texts: Single supply differential balanced preamp

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I'm trying to build a single supply balanced preamp for an electret mic. To further complicate matters, I'd like to impedance balance the mic output to take full advantage of the preamp's noise rejection capabilities. Here's what I've got so far:

There are a few problems with the circuit:

gain is not as expected. Removing the 2.2K resistor from pins 1 and 3 on the left of the diagram increases the gain substantially, but the cable is no longer impedance balanced.
there is a lot of hum, which is corrected by replacing the 470K resistor at pin 3 on the opamp with a wire to the voltage divider. However, I'm assuming that the opamp is no longer functioning as differential in this case.

I've run out of ideas - can anyone suggest anything that might remedy these problems?

Thanks

Thanks for the replies so far everyone. I've made a slight change to my original design that seems to have fixed the problem:

The only difference is that I moved the 470K resistor from pin 3 on the opamp to ground (as it would be in a split supply design) and connected pin 3 directly to the voltage divider. This has given me the desired result of the correct gain with the hum reduction. Is this the proper way to set up a single supply balanced differential opamp?

Thanks again


texts: In a points ignition system, should the condenser(capacitor) be attached to the coil terminal or to the breaker points

texts: Is there any difference in the function of the circuit if the capacitor has a shorter wire path to the coil or to the points?


texts:
I have a .OLB file for OrCAD schematic where there are multiple part in.

I an open the .OLB file using File => Open => Library, and I can also successfully place parts in a design.

From previous work I know that it is possible to print all the part on a single page, with each part in a frame.

How to show or print all the parts in an OrCAD library (OLB) file?


texts: U.S. Electricity Generation and Consumption and Average Utilization

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I would like to confirm that I am on the right track here with respect to electricity generation and consumption.

Given that in 2016 the total United States consumption of electricity was 4,137,100 gigawatt-hours (GWh).

Given that in 2016 the total installed electricity generation summer capacity (peak capacity) in the United States was 1,074.3 gigawatts.

Given that there are 8760 hours in a year.

Dividing consumption by hours ( 4,137,100 / 8760) results in 472.27 gigawatts.

472 gigawatts is about 44 percent of peak generation capacity.

So can I assume that the average utilization of our peak electricity production capacity over the course of a year is approximately 44 percent.

Thanks in advance


texts: Can zebra strips (elastomeric connectors) be cut to size?

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I have a handheld radio with an LCD display. Due to time and climate, the rubber in the elastomeric connector seems to have gone hard and as a result the LCD shows the usual signs of failure, letters and symbols blinking off and disappearing, etc.

I've looked hard and long for a matching replacement, but the only elastomeric connectors I can find online are of a very few, very specific sizes, and of course none of them match.

Can I just buy a larger one and cut it down? If so, how do I best do this, just a very sharp knife or do I need something else? Or did I miss a source where I can get them in more sizes? I can't even find one in the right thickness.


texts:
I have looked at how the Sigma-Delta ADC works and I understand it. However, it seems to me that there is not a lot of literature about the Sigma-Delta DAC.

I want to build a model of it in Simulink. Can someone explain to me how it works?


texts: When is PCB thermal destruction desirable?

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In the Wikipedia page for FR-4, it contains this excerpt:

FR-4 epoxy resin systems typically employ bromine, a halogen, to
facilitate flame-resistant properties in FR-4 glass epoxy laminates.
Some applications where thermal destruction of the material is a
desirable trait[citation needed] will still use G-10 non flame
resistant.

What are they talking about? Maxwell Smart self-destruct boards? I expect that valid reasons do exist.
I was investigating alternative composite materials for DIY PCB substrates for third world, especially including PET, the same material in polyester film caps, so if you know any, please let me know.


texts: What is the usage of Zero Ohm & MiliOhm Resistor?

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I am new to PCB design and I noticed that some schematics use 0Ω or 100mΩ resistors. What is their purpose and why do we need to use them in our PCB design?

Normally if we wish to probe how much current the load is taking, we put a jumper pin across the PCB trace (then measure current across the pin using a multimeter). Adding resistors for this purpose seems like it would waste a lot of PCB real-estate. Is this the sole reason why 100mΩ resistors are being placed (since I = V/0.1Ω) instead of a jumper pin?

If so, is there any consideration we should take when placing such a mΩ resistor on board so it doesn't affect the signal or behaviour of the circuit?


texts:
I'm trying to design a bidirectional current source for the purpose of measuring very small (0.0001 Ohm) resistances. I've come across this circuit:

I can see that the transistors are there to 'boost' the current but I don't understand the purpose of the 1K resistors and the capacitor. I also don't follow how I can increase the current rating of this pump to 1A.

I've simulated the circuit in LTSpice and it works very well at 100mA but when I try to source or sink 1A I only get 850mA out.

Any suggestions on increasing the current sourcing/sinking ability of the above circuit to 1A or any other suggestions for such a pump?


texts: Output drive vs. absolute max output current

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In many Texas Instruments datasheets (e.g. this one) there are two different stated values for current per output:

Output drive, stated as 4 mA at \$V_{cc}=5 V \$, page 1.
Continuous maximum current per output, stated as 25 mA, page 6.

My interpretation here is that if the device is operated at \$V_{cc}=5 V \$, TI guarantees that it can provide 4 mA per output. However, along with the second line it means that each output might also be able to provide \$4 mA < I_{output} < 25 mA \$ without damage, but the manufacturer doesn't recommend more than 4 mA at this supply voltage. Is this correct?


texts: Can you debug dsPIC33F series with PicKit 2?

texts: According to Pickit 2 readme it should be able to program it, but the dsPIC datasheet is not clear on debugging. Anyone had experiences with dsPIC33 and pickit 2?


texts: Can I tell if the HC-06 bluetooth is connected?

texts:
I seem to see that the HC-06 device behaves like a serial device with TX/RX.  I also understand that this needs to be "connected" to a blue tooth master to send/receive data.  Is there a way that I can tell from the HC-06 end whether or not it has a connection to its partner?

I plan to drive the HC-06 through an Arduino.


texts: What are the technical challenges to store electricity from lightning strikes?

texts:
I ask myself that question every time I watch a Tesla documentary.  So, let's get some answers down so the smart ones can think about it and we can clean-up our environment.  There is free electricity all around us for crying out loud ;)

If the question is too broad, then here is my simplified idea based on my limited electrical/electronics naval training which can be critiqued:

Erect a, possibly very tall, tower completely grounded to earth.  Connect one terminal of a possibly very large capacitor to the tower.  A current detection circuit is connected to the tower-to-earth circuit which, upon a lightening strike, switches the current from flowing to ground to flowing to the capacitor and charging it.  After the current ceases, the current detector switches back to ground the tower.  Then, draw current from the capacitor as needed.


texts: Uln2003 stepper motor controller chip fried?

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So I may have fried 6 boards and am a little unsure as to why.

The apparatus is a rubiks cube solver. A quick Google search says the torque required to rotate a face is between 38mnm and 247mnm which the motors should almost definitely be able to handle? Says full step 28byj-48 motor can  deliver 1.288nm of torque at 200ma.

I had them all individually working with the 5v  power supply of a raspberry pi. When I hooked up a 5vdc 3a transformer in parallel to each of the motor controllers they didn't spin (unsure if the apparatus has to much load for the motors to handle and thus overloaded the chip) or (unsure if I wired them incorrectly for some reason).

Do the motor controllers pull too much current if to much load is applied to the motor? Enough to break the transistors?

Maybe I rotated the motors a bit getting the cube in place forcing them to enduce voltages to the ic.

Now when I connect only 5v to any of them the chip overheats and I have to unplug it. Should I be buying more darlington transistor ics to replace them, am I missing something? Or should I be buying servos instead? (it would suit the application better, quicker spin etc)


texts: I have a soldering iron which allows the use of exchange-able tips, however I am unable to get certain tip types for my iron. Can I get a tip designed for a different iron if I match both the wattage rating and barrel size? It's a 50W iron with temperature control.


texts: Calculating discrete-time transfer function

texts:
I have a continuous function
\begin{equation}G_p(s) =  {1\over s^2} \end{equation}
which I am trying to combine with a zero order hold (with a sampling time of 1 second) to produce a discrete function. I started by combining the plant with the hold to obtain
\begin{equation} {(1-e^{-sT})\over s^3} \end{equation}
I know
\begin{equation} {(1-e^{-sT})} \end{equation} is equal to

\begin{equation} {(z-1)/z} \end{equation} and

\begin{equation} {1/s^3} \end{equation}
is equal to
\begin{equation} {T{^2}z^{-1}(1+z^{-1})\over (1-z^{-1})^3} \end{equation}
where T = 1.
Next, I multiplied these together to obtain,
\begin{equation} {z^{-1}(z-1)(1+z^{-1})\over z(1-z^{-1})^3} \end{equation}
which cancels down to
\begin{equation} {z^{-1}+z^{-2}\over z^3-2z^{2}+z} \end{equation}

When I convert the continuous function to a discrete function in matlab, I obtain
\begin{equation} {0.5z+0.5\over z^{2}-2z+1} \end{equation}

Why am I getting a different result than matlab? Is there something wrong with my method?


texts:
I am trying to analyze this circuit using norton.

Load (20 Ω) is connected between A and B.

I have removed the load and calculated the norton current to be -2A.

Now I try to calculate the norton resistance. Without the load, I short circuit the voltage source and remove the current source.

I end with this!!!

what??? the circuit is interrupted. There is no more A or B, or \$ V_{AB} = 0 \$

Is the norton resistance 0 or infinity?

How do I do that? How do I interpret that?


texts: Reading core loss graph of an inductor core

texts:
The question is somehow unrelated but I hope someone answers,

From the above graph, how can I get the value of 0.3T line @ 25kHz ? The scales in the axes confused my mind.


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I have a data signal, select and clock signal which I am sending from the FPGA to another chip and I need to constrain them so I don't violate setup/hold time etc.

I have tried to write and SDC file, but looking at the signal on the oscilloscope it doesn't seem to work, both clk and data transition happen at the same time.
Setup is min. 1 ns and hold time is 0.2 ns. I have assumed 0.5 ns clock jitter and 1 ns pcb travel time. The tx_clk is derived from a PLL (2MHz).
My sdc file looks like this:

create_clock -name clk_main -period 25.000 [get_ports {clk_main}]
derive_pll_clocks -create_base_clocks
derive_clock_uncertainty

set_output_delay -clock { u_nios_system|altpll_0|sd1|pll7|clk[1] } -max 2.5 [get_ports {tx_data[*] tx_sel}]
set_output_delay -clock { u_nios_system|altpll_0|sd1|pll7|clk[1] } -min -add_delay 0.3 [get_ports {tx_data[*] tx_sel}]

Am I misunderstanding how to calculate the appropriate delays or is there something wrong with the way i am applying the constraints?

