texts: Comparison between MOSFET, MODFET, and MESFET?

texts:
I am taking a course on semiconductor physics and am learning about MOSFETs, MODFETs, and MESFETs.

I know the general structural differences between each one. A MOSFET is a metal, oxide, and semiconductor and you apply voltage to the gate to create an inversion layer in the semiconductor. A MODFET is similar to a MOSFET but its oxide is a doped AlGaAs combined with an undoped GaAs to create a strange dip in the band energy. This (somehow) creates a larger mobility for carriers in the 2-Dimensional Electron Gas layer.

A MESFET, I think, is the most dissimilar to the others because it is just a metal on a semiconductor. And you apply a voltage to create a large enough depletion region to completely deplete the layer so charge can't flow.

But what are the advantages and disadvantages to each one? Why would you want to use a MOSFET when the MODFET supposedly has a higher carrier mobility? Why would you use MODFET over a MESFET?

I am trying to construct a chart comparing and contrasting their characteristics, including (but not limited to): fabrication and structure and strain, parasitic effects, depletion region creation and shape, mobility of carriers, barrier height.


texts:
I'm designing a ATmega-based microcontroller test board. One of the features I want to include is a Real Time Clock with a Maxim DS1307 IC. Instead of including a traditional coin cell battery backup, however, I want to use a really small supercapacitor.

The power draw of the DS1307 is typically around 500nA in backup mode. Panasonic makes a really small 0.015F 2.6v supercap which looks like it would work. How can I estimate how long the RTC will run on this supercap?


texts:
I found this circuit which generates an offset voltage to the hystersis (so the threshold voltages are for example not -3V and 3V but -2V and 4V).

It would be the same as if you remove R1 and put a voltage source between R2 and GND, right? The circuit above just realizes that?

How does this exactly work and how can I calculate the resistors? I don't understand how it works with R1. The voltage where R1 is connected to is the same as the positive battery voltage of the op-amp. The output will change between 5V and -5V.

For my logic, 2.5V should drop on R1 and 2.5V on R2. However, there are also 5V (or -5V) that need to drop on R_hyst and R2. How does that work? What will be the final voltages and how to calculate it? An explanation would be awesome.

Thank you


texts: New soldering iron turns black as soon as it reaches 350C

texts:
I can't even tin it as it turns black befor I reach melting temperature. I tried 6 different tips and result is the same - it turns black and solder doesn't stick, I've no Idea what to do at this point also it smokes when reaches about 350C.

Is it just broken soldering iron and I need to buy a better one or I don't understand something?

I only tried Eutectic Solder, 5 tip were from same source 1 from other. I don't know brands.

Soldering iron is one of those cheep chinese variable temperature ones

Here's photo of it


texts: Non-inverting op-amp configuration with capacitor

texts:
I don't really get what is the purpose of the capacitor C1 which is connected in parallel with the feedback resistor. After my knowledge, if we modify the input signal frequency the over all gain will modify accordingly because of the impedance of the capacitor which effects the feedback resistence.

A lot of times I hear that it's useful for stability but I don't get why and how to calculate its value. Is it related to the fact that after a certain frequency the op-amp can cause lagging phase shifts and the capacitor prevents this? If so, why is that?

Thanks in advance.


texts:
I'm putting together an experimental geo resistivity measuring device following vague instructions found on the internet. I was wondering if it is safe to connect a Mastervolt AC MASTER 12/500 inverter to a MDQ 100A 1600V rectifier. Also I would like to know what approximate DC voltage would I obtain?

http://www.mastervolt.com/products/ac-master-12v/ac-master-12-500/
http://goldelectric.ca/download/MDQ.pdf

Thanks!


texts: My question is regarding the hookup of a radioshack bright rgb anode led.  I have the led common going to a 5v supply and the other pins are going through a 330ohm resistor to 3 PWM output pins (9,10,11 on the Arduino Uno). I set the pinMode() on each pin to OUTPUT, and then I do a "analogWrite(RED_PIN, 255);" and set the other color pins at zero.  It should be red, instead it's dark purple.  If I do a "digitalWrite(RED_PIN, LOW);" the red led is fully lit.  My question is why is the digitalWrite() working and the analogWrite() not? I am new to electronics so excuse me if I used the wrong terminology, I'll do my best to clarify.


texts: 90 degree phase difference in current between inductors

texts: The schematic is a circuit I am designing. The current through the leg with the inductor and capacitor in series must be 90 degrees offset from the other leg. The rectified current pulses through both legs must be equal. How do I calculate the value of the capacitor?  - Disregard the 3rd (secondary) inductor.


texts: Is 12/2 UF wire suitable for a 500 foot circuit with four 400 watt heaters for watering troughs in various locations - 120 volt system?

texts:
12/2 UF wire buried in the ground.
500 feet
20 amp circuit
4 watering troughs that draw 400 watts each in various places throughout the circuit
500 feet being the last one

Is this wire suitable?


texts: What the different values written on Relay mean?

texts:
I want to know what are the different values written on the relay

I understand:

10A 250VAC is the max Voltage, Current the relay can handle
SRD-05VDC-SL-C specified the voltage that triggers the relay (is 'triggers' the right term?)

But then what are the remaining values?

10A 125VAC
10A 30VDC (I think this is the Max DC Voltage, Current the relay can handle)
10A 28VDC


texts:
I am currently investigating on how to build RF transmitter and receiver circuits to try and build an RC device from scratch. I've come across this Pierce Oscillator Diagram and build it on a breadboard to test it using a 27 MHz crystal resonator.

I understand the general working principle of a Pierce oscillator, but I don't understand how some of the components work within the circuit. I don't understand what the purpose of the Inductor and the 330k Resistor in this circuit.
It would also be helpful to add some simple math to help describe the diagram and perhaps suggest how to modulate using the oscillator as a carrier wave for an RF remote control device.


texts: HID "report descriptor" includes set/get features?

texts:
After reading about HID report descriptor, it seems that it only includes "input report".

http://www.rennes.supelec.fr/ren/fi/elec/docs/usb/hid1_11.pdf

But what about get/set features ? Why it is not part of it ?

Thank you


texts: How are system configuration flash or eeprom chips programmed?

texts:
I've seen, quite often actually, a circuit that will have an eeprom or flash chip soldered next to the application chip.  Take a look at the ESP8266, it has some kind of programmable memory that sets up the SoC.

My question is how was that eeprom/flash chip programmed if there aren't any programming ports on the application board?  Is there like some pogo-pin programmer used during assembly or a socket that they drop each and every one in before soldering?  Those options seem incredibly time consuming.


texts: Current Flowing in Antennas for Radio Signals

texts: How does current flow through antennas to transmit radio signals? From what I know, in order for current to flow, there must be a load across the circuit.


texts:
I want to receive 5-bit serial words using a microcontroller's hardware UART at 45 Baud. This is the basic protocol for teletype machines. Since the baud rate is 45, I really want this done in hardware so that I am not spending all the processor time polling a pin, and for ease of programming.

Are there microcontrollers that can do 5-bit serial data in hardware? Is there a reasonable hardware/software implementation that won't tie up the processor?


texts:
If an ADC has N bits of data, but only M Effective Number of Bits (ENOB), should I just throw away the least significant (N-M) bits if they are simply noise?

If those bits don't add any useful information, I can reduce the size of multipliers and such.


texts: How many times of a frequency of a PWM can properly generate a sine wave to drive a motor?

texts:
I know PWM with dense and loose duty cycle is used to generate sine wave for applications such as 3-phase motor driving. But, How fast does it require to properly generate a sine wave to drive a motor?

I mean, if a sine wave is 1 Hz, how many times of the PWM base frequency is required to properly generate a sine wave PWM?

