texts: Thevenin equivalent resistance of circuit with diagonal resistors

texts:
I'm trying to find the Thevenin equivalent for part A of this circuit:

I begin by opening the circuit at the dotted line of part A. Then I try to find \$V_{oc}\$ across the two terminals that are open. I can see that the 47kΩ is in series with the 18kΩ since no current flows to the open circuit, and that the 15kΩ is in series with the 33kΩ. However I'm having a lot of trouble redrawing the circuit. Not really sure about how to make it look simpler. Any ideas?


texts:
Why do USB plugs only fit one way into USB ports?

Forgive my ignorance, but there are several types of plugs that are "omnidirectional" and do not have to be oriented a certain way to fit into the corresponding plug (pursuant to shape). In the case of USB, when you're trying to plug one in blind, it can be a bit annoying if you happen to be trying to do it upside-down.

I'm guessing this has to do with the pinouts, but then why doesn't the USB standard just negotiate for "pin 1" when something is plugged in, or use a functionally symmetrical pinout layout?


texts: Why are both fuse and earthing are needed?

texts: This question arose in my mind today that when you already have the fuse for safety precautions why do you need the earthing?


texts: AD620 pH probe has a positive voltage offset!

texts:
I am a chem eng. but little background in electronics.

I'd like to interface a pH probe with an AD620A, the original PCB that came with pH probe was damaged by a current leak in the solution.

I made the following circuit in spice and on breadboard.

A pH probe has high impedance (>10Mohm), the AD620A seems OK to me for this application with its low bias current. Is that correct?

The pH probe ranges from -200mV to +200mV, little less range from pH4 to 10.

+Vs = +8.46V
-Vs = -8.33V
+IN = positive pH probe
-IN = ground pH probe, connected to GND and Vref pin of AD620A.

Output voltage should be centered on 0V as seen on screenshot, but in reality I read the following:

gain 4.4K
pH10: output = 0.82V (should be near -2.0V)
pH7: output = 2.51V (should be near 0V)
pH4: output = 4.92V (should be near +2.5V)
(R²=0.99 for linear fit, readings are stable)
In this configuration I could feed my ADC, would DC offset increase or decrease in time or with different power sources? Linearity is good enough for my application.

gain 3K
pH10: 0.93
pH7: 3.47
pH4: 6.87

The output never goes negative. I checked my negative voltage -Vs directly at the AD620 pin too. I tried putting 1M and 3M resistors on inputs with ground, but it seems it's not high enough or it's not the good direction.

What should I do to restore DC offset to zero? Should I apply negative voltage on Vref?

The DC offset is roughly +2.5V with the 4.4K gain.


texts: Device tree binding: can not make work my touch device

texts:
I have a touchscreen that the touch pad doesn't work. It uses i2c.

This is the driver: goodix.c.

This is how I should add the node to the device tree: goodix.txt

This is the device tree: imx6qdl-sb-fx6.dtsi

And this is the node that I put as child of /i2cmux/i2c@0:

            gt9271@XX {
                compatible = "goodix,gt9271";
#if GOODIX_5D
                reg = <0x5d>;
#else
                reg = <0x14>;
#endif
                interrupt-parent = <&gpio1>;
                interrupts = <4 0>;
                irq-gpios = <&gpio1 4 GPIO_ACTIVE_HIGH>;
                reset = <&pca9555 11 GPIO_ACTIVE_LOW>;
            };

The driver loads correctly:

root@cm-fx6:~# dmesg | grep Goodix
[    4.811992] Goodix-TS 3-0014: ID 9271, version: 1020
[    4.828035] Goodix-TS 3-0014: Invalid config, using defaults
[    4.832665] input: Goodix Capacitive TouchScreen as /devices/soc0/soc/2100000.aips-bus/21a0000.i2c/i2c-0/i2c-3/3-0014/input/input0

But there are no interrupts generation when I touch.
The initialization phase (check goodix_reset function) is neither performed as it should. This is what I should see (with an oscilloscope) during power on: http://imgur.com/a/puLsu.
But INT and RESET pins remain HIGH at all time.

I've wrote reset instead of reset-gpios as described on the documentation because otherwise I get error trying to get the pin. The error is -16 which means the resource is busy, because pca9555 11 is being used by another device too (check mipi-dsi-reset node). Btw, pca9555 is an auxiliary gpio controller.

Any clue on what is happening and why the pins don't act like the driver dictates? It has been already discarded to be a connection problem: if I don't load the driver and try to set gpio4 to 1 or 0 I see it reflected on the pin (both sides).


texts: Unknown symbol in thermostat schematic - two oblique lines inside a circle

texts:
Full diagram:

What does the circle with two oblique lines inside it represent?
It's an Emmeti Termec thermostat


texts: Does current have a physical effect on wire?

texts: Does current have an effect on the wire it moves through? I think I heard somewhere that over time small wires in CPUs can move because of the current going through them. If it is a thing what's the technical term for it?


texts: Adding an optional external power supply to Arduino Shield

texts:
I'm designing an Arduino shield that uses two sets of Adafruit's NeoPixel arrays. NeoPixelRing (D2) can be powered from the arduino, but the optional NeoPixel_Strip (D1) may need an external 5V power supply (depending on how long of a strip is added). My current design has a barrel plug on the shield and uses a DPDT switch to select whether the arrays are powered by the Arduino or the external 5V. I want to make sure that the ring is usable even if no external supply is used, and my impression is that back-feeding 5V into the Arduino is a bad idea (for some reason). I have two questions:

Can I safely connect the ground of the external supply to GND2 of the Arduino? That would allow me to only have a simpler SPDT switch.
Is there a way to automatically do this switching with a transistor (or whatever). ie. "if J1 is 5V, then connect it to VDD of the neopixels, otherwise connect Arduino 5V to the VDD of the neopixels"?


texts: Class A Amplifier Design: Emitter Resistance Voltage Drop

texts:
I am trying to understand the design principles of Class A amplifiers, primarily for audio purposes.

I have read several times that "the voltage drop across the emitter resistor should be in the region of 1 to 2 volts"...

To me this seems like a backwards way to design an amplifier, and it confused me. Why would one specify this voltage drop before anything else? Surely the voltage drop should be calculated from the current flow through the amplifier? (This is what I was thinking until today.)

Then I had a thought - I believe that the transistor will have a parasitic resistance which (for some reason that I do not yet understand) appears as if it were a small resistor connected in series at the emitter.

This resistor will create some voltage drop - so my thoughts are that perhaps this voltage drop (for some reason that I also do not yet understand) is always much less than 1 to 2 volts? At least this is my guess, I have no idea if I am along the right lines here.

To make this concrete with an example, please see the following webpage:

https://www.electronics-tutorials.ws/amplifier/input-impedance-of-an-amplifier.html

Under Single Stage Common Emitter Amplifier the author states,

  Firstly lets start by making a few simple assumptions about the single stage common emitter amplifier circuit above to define the operating point of the transistor. The voltage drop across the the Emitter resistor, VRE = 1.5V, the quiescent current, IQ = 1mA

My question here is, why was this value, of 1.5V for VRE, chosen first, and why was it chosen to be this value?

Further to this, the author states that IQ = 1mA. Does this mean that the output current from this type of amplifier must be between 0 and a maximum of 2mA? (My understanding is that the quiescent current is half the maximum output current. Is that correct?)


texts: What are some good replacement ICs for DIP UARTs?

texts: Recently, I have been developing an SBC based on the Zilog Z80 microprocessor. Since my first design, a serial connection has been essential for the board to communicate with a PC or terminal. For this purpose, I have been using Zilog's own Z80 DART (or SIO/0) because of how easy it is to interface with the Z80. However, it has been getting harder and harder to find distributors who sell these chips or similar ones, such as the 6850, for a reasonable price. Is there a newer chip or technology that I could use that would come in a DIP package and is relatively easy to interface with the Z80?


texts: High Voltage Push-Pull MOSFET logic gates

texts: Hello, I would like to implement typical MOSFET logic gates in my circuit with V+ at 24V and Input ranging from 0-24V. This posts a problem for the MOSFET however as I would either exceed the gate voltage thresholds or end up turning on both gates when the input is in between High and Low (e.g. 12V). What can I do to improve the design?


texts: Does anyone use op-amps for modelling physical systems any more?

texts:
I am studying for my System Modelling and Simulation exam. So the textbook says there are three categories of models.

Graphical - block diagrams and signal flow graphs.
Physical - physical similarity models and physical analogy models.
Symbolic - linguistic and mathematical models.

Putting aside my suspicion that a block diagram is no less a mathematical model than a system of differential equations, here is my question.

They define physical similarity model as a scaled down version of the original system. On the other hand, physical analogy model, is using electrical circuits to model the real system.

I thought this was last done 40 years ago, and currently nothing can beat the computational power of modern digital computers. Are analogue electrical circuits still used to model some systems?


texts: Can you interface a Modelsim testbench with an external stimuli

texts:
I am working on a team that is doing both driver software and FPGA development.  The FPGA simulation is being done in Modelsim and driver software is written in C.  To minimize integration risk, I would love to be able to model the interaction between the two halves of our product before putting it on hardware.

I know Modelsim supports a testbench which lets you provide stimulus in the form of a text file with times and values to input.  I'm wondering if Modelsim has a mode which allows you to hook up a pipe to an external application (such as our driver), and run a sort of distributed simulation where the software can push values into the testbench, then observe the results later.

The trick that I cannot do with a text file input is have the two halves of the product interact.  I need to have the software "write" values into the FPGA simulator, read the results, and then write new values into the FPGA which are dependent on the results it read.  Text files require the inputs to be independent from the output.

I've done searches on both StackExchange and google, but I have not been able to come up with a set of keywords to narrow my search enough to either identify the behavior I am looking for, or determine that it does not exist.


texts: Grove connector SMD footprint dimensions

texts: I'm creating layout for my PCB and I want to use Gvove connector in SMD package (http://www.seeedstudio.com/wiki/images/e/e0/3470120P1.pdf). But footprint from the datasheet doesnt have all the required dimensions. May be somebody knows the dimensions B,C,D ?


texts: RC integrator: why does it convert a triangular wave into a sine wave?

texts:
The output voltage of an RC integrator circuit is proportional to the integral of the input voltage.
This means that a triangular wave should transform into a quadratic curve (since the integral of a linear function is a parabola).
Why does it convert a triangular wave into a sine wave then? What am I missing here?


texts: Can Quartus help the user find out power saving if one uses clock control block to disable clock?

texts: The clock control block can be used to disable clock to a section of the design thereby achieving clock gating. Can Quartus help the user find out how much saving such a measure will help achieve in the design?


texts:
I have a little problem with the subject Theory of signal. We were told to make amplitude and phase spectrum of cosinus in MATLAB, but we don't have results nor materials from our teachers, so we have to study from many different materials and you can imagine what this is like. So I'm a little confused.

