texts: What would be the simplest BJT based *linear* ramp generator?

texts:
Let's say I have a 74LS161 based counter, and I want an analog ramp generator which will linearly increase until the ripple-carry-output goes back down (so that the ramp goes up the entire time the counter counts, and at 0 it starts over. Trying to avoid yet another chip and I need all the counter bits to count on the up-slope. And I don't want any other ICs for this, just standard BC548 or so NPN or perhaps BC558 PNP, few of resistors and a capacitor.
I thought starting up by something like this:

simulate this circuit – Schematic created using CircuitLab
If I do this I see the voltage on the RCO pin break down when it goes high, so I supposed I could add a 220Ω resistor in series to the base of Q2.
I haven't tuned the capacitor yet, at this point I have a 1 nF and it definitely charges too fast. That's why I plan 1 μF next.
But then I still have the problem that even if I can make that work, I activate that discharge transistor Q2 too early since the RCO goes up as soon as the output is all high. I have an inverter stage still from a 74LS04 hex inverter on the same board, so I suppose I could run the RCO through the inverter and then build a positive edge detector with another capacitor which would just pulse long enough to open Q2, and then shut off and stay shut off until the next rising edge of the !RCO signal.

simulate this circuit
Will it fly with some proper selection of R and C values? Maybe there is even a way to avoid the inverter stage?
UPDATE: I already got a better answer with the PNP transistor, but I have almost made it work with the NPN and just showing the scope tracing for this. I used 4.7 μF and the right kind of slow enough counter stage, to get this:

but indeed, with the PNP and 47 nF I get this on the same counter stage: so that is much better!

What I find difficult is to get it to work on the faster end of the counter. Am already down to C1 = 33 pF and still it's too slow for the 15 kHz that I need it for. I guess I need to reduce R3 to something a lot smaller. Is there a lower limit though? I tried going down 10-fold to R3 = 1 kΩ and while I can get a couple of more counter stages down with that I also have a lot less amplitude.
I need one at 15 kHz and the other at 60 Hz (haha, guess what I need those for :) )


texts:
I have a micro controller ATxmega128A1U (datasheet) which will have switches and potentiometers attached to the GPIO and ADC input pins. These inputs will have about 2-3 meters of cabling from the panel to the micro-controller.

1) What sort of protection do I need to put on these inputs? Would a TVS diode arrays be necessary? (something like this perhaps)

2) What sort of filters do I need to put on the lines? Would some simple ferrite chips be enough and how do I chose a ferrite based on frequency response if I don't know what sort of noise may be coupled to the system when deployed?

3) Anything else I need to design for when having cabling this long?

Thanks in advance for your help!


texts: The bottom 'pin' of a edge mount HD-BNC connector

texts:
I find except edge mount SMA connectors, there are also HD-BNC edge connectors, such as this. The recommended PCB land doesn't show the bottom pad.

For smaller SMA connectors, I usually solder the bottom pin to the bottom of the board. But for this BNC edge connector, it is a little 'bigger'. So, I wonder what's the pron's and con's to solder the bottom pad, except for making the connection more robust?


texts:
I'm converting lots of USB card readers to be mounted directly on the tablets. One (relatively trivial) problem is that the readers come with long 6ft USB cables which I'd like to shorten to about 1ft so they don't need to be "coiled". I can either splice the cable or hope to buy a pre-made shorter ones. For the latter, I'm not sure how to search for the cable that would have the pictured connector for my mini-boards. From the image, can you tell the connector type I need?

To the best of my abilities, the pitch distance is 1.18mm.


texts: how to understand the permissible voltage and current of film capacitor?

texts:
I use the 0.12uF metallized polyester film capacitor Model ECQE2124JB which
has 250VDC rated voltage. I have a sine wave across the capacitor, then can I
think that the maximum AC voltage is 250/1.414=176.8 Vrms? But from the characteristic datasheet, the permissible voltage is less than 40Vrms at sinewave. What's the difference? If I use the capacitor in a LC resonant circuit, does it mean the RMS resonant voltage cannot exceed 40Vrms?
In my opinion, the permissible current is calculated as I = 2*pifC*V, for my application f = 10KHz, so I = 2*3.14*10kHz*0.12uF*250V=1.884Ap = 1.33Arms. Is it right? But from the characteristic datasheet, the permissible current is only about 0.2Arms. Why that?
In my LC resonant application, the mearsured current across the capacitor reaches 3.5Arms, but the peak voltage will not exceed 250VDC. It also conflicts with Vrms = Irms *Xc, where Xc is the impedance of the capacitor.

https://industrial.panasonic.com/ww/products/capacitors/film-capacitors/film-cap-electroequip/ecqeb-dc-rated/ECQE2124JB


texts:
I just discovered DIN rails for industrial kinds of loads (10's of amps).  I'm using these parts, and am wondering whether I should jump on both sides.  It seems like more connections would mean lower resistance and that it could handle more current.  This comes at the cost of consuming another jumper, though.  Does it make a difference?

jumper: https://www.digikey.com/products/en?keywords=277-2115-nd
terminal block: https://www.digikey.com/products/en?keywords=277-2027-ND


texts:
I am building a circuit that uses an LC bandpass filter (with the inductor and the capacitor in parallel between the signal and ground lines). However I am having a problem in that there is no way that I can tell to change the passband width of the filter.

I have given details of my specific situation below, I am really wanting a general answer: how does one change the passband width of a parallel LC filter? This seems like such a simple question, but Google has failed to give me the answer.

Specific situation: I am trying to build a shortwave radio receiver. As such, I am needing a passband width of somewhere around 5kHz to 10kHz. However with my current component values, which is a 2.844uH inductor and a variable capacitor which at 50pF is supposed to give a tuned frequency of 13.333MHz for the receiver, the passband width is somewhere around 5MHz which is obviously way too high. According to a simulation which I ran, I need to put a 1 megaohm resistor between the antenna and the LC network, but that blocks most of the signal from the antenna.


texts: If you have a MOSFET in series with a thyristor, can turning the MOSFET off cause the thyristor to turn off?

texts:
This is a purely theoretical question. The values in the circuit below do not matter, and I understand the circuit is completely useless.
Consider if SCR1 and M1 are both turned on so that current is flowing through the resistor.  If you turn off the MOSFET, will the thyristor turn off? If so, how long will it take, assuming it has a typical turn-off time of \$ \text{T}_q\$.  Thanks a lot for the help!

simulate this circuit – Schematic created using CircuitLab


texts: How do you find the voltage across a capacitor at time t= 0 and t = infinity?

texts:
Here is a diagram of the circuit, I am confused about problems a and b.

How do I go about solving these two problems? Thanks!

By the way you don't have to tell me the answer, I just want to know how I should think about it, or any helpful hints would be appreciated. Thanks.


texts: How power system is designed for extreme small system, such as google contact lens?

texts:
I just read this news and got very curious: http://www.takepart.com/article/2014/07/23/goodbye-finger-pricking-how-googles-smart-contact-lens-really-helps-diabetics

Google is designing "Google Contact lens", through which people can read Glycemic Index. How power system is designed for this kind of electronic system? Is there a battery inside? If so, how is it charged?


texts:
I am running 2 DC motors with 3 SN754410's: each motor gets one half of each bridge. Everywhere I look I see that pulling both logic inputs low with the enable high should brake the motor by shorting its leads together. However, when I measure the resistance between the two motor power leads (motor disconnected) with the enable high and both logic inputs low, I get a resistance of 60 Ohms. The H-bridges are otherwise functional

Accordingly, I am attempting to implement an alternative brake. I have some of these (http://www.vishay.com/docs/91217/91217.pdf) 30A power transistors lying around. Could I use them to brake my motor by putting one from each motor lead to GND (see below for setup when I want to brake) and turning them on when I want to brake?

simulate this circuit – Schematic created using CircuitLab

I am not using a relay as they are too slow for my code: I get shorts through the bridges when the bridges turn on but my relays have not finished switching.


texts:
I've got an RC car with a 4xAA battery pack as one unit. I looked for a replacement battery and typically these are 700-1000mAh rarely exceeding this capacity. The 700mAh battery costs as much as 4 separate AA 2800mAh batteries.

I was wondering why are the typical capacity for these types of batteries on the market are so low as opposed to individual AA accu batteries? Can I just assemble 4 x 2800mAh individual batteries and get a 2800mAh battery pack that will run 4 times as long? Will the original charger work OK for this?

Or are there any issues with this approach? Maybe there's a reason they don't do 2800mAh batteries for RC cars (or they're not widely spread)?

Thanks for your advice


texts: Why are switching losses proportional to switching frequency?

texts:
Actually in soft switching converters an increase in frequency increases switching losses?

Can anyone explain why?


texts:
I have this Power Supply

There are two modes, Constant current and constant voltage.

When does this two modes come into picture under which circumstances.

Can someone explain?


texts: Does a transistor change the source of current? (re: esp8266 and infrared transmitter circuit)

texts:
I'm trying to connect an infrared transmitter LED to a microcontroller (ESP8266/ESP8285).

The infrared LED is a TSAL6200 with a forward current of 100 mA.

The ESP8285 datasheet shows max current ("Imax"?) of 12 mA so I think the GPIO pins can only provide 12 mA.

Therefore, I believe I need to use a transistor as a current amplifier.  There are many examples of this.  However I'm still learning the basics of transistors (and electronics!).

I'm going to use a BC547 NPN transistor which requires 700 mV for Base-Emitter saturation.  (I also must make sure the current from Base-Emitter is low?)

So... if I connect the collector to the ESP8285 VIN (probably coming from a voltage regulator?) then the current will flow from VIN (voltage regulator?) to GND therefore the VIN (voltage regulator?) will be "providing" the current instead of the GPIO pin?

Can anybody tell me if I'm understanding correctly or explain anything I might be missing?


texts: I am perplexed about learning electronics. I have basic understanding of components such as inductors, capacitors, etc. But I don't know how to proceed further in field of electronics. *Please suggest me resources and techniques to enhance my aptitude in this subject.


texts: Measuring floating gate potential with minimal leakage current

texts:
I am working on a sensing device where the voltage of a floating node is dependent on the quantity to be sensed, as well as the net charge stored in the node. I would like the device to be only sensitive to the external physical quantity, and thereby reduce as much as possible the time-variation of charge on the floating node.

In a typical scenario with solid-state memory devices, you would have a MOSFET whose gate is insulated in all directions, and a control gate coupled capacitively to it (and possibly also charging it through tunneling). The floating gate potential induces a certain channel conductance which can be measured with additional circuitry around the MOSFET.