I guess 100 times would be fast enough, 1000 times would be perfect, 50 is barely enough, and 10 is not enough based on my imagined drawing of PWM in my mind.

Is there a standard or commonly used number of times to generate a sine wave? Thank you!


texts:
I'm building a design involving Toshiba's TB6600 chip which has an unusal HZIP25-P-1.00F package. I've seen implementations where folks have bent the pins manually and soldered them horizontally such that a heatsink can be bolted directly onto them.

However, I did not want to do this. Instead, I thought of attaching an aluminum right angle bracket to a normally mounted chip (vertical). One side of the right angle bracket would be touching the chip's heatsink area while the other side will be touching an exposed pad on the PCB. This same exposed pad is present on the bottom copper side as well and is connected with the top copper using thermal vias. A large finned heat sink is then fitted onto the back side of the PCB and connected to this bottom copper side.

I haven't gotten around to doing calculations on this yet but any thoughts on if this is a good idea?


texts:
I want to make a CAN bus sniffer for 250 kbit/s using my computer. After some research I've found that MCP2551 is some kind of voltage level regulator for CAN's physical layer. Keeping that in mind, I'm wondering if this setup could work. I just want to record the exchanged messages for automated test purposes, not be a part of communication:

PC <-> USB-UART (perhaps CP2102, bacause I already have one) <-> MCP2551 <-> CAN bus

If not, what kind of signals have to enter MCP2551 in order to make me be a part of the bus?


texts: Simple coountdown timer IC that is independant of supply voltage

texts:
I'm designing a shutdown circuit that switches off a SMPS regulator after a 10 second time interval.

This is a battery powered application and the battery voltage could be anywhere between 7-15V.

I've looked at capacitor circuits and 555 timers and it seems to me that their timing will be dependent on the input voltage supplied - is this correct?

I just need a very simple IC with a pin that goes high 10 seconds after a switch is pressed, where the timing is independent of the battery voltage.

Regulating the voltage is not an option - I already have a regulator in the circuit and I'm trying to switch it off!

Any suggestions would be greatly appreciated, thanks in advance!


texts: When can the output of any flip flop (e.g., JK FF) be indeterminate?

texts:
I came across following problem:

  In an SR latch made by cross-coupling two NAND gates, if both S and R inputs are set to 0, then it will result in
  A.  Q = 0, Q' = 1
  B.  Q = 1, Q' = 0
  C.  Q = 1, Q' = 1
  D.  Indeterminate states

I (wrongly) felt that answer would be option D, indeterminate state. But it was option C. The explanation given was:

  Here we know that the output will be definitely 11. So its not indeterminate. However its invalid.

I understand that this is true for an SR latch.

But now I am thinking when the output will be indeterminate.

Can we call output of a level-triggered JK flip flop (with clock duration more than flip flop delay) to be indeterminate when J=K=1? I know this corresponds to toggle state, but due to race around condition, can we call it indeterminate?


texts: Where the positive and negative side of an AC adapter?

texts:
As you see in the picture below,

I got an AC adapter and cut off the two ends but I forgot to see where the positive and negative side. I Also have no electrical equipment to test it. After that I took a small LED for a speaker so that I know if the diode is reversed or forward bias for a split second. I know that it will burnt out because of the high current. But even though if it lights for a split second and then burn, then I would know it is in forward bias and if it does not, I know it is in reversed bias. Why I am  trying to find which side is + and which side is -? The reason is because I want to charge a 12 V lead acid battery without damaging it for reverse polarity and also have no equipment to check :).

Does anyone has an idea how to check which side is - or + ?

Anyone has an idea how to check


texts: Active Low LED and Active Low Switch behavior on FPGA counter-intuitive

texts:
I was following a tutorial to get started with Libero SoC with MicroSemi SmartFusion FPGA.  I coded a small LED toggle module
module led_toggle( i_sw , o_led );
    input   wire [1:0]  i_sw;
    output  wire [4:0]  o_led;

    assign  o_led[0] = i_sw[0];
    assign  o_led[1] = i_sw[1];
    assign  o_led[2] = i_sw[0] &  i_sw[1];
    assign  o_led[3] = i_sw[0] |  i_sw[1];
    assign  o_led[4] = i_sw[0] ^  i_sw[1];
endmodule

Pin mapping
i_sw[0] to on-board switch SW0
i_sw[1] to on-board switch SW1
o_led[7:0] to on-board LEDs D[4:0]

After synthesis, place and rout, I flash the FPGA with the bitstream.
On pressing SW0, led D0 lights up and on pressing SW1, led D1 lights up. This is as expected.
However, it seems leds D2, D3 and D4 donot light up according to the AND, OR and EXOR combination of SW0 and SW1 as per my Verilog design. In fact working backwards from the behavior on-board, the logical expressions for them are
LED D2 = Sw0 | SW1 instead of designed (SW0 & SW1)
LED D3 = SW0 & SW1 instead of designed (SW0 | SW1)
LED D4 = ~(SW0 ^ SW1) instead of designed (SW0 | SW1)

Now in the same tutorial it is mentioned that

Keep in mind the switches and LEDs are active low. That is, the switch
creates zero when pushed and the led illuminates when a logical 0 is
applied.

So an active low switch with an active low LED is buffer like behavior i.e. LED ON when switch pressed  and LED OFF when switch de-pressed. However it doesn't explain the unexpected behavior with leds D2, D3 and D4.
So what am I missing here ?


texts: How does this diode improve the common mode conducted noise?

texts:
This image was taken from UCC28881 (page 16)

The desciption in the body says:

  A half-wave rectifier is chosen and implemented by diode D2 (1N4937). It is a general purpose 1-A, 600-V
  rated diode. It has a fast reverse recovery time (200 ns) for improved differential-mode-conducted EMI noise
  performance. Diode D3 (1N4007) is a general purpose 1-A, 1-kV rated diode with standard reverse recovery
  time (>500 ns), and is added for improved common-mode-conducted EMI noise performance. D3 can be
  removed and replaced by a short if not needed.

My question is how does D3 improve the EMI noise performance ?


texts:
It seems that both 49.9Ω and 50Ω resistors are a thing:

https://www.mouser.co.uk/Passive-Components/Resistors//N-5g9n?P=1z0wnltZ1z0wljo
https://www.mouser.co.uk/Passive-Components/Resistors//N-5g9n?P=1z0wljoZ1z0x8f8

Given that they're typically 1% tolerance, why have both? In particular, why even bother with 49.9Ω?


texts:
I am working on a HDMI dongle based on I.MX6Q with reference to the design files shared in Freescale community.

I want to feed HDMI input to processor. As there is no HDMI input available with I.MX6Q processor, I am considering to use camera input port (described in section 37.1.2.1.1 of I.MXQ Reference manual) which is having parallel input upto 20 bits & I2S interface for audio connectivity.

But the HDMI receivers available in market like ADV7611 come with 24 bit RGB interface. As our processor input port has only 20 bits, we will have to ignore 4 LSBs in total(we havent finalized the bits to be ignored).

Are there any drawbacks to this approach in terms of picture quality?

Also, are there other means of converting HDMI to some serial interface that will be available in I.MX6?


texts:
Seeing as smart meters are becoming more and more popular (in particular countries), I would like to understand smart meters and thought knowing the OSI Model would be a good place to start. I already have a basic understanding of smart meters and the use of networks  etc. but my limited knowledge hasn't allowed me to define each layer of the OSI.

So far I've only really got two layers:

Application layers - define the content of the data messages and the way they're presented.
Physical layers - define the communications medium and methods of data communication.