Any help would be greatly appreciated.


texts: Why All DDR's (DDR, DDR2, DDR3) internal clock sets to 200MHz

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If we see the DDR Upgrade technology explain below the internal clock of all DDR is set to 200 MHz.

DDR

For example,DDR-400

Efficient frequency data bus is 400 MHz

True clock rate (IO buffer frequency) is 200 MHz

Internal clock rate of DDR memory is 200 MHz

So In order to transfer 1 bit per clock (via each data line) along the external bus operating at the effective clock rate of 400 MHz, 2 bits must be transferred per clock of the internal 200 MHz data bus.This data access scheme is also known as 2n-prefetch.

DDR2

DDR2-800 memory chips
Efficient frequency data bus is 800 MHz

IO buffer frequency is 400 MHz

Clock rate of the internal data bus is just 200 MHz

So in order to transfer 1 bit (via each data line) per clock of the external data bus operating at the efficient clock rate of 800 MHz, 4 bits must be transferred per
clock of the internal 200 MHz data bus.So this data access scheme is also known as 4n-prefetch.

DDR3

DDR3-1600 memory chips
Efficient frequency data bus is 1600 MHz

IO buffer frequency is 800 MHz

Clock rate of the internal data bus is just 200 MHz

So in order to transfer 1 bit (via each data line) per clock of the external data bus operating at the efficient clock rate of 1600 MHz, 8 bits must be transferred per
clock of the internal 200 MHz data bus.So this data access scheme is also known as 8n-prefetch.

Now Here is my question

1. For increasing the data Bus speed why can't we increase the internal clock?

2. If we increase the internal clock what are the consequences can be faced?


texts: Re-winding an inductor to decrease inductance

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I found a bunch of good size inductors in a bunch of old boards (16 of them, more to desolder). Luckily I had the service manual of said boards and I know the specs of the inductors: 22uH 9A 500V.

I need 15uH and 7uH inductors. How can I calculate how many turns to remove from the coil to get to the needed inductance? I don't have an L meter (that's a future project).

I counted the turns. There are about 50 turns of 1mm wire in a core that's about 21mm outer diameter, 9mm inner diameter and 8mm thick (I'm guessing the values from measuring and subtracting/adding the wire diameter).

The color of the core is a dark reddish-brown.


texts: Are permanent-magnet motors equally (in)efficient as motors vs. as generators?

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Given a permanent-magnet motor with an efficiency of 80% that converts 100W electrical input power into 80W mechanical output power, would the motor have the same efficiency if used as a generator?

In other words, would using the motor as a generator with 100W mechanical input power produce 80W electrical output power?

For what types of electric motors would this hold true or not hold true and for what reasons?


texts: liquid level switch and solenoid valve circuit

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I am trying to make sure that I have this circuit hooked up right before I actually put it to use. I’m planning to use the liquid level switch (McMaster PN:50195K93) to open the solenoid valve (McMaster PN:4639K151) and add water from the Dosing tank to the Feed tank when the liquid level is too low (see diagram below).

The liquid level switch and solenoid valve both operate on 120 VAC, but I just wanted to see if anyone can let me know if the circuit looks right. I feel like there should be a resistor between the outlet and the liquid level switch so that there is something for the voltage to drop across when the circuit is open, but I’m not sure.

Lastly, there are only two wires coming from the liquid level switch and solenoid valve (2 wires each), but is there a way to add a ground to the circuit or is that something that I shouldn't be worried about? The solenoid valve is partly made of metal (316SS) and the liquid level switch is plastic (polypropylene), but I don’t see any spot on the solenoid valve to attach a ground. Any help would be much appreciated.


texts: Can I connect directly a 3.7V 18650 li-ion battery to a mobile (cellphone)?

texts: If I remove the 3.7V battery from my mobile, is it possible to connect to the battery +/- terminals a 3.7V li-ion 18650 battery?


texts: Why is it "Vactrols" are not commonly used?

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I've been trying to get my hands on some Vactrols (opto-variable resistor) for a long time, unsuccessful. Not even digikey has them.

some examples: VTL5C2, VTL5C3, NSL32

Can't see them as "too expensive to manufacture" considering you can improvise one using an LED+LDR+Tape, but it's in no way as "linear" or robust as the actual components.

Anyone knows the story behind it?

Edit: So there are places where you can get them, but at least where I live it's something almost unheard of..
They look usefull in many ways (at least to me), yet I've seen them nowhere except some old audio equipment..

Edit2: Ok, so what could be the alternative to a vactrol if I require exactly that, a significant  resistance change controled by voltage, (MOSFET as resistor is not an option for me because of the very low resistance range). Is there such a device/equivalent circuit that allows all this with the simplicity of the vactrol? This is a hypothetical question, based on many compressor units I have seen and seems Hard to achieve such functionality in such a simple way, the closest I've seen are OTA based for closed loop circuit, but they arent nearly as simple as vactrols.


texts: Can I slow a CMOS output through an RC filter?

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Is it good practice to slow down the slew rate of a CMOS output by putting an RC filter on it? What happens with impedance matching after I do this? Or can I just set the RC filter with such a low cut-off that transmission line effects don't need to be considered?

The CMOS output that is concerned here has a minimum 10-90% rise time of 1ns. Since I am running a trace that is around 250mm from this output, I want to minimize signal integrity issues.


texts: A quick generic question about eagle cad footprints

texts: I am trying to make my circuit board using Eagle CAD and have found some ready made footprints of some 1206 size SMD resistors. Now I know 1206 is basically 3.1mmx1.55mm as a standard size however if I download one from the element14 website then the footprint is not made to scale(Its actually 132mmx68mm.) Is there any reason for this? It cant be useful in making a circuit and sending it off to a fab house because the size is incorrect.


texts: Kirchhoff's loop equation when there's a current source in it?

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How do you get the loop equation (using Kirchhoff's 2nd law) if there's a current source in it?
I mean, does the voltage after the current source decrease or increase?

Example:

I'm talking about loops B & C.


texts: LED Resistor Choice with changing voltage

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I'm planning on adding leds to a small quadcopter which runs on a 1s lipo battery. I am planning on attaching the leds straight to the battery rather than the regulated voltage the main circuit board uses.
The battery when fully charged has a voltage of 4.2 volts and a nominal voltage of 3.3.

Assuming an led with a 2.5v forward voltage and a 20Ma forward current. the calculations at either range result in either a 100ohm resistor (for 4.2 volts) or 47ohm resistor (for 3.3 volts).
What size resistor should I use? should I use the 100 ohm resistor and let the brightness dim towards the end of the battery life?

In general what is the best way of selecting components where the system is not complex enough to warrant using a voltage regulator?


texts: End of loop resistor or "terminator resistor"

texts:
In fire alarm control panel, I saw that at the end of the fire loop a 4.7kΩ resistor is used.

My question is why we use the value 4.7kΩ? Is their any law for this choice?


texts: Which filter is good for GSM transmeter design Butterworth, Chebyshev or Bessel?

texts: I have to select a filter design topology among Butterworth, Chebyshev or Bessel. Based on your experience, can you suggest which filter is the best for GSM transmitter design?


texts:
how can I calculate the value of the schottky diode?  I use 4 MOSFET N-channel IRF1404 instead of IRF510 in the schematic
The motor should withstand currents up to 100 A and 12v


texts: Can keypad common be connected to microcontroller?

texts:
I want to use a keypad with a microcontroller. An example schematic is shown below. The pins 1, 2 and 3 are inputs with internal pull up resistors enabled and the pin 4 is output set to LOW. The real application will have much more switches.

My question is about the pin 4. Can I ground the keypad through the microcontroller? Or is it somehow stupid? Id like to do so because it would give me flexibility to set the grounding pin in software and the circuit could be more easily changed later. The switches and the MCU are on different circuit boards connected with a cable. That way the switch board could be changed without much attention to pinout.

One potential problem i've thought is what will happen if someone depresses all the buttons at once. Then all the current from the pull up resistors would go to the pin 4. I calculated how much it would be but it turned out not to be a problem.

Is there something else to consider?

simulate this circuit – Schematic created using CircuitLab


texts: DC test equipment to see voltage extremes?

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I want to experiment with magnets and coils to produce voltage.  I need test equipment to find the highest positive voltages and the lowest negative voltages obtained during tests.

My needle driven testers move too quickly for me to accurately gauge them.  And my digital meter does not refresh fast enough to see the extremes.  I can't afford an expensive oscilloscope.

Is there an inexpensive software type oscilloscope or other test equipment you can recommend that will record the entire voltage wave form in order to see where the extremes fell?
.


texts: Finding the current flowing in parallel circuit

texts: Lets say we have a circuit with a voltage source and a 5 ohm resistor. The voltage source is 20 v and so the current flowing is 4 amperes (according to ohms law). Now, we add a short wire in parallel to the resistor (you can think of it as having a resistor whose resistance is 0 cpne ted in parallel with the first resistor. Finding the current flowing in each wire is hard since as you can see, we first need the equivalent resistance. The equivalent resistance is (1/((1/5)+(1/0))) and it turns out to be 0. Now using the current divider formula, each current yields 0 ampere which is wrong. Thanks


texts: I want to do make an and-gate but why do I get high when my swich is off?


texts:
We are trying to build an RC interface to transform a PPM signal from the RC (remote control) into a PWM signal for motor controls. The idea is to build a 2-channel robot that goes forward % back, right & left.

Right now we face the issue that the  that we intend to use PIC16F628A to generate this signal, but this chip only has 1 CCP port. As I understand it, the CCP pin is how the PIC detects external interrupts.

So how do I implement the 2 interrupts needed? Do I grab another PIC or is there any way I can use some other pins to handle the required interrupts?

Any help much appreciated

EDIT for clarification: PPM - pulse-position modulation:

The remote control will send a signal that has it's information stored in the duration of the uptime of the pulse. If there are no inputs, the receiver will transmit a pulse of 1.5ms. This will correspond to an output PWM of 0%, the motors that will receive this PWM will not be moving.

If the duration of the PPM pulse is 2ms, this means that the control is moving forward or to the right (depending on the channel being used), and 1ms if the control is moving back or to the left (again depending on the channel)

Currently we are using the PIC in capture mode, as soon as the rising edge of the pulse is detected, we start the timer, which is then only stopped once it detects the falling edge.

This will give us the information we need to send the PWM signal. 2ms means 100%, 1ms means -100%, and 1.5ms means 0% (motors off). An H-bridge will be used to correct the direction of the PWM for the negative values, but this has already been implemented.

We are using this PIC because it's what we have at our school, and some other teams have used it before and it has more references. If there exists another PIC that better does what we intend, please let me know as well, but I'm not sure that is necessary.


texts:
I am currently working on building a quadcopter with brushless motors. I decided to try to build the ESCs by myself with some MOSFETs. I am using an Uno as the main controller on the receiving end. Before I started building I want to verify that I will not destroy my motors.
What I am thinking on doing is sending a PWM signal to the MOSFETs which would turn each motor on and off in a fashion that would rotate the motor fully. Would this work without destroying the motors? I am using an 11.1v LiPo so there is a fair amount of current flowing. Also, would I need any current limiting resistors or can I just have a dead short through the windings?