However, I did some graphs, that should be what I want, according to instructions, but I have never seen something like that, so I'm not sure, if that's right.

Do these graphs make any sense to you? I used fast Fourier transform (fft(y) in MATLAB) on the signal and then plot the result of transform versus sample frequency and I thought it's possible to get phase of the signal by angle(fft(y)), so I plotted this on the last graph.

I would like to apologize for incorrect notions I might use, 'cause I'm not a native english speaker.

Thanks for any help.


texts: Will running a signal through a voltage divider change its phase?

texts:
I'm reading a web page about filters (https://www.sensorsmag.com/components/introduction-to-analog-filters) and noticed something that doesn't make sense.  The web page says if you run a signal through a voltage divider it will change the phase of the signal (here is a screenshot):

This is confusing to me because my understanding of resistors is that they have only a real part to their impedance which would mean that they don't change phase.  Can someone explain to me how running a signal through a voltage divider will change the phase?


texts: Switch audio from one source to another one

texts:
I am currently working on a project where I have two GSM modules in a single product. Those modules have each one a mic port and speaker port.

They will not be used simultaneously but they will be both including on the PCB of the device. I need to be able to switch automatically from one module to the other one depending on the gsm network availability. However, our customer have only one mic plug 3.5mm jack and one speaker plug 3.5mm jack.

Hence I need to connect this only plug (one for mic and one for speaker) to a kind of switch to redirect the signal properly to the module which is currently used (face to gsm network availability).

I am a bit confused by which device to use to perform this 'audio switch"

If anyone has idea about the component that woudl be best suited for this...?

Thank you

but only one jack plug for eacc (one jack for mic, one jack for speaker)


texts: Standard Meaning/Purpose of Exposed Areas on a PCB?

texts:
I noticed that on some circuits, there will be dots or rings of exposed circuit material.

Take for instance the back plate of a Nest thermostat:
https://d3nevzfk7ii3be.cloudfront.net/igi/6J2elHPEJArWXaE6.huge

There is a thin ring around the inside, outside, and several dots of exposed brass colored PCB metal.

Is it a fair assumption that these always connect to ground? Or is this something that isn't standard?


texts: How I do make charge-discharge graph in Semestrix? What is the problem of mine?

texts:
I don't understand why graph is just pulse. Even that has resistance and capacitor.
Can you give me advice about how to correct and how to do? Thank you!
I am sorry about my not good English ability and style looks newbie.


texts:
I'm want to build a lighting circuit just like a LED strip with 42(or 24) LEDS but I want to make it myself.
My questions are:
Would a AA battery be enough for all these LEDS?
Is this circuit correct?

Thank you


texts: Parallel MOSFETs in saturation/active region

texts:
Am I right that when MOSFETs are connected in parallel for them to share the current equally (See Parallel MOSFETs) they have to be operated in the triode region?
I have an electronic load with 3 parallel MOSFETs and one opamp with 1 shunt in the negative feedback configuration with the opamp driving all 3 MOSFET gates and when in the active region all the current goes through one of the MOSFETs.
What is the easiest way to get a more even current distribution in the active region in this application?


texts: Why the time of execution is never shown in any Instruction Cycle?

texts:
In case of timing diagrams of 8085, what I saw is that, always Opcode Fetch, Memory Read/Write, IO Read/Write is shown but execution is never shown. Is it because the execution time is too less compared to others?
Thanks in advance.

For example, In case of MVI A, 55H they show 4 T state for Opcode Fetch, 3 for M/m Read that's it. No T state for execution is ever shown.

Reference: Ramesh Gaonkar 8085 Microprocessor Book.


texts:
simulate this circuit – Schematic created using CircuitLab

OK. So I've been told that the current flowing into the current source (that is, into the arrow's behind) is the same as the current coming out of the current source (that is, out of the arrow's head).

If this is the case, then why is it a current "source"? It's not providing any extra current!

I know this is a fairly elementary question, but I haven't found a good answer elsewhere.

Thanks.


texts:
I have been looking on Google for a project that involves 2 Arduinos communicating with Bluetooth. The only examples I can find are with an Arduino to an Android phone.

Does anyone have links to let me know how I would go about hooking two Arduinos up to Bluetooth?

The Bluetooth module I'm using is the Bluetooth RF Transceiver Module Card RS232 TTL (i guess better known as the HC-05). Here is an ebay link.


texts: how create a square signal between 0.2 volt and 0.8 volt

texts:
i am working on a signal comparator. I want to create a signal output of 0.2 volt if the input is under reference value and 0.8 volt if the input is over the reference.  I am doing it with an arduino and usign a poteciometer to change the reference between 0.3 volt and 0.7 volt.

The input signal is changing between 0.85 and 0.05 volts with frecuency of 3 Hz as maximum.

This is the simulation suggested:


texts: How can I build proper laplace RLC circuit

texts:
I think there are two different circuits over the picture. But for equations they are acting same to me. I mean DC source of left circuit look like an initial voltage for C. After inver Laplace I have a capacitor voltage start with 40  even there's no initial voltage.

For the \$ R= 2 \$, \$ L= 20 \mu H \$ \$ C= 0.28 \mu F \$ \$ V=40 V \quad I0=14.55 A \$

Matlab ilaplace gave

\$ I(t)=14.55\rm{e}^{-50000t}(\cos{419608.6t}+0.208\sin{419608.6t})\$

To find Vc

\$ v_c(t)=\dfrac{1}{C}\int_{0}^{t} i(t) dt +C_0\$

and witout \$C_0\$ matlab int command gave this;

\$ V_c(t)=119.06\rm{e}^{-50000t}\sin{419608.6t}- 40 \rm{e}^{-50000t} \cos{419608.6t}\$

Now for left circuit \$C_0=0\$ But that means in the graph for \$t=0\$ Vc start with -40 V. İt looks wrong for me on the other hand i need add + or - 40V for \$ V_c(t)\$ but graph is more meaningful without adding  \$C_0\$


texts:
Both 60950 (Table 2N – Minimum creepage distances) and 60335 (Table 18 – Minimum creepage distances for functional insulation) seem to specify a minimum creepage distance of 0.4mm (~16mil) with a IIIa / IIIb material group and pollution degree of 2 at <=10V.

This seems crazy big, and I know that many boards are in production with significantly smaller spacing between low voltage traces.  With the pad spacing between common microcontroller pins, for example, this is impossible to achieve.  Am I understanding this requirement correctly?


texts:
I know nothing about MOSFET, yet, so I'm fumbling in the dark here.
What I want to achieve is a high side switch using an N-FET. All guides I've been reading says "low side switch = NPN or N-FET", "high side = PNP or P-FET". I want to control a very small 3.3V-load (50mA) using a microcontroller (5V), and since a BJT has about 200mV for Vcesat I thought that a FET might be better to get rid of that drop.
I setup a simulation just to test the idea, and I can see 3.3V on the source pin when the gate is high. But obviously, current cannot flow in the direction I want. Is it possible to make this work with an N-FET, or do I need to bite the bullet and buy a P-FET?
EDIT: datasheet for the FET in question. ON-characteristics for Vgs(th)  says "max 1.5V". 5-3.3 = 1.7V in my case, shouldn't that be enough?


texts: Help with high current single cell lithium charging

texts:
I am designing a system to charge a single cell lithium battery. It requires pass-through, path-selection, over and under voltage protection. The bottom line is this system needs to power a device while unplugged, and continue powering it while it is plugged in charging the battery. This is for a research project, not any sort of commercializable product. It also has an expected lifetime of only about 3 weeks, so battery degradation isn't a huge deal. After trying numerous boards out from various suppliers, and even attempting to make our own we found one that almost works like we need it.

http://www.ebay.ca/itm/1-x-PCB-Li-ion-Lipo-Battery-3-7V-step-up-Convert-to-Output-Power-DC-5V-DLX-UPDC/130725341903?_trksid=p2050601.c100085.m2372&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20140211132617%26meid%3D9d35d42468324327b2bb8abeed10b780%26pid%3D100085%26rk%3D4%26rkt%3D4%26mehot%3Dpp%26sd%3D181190701564%26clkid%3D3380855727044982483&_qi=RTM1963932

The problem is the pass-through current is too low, and the charging current is too low. Ideally we need something that works like a laptop where it continues to be powered whether it is charging or not. Right now it can output 1A maximum. We would like to double that to 2A if possible (or more up to 3A even).

With an approaching deadline is there a board available online that we are missing that does all this, or is there a modification/new design we can use to make this work?

Thanks for you help in advance!


texts:
I have two potentiometers and a single voltage reference, connecting them causes a few mV voltage drop in the simulator:

Adding an op amp solves the problem but then comes input offset voltage and temperature stability problems:

simulate this circuit – Schematic created using CircuitLab

How do I properly use a single voltage reference for two potentiometers without getting voltage drop?


texts:
My compiler complains about inferred latches in my combinatorial loops (always @(*), in Verilog). I was also told that inferred latches should preferably be avoided.

What exactly is wrong with inferred latches? They certainly make combinatorial loops easier to write.


texts:
I was examining the specs of a breakout board.

It says in there that,

  Integrate 10 dof sensors

  Adxl345 accelerometer

  ITG3200 gyro

  HMC5883L Compass

  BMP280 pressure sensor

Why is it called as a 10 DOF sensor? In past I was dealing with some IMUs consisting of an accelerometer + a gyroscope and they were called as 6 DOF sensors. Which was a little bit more understandable, I was thinking that 3 measurements from accel and 3 from gyro = 6 degrees of freedom. However in the above case, I am not sure.


texts: Voltage regulator or resistors to change voltages for motors?

texts:
After doing a little research I found out that I can change voltage by either using a voltage regulator chip or resistors. I have a couple different scenarios in which I'll have to drop the voltage for my motors and I was wondering which method to use for each application.

I'm using an H-Bridge to drive a bipolar stepper motor rated at 3.1V. I need the stepper motor's speed to change. Does the H-Bridge in this circuit drop the voltages as necessary to change the motors speed or is it simply able to rotate in either direction at a constant speed? http://arduino.cc/en/Reference/StepperBipolarCircuit

Driving a 7.2V DC motor with a PWM output ( http://www.vexrobotics.com/276-1668.html). I believe I'm supposed to wire up the power and ground of the PWM to the motor's 7.2V power supply and wire the signal wire to one of the Arduino's ports. This motor would also have to change speed.

Running a 12V air compressor.

Although I'd like to use resistors for all of my voltage drops/increases I believe I read somewhere that it cant be used if the appliance its connected to has to change voltages (ex. a motor that needs to change speeds.)

**All of these will be powered by one or more 9v batteries.

EDIT

Thanks! So to summarize what I should do...