Any help with separating these into physical, data link, network, transport, session, presentation and application would be brilliant.


texts: Recommendation for default settings for unused pins on an STM32 (ARM Cortex M3) - pull up/pull down?

texts:
We are currently using various variants of the STM32 microcontroller family. I would like to know the following:

What are the recommended default settings for pins of the microcontrollers in general  if you have the option to select both pull ups or pull downs? What are the pros and cons of going with one or the other? (Assuming you will set them up by default as inputs)
In particular I would like to know what to do with unused pins for the STM32 microcontroller family. It is obvious to me that we should not leave the pins floating, (which is all that the datasheet says, :( ), but should I should set them to input with pull ups or inputs with pull downs? In particular, I would like to choose a setting that is least susceptible to ESD and also if possible, consumes the least amount of power.
For critical pins, should we rely on the firmware to correctly set up the pins to the correct default state or should this responsibility lie with the external hardware  (connecting external pull ups or pull downs)? If the values chosen for the external resistors is greater than the internal pull ups or pull downs, the setting in firmware does not matter.

The pro that I can see for doing the above, is that if the micro does not initialise properly for whatever reason (faulty hardware or the likes), we are not relying on the firmware to set up the pin correctly.

The con I see is that it costs more to do this is hardware.

Any light that you can shed on the above will be really appreciated.

Thanks..


texts:
Now, I know that this question has been asked so many times that it seems like I'm trolling, but I must point out that I couldn't find the right answer to this question anywhere.

So yeah, CMOS and TTL are different. Logic levels, speed, drive current, power consumption, and so on.

What I'm wondering is what is their difference from a designer's perspective.

For this question, I'll be designing a small computer, say, a Z80 or a 6502 or 8080 or whatever. Let's use HCMOS and LSTTL as our examples.

Does it really make a difference, practically?

The clock rates are low enough that gate delays are not an issue. I'll power this from AC mains so power is not an issue. I'll stick to one logic family or the other so compatibility is not an issue. So what's the incentive to choose one over the other?

Say I want to make this device as reliable as possible. Also, I want to make this device repairable.

So which logic family should I use?

I'm talking about product lifetime. Should I stick to one type of IC because they are more reliable? What's the MBTF of these devices?

Also what if, in a few years, they stop manufacturing some of these ICs? For example, if you've got a Motorola ECL-family computer, if an IC breaks, you're outta luck. You'll have to kludge your own or scrounge for some old rare ICs. I've heard that large FIFOs and PROMs and SRAMs in the 74xx family have also been discontinued. So if something breaks, I want to be able to buy readily-available parts and fix it.


texts: Is it possible to set a breakpoint in AVR Studio in files other than the one where the main() function is?

texts:
If I have a project with more than one translation unit, AVR Studio only allows me to set breakpoints in the main c file.

It doesn't matter if I include the other files directly by #include "something.c" or by using their header.

A quick search on various embedded forums didn't result in any answer or even discussion regarding this topic. Is everyone using a single translation unit when debugging, or did I miss a feature in plain sight?

The project was generated by CodeVision, if it is of any relevance.


texts: Can I use a 5v xtal osc with a 3v MCU? Will a simple npn buffer work?

texts: I have several crystal oscillator cans that run on 5v. I have a PIC24HJ128 on a breadboard. The PIC uses 3v. I want to use a simple npn transistor to buffer the osc out into the CLK in. Will this work? Does anyone have any advice?


texts:
Here is the solution that I have so far.

How are the values of Vx different if we solve it using KVL and different if we use Ohms Law?

And to verify the power law, do i need to calculate the current through each voltage source?


texts: Will checking the backup voltage on an RTC drain it's backup battery?

texts:
I'm working on an ATMega project that will be keeping time and I'm trying to make it so you have an option of either software time (millis() based), DS1307, or DS3231 (ChronoDot) RTCs.

At the most basic, what I would like to do is have headers for a ChronoDot available to solder in and then somehow in software detect if the ChronoDot is attached and switch to using that. It would typically be easy enough to check that either the DS1307 or DS3231 is present as they use the same I2C register, but after that initial check they do deviate from one another a little and the latter has more features. So I still want to determine which is connected. In general, I plan on having a place directly on board to solder in the DS1307 as the default option and the DS3231 support would be with a complete ChronoDot only via dual 4 pin headers. The ChronoDot would essentially fit over the place where the DS1307 would normally go (it would not be populated in this case). The main reason I'm focusing on the ChronoDot specifically is that it's popular, easy to acquire and doesn't require SMD soldering for the end user (this if for a kit). So, here's what I'm thinking...

The both the DS1307 and DS3231 have a Vbat line on the chip, but it's not really needed for anything. However, the ChronoDot has an actual VBat pin on the breakout board. I could maybe hookup only Vbat from the ChronoDot header and not the DS1307 and connect it to a digital input pin on my ATMega. But have that input pin pulled down to ground by a resistor (not really sure what value... maybe 4.7k?). If my EE theory is correct I can then read that pin and if I get a low, there's no chronodot but if I get a high, there is.

Something like this:

simulate this circuit – Schematic created using CircuitLab

My main question here is if doing this will just end up draining the backup battery on the RTC? Normally there would be no current drawn from the backup battery while main, 5V, power is supplied but would hooking this up to a digital input make it draw power from the battery all the time? Or, is there a mode I would need to put the pin into after reading from it in order to "disconnect" it, so to speak? I know I could change it to output, but I believe that if it's set as output and low I would basically be grounding the battery.

Anyways, my EE courses were a long time ago. Any help on the theory here would be appreciated.


texts:
Searching for "GPS protocol" reveals many sources for processed GPS data, e.g. NMEA or binary outputs of GPS units.

Where is the official documentation for the GPS satellite - receiver protocol? Or any interesting supplemental material that might explain it?

Context: I'm especially interested in learning about how (e.g.) the almanac and ephemera are transmitted.


texts: When IGBT is off what is the leakage current between collector and emiter?

texts:
When ı saw datasheet of IGBT, there are two terms of about leakage current between collecter and emiter. But ı can not be sure is these terms are about leakage current?

These terms are Ices and BVces. My questions are listed below.

1- Is Ices leakage current between collector end emiter ?

2- IF Ices is leakage current, is there any connection between BVces and Ices?
For examples BVces = Ices*Rces. Is this true ? If this equation is true, Can ı say Rces is isolation resistor when IGBT is off?

Datasheet link : https://m.littelfuse.com/~/media/electronics/datasheets/discrete_igbts/littelfuse_discrete_igbts_xpt_ixy_8n90c3_datasheet.pdf.pdf


texts: Microcontroller to PC via USB - do I need to use isolation?

texts:
I want to connect my microcontroller (dsPIC33E) to a PC via USB. Since the particular microcontroller doesn't have a built-in hardware for the USB protocol, I have to use an external chip (e.g. TUSB1106PWR or MAX3454EEUD+), i.e. a USB transceiver that I plan to connect to a UART port of the microcontroller.

The microcontroller has its own isolated power supply (3.3-5V), and what I want to know is do I need to isolate the data bus via optocouplers?

As I see it, there are three options regarding power supply:

To use a separate (isolated) power supply for the microcontroller. The same (isolated) power supply is used to supply the USB chip, i.e., voltage supply and ground pins on a USB connector are NC.
The microcontroller is supplied by its own (isolated) power supply, and the USB chip is supplied by the USB port/cable.
Everything is supplied by the USB - the microcontroller and the USB chip. In this case, I don't need to use the isolation.

Addition to the original question:

Let's say that a microcontroller has its own (isolated) power supply, and the same power supply is used to supply the USB transceiver. Now PC has its own (possibly isolated) power supply. I have a situation exactly like this.

I'll now write a series of questions, I apologize if I oversimplified the questions. Simply yes or no will do with a reference to a question:

Q1. If the two grounds are not tied together, then there is no voltage between the two grounds, since there is no reference point - correct?

