are 1 second) but it doesn't work at all. Instead, it waits forever, but using

void delay(float cycles){
 int i;
 for(i=0; i<cycles; i++);
}

just work fine if for example I want for the program to wait 2 seconds making cycles=10000000, does anyone know why?


texts: What is the name of these little plastic things that protect wires from being cut into by the sharp edges of a drilled hole?


texts: How to represent the lag/settling time of a DC motor?

texts:
I have a 12V brushed DC motor and I need to calculate its lag/settling time or latency in other words. I did some experiments in which I gave motor DC supply of 5 volts recorded motor's steady-state speed using tachometer and then calculated the time it takes to reach steady-state using a stop-watch. Then I repeated the same experiment with following voltages: 1V, 2V, 7V, 10V, 11V, 12V.
I have recorded the readings in a table with Voltage, steady-state speed and time taken to reach steady-speed.

As I am working on a project, I need to present about my findings of the response time of the motor. My question is that is there any better way, some kind of standard way,  to represent the settling time of a motor, instead of associating it with a different voltages as I have done?

Or, is the settling time associated with only with the supply voltage of the motor mentioned in motor ratings which is in this case 12V?


texts: JFET Creating DC Offset In All-Pass Filter Output?

texts:
Full disclosure, this is a circuit I've constructed as part of a lab at school, however this isn't a specific question I need to answer in the report, this is something I've observed and can't explain and would to figure out for myself.

We're constructing a phasor effect filter by cascading four all-pass filters and summing this signal with the input signal. The filter imparts a +180 to 0 degree phase shift depending on the input frequency and the location of the pole/zero frequency. If each of the four filter imparts a 45 degree phase shift on an input sinusoid, then the sum of the input and the output of the cascade will be zero (the result of the consecutive  filters is a net of 180 degrees of phase shift).

Anyway, to control the pole/zero frequency we're using a JFET, and the main problem I've noticed is that adding the JFET to the circuit creates a DC offset in output which I cannot explain.

Here is the circuit for one of the filters. (R4 and R5 are just a voltage divider to get the gate voltage to the right level).

simulate this circuit – Schematic created using CircuitLab

I don't have a photo of the scope capture (though I may be able to grab one later), with the control voltage (Vc) tied to ground, which should turn the JFET fully on (with a R_DS_on resistance of about 300 ohms), the output has a positive DC offset. Removing the JFET from the circuit makes it disappear. The offset amplitude seems to have some sort of mild frequency dependence?

If it matters, the op amp we're using is a TL071.

I know I can mitigate this effect by AC coupling each stage, which I may vary well do, but I would like to figure out why this is occurring.

Any insight would be greatly appreciated.


texts: what does A64 with DDR3 bus mismatching cause?

texts:
I have a new design using A64 CPU and DDR3. I have first prototype with temperature problem.
I have already read a lot about mismatching problem, and I need to setup the layer stackup to get the requiered matching impedance. I have high temperature on the CPU & DDR3.
My question is: does mismatching cause this temperature rise? or I have to look for an other reason?
Thanks


texts: Steady State speed of rotor in following doubly excited system

texts:
I'm trying to analyse following system  -
A three phase armature winding on stator and on rotor field winding and both stator and rotor are cylindrical . And armature winding is connected to a three phase balance ACsupply while field winding is connected to a DC supply
At t=0 ;
Both supplies are open (off) and I start rotating rotor manually by applying external torque
At time t ;
When at time t rotor reaches to synchronous speed (equal to speed of rotating stator field ) at that instant I closed the both supplies and remove external torque
but I'm not sure what will be the steady State speed of rotor (what is best way to approach)  whether it keeps rotating with synchronous speed or it will stop or reach at a speed in between zero to synchronous speed ?
Assuming  following two cases -
1.no load torque after t

a contant load torque after t


texts: If I say something like "SPDT switch" it's assumed to be a non-momentary switch.  Is there standard nomenclature for unambiguously specifying a non-momentary switch?