Stepper Motor - Wire the inputs to an H bridge with a 3v power supply. (2 AA cells in series) Although I'm planning on giving the stepper motor a seperate power supply to simply things, if I were to run it off the same power source (6 AA cells) as the Arduino, can I use a resistor to drop 9v to 7.2v and than supply that power to an H-bridge? Which would than be connected to the stepper motor.

7.2V DC Motor - Use an h-bridge to pulse 7.2V to the power and ground of the PWM and pulse the signal wire to control the motors speed? Or can I use resistors to drop 9v to 7.2v and than simply pulse the signal wire to control the speed? I'm not sure if the problem with the resistors dropping varying amounts of voltage depending on the motor's load      would persist in this scenario. (Kind of similar to the stepper motor scenario except I'm pulsing the motor through a PWM motor controller instead of an H-bridge.)

12V Air Compressor - Wire several cells in series to hit 12V and than turn it on/off by using an H-bridge.

I actually have several 12v golf cart? batteries which can be found here http://www.andymark.com/product-p/am-0844.htm.
If I were to use this, it would be with the 7.2V DC Motor and 12V Air Compressor. (The Stepper Motor is going on a
moving vehicle which is way too weak to carry the battery.) I was thinking about using these batteries but I thought
the amperes it gives out would far exceed what any of my appliances can handle. It'd be awesome if I can use this though!
I'm constantly going through AA/9v batteries and its been getting quite expensive.

****EDIT 2****

This is the diagram for the stepper motor circuit. It's set up pretty much the way I'm planning on running it.

This is the diagram for the 7.2V motors and 12V air compressor. The batteries shown there is actually a ~12V car battery. I'm still trying to figure out how I'm supposed to drop the voltage to 7.2. I looked at the LM317 adjustable voltage regulator but it can only handle current up to 1.5A and the motor I'm planning on using has a stall torque of 3.6A. The motor I'm using is NOT a servo but it's connected to a 3-wire motor controller (http://www.vexrobotics.com/276-2193.html) which uses a standard PWM signal to drive the motor.  My plan is to connect the 7.2V power supply to the power and ground of the motor controller and to connect the motor controller's signal wire to one of the Arduino's ports.

The air compressor isn't shown but I'm assuming I can power it directly through the battery (with an H-bridge in between as a switch).


texts: Choosing R when designing CMOS Amplifier

texts:
I am trying to design a two stage amp like the one pictured above. I want the overall small-signal gain, |Av| = vo / vid = 240 V/V = (47.6 dB). I know in theory how to achieve this but am having trouble with the equations.
I know that:
Vt0 = 0.7 V
kn = 50 A/V^2
kp = 20 A/V^2
W/L = 100:1 for both NMOS and PMOS.
The output conductance at a bias point of ID = 10 mA as 200 mhos for the NMOS device and 500 mhos for the PMOS device.
If needed I can also assume that:
tox = 90 nm
Nsub = 3.7*10^15 cm^-3
Due to a current mirror the current (Id) will be the same through the differential stage (M1-M4) and the PMOS common-source amp(M7). Transistor M8 provides bias current for
M7 and functions as an active load on M7. I believe M5 and M6 act as a current source that keeps the current Io constant. RD7 and RD8 are used to venter the DC output at 0V. One or both will be zero for any calculation.
If I can get an equation for the gain through the differential amp (input: vid, output: between M2 and M4 going to M7) and an equation for the gain through M7 I can multiply them for the overall gain
What should I set R to in order to achieve an overall gain of


texts: Using Bluetooth to rapidly connect and send data?

texts:
I have an idea for a distributed communication platform that I want to build.  For my project, I would have many phones, and I would like to send ~20kb of data between each phone at a minimum range of 2 meters or 6 feet.  I was hoping to find some way to utilize a phones Bluetooth transceiver for this purpose and do the following:

Identify Bluetooth enabled phones
Identify if a phone has 'opted in' to the communication platform
Open a connection between two participating phones and engage in a two-way communication of about ~20kb data.  Probably considerably less data in practice but I want margin.
Close the connection.  Add that phone to a list so they don't connect again.

Is there anyway to do this with current phone Bluetooth?  I read something about 'Bluetooth mesh networking' and 'Bluetooth radio' but I was hoping someone could point me in the right direction, or confirm that these technologies would be a good place to start.
Its worth noting that if this process drains too much battery life, the project is Dead on Arrival.  Also the phones should not have to be close to each other for more than maybe a couple seconds to get the job done.  Please let me know any thoughts.


texts: How to reduce the frequency of ferrite core transformer?

texts: I am trying to do a inverter using ferrite core transformer, but the problem is the frequency output from the ferrite core transformer, If I am using that, I will be getting 230V AC but the frequency is much higher >10KHz. Please guide me to obtain 230V, 50Hz AC supply from ferrite core transformer.


texts: Controlling 1 fan with 2 different computer power supplies

texts:
Ok here is my scenario:

Because our 2 gaming computers are pretty noisy, we moved them to another room in a closet. There are vent holes to the outside of the building, and now that the summer comes I want to add a small computer fan (12V 0.3A) to push the warm air out. The plan is that if one of the 2 computers is turned on the fan should spin.

What I have done so far... and it works:

I extended cables from both computers from the PSU (GND and +12V) to a little box.

I added 2x 1N5059 diodes in parallel on each +12V from the PSU going to the fan.

I know now the diodes can handle up to 2A, so one of them on each +12V line should have done the job.

As I said, it works as expected and does what it should, but, and this is my actual question:

I know diodes allow a very small amount of current in the other direction.

Do I need to be concerned that one PSU could break the other one in long term use?


texts: Driving Relay Board with Shift Register (Shift vs Sink)

texts:
I am trying to drive some ebay bought 8 channel relay boards.  They are pretty simple, have a launchpad or arduino toggle a pin and the board turns on.  However, I need to use a shift register with them.  I have absolutely no idea how to think about this,  here is my problem:

I would like to use something like 74HC595.  The relay needs 20mA to turn on however, the 74HC595 can't do this all at once (have all outputs on)

The TPIC6B595 has sufficient current capabilities.  However, I cannot for the life of me figure out how I can get the pins to do what I want if the shift register is sinking the current instead of sourcing.

I have google around but can't seem to find a powerful enough shift register that sources current.

I would even be fine driving a darlington array from the shift registers, but they sink current too.  (ULN2803)

Am I thinking entirely wrong?  I feel pretty stupid.

EDIT:

Ok, I have been playing with a circuit simulator.  I think this is what I want?  at least it will explain it a little better.

(The relays I have are Active LOW)


texts:
I know why we need a pull-up resistor on the reset lines, but what is the reason for a capacitor parallel to the reset button?

I saw it on Texas Instrument's schematic for MSP430F5529 launchpad.


texts:
I was designing pcbs and my head engineer told me that if input supply is large then there should be a separate layer for ground and positive supply as this will reduce EMI effects on the nearby components.

What exactly EMI does to a component such as an inductor?  May be induce voltage and cause the component to burn out or change the filters characteristics ?

Any help would be appreciated.


texts: Generation of triangular wave from passive networks

texts:
I wanted to generate a triangular wave from a pure sine wave using only passive networks (RLC circuit only.)
I wanted to realize such a network and at first I thought maybe the Fourier transform (of transfer function) does the work but then I thought due to delta function present in denominator of transfer function (dividing Fourier transform of triangular wave to Fourier transform of sine wave) it's not easy to get desired result.
Then I thought maybe the Laplace transform will work but this time, the unilateral transform of the transfer function is a non rational function and I don't think it's realization with only RLC circuit is possible.

Is it possible to design such a circuit (only RLC) which outputs triangular wave for sinusoidal input at steady state, just after applying sinusoidal input?

If it is not possible to design such a passive network then how to design a passive circuit that has anoutput is pretty close to triangular wave for same sinusoidal input?

What is best way to approach  problem like this, so that we can reach at conclusions about desired system quickly?


texts: How does sin/cos encoder increase the resolution of an incremental encoder?

texts:
Is it possible to explain the advantage of sin/cos encoder when used together with an incremental encoder? Here is a related paper but I don't understand how does it improve accuracy. I basically don't get what interpolation is and how does it help to improve the usual incremental decoding. I checked this but couldn't find a pictorial/graphical way to grasp the idea.

In a typical square-wave incremental encoder edges are counted and processed to obtain the rotation angle and direction or speed.

But these sin/cos encoders add an extra to this principle. They call it interpolation. Is it possible to explain how two sines and cosines are processes and contribute to the accuracy here? Simple graphical explanation would help a lot.


texts: How to connect this circuit?? - Digital logic

texts: I unsure how to connect the components together, do you guys have any tips or hints??


texts: How to PCB layout WM7230 MEMS digital microphone?

texts:
I'm trying to figure out how I'm supposed to get traces to the four internal data pins of the Wolfson WM7230 Digital Microphone part.

It's got a ground ring that is supposed to have a tight solder seal. You can see from the datasheet recommended PCB pattern, that the four internal pads are completely surrounded by the copper ground ring.

I thought it was bad news to put vias in the pads themselves. This thing is a pretty small part; is the intention that I put via's immediately next to the pads?

Tried to find some example layouts with Google, but no luck.

Thoughts?


texts:
I've got a few questions about a task from my exam preparation paper. The sketch below shows the circuit in question. It is given that U_E varies between 0V...3V. The operating voltage U_B is 10V. The op amp and diode are ideal at the beginning (it does not say at which point in time they must be not seen as ideal anymore). The four tasks are the following:

1. Give an algebraic expression for the differential amplification \$v_1=\frac{dU_A}{dU_E}\$

My solution: \$v_1=1+\frac{R_2}{R_1}\$ (non inverting op amp)

2. What is U_E's value such that D1 is conducting? What is U_A then? Give algebraic expressions for U_E and U_A.

My solution: \$U_E>U_B*\frac{R_3}{R_3+R_4}\$ thus \$U_A>U_B*\frac{R_3}{R_3+R_4}*(1+\frac{R2}{R1})\$

3. What is the differential amplification v_2=dU_A/dU_E if D1 is conducting? Give an algebraic expression.

My solution: \$\frac{dU_A}{dU_E}=\frac{R2}{R4}+\frac{R2}{R3}+1+\frac{R2}{R1}\$

4. U_B is 10V. At which value U_E does U_A saturate? Give an algebraic expression for U_E. What is the differential voltage u_d as a function of U_E if saturation occurs?

I don't really know how to solve this task so I'd be glad if anyone could help me out.

Moreover I am not quite sure about my solution to question 2 and 3.

simulate this circuit – Schematic created using CircuitLab


texts: How is voltage applied across a capacitor changing when I connect it to a DC power source?

texts:
Current entering/leaving a capacitor is proportional to the change in voltage applied across its plates.

Lets say I have a capacitor in series with a DC power supply, a resistor, and an open switch. Once I close the switch, the voltage across the capacitor is equal to the voltage supplied by the DC source, but this voltage remains constant since DC power supplies are obviously constant.