My problem is that the process I am using (TSMC 65nm) has very thin MOSFET gate dielectric, so there is a non-negligible leakage current (on the order of 100 pA) due to electron tunneling across the gate dielectric. The charge stored on the floating node would be on the order of pC so with such currents, the variation will be fairly large and this would provide very low retention.

Are there alternative known ways to measure a floating node potential while drawing as least current as possible from it? One possibility is of course to increase the dielectric thickness of the MOSFET (or its permittivity) but I am constrained with whatever values the process uses.


texts: Capacitor voltage in a 555 timer circuit

texts: If I change a 10V capacitor in a timer circuit with a 16V capacitor, will the circuit turn on longer?


texts:
I am trying to get started with xmega and have a ATxmega32A4U on a breakout board with 4 100nF caps for decoupling and a Zeptoprog programmer connected to the 2 PDI pins, ground and Vcc

I'm not getting the expected response when using avrdude (avrdude version 6.1 with -v and -F flags)

avrdude: stk500v2_command(): error in CMD_XPROG: Failed
avrdude: stk600_xprog_program_enable(): XPRG_CMD_ENTER_PROGMODE failed
avrdude: initialization failed, rc=-1
avrdude: AVR device initialized and ready to accept instructions
avrdude: Device signature = 0x4003ef
avrdude: Expected signature for ATxmega32A4U is 1E 95 41

The last byte of the device signature varies randomly and the first two don't change. It makes no difference to the avrdude output whether the PDI is connected or not.

Without the xmega connected to the PDI pins I get the following trace (yellow is PDI data, blue is PDI clock/reset)

With the xmega connected to the PDI pins I get the following, which shows a second data sequence which I assume is a response, since it's not there otherwise.

There appears to be some good data, but also two small spikes. This is the second spike zoomed in:

Are these spikes causing the error (and if so, what are causing the spikes), or is there something else I can try?


texts: Relating Hall sensor outputs to absolute rotor position (Which combination corresponds to which angle)

texts:
I have a working 6-step BLDC commutation which works based on the Hall effect sensor outputs. I would like to apply the same code to another motor, which doesnt have Hall sensors but an absolute rotor angle sensor.

The way i am planning to do it, is to mimic the hall sensor outputs, commutating the motor every 60 degrees. My problem is i couldn't figure out, which Hall output corresponds to which absolute rotor angle (60, 120 , 180 etc). Just knowing one, for example (1 0 0) corresponds to 60° would solve my problem.

The 6-step commutation control scheme is just designed around hall sensor outputs, without relating those outputs to absolute rotor angle.

Any help is much appreciated.


texts: Effect of electron discrete nature on current density

texts: Coulomb’s law states that the current that flows through a wire is proportional to the applied voltage. For sure there are many physical effects (linear and non-linear) that participates in the voltage-current relation making this law valid only in ideal systems. I’m familiar with many of them, for example the temperature coefficient of a material. But I never heard of any effect that suggests the current density is somehow affected by the fact that electrons are discrete entities. I mean, my common sense says the higher the current density the higher the probability of electrons interacting to each other which could lead to a higher resistance and eventual saturation. Am I making any sense here? Does such behavior happen?


texts: Lightning bolt vs. batteries: a coulomb in everyday terms

texts:
I am trying to decide if the information on the wikipedia page

http://en.wikipedia.org/wiki/Coulomb#In_everyday_terms

is reasonable.  In particular the statements that a lightning bolt has about 15 coulomb, where a battery has 5000.  My first instinct is that this is clearly wrong (a lightning bolt being such an energetic event, and a battery seeming mostly innocent), but then on reflection a lightning bolt does last only an extraordinarily short amount of time.  In the end I am not sure how to check if this makes sense.


texts: Is spatial multiplexing always required to define MIMO?

texts:
From Wikipedia:

In radio, multiple-input and multiple-output, or MIMO (/ˈmaɪmoʊ, ˈmiːmoʊ/), is a method for multiplying the capacity of a radio link using multiple transmission and receiving antennas to exploit multipath propagation.

Spatial multiplexing or space-division multiplexing (often abbreviated SM, SDM or SMX) is a multiplexing technique in MIMO wireless communication, fibre-optic communication and other communications technologies used to transmit independent channels separated in space.

But consider this radio unit from Mimosa Networks: https://mimosa.co/products/specs/b5c
This is a dual-polarization 4x4:4 MIMO microwave radio unit. It connects to a dual-polarization parabolic antenna via two RF cables.
According to their chat support, it creates 4 separate channels by using 2 separate frequency bands per polarization:

Channel 1 - Horizontal_frequency1

Channel 2 - Horizontal_frequency2

Channel 3 - Vertical_frequency1

Channel 4 - Vertical_frequency2

But isn't this frequency-division multiplexing (per polarization)?


texts:
I'm looking to build a small robot using inexpensive DC micro gear motors. I would like to be able to measure the speed (count rotations) of the motors for accurate positioning etc. I'm aware that they have the encoder versions of these motors, with hall effect or optical sensors connected. However I started wondering if there might be smarter ways to be able to detect the rotations without having to purchase more expensive encoder motors.

Is it possible/practical to be able to somehow measure the pulses generated by the switching of the armatures?
Is this something that could possibly be detected by measuring variations in the current being drawn by the motor?

I'm aware that DC motors create a lot of electrical noise from the commutation of the brushes, which requires capacitors etc. to suppress. It seems that it aught to be possible to use some of this "noise" to detect the rotations of the motor.

edit: I've realised the title of the question perhaps is not quite accurate. I don't need to detect the actual speed of the motor directly, but rather to just detect and count rotations, or more accurately, the angular displacement. From this I can calculate everything else I need to know, speed, distance travelled etc.

After a bit more googling, it seems it is possible to calculate the speed of a DC motor, by measuring the back-EMF. The calculation is quite complex, and depends on knowing various characteristics of a particular type of motor.

As described here...

There is even Arduino code provided. In my case though, despite the incorrect title, I am actually mostly interested in measuring (or calculating) the angular displacement, to find out exactly how far each wheel of the robot has travelled, to then be able to determine orientation and position.

I'm not sure this EMF technique will provide the accuracy I'd need for that.

Anyway this does give me a bit more confidence that what I'm wanting to do may be possible.


texts:
I am designing a small sensor which fits into a custom aluminum enclosure.
The sensor uses CAN bus and a long cable to connect it to the host and power. The shield of the cable will ground the enclosure through the connector.

While developing the sensor I realized how important it is to ground the enclosure, otherwise my ADC readings are more noisy.

Now my dilemma is that if my costumers forget to ground the shield or use a shielded cable (which they will) the performance will be poor, as the enclosure will be left floating.

Connecting the power ground to the enclosure (shield) inside also seems like a bad idea as this creates a ground loop.

Is there any way I can get around this problem? An AC coupled shield?


texts: Can I use a RF and/or Time-domain reflectometer to find 'wet contact'?

texts:
Friends of mine have a circuit where the RCD trips but only after prolonged rain. There are a number of garden and security lights on that circuit so I very much suspect there is a junction box where water gets into it.

There are two challenges:
 - Find where the cables are buried.
 - Find the 'wet' junction box.

I assume this is a problem which electricity distribution companies have to cope with more often and that there is a well know solution.

For 1: Find where the cable are buried.
I was thinking to put an RF signal on the cable and then use an antenna/coil to find where they are.
(Of course first disconnect it from the mains)

For 2:  - Find the 'wet' junction box.
I was thinking of borrowing a  Time-domain reflectometer (Or set one up with a pulse generator and a scope). But I have no idea how accurate those are, especially with multiple junction boxes upstream.

I am hoping for somebody with practical experience or knowledge/tips how/if these methods would work?

I have a scope, pulse generators, multi meters, a spectrum analyzer and a small electronic lab available.


texts:
I am designing a motor controller with an Arudino, UBEC, and ESC. The Arduino will control Servo Motors and Brushless Motors. I want to make sure I understand how to hook up all the devices to avoid issues. I have been researching ground loops and want to make sure that I won't have any electrical issues. I have attached a schematic of what I believe is the correct hookup guide.

The black wires are ground, orange is power, and green is the signal wire.


texts:
If I am correct, a typical loudspeaker's impedance will change depending on frequency. The impedance will be comprised of the resistance and the reactance of the voice coil. As frequency increases, so will inductive reactance.

Are there any other components to be considered in calculating this impedance - for ex - capacitance?
Also, is the actual physical movement of the voice coil within the magnetic field a consideration in any way?

Thanks in advance.


texts:
Hi I sorted of had an epiphany when thinking about EMI shielding a PCB...

If the frequency of the system on a PCB was constant ( lets 20MHz digital system or something) could I take advantage of that fact and design a trace around the perimeter that will prevent that frequency from being transmitted in or out?

For example a circular trace with a diameter that is half the wavelength, an EM wave would induce a current in the loop equal and opposite to itself causing the net energy seen inside the loop to be 0. Right?

Of course this only applies if the wave is polarized in the correct direction but since all the PCB traces are also only polarized that direction it should not matter.

(I know for MHz a half wave is fairly large and impractical but just ignore that part of it)


texts: How should unused I/O pins be configured on ATMega328P for lowest power consumption?

texts:
I'm trying to reduce power as much as possible in an Arduino board I have created. How should the unused input pins be configured? There are a few answers (here, here) already for this, but I'm after something specific to the ATMega328P.

Set pin to input, drive pin high to engage internal pull-up
Set pin to input, drive pin low
Set pin to input, external pull up
Set pin to input, external pull down
Set pin to output low
Set pin to output high
Set pin to output low, external pull down


texts: Unplugging Ethernet Cable Leads an Abnormal Power Supply Fail

texts:
I've been working on a smart home control panel. It's basically a 10.1" fat-a$$ Android tablet having two ethernet ports, USB 2.0 ports, RS-485 interface, KNX interface, etc.
The first ethernet interface has a KSZ8081RNA Eth Phy which is connected to the processor through the RMII interface. The other ethernet interface has a LAN9512JZX Eth-to-USB bridge + USB hub combo and is connected to the processor through the USB upstream port.
The Problem
Both ethernet ports work correctly. No problems in terms of connection and performance. But, when I unplug the ethernet cable from the 1st ethernet port, the KSZ8081RNA gets damaged which results in short-circuiting of the supply pins. I tried this 3 times on different boards (same components) and got the same result twice. The 3rd try gave me a different result: PMIC got damaged. I don't see any problems with any plug-unplugs to the other ethernet port.
I can't share the schematics of the full board here, but here's the schematic of the problematic ethernet interface:

Please note that the design of the ethernet interfaces is based on the respective eval boards: EVAL8081 and EVAL9512. One main difference: I'm using this mag-jack instead of an RJ-45 connector plus external magnetics.
Some extra technical info:
The system is driven by a Rockchip PX30 processor and Rockchip RK809 PMIC + codec combo. PMIC gets a clean 5VDC from a synchronous buck and generates all the necessary voltages (3.3V for sensors and peripherals, 1.2V for RAM, 1.8V for ADC, etc). Both ethernet controllers are supplied from the same 3.3V output of the PMIC. This 3.3V output is taken from one of the buck converters of the PMIC and is used only for ethernet interfaces.
Questions and Thoughts

Both eval boards use linear regulators. I'm using a buck regulator. Could this be the issue? The PMIC has LDOs but I'm using those for analog supply requirements of PLL, USB, PMU, etc.