Thanks


texts: Why current does not flow through the 8500 ohm resistor?

texts:
I solved the below problem with the think that the emitter current from Q1 is divided to two paths. One is from emitter to 8.5k resistor, and the other is to the base of the Q2. However, from the answer sheet, I found that the emitter current from Q1 does not flow through the 8.5k resistor.
I thought because the base resistance of Q2 is high enough so that we cannot neglect 8.5k resistor. Can anyone explain why am I wrong?

All the answers I found solved problem like the below, ignoring the current to the 8.5k resistor. However, assuming the emitter voltage of Q1, V_E1,
(β+1)I_B1 = V_E1 / 8.5k + I_B2
What could be the problem in this approach? Thx in advance


texts: Measuring Current, Resistance and power capacity of an Incandescent bulb

texts: We are making a cheap 1000w load bank, using 10 incandescent bulbs of 100 watts each, connected parallel to vary the load. On a 230V AC 50Hz Home Supply. I am able to measure the current, but when I measure the resistance it dosent match up V=IR. We are building a DC supply and we intend to test the rectified DC on the Load bank. I agree to P=VI and since I am able to measure both V & I, I should get P, but my concern is R dosen't add up and am concerned if I am missing something.


texts: is there any first order circuit with a second order derivative of supply voltage in equation

texts:
I wanted to check if there could possibly be any first order circuit but with a second-order-derivative of the supply voltage appearing in the circuit equation,

something like this for a capacitive circuit:

$$a * \frac{d(v)}{dt} + b * v = \frac{d^2(Vs)}{dt^2} + c * \frac{d(Vs)}{dt} + e * Vs$$

or like this for an inductive circuit:

$$a* \frac{d(i)}{dt} + b*i = \frac{d^2(Vs)}{dt^2} + c*\frac{d(Vs)}{dt} + e*Vs$$

or even a combination of a capacitor and an inductor.

where Vs is the supply voltage, and a,b,c,e are constants, and v is capacitor voltage and i is the inductor current.

thanks.


texts: Continuity of a current through an inductor

texts:
According to this website,
the current through an inductor is always continuous unless there is an infinite voltage or current.
but

simulate this circuit – Schematic created using CircuitLab
Now I know that the circuit was working before t=0 so the current on \$ i_{L1}(0^-)=10[A] \$ and \$ i_{L2}(0^-)=0[A]\$ and at t=0 they are connected in series so \$ i_{L1}=i_{L2} \$ so at least one of them has to be discontinuous.
Where is this "infinite voltage" coming from?


texts:
I am trying to find the associated input impedance to the SA605 mixer RF inputs. I have found several App notes associated with the Chip that discusses the design. On the datasheet they present the following:

My question is how do I use this information to find the associated impedance at 88.1MHz?


texts: Can the CMOS 4014b be used as a SIPO shift register?

texts: I'm currently working on a school project that requires the use of an 8-bit shift register. I collected the components for the project on the last day of school rather hurriedly, and I picked the first 8-bit shift register that I found, which was the CMOS 4014B IC. I'm now trying to wire it up, and I need it to be a SIPO shift register. I can find almost no resources for the chip's operation. The datasheet suggests that the ABCDEFGH pins are all parallel input pins; however the chip also has a serial input pin and a P/S control pin. I don't fully understand what the datasheet says about the P/S pin but it sounds to me that it enables serial inputs to the chip. Can I use it as a SIPO shift register? If so, which pins are used for the parallel outputs?


texts: Using Matlab to send digital signal from National Instruments device

texts: I currently have a circuit set up with an NI USB-6501 connected to a mux and was wondering how to use MATLAB to send a digital signal from the NI device to the mux.


texts: I have a question concerning the resonance (or anti-resonance) frequency of a circuit. Will taking into account frequency-dependent behavior of the passive components change (skin and proximity effect in resistors, and flux penetration in inductors) change the resonance frequency of the circuit?


texts:
I want to drive a strip of LEDs from a microcontroller using PWM to control the brightness. The strip I have takes about 1.5A at 12V. I'm only familiar with purely low power digital electronics so wanted to check if these assumptions are correct and get any advice :-

If I use an NPN transistor to drive this, the transistor when turned on will drop about 0.7v so will dissipate over 1Watt when turned on.
This would require a reasonably chunky transistor and a heat sink which I want to avoid if possible.
So I'd be better using a mosfet that has much lower resistance so I might be able to get away with a smaller one and perhaps no heatsink?
However looking at the spec of the various MOSFETs I can buy it looks like any that can pass this amount of current require considerably more than 3.3v I can get from my microcontroller to turn on fully.
So am I best to have a small NPN transistor switching 12v to the input of a mosfet to control the actual LED strip? (Sorry I can't draw a diagram on this computer but can add one later if needed)

Are my assumptions correct, and does anyone have any advice or a better way?
I'd also be interested in recommendations for suitable parts although that's not my main question.

(Edit: I looked for other posts that answered this and didn't find anything that was quite what I wanted, if someone has a link to a duplicate then please post it and I'll happily close the question).


texts: How is this piezoelectric effect converted to voltage?

texts:
The data-sheet of this accelerometer says:

  This piezoelectric accelerometer may be treated as a charge source.
  Its sensitivity is expressed in terms of charge per unit acceleration
  (pC/ms–2, pC/g).

Is it possible to convert this pC/g to V/g? How is it converted to voltage so that it is amplified?


texts:
I would like to build a simple control circuit for a 12v silicone heating pad. I think what I'm looking to make is a thermally controlled relay: I want current to flow when the temperature is below freezing and turn off when above freezing (or thereabouts - precise temperature control not necessary).

What could I use to sense and control temperature? I'm looking for small, simple, cheap and low power.


texts: A switching boost converter biasing a tube preamp - saturation issue

texts:
I am designing a 9V-battery powered tube preamp (for electric guitar), based on a Russian rod tube (1j24b). The latter is a pentode, and works with about 45V on its screen grid and at least 30V on its anode. I have used a LT1172 switcher to implement a switching boost converter, in order to convert the 9V from the battery to about 60V, 1mA for biasing the tube.

This is the boost converter:

simulate this circuit – Schematic created using CircuitLab

The voltage from the boost converter goes to the tube, which is biased this way:

simulate this circuit

(sorry for the bad symbol for the tube - I did not find anything else).

Here,
a: anode
f+: filament, positive
f-: filament, negative
g1: control grid
g2: screen grid
g3: suppressor grid
SCN: internal screen

Actual voltage readings from a digital multimeter are shown. The anodic current is about 1mA. No current is absorbed by grids and screen; the 1.2V filamentary power supply is obtained from the 9V battery through a voltage divider; the filament current is about 13mA.

The issue is that the output signal is saturated in the positive semiwave. A screenshot from an oscilloscope reading, with 500mV p-p input, 500 Hz, and 2V/div:

If the resistor on the anode is reduced, the gain reduces, but saturation always occurs at the same output signal amplitude (higher input signal). This suggests that the problem is not with the control grid, but with the anodic circuit.

Also, since saturation is in the positive semiwave, it happens when the input signal is in the negative semiwave and the anodic current is lower than its bias.

At the onset, saturation happens also in the negative semiwave, then slowly that part of the signal smooths out and the positive semiwave saturates further, up to the reported waveform.

Lastly, I note that the p-p output amplitude is roughly 8 V, which is the actual reading of the battery voltage when I powered up the circuit and took the screenshot. This seems to suggest that the amplitude of a varying signal at the output (thus, powered by the boost converter) cannot exceed the supply voltage to the boost converter. It seems to me that the problem is with the boost converter, but I do not understand it, nor have found any mention of such an issue in the design manual - so I do not know how to overcome it.

Any idea?


texts: Rotary encoders to ensure 2 wheel robot goes straight!

texts:
I have successfully counted the rotary encoders on the wheel of my robot so this is not a problem.

My problem is what to do with this number.

Basically, the bigger problem is that I need my robot to go straight and I want to do it using only two encoders (one on every wheel).

Even if I send the same amount of power to both motors the robot does not go straight. This is why I decided to use encoders, so no matter the power on the batteries, or the conditions of the motors; the robot will go straight.

So, now that I have successfully counted the "clicks" on the encoder I need to know what to do with the number to make sure the tow wheels are synchronized.

This is the code I am using (Arduino):

  digitalWrite(dirMotO, HIGH);
  digitalWrite(dirMotE, HIGH);
  //digitalWrite(motO, HIGH);
  analogWrite(motO, 150);
  //digitalWrite(motE, HIGH);
  analogWrite(motE, 150);

  PololuWheelEncoders::getCountsAndResetM1();
  PololuWheelEncoders::getCountsAndResetM2();

  while(PololuWheelEncoders::getCountsM1()<clicks && PololuWheelEncoders::getCountsM1()<clicks){
    if(PololuWheelEncoders::getCountsM1()>=clicks){
      digitalWrite(motO, LOW);
    }
    if(PololuWheelEncoders::getCountsM2()>=clicks){
      digitalWrite(motE, LOW);
    }
  }

I thought this code would make sure that if one wheel gets to counts before the other it would stop and wait for the other wheel but the robot does not go straight.

I would really appreciate some help on this.

Thank you!


texts:
I'm new to electronics and Arduino. I bought the Arduino starter pack and I did the first exercise: connect a LED and a resistor.

But after I tried to connect more LEDs, and when I connect 3 LEDs they light up little (they seem off if I don't look carefully).

Why is this happening?

I know that when I use only one LED, it has a potential difference of 2V and need 5 - 20mA or it will burn, so:

R=V/I => 5-2/0.015 = 200ohm <210ohm


texts: Is there such a thing as a "multi-way voltage selector" switch?

texts:
I'm looking for an 8 way DIP switch, that allows me to select between two different source voltage inputs. The most convenient would be a DIP switch with 10 pins: 2 inputs (e.g. +5 and +3.3) and 8 outputs. But of course an 8 way SPDT switch would do (24 pins), as I could just solder all the +5 and +3.3 input pins together.

At first I thought this would be the most common use of a DIP switch but I cannot seem to find such a switch.

Let me explain what I'm trying to do. I am making a breakout PC board for an Arduino Mega, which will have 8x RJ45 sockets (more accurately called 8P8C).

Each 8P8C socket will have 6 of the CAT6 cable cores reserved for breaking out IO pins, and the remaining two to power external devices.

I would like to be able to select the voltage supplied to external devices, individually for each connector. So I could choose that each CAT6 cable carries either 5V or 3.3V. But to reduce my board size I don't want 8 separate SPDT switches. Instead I'd like an 8-way DIP switch.

However upon looking, it seems DIP switches are almost exclusively SPST type. A quick google for "SPDT DIP" brings up a page on Mouser, however I cannot see any such switches.