This is all under the assumption that all components are ideal. I know that for current to enter the capacitor, the voltage across it has to be changing, which is what happens in the real world. Where does this change in voltage come from?


texts: How to display 2 digit number in binary adder circuit?

texts: I've made 4 bit adder circuit using 4008 IC. And the sum output of the two 4 bit numbers from that IC was feed to one BCD to 7 segment decoder (74LS47) so that I can get decimal output. But since I can't diplay numbers over 9, I need two 74LS47 ICs. But what additional circuitry shall be made so that it can stop that overflow over decimal no. 9? And suppose my two binary numbers to be added are 101(5) +101(5) I will get binary output of 1010(10). How can I display this using two BCD to 7 segment decoder ICs?


texts:
I have a doubt on stack implementation in 8051 and I don't even know if I'm asking it in right way so please pardon me. I've been reading stack implementation in 8051 and many textbooks and references it's mentioned that when we push the data then first SP is incremented and then the value is stored. So I've understood it like the following using an example :

  push A    // if by default SP is pointing at address x then the value of A is stored in x+1 location ?

Is it correct ?

EDIT:
And if I want to access the value 'A' after pushing it by register or pointer then do I have to access from 'x+1' location ?


texts: Why LED signboards shake when I eat an apple?

texts:
while I was sitting in city center with so many LED (especially red ones mounted) signboards and I was bitting an apple, the signboards suddenly begin to shake for only a second while my head is shaking.

I couldn't understand why this had happened to my eyes? Maybe the XTALs in the LED-driver-circuits are out of the frequency because of high voltage or so many times these are used, and/or grid's frequency has been added on to the device.

What should be done to prevent this frequency shake?

Is this topic belongs to harmonic distortion - THD ? That maybe a reason by XTAL's frequency?


texts: Inductance of air core coil decreasing due to ferromagnetic object put in it?

texts:
I have built a Colpitts oscillator which you can see in the schematic below. Note that the values for R1 and L2 are not correct since I use a self-wound air core coil for L2 which means I can only approximate the inductance with calculations. As for R1 I use a potentiometer to try multiple resistance values. However, the value given is in the range of values I tried.
The circuit outputs approximately 3V at 700kHz.

When I put an iron core or any other ferromagnetic object into the originally air core coil L2, the output frequency will increase and the voltage will decrease.
I thought that the frequency would increase since it is given by \$f = \frac{1}{2 \pi \sqrt{LC}}\$ and because the inductance should increase due to the iron core.
Could it be the case that the inductance decreases? If this was true why on Earth would this happen?
The same thinking applies to the voltage. According to the formula of voltage in LC circuits \$V(t) = -\omega_0 L I_0 cos(\omega_0 t + \phi)\$, the voltage should increase, but it decreases.
This all implies that the inductance is actually reduced by the iron core.
Can this be the case or is there some other explanation for this behavior?


texts: If npn transistor switch is saturated, does base get galvanically connected to emitter?

texts: Playing with Christmas lamp TRIAC, I got this question. Suppose some transistor is saturated, if gate current is >= 1ma, and I want to control it with 5V Arduino (or STM\PIC\etc) port. So I need to add Rb around 5K into base. Hovewer, if my transistor collector connected to 400V mains, and transistor fully opened, does base got connected to 400V too (via Rb=5K, making current around 80ma), destroing my Arduno, board, house and so on? Or I missing something?


texts:
Working on existing PCB which has reset issues. Have been able to solve all reset problems except the following:
Using a PCB mount T9AS1D22-24, upon micro going low on Q3 base (K3-A coil de-energize), micro will occasionally reset.
Have attached circuit for viewing. Anyone have suggestions on how to better filter this?

Relay giving me fits is http://www.mouser.com/ds/2/418/NG_DS_1308242_T9A_0915-719064.pdf


texts: Can a heatsink protect a PYNQ-Z1 board from damage? If so, which one should I use?

texts:
I'm going to purchase a PYNQ-Z1 FPGA development board from Digilent (Link: https://store.digilentinc.com/pynq-z1-python-productivity-for-zynq/). However, some of the comments on the linked page say that the board runs very hot and they should have included a heatsink or fan.

As the board is rather expensive and I want to protect it from damage, I'm thinking of also buying a heatsink. The main chip is a ZYNQ XC7Z020-1CLG400C (BGA, 0.8mm ball pitch, 17x17 mm package).

So I did some research and found at least one heatsink designed for this size of chip, linked here: https://www.digikey.com/product-detail/en/advanced-thermal-solutions-inc/ATS-55170D-C1-R0/ATS1264-ND/1284978

I'm wondering whether it's a good idea to install this heatsink, or whether it's unnecessary or even dangerous, or whether a different kind of heatsink would be better. At 9.5mm in height, I'm also worried that this heatsink might interfere with the Arduino interface, but I would need better measurements to be sure.


texts: Is it possible to use a MAX232 to convert 0 to 5V PWM to 0 to 12V PWM to input to a motor driver requiring 0 to 12V PWM logic?

texts:
I'd like to drive a 16kHz PWM signal at 0.5mA into the input of a motor driver expecting logic levels of 0V for LOW and 12V for HIGH, and expecting a PWM signal around this frequency. The PWM signal will be generated by an Arduino Uno (ATmega328 mcu) with 0-5V logic (0V LOW, and 5V HIGH), and capable of driving 40mA max.
The motor driver PWM input will be used by the driver to produce a PWM output at the motor, with real power to rotate the motor. So, this input PWM is just a low-current 0.5mA signal, NOT a high-current PWM. The PWM duty cycle controls throttle. Let's assume that a 10% duty cycle error is the max acceptable, meaning that the slew rate must be this or better:
1/16000 cycles/sec * 0.1 * 1e6 us/sec = 6.25 us rise time from 0 to 12V

So, slew rate must be 12V / 6.25us = 1.92V/us, or 0.52us/V (however you want to look at it), or better.
The motor driver input registers a HIGH from 2/3 * 12 = 8V to 1.25 * 12 = 15V, and a LOW from -0.5V to 1/3 * 12 = 4V.
It's been suggested here that a MAX232 can also be used to convert a 0-5V input PWM to a 0-12V output PWM to be used as a logic signal to a motor driver requiring 0-12V PWM logic.
Is there some MAX232 chip configuration which makes this possible, to convert 0-5V input to 0-12V output, to be used with PWM?
I don't believe there is, and have instead suggested using a half-H-bridge IC to do the job. I've received a lot of push-back and criticism for some reason for suggesting an H-bridge IC, however, and I'd like to know if I'm missing something here, and if so, what.
Here's the MAX232 datasheet. It indicates it requires a single 5V supply to Vcc to accept 0 to 5V input logic levels and convert them to -7V to +7V output logic levels (see VOH and VOL in table in section 7.6 of datasheet) in order to convert 5V TTL logic to +/-12V (or similiar: +/-7V is good enough) RS-232 logic levels. (Of course, it does this in reverse too, but I only care about this direction).

Update:
My conclusions:
You don't know what you don't know until you either know it, or know you don't know it.
So, after already having thought about it myself, and now after seeing a couple answers here, it still seems to me that a MAX232 definitely isn't suited for this job unless one is mistaken about what the motor input signal voltage range is, and it can actually handle the RS232's -7V as a valid LOW input signal and +7V as a valid HIGH input signal.
If that is not the case, choose something other than a MAX232 chip to do the job.


texts: Influence of a magnetic field on coil impedance

texts:
If you take a coil and make a current flow through it, the coil creates a magnetic field. This field induces a voltage into the coil that produces a counter current that weakens the primary current and voltage. If you then measure the voltage and current you can calculate the impedance of the coil.

My question now is, is the impedance higher before the self-inductance or lower ? In other words, how does a magnetic field influence the impedance of a coil ? The complex impedance Z equals u/i ( complex ) but does u and i decrease proportionally or does u or i get smaller faster and make the impedance increase/decrease ?


texts:
I'm making my own board based on Arduino. To power it I use one LIR2032 cell (button cell 3.6V li-ion battery) that's driven through 3.3V LDO voltage regulator. So far I have tried two different regulators:

MIC5504-3.3YM5-TR
LD59015C33R

and none of them worked, both did not give any voltage at the output.
So far I have tried:

connecting ENABLE pin to VIN (in the second one could be left floating, PCB has an error design  with EN disconnected but I've already corrected it!)
replacing part (in case of ESD)
correcting joints (in case of cold joints, multimeter shows proper connection)

The voltage regulator is wired the same way as shown in the datasheet

.

The board works when powered via other source of power so it's not the case of it just not working. Trying different batteries and higher voltages did not solve the problem, output still shows 0V.
I have no idea what could be wrong, I hope you can help me with that!

If you have any other regulators to recommend please comment, board needs no more than 100mA.

(Yes component is bigger than the pads :) MIC5504 is slightly larger than LD59015 but I managed to solder it properly)


texts: Corresponding SMD component - S280 label

texts:
What kind of component is this?
Looks like a capacitor but in a white color, measures give high ohm values like 60K

Manual: https://dl.dropboxusercontent.com/u/18602178/Vestel%2B17MB37.pdf

Last picture is from Google, for reference, same model


texts: Simple fast short circuit protector for circuit

texts:
I am trying to design a simple short circuit protector for the below circuit.  Any short circuit simulated by switch SW1 turns off LED D2 only not LED D1. Currently both LEDs turn off and for safety with a fuse circuit is current limited for 100 mA.
An isolator should activate if the circuit draws  more than 25mA. Normally when both LEDs are working the circuit draws only 18 mA.
The circuit total load current 18mA is monitored and tolereance of +/- 1 mA only allowed by other control circuits. If loaded current exceeds +/- 1mA limit it will register as fault by  current monitoring circuit.

The below isolator circuit with MOSFET designed to isolate Led d1 in short circuit without power to Led d2. but not working as expected.
Any short at SW1 will turn off the MOSFET,  as gate  source voltage equals to zero and isolate LED D1 from LED2,   and protect circuit  total voltage dropping to zero from 9 v.
What's wrong with this approach?


texts:
I am looking to replace this USB port on a new laptop which snapped inside the connector.

I know it is a USB 3.0 socket, but not sure on the exact part number or type of socket.

I found this online: http://www.maplin.co.uk/p/maplin-usb-30-socket-a-pcb-n08jt which looks very similar, but the one I need seems to mount in the middle of the PCB, rather on the top

Any help would be great.


texts:
Maybe this is very stupid question but I want to know if I can connect two or more voltage regulator (like LM7L05) to add ampere? Say if 1 is able to source 100 mA then combine 2 to draw 200 mA? Sorry if this sounds stupid!