Q2. If we tie together the two grounds, that becomes a reference point for the whole system. If both supplies are isolated, or at least one of them, then there will be no voltage difference between the two grounds. Tying them together we would simply reference those two grounds - correct?

Q3. If the two power supplies are not isolated, and they are both connected to the AC mains, then something really bad could happen, since the two grounds can be at a different potential, and they are both referenced to N. If we tie the two "grounds" together, due to the voltage difference current will flow from higher potential to lower, and depending on the voltage difference, something might get burned - correct?

Q4. Since D+ and D- come from the PC side, if we don't tie together the two grounds, then the USB transceiver wouldn't be able to represent voltage levels on D+ and D-, since there is no reference point - correct?

Q5. If USB transceiver operates in a differential mode (it looks for the voltage difference between D+ and D-), then we don't need to reference PC's ground at all, i.e., we don't need to tie the two grounds together - correct?


texts: Help Shielding RF Anechoic Chamber - FM Stations

texts:
a collegue and I acquired a surplus small anechoic chamber (8 ft x 8 ft) for making some pre compliance test measurements, and we're running into the issue of FM Stations being only attenuated around 20dB inside. We're looking for at least 80dB attenuation on these stations (around the 100Mhz range). The chamber is made of steel, and we've tried wrapping it in aluminum foil and grounding it, which should give us much greater attenuation. However this does little.

What would you recommend pursuing to adequately shield this chamber and greatly reduce incoming unwanted FM stations?


texts: How can I make it so that customers who buy my arm based product can easily update the firmware?

texts: I'm building an arm-based (stm32F7) hardware device which will have a USB port. I would like to be able to update the firmware and distribute it such that customers with my device can easily install new firmware without having to install an IDE or do anything complex. I am writing a computer side program that communicates over USB serial, so I would like this to also function as an update utility.


texts: How do you get transistor voltage when you only have currents?

texts:
β=50 I need to find Vbe and Vce
So obviously it is a NPN transistor, the current is flowing in the same direction so it is in active mode.
Ie=Ic+Ib
1.2mA=1mA+Ib
Ib=0.2mA
Vbe should be around 0.7V for it wok but what about Vce?


texts:
I have a Pololu 3.3V step-up converter - U1V11F3. I tested it by connecting a regular 1.5V alkaline battery for input and a resistor at output. With no load or small load (10K) it keeps the output voltage at 3.3, however with higher loads (100 ohm) it drops the voltage to 3.13 with a current of 31 mA and with 47 ohm and current of about 60 mA it drops to 2.7-2.8

I have noticed that the current for the battery goes as high as 150 mA during that time and the measured voltage drops from 1.46 to 1.24

Does this mean that the battery is not able to provide a high enough current? Looking at the datasheet for the converter chip it should keep the voltage up to 300 mA output current. My intended use for the converter is an Arduino compatible node with RFM69HW chip that should sleep most of the time, but wake up and send radio data which should increase the current to about 130 mA for short periods of time, but obviously the converter can't keep up with the demand. I can try not to use the highest power of the chip, but still the current will be in the tens of mA which apparently will not work.

Does anybody know if other chips are working better? Or has anyone experience with a similar working configuration?


texts: I have a package of 10 inductors, all of which are supposed to be 22µH, but they all have "220" printed on the case. It does not seem right when I compare to an otherwise identical (same type) inductor with an inductance of 3.3µH, which has "3R3" printed on it. Is it just odd ordering or am I missing something? Inductor is an SDR0604 type.


texts: Are FPUs made of ALUs, and how many ALUs are needed to make up an FPU?

texts: In GPUs/CPUs, are FPUs made up of ALUs? If not, what would be a smaller "logical unit" that FPUs are made up of? If FPUs are made up of ALUs, how many ALUs would it take to make up a 16-bit FPU? 32-bit FPU? 64-bit-FPU? Also, correct me if I'm completely not understanding the make-up of FPUs correctly. I'm a bit confused about this topic, and I've only studied how ALUs function, so I may be understanding this concept completely wrong.


texts: How is transition from three-phase distribution without neutral to three-phase consumption with neutral achieved?

texts:
A typical distribution grid supplies 6 or 10 kilovolts AC to a substation near the consumers. This is typically done with a three-phase line without neutral - just three wires going in parallel. Then there's a transformer that lowers the voltage to something like 110 or 230 volts AC.

The consumers typically have single-phase load and so here comes the neutral - we now have three phase wires and the neutral wire as the transformer output and those single-phase loads from different consumers are connected to phases in round-robin fashion so that the current in the neutral is hopefully minimized and phases conduct equal currents. Yet unless the load is perfectly balanced different phases will conduct different currents on the secondary side of the transformer and the difference is the current flowing through the neutral.

How is that addressed on the primary side and the high voltage line where there're just three phase wires and no neutral wire?


texts: Ignored holes in calculation of current in npn transistor

texts:
Question:

  In an \$p-n-p\$ transistor, \$10^{10}\$ electrons enter the emitter in \$10^{-6}s\$ Calculate the emitter current.

My problem:

The lame way to attempt this question is to say that:

$$\text{current}=\frac{\text{charge flown}}{\text{time taken}}=\frac{\text{electrons flown}\cdot\text{charge on one electron}}{\text{time taken}}$$

But! We were taught in junction diodes, that holes and electrons both contribute to the total current. There will be as many equal and opposite holes flowing from emitter to base as many electrons enter the emitter. Hence, the correct answer should be:

$$\text{current}=\frac{2\cdot\text{electrons flown}\cdot\text{charge on one electron}}{\text{time taken}}$$

with the extra factor of \$2\$. But, my book has taken the first answer as correct. What is the fault in my logical reasoning?


texts: Can you turn on a NMOS with a lower voltage than at the drain?

texts:
So, a NMOS can be turned on if the \$V_{GS}>V_{TH}\$.
If the circuit is such as below:

simulate this circuit – Schematic created using CircuitLab

So, say that the \$V_{TH}\$ is quoted as being 3V, initially, this would be OK as \$V_{GS}\$ would be 5V and hence, greater than the threshold required.
My question / wondering is: as soon as the FET starts to conduct, the voltage present at the source will become the drain voltage, in this case, 3V. This, in turn, causes the \$V_{GS}\$ to become 2V, which is now below the threshold voltage.
Would this cause the FET to turn off as the gate-source voltage is now less than the required threshold?

This isn't exactly the same question as the title would indicate, but it is the exact situation I am facing. I suppose it is the same principle as if the drain voltage were to be > 5V.


texts: Can a wifi transmitter generate RF of different frequencies?

texts: If I have a micro controller (let's say a Raspberry Pi) that is able to connect to wifi (using a wifi transmitter), would it be possible to generate RF signals of other frequencies?  I figure it should be able to since wifi is just a 2.4 or 5.0 GHz RF signal and it must be able to generate signals if it is able to send information back to a router (or wherever else it is connected to).


texts: Placement of Through Hole with a High Tolerance Dimension

texts:
Beginner question here.

What does one do about the placement of the through hole when one dimension
of the part has a high tolerance.

For example, I place the through hole anticipating the center of the components leg
to be 3.35mm from the end of the piece. Since the center could actually be anywhere from
3.20mm - 3.50mm given the tolerance, does one typically:

1) Increase the through hole size to compensate possible errors?
Wouldn't this lead to loose connections?

2) Simply scrap the piece if the tolerance doesn't allow proper mounting,
accepting occasional losses.