This surprises me, as I would have thought the most common use for a DIP switch would be a "selector" switch of some kind.

Do these things exist, or have I misunderstood what I'm looking at?


texts:
Im trying to use a Freescale FRDM-KL25Z,

I have been looking at the datasheet to see if I can find the maximum oputput current of the pins with no luck, im assuming its 500mA since its powered via USB

I already have my code up and running, basically im using a potentiometer connected to my ADC to change the frequency from my PWM, it comes out at the port i assign however how can I drive a DC motor without blowing the FRDM-KL25Z or anything else, the first thing it came to mind was look in the internet i found several diagrams showing a zener diode to protect the motor, but i lack the knowlege of why is that zener there, and then i found the use of NPN transistors, however that would mean im using the PWM to open and close the transistor several times while i use an external power supply instead of the power provided by the board, so I ask here, is it possible to make the motor spin WITHOUT an external power supply?

This is the most complete circuit that I have found, but still im wondering if there is a better way to do it, also D3 is a normal rectifier diode instead of a Zener in this case

Heres another pick where they use a resistor to limit the current going to the transistor (i asume its in order to drop the output current as low as possible) while using an external power supply to feed the motor


texts: Verilog: Sampling short, external, asynchronous input signals on a FPGA

texts:
I want to sample an external, possibly very short interrupt signal in my FPGA softcore. I did some research in some digital logic design books, and found this solution, where A is the input signal. The problem here is that it is way too short to be sampled by the synchronous flipflop shown, so a latch is used:

I am now wondering how this can be implemented in Verilog for use in a FPGA, I do not know how to tell the synthesis tool to place a latch there. How can this be done? Also, the design doesn't show how to reset Q - in the plot, it stays high for the rest of the example. How do I reset the whole design to be ready for the next interrupt signal?

Additionally: Do I need to put this signal through a few chained flip-flops to combat metastability, or is this design safe as-is?


texts: Is the link between the earth/chasis terminal and the utility transformer established through a dedicated wire or the soil?

texts:
I was following a tutorial on power supply transformers and at the very beginning I have encountered the following illustration:

I added the names TG and HG for the LV transformer ground and the local ground nearby the house.

In the illustration it is not clear to me whether there is an actual wire between HG and TG or the soil establishes the connection.

My question is: in a modern power system would there be an actual wire between TG and HG or it is the soil itself provides the path?


texts:
I've been trying to work on a few problems, though I'm not sure how to rewrite this a few circuits using only NAND/NOR -->

an example is shown below;

How am I able to rewrite only using NAND + NOR gates if anyone is able to help me on this.

Thank you.


texts: MQ5 Gas Senor module - How to Callibrate

texts:
I have just bought MQ5 Gas Sensor module for Arduino, (http://www.dhgate.com/product/100-pcs-lot-gas-sensor-module-mq-5-lpg-natural/133345721.html)

According to the Data sheet,

  "Resistance value of MQ-5 is difference to various kinds and various
  concentration gases. So, When using this components, sensitivity
  adjustment is very necessary. we recommend that you calibrate the
  detector for 1000ppm H2 or LPG concentration in air and use value of
  Load resistance ( RL) about 20 KΩ(10KΩ to 47KΩ)."

It says to calibrate the detector to 1000ppm.
What is meant by ppm here ? is it the resistance ?

Also,
There is a knob through which i can very the resistance, but how am i supposed to know what is the current value of the resistance when i am changing it ?

Datasheet link: http://www.dfrobot.com/image/data/SEN0130/MQ-5.pdf


texts: What does the T stand for in AXI4-Stream's TDATA, TVALID, TREADY, etc.?

texts:
In the AXI4-Stream protocol, the names of the signal that make up a stream are prefixed with T: TDATA, TVALID, TREADY, TLAST, etc.

Does the T prefix have a meaning? "Transfer" comes to mind, but that term is also used in the (non-stream) AXI4 protocol, where the signal names are not prefixed with T.


texts: Driving a 14-pin with DFB laser using D2570H

texts:
For our project, we would like to use the D2570 DFB laser from Agere system since it has a built-in photodiode with a TEC sensor, thermistor and a bias-tee embedded in an 'all-in-one' package.
However, we don't understand the principle of the bias tee connected to the cathode of the laserdiode. How does it work? Normally, a bias tee consists of an inductor and a capacitor where AC current will be superimposed on DC current. This Bias tee would then be connected to the anode of the laser diode to modulate the current.
Further, the datasheet mentioned that pin 11 and pin 13 should be grounded, but should pin 8 to 10 also be grounded since it doesn't mentioned it?

A link to D2570H page 2:
https://www.digchip.com/datasheets/parts/datasheet/020/D2570H-pdf.php


texts:
I just finished to write a pretty complete design on ISE 14.7 targetting a Virtex7 device. The behavioural simulation (on Isim) takes a while but works perfectly.

Therefore, I tried to move to the next step adding a Time Constraint by double clicking on my top module -> User Constraints -> Create Timing Constraints in the ISE interface. This action triggered the synthesis and it's now more than 24 hours that ISE is trying to "Optimize" one of my module.

I don't mind about letting the program running for other 24 or 48 hours but I am suspecting that something is wrong with my design ... I know that it might be pretty eavy since I use many logic cores instances but I am afraid it doesn't justify the delay for the synthesis.

My design can be found at the following link:
https://dl.dropboxusercontent.com/u/12734577/fourier_QAM_modulator.zip

Does anyone have an idea about how to solve my problem ?

I thank you in advance,

Best regards

Edit:

For posteriority, the full code is available here; details and explanations can be found in the paper.


texts: Car Key Fob doesn't transmit RF, althougth everything else seems to be working

texts:
Before starting to describe the problem, I need to say that this is my first time posting on electronics.stackexchange. I don't have a deep knowledge of electronics but I usually can diagnose a problem. I work as a software developer for a company that works a lot with electronics, so my limited knowledge comes from that.
That issue that I bring you today is more of a personal one. I bought a used vehicle a couple of months ago (Peugeot 207) which came with two keys.

One key without remote control (only opens doors by using the lock). The only electronic aspect of this key is that it has the immobilizer needed to start the car.
One key with remote control (the original key from manufacture).

Right after buying the car, I noticed the problem. The remote control wasn't working. Nothing would happen whenever I clicked the buttons. It was only some days of persisting with methods of "synchronizing the key" that I found that the remote control was actually working, but only when right next to the steering wheel. I quickly found that the receiving module of the car is located on the steering wheel, so it made sense, the remote control was working but with an extremely low signal.
After searching the topic for some time online, most people with identical problems found it to be an issue with the battery contacts or the battery itself. At this point, I had already changed the battery to a new one, but for the sake of being sure, I changed again. I changed batteries twice with trusted brands and I even tried using a power supply directly connected to the contacts. Nothing different happen, the remote control would still work only next to the steering wheel.
At this point, I gave up for some days, I was wasting too much time on this issue and I was having no progress. When I decided to try again, I found that the remote control was not working at all now. Not even next to the steering wheel. I thought that maybe I had to synchronize the key again but that didn't work either.
This made me even more persistent in finding the source of this problem. I was yet to understand if this issue was from the key or from the vehicle module. I have no other key with remote control to compare with.
Luckily, I work in a place with a lot of electronic testing devices. So I decided to use them to diagnose this problem.
I started with the basic, is the PCB even reacting to the button presses? I used a multimeter to compare the consumption whenever I clicked a button. It was pretty obvious that it was working. When I click a button the consumption peaks at 11mA.
Great, that is good. But now the real test. I have the luck to have an RF analyzer at my work, this is the best I could have asked for. So, I configure it to 433Mhz and place the key inside the chamber while I press the buttons. That when I noticed, no RF is being transmitted at all. None that can be detected. I compared it with a key from a colleague and it was pretty obvious that the machine was working correctly.
So, this is what I have, a key with remote control that in every way seems to be working, but not transmitting any RF signal.
I thought to myself, it is probably the antenna, but where is the antenna (I am not great at electronics sorry). From online sources, everyone refers that the brown component (left top corner) is the antenna coil. But from what I found, that is the antenna for the immobilizer. The immobilizer is working great, so I don't think that will solve my issue.
I can't find anything online that tells which component can I try to replace. What are your thoughts on this? Any professional opinion is welcome.

Thanks for your time!


texts: LTspice .meas command: unexpected single fail in step when the rest passes ok

texts:
I have been working on an assignment for my uni course. The task is to simulate and present results of a simple bandpass filter.
I tried to perform analysis using .step and .meas commands as can be seen below:

Unfortunately the step analysis fails to find the f0 when the capacitance is 17nF (step 8) When i increase the number of steps some of them fail too.
Rest of the .meas commands executes properly and I don't know why it happens. The whole simulation also executes properly.
I managed to find that when I changed solver to normal got 2 fails in this simple 20 values sweep.
Maybe it has to do with my commands or initial simulation parameters like Gmin, Abstol, Reltol etc.

Please help :(

asc file can be downloaded from here: https://drive.google.com/open?id=1AwvurCTqInAp89SrHH47EMbKgvqiRny_


texts: I saw a video where a person wired a resistor to the outer pins of a potentiometer to lower the resistance. Does this work? And if it does, can I still use the wiper and an outer pin with it lowered? Here is the video for reference https://www.youtube.com/watch?v=W-TmOLPDLhc&t=66s.


texts: It is better to have a negative clock skew?

texts: Is it better to have a negative clock skew? Why? If we compare it with a positive clock skew, which is better?


texts: CMOS technology, use a NMOS or PMOS as series switch?

texts:
A general question regarding switches in CMOS. Have a look at the schematic below (symplified current mirror)

There is a input reference current, on/off switch, a PMOS mirror and the resulting output current. In literature I noticed that the switch is implemented as a PMOS, but sometimes also as a NMOS. Beside the difference in logic functionality, what are the differences? Which is prefered? Thanks in advance.


texts: Why does my op-amp circuit always give the same output?

texts:
I have an op-amp design same with the picture seen below with TL072.I have an analog sensor that goes as Vin. I am giving 3.3V from an arduino to power it. And reading values from an analog pin.

The problem is that the output gives constant 1.2 V while sensor and resistors are disconnected and 2.3V while they are connected.

r2=220 ohm|
rf=2.2k ohm|
sensor gives output between 0-200 mV

*Image taken from http://www.electronics-tutorials.ws/opamp/opamp_3.html


texts: Hi I make this class A amplifier but how to replace R5 (10 ohm/10 W) with transistor because its getting really hot and how to achieve up to 10 Watt with +/- supply. I have +/-25v with 4A please help


texts:
I'm trying to drive USB host as MSC and HID on STM32F4, I have one STM32F407 Discovery board and one custom design PCB based on STM32F407.