Note: I know I can search regulator to source more current but in this question, I would like to understand that if I can connect multiple regulators together!


texts: What happens when I overload an induction generator

texts:
I am trying to generate power with a small induction generator.
The RPM is constant.
What will hapen when the rated input torque is exceeded?


texts: The power supply from a solar charger board has USB connection. But on my sensor board, I need only the VDD and GND. Can I simply cut one end of the USB cable and connect the VDD and GND wires to my sensor board?


texts: How should sampling frequency, switching frequency, control loop update frequency, and anti-aliasing filter corner frequency relate?

texts: Suppose one is designing a processor-controlled switching supply. In general, how does one properly select switching frequency vs. control loop update frequency vs. feedback sampling frequency vs. feedback anti-aliasing filter corner frequency? I think control loop update frequency should match switching frequency, and that the feedback sampling frequency should be at least the switching frequency. I also think that the anti-aliasing filter should be a lowpass that cuts frequencies above half the sampling frequency (though of course doing that perfectly is impossible). Is that accurate? If not, where am I wrong? Should the sampling frequency in fact exceed the switching frequency? Should there be some digital filtering involved as well?


texts:
I need to send integers from my micro controller board (PIC16F877) to the PC. I'm using MAX232 for this. I need to use a code similar to this (coded using mikroc 8.2).

Please note that this is not correct (actually the line Usart_Write(count); will not work as intended). But it'll show what I'm trying to do.

#define BAUD_RATE 57600
#define DELAY 500
int count;

void interrupt(){
     if(INTCON.INTF == 1 ){
          count++;
          INTCON.INTF = 0;
     }
}

void setup(){
     INTCON = 0x90;
     TRISB = 0x01;
     Usart_Init(BAUD_RATE);
     count = 0;
}

void main() {
     setup();
     while(1){
        Usart_Write('>');
        Usart_Write(count);
        Usart_Write('<');
        count = 0;
        delay_ms(DELAY);
     }
}

The application is simple. The variable counter is incremented with PORTB0 interrupt and counter value is needed to be send to PC.

Can someone show me a correct (and simple) way to do this..


texts: Compensation capacitor(s) in instrumentation amplifier

texts:
I wonder whether the discrete 3-opamp instrumentation amplifier requires any compensation capacitors:

simulate this circuit – Schematic created using CircuitLab

Is it in general recommended to add compensation capacitor(s)?  For example, in parallel with the RD connecting OA3 output to OA3 inverting input.  What about one in parallel with RF1 and one in parallel with RF2?


texts:
I am working on duplicating a product according to the Microchip datasheet. http://ww1.microchip.com/downloads/en/appnotes/00857b.pdf
My question has to do with something I found in the schematic (page 29, and also inserted below). That is, the bypass circuitry at supply of each of the two main drivers appears to have a path straight to ground from +12V (see below). How will this power the drivers at all connected like this??? I figure I am just understanding this wrong and it is not a typo because its coming from Microchip and not some Joe-Schmo. Can someone explain this to me? Thanks in advance.


texts: 74181 ALU not working properly cascaded to add 8 bit numbers

texts:
I'm trying to make a homebrew CPU but having problems with the 74LS181 ALU, which I'm simulating in Logisim software before diving into real ICs and breadboards.

I've cascaded two 74181 following instructions found in many sites such as this.

This works fine with most of addings I tried, but some don't work.

For example:

0010 0111 (39 in decimal)
+
0000 0001 (1)

leads to a 0010 0000 (32) result.

I know it should have something to do with the fact that 74181 uses signed numbers represented in two's complement. The least significant nibble in the example (0111) represents the max positive number with 4 bits, so when incremented by one goes to zero...

Is there any way to make 74181 work with only positive numbers? Or solve this issue in any other way.

I'm frustrated because with this problem the ALU is completelly usesless.

link for 74181 datasheet

link for project (has image of error on simulated ALU) - link on comment bellow


texts: Is this motor humming because of a short circuit?

texts: I disassembled my vintage grinder to grease the bearings, on reassembly it hums when the switch is turned on. The centrifugal switch appears to be functioning normally. The only possible aberration to my mind is the resistance value between the motor run lead and neutral, I would've expected significantly higher. Am I overlooking something or is this motor bound for the bin?


texts: What exactly do the well taps in MOSFETs do and how?

texts:
Do they affect the flow of charge carriers or charge concentrations at all in the device? How so? Up to this point I've tried to visualize the effects that the various doped areas had on device operation (w.r.t. how the charge carriers are affected) but I'm having a little difficulty doing so with the well taps. How do they affect the movement of charge during device operation? Do they redirect/divert current somehow?

I'm also a bit confused as to what their main function is, as I've read both that they're used mainly to a) prevent latch-up and b) lower the resistance of the wells. For each of these functions, how is this achieved? That is, what exactly are the mechanisms by which the well taps provide said functions?


texts:
I am interested in understanding better how the regulation for a buck converter works, I don't understand it now and havn't found litterature really explaining it so far, so I am asking you here.

The topology would be a buck converter, with a fixed switching frequency fs, an inductor L, a capacitor L and an output impedance of Rout. The duty cycle is D. There would be two regulating loops, one for voltage and one inner loop for current control. I added a figure to explain these loops (idea)

Now the thing is, up until now I actually thought that in dc/dc converters like the buck you have a fixed input voltage, want a certain output voltage and then set D accordingly to Vout = D * Vin.

What is wished for here is to also have a possibility for current regulation to limit the current to a maximum value for example.
But I really do not understand how you can regulate both independently. For me there is Vout/Vin = D = Iin/Iout, and therefore if you want to limit the current you actually change the output-to-input voltage ratio. Could someone explain?

Second question (possibly the same, but a particular case): if such a converter is tested, it would be possible to connect input and output and to let a regulated current flow while supplying the losses from a (low) power source. Here's a schematic:

I know it works, but not how since I did not understand the current control. I guess you set a Uin =/= Uout and then a current (limited by the regulation, and not by the very low impedance path) flows? Could someone please explain this?

Any help would be greatly appreciated!

Cheers


texts: Charging a capacitor with a ferromagnetic generator

texts:
I am doing my internship and the company is making a ferromagnetic generator which indeed uses magnetic transition to create a flux and finally EMF. I am assigned to design a circuit which takes the EMF created and store it in a capacitor.

I have done much research but I am not sure how to tackle the generated EMF. It is basically a high voltage pulse but I am not sure if I need to use a diode first to eliminate AC or if I should use a current limiter of any sort.

I can understand if there will be any critique that this is a very wide question but I only want to have some recommended reference or article to just gather my thoughts.


texts:
I have connected an IR2112 as a low side gate driver in Proteus.
Its output is very bad (blue graph.) It is even worse at higher frequency (given is 7812 Hz.)

Is this how the IR2112 supposed to behave?
Here is the schematic:

SD, COM and VS connected to ground. VC is 19V, LIN in shown in first picture (green graph.)


texts:
I'm trying to get my LCD to display "Voltage= (variable)". I have it programmed to write the text and I have a pot wired to my arduino and I'm trying to get a voltage number to come after the equals sign.  How can I program it so when I turn the pot that the actual voltage will come after "Voltage="?

Here's my program

#include <Wire.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27,16,2);
void setup()
{
}
void loop()
{
lcd.init();
lcd.backlight();
int sensorPin = A0;
int sensorValue = 0;
sensorValue = 0.004882812 * analogRead(sensorPin) + 1;
lcd.print("Voltage=");
lcd.print(sensorValue);
}


texts:
I'm looking to confirm I have the correct process to determine an average current for the following switched circuit:
I peak is given as 10A
I rms is given as 1.8 A. From: $$Irms = Ipk\sqrt{D}$$ I get a duty cycle of 0.0324, which then results in 0.324 A as the average current. Is this correct?


texts: Should you try and minimize via quantity?

texts:
I have a 6.5" x 4.5" double sided board that is mixed analog and digital.

I have partitioned the analog and digital grounds from each other and have zero ohm resistors that bridge the two grounds together.

But my layout involves a lot of vias. When I looked at the drill output file, its about ~400 vias. The bottom traces are kept as short as possible so as to just allow routing on the top layer, but because of that, I have a lot of vias.

Is this common to have so many vias? Should I look to make longer traces to reduce via count?

Update Added top and bottom layers


texts: Can't run two RFID readers off the same 5V rail

texts:
I have a circuit consisting of an Arduino Mega2560 connected to a 134.2kHz RFID reader from Priority1Design. The RFID reader works fine by itself, however as soon as other components are connected to the 5V rail it stops reading data.

I've done some measurements and the current going to the reader does not ever exceed 35mA and the voltage sits around 5V. When another component is connected to 5V and GND (say, another one of the same RFID readers without Tx and Rx connected), the voltage over the original RFID reader drops by about 50mV and the current remains the same (the Mega can provide more than enough current for both of the RFID readers).

I've performed some experiments where I try reading with both readers connected, then I unplug the second one and the first one will start reading again. I've also tried connecting decoupling capacitors between the 5V and GND pins of each of the readers (as close to the reader as possible), but nothing changed.

Here's a schematic of the effective circuit:

simulate this circuit – Schematic created using CircuitLab

When SW1 is open, RFID1 reads properly. When SW1 is closed, it cannot read. I've also noticed that when I probe Tx or Rx with an oscilloscope, it cannot read anything either.

If anyone has any suggestions as to how to fix this, it would be greatly appreciated.


texts: Is this class AB design OK? I get distortion at the output

texts:
I'm need of an amp that could charge small capacitors 'fast'. The capacitors are actually a disc with one side grounded and the other side coated in oxide so effectivly this is a series of small caps as the disc keeps moving. By charging the caps to different voltages, data is stored on the disc.

The circuit is not very complex, there is a non-inverting JFET input op amp that gets an audio signal and outputs it into a class AB BJT amp. The transistor bias is set using a textbook trick for self biasing of sorts. The negative feedback for the op amp is taken from the output of the transistor amp through a resistor that sets the gain together with R8 (it's actually a 50K trimmer). The problem I am having is that the output is distorted at any gain setting. Is there something fundamentally flawed in the design?


texts: How can I make the power amplifier stage for this audio amplifier?

texts: How can I implement a Power Amplifier stage for powering an 8 ohm load? I tried making an AB amplifier, but either it doesn't work or I'm just not able to make one. The output of the third op-amp is a 20V sine wave. This, however, can be changed. I just can't seem to be able to make a power amplifier stage for such a low output impedance...


texts: How to convert files from Cadence to Eagle CAD?

texts: Is there any free software that can convert Cadence files (.dsn, .opj, .brd) into Eagle CAD files (.brd, .sch)?


texts: VBAT pin and external crystals in STM32F030R8T6

texts:
STM32F030 Datasheet here.

On page 14, it's mentioned that:

  "System clock selection is performed on startup, however the internal
  RC 8 MHz oscillator is selected as default CPU clock on reset. An
  external 4-32 MHz clock can be selected, in which case it is monitored
  for failure."