I'm using this ferrite bead on the 3.3V supply line before applying it to the chips. Could this cause a back EMF? I know, this is a silly question. But I can't perform any test as there are nearly no remaining test boards.


texts: Where is my mistake in this power distribution system homework question?

texts: I have attempted to solve this problem, but the answers don't match. Where am I making a mistake?


texts:
I own a Tx/Rx Radio Direction-Finding (RDF) set for a sport called falconry, basically, locating & recovering a pet falcon after flight.

The Tx tag is at 218.025MHz from Marshall Radio Telemetry :

The Rx is a 10-channel receiver, TRX-10S, from Wildlife Materials Inc. :

I believe all systems for wildlife tracking from different manufacturers are compatible and speak the same modulation language.

Now, I want to know the modulation technique used by the Tx tag, I have my beloved Rigol DSA815-TG spectrum analyzer, but the problem is that, as with all RDF beacons, the signals they transmit are intermittent. They have the famous "Tet...Tet...Tet..." beep fashion... so I can't see the spectral content for an adequate amount of time -- and that is only when I'm able to pick it up (some times the spectrum analyzer misses it...)

My -clear- questions are :

What is the modulation technique used in those wildlife tracking beacons?
Whether I knew a straight answer to (1.) or not, what is a reasonable setup with my Rigol to see the signal?

For reference:

Tx Link : Marshal Radio RT Standard

Rx Link : TRX-10S


texts: Why aren't headphone jack shaped plugs used for data?

texts: With Apple's lightning cable, and USB 3.0, reversible cables are taking off, and I personally think this is very convenient. But we have had better than reversible for a long time, in the form of the headphone jack, which can be inserted in any direction, not just 2 directions. Why isn't a headphone jack shaped connector used for data more often? All I ever see that shape used for is audio and power supplies (I've seen it used once for data, in the iPod shuffle, but thats it).


texts:
I plan to build a bench supply using a used ATX desktop computer PSU, with 3.3v, 5v and 12v binding posts as well as a cheap voltmeter-ammeter combo module (DSN-VC288). I know it's going to be inaccurate and have terrible ripple, but it would still be a nice addition to the variable bench supply I already have.

Now, I would like to add a rotary band switch to toggle the voltmeter-ammeter module between the three outputs. However, passing the output current through the band switch is not an option, as the switch is only rated for 300 mA, and the supply should go up to at least 5A (will be adding fuses on each of the outputs).

I have a bunch of IRFZ44N MOSFETs lying around which can handle 35A continuous DC, so my first instinct is to use those to switch the currents when the rotary switch is turned. However, I wonder if I am overcomplicating it - or using the wrong tool for the job?

I am fairly new to electronics so it's very possible that there is a standard way to do this that I'm just not familiar with. Or is the MOSFET route a viable solution?


texts: High voltage drop when load is connected

texts:
I'm getting 6 volts open circuit voltage. Whenever I connect a load (resistors), there is a huge drop in voltage values. Does it signify power input is less or is there any other reason for the same?

I'm using a thermoelectric module as a power source.


texts: Looking for some help identifying an AT90USB646-based board

texts:
I inherited this single board computer a while back - clearly some kind of developer board that has LEDs, I/O ports, two USB ports, an 8x8 LED matrix, buttons, sound, SD card slot, etc - like a super Arduino of sorts.

Unfortunately, not a single identifying name, mark or number on it that I can find!  It does have an Atmel AT90USB646 main processor.

Also, it comes in a blue plastic project box with a board layout diagram on it, plus programming instructions...

  To Program:

  Connect 'Programming USB' to Computer
  Press both 'Programming Button' and 'Reset Button' at the same time
  Release the 'Reset Button' first

Can anyone identify it from this picture?


texts: I am restoring A Heath Kit SB200 Linear Amp.

texts: I am restoring A Heath Kit SB 200 Linear Amp. I have started to replace all the caps in this unit. It uses about 12 .02uf ceramic disc caps for RF bypass throughout. I am wondering if i can use .01uf in there place as I can not source .02uf caps. Also there is no indication on the .02 caps in the unit as to there working voltage. Also nothing shown on the schematic.


texts: definition of power signals and energy signals

texts: Why is it so that for a signal to be an energy signal it must have power zero and for a power signal the energy value should be infinity ?


texts: Measuring current with multimeter (broken?)

texts: I just got my first multimeter from Home Depot and it was $60. It's the Extech EX330 and it works fine except for when I measure current. I am doing it correctly and the fuse has not been blown. When I put it on the amp setting it reads .06 A when I put it on milli amp setting it reads .06 mA and when I put it on the micro Amp setting it reads .6 uA.  I have no idea if I should take it back or if I am just reading it wrong. Please help.


texts: Peltier Module constant time and thermal Load

texts:
Hi everyone I am new to this forum.

I am doing a project where I need to control one of the sides temperature of a Peltier device against human skin. So one side is in contact with the skin, and the other with the heat sink.

I need the time constant of the Peltier module, and doing a lot of research I found that as soon as the power supply drives the device, it will settle to the desired temperature very quickly. Let´s say 1 sec (to achieve cold temperatures) to 3 seconds (hot temperatures). But this case is only when there's no thermal load. So this time will vary depending upon the temperature, mass, specific heat and other factors of the thermal load, which is skin in my case.

So I know the settling time required to achieve the desired temperature under no-load conditions of the Peltier device. Also I know how long the thermal load takes to acquire that temperature by thermal conduction. My question is:

Can I say that the final settling time of the Peltier module will be ts + tc? where ts = time constant of the skin, tc = time constant of the Peltier side under no-load conditions.

For example, a certain TEM can achieve a temperature of 10°C in 1.5 seconds on one of its sides. The skin is about 36°C and (doing quite roughly considerations) will acquire that temperature in 0.384 seconds.

So the final settling time for that side of the Peltier device is 1.5 + 0.384 = 1.884 seconds


texts: How to obtain Thevenin's equivalent resistance in this example?

texts:
Look at this example:

In this example, they ask the value of Resistance R knowing the current that goes through there is 1 Ampere.
My teacher teached to us a shortcut of how doing it by thevenin's theorem.
First I removed Resistance R and inserted it on thevenin's equivalent circuit, opening the circuit on points A and B, and then I proceed the execution keeping it open on A and B.
I would like you to specifically answer my questions:
1) when I open it on A and B, supposedly, doesn't the current stops going there?? Is the current zero on the branch that is going to terminal A? I always thought it was.

2) how can I get equivalent resistance?
-I can't do conversion Delta-Y because the fifht resistor has disappeared when I opened it;
-Maybe I can put a current source of 1 Amper on terminals A and B and calculate Voltage AB;
-Any other idea?
Maybe in this exercise I can't simply do using the shortcut my teacher told us.

Please be patient and help me. Sorry for my mistakes.

-


texts: Why does short distance wireless energy transfer have such low efficiency?

texts:
Wikipedia and numerous other sources cite the following statement about Magne Charge high-power inductive charging system:

  For example, the Magne Charge system employed high-frequency induction to deliver high power at an efficiency of 86% (6.6 kW power delivery from a 7.68 kW power draw).

The Wikipedia article on inductive charging has a citation near that statement, but it leads to a Magne Charge user manual that doesn't back the "power draw" part of the statement and doesn't give any details on where energy is lost.

Now a system like Magne Charge features two coils that are both rather large - the off-vehicle "coupler" used with Magne Charge is something like 100 millimeters in diameter and they are placed very close to each other and aligned in parallel during charging. There's no long-distance energy transfer. This looks almost like a plain old transformer (yet with an air core) and I've never heard of a 7 kilowatt transformer wasting as much as 14 percent energy in conversion - dissipating about one kilowatt of power would just melt the transformer.

How realistic is the "86% efficiency" claim? What would account for such huge losses?


texts: How to connect capacitors to SIM800C gsm module

texts:
I am powering a SIM800C from a 3.7V Li-ion battery. If the battery charge drop below 85% (it still has 4.1V measured without load), the module keeps restarting during startup. This probably happens because of a high load (up to 2A) that causes a voltage drop. According to the SIM800C manual, this could be avoided by using capacitors. I have tried to interpret the reference circuit from Simcom and I use the recommended capacitors but this does not help. Am I connecting the capacitors the right way?

This is the reference circuit from the SIM800C manual:

And this is how I have made the connections:

CA is a 100uF tantalum capacitor and CB is a 10 uF ceramics capacitor.


texts:
my 12V external power supply broke and it looks like I need to replace transistor. On my board is installed transistor UTC 5N60l. I've searched for a while and found a schematic for my power supply board. But from a schematic, there should be IRFS730 transistor (Q1 in the scheme). I'm a newbie, so could you please tell me what's different between these two transistors and what should I use next time? Adding schematic.

Thanks


texts: Simple function generator using microcontroller

texts:
Is it possible to make a function generator with a microcontroller (PIC18F4550 OR PICAXE20X2)?

I am thinking that for generating square waves it can be enough to make a pin output high and low on desired time frames. But how about a sinewave? Maybe it is possible with the same idea but putting a inductor or something at the output?

If you generaly think this can work I want to start doing it!

UPDATE
First of all I have to thank all the answers, it really gave me some nice start points.

I have a rather good experience with PIC18F4550 as I did lots of small home project around this chip. So it would be my main choice.
Here is a link to its datasheet

My main points is now as following:
1- Best way and mathematic approach for square waves
2- same thing for sine waves
3- Amplitude and frequency control


texts: What happens to AVR registers during multi-cycle instructions?

texts:
This is more of a theoretical question... (Also my first on Stack Overflow)

I am wondering what happens to Atmel AVR microcontroller (i.e. ATTINY85) registers during a multi-cycle instruction.

i.e. ADIW takes two cycles to add an immediate to a two-byte (word) register.

I imagine that during the first cycle one of the bytes is operated on, and then in the next cycle the other byte is operated on. But is this process defined anywhere I can read? And what about the other multi-cycle instructions?