3) So if the legs diameter was 0.5mm, what would be the best size PTH in this case?


texts: Is it possible to import a gerber file into Fritzing or do I need to change the format? If I need to change the format, what do I change it too?


texts:
I'm quite new at MCU programming (mechanical engineering background), but managed programming an Attiny85 to source an LED and switching modes (blinking/solid) by using a switch. I would now like to run this from 2x CR2032 (max ~6.2v) that exceed the max voltage (5.5v)rating for the Attiny. Power consumption is very important here so I would like to reduce unnecessary losses to an absolute minimum.

After reading this thread (Sink or source from AVR) I tried to switch my program to current sink. That is now working on 5v by setting the pin as an open-drain by using:

PORTB &= ~(1 << PINB1);

DDRB |= (1 << DDB1);        // LED ON (DDRB set as OUTPUT) --> sink
DDRB &= ~(1 << DDB1);       // LED OFF (DDRB set as INPUT) --> float

I was thinking of using a diode to drop the voltage under the specified 5.5v for the Attiny Vcc (as the current here is now almost 0 there should be no significant power loss). However the datasheet of the Attiny is mentioning:

In the previous hyperlinked thread it was stated that a 5v MCU could even drive 9v LEDs, but am I correct that this is not allowed for the Attiny85? How dangerous would this be? Also when floating the Vcc is not identical to the voltage on the pin. Is this a problem?


texts: Engineering very high impedance resonator with coplanar waveguides

texts:
I have very little knowledge of electrical engineering, so please understand if my questions are somewhat trivial.

I have read that a coplanar waveguide (CPWG) acts as a lumped LC oscillator circuit, and its impedance is usually set around 50 ~ 100 Ω. My questions are:

Is there any fundamental/practical upper limit of impedance for a single CPWG?
Can identical CPWGs be serially connected - as we do for normal resistors, coils, and capacitors - to increase the circuit impedance?

The reason why I am asking this is that there are potential applications for the resonators with very high impedance values (say, larger than 10 kΩ), for quantum information science.


texts: Verilog Code: When should I bother making a detailed code if I can make it shorter?

texts:
I made 2 verilog codes for a BCD adder. On the first code:

I made a carry look ahead adder module
That adder module is then instantiated inside the BCD_Adder module to add two 4 bits
Then I use my own function(use of truth table and K-map) to know if the sum from the adder module is >9, if yes add 6 but if not then add 0.

module carrylookahead(input[3:0]a,b,input c0, output[3:0]s,output c4);
  wire[3:0] P,G;
  wire[4:0] c;
  assign c[0]=c0;

  assign P=(a^b),G=(a&b); //Propagate and Generate
  assign c[1]=G[0]||(P[0]&&c[0]),
         c[2]=G[1]||(P[1]&&c[1]),
         c[3]=G[2]||(P[2]&&c[2]),
         c[4]=G[3]||(P[3]&&c[3]);
  assign s=(P^c[3:0]);
  assign c4=c[4];
endmodule

module BCD_Adder(input[3:0]a,b,input c0,output[3:0]s,output c4);
  wire[3:0] fx,s_t;
  wire c0_t,c4_t;
  assign c0_t=1'b0;

  carrylookahead m1(a,b,c0,s_t,c4_t);
  assign c4=(c4_t)||(s_t[3]&&s_t[2])||(s_t[3]&&s_t[1]); //func to know if BCD sum needs plus 6 or not
  assign fx={1'b0,c4,c4,1'b0};
  carrylookahead m2(s_t,fx,c0_t,s,c4_t);
endmodule

On my second code:

I use the plus operator so that I won't need to make my own carrylookahead module
I use magnitude comparator operator (>) so that I won't need to make my own mathematical function to know if the sum is greater or less than 9.

module BCD_Adder_v2(input[3:0]a,b,input c0,output[3:0]s,output c4);
  wire[3:0] s_t,fx;
  wire c4_t;
  assign {c4_t,s_t}=a+b,
         c4=(s_t>(4'b1001)),
         fx={1'b0,c4,c4,1'b0};//if s_t>9 THEN fx=6 but if not then fx=0
  assign s=s_t+fx;
endmodule

Both works the same way in my test bench, my question is when should I bother to make a detailed module like what I have done on my first code? I thought that my first code will have fewer gates needed since compared to the second gate I did not use a plus operator and a magnitude comparator operator.


texts: Homebrew linear PSU leakage current/voltage origin

texts:
I made a 13.8V 10A linear power supply from a transformer took from a computer UPS whose battery was dead.
Now the issue is when I touch the output of the regulator leads, or the power supply casing I felt a slight tingling sensation. I measured the voltages using a multimeter with one lead referenced to earth and got these readings,
negative rail and earth = 34 VAC
positive rail and earth = 34VAC
Casing and earth = 15VAC
some parts of the transformer and earth =15VAC.
This stray voltage was interfering with my other circuits I'm testing. Fortunately I was able to solve the problem by earthing the case and the output rails directly, but I still
read a 1 to 2 Volts on my DMM.
How is this effect happening?
How do I get rid of this completely?
Also I can read a 700mV on a 1N4148 RF detector probe in the close proximity to my PSU when ever I touch it or attach a 10cm wire to it. Is it just static from all the switching devices in my house or does it have to do anything with the PSU.
Here is the schematic,

simulate this circuit – Schematic created using CircuitLab


texts:
Three is the minimum number of phases determined to generate and transmit power in the most cost effective manner and it is also helps to built self starting motors.

Throughout the history of power technology, various systems were invented and tested from DC, various combinations of polyphase systems and frequencies. Diminishing benefits of more than three phases for polyphase systems is well understood and suddenly at some point of history THREE is determined to be the best solution.

My question is who is the individual or group of people finalized the decision? Nikola Tesla himself or some regulatory body?


texts:
In the context of an academic project, I designed a PCB which includes an MCU (EFM32), a GSM module and a GPS module. One of the main target was for the system to be low power. However, now that it is time to measure my results with a DC Power Analyser I get surprisingly high values of current consumption.

Of course, it could be an hardware design problem and I won't omit this possibility but obtaining 5+ mA while my MCU is in sleep mode (should consume just some uA), the other modules are not powered and with low quiescent current voltage regulators (all < 20 uA) makes me question my measuring methods.

Here is some possible answers I am considering to my problems

The PCB was in debug mode (wired to a Starter Kit) while I was measuring. Does it matter? If yes, what is the proper way of doing it?
I plugged my DC Power Analyser directly on the pins of where a Li-Ion battery is supposed to be plugged. Therefore, it is under the control of a battery charge circuitry which could bias the measurement by trying to charge the DC Power Analyser. Is it possible?

What do you guys think?


texts: Q value of a passive single stage RC low pass filter

texts:
I'm a student trying to understand filters. I would like to know what the Q value of a series RC low pass filter is. As far as I'm aware, one can't design for it, but I'd still like to know what it is! Surely it must have a Q value!

Also, is it possible to increase the rise time of a critically damped Sallen Key low pass filter? From what I understand, the parameter Q (or \$ \zeta \$) define the rise time. I would've perhaps thought that cascading Sallen Key filters would allow for a sharper rise time.


texts: In a cpu, why are/were Index Registers needed? You can of course live without them, but why would you want them? Wikipedia says that they are used for vector/array operations, but I'm not really sure what that means. (I am deciding on the architecture of my home-brew cpu)


texts: How to identify 422 or 485 bus from the PCB

texts:
I have a very old CPU card, maybe 1980's. It has following chips on it and most probably these are used for communication with the rest of the system.

SN55188 Quad Line Drivers

SNJ55189 Quad Line Receivers

I cannot power-up the board. But I need to figure out the communication bus type used in it. Looking at the above IC's can I safely say that:

It's not using TTL signals on bus.
It's not differential 485 bus.
It's using differential 422 bus.


texts: If I have a power tool in a wood box do I need a ground?

texts:
I am using an old treadmill motor to build myself a variable speed disk sander. The motor is a 2 1/2 hp DC motor and I am using an mc-60 speed controller.