I believe that microcontroller can be run perfectly using internal crystal. Am I right? If I am, then in what cases would someone want to connect an external crystal to the controller? Is it to run the controller at a lower frequency (to save power)? I think this can also be achieved by setting some prescalers on the internal clock. Are there certain applications which mandate the requirement of an external crystal? If yes, what could they be?

Page 21 says:

  The RTC clock sources can be:

  • A 32.768 kHz external crystal

  • A resonator or oscillator

  • The internal low-power RC oscillator (typical frequency of 40 kHz)

  • The high-speed external clock divided by 32

Will RTC be able to keep accurate time on internal clock source? I am fine with +-5 seconds per day. Can I achieve that comfortably?

I have always seen 32.768 kHz crystal being used with RTC chips which makes it easy to count due to 2^15 value. However internal clock source gives it a 40 kHz signal. Could there be any issues arising due to this?

Usually in microcontrollers with internal RTC, there is a dedicated VBAT pin which is used to keep the RTC alive during power failure. I couldn't find such a pin on this device. Where can I connect the battery to get the intended backup supply for RTC? There are multiple VDD pins but I am unable to make out whether one of them is VBAT pin or not and if yes, then which one. Pin definitions are from page 28-33.


texts:
I was thinking about a power circuit in which the power can be supplied on the same rail through a solar panel or an ac adapter. I automatically thought to add diodes in series to form an OR gate, so the panel wont supply the ac adapter and vice versa. But then I thought- do I really need to protect the solar panel from reverse current? What would actually happen?

What happens if you supply power to the solar panel, not from it? I would appreciate all help.


texts: What is the difference between the I2C interface and the "Grove" system?

texts:
The Grove system has various sensors and boards that to me all appear to be I2C-based, with a standard connector shape/size added to them - however I am not sure if this is exactly true or not - is there any way to find out? are the specifications different somehow?

For example, looking at the hub for it

I don't see any special circuitry or anything, and it claims to be an I2C hub - is it really just a form factor on top of the I2C interface?


texts: Can a textile fiber cause an electrical short?

texts:
Let's say you are cleaning some USB ports/plugs with chenille pipe cleaners moistened with alcohol.  As you can see from the image of a USB port below, the raised wire contacts inside the port could cause chenille fibers to become stuck to them (and indeed that happened to me recently).

According to Wikipedia, chenille can be made from cotton, acrylic, rayon or olefin.  A couple of resources I found said that those materials are all electrically conductive to some degree:

cotton is "slightly conductive"1
acrylic has "fair to good" electrical conductivity2
rayon has "fair" electrical conductivity2
olefin has "excellent" electrical conductivity2

So if a chenille fiber got stuck inside a USB port, could that cause any problems with the operation of the port (such as by creating an electrical short if the fiber touched 2 of the wire contacts)?


texts: Driving a 12V door strike from 3V3 BeagleBone?

texts:
I'm trying to control a 12V electronic door strike lock from my 3V3 BeagleBone.

Here's a diagram of my circuit:

My circuit probably needs a NPN transisor of some sort, but I'm not sure which one would work. Also, because the strike lock is a solenoid, do I need any diodes/other protection in my circuit to prevent over-voltage/other bad things?

Thanks. Your help is much appreciated!


texts:
I'm trying to implement an LED driver and I found the next circuit in PSoC's Guide on how to use the GPIOs.

Thing is I don't get if it's a must to include the R3 resistor and the Q2 transistor or if it's enough configuring the Pin_4 as Strong Drive??

thanks!!


texts: IR LEDs for illumination, as used in night-vision cameras

texts:
Being aware that IR LEDs come in various frequency-ranges, illumination intensities, sizes etc., was wondering if someone can help me identify the right type of IR LEDs, a cluster of which could potentially be used to illuminate a dark-room, s.t. I can use my standard web-cam to serve as a night-vision camera ?

Professional surveillance cameras seem to have things like "IR cut filters", which I believe are optical parts that are moved-in/out electro-mechanically, to help them work well, both in night and day. Do their optics (s.a., the lens, sensors) also have some differences, say compared to those found in commonly found webcams ?


texts:
A few years ago, I designed an MCU-controlled dimmer driving a 150W mains halogen lamp. This is in Western Europe; 50Hz 230VAC. It uses X2-rated capacitors as capacitive droppers for the power supply, and another X2-rated capacitor for interference suppression:

The dimmer has gradually started misbehaving, and on debugging I found that all of the X2 caps have died (meaning they have less than 10% of their rated capacitance remaining):

The caps in the picture:

C1, capacitive dropper, should be 100nF, measures 6.4nF
C2, capacitive dropper, should be 100nF, measures 6.9nF
C5, interference suppression, should be 100nF, measures 1.4nF
Cnew, fresh-ish cap from my junk bin, measures 93nF

All of them measure open circuit (>40MΩ) on resistance.

C1, C2, and Cnew are labeled MEX/TENTA MKP 0.1µF K X2 275VAC 40/100/21 [approval logos] EN 60384-14 01-14 250VAC; 275VAC nominal rated (significantly higher withstanding voltage, datasheet here). They are all from the same batch, bought in Sep 2016. I suspect 01-14 is a date code, so they'd be from early 2014.

C5 is from the same brand; it has virtually the same markings (except EN 132400), but is physically larger. I got it as part of some Velleman kit years ago, where it was also used as a suppression cap. No datasheet.

What caused these caps to lose their capacitance?

Is this deterioration  normal behaviour for X2 caps? The dimmer saw a lot of use, being powered for an estimated 7000 hours.
Should I have derated the caps more? I agree 230VAC is pretty close to 275VAC, but as I understand it that is their nominal rating, and they should be able to handle transients way above that. Also, 275VAC seems by far the most common rating available on Digikey and the like.
Am I using the capacitors wrong somehow?
Are these capacitors from a bad brand/series/batch?

Update: Possibly relevant: the dimmer is powered through a mechanical switch, and has seen an estimated 1000 on/off switch cycles over its lifetime. Perhaps the transient from mechanical switching played a role?


texts: MATLAB How do I pass a signal into a low-pass filter in matlab?

texts:
I'm having trouble figuring out how to pass a signal into a low pass filter using MATLAB.

I am given a .wav file and am following instructions on how to remove high frequency noise compenents from taking the Discrete Fourier Transform(DFT) of the audio signal. The idea is that there is a secret message in the .wav file that is currently being hidden by a lot of unwanted frequency noise. I am supposed to get rid of said noise.

My script is currently as follows:
[y, Fs] = audioread('horrible_noise.wav');
y = y(:.1);
plot(y)
NFFT = length(y);                             % number of discrete points
Y = fftshift(fft(y,NFFT));                               % DFT of the audio signal
F = ((-1:2/NFFT:1-2/NFFT)*Fs);                 % Range of the frequency of the audio file
magnitude_Y = abs(Y);                                % Magnitude of DFT
phase_Y = unwrap(angle(Y));                      % Phase of DFT

I'm supposed to plot the magnitude and phase and explain any trends in the plots.

plot(magnitude_Y,F) plot(phase_Y,F)

At this point, I am supposed to remove the high-frequency components that are unwanted by setting them to zero. Which is apparently done via low-pass filtering. This is where I am having trouble. I have seeked help on this and came across commands such as using butter, fft, etc. I have no idea how to use those functions and don't even know if that is the right way of approaching my problem.

So again, I would like help on passing this signal(DFT) into a low-pass filter to get rid of unwanted noise. Thanks.

Audio signal in question - Warning, the sound isn't pleasant to listen to. Would recommend lowering your volume.


texts: Current tranformer, burden resistor calculation

texts:
I have 1:50 wound current transformer and I don't have the datasheet. Could anybody help me to calculate the burden resistor?

Maximum current to be measured: 2A

Max output voltage to ADC: 5V


texts: How to calculate PAM signal power spectrum

texts: How to calculate power spectrum of given signal


texts: Can we sample two signals simultaneously using the ADC (analog to digital) of AVR mircocontroller?

texts: I am making a project of noise cancellation using least mean sqaure algorithms through microcontroller. In that I need two signals to implement LMS algorithm i.e noisy and noise+clean. So my question is how can i sample these signals simultaneously? Is there any way to sample both signals at the same time?


texts: Changing addresses faster than a parallel SRAM's response time

texts:
(Parallel) SRAM data sheets often list response times such as 70ns.

If /CE and /RD are held low, and the address is changed every 35ns, what will be the output on the data pins?

I am expecting either the contents of those address (delayed by 70ns) or a complex mess dependent on the row/columns of the addresses.

i.e. Is the response time a uniform delay, or a maximum upper bound on a non-uniform delay.


texts: Protecting components from catastrophic age-related battery failure

texts:
As someone who does a lot of restoration work on old electronic devices of all kinds, finding old, leaking batteries well beyond their use-by date is common. Finding that the battery leak has destroyed numerous traces or other components on a packed PCB is also common.

The first step taken when addressing a device like this is to remove the battery before it can do any more damage, neutralize whatever caustic gunk is still on the board, and then remove the debris and test before installing a compatible battery.
However, this is prolonging the inevitable. The new battery will eventually fail in the same way, with its seals giving way and releasing electrolyte into the surroundings, possibly years in the future.
Many of the devices this is happening to will sit without being energized for a long time, so regular checking of the battery is not feasible.
My question is: is there some "standard" method you could use to protect the PCB from this failure case when, not if, it happens?
One thing I've seen done is wiring the battery to the PCB terminals and placing the actual cell far away from the board, and that is definitely viable. Still, I'm looking for more options, ideally, a canonical option, if one is known.


texts:
I have a Mechanical Engineering Master Thesis about positioning control of a pneumatic system with Model Predictive Control. I am primarily an electrical engineer and i do not know much about electronics. I need to design an interface card in order to connect a valve (5/3 way), two pressure sensors, a linear scale to my NI-PCI-6010 data acquisition card.

I have a bunch of questions about them. I tried to find solutions about them but none of them is enough for me. I wish you can help me.

However proportional valve (http://xdki.festo.com/xdki/data/doc_ENGB/PDF/EN/MPYE_EN.PDF) needs to be driven with 4-20 mA, my PCI-6010 card (http://www.ni.com/pdf/manuals/371498a.pdf) doesn't support it as i understand. Its analog output have a range of -5 to +5 V, i need to convert it into 4-20 mA.

First of all, do I need to convert -+5V or can I use 0-5V instead? I have seen lots of voltage-to-current converters in other websites, but all of them is about converting 1-5 V to 4-20 mA, I think there is an offset problem for 0-5V. I have found a non-inverting summing amplifier that can do what I want, but when input voltage reaches 5V, output current reaches 20,496 mA and this is surely a problem, also i need linearity.