I'm using Keil compiler and ST std periph library, and for USB using STM32_USB-Host-Device_Lib_V2.1.0 (and V2.2.0). For MSC part after some tries it worked and know I can read and write data on USB flash. But for HID it doesn't work correctly. I've tested many projects on both boards with many HID devices (mouse, kbd, barcode scanner, ...), in all cases the board detects device attachment and its speed, but it doesn't proceed more. Actually it remains in HOST_CTRL_XFER state and doesn't complete the enumeration phase (I found this in debug mode, the MCU works but it loops in some functions).

As the ST document says it's an intermediate stage that should be passed:

But for me it doesn't pass successfully.

Edited:

I think I have problem with descriptor configuration for HID device, I don't know how I can edit the descriptor to pass successfully from enumeration phase.


texts: Can I use one pin as I2C clock or data AND as GPIO?

texts:
It happened to be that I run out of pins on ATmega48PA. So I have a pull-down buttons on the pins dedicated for I2C:

And now I need to add I2C bus to this device with as much backward compatibility as possibe.

The thing I'm going to implement is to keep buttons as it is with I2C devices on these ping as there are no buttons at all. And I hopefully will have both working.

By saying this I mean the following schematic:

Why am I so sure?

Both I2C and buttons works as "pull low" logic. So there will be no conflicting outputs with excess currents.
My controller will be I2C master. So I will be able to switch pins to GPIO mode, read the buttons ad go back again to I2C mode after that. Or do it vice versa: switch pins to I2C mode when I2C interaction will be needed.

The only thing I will not be able to avoid is that I2C bus become unusable while any button is pressed. I think I can deal with it.

The second thing I am afraiding of is that the button press can be treated by slave as I2C transmission and it will stuck with this wrong data. My only hope is that the slave will "forget" all wrong bits and it will not influence on the further communication.

So my questions is: does anyone experienced with such weird schematic? Did it work?


texts: VHDL - rand*real(2**32-1) : can this cause an overflow issue?

texts:
I'm studying VHDL implementations of multipliers: I found this one and i'm trying to modify it. Default word size is 8 bit and the design is working (both simulation and synthesis) for any size up to 30 bits. I want to set it to 32 and simulate in Vivado 2018.3.
Here's the test bench:

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use ieee.math_real.all;

entity tb_mult_booth_array is
  generic(
  word_size_a   : integer := 32;
  word_size_b   : integer := 32;
  use_pipelining : boolean := true
);
end tb_mult_booth_array;

architecture tb_arch of tb_mult_booth_array is

  constant no_of_rows : integer := integer(floor(real(word_size_b+2)/2.0));

  signal clk : std_logic := '1';
  signal rst : std_logic;

  signal a : std_logic_vector(word_size_a-1 downto 0);
  signal b : std_logic_vector(word_size_b-1 downto 0);
  signal p_dut,p_ref,p_refd : std_logic_vector(word_size_a+word_size_b-1 downto 0);

begin

  clk <= not clk after 5 ns;
  rst <= '1', '0' after 10 ns;

mult_booth_array_inst : entity work.mult_booth_array
  generic map (
    word_size_a   => word_size_a,
    word_size_b   => word_size_b,
    use_pipelining => use_pipelining
  )
  port map (
    clk_i => clk,
    rst_i => rst,
    ce_i  => '1',
    a_i   => a,
    b_i   => b,
    p_o   => p_dut
  );

  process
    variable seed1, seed2: positive;
    variable rand : real;
  begin
    a <= (others => '0');
    b <= (others => '0');

    -- Random Stimuli Generation
    loop
      uniform(seed1, seed2, rand);
      wait until clk'event and clk='0';
      a <= std_logic_vector(to_unsigned(integer(trunc(rand*real(2**word_size_a-1))),word_size_a));
     uniform(seed1, seed2, rand);
     b <=    std_logic_vector(to_unsigned(integer(trunc(rand*real(2**word_size_b-1))),word_size_b));
     p_ref <= std_logic_vector(unsigned(a) * unsigned(b));
    end loop;
 end process;

delay_ref: if use_pipelining generate
    ref_delay : entity work.register_chain
  generic map(
    word_size => word_size_a+word_size_b,
    delay => no_of_rows-1
  )
  port map(
    clk_i => clk,
    rst_i => rst,
    ce_i => '1',
    d_i => p_ref,
    q_o => p_refd
  );
end generate;

forward_ref: if not use_pipelining generate
    p_refd <= p_ref;
end generate;

process
variable seed1, seed2: positive;
variable rand : real;
begin
    wait until rst'event and rst='0';
    for i in 0 to no_of_rows-1 loop
       wait until clk'event and clk='0';
    end loop;
loop
    wait until clk'event and clk='0';
    assert (p_dut = p_refd) report "Test failure" severity warning;
end loop;
end process;

end architecture;

The simulation is halted at 1st clk negedge, with the error msg:

  ERROR: [Simulator 45-1] A fatal run-time error was detected.  Simulation cannot continue.

Vivado points to this line:

a <= std_logic_vector(to_unsigned(integer(trunc(rand*real(2**word_size_a-1))),word_size_a));

I was not able to find other infos in the logs. In the paper referenced in the opencores page they test operands up to 64 bits so I guess this should work.

Any hints?


texts: Amplifier noise output against source resistance

texts:
I’m doing an experiment measuring the noise output of a two stage amplifier with different source resistances.
I’ve found results for a range of resistances. I have plotted these results noise output in dB against source resistance on a log-linear graph (resistance plotted logarithmically.) I get an S shape.

I’m struggling to fully explain this shape.  With the noise model I have the noise would continue increasing at higher resistances.
Why does it start to flatten out? The amplifier is nowhere near saturation.


texts:
Checking Vishay AN54 using IL300 for current loops, the Figure 6 (Isolated 1 V to 5 V, 4 mA to 20 mA Transmitter) circuit is explained but I really don´t get exactly how it works.

Other interesting document on this IL300 device is here, where multiple circuit topologies are explained (included the one similar to the figure, in fig.15, page 8).

I have imported this design to LTSpice to check how it works.
After checking the simulation this is how I think it works (please correct me here if any of these points is not correct):

1.- K1 = K2 so IP1 = IP2.

2.- To set IP1 just take Vin and R1. IP1=Vin/R1

3.- As IP1 = IP2, current through R3 is equal to current through R1, IR3 = IR1.

4.- Due to negative feedback in U2, VR3 = VR4, so loop current can be configured changing the value of R4. Iloop = IR4

5.- 100pF capacitor is placed in order to avoid voltage ripple.

6.- Transistor is placed to reduce thermal drift of U1.

So, main operation of the whole circuit is more or less understood.

The main question comes when, checking the current at the output of U1, this current is exactly the same as the one through R1.

UPDATE

Please check the simulation and the analysis of the current in both U1 output and R1 output:

Please keep in mind current sign just depends on how it is being measured...if the current is measured at the base of the transistor, both R1 and U1 output current are exactly the same.

Can anyone help me here to explain how the current in R1 is being replicated at the output of U1? I still don´t get it.


texts: Why more bandwidth means more bit rate per second?

texts:
According to this link ( and some other sources I have found ) more bandwidth on a wire means more bit rates per second...

Can someone try to explain why this is so as simple as possible?

This is all I know so far ( that I was able to learn by myself: )

-> Data is sent through a wire using frequency modulation, meaning, the voltage on the wire changes over time. At the end node, this signal is decoded.

-> A voltage in a specific frequency can be sent over a wire. ( Like a voltage change with a frequency of 5 Hz. ) That will be a sinusoidal signal.

-> To represent a data ( something like 10111001 ), you need to mix up a number of voltages in different frequencies so that it looks something more like:

My exact questions are:

-> Can this be done with any frequencies that is chosen? For example, can I achieve the desired signal with using frequencies between 10 - 20 Herz, OR 50 to 60 Herz? Or do I need specific frequencies?

-> How does the bandwidth ( the frequency range I can use ) affect, how fast the signal goes on the wire? ( the bit rate? )

I am all trying to learn this stuff by myself with not much of an Electrical Engineering background, so if you can try to keep it simple, it would be very helpful.

Also any advise on background info that I require first is much appreciated.


texts:
I am trying to send some hex data over TCP using SIM900A module. But the sequence of data has a byte with value of 0x1B which is the escape character. As a result the module terminates the command immediately.

Does anyone know by which I can overcome this problem?

I am trying to access the google maps (http://www.google.com/glm/mmap) api. It needs some data that should be some hex characters. Some sample data array of the format (0x12,0x15,0x1b.....) that needs to be posted. So I am using the following commands

AT+CIPSTART="TCP","www.google.com","80"
AT+CIPSEND

So here I get the > prompt from the module. So I send the following data afterwards

POST maps/glm HTTP1/0
Content-type: application/binary
Content-length: 100

After this I send the hex data. So I am using linux echo to send the hex data. So I send as

echo -ne "/x12/x15/1b/......." > /dev/ttyUSB1

But in sim900 usually we send 0x1A(ctrl+z) to send the data to the server. But it also uses (Esc) or 0x1B to exit sending the data. So this 0x1b I am sending causes a exit skipping the rest of data.


texts: Why do two transfer functions of a circuit have same denominator?

texts:
I am investigating a linearised common-emitter circuit of the form:

simulate this circuit – Schematic created using CircuitLab

I am interested in the isolated transfer functions of each input to the voltage across the load. The power supply to the output takes the form:

$$
H_\mathrm{sup}(j\omega) = \frac{b_3 s^3 + b_2 s_2 + b_1 s}{a_3 s_3 + a_2 s^2 + a_1 s + 1}
$$

And for input to output:
$$
H_\mathrm{in}(j\omega) = \frac{b_3 s^3 + b_2 s_2}{a_3 s_3 + a_2 s^2 + a_1 s + 1}
$$
where all coefficients have been normalised by the constant term \$a_0\$.

From the investigation I have found that for both transfer functions, each coefficient \$a_x\$ (where \$x\$ relates to the power of the Laplace variable) are exactly equal for both transfer functions.

Why is this?
How is it best to illustrate this property, e.g. Signal flow diagram, block diagram, etc. to see why this is the case intuitively?


texts: How can PCB trace have 50 ohm impedance regardless of length and signal frequency?

texts:
Hmm, this seems to be just another question on line impedances.

I understand that when we say "transmission line" effects we talk about things like cross talk, reflections and ringing (I guess that is just about it). These effects are not present at low frequencies where the PCB trace behaves like an "ideal" transmission medium, more like we expect a wire to behave in our early school days.

I also understand that the 50 ohm value comes not from the line resistance which is going to be very small and less than 1 ohm. This value comes from the ratio of L and C on the line. Changing C by changing the trace height above ground plane or changing L by changing the trace width shall change the impedance of the line.