Essentially I'm interested in the state of the microcontroller after each individual cycle, even within multi-cycle instructions.


texts:
I need a power supply capable of supplying 7.5V at 6A using linear devices. To minimize power dissipation at this current level I have decided that using a LDO would allow me to lessen the power I need to dissipate by allowing me to have a lower input to output voltage.

I have selected to use the TL1963AKTTR. To acheieve the required current I think I should be able to use a PNP transistor such as the TIP2955 to boost the current similar to how it is shown in this circuit.

EDIT: Sorry, would this work as I expect


texts: Is connecting two GND planes with vias a standard practice?

texts:
I've been studying the Arduino Uno layout and noticed that there are about 40 vias that connect the GND polygons on the top and bottom. Here's a picture with the vias circled:

Is this a standard practice? I'm a hobbyist and a novice when it comes to PCB design, but I've never seen this before..


texts: How can we obtain frequency difference of two waveforms?

texts: Given a reference waveform from the transmit, how can we detect the change in frequency of the resulting transmitted waveform using a PLL (like an LM565). Most resources only discuss about getting the phase difference.


texts: How a DC motor works when connected to a power supply but no resistor?

texts:
I connected a 12V DC motor to a battery of 12V only. The motor rotated perfectly fine.

But my question is that if you don't have a resistor attached to the circuit, as per theory the current is infinite and this should burn the motor but it doesn't happen like that in reality. Can someone explain why and how ?


texts: Alternatives to mounting tube sockets on a PCB

texts: It occurred to me that since tubes get inserted and removed that this could cause some flexing in the board and break things. Whats the alternative to not mounting it on the PCB for a more physically and electrically robust interface?


texts: Resistive touchscreen - when measuring X, why doesn't Y affect the reading?

texts:
A resistive touchscreen (4-wire) looks like this as a schematic:

To read an X position, you put voltage across X+ and X- and then read the voltage between EITHER Y pin and ground. How does the Y position of the touch not affect the reading?

Example, you put a voltage to V+ and ground V-. You press in the centre of X at the very top of the screen. So the values of East and West are equal, but North is zero and South is large. The voltmeter (or ADC in the real world) is placed across Y+ and ground, which is the same as X-. The measurement shows the voltage across East, which is what we want.

Now you press in the centre at the very bottom of the screen. South is now in series with the voltmeter, is it not? I'm still pretty green at electronic theory, but why doesn't this affect the reading? TL;DR stop reading now if that is clear, the rest is explaining because I'm not sure if it is.

To put it another way, I hope I'm not repeating myself unnecessarily, but in the below image, the measurement I WANT is assumedly the voltage across X1, but I can't get that without incorporating X4.

I can't find anything to explain the effect of a resistor in series with a voltmeter, if you can point me to that it might answer my question.

Also am I correct (in this particular case) to treat an ADC as a voltmeter? The output from the ADC is over SPI, and I've got that part sorted, so I'm treating measuring the ADC output (0-1024) as the same thing as reading the voltage (0-3.3V). If I'm wrong here, this is out of scope for this question but I'd appreciate the nudge to stop me running in to a different problem.


texts:
Here's a circuit of an amplifier in the CB configuration:

The small-signal equivalent is (using hybrid-pi model)

I want to calculate the input resistance \$R_{in}\$. If I'm not mistaken, the blue arrow in the first picture indicates the direction in which we should look in order to calculate \$R_{in}\$ (looking from the emitter). But if we connect a test source \$v_{x}\$ in parallel to \$R_E\$ we get that $$R_{in} \equiv \frac{v_x}{i_x} = R_E \parallel r_{\pi}$$ (since \$R_E\$ is parallel to \$r_\pi\$).

However according to the answers \$R_{in}=R_E \parallel \frac{r_{\pi}}{\beta + 1}\$ for some reason. I fail to see how is that the case. Any suggestions?


texts: Use of choke to create analog ground: mistake?

texts:
Not infrequently I see designs that implement an analog ground like in the following schematic:

This is a breakout module that includes an electret microphone module and amplifier that could feed into the A/D converter of an arduino or similar. (It's Adafruit 1063, not to pick on them particularly, just an example).
The feature of interest is the choke FB1 in the ground line to create a separate "AGnd" Analog ground. I think the intent might be to run the Max4466 amplifier on a clean ground, separate from the noisy digital ground.
Now, it's certainly a good idea to separate AVCC from VCC with a choke, (as is done here with FB2), and bypass it with a cap to ground (not done here).
However, the choke in the ground conductor is a problem. The microphone and amp inputs are referenced to AVCC, but the amp output is referenced to the external ground. The consequence surely must be that half the noise on (external) VCC (JP1 pin 1) appears at the analog output (JP1-pin 3).
And indeed, this circuit produces very noisy output, when used, for example, with an Arduino and an SD card module as a sound recorder. (SD cards are latter notorious for VCC noise while writing.) This is greatly improved by replacing FB1 with a short, and adding better filtering in place of FB2.
My question:
In general, is there ever an argument in favor of putting chokes in the ground network to create ground branches that have some high-frequency isolation? My inclination is that grounds should always be as low-impedance as possible, with due regard to current flow issues, return paths etc to avoid unwanted voltage drops (star ground considerations etc), and not deliberately partitioned with chokes. But I've seen the addition of chokes to ground branches enough to wonder whether there is some argument in favor.


texts: I have this old car stereo and would like to add aux cable option to this player. Is it possible?


texts: STM32F - how to config DMA transfer to SPI triggered by Timer?

texts:
I am trying to make a project with the STM32F746ZG Nucleo board using the DMA to make a transfer of 16-bit values to a DAC connected to the MCU by SPI. I am using the STM32CubeMX to generate the init code and also the HAL Cube libraries to develop the code.

You can see the idea in the attached image,

I have configured the Request channel for DMA using the TIM7 peripheral so I can request in Stream2 (this is specified un the user manual). But I need now to configure the memory location and from where to read the data and also the SPI3 memory direction so I can send it to the DAC device.

The problem es that I can't find the code configuring this in the code generated by the STM32CubeMX and there is no example of this kind of application in the STM32CubeHAL examples so I am stucked.

Has anyone made a similar application tell me how to configure correctly the DMA to make a transision from MemToPeripheral?


texts: What is difference between Power-GND vs Pre-GND?

texts:
I would like to know the difference between different types of Grounds like Power-GND vs Pre-GND. Are all the grounds not same? Cant we connect the device to any one of these grounds?

In my application I have a low frequency audio amplifier called "TA8229K" which has 15 pins.
On this picture, on this diagram there is written that only 3 ,5 and 7 pins might be connected to Power-GND.
1) At first which one is the Power-GND? Is it a negative direction of 9v battery?
I think that 4 and 8 Pins might be connected to positive direction of 9v battery (Where is written VCC).
Am I right?
Also There is written that 14 and 15 pins might be connected to Pre-GND1 and Pre-GND2.
2) which one is the Pre-GND1 and Pre-GND2? Is it a negative direction coming from low frequency audio device?
Also there are other pins like 9, 10, 13 which are connected to some kind of GND on diagram, but there is no written which one is!
3) Where should I connect those 9, 10, 13 pins?
4) Where should I connect first pin (1 pin)? What does it mean N.C.  ?


texts: What happens if I accidentally connect an Ethernet device to my 1-wire bus?

texts:
I have built a networked temperature sensor by connecting several DS18B20 temperature sensors to my Arduino. I've tried to visualize the setup with this schematic (sorry if this doesn't make any sense, I'm not really experienced with electronics):

simulate this circuit – Schematic created using CircuitLab

I've distributed the DS18B20 sensors in multiple rooms in our office and used existing unused Ethernet cables to connect them. The pins of the patch cables are used as follows:

n/c
n/c
n/c
1-wire bus
GND
5V
n/c
n/c

This wiring is probably non-standard even for 1-wire, but as I'm using an altered ISDN hub (I've removed the resistors) I'm limited to 4 pins and so I made up my own wiring. The DS18B20 sensors are directly connected to these pins of the plug, without any additional components. On the Arduino side, there's a small circuit board with the pull-up resistor that connects to the 1-wire hub.

My question now is this: what could happen if someone accidentally connects an Ethernet device to the 1-wire bus, or vice versa, a temperature sensor to the Ethernet bus? Could the 1-wire bus or the temperature sensor damage a PC or a switch?


texts:
Here is the setup:

I'm using the Arduino Mega's SPI functionality to send signals to multiple DACs. For digital isolation, I am considering the HCPL-2631 or the ACPL-064L. The problem with these two is that output signal is inverted.

One solution is to feed the optocoupler's output signal through a set of inverters.

Could I accomplish the same by inversing the input polarity of the optocoupler?

Also, are there optocouplers with non-inverting logic that are suitable for digital isolation between an Arduino and a DAC?


texts: Are differential line drivers "active" circuits?

texts:
Some quadrature encoder datasheets describe their outputs as either Differential Line Driver or Line Driver. On closer inspection of the diagrams, they appear to be the same thing (differential line drivers).

However, my research tells me that a differential line driver provides 0-0.8v when Low, and 2-5v when High (TTL?). I.e. an "active" circuit without floating, and therefore no need for pull up/down resistors.

On the other hand, I found this definition for Line Driver:

"A line driver is a sourcing output. When in the on state, a line driver will supply Vcc. In the off state, a line driver will float. Because of this, a sinking input is required for proper operation. Please refer to the table below for a simple example of a line driver."

This implies a pull up/down resistor is needed.

So, what is the difference/similarity between the two, if any, in regards to quadrature encoders?


texts: At what distance(s), approximately, are high-voltage DC (HVDC) power lines more efficient than AC lines?

texts:
I hope this is not a duplicate, because I am sure other people have the same question...
And could someone explain the reasons why?
N.B.    From the 'scienceabc' website linked to below:
Despite being so celebrated, DC exhibited a major problem — transmitting it over longer distances was really difficult. The wires lost power and had to be rejuvenated using additional circuitry.


texts: How to wire a 8-directional switch (Alps RKJXW)

texts:
I would like to use the following component in my design:

https://www.alps.com/prod/info/E/HTML/MultiControl/Switch/RKJXW/RKJXW1014002.html

This is a 8 way directional switch with push button (it also has an encoder (photo interrupter) and I have already figured that part out and it works fine).

What I don't understand is how the different switches should be wired to a micro-controller.

There are 3 inputs (A to C) and 4 outputs (a-d).
See the image below:

As an example according to the connection chart, if S3 & S4 is activated then the joystick is in direction A, but at the same time S8 & S7 would also be activated and that would imply the switch is in direction E.