I am wiring it all up according to the wiring diagram, but my power cord no longer has a place to ground to. I built the body of the sander out of wood, and the only metal that it has is the small aluminum case for the speed controller which I believe is not suitable for a ground anyway.

What should I do with the ground? Does it cause any safety concerns if I just cap it off?


texts: Help explaining negative (ground) power connection through TV setup even though wire not connected?

texts:
After attempting to use a power inserted for the OTA antenna I discovered an unexpected problem. The inserter is powered by an UnGrounded Ac/DC adapter (Wal-wart as they are often called). All worked fine until I connected the coax and discovered that the device will stay powered on even when the negative is disconnected from the AC/DC adapter.
After much trial and error I discovered that the mysterious ground / negative was going through the coax cable to the PVR and TV, then through RCA, HDMI, and coax between the PVR, TV, and DirecTv receiver. Only once was each device fully unplugged from one another would the inserter power off without any/ issues.
After more headache I figured out this was occurring because the DirecTv dish and OTA antenna are sharing the same grounding Stake outside. After disconnecting one of the grounds from the stake the problem disappeared.
Attached are diagrams of the configurations for clarity. I am extremely confused on how this is working. My knowledge of DC power is that both the positive and negative must be directly connected in order for the circuit to be completed. In my scenario only the positive needs to be connected and the circuit works. At first I believed the earth ground on each power supply was causing the issue, but nothing has a ground plug besides the PVR. All devices with TV 2 have no ground and have been eliminated as a potential issue.
Any insight on what could be happening and how is appreciated! This problem has truly piqued my curiosity!


texts: Staggering PWM waveforms for servos to minimize current spikes

texts:
If I'm controlling multiple hobby PWM servo motors, is there an advantage to staggering the pulses sent to each servo?

By which I mean, each servo needs to see a pulse of width ~1ms every 20ms. Let's say I have 20 servos. If I send a 1ms pulse each ms to a different servo, then will that change the spikiness of the current draw, or otherwise improve the circuit?

Intuitively it seems that sending the 1ms pulse to 20 servos all on the same 1ms tick could cause a synchronized current spike, thus maximizing the chances of tripping a fuse in my power supply.

Is this a real concern?

(I ask because the Adafruit PWM python library has the capability to specify rise and fall times for pulses to a given servo, rather than just specifying the frequency. I can see no reason to build the API this way unless you'd want to stagger the signals for some reason).


texts: I'm uncertain of the term "fat" when referring to NMOS and PMOS. Tried google and nothing. Could I get a little clarification?


texts:
I'm completely new to Atmel ARM microcontrollers and beyond a single class a couple of years ago and some arduino tinkering, new to "proper" mcu's in general.

So therefore I am having trouble with the simplest of tasks, that is building a simple LED blink program and programming it to the chip.

The MCU is an ATSAM3X8E, mounted on an arduino due (but I am not using any arduino software, I'm trying to treat it as a simple breakout board for the MCU).

I am using an example project that came with Atmel studio 7 called clock_example11 (which is apparently made for the arduino due so the board config should be okay?) except I just tried to modify the blinking LED to pin 14 of port B. It builds seemingly fine.

So then I tried programming it over USB, using the SAM-BA 2.15 software. I start the program, connect to the chip successfully (with the "at91sam3x8-ek" board preset), I select the built .bin file as the send file name in the flash tab and send it to address 0x80000 which if I understand correctly is the start of the flash and is where the chip boots from if I set the boot from flash bit. Then I send the file, and when I try comparing the memory with the sent file, it matches, so the flash was programmed successfully it seems. Then I execute the "boot from flash" script and even "select flash0 for boot" for good measure.

But, nothing happens. The LED doesn't blink. And I don't know where to go from here. I don't know which of the steps I did, if not all of them, are wrong. Can someone give me some tips? Here is the main source file:

#include "asf.h"

/* Global ul_ms_ticks in milliseconds since start of application */
volatile uint32_t ul_ms_ticks = 0;

/**
 * \brief Wait for the given number of milliseconds (using the ul_ms_ticks generated
 * by the SAM microcontroller system tick).
 *
 * \param ul_dly_ticks  Delay to wait for, in milliseconds.
 */
static void mdelay(uint32_t ul_dly_ticks)
{
    uint32_t ul_cur_ticks;

    ul_cur_ticks = ul_ms_ticks;
    while ((ul_ms_ticks - ul_cur_ticks) < ul_dly_ticks) {
    }
}

/**
 * \brief Handler for System Tick interrupt.
 *
 * Process System Tick Event and increments the ul_ms_ticks counter.
 */
void SysTick_Handler(void)
{
    ul_ms_ticks++;
}

/**
 * \brief Initialize the clock system and blink a LED at a constant 1 Hz frequency.
 *
 * \return Unused (ANSI-C compatibility).
 */
int main(void)
{
    sysclk_init();
    board_init();

    /* Setup SysTick Timer for 1 msec interrupts */
    if (SysTick_Config(sysclk_get_cpu_hz() / 1000)) {
        while (1) {  /* Capture error */
        }
    }

    while (1) {
        ioport_toggle_pin_level(IOPORT_CREATE_PIN(PIOA,14));
        mdelay(500);
    }
}

EDIT: I think my code was the problem, because now I was able to program the chip. For the record I modified the main function to this: http://pastebin.com/f0Vnw2Q3


texts: How do ohm meters measure high resistances?

texts:
I'm sorry if this is a stupid question, but I'm an apprentice and this doesn't make sense to me. I'm given to understand that an ohm meter measures resistance by passing a small current through a circuit and then internally calculating the resistance from the drop.

But my meter can measure in the kohm range. Isn't this enough resistance to completely block the small amount of current from the meter? What am I not understanding?


texts: Understanding MOSFET ouput characteristics on a log-log scale

texts:
I am a second year BS Electrical Engineering student, and I am working on making an autonomous robot in my summer vacations, nowadays.

Right now I am designing an H-Bridge using discrete components for my robots' drive motors.

So, here's what I have done already.

After selecting the package of the MOSFET, and then finding the amount of power it can dissipate, given the operating temperatures, I was able to calculate the maximum allowed Rds(on) of the MOSFET to be selected. I then went on to select the right MOSFET i.e. IRF1010Z.

Now, when I went to look the output characteristics of this MOSFET in order to find the right gate voltage to apply to, so that Vds is low and that the MOSFET is able to conduct a maximum of 5A. However, the output characteristics of the device are given on a log-log scale that I don't seem to understand. The graph doesn't exist for low current values of (0-5A), which is the range I want to work on. So please help me understand the output characteristics of this MOSFET device. Here are the characteristics,

Maybe, a Vgs of 5-6 V will be fine, but what confuses me is the nonexistence of the graph for low current values.


texts: Why the conversion to intermediate frequency?

texts:
While studying about various communication systems (superheterodyne receivers and television receivers, to name a few) I often come across blocks that convert RF signals to intermediate frequency (IF) signals.
Why is this conversion needed? Can't the RF signals be processed directly without converting them to IF signals?
I referred this question, but its answer didn't explain about the need for IF conversion.


texts: Is there any relation between Watt and Decibel

texts:
I really don't know much about radio signals.

But I want to know that is there any mathematical relation between antenna dB and the output of an RF circuit (I have heard they say this circuit is 200mW for example)?

I want to improve the range of an RF circuit. but I don't know whether it is possible to do it by a different antenna (with higher dB) or I have to make the output of my signal more strength?


texts:
From the manual for a Repeater unit (page 10 in pdf document).