We all know that the reactance of L and C is dependant on the signal frequency as well. Now my questions:

Why should we not call this as line reactance only rather than line impedance?
How can it be just 50 ohm? It has to be signal frequency dependent right?
E.g 50 ohm at 1 MHz
Will the world end if I chose to do a 100 ohm or 25 ohm trace instead?  I know that while we like to say 50 ohm as a magic number, it will be within some range around 50 ohm and not 50.0000 ohm exactly.
Is there any time when the actual resistance of a PCB trace may matter?


texts:
Many farms use electric fences to discourage animals breaking through to neighbouring paddocks.

These electric fences have regular (say once per second) high-voltage spikes of between around 100 V and 120 kV.

Would it be possible to "harvest" this as a power supply for remotely-deployed electronics? e.g. a coil wrapped round the electric fence wire, with a high resistance to ground, trickle-charging a battery.

Ideas welcome.


texts: Playing with a shift register and some LEDs

texts:
Building on this question, I've now got a shift register to play with, and I've been trying to work it manually with a couple of switches, like so:

I have resistors (2.2K) between the switches and VCC, even though that's not shown in the schematic. It doesn't work, though.

When I press the clock switch, sometimes an LED will light, and sometimes it won't. Sometimes several LEDs light. Never does it "shift" a zero "bit". If I just hit the input switch a bunch of times, it shifts in bits, sometimes one at a time, sometimes several at a time.

What gives? What have I done wrong here?


texts: Can I use a 78S05 regulator in place of 78L05?

texts:
I'm trying to do this circuit :

Can I use a 78S05 regulator instead of the 78L05? Or I need the 78L05 to realize this circuit.

Best regards


texts:
I wanted to fix an older divice of my grandma and figured out that a resistor has a crack.
So I tried myself on color-tables but the two gold rings in the middle are confusing to me.
Any hint is appreciated.
Ring-colors from left to right on the picture are violet, gold, gold, black, brown (on a blue body).


texts: Voltage divider, how do I calculate Vout?

texts:
I try my best to translate it.

\$Z_2 = 20\Omega\$, and \$Z_1\$ is resistance variable which ranges from \$10\Omega\$ to \$200\Omega\$

I need to calculate \$V_{out}\$ for the value \$Z_1 = 15\Omega\$ and again for \$160\Omega\$.

This is some information  I've tried

$$V_{out} = V_{in} \times \frac{I\times Z_2}{I\times(Z_1 + Z_2)}$$

Therefore

$$V_{out} = V_{in} \times \frac{Z_2}{Z_1 + Z_2}$$

Now I can get the \$V_{in}\$ (from a book) using the equation:

$$V_{in} = I (Z_1 + Z_2)$$

But if I combine \$V_{in}\$ into the equation, I get:

$$V_{out} = V_{in} \times \frac{Z_2}{Z_1 + Z_2}$$

$$V_{out} = I\times(Z_1 + Z_2) \times \frac{Z_2}{Z_1 + Z_2}$$

Which is missing information for the \$I\$?

Is there another way I could calculate the \$V_{out}\$? or this question is just formed incorrectly?


texts:
I want to use HCPL3700 optocoupler for sensing 220V (line).
I design a circuit but I want to ask some questions.

HCPL3700 is an open-collector output so I pull-up Vout. In AC voltage sensing some people says HCPL3700 is halted on zero-cross so I add a cap (C30) is this (10uF) enough for zero-cross pulse filtering?
I add a resistor (R29) (100k) to the input of HCPL3700 for 200V threshold is this ok?

thanks


texts: Build an FSK modulator using the HB100's transmitting signal

texts: I want to use the HB100 to make an FSK modulation on a microwave signal. The reason why I use HB100 is that in this way the RF circuit is ready. I thought about doing an FSK modulator like the scheme attached in this question and I would ask you if it is feasible. I make the modulation on a low frequency VCO (for example 1 kHz) controlled by a microcontroller, the I put HB100's transmitter signal and this low frequency signal to an rf mixer like the mixer implemented in the HB100. In this way I get a signal centered at 10.525 GHz that varies its frequency depending by the low frequency VCO (fHB100 + f0, fHB100 - f0). Can I use this approach to make an FSK modulation?


texts: Voltage at UART Tx and Rx pins with no connections

texts: What should I expect at UART Tx and Rx pins of 8051 when the pins are not connected, i.e hanging. Using multimeter, I found Rx pin high, and Tx pin low. Is it OK?


texts:
What does it mean code for TFT LCD rgb?

i dont know ("%s") or ("\x12" "kwh") or "%4u:%02U:%02u" ?


texts: Understanding the the setup of a Timer on an STM32F10x

texts:
I'm trying to understand how to correctly setup the timer on an STM32F10x.

The board is running with an external crystal of 16 MHz, and I'm using the PLL:

/* PLLCLK = 16MHz / 2 * 9 = 72 MHz */
RCC_PLLConfig(RCC_PLLSource_HSE_Div2, RCC_PLLMul_9);

so the board is running at 72Mhz. I'm configuring the timer as follows:

RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE);
TIM_TimeBaseInitTypeDef timerInitstructure;
timerInitstructure.TIM_Prescaler =72000-1;
timerInitstructure.TIM_CounterMode = TIM_CounterMode_Up;
timerInitstructure.TIM_Period=1;
timerInitstructure.TIM_ClockDivision = TIM_CKD_DIV1;
timerInitstructure.TIM_RepetitionCounter=0;
TIM_TimeBaseInit(TIM3,&timerInitstructure);
TIM_ITConfig(TIM3, TIM_IT_Update, ENABLE);
TIM_Cmd(TIM3,ENABLE);

To make sure that I set the correct frequency I am toggling a pin using the interrupt, but when I measure with the scope I get 2.784 kHz. Can anyone tell me why I get this frequency?


texts: Performance issues when using CMOS SR Latch with 180nm transistor models in circuit simulator

texts:
I am trying to incorporate a CMOS SR latch made with 180nm Level +49 transistors into a larger circuit but am running into issues. I am hoping this community can point me in the right direction of possible solutions.

First, I made a CMOS NOR gate with the transistor model in xyce (an open source circuit simulator) and built them into an SR latch. I was able to get the NOR gate and SR latch working, or so it seems. I used the following configuration exactly as shown.

This is the SR latch behavior for the SR latch I built with the transistors:
(I am using matlab to read the csv outputs)..

V(2) is RESET, V(3) is SET, V(4) is Q

And this is the behavior for a xyce SR latch built with ideal NOR gates

(not a fast pullup time but decent enough); note: These simulations are about 300ms long

I also want to include some parameters I am using for the SR latch made with ideal NOR gates in case they ring a bell for anyone..

    * Ideal NOR gate default parameters:

.param R1HI=5 R1LO=200 R0HI=200 R0LO=5 RIN=1000 R1=100

.param SW=5.e-9  CAPOUT=1.e-12  CAPIN=1.e-12

*SR Latch Digital model card

.model DMOD DIG ( CLO=CAPOUT  CHI=CAPOUT

+ S0RLO=R0LO  S0RHI=R0HI  S0TSW=SW

+ S0VLO=-1  S0VHI=1.1 ;logic margins LOW

+ S1RLO=R1LO  S1RHI=R1HI  S1TSW=SW

+ S1VLO=1.7  S1VHI=1.9  ;logic margins HIGH

+ RLOAD=RIN   CLOAD=CAPIN

+ DELAY=2ns )

I built these and tested them in separate files even using the same node names.

However, when I incorporated them into the larger circuit, the ideal SR latch worked in unison with the larger circuit as expected, but the CMOS latch had erratic behavior with no distinguishable pattern. The simulator still generated output but the behavior was not at all what was expected. The CMOS SR latch stopped resembling an SR latch, as far as I can tell. This is strange because they both had pretty much identical behavior in their respective simuations (save for the pullup time on the ideal latch).

Are there any modifications to the CMOS circuit that could resolve an issue like this?
What test could I perform on the SR latch, nor gate, or nmos/pmos transistor to see what is causing this difference in behavior?
Kind of following up on the first bullet point, when building gates out of transistor models like these, should I include external resistances/capacitances/etc to eliminate possible strange behavior? etc

Any help appreciated! I will do my best to clear up questions if there are any.


texts: Mains transformer blew up amplifier, incorrect description in wiring instructions?

texts:
I am assembling a power amplifier from a kit I purchased from Velleman (Module: VM100). With the amplifier I purchased this mains toroidal transformer - .

The amplifier came with these instructions:

Here is a photo of the PCB, you can see the male connectors are labelled as such (the manual states Y: yellow, R: Red, B: Blue, G: Grey):

Yellow : 25-30V AC
Red : AC-0
Grey : 25-30V AC-0
Blue : AC

I connected the transformer as described, however when I powered up the transformer the amp blew up. I suspect this is because I have connected the transformer to the amplifier incorrectly, and on closer inspection of the Transformer I found the following wire labelling:

Pri:

0.....240V 50-60Hz (Brown Blue)

Sec:

0.....30V-2A (Red Yellow)
0.....30V-2A (Black Grey)

If I am reading this correctly I should have connected this transformer to the PCB is as follows:

Connect the following wires to mains:

Brown = 0V (Neutral wire)
Blue = 240V (Live wire)

And the following to the PCB:

Red = AC-0
Yellow = 25-30V AC
Grey = 25-30V AC-0
Black = AC (not Blue = AC)

Is this new reconfiguration correct?


texts:
I have an experiment where I plug a sensor to an ESD (Electrostatic Discharge) protection circuit. Sensors are very expensive and very sensitive to ESD.
I have tested my protection circuit it is working fine. I was wondering what is an easy way to build a ESD sensitive device, so every time I test my ESD protection circuit, I don't plug my expensive sensor to test. I want to have an alternative to my sensor, for example something that if I touch when I'm not grounded, would blow or show me that it is sensitive to ESD. OR in general would let me know that the environment has some static charges.

I'm not an expert in circuits, I have googled my question and found very complex circuits. I would like to hear your opinions.

Thank you in advance,


texts:
For some active filter circuit I have derived the following transfer function:
$$T(s) = \frac12\cdot{s^2+{1\over2R_1^2C_1^2}\over s^2+{1\over R_1C_1}s+{1\over2R_1^2C_1^2}}$$

I need to show that this circuit implements a notch filter, for which the transfer function is given in the following form:
$$T(s)_\text{NF}={s^2+\omega_0^2\over s^2+{\omega_0\over Q}s+\omega_0^2}$$

It is easy to see that my transfer functions almost corresponds to the given form except for the constant factor of \$\frac12\$ before the fraction. Should I be bothered by this factor, i.e, does it influence the derived TF to be not of a notch filter TF form?


texts: Charging 18650 battery with built-in PCb

texts:
How would I charge an 18650 battery with a built-in protection circuit?
This is for an infrared camera. I normally could charging the device via micro usb but port broke.
4 wires are soldered to the PCB. I assume 2 are used for charging the battery and 2 are for powering this device. All wires go to a 4 pin connector which plugs into the device. The only hobby chargers I saw with you 4 pin ports were for charging 3S cells. I think connector is a male JST.