Could someone please describe what I am missing here. How should these input/output be connected.


texts: Back up 9V battery when circuit is unplugged from AC

texts: I have to work on a circuit that basically goes like this. I have two voltage sources, a 9V battery and AC. The AC is the main source, however, when this is unplugged, the 9V battery must come to the rescue after 5 seconds. For this work, I truly have no idea of where to start with, so it would be great if your could guide me. I'm not asking for anyone to solve my problem, but if you could help me with a starting point that would be very welcome.


texts: How can I extend the bandwidth of a soundcard?

texts: I want to extend the bandwidth of a PCIe or PCI soundcard to accommodate more spectrum for my SDR radio. I'll start with one that has a great noise floor spec. and no ripple in the passband. All I've found so far is the M-Audio Audiophile 192 and it's an old design. I'm guessing that they all have an anti-aliasing filter. I'm wondering if it's possible to bypass that and work on the amplifiers to make the passband flat to 100kHz?


texts: Why is this circuit using a branched 5V wire?

texts:
There is an article for using MQ-135's 5V analogue output with a Raspberry Pi. The picture below is from the article. I only added the [1] mark and pin explanations on it for the sake of question.
At [1], why is the wire branched? The Pi pin is a 5V pin, and it is branched to the MQ-135's port and to the converter's HV. Is this just to save the 5V pins (Pi has two 5V pins)? Or must the two be connected to a branched from a single 5V pin?

Also, why use wire branching? Couldn't it be like this, without branching?


texts: How does the 4017 decade counter drive a set of servos?

texts:
I have just become aware that people are using 4017 decade counters and an Arduino to drive relatively large numbers of servos from relatively small numbers of pins. Not being an Arduino connoisseur myself, however, I have not been successful in my attempts to decode the software that makes the magic happen.

My question is, in non-code, what exactly is going on here that makes this possible?


texts: Do Professional Manufacturers Violate IPC Standards?

texts:
I lay out simple boards using BGA packages and often ignore my EDA tool's courtyards. I know these courtyards are set by IPC standards to allow for good design, but then I look at boards like the iPhone X's motherboard and think, darn, Apple's cheating! Their courtyards are non-existent and they have decoupling capacitors side by side with their silicon!

So basically, why can they "break the rules" while I need to keep my components spaced apart?


texts: Thermopile temperature sensor (non-contact) amplifier design

texts:
I'm trying to design a circuit that amplifies a group of thermopile sensors (datasheet) from a mV reading to a V reading (gain ca. 100-1000) for a uC's ADC input. These sensors have a typical resistance around 200k Ohms, and a full range output voltage from -1mV to 5mV. The sensors have a response time of around 22ms, and I probably won't need to sample them faster than 10 times a second.

Since I have a few sensors (around 10), I'm thinking the best way to approach this is to mux the sensors (say via a standard 16 to 1 4067 CMOS mux), then amplify the signal.

Naturally, the low input voltage and high impedance of the sensors seem to be quite troublesome. I'm assuming the CMOS mux will generate primarily Johnson-Nyquist noise on the order of at most microvolts(<< mV), so it won't be problematic.

If that's the case, it looks like a precision operational amplifier (something like LMP2011 or AD8538) would allow me a low input bias current (dropping the input signal voltage minimally) and a low input offset voltage (to minimally skew output results), which I hope would work for the application.

This option seems popular on the internet, but I was wondering if you folks at EE.SE would have some suggestions for other ways to amplify these low voltage, high resistance signals.

PS: In effort to make this question useful to future readers I've tried to provide it in as general form as I could, but I can provide more details as to my design requirements/constraints if need be.

EDIT: Amphenol does not provide any clues on the datasheet as to how to use the sensor, but it does have an example circuit here under the PDF located at "Thermopile IR Sensor Applications" in page 3. The circuit provided is very similar to the one mentioned earlier


texts: Adruino External Pull Up Resistor Confusion

texts:
I have a project where I want to add a flex fuel sensor to a car that doesn't have one.  I have the flex fuel sensor installed and wired.  My plan is to use an Arduino to read the signal from the sensor and convert the frequency to the ethanol percentage.  I purchased an Arduino clone with the ATMega34U4 chip.

This is the documentation on the flex fuel sensor:

The fuel sensor uses a microprocessor to measure the ethanol percentage and fuel temperature, which it uses to produce and output signal. The fuel sensor signal is a square-wave voltage signal. The signal varies in both frequency and pulse width:

The frequency of the signal indicates the ethanol percentage. The output frequency is linear with respect to the percentage of ethanol content in the fuel. The PCM provides an internal pull-up to five volts on the signal circuit, and the fuel sensor pulls the 5 volts to ground in pulses. The normal range of operating frequency is between 50 and 150 Hertz:

50 Hertz indicates 0% ethanol

150 Hertz indicates 100% ethanol

The pulse width indicates the fuel temperature. The normal pulse width is between 1 and 5 milliseconds:

1 millisecond indicates -40°C (-40°F)

5 milliseconds indicates 125°C (257°F)

I know next to nothing about electronics, so what confuses me is the pull-up resistor.  I have read about the internal pull-up resistor but the value on that seems too high, according to this (http://nefariousmotorsports.com/forum/index.php?topic=9168.0) the resistor should be 1.2 to 3k whereas the internal is closer to 30k.

So my question is how would I solder the pull-up resistor?  I tried soldering one end of the resistor to pin 10 and the other end to the VOUT wire on the flex fuel sensor but that gave inconsistent readings at best.  Here is a pinout for a similar product (https://www.sparkfun.com/products/12640.  How do I solder this pull-up resistor into this system?

Below is my code.  I see mostly zeroes after H: and L:

int inputPinNumber = 10;
double sum = 0;
int count = 0;
unsigned long pulseTime = 0;
int frequency = 0;
unsigned long high = 0;
unsigned long low = 0;

void setup()
{
    Serial.begin(57600);
    pinMode(10, INPUT);
    LCD.init(0x3C);
    LCD.clearDisplay();
    LCD.setTextWrap(false);
    LCD.setTextSize(2);
}

void loop()
{
    high = pulseIn(inputPinNumber, HIGH);
    low = pulseIn(inputPinNumber, LOW);
    pulseTime = high + low;

    LCD.clearDisplay();
    LCD.setCursor(0, 0);
    LCD.print("H: ");
    LCD.println(high);
    LCD.print("L: ");
    LCD.println(low);
    LCD.print("C: ");
    LCD.println(count);
    LCD.display();
    if (pulseTime > 0)
    {
        sum += ((1000000 / pulseTime) - 50);
        count = count++;
    }

    if (count > 50) {
        LCD.clearDisplay();
        frequency = (sum / count);
        Serial.println(frequency);
        LCD.setCursor(0, 0);
        LCD.print(" E");
        LCD.println(frequency);
        LCD.display();
        sum = 0;
        count = 0;
    }
}


texts: LTSpice: Unknown circuit node using LMC662

texts:
I am trying to simulate a simple circuit using the opamp LMC662 from Texas Instruments. I imported the file as provided in the product website: www.ti.com/product/LMC662/toolssoftware
However whenever I run any simulation i get the error:
G4: unknown circuit node: "1" requested in behavioral source.
I have no idea what this means and how to solve it. Only thing that I found is that in the model file there are the lines:

G4  98 16 POLY(2) 1 49 2 49 0 3.54E-8 3.54E-8

G4  98 16 POLY(2) 1 49 2 49 0 3.54E-8 3.54E-8

which refer to node 1, which is defined as the non-inverting input of the opamp:

.SUBCKT LMC662/NS   1   2  99  50  28

Im attaching a screenshot of the schematic.

Any help is greatly appreciated!

PS: The ltspice model is here (it's in the zip file).


texts: Do not connect Vdd and Vss with AD732x ADC?

texts:
According to the AD732x datasheets, especially the figure of "Equivalent Analog Input Circuit (Single-Ended)", do not connect Vdd and Vss should have no effects except on throughput rate (should be a litlle less).
So I've tried it on the AD7323 and it's working well without Vss and Vdd (no connections) with a range of +/-10V input, but Vcc has to be at 5V and not only 3,3V (otherwise under -6V there is a saturation).
I also note that connecting Vss to 0V will normally block -10V to 0 input range due to the clamp protection.
So my questions are : how are Vss and Vdd used in these ADC so that it's possible to works without it ? And why under -6V with +/-10V input range, there is saturation with Vcc=3,3V ?


texts: Vector network analyzer for SMPS feedback loop measurements

texts:
Does there exist a ready-made design for implementing the measurement hardware? You can buy the analyzer package from e.g. Omicron Lab but it's a hideously expensive piece of kit (4490€) considering what you're actually buying. Never mind Ridley's version at $17.5k.

It's possible to measure a SMPS circuit feedback loop bode plot by injecting a signal into the loop and measuring the response. Theoretically you can do this with a signal generator, transformer and 2-channel oscilloscope. In practice it's not that simple - to start with, finding the right transformer to do your testing between, say, 10Hz and 1MHz. Has anyone managed to do that in a reasonable way using "homebrewed" equipment?

Like so:

Basically what that very very expensive equipment does for you is to generate and record the various test points which is a tedious business at best.


texts:
Can someone help me work out total amp draw for LEDs with an in-series resistor?

I am getting conflicting answers depending on where I look.

One way tells me the amp draw is the total amp draw of all LEDs combined, same as supply voltage.
Another way seems to indicate that the total amp draw is singular, as in 3 LEDs with an in-series resistor (each LED being 20mA) will still only be 20mA.

EG:

12v + ---->|---->|---->|---///---- -

12v DC
LED = Vf3.8/If20mA
R = 33ohms

Would the amp draw be 20mA or 60mA?

Further on from that, for multiple chains like that running from the same source, EG, 20 chains in parallel of x3 LEDs (each with in-series resistor),
400mA or 1.2A?

Hopefully I have explained my question right, but probably got some vernacular wrong, so I apologise in advance.

Thanks

PS: Apologies for the Resistor not showing correctly, having trouble getting the ASCII to display correctly


texts: Oscillator circuit with TL071 opAmp for amateur very short range AM radio

texts:
I stumbled upon this nice video and thought I'd try to reproduce the experiment. Basically the video shows how to build an AM transmitter circuit using an opamp, some resistors and a capacitor. This is the circuit schematics for the oscillator that should generate the carrier wave:

simulate this circuit – Schematic created using CircuitLab

The carrier wave should be at the OUT node right? My problem is that I do not understand how can this circuit oscillate since it is getting constant voltages as input and the video does not say anything about any function generator. My guess is that instead of 9 Volts in the voltage divider I should use a function generator with the carrier wave (possibly a 9V sine wave). Am I right or did I miss some component/key concept? Also by simulating the circuit with the potentiometer set to 0 on LTspice I get no oscillation at the OUT node but just a constant voltage (as expected) of 3.6V.