I have found an IC that can convert 0-5 V to 4-20 mA (XTR110, I think you all have a word to say about it), but I cannot wait to purchase it, because i couldn't find any distributor in my country. So that I want to design a PCB in order to get over this problem.

Also I don't want to use a passive voltage-to-current converter. Here is the circuit I designed.

V1 = 5 V, Vref = 1 V (for offset problem)

Also; when V1 = 0V, output current is 4,037 mA. But it is not a big problem. Other values are;

V1=1 V, Iout=7,329 mA

V1=2 V, Iout=10,62 mA

V1=2.5 V, Iout=12,267 mA

V1=3 V, Iout=13,912 mA

V1=4 V, Iout=17,204 mA

As you see, I cannot achieve a setpoint value for my valve too (It needs 12 mA for middle position).

Of course I don't want you to do my thesis for me, but I stuck on early stage of my thesis and if I cannot found a solution about it I absolutely have a real bad time.

Thanks in advance.


texts: Why do PTC fuses have different voltage ratings depending on package size / hold current?

texts:
I've been trying to figure out the PTC fuse I want to use in a little automotive power supply circuit and I'm a little disconcerted by the max Vdc ratings most of these things have.

For instance, looking at Littelfuse's offerings for SMD PTCs... I want something that trips at 3.5A.  For the given trip current, only their higher package sizes (like 5mm x 4mm and up) have Vdc max ratings that are over 12V.  Yet, they have stuff in the 1210 package that is listed as handling hold currents in the range I want.. albeit with a low max Vdc rating.

At a very basic level.. if the fuse is rated for a given current, why is voltage an issue?  This is what I don't understand. :(


texts: Thermoelectric cooler powered by 12V battery too hot?

texts:
I am very much an amateur when it comes to this stuff.

Basically I have a set up that goes as follows:

Aluminum plate -> TEC (cold side) -> TEC (hot side) -> heat sink -> fan.

The battery is 12V 7Ah (SLAUMXNPG7-12). The TEC is 12V 4-6A (TEC1-12706).

The set up has no thermal paste or anything as I am just testing that is works before sticking it together.

The problem is that both the cold side and hot side are hot (though cold side is less hot). I am aiming to make a wrist cooling device as seen in this tutorial.

I have read that it is important to limit current to TECs else they will just heat up. Is this true? If so how would I do that?

Perhaps the problem is the thermal plate not getting cooled efficiently by the small fan and / or not transferring heat efficiently thanks to lack of thermal paste.

Anyone out there can help me? Thanks.


texts: What Happens when Read or Write Failures Occur on SD Card?

texts:
I have been happily backing up and copying SD (including microSD and SDHC) cards from a Linux PC using the following commands:

dd if=/dev/sdb of=sd.img bs=4096 conv=notrunc,noerror
dd if=sd.img of=/dev/sdc bs=4096 conv=notrunc,noerror

However, I know that there is the possibility for blocks to go bad on the SD card. I assume that this failure can occur on read or on write.

My question is, what happens on a read error? Do the errored bytes get set to 0x00 in the image file? Do they get set to 0xFF? Or do they disappear (changing the file size)?

Likewise, on write, what happens when there is an error? Will the SD card automatically write the data to another block? Or will something else happen?


texts:
simulate this circuit – Schematic created using CircuitLab

I'm trying to find the equivalent capacitor for this diagram but I'm having a little trouble understanding what capacitor is parallel/in series to what capacitor.

I know the equations. From looking at this I believe C1 and C2 together are parallel as are C3 and C4 together. Would the resulting two equivalent capacitors then be in series with each other?


texts: Does current flow through the potentiometers of buck and boost converters?

texts:
I'm working on a project where I'm replacing the trimpots on a buck converter and a boost converter with proper potentiometers. The new potentiometers will be wired to the converters instead of soldered directly on, so this poses a problem: What wire gauge should I use?

Let's say my loads will be maximally drawing 10A. Does that mean I need 16-14AWG wire to attach the potentiomters? I don't think so but I don't totally understand these things. My current understanding is that the potentiometer acts as a voltage divider and it is the center pin which tells the chip how to limit voltage or current by being at a certain voltage.

The answer may be that it depends on the converter but I think there is a general pattern here. To give an example though, I'll be working on this Chinese converter (Google translate) Update: This post is the most information I can find on it.

As I understand it, it's based on the UC3842A SMPS controller driving at least one power MOSFET (I also see a big N-channel and then the smaller BU806 NPN.) I don't know if that's enough information to answer my question though. It seems like, if it works the way I think it does, it's pins 2 and 3 on the UC3842A which read the potentiometers.

Another example is the LM2596-based boards. I suspect they work in a similar way (and are a bit easier to understand.) There's one more board/chip that I'm interested in but I don't have any information on it yet since it's not in my possession and there's very little details online. If it's okay, I'll leave the ebay link here.


texts: Generating a realistic sine wave in MATLAB

texts:
I'm working on a simulation on MATLAB and I need a realistic sine wave which has harmonics. So I know there would be harmonics at 2f,3f... but I am not sure how to determine their amplitude. I tried to use Fourier and Bessel expansion, but I'm not sure about their implementation on MATLAB.

What can I use for that purpose? Any advice appreciated.


texts:
As you know if you have a 4 bits multiplexer, if you input 0101 the output 5 goes high, but right when you input another thing like 0001, output 5 goes low and output 1 goes high.

I need the multiplexer to remember the output state like a flip-flop, so when I change from 5 to 1, 5 remains high until I send another signal to it. Does this kind of IC exist?


texts: can I use a 5v 1a charger with a 5v 2a device?

texts:
Possible Duplicate:
  Choosing power supply, how to get the voltage and current ratings?

I have a new tablet with a charger that reads 5v 2a, can I charge the tablet with my phone charger, which reads 5v 1a? Thanks!


texts: How is torque proportional to current and magnetic flux in a DC motor?

texts:
It is well known in physics that a rigid body having a current \$i\$ in a closed loop under a magnetic field \$\vec{B}\$ experiences a torque which is
\$\vec{T}= \vec{m}\times\vec{B}\$
where the magnetic moment \$\vec{m}\$ is defined as a vector perpendicular to the plain of the coil itself and it has a module equal to the product of the current with its enclosed area.
\$ \vec{m} = i\vec{S}\$
My problem is that I would like to understand in which way in a DC motor the torque \$\vec{T}\$ on its rotor is proportional to the product of current \$i\$ and the magnetic flux \$\phi(\vec{B})\$ .
\$
T = K \phi(\vec{B})i
\$
as reported (without demonstrations!) in an engineering book I am dealing with.
Particularly my need of clarification comes from the following consideration: when the flux \$\phi(\vec{B})\$ is zero then the torque \$\vec{T}\$ is at its maximum, while, when the flux \$\phi(\vec{B})\$ is at its maximum then the torque \$\vec{T}\$ is zero.
For the purpose of a clear understanding I report in the following picture a simple scheme of a DC motor:

According to Lorentz equation, the force (green arrows) applied to the rotor
\$ \vec{F} = i\vec{l}\times \vec{B}\$
which means the force is constant in both module (\$F = ilB\$) and direction all over the rotor movement around its axis. What is not constant is the torque \$\vec{T} = \vec{b}\times\vec{F}\$, the module of which being
\$T = ilbB\sin{\alpha}\ = iSB\sin{\alpha}\$
where \$\alpha\$ is the angle between the plain of the coil itself and and the Lorentz force (which is slightly different than 90 degrees in the configuration of the previous picture.)
Now the equation \$\vec{T} = \vec{m}\times\vec{B}\$ is well satisfied but, as I previously mentioned, when the flux \$\phi(\vec{B})\$ is at its maximum than the torque \$\vec{T}\$ is zero, while when the flux \$\phi(\vec{B})\$ is zero than the torque \$\vec{T}\$ is proportional to product of \$i\$.
Is there anyone who can clarify me this issue, please?


texts: Does Carrier frequency offset (CFO) means difference of the message frequency and integrator?

texts:
Can anyone here tell me what is CFO? Initially, I thought it might be when the message signal mi, that is
$$r(t) = 2P cos(2\pi fc*fi+\delta f)$$ doesn't match with integrator  $$\int_0^T r(t) *  cos((2 \pi(fc + fk)t )dt$$ when fi doesn't match fk then we have a value of $$\delta f $$and that is CFO but I think it isn't the case as some times fi matches fk but still we have an equation for CFO? And can someone tell me how it affects BER? Should we multiply  $$y= h*x + N $$ with CFO factor?

Source :
enter link description here


texts:
Would it be beneficial to feed a voltage regulator tube with an inductor (as in the following pic)?

I'm thinking that a 50vdc air-gaped reed relay coil would do the trick. They measure about 1.9k each (@ 2mH), so they should be able to handle around 25mA. Perhaps this would filter some of the power line RF which the tube is unable to regulate.

Would there be any potential issues?

Would this actually be useful at all, or just a fancy resistor substitute?


texts: How do you do operations on large numbers using a small fixed-width ALU?

texts:
I am wanting to design a simple calculator like what you would find in the dollar store. Something like this:

This little guy can display a number 8 digits long, meaning 99999999 is the largest number that can be displayed in this format.

I am familiar with how a simple ALU works with two registers as input.

Now, if I where to use a 32bit register for calculations, then everything would be OK since the register can hold 99999999 just fine. However, I want to understand the process of using two smaller registers to hold bigger numbers and how that works with an ALU?


texts: Recommendations for converting 2~7V to 5V?

texts: I'm looking for a switching regulator chip (buck-boost, sepic, or other topology) to convert 2~7V input to 5V. I realize it's easier to have an input voltage range that's consistently higher or lower than the output, but this is what I need. It also needs to support 10W output (2A@5V), and I'm looking for a relatively low-cost solution with minimal external component count. Any suggestions?


texts: How do I safely interface an NPN or PNP sensor output with the GPIO pins on my Raspberry Pi?

texts:
I am trying to use this industrial color sensor to detect different colored objects using the Raspberry Pi.

I programmed in the colors and the display on the sensor shows that it is able to correctly identify them.

The sensor is programmable to allow you to set each output as PNP, NPN, or Push-Pull.

Assuming I am running the sensor off of a 12v wall wart (Sensor Operating Voltage is 10-30 VDC). What is the best way to interface the NPN/PNP switching outputs with the 3.3v GPIO pins on the Pi?

I was planning on using an optoisolator to protect the Raspberry Pi pin from the 12v power.

What's the preferred way of connecting an NPN/PNP output to a 3.3v GPIO pin?

Here is the wiring diagram from the sensor manual.


texts: Pass Transistor: discharging of the capacitance

texts:
let's consider this pass transistor logic:

Let's assume that the MOSFET is always active (CK = high for a N-MOSFET). Now, immagine that at the beginning Vin = 10V and Vx = 0: the capacitance Cx will be charged and at the end we will get Vx = 10V.