PJ-100-D is printed on the other side of the circular board.
Thank you


texts: How to identify transformer pin out in genuine mobile charger?

texts:
can't find any information about it on Internet  ,does there any practical procedure  to identify, like removing it from circuit and measuring its coils resistance.
or a website that i can find information about it.as i think it is sort of fly-back oscillator.
Thanks in advance.


texts:
DISCLAIMER: I am just tinkering with electrical engineering and can barely do the basics yet.

Background

I have done a little work on a breadboard connected to my Raspberry Pi, but today I wanted to put my new battery pack to use. I set up a simple circuit to control the brightness of an LED with a potentiometer and it worked just fine. Then in my usual how-much-can-I-change-before-it-breaks fashion, I removed the resistor to see how bright I could make the LED before it burned out (yes I know it was a dumb idea). I got the LED up until it turned red (it was a green led) and then started smelling something burning. The LED was fine but the potentimeter was what was making the smell. Yes, I unhooked everything as soon as I stared smelling burning.

Question

What did I do? I looked online and didn't find anything about burning out a potentimeter.


texts:
I'm trying to understand solar panel Maximum Power Point Tracking theory and how it is done practically for charging battery banks.

I think I understand MPPT in a general sense: the solar panel has VI curves which define a specific load in which you will extract the most power. These curves change with environment conditions like light levels, temperature, etc, so the tracking algorithm tries to dynamically find the best load value. It's usually not practical to just change the actual end load that we want to power (and often can't), so we use a switch mode power supply to adjust the output voltage, changing the output current. To balance Pout = Pin (assuming ideal switcher), the panel's current draw changes, and this is how we adjust the operating point on the panel's VI curves.

So my question is this: We are changing the output voltage to get the maximum power, but don't batteries typically need a specific voltage to charge them efficiently? Is it better to shoot for MPP of the solar panel or shoot for optimal charging conditions for the battery?


texts: Need to use decoded image as reference image, not original. Why?

texts:
I'm trying to review the P frame.
but I don't understand this
"Why not we use original image instead decoded image to P-frame?"


texts: Propeller from Parallax Inc.(P8X32A-D40) books

texts:
I am keen on microelectronics and micro controllers for robotics and currently using  a  micro controller in a 40-pin DIL package(P8X32A-D40), Propeller from Parallax Inc.
I was wondering if any who also uses this and can recommend some good books on the Propeller and cogs and applications.,


texts: What effect does switching frequency have on a switching booster circuit?

texts: In what cases/application is a high switching frequency desired and vice-versa? I'm trying to choose a DC-DC booster IC and I don't quite know how the switching frequency will affect the circuit. Only thing I can think of now is the speed of the Schottky diode that goes after the inductor, but other than that, I don't know. Google isn't very helpful on this one (or maybe I 'm not use the right keywords) so any help is greatly appreciated.


texts: Understanding the relationship between LoRa chips, chirps, symbols and bits

texts:
I'm trying to understand the actual relationship between LoRa chips, "chirps", symbols and bits. I don't mean just the equations that relate the various rates, but actually how these things relate quantitatively.
The Semtech document AN1200.22 LoRa™ Modulation Basics contains some basic equations and definitions related to various rates. As far as I can understand, the chip rate CR is always going to be numerically equal to the selected bandwidth. So if the selected bandwidth = 125 kHz, the chip rate is 125,000 chips/second. The symbol BW is then used interchangeably with chip rate.
The spreading factor relates chips and symbols. \$2^{SF} chips = 1 \ symbol\$. So the symbol rate SR is related to the chip rate (as BW):
\$SR = \frac{BW}{2^{SF}}\$
In the implementation of the LoRa modulation, every 4 bits of data will be encoded as 5, 6, 7, or 8 total bits as a form of forward error correction, and these are selected by setting the coding rate CR = 1, 2, 3, 4. So the actual rate of user data bits must be reduced by the factor:
\$BR_{user} = BR\frac{4}{4+CR}\$.

This concludes what I think I understand so far. I don't know what chips or symbols actually are. For example, there is an extra SF term in the final relationship between bandwidth and raw bit rate, which I do not understand.
\$BR =  SF\frac{BW}{2^{SF}}\ = SF \cdot SR\$
This says that one symbol is equivalent to SR bits, or between 6 and 12 bits in the LoRa available settings. Is that correct?
I have found here (also, watch after 13:00 in this video EDIT: video of the more recent and more in-depth talk) a definition of chirp rate as the first time derivative of frequency df/dt. That would give it units of \$time^{-2}\$ but the expression shown there is different. Perhaps this is the rate of complete sweeps (chirps), rather than the rate of change of frequency?

above: screen shot from here.
Question: What is the relationship between chips and "chirps" - can the chips be visually distinguished in the spectrograms - can one see where each chip begins and ends? Also, are there indeed between 6 and 12 bits per symbol?

Below are some illustrations of spectrograms of LoRa signals. It looks like during each chirp, there is roughly on average one instantaneous shift in frequency per nominal chirp period, but I don't know if that holds in general.

above: LoRa spectrogram from LinkLabs: "What is LoRa?".

above: LoRa spectrogram from Decoding the LoRa IOT Protocol with an RTL-SDR.

above: screen shot from Reversing LoRa (PDF).

above: from Decoding LoRa - cropped from here.


texts: Leakage Current of Battery in Parallel with Capacitor

texts:
I am creating a microprocessor design that will have a battery backup in case the mains power goes down.

My plan is to have 2 3.6 V batteries in parallel, so that either may be swapped in/out while maintaining battery power to the CPU.

The batteries are rated 2.4 Ah, and the CPU should only draw about 8 uA when on battery backup; the CPU should survive for a very long time on battery power.

I want to also include a cap in parallel with the batteries, that would keep the CPU powered for minutes / hours. My question is, if I used something like this http://media.digikey.com/pdf/Data%20Sheets/United%20Chemi-Con%20PDFs/KMH%20Series.pdf which has a leakage current of approximately 3 mA, am I going to start burning the batteries through the Cap's leakage current?

Reference schematic below. Assume SW1 only closes once main's power has been disconnected.

simulate this circuit – Schematic created using CircuitLab

So here are my questions:

Is the 3 mA leakage current in the datasheet realistic? Or is this a drastic over-estimate?
Are there alternative cap's which have leakage currents levels of magnitudes lower?
Will the batteries leak through the cap even when "SW1" is open?
Are there any widely-used ways to implement my idea (cap in parallel) that won't drain the batteries?


texts: How to determine lithium battery versus the internal battery cells

texts:
I have a Lithium Ion Polymer battery (EEMB LP963450) and I am trying to determine how many cells are in it, and something is not making sense with my math.

Here's the formula I am using:

Determine the number of cells in a Lithium Battery:

Battery Voltage Rating / Nominal Voltage Rating = # of cells in series
Battery Capacity / Nominal Capacity = # of cells in parallel
number of cells in series X # of cells in parallel = # of cells total

Here are the battery specs (at least what I have found):

Battery Voltage Rating = 3.7 V (uncertain)
Nominal Voltage Rating = 3.7 V
Battery Capacity = 1800 mAh (uncertain)
Nominal Capacity = 1800 mAh

Based on the numbers above, here's my math:

3.7 / 3.7 = 1
1800 / 1800 = 1
1 X 1 = 1 cell

About this point, you may be bored and asking, "yeah, so, what's the problem?" (if you think I have this correct)

So here's the problem.

With only one cell, this single-cell battery has 6.67WH ((mAh)*(V)/1000 = (Wh)) which is considerably over the 2.7WH per Lithium Ion cell for unlimited travel allowed on airplanes.

But this is a small battery so I am thinking I have something incorrect.

Maybe the Battery Voltage Rating and Capacity are not correct?

Maybe I'm plugging the numbers in wrong or not converting something I should be?

So my question is,

How do you determine how many cells are in a Lithium battery?

FYI Data

Specs for this battery can be found here
US Federal Law on Lithium battery air travel
I've found this FedEx document too but all they do is mention you have '6 cells' and don't say how they got that number.

From EEMB:

  Dear Phil,   Thanks for your inquiry. This is Donna from EEMB, glad to
  work with you.

  For the model LP963450( 3.7V/1800mAh), it is a single cell, and your
  following understanding is correct.

  For the battery pack, it is consisting of the cells connected in
  series or in parallel. If the battery stacked in series, the voltage
  rating will be added multiply. If the battery satcked in parallel, the
  capacity will be added in multiply.  The following example is for your
  ref.

  1) model LP963450-2S  ( 7.4V/ 1800mAh), 2 cells in series, the voltage
  was added

  2)model LP963450-3P ( 3.7V/ 5400mAh), 3cells in parallel, the capacity
  was added

  3)2LP963450-3 (7.4V/5400mAh), the battery stacked with 3 cells in
  parallel , and then 2 battery pack in series , totally 6 cells

  Hope it is clear. Any problems, please let me know. Have a nice day.

A great article on Lithium-polymer batteries:
The Basics of Lithium-Polymer Batteries


texts:
I am using MPLABX simulator to simulate some code. I want to create some signal for an external pin of the MCU using the stimulus. To do this I need to attach an .scl file with the code. I do have the code as a text file.

How do I convert this text file to a .scl file ?


texts:
I have a circuit board I took from a broken wireless headset, and I plan of reusing it by soldering a 3.5mm plug to where the speakers was connected. So I could plugin whatever headset I want. But today I noticed that the circuit board have 4 pole/pins. L- L+ R- R+ while the plug only have R+ L+ and ground. Can I simply take R- and L- and solder them both to ground, or do I need a components to combined them first?

Normally I just trial an error, but since I only have one board I don't want to damage it by doing something dumb.


texts: What's the difference between large and small scale signals

texts:
While reading about signal propagation, you encounter the two confusing terms, large-scale and small-scale. What's the difference between them! And what's the difference between the large-scale and small-scale SNR.

Regards,


texts:
I read in a book that image-1 is not a valid connection since you apply on the same two terminals a and b different voltages however image -2 is said to be a valid connection and I don't understand why since even if i have the 5A current source it supplies current and does not effect on the voltages across it's terminals so the circuit remains with different voltages across it's terminals.

Thanks.


texts: Is it safe to put a lithium ion battery on the wheel of a bike?

texts: I am working on a project where I attach an LED strip, Arduino, and a power supply onto the wheels of a bike.  For the power supply I was looking at using an Anker portable charger (like this one: https://www.amazon.com/Anker-PowerCore-Lipstick-Sized-Generation-Batteries/dp/B005X1Y7I2/ref=sr_1_13?s=wireless&ie=UTF8&qid=1492907509&sr=1-13&keywords=anker)  I noticed that it had lithium ion battery cells though and I have heard that lithium ion can explode if it is cut.  What I am wondering is if it is safe to use that as the power supply on a bike wheel.  There is a possibility it could get hit pretty hard or cut in an accident if it got caught in the gears of a bike.  Would using AA batteries be any safer?


texts: How can I find the drain transfer function of a MOSFET on LTSpice?

texts:
I am trying to get the drain transfer function of a MOSFET by setting the drain to source voltage as the input and the gate to source voltage as the output. I created the following circuit in LTSpice:

When I run an AC simulation, the Bode plot shows no change in the gain with an increase in the frequency.