EDIT: the circuit should work in the 300kHz - 1.2MHz range


texts: LED lamp increased power consumption after installation: Why?

texts:
I'm new here, but I've been checking your forum few times before, never registered. Anyway...
I have a problem at my home. I'm not very electrical kind of guy, so these questions may be easy to answer to some with more experience in this field.

I bought a 5730 LED lights from eBay, of consumption stated at 2W per light bulb. I have 19 bulbs installed and are all wired to an adapter. The consumption when first installed was around 42-45W. But now, after two weeks use (may have happened even earlier) the lights are consuming 70W!

What is going on?! How could this be?!

Thanks to anyone who could help me out

OK, I'm not sure what info I have to give, please do understand I'm not good with this stuff. But here is goes in my own words, very amateurish discription:

Led are like this:
Base: G4

Led type: 5730 5630

Input: AC 12V

Power: 2W

Color: pure white (6500-7000K)

Lighbulb consists of 15 x 5730 LED

I wired all of them (19) to an adapter (12V, 5.8A). I wired them like this:
I took a wire and went from adapters wire + to lighbulb wire +, then to next lightbulb etc.
I did the sam procedure with - polarity.

To measure the usage I used a wattmeter, commercial one you put in the socket and then you plug in device switch to show you Watt usage and that's it.
When I first pluged it in it showed 40-45W. That's ok. Then when I tested it 2 weeks later 70-75W. That's not OK :(
I'm from EU.


texts: How to explain this difference in pinout?

texts:
Seemingly illogical pinout has been discussed before, but my question is different.
Have a look at the pinouts for the Si8540:

One would think that the pin order would be the same for both packages, maybe rotated, but that would be it. Instead the SOT-23 pinout is almost a mirror image of the SO-8's. Now SO-8 nor SOT-23 are flip-chip, so the die isn't mounted upside down on either, and I can't imagine that they would make a different die for the other package. I can only presume they crossed the bonding wires.

Looks like asking for trouble IMO, so why is this done? I can't think of another explanation.


texts: Is it possible to drive a capacitive touch screen work as a touch simulator?

texts:
I want to simulate a finger touch/move/etc. on capactive touch screen. Obviously using a robot arm and stylus pen is a solution, but it was expansive and the structure was too complex. It would be elegant if we can lay something (another capactive touch screen) on the original screen and drive it to simulate a finger.

I learned that a capactive touch screen is somewhat a row/column selection capacity matrix. So is it possible to make a driver system to activite certain areas in the screen and make it recognized as a finger touch?

The problem want to simulate a static touch area, but I want a CONTROLLABLE/PROGRAMMABLE
 activition of ANY area in the screen.


texts: How do I use superposition to solve a circuit?

texts:
Yes, this is a pedagogical question. While answering another recent question, I wanted to refer the OP to concise instructions for using superposition to solve circuits. I found that all the easily found resources online were somewhat deficient. Typically they were unclear about what kinds of circuits superposition applies to, or about the actual method to apply the superposition theorem to a circuit problem. So,

What kinds of circuits can be solved by superposition?

How are different kinds of sources treated when solving by superposition?

What are the steps to solve a circuit using the superposition theorem?


texts: To ground or not to ground: portable power supply

texts:
So I'm creating a backpack system to carry around and shine a 100 watt HID lamp (using the arc tube for UVC mineral collecting.) This system currently includes a 12v lithium battery, a power inverter to 120vac, and a 120v ballast setup (including a 300vac cap) that drives the HID. The actual voltage output to the HID is 20-30vac.

With all these different voltages, I'm a bit confused about ground. Should I have some sort of common ground in this system, or should every part be isolated?

Again, all this will be sitting in a backpack while the light will be in hand. So also figuring out whether I should build a box containing these things out of aluminum or something non-conductive instead like wood.


texts: Does the Free Space Path Loss model apply to all types of electromagnetic waves, including light?

texts:
The free-space path loss model describes the attenuation of the electromagnetic (EM) signal as a function of the distance between Tx and Rx. Does this model also apply to visible light, having in mind that visible light is EM too?

In radiometry there are different metrics and units which characterize the visible light. For example:

Radiant energy - Energy of electromagnetic radiation.
Radiant energy density - Radiant energy per unit volume.
Radiant flux/power (W - watts) - Radiant energy emitted, reflected, transmitted or received, per unit time.
Radiant intensity - Radiant flux emitted, reflected, transmitted or received, per unit solid angle.

If we want to create a communication system based on visible light, I assume 3) is the one to consider first.

Channel model:

In wireless RF communication there are channel models, such as the Lognormal shadowing model, which consider: attenuation, shadowing (and multipath).

In the Lognormal shadowing model, attenuation is explained as geometric path loss and random shadowing (additive gaussian random variable):

Is there a well-established channel model for outdoor visible light communication?


texts:
A couple of questions about modem:

I have been reading up on AT commands, and I see they're used to control the modem. They are sent over a serial connection so does that mean they are sent over UART?

The modems used in smartphone and other embedded modules like GPS/GSM serve a similar purpose as a modem connected to the ISP does, which is to modulate and demodulate the incoming/outgoing signals, yeah?

What does it take to implement AT commands? say you want to add some for your custom project. Is it as easy as parsing strings from the console?

Is there any point in having antennas on the modem particularly for one that's connected to the ISP via a cable? Having antennas on routers make sense since the signals are being "routed" to multiple devices


texts: Simultaneous Buck-Boost or Flyback Regulator - Help Selecting Chip

texts:
I have been trying to find a switching DC power supply that outputs a constant voltage of 12VDC, given a variable input between 4V and 25V. It's to my understanding I'd need a buck-boost converter, but many of the buck-boost converters I find on Digikey seem to show only a single application circuit for buck, and one for boost for the same chip (ie: no circuit that can do both simultaneously).

I am currently using the LM2577, and interestingly enough, it can accept a 12.5V input from a wall wart, as well as a 9V battery, and still has a constant 12V output. I don't know if for this type of chip though, if it makes sense for the input voltage to be greater than the output voltage, because it is a boost/flyback regulator.

So the first part of my question is: can someone recommend a good simple through-hole DC-DC converter that can take an input on the range [4V, 25V] DC and output a constant 12V DC output?

Second, I'm a bit confused on the terminology on Digikey, and Google has only gotten me so far. Could someone point my in the direction of a description of the various topologies? I get what a buck, boost, and buck-boost chip is, but the multiple combinations of boost/buck/forward-converter/flyback/inverting is somewhat daunting. Does flyback imply it is a buck-boost, even if the title is "Step down (buck), flyback", etc? Some such examples are:

Step down (buck)
Step down, flyback
Step down (buck), step up (boost), flyback
Step down (buck), step up (boost), flyback, inverting
Step up (boost), Cuk, Sepic
Switched capacitor (charge pump), flyback


texts: Tiva-C Launchpad - Sending a Tx signal over long distance

texts: I have a 5v square wave signal being sent from a microcontroller at a baud rate of 115200.  I would like to send this signal over longer distances, say 15+ feet.  What is the best/simplest approach to ensure this signal is sent cleanly over the longer distance?


texts: How can current-limiting supplies be possible?

texts: Knowing Ohm's law, the current drawn is directly proportional to the resistance. In some power supplies, you can limit the current. Let's say the voltage is 12 volts, it supplies 1 amp, and the resistance is 8 ohms. The current going through should be 1.5 amps, but the supply can only deliver 1. How can this defy Ohm's law, and limit the current?


texts: PCB Current Draw vs Temperature Rise Interpretation and Question

texts:
I am using this tool for current calculation

While changing the input parameters i realized Temperature Rise °C is affecting the current draw.(you might say OF COURSE!)

At Ambient Temperature = 25°C

Temperature Rise = 10°C :
 50A current at 2oz copper at outer layer the required trace width is 33mm

Temperature Rise = 30°C :
 80A current at 2oz copper at outer layer the required trace width is 33mm

Does this mean that the same amount of cooper in pcb (same trace width) actually can handle and conduct higher 80A current but the pcb temperature will increase 30°C more as a cost. Is this correct.

If so do we need continuous amount of current draw to reach that temp rise. (If we draw 80A for short period of time like a peak does it still increase 30°C)


texts:
I read the ATX power supply design guide, and I have a question related to the PWR_OK line specifications.
In "Table 21. PWR_OK Signal Characteristics" I saw the following:
"Logic level high  - Between 2.4 V and 5 V output while sourcing 200 μA".
My question is: what does this mean exactly? When PWR_OK is high the current will be limited by the PSU at 200 uA, so I will not be able to draw more than that from the PWR_OK line?. Or if I am trying to interface something with the PWR_OK line I should take precautions not to draw more than 200uA?


texts: Electret microphone: selecting a bias resistor

texts:
I have inherited a circuit from a colleague using a MAX4063 pre-amplifier and an electret microphone. It's almost identical to figure 4 from the preamp datasheet:

But where that circuit has 2× 1 kΩ resistors in series, I have just one. I'm not happy with the overall volume and noisiness of the audio, and I'm starting to wonder whether the 1k resistors are too small, as they're smaller than the 2.2k output impedance of the microphone.

How, in general, should I select the bias resistor for an electret in this situation? What's the relevant theory?

Edit: While all the answers so far have been useful, I'm still interested in having an analytic understanding of why the bias resistor should have a particular value; I've seen other electrect circuits on the internet with values up to 10k, which must make some difference to something?


texts: Orthogonal Frequency Division Multiplexing - calculate what frequencies are orthogonal?

texts:
So, I work at an ISP that uses wireless and DSL.

Something that keeps coming up is something called OFDM. It's used by some of our wireless solutions, and I understand (or at least think I understand) that DSL's G.dmt uses OFDM.

I'm trying to get a high level idea of what OFDM is.

From reading Wikipedia and the like, it sounds like you pick many different frequencies and transmit on them simultaneously. (I'm guessing you just switch the individual frequencies on and off, but I could be wrong on that, too).

I gather that it is not too hard to isolate one frequency from a signal mathematically.

From what I understand, the frequencies are picked so that they will cause the least interference with each other. How do they determine what frequencies are orthogonal?

I have tried to figure this out, but the problem is that most places seem like they are talking college textbook level with not enough context for me to catch on.


texts: How can we determine memory usage of a microcontroller

texts:
How can we determine how much memory is being used, or will be used by firmware in a microcontroller? What tools can support this?

Generally we don't use dynamic memory in embedded systems, but how can we determine the worst case stack usage for example? A compiler can't be enough.