Transmit LIU Waveshape (Build-out)
S2-4: ON          S2-5: ON        S2-6: OFF      75 S ohms w/ High Return Loss
S2-4: OFF         S2-5: ON        S2-6: OFF      125 S ohms w/ High Return Loss

Here is the link to the manual in PDF format


texts: Current limiting range on LM723 (from 0 to 5A)

texts:
I am building a power supply with LM723 and my intention is to have 0-30V and a range of 0-5A variable. I am regulating voltage normally, however for current limiting, if I want to regulate small current amounts like 10mA, 100mA I need a shunt resistor with high value, which is not viable for 5A, since with LM723 I need a 0.67V voltage drop to limit current.
Currently I am simulating my design with three parallel 0.33 Ohm shunt resistors, which will give me approx. 600mV voltage drop. That works for 5A, but nothing lower. When I calculate the resistor needed for a low current scenario, the value is too high to withstand the 5A.
I tried using a non-inverting amplifier to sense the difference and increase the voltage output, but the difference between R1 and R2 on the amp-op won't work well.
Any suggestions on how to do this? Is amplifying the voltage drop to input it on the LM723 even a good idea?
Thanks.


texts: How to convert mm to xy coordiantes in pcb xy files

texts:
i have few pcb gerber projects which come along xy files in txt/xlsx format , these xy files have x y values in mm/inches/mils for every element on the board.
am developing gerber editor for gerber files which will search for elements on that baord.

what i have done.

-> Gerber layer files are loaded by user

-> Gerber layer files are rendered to 600 DPI image.

-> User load xy file like: ::

  http://pastebin.com/nLpDBbES    or      http://pastebin.com/XMXS0gxg

-> then with Jquery user can goto any xy coordinates on that image.

so problem is am unable to convert correctly these xy values which are in mm/mils format to xy coordinates for windows web browsers

although for one project which have xy file : http://pastebin.com/nLpDBbES   i setuped some alogo to convert is xy value from mm to coordinates worked however its not working on other projects, so what i did is take mm x y values and multiply 12 with it and then would just flip value because xy coordinate system in web browsers would start from top left corner however in real life positive xy occur in first Quadrant which will be left bottom corner.   ... the project final rendering dimension was 1350x1107  : http://i.imgur.com/L8c9XLQ.png

so any PCB industry expert have worked with it , help will be appreciated .

thanks


texts: why three phase induction motor draws current with spike at low frequency by using VFD?

texts:
I have built Variable frequency drive (VFD) for a three-phase induction motor using V/F constant control. while I was testing 15HP three-phase induction motor without load with my VFD, the motor draws current with a spike at low frequency. Low frequency means (10 to 20 HZ), and the current value is about to 1A to 3A.  This only happens when I start the motor from 0 HZ to 20 Hz. when the motor reaches to above 20 HZ, the current value becomes low (1A) and smooth.
My question is to you what will be the factor that draws the current with variation at low speed or at low frequency. ? what should I have to notice?
is there any winding arrange of the three-phase induction motor for starting torque that is drawing current more also at low frequency?
or I should not run motor below 20HZ?


texts: Shorted antenna DC-blocking capacitor value

texts:
I have an antenna that contains a DC short to ground ( a PIFA antenna at 1575 MHz in this case ). However, my device cannot tolerate a DC short to ground, so I need to include a blocking capacitor in series with the antenna.

How can I find the value of the DC blocking capacitor of a shorted-to-ground antenna?


texts: Tektronix TDS3000 series max trigger rate

texts:
So I am making a testing stand for some equipment and I am using an old TDS3034C Tektronix scope for most of my measuring purposes. I've connected it to the computer via Ethernet and using PyVisa to connect to it and acquire all the data I need automatically. However, I've ran into a problem.

Say, I need to calibrate one of the electronic subsystems. So, I connect a signal generator with variable amplitude both to the system's input and to the oscilloscope to trigger it and the system's output to a separate oscilloscope channel. Then I set the TDS3034C into average measuring mode (since it transfers the measured data to the computer very slowly) and start the test.

If the signal generator's period is smaller than about 50ms, then oscilloscope seems to lose events. I make 100 impulses on the signal generator, while the scope registers anywhere from 20 to 99 triggered events depending on the generator period (from 1ms to 50ms, that's from 1000Hz to 200Hz), and only occasionally all 100.

What could be the problem here and how do I combat it? How do I set the optimal generator frequency/period? What is the tds3034C max trigger rate? I couldn't find it anywhere in the oscilloscope manual. Both it's analog bandwidth and ADC frequency should be more than enough (I do understand that these characteristics have nothing to do with the oscilloscope max trigger rate, but still)

The problem seems to occur regardless of the TDS3034C connection to the computer.

Edit: During the trigger I acquire 500 points, that's the "fast" mode. The horizontal scaling is 10ns, trigger is placed at 50% on the horizontal scale (50% pre-trigger). The whole horizontal scale is 10 divisions * 10 ns / division = 100ns. So, nor the trigger delay, nor the number of points acquired make an impact. If I change the horizontal scaling to 100ns/div, the situation is obviously worsen, but not drastically.


texts:
I am trying to make a good layout for the LAN9252 mac and STM32F7 controller, running at 80 MHz and I had to route data tracks with different lengths.

The question is should I use nets lengths matching tool in QSPI at 80 MHz?


texts: Variable output PSU switch configuration

texts:
So I am designing a switchable voltage 9V/18V power supply and was wondering, what's the best way to switch between outputs, that's the current schematic I came up with:

Original image size

So my question is, will this work and is this the best way or is there a better one?


texts:
I made a circuit that modifies a signal so it can be safely read by an ADC.
I'm using an op amp to shift the signal +2.5V so I can measure AC. When I do this shift another signal appears. About 40mV amplitude, 8kHz freq. But only if the op amp is TL074 or TL084. If using LM324 I don't get that. I also don't get that signal if I'm not using the +2.5V offset.

What could be causing that?

Link to schematic


texts: Why should we not change inputs to a sequential circuit (Moore machine) at the clock edge?

texts:
The code included here takes a bit stream of binary digits, Least Significant Bit (LSB) first, and outputs the two's complement of the complete stream, also LSB first. A Moore State diagram is attached.
Now when I try to test the code in a testbench, the states don't get updated as intended.
The FSM:

The design:
module seqDetector( input in,
                input clk,
                input rst,
                output reg out);

//Moore Machine

parameter   SX = 3'd4,
            S0 = 3'd0,
            S1 = 3'd1,
            S2 = 3'd2,
            S3 = 3'd3;

reg [2:0] cur_state,next_state;

//next state assignment
always @(posedge clk,negedge rst) begin
    if( rst == 1'b0)
        cur_state <= SX;
    else
        cur_state <= next_state;
end

//next state calculation
always @(cur_state,in) begin
    case(cur_state)
        SX: if(in == 1'b0) next_state = S0; else next_state = S1;
        S0: if(in == 1'b0) next_state = S0; else next_state = S1;
        S1: if(in == 1'b0) next_state = S3; else next_state = S2;
        S2: if(in == 1'b0) next_state = S3; else next_state = S2;
        S3: if(in == 1'b0) next_state = S3; else next_state = S2;
    endcase
end