However, when I change the gate to the input and the drain-source as the output, I get the waveform that I am expecting.

Does anyone know why this is happening? Is the circuit even set up in the right way to get the transfer function of the drain?

Edit 1:
The circuit I am trying to model is below. I am trying to find the transfer function where Vd is the input and Vg is the output.

Updated LTSpice schematic:


texts:
I have 6 volts batteries and I created a simple circuit of battery level indicator, the battery needs to supply another circuit and I need to connect the battery indicator level to the battery. And all the connected wires are connected to one supply. What will the battery level indicator read? The voltage from the supply or the voltage of the batteries? Dont have a picture of it. Please ask me if you need some clarifications.

Thank you for answering this question.


texts: While discussing eigen functions of LTI system, why we ignore the natural frequency term in response?

texts:
Consider the LTI system, a series RL circuit (initially at rest).

If we define voltage as input and current as output, whatever be the forcing function, output contains a component \$ e^{-Rt/{L}}\$ corresponding to the particular system.

http://www.intmath.com/differential-equations/5-rl-circuits.php

We also know \$ e^{st}\$ is an eigen function of LTI system which means if we apply an input of \$ e^{st}\$, a scaled version H(s)* \$ e^{st}\$ will appear  as output. Output contains only the frequency corresponding to input (forcing function). Hence we hear statements like 'Linear systems do not introduce new frequencies(harmonics)'.

Isn't the first case and second argument contradictory? How can we explain the absence of natural frequency(\$ e^{-Rt/{L}}\$) term in latter case? Also how can we impose initial conditions at t= \$-\infty\$ for these everlasting inputs of kind \$ e^{st}\$?

Note: A similar situation arises for LC circuit analysis, where output contains a terms corresponding to natural frequency \$ \omega_0\$.


texts: Safe to use PWM source to control lights via MOSFET?

texts:
I'm a bit of a noob when it comes to electronics so looking for some advice on this project I have in mind.

Introduction

The goal is to have my garage door opener (GDO) switch a secondary set of 12v or 24v lights on and off.

The GDO has it's own LED lights and I've measured the output (using my inexpensive multimeter) to be 18.4V. The LED lights dim then switch off after a period of time so I'm assuming it's using PWM.

The GDO also has a 24V 55mA output for accessories.

I don't yet have a specific secondary light I will use but one that I have in mind is rated at 24V 1W.

My plan

I'm thinking of using the IRF540N MOSFET to switch the secondary light on and off with the advantage of also having the PWM of the source dim them.

I'm thinking I could simply wire the Gate of the MOSFET into the LED source. I would then wire the Drain to the negative terminal of the secondary light and wire the Source to the ground of the LEDs and ground of the 24v source (which is probably common ground but I should probably check first).

My main concern is that I don't know if the MOSFET will over load the LED power source. I really can't mess around too much because it's an expensive door opener :)

Alternative

Since my original plan could possibly damage my GDO if I'm not careful my other plan is to use an LDR circuit to switch the 24+ on and off without the fancy PWM.


texts: How to define the initial charge of a capacitor in SPICE

texts:
I would like to simulate a circuit with a capaciot in LTSPICE. In the first hand, I have tried to charge the capacitors in a period of time. However, the charging current is very high and I am not sure whether the capacitor will be completely charged or not.

Therefore, I am looking for a way to initiate the initial state of charge of a capacitor in SPICE.


texts: Identifying shorted capacitor on laptop motherboard

texts:
Background:

My Asus U47A laptop stopped charging or running off the AC adapter.
With the help of diagnostic tips on the internet, I found the culprit to be a faulty ceramic cap near the input jack on the motherboard.

One end of the cap goes to ground, the other seems to go the "gate" of an N-Channel Mosfet (datasheet) just above it.

Problem:

I have removed the faulty cap, and I no longer have a short at the input jack... Now how do I determine the right capacitor as a replacement?

Also, is it likely that the faulty cap damaged another component or resulted from another faulty component?

Pic of the faulty cap


texts: Whitenoise Signal from Microcontroller Amplification IC Advice

texts:
I'm looking to hook up a piezoelectric PZT to a microcontroller that will be providing a white noise signal.  However, the 5ish volts that the microcontroller can spit out isn't strong enough to vibrate the PZT as energetically as needed.  Experiments have shown that a signal with 25 volts is the minimum needed (the PZT can handle voltages up to 300V) for the purpose.

The whole experiment is in a limited amount of space and (for now) run by several 9 volt long-life lithium batteries hooked up in parallel.  Given those constraints on space and power, what is the best device, or at least the best category of devices for this job? If "nothing" is the answer, how best can I rearrange the batteries to provide for an alternative?

I don't mind having to assemble a few things together, but if the problem could be solved with one circuit or device, that would be ideal.

Thank you for your time and brain power.  If I'm missing any vital details, I'll do my best to supply those upon request.


texts: Connect 3-port and 1-port devices defined by S-matrices

texts:
There are two linear networks.
The first is defined by 3-port S-matrix:

\$\mathrm{S}_\mathrm{A} =
\left[
 \begin{array}{lll}
  s_{11} & s_{12} & s_{13} \\
  s_{21} & s_{22} & s_{23} \\
  s_{31} & s_{32} & s_{33}
 \end{array}
\right]\$

The second device is defined by reflection coefficient \$\mathrm{S}_\mathrm{B} = s_{11,B}\$

How to calculate the resulting matrix

\$
\mathrm{S}_\mathrm{C} =
 \left[
  \begin{array}{ll}
   s_{11,\mathrm{C}} & s_{12,\mathrm{C}} \\
   s_{21,\mathrm{C}} & s_{22,\mathrm{C}}
  \end{array}
 \right]
\$

for circuit, in which 1-port device connected to the third port of 3-port device


texts: A GPIO pin opening/closing a high power circuit?

texts:
sorry if this a very beginner question but I'm still quite new to the field of electronics generally.

I have a requirement to connect a Raspberry Pi to an existing electronic lock, and hopefully use a signal from one of the GPIO pins to cause the lock to unlock. I've been advised that the electronic lock is a 1A circuit, at (I think) 12V, and that any time the circuit is closed, the lock is triggered. Meanwhile, the RPi operates at 3.3V, with a 2-20mA output per pin and a 50mA limit.

Given this, what solutions do I have for allowing a logic signal from the RPi to control the much higher-power lock circuit? Initial research seems to suggest simply a transistor or relay of some sort would suffice, but my attempts to understand how I'd wire these together have been spectacularly unsuccessful. All my programming for the RPi is fine, I can drive the pin (or several pins if needed) high or low at the appropriate time - I just can't figure out how to let it control a 1A circuit. Do I need a full circuit of some sort that connects to both, or is there a way to just use a single component here?


texts: Transmission Line Model, Symmetric vs Unsymmetric

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Can someone please explain what's the difference between a symmetric vs unsymmetric  transmission line model ?

The normal un-symmetric one has R and L in series with G, C in parallel. While the symmetric model has the R and L divided in two halves and distributed on the two sides of the parallel G and C.

Is there any advantage what so ever of representing the same thing two different ways? We can get to the telegrapher's equations either way, so what's the point? Is it that the transmission line model should represent the line as being same from either point?


texts: MC34063A Poor load regulation in case of boost and buck converters

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I'm using following circuit for a boost converter using MC34063A IC.

The circuit is designed for 24 V, 250 mA output. The simulation works fine but the actual circuit on a PCB behaves weirdly. In case of no load I get the very high output of 43 V which doesn't change even if I change the value of potentiometer (R45). This is, I think, the no load behavior of a boost converter, we need a minimum load, so this makes sense. So if I put a load of 1 kohm, the output drops to 25-29 volts, over the complete range of potentiometer(R45). Now if use a load of ~150 ohms (160 mA at 24 V), the output drops to ~16.8 V and doesn't change by changing the value of R45. What could be the issue here?

Similarly, I use following circuit for a buck converter, designed for a 3.3 V, 100 mA output. With 7 V input the converter works fine, but with 5 V input the voltage drops to 2.9 V, and doesn't go to 3.3 V at any value of potentiometer.

Edit 1: Following is the layout for boost converter. I had to remove the rest of the pcb's components and tracks to make it more readable.


texts: Looking for ideas: An easy way to identify a frame of VGA or DVI video?

texts:
I'm looking to make an auto-restart solution for a computer.  I have a server with a BIOS that, if every slot of memory is full, automatically downgrades the speed of all the memory - it's an architecture limitation.  And I am running it with all memory slots full.  The result is that on startup, I also get a message warning me that system settings have been changed due to overclocking. (Not entirely accurate, but it's what it does).  I cannot get rid of this message - it's a fixed limitation.  The result is that every time the system restarts, I have to manually hit enter on the keyboard to bypass the message.  This makes it really un-handy when Microsoft decides to force an update of Windows, or a power failure occurs (no UPS) when I'm away from home.
Before you say "replace it with a better one", I'm wondering if there is another solution - to detect the "overclock" message and emulate the enter key press.  What kind of developer boards are available that would be fast enough to detect a single frame of VGA or DVI video (it has both outputs)?  It's always the exact same output.  I could monitor the server's video out and send a message to, say, an Arduino, that would emulate a keyboard and send the enter command when it detects the overclocking message.
I'm sure a Raspberry Pi could handle this task, but I'm wondering if there is perhaps an even more application-specific one I don't know about or a better way to do this.
Thanks for any ideas


texts: Use cell phone batteries as a battery pack

texts:
In my circuit, I used a simple charger circuit that works fine with standard battery packs that come with an overcharge/discharge protection circuit like this (green PCB inside.)

But I have some restrictions in my case and needed to use shaped batteries and found cell phone batteries like this

Currently, there are many batteries from different companies which I can find many good shapes and capacities. I have two questions in general:

Are they as good as these standard batteries, I mean in life quality and capacity?
Do these batteries come with charge/discharge protection circuits? If it varies how can I check them because most of them cannot be opened easily.


texts: Which type of motor use in oil-free air compressor? And how to detect stall?

texts:
I got 220V AC single-phase air compressor which labeled "Oil-free" and it look like this.

Some time the motor fail to start and got smoke out. (Some people says that happen when start motor with high air pressure in tank. Maybe start torque is too low to pump the air into pressurized tank.)
I called this situation as "Stall".
So my questions are.

Which type of motor used in that compressor? There are four wires, two for line and neutral, two for capacitor. I measure current about 3 A for L-N and 2.5 A for capacitor.
Any ideas how to detect or prevent stall? Can I just detect over-current using fuse or detect phase shift between 2-coil?