For example we may not know until run-time how many times a function could be called, potentially causing a stack-overflow.

can a debugger tell us exactly at any point in the execution flow, how much memory is being used?


texts: How does the pull down resistor work in this circuit?

texts:
Here's an image from another question:

I get what the pull down resistor is there to do, but I don't really understand exactly how it works.

When there is no voltage applied through the base wire, why does any induced current then go through R2, but when a voltage is applied, it goes to the transistor? My understanding is that voltage always follows the path of least resistance, so if applying say, 5v turns the transistor on, that means that the transistor has a lower resistance than R2, so I would also assume any induced current would also flow through the resistor - so why does it then go through R2?


texts: Powering two devices with a Li-Ion battery

texts:
I have a Li-Ion battery powered device that can be plugged in a computer for charging purposes as well as for data transfer.

What I would like to do is have data transferred to the device via a Raspberry Pi as well as have the device’s power shared with the Pi. Would this be considered safe as the Pi could try charging the device that it’s sharing a battery with?

Here is a diagram that I have drawn:


texts: Noisy data line clears up on wiring up multiple output pins of uC to Logic Analyzer

texts:
Some people reading my question might be familiar with a string of questions (latest being this one) where I have been asking about how to decode data from an ISM-band ASK/OOK type RF receiver module. One of the excellent techniques I learnt from one of the answers was to use the pin-toggling to debug my program, using a logic-analyzer. The uC platform of my choice is Arduino (at 20MHz).

Now from my previous post it would be clear that I was dealing with the situation where the valid received data (encoded) was to be found from a data stream which seemed very noisy with high frequency signals, and I thought that I'd found a satisfactory rationale to ignore the high frequency signals by discarding them in software if the duration in that state was lesser than that of valid signals expected. This seemed to be going well for a while, and I started making some progress.

In debugging some of the problems I was facing, I landed up adding 5 additional lines to the logic-analyzer (in addition to the RF Rx data going from the RF module to uC). These additional lines would toggle in software based on various runtime conditions in the program, s.a. ISR invocation, every 100th main loop() invocation, meeting some conditions etc. To my surprise, I noticed that with this, my "noisy" RF-RX data line had cleared up, or rather instead of the high frequency noise, I was seeing low frequency noise, and the lengths of marks/spaces have become much longer than that of the valid RF data signal. So to validate my observation, I plugged out my debugging pin lines. Lo-and-behold, the noisy chatter was back. I computed the smallest pulse duration, and also the typical pulse-duration in both of these cases, and there is an order of magnitude difference. The observation is highly repeatable.

My circuit is on breadboard, and I am using home-made connectors (between 6cm - 15cm), i.e. the stiff single-strand copper wire, you find in Ethernet (CAT-5) cables. My logic-analyzer's unused inputs are all grounded. It is the Openbench Logic Sniffer.

My question is, how do I explain this ?

Edit:
Thanks to many of the tips, clues I received here, I believe that I've managed to isolate the behaviour to usage of Pin# 13 on Arduino, although I can't quite (yet!) nail it, i.e. what exactly is the reason for the behaviour.

I have confirmed by several rounds of tests that, if I have my ISR() logic mapped to Pin#13, s.t. whenever a particular external interrupt (#0) is triggered on either rising or falling edge, I use pin#13 to make the waveform accordingly, i.e. to follow the state of pin with external interrupt#0.

If instead of Pin#13, I use any other digital I/O pin, I notice that the noise goes back to being high-frequency noise, but if I use pin#13 for the above-stated purpose, then the noise switches back to low-frequency noise.

Reading Arduino reference manual, I see this text, but I believe that it is not relevant as in my case the pin is configured for OUTPUT, not INPUT.

  NOTE: Digital pin 13 is harder to use as a digital input than the
  other digital pins because it has an LED and resistor attached to it
  that's soldered to the board on most boards. If you enable its
  internal 20k pull-up resistor, it will hang at around 1.7 V instead of
  the expected 5V because the onboard LED and series resistor pull the
  voltage level down, meaning it always returns LOW. If you must use pin
  13 as a digital input, use an external pull down resistor.


texts: VHDL nested generate statements: how to refer to label?

texts:
I have this code that attaches a label to components instantiated inside a for...generate statement. So far everything works fine:

outer: for index in 17 downto 0 generate
attribute RLOC of EX_do1: label is "X0Y" & integer'image(index / 4);
begin
  EX_do1: FDC port map( ... );
end generate;

However, I want the attribute only on instances 0..15. So I tried this:

outer: for index in 17 downto 0 generate
begin

  inner: if index < 16 generate
    attribute RLOC of EX_do1: label is "X0Y" & integer'image(index / 4);
  begin end generate;

  EX_do1: FDC port map( ... );
end generate;

Now I'm getting the error message <EX_do1> is not declared. I tried moving inner before the begin of the outer statement, but same result. How can I refer to the flipflop?

I assume it would be possible by pulling the component initialization into the if-block and repeating it again in an if-not-block, but I am trying to avoid redundant code.


texts:
I was looking at this schematic for an old (pre USB) mouse:

when I noticed it had a crystal on it (Y1). I was curious why a mouse would need a timer?  Wouldn't it be able to use the clock from the computer?  Also if it has its own crystal couldn't it get out of sync with the CPU clock?


texts: Switching ethernet connection without a switch

texts:
I want to make a system to configurate ethernet connections to make different topolgies like ring or bus.Using 100baseT. Lets say i have 8 RJ45 female jacks and i would like to connect 1 female jack to other one like this
EN2TR1 and EN2TR2 arethe ethernet interfaces of the EN2TR module of control logix, AENTR1 and AENTR2 are the ethernet interfaces of the FLEXI/O Allen Bradley Module, ETAP 1 and ETAP 2 are the ethernet interfaces of an ETAP . They are configurated as a ring topology right now. What i am trying to do is a PCB able to do a connection between port 1 and port 6 also it could be disconnected using a micro controller. I was planning to do it using relays. I would use this to reconfigure ethernet connections and make a variety of topologies. I know i could just disconnect an ethernet cable and just port it directly to other port but i am looking to do it without disconnecting, just giving the ethernet cable a path to other port using relays if posible.
Thanks


texts: How would I design a clocked D latch from first principals

texts: I would like to understand the design process for a Clocked D latch from first principals.  Is it the same for any combinatorial circuit: Truth table - Kmap the build?  Just i am having an issue with the feedback in this type of circuit.  It's really sequential, but it seems to me that all sequential designs using state tables always infer the use of a latch or more to store the state. I'm Kind of going round in circles with this one.  Every search I do always just shows the circuit and truth table which is fine but would like to design one from the ground up.  Can anyone help clear the mud?


texts: Interfacing two PIC microcontrollers, of different power sources?

texts:
I have two different circuits with 5v for each, and they are using PIC microcontroller, how can I send a data (voltage) from the first PIC using output pin to the other PIC using its input pin? I measured the output from the first PIC, it is 5v (great), but measuring it using the ground of the other circuit it is ZERO, why??????

Note: NO COMMON GROUND, THEY ARE ISOLATED CIRCUITS.


texts: Multiple "typical characteristic" charts in FET datasheet

texts:
Looking at following datasheet: https://www.onsemi.com/pub/Collateral/2N5457-D.PDF
I'm puzzled as to why there are multiple "typical characteristic " (pairs of) charts. As far as my understanding goes, FETs are voltage controlled devices so why do we have multiple (and contradictory) values of drain current for given drain-source voltage and gate voltage? (figures 2, 4 and 6).


texts: How can I check in an OpAmp datasheet if the OpAmp is push-pull?

texts:
I am looking for an OpAmp which I want to use as voltage follower after a DAC. The OpAmp should be able to pull 3mA. And it should have Rail to Rail input and output.

How can I check in a datasheet if an OpAmp supports push-pull?

First I looked at several distributors like DigiKey. Some allow search for rail to rail (it seems that is output). Others also include Push-Pull. I also looked at the TI search page. There are lots of criteria but no Push-Pull.
http://www.ti.com/amplifier-circuit/op-amps/overview.html

After comparing several lists from distributors and TI I found the LMH6645 which fulfills all my criteria. In the datasheet it is described as Push-Pull and it shows Output Current: +/- 20mA. I guess the "-" indicates that it can pull up to 20mA.

Another interesting OpAmp is the OPA333. But it does not have the words Push-Pull in the description and no "-" in the output current. Is that the only way to find out that this is not push-pull?

It seems now I found what I want, the LMH6645. My question is: Is there an easy way to search for a push-pull rail to rail input and output OpAmp? Or is it really necessary to spend an hour looking through several lists and datasheets?

And at least for me similar search problems exist with other parts. Is it really necessary to study lots of datasheets to find parts? I think my search criteria are not exactly exotic.


texts:
So by using KCL to solve for a node voltage Vds (branch consisting of only a resistor Rds -> Ids = Vds/Rds,) if I obtain a negative answer for Vds, does this mean that the sign I used for the current flowing through Rds is actually reversed and that my answer is correct?

In other words, if you're solving for the voltage and you obtain a negative result, how do you interpret it and what would the correct answer be?


texts:
I have a few questions related to impedance matching when designing a PCB board for an FPGA. I am Using Artix-7 XC7A200T-1FBG 484C. If have read this  http://www.xilinx.com/support/documentation/user_guides/ug471_7Series_SelectIO.pdf
and
http://www.xilinx.com/support/documentation/user_guides/ug483_7Series_PCB.pdf

The document says impedance matching depends on drive strength. I am using default drive strength. Can anyone guide me if there is a best known impedance match for 12mA?  And how to perform that impedance matching.


texts: What is the conventional circuit to control a P-MOSFET with MCU?

texts:
How a P-MOSFET works is clear, there is plenty of documentation on the web. But what's the standard circuit to use them as an ideal switch with an MCU is not that clear, in my opinion.

I saw there are a lot of circuits that use an upstream NPN transistor or a N-MOSFET to control a P-MOSFET's Gate. And how they work is very clear. However, every circuit of these have to switch a voltage higher than MCU's voltage.

Given this circuit:

It doesn't seem to me that this could work without an upstream component that will connect to GND the Gate, given that the Arduino's digital pin isn't an open-drain INPUT, but works like an OUT. In other words, voltage or no voltage. These are my considerations about this circuit, please help me and everyone to understand answering these points:

The pull-up resistor function is to define the default state of the P-MOS Gate. The pull-up takes the Gate to +5V, in this case. So default state = OFF
When the Arduino digital pin is +5V, the Gate still stays at +5V.
When the Arduino digital pin is 0V, the Gate still will be +5V, given that the Arduino's pin isn't an open-drain pin. In other words, that pin doesn't connect to GND, letting the current flow and to take the pin to the 0 digital status.