Now suppose that Vin becomes 1V: the capacitance will discharge itself until it reaches the value 1V. But, which is the resistance to which it discharges itself? If I look to the previous circuit I see, since the transistor is ON, simply a voltage source equal to 1V in parallel with a capacitor which is precharged to 10V.

Is it the internal resistance of the voltage source connected to Vin, the internal resistance of the transistor etc?


texts: What is this circuit gain when set is in [0,1]?

texts: When set is 0 or 1 I could find it. It either attenuates by 10 or amplifies by 10. However, the circuit becomes different when it is between 0 and 1.


texts: Information tables for operational amplifiers

texts:
Is there a place in the web (or elsewhere) where it is possible to find tables for operational amplifiers (and why not, other electronic components) like the one, for instance, in "The Art of Electronics", table 4.2.a.

I know big companies have their own catalogue, but it would be nice if this was done by electrical engineers for all the companies, possibly with some filtering system.


texts: 6 LEDs in parallel with a single resistor to simplify soldering

texts:
I'm trying to wire up 6 RGB LEDs in parallel, all controlled from a single source (well, three sources, one for each colour). The LEDs came supplied with resistors to limit the current of 270 Ohm for a 5v supply.

The problem is, 6 LEDs x 3 colours = 18 resistors, which is a lot, and means I need a much bigger board and a lot more soldering.

So, can I instead wire the LEDs in parallel with each other, with a single resistor protecting all six? (3 resistors in total, one for each colour). How do I calculate the value of that resistor?

More details:

The LEDs are being driven from a ULN2803A to supply a bit of current, which is in turn controlled by a Netduino providing a PWM signal on the three channels.

These are the RGB leds in question. If I've correctly understood the data sheet they want 20mA of current, and forward voltages of 2, 3, 3 volts (for R,G and B respectively?). The supplied resistors were all 270 Ohm, so the channels may not be balanced quite right.

For extra credit: I'm only using 3 of the transistors in my driver chip, which has 8 in total. could I wire the PWM from the netduino to a second trio of transistors, and split the LEDs into two groups of three? Is it worth the effort?

PS I don't have any diagramming tools to hand, but I can provide a diagram (drawn in paint) if it would help clarify my question. (see also this meta question)


texts: LM317 voltage regulator circuit drops Vout on load

texts:
I'm attempting to build a voltage regulator circuit for a DIY stir plate using a CPU fan supplied to an LM317 voltage regulator circuit.  I have everything wired up on a board just like the diagram, but using 1kΩ and 10kΩ resistors (which according to this calculator should give the same voltage out).  I'm feeding it 12V of DC power from a DC power supplying up to .3A.  Measuring the Vout of the circuit without a load attached gives the expected ~12V and drops to ~0V when I dial the potentiometer down.  However, once I add the fan, it won't move and the Vout measures a max of 2.1V.

The fan claims it needs 12V and .1A - I'm assuming this means it's ~120Ω.  I've also tried swapping it for resistors that I had laying around.

Measured Vout under various loads:

Fan: 2.2V
220Ω: 3.6V
1kΩ: 7.3V
100kΩ: 8.6V
1mΩ: 11.3V
no load: 11.3V

For diagnosis, I've tried swapping my R1/R2 resistors from 1k/10k to also try 10k/100k, 100k/1m, and 220/1k (no 100 laying around).  It's pretty common to see these as different combinations on other stir plate instructions I've read, and the LM317 calculator says they should give the same voltage.  All of these combinations gave nearly identical Vout for the variety of loads.  The voltages also stay the same with or without the capacitors, which I read were optional.

Can anyone point me towards what's probably wrong, or how to further diagnose it?

EDIT: Solved! I had the LM317 flipped around backwards due to some bad labeling on the bag the component came in.  I checked another company's data sheet and flipping it around fixed it.


texts: Inexpensive medium-range wireless for small projects

texts:
I'm building a few sensor projects that will need to pass status messages wirelessly. The required range is standard household distances; 30 to 100 meters indoors, through walls, etc.

The XBee offerings appear to be all the rage lately, but at around $20 to $50 each, those devices would increase the project cost by one or two orders of magnitude. Conversely, the cheap no-name wireless offering reportedly have some reliability issues and are difficult to get working if you can do it at all. It would be much better to go with something with a bit more engineering behind it. Low-power would also be helpful in some of the installations, but it's not critical at the moment.

What inexpensive wireless options are there for small projects? Something that combines both the microcontroller and the wireless into a single package would also help defray costs. But again, XBee is expensive even for a microcontroller.

I haven't settled on a MCU yet; I'm considering the PIC, AVR, and MSP430 and leaning toward AVR since I typically use that for prototyping anyway; but really anything with a decent ADC and PWM will do.


texts: What is the best way to rectify 1MHz, 50V 0.1% duty cycle signal?

texts:
I would like to power a 5V micro-controller remotely. I have a piezoelectric transducer that will pick up mechanical energy from a vibrating plate. I've already measured 48V at 1MHz on my oscilloscope. However, the duty cycle is only about 0.1%. The plate vibrates ever 1 second or so.

I believe it's recommended that the Zener diode be rated for about 25% less voltage than the output of the bridge.  If I use a much smaller Zener I'm afraid I will exceed the max current rating of Zener.

Am I going about it all wrong?


texts:
I'm having issues with deployed knob pots after they've been in use for a while.  It's been an ongoing problem that we don't see at our local facility.  I'm wondering if any of you may have experienced this problem, and more importantly, are aware of a solution.

Pot: Bourns 3590S-1-203L, 10-turn, panel-mounted, 20k, knob-pot.

https://www.bourns.com/pdfs/3590.pdf

Problem:

Durability.  Common occurrence of glitchy output after some time (months/years) in use.

A picture showing traces from both a good (blue) and bad (black) pots, turned by hand:

Initially, there are no indication of problems.  Glitches manifest
after some time...
Once a pot develops glitches, they are permanent and always appear at
the same location in the 10-turns.
Glitches may appear, seemingly, at any location in the ten-turn
range.
Duty cycle is low.  Lets say a full ten turns forward and back every
day (which would still be an over-estimation).
The pot setting may remain (energized, or not) at the same location for days, weeks.
Although discouraged (and unusual), the system may be power cycled
with the wiper set in any location. It should typically be set to full CCW.
We are very careful when hand-soldering leads, using a heat-sink on the
pot tabs.  High quality, temperature controlled irons.  Experienced
assemblers. SAC305/ No-Clean flux.
The pot wiper is placed at one extreme location prior to soldering
(mainly as a way to determine if this problem could be a result of
heat damage during soldering).
Working environments tend to be environmentally controlled.  Even
though high-humidity is unlikely, it's possible.
Knob pot dial and panel are well earthed, with a dedicated chassis conductor.
We've seen failures for pots with both plastic and metal shafts.

Here is a copy of the driver and buffer circuits for the 20k pot:

The problem pot is the "Panel_Cmd_Knob_Pot" connected to the top 3 yellow ports.

(Not shown above is U2A.  This section is used as another low-speed buffer elsewhere.)

The +/-12VDC supplies come from +/-15 rails (switching supply), linearly post-regulated on-board (LM3937/LM2990 series).

All connections are 'permanent' (no hot-plugging).

What I plan on trying next:

Add a series resistor from the knob pot wiper to the U2B buffer input.  Perhaps current-limiting power-up transients, that may or may not exist.

Any better ideas?

Updates:

5/22: Sent suspect pot to Bourns for eval.
6/5: Requested status update from Bourns.  No response yet.
7/22: Bourns has acknowledged that they have the pot in hand, and the fellow who would look into it is back from traveling.  However ever since, they've gone dark and appear to be unwilling or unable to provide any insight.  Suggestion: Don't do what I did and/or avoid these parts.
9/10: Bourns has stayed quiet.  Giving up, and closing this question.

-Chris


texts: High current solid state battery disconnect

texts:
I need to design a solid state switch to disconnect a battery (28V) from a load that can go to a maximum of 70 Amps in a 40C environnement.
An SSR like the Crydom D06D100 could handle this using a very large heatsink and I suppose it would be the same for whichever big MOSFET I find.
How do the following products achieve this objective without using such a big form factor?
https://www.modernracing.net/product/mr-solid-state-battery-disconnect/
https://perfectswitch.com/dc-solid-state-relays/uni-directional-dc-relays/
https://verticalpower.com/index.php/products/pps


texts:
I'm trying to design a circuit that "multiplies" two signals.

I have an electrical unit with two separate circuits. One circuit drives the other one with a square signal. The width of the square signal is on the order of milliseconds. The amplitude can be set anywhere between 0 V and 10 V. The input resistance of the second circuit is 10 kΩ.

I would like to "multiply"/chop this signal with an LVTTL control signal. The width of the LVTTL can be as low as 50 ns. The amplitude is ~2 V. I want to pass the original signal if the control signal is high (2 V) and set it to zero if the control signal is low (0 V).

So far, I have tried to use a two-stage n-type MOSFET but the output dips to -0.5 V for a short time at the rising edge of the LVTTL signal. I tried different loads and stuff but did not get any good output.

Do you know any circuit that does what I need?
I have a buffer circuit, do I need it?
How to avoid the negative potentials on the rising edge of the LVTTL signal?

I can upload my LTSplice circuit if you want, or you can direct me to the right discussion group.

Here are images from LTSpice:
The 1st graph outlines my circuit, the 2nd, and the 3rd graphs show my input signal and my LVTTL control signal. The 4th and 5th graphs show output signals vs different input amplitudes. The 6th graph shows the signal at the output of the first MOSFET. The last two images show the outputs vs the stage 1 signal (output of the first MOSFET)


texts: What detection method does phased array radar use?

texts:
I have been learning about radar technologies for a while, with the intent of building one for fun. When looking at Phased Array radars, there is plenty of information on the beamforming math and cool animations showing the wavefront. But there seems to be little information on what goes on in the other parts of the system (see below). For instance how is the data interpreted? How is the signal received?

I was thinking that you can just hold the phase shifters constant and have the return signal just travel back through the rf chain to a circulator to split off the rx. (Are phase shifters in the real world bi-directional?)

I was looking at some kind of Frequency-Modulated Continuous-Wave setup because it cam be realized pretty cheaply with fairly low bandwidth ADC requirements but I am unsure if this can be applied to Phased Array Radar, or if there are even better techniques out there.


texts:
I'm having a custom cable made that will only use 2 of the 4 pairs for Ethernet.  I'm connecting a 10/100 Mbps device to a network with other GigE devices.

Pinout is clear:

However, I have seen one similar adapter online that places a resistor across the unused pairs - (See second device).

Are those resistors necessary? If so, recommend resistance? Any further advice making 4-pair GigE and 2-pair 10/100 devices play nice?

Thanks