Am I wrong?


texts: What's wrong with this power latch design?

texts:
I've been trying to design a push-on, push-off power control circuit, and came up with this design:

simulate this circuit – Schematic created using CircuitLab

Theory of operation:
Pressing the button causes the gate of M1 to go high, forcing the gate of M1 to remain high through R2, latching M1 on. Q1 is turned on through R4. This causes the left hand side of the button to go low. Pressing the button again causes the gate of M1 to go low, turning off M1 and Q1, causing the left hand side of the button to go high in preparation for turning on again.

This doesn't work in practice. What have I missed?


texts: Short-circuit primary side of a transformer to collect all the spikes at the secondary

texts:
Abruptly detaching a power source from a coil produces a back-emf: this is a well known fact.

What I would like to achieve, in my experimentation, is to convey ALL the collapsing magnetic field to the secondary side of a transformer, shorting the primary side immediately before the magnetic flux starts to collapse.

This requires a very fast switching system, probably through mosfets.

As a power source, I have a 12V/10A battery and the transformer is a big MOT (Microwave Oven Transformer): at the moment the power reaches the primary coil passing through a SPDT relay and, when it switches, the power is disconnected and the primary coil shorted.

Unfortunately the relay is not so fast to achieve the desired result so a small arc can be observed at the internal relay contacts, showing that the magnetic field has collapsed on both ends of the transformer.

Is there a way to overcome the problem?

A circuit diagram will be appreciated a lot!

Edited on 25/03/2015

The primary feeding/detaching source/shorting the primary/re-attaching source/feeding sequence (in a countinuous loop) of the primary side has to be accomplished thousand time per second...

I have to collect the spikes of the back-emf (due to the collapsing magnetic field) ONLY on the secondary side!

Like in a water pump, the water (electric field) must flow in one direction only; when the magnetic field collapses (using the above analogy) acts like a water flow under pressure which tries to exits from any hole in the piping system: I want to seal the entrance (primay side of the transformer) when the pressure is at its maximum level and convey all the flux to the exit (secondary side of the transformer); no way for the water (electric flux) to flow back to the entrance.

So, in essence, I need an electronic "valve" rapid enough to avoid the back-emf on the primary side.


texts:
I came across following question

  The 3 bit ripple counter is to be designed as MOD 4 counter. What should be the architecture of the ‘Logic gate’?

  A. a 3 bit input AND gate
  B. a 2 input AND gate
  C. a NOT gate
  D. a wire connection (no logic gate needed)

The answer given was:

  In fourth state, Q2 becomes high first time. So it suffices to simply connect Q2 to clear inputs so that all flip flops gets cleared.

I did not get how "fourth state, Q2 becomes high first time".

I tried out the problem myself and I got two different answers:

Solution 1

The count will be: 000,001,010,011. So in last count Q0 and Q1 both become HIGH for first time. Hence we should have ANDed them (that is Q0Q1) and applied output of the AND gate to all clear inputs.

Solution 2

I tried preparing k map for clear logic:

    Q0'Q1'  Q0'Q1  Q0Q1  Q0Q1'
Q2'   0       0     1     0
Q2    X       X     X     X
                    |
                    V
                   Q0Q1

From above k map also I got Q0Q1 as reset logic.
However, should we keep reset logic low for four states for mod 4 counter and then make it high in 5th state, like below:

    Q0'Q1'  Q0'Q1  Q0Q1  Q0Q1'
Q2'   0       0     0     0
Q2    1       X     X     X     -> Q2

By above k map, we get Q2. This matches with give answer (option D) that simple wire connection will suffice, just connect Q2 to all clear inputs. But I feel
this requires fifth state 100 to occur and then it prevents sixth state by clearing all flip flops.

What is correct here?


texts:
I have a used OCXO Morion MV85. According to datasheet linked above, it has GND, VCC or Uin, RF out and VFC pins. As far as I was able to find out by googling, the purpose of VFC pin is to adjust oscillation frequency via its voltage. Unfortunately I wasn't able to find an example circuit diagram showing the connection of VFC pin to anything. Here is my best guess so far:

Reference pin accepts, not provides volatge, and should receive one between VCC an some value, determined by R1 resistance. Adjusting R1 should affect frequency at RF OUT pin.

My question is - am I right

Providing voltage to VREF
Making its value between VCC and something (maybe I should add one more resistor in series)?


texts: Do electric gloves degrade in voltage protection over time?

texts:
I am looking to buy a pair of electric gloves for PPE (Personal Protective Equipment). However I just found out that their voltage protection doesn't stay constant.

Do these gloves need to be tested?
Electrical gloves need to be tested twice a year to ensure they are
protecting you against low, medium and high voltages. Ensure to check
the stamped dates on the gloves.

See: https://ph.rs-online.com/web/p/work-gloves/9182243/?cm_mmc=PH-PLA-DS3A-_-google-_-PLA_PH_EN_Catch_All-_-Fusion-_-9182243&matchtype=&pla-366797395360&gclid=Cj0KCQiA0rSABhDlARIsAJtjfCeAEA2t1M_xQ1YxxcZRQssqx1iuW2rQyBDikEdoiqP6hg0WVwhNaOYaAovEEALw_wcB&gclsrc=aw.ds
Is there a formula to calculate the drop in voltage protection of these voltage gloves over time (through not using them)? Or is it just a general guideline to have electric gloves be tested twice a year? How long do these electric gloves generally last?
Does the drop in voltage protection that they offer become greater through use?
I would like to know this information so I know how often I should be replacing these electric gloves. My mains at my area is 220V so those gloves should fit the bill.


texts: Using I2C and SPI communication on the same same clock and data lines

texts:
I am using a PIC18F25K80 with multiple slave devices. All of them uses I2C except one. What i want to know is that can i first use I2C with the devives that uses I2C and then close I2C, change clock speed and switch to SPI mode ? Is this poosible without causing a conflict ?

Note - When I am in the I2C mode the chip select is set so that the device using SPI mode is inactive. Only after finishing the I2C mode I am making the device active.


texts: The right fuse (inrush current problem )?

texts:
Hello Electrical Engineers, just a quick question I need to get a fuse between the mains voltage (120V) and the adapter. I know that the load will draw around 30mA and has an operating voltage of 24V.
I was thinking myself:
If the output current after the adapter (gst60a24-p1j, 60W laptop adapter) is 30 mA and 24 Vdc and the input is $$120 V_{ac}$$ the input current would be $$6*10^{-3} A $$ or 6 mA with an efficiency of 90,5% that would be $$6.57*10^{-3} A $$ or 6.57 mA . There are other factors, however: the low efficiency with this small current for this large charger and the biggest problem; the inrush current. The inrush current is stated at 35 A for this adapter. The fuse which I would like to pick a 4 A fuse (SIBA 7008913.1.25), has an $$I^2t = 16 A^2s$$
I don't know how to process this information to know if the fuse will blow or not. Can someone please help me?
TL;DR Is this the right fuse, or explain to me how I can use I²t to determine what is the right fuse value? (see image for visualization).
setup: https://imgur.com/Fg0K2I2
datasheet fuse: https://imgur.com/a/92GW26x (2 pics)


texts: mesh analysis with current sources + dependent current source

texts:
I need to find Ix with mesh analysis method. I will really appreciate your help.
So, I turned Is2 to a voltage source and tried writing equations for a super mesh and KCL. anyway, I miss something in this problem or I got something totally wrong with my approach towards the problem


texts: What is meant by taking dual of a boolean expression?

texts:
I read online that if we have a set of SOP terms giving a boolean expression, then the POS terms of the complement of the SOP terms will give the same expression.
POS(f)=SOP(f').

This is called taking the dual of the expression. How does this work?

If I have:
f = BD + AC + CE

Its complement:
f' = (B' + D')(A' + C')(C' + E')

What is meant by taking the dual of f, and how do we get f in POS form?


texts: Does the body of the MOSFET consume current?

texts: Does the body of the MOSFET consume power and pass current if it weren't grounded? Like if I had a body bias and the value of Vsb wasn't zero, so in this case the diode inside the MOSFET must pass some current? Does it or not? And if it does, where does this current go and doesn't it make the MOSFET heat up?


texts:
I'm using an optoisolator for high side switching a Nixie tube.  For some reason, the optoisolator is not fully turning off, allowing the a very minimal amount of current to flow through the Nixie tube.

How can I make sure the optoisolator is fully off, so no current will flow through the Nixie?

I'm switching the optoisolator with an Atmega8515 microcontroller.

I've attached a circuit diagram.

Thanks for any help you can provide!


texts: ESD protection to the ground or chassis?

texts:
How to add ESD protection diodes to all cables (I/O, positive, ground)(see pink box below). Should I connect them to the chassis or battery negative terminal?
There may be some potential difference in ground and chassis due to large currents in ground cable (blue).

My initial guess is that I add ESD diodes between GND2 and IO/power lines
Do I need some protection device between chassis and GND2?

EDIT! It is observed that zapping the left side chassis with some 10kV causes the "Device2" to restart(fail). So there must be an arc between right side chassis and "Device2" somewhere because the ESD discharges through right side chassis.


texts: Use potting compound to secure solder joint

texts: I would like to solder a wire to these 2 pins. I was wondering whether I should protect the solder joints, as the cables may shift over time (and tension). Should I put glue on the around it to make sure it won't move (and of course keep the solder)?


texts: Why I need those capacitors in USB 3.0 transmission lines?

texts: In this picture (originally posted in this thread), there are capacitors called "AC Capacitor". Why do I need those capacitors? It is a USB 3.0 SuperSpeed connection, so it would not be an AC-Powered device.


texts:
Pioneer, Kenwood, Sony, Onkyo, Denon you name it, they all have a similar circuit like this:

Why they use C1 and C3 for?
Thanks


texts: How measure(Voltage reference points) for SPI flash Data Output parameters (tCLQV,tCLQX)

texts:
we are using MT25QU256ABA8ESF SPI flash as boot flash.
It operates in QPI mode @ 120Mhz.
As part of DVT we are measuring timing parameters for both Data Input & Data Output at Flash pins (No option to measure at the controller pins).
Data Input parameters tDVCH(setup), tCHDX(hold) are clear.
they have defined thresholds as 0.3VCC, 0.7VCC based on rising /falling.
But for Data output parameters like
tCLQV ( Clock Into Output Data Valid)
tCLQX (Output hold time)
There is no clarity on the Voltage levels.
For tCLQV where i can make sure Output data became valid, Is it for HIGH can i take VCC and for LOW can i take GND