//output calculation
always @(cur_state) begin
    case(cur_state)
        SX: out = 1'bx;
        S0: out = 1'b0;
        S1: out = 1'b1;
        S2: out = 1'b0;
        S3: out = 1'b1;
    endcase
end

endmodule

The testbench:
`timescale 1ns/1ns
module tb();
initial begin
    $dumpfile("2's.vcd");
    $dumpvars(0,tb);
end

reg clk;
reg in;
reg rst;
wire out;

initial begin
    clk = 1'b1;
    forever #5 clk = ~clk;
end

seqDetector s0(in,clk,rst,out);

initial begin
    fork
    #0 rst = 1'b1;
    #10 rst =  1'b0;
    #20 rst = 1'b1;
    #10  in = 1'b0;
    #20  in = 1'b1;
    #30  in = 1'b0;
    #40  in = 1'b1;
    #50  in = 1'b1;
    #60  in = 1'b0;
    #70  in = 1'b0;
    #80  in = 1'b1;
    #90  in = 1'b1;
    #100 in = 1'b1;
    #110 in = 1'bx;
    #120 $finish;
    join
end
endmodule

The problem is portrayed in the following graph:

But when we change the testbench such that the inputs are delayed by 1 ns past
the clock edge, the existing  problem is solved and functionality is
achieved. But there are a few glitches the origin of which I am unable
to figure out, as shown here:

seqDetector s0(in,clk,rst,out);

initial begin
    fork
    #0 rst = 1'b1;
    #10 rst =  1'b0;
    #20 rst = 1'b1;
    #11  in = 1'b0;
    #21  in = 1'b1;
    #31  in = 1'b0;
    #41  in = 1'b1;
    #51  in = 1'b1;
    #61  in = 1'b0;
    #71  in = 1'b0;
    #81  in = 1'b1;
    #91  in = 1'b1;
    #101 in = 1'b1;
    #111 in = 1'bx;
    #120 $finish;
    join
end

So the first question is: why is there a problem when I change input at the edge of clock, from the perspective of writing a Verilog code?
And the second question is: what is the cause of the glitches in the next_state variable?


texts: Can I use a crystal with smaller PPM value?

texts: The manufacturer recommends that I use a crystal with a tolerance of +-100ppm. Can I use a crystal with +-20ppm for better accuracy?


texts: Arduino to Android serial communication issue

texts:
I've been trying to use this  serial for android library now, but I can't make it work. I'm trying to run this little program in android:

    // MouseLib.ino
    #include "tracker.h"

    PositionTracker tracker(6,5);
    void setup() {
        Serial.begin(115200);
        tracker.init();
    }

    void loop() {
        Serial.println("?");
        delay(20);
    }

Where the tracker is as follows:

    #include "Arduino.h"
    #include "ps2.h"
    #include "tracker.h"

    PositionTracker::PositionTracker(int _clkPin, int _dPin){
        // x = y = ldX = ldY = lX = lY = 0;
        clkPin = _clkPin;
        dPin = _dPin;
        sensor = new PS2(_clkPin, _dPin);
    }

    void PositionTracker::init(){
        sensor->write(0xff);  // reset
        sensor->read();  // ack byte
        sensor->read();  // blank */
        sensor->read();  // blank */
        sensor->write(0xf0);  // remote mode
        sensor->read();  // ack
        delayMicroseconds(100);
    }

The code works fine when I plug Arduino to pc, but when i plug it in an Android device it just doesn't work. If I comment the "tracker.init()" line, it works fine for Android. If I use the example from ps2 library, it works fine as well.
Oh, and I'm using the sample app for the serial library on a Moto G. Any ideas?

Links for the libraries:

USB Serial for Android: https://code.google.com/p/usb-serial-for-android/
ps2.h(mouse communication): http://playground.arduino.cc/ComponentLib/Ps2mouse

EDIT

Right after posting this, I've found the issue: I was looking at the wrong website for the library. The answer was posted on their wiki already.

From the library's wiki (can't post the link, as I'm low on reputation):

  Some Arduinos use the DTR line to determine serial channel readiness. In your Android code, call setDTR(true);


texts:
Usually we are not able to see infrared rays with our naked eyes.
But we could see it when we watch it through a digital camera (or mobile camera).
Why it happens?


texts:
I was given this problem in a problem set. I want to ask what will the voltage at Base when \$ \beta \rightarrow \infty\$.

My answer to the problem - When \$ \beta \rightarrow \infty\$ then width of base would be negligible then collector and emiiter would be nearly short. Also, as \$ I_B\$ would be zero, we can remove the wire EI. So the voltages of collector, emitter and base would be same.

I just want to confirm is my answer right.


texts: Which informations do I need to calculate the efficiency and horsepower of a 3 phase induction motor?

texts:
As far as I know the magnetic force is responsible for the motor rotation. So, horsepower of the motor is mostly related to magnetic flux on the coils (windings). Also magnetic flux is directly related to inductance (Number of turns) and the current flow on the coil. Am I right so far?

This is a simple illustration of a 3 phase induction motor:

In the center of the stator, there is the rotator (not shown in the picture). And here is the equivalent circuit of the induction motor:

And here are the things that I do not understand:

1- What is magnetizing reactance of the winding? I've read a few explanations about it but really I could not understand. Isn't it normal for reactance to have magnetic property? Could you explain me this property in detail?

  XM is the magnetizing reactance of the winding.

2- Why do we want high power factor?

Should not we want just the opposite? Because we only care about the current flow on the windings? Power factor of an inductor is related to serial resistance and inductance value of its equivalent circuit. If we draw the same amount of current on two inductor which have different serial resistor values, the one with the lower power factor will consume less energy but the amount of the magnetic flux will be same. Right?

For example, this inductor has 1 mohm serial resistor an it consumes avaragely 13.874uW.

this one has 500 ohm serial resistor as you will see current and the voltage are synchronous:

But this consumes 6.1361W! And they are doing the same job?!

So, does power factor mean something else for motors, or did I understand the concept wrong here?

3- How can I calculate the horsepower and the efficiency of my motor?

I designed a 3 phase motor driver which drives 3 coils (100 mOhm series resistance and 2 mH inductance).

And this is the timing, current waveform of the coils and the total power consumption of the system(with all the other logic and analog circuits):

avarage power consumption is 145.33 W. Coil currents are distorted as you can see but RMS current is 4.88 A for each:

I saw this online electric motor calculator. It requires Current(A), efficiency(%), Power factor(0-1) and Voltage(V) to calculate the horsepower. But I don't know what are meant by those. Which current? Efficiency of what? Power factor of what? Is it supply voltage? I am really messed up here. I appreciate any help. Thanks.


texts:
I'm planning to use TUHS3F05 for my ESP32 project. I'm very space limited so I need to optimize place as much as possible.

In datasheet it is recommended that TUHS* it should be used with other components yet in my testing it worked great without them (I was testing for over 10 days without any issues).

My questions are:

can there be any shot or long term problems of using my schematics?
why they need so many external components?
are there any other so small factor AC-DC solutions?

This is recommended TUHS* schematics:

This is my schematics:


texts: How to interpret negative voltage in this schematic?

texts:
I got the following schematic from a book. This schematic was shown during a discussion about loads in voltage divider which require negative voltage.

Questions:

The voltage value -25V at the bottom, what does it refer to? This can't be the electric potential near the negative terminal, because that's supposed to be 0V, right?
The 0V ground at the right side, does it refer to the voltage source's negative terminal?

Thanks!


texts:
I have an "ultra-low-power" MCU STM32L011F4. According to the specs its powering voltage range is from 1.65 V to 3.6 V. I want to power it with a LiPo battery with nominal voltage of 3.7 V. Which is slightly larger.
But according to the table of absolute maximum ratings from the datasheet its maximal value of VDD–VSS is 4.0 V.

How bad would it be to power the MCU directly from the battery? Should I put a diode to drop the voltage a bit?
Or would it be beneficial to use a proper voltage regulator?


texts:
Show that for a transistor with α close to unity, if α changes by a small per-unit amount (Δα / α), the corresponding per-unit change in β is given approximately by
$$\frac{\Delta\beta}{\beta}\approx\beta\left(\frac{\Delta\alpha}{\alpha}\right)$$

I know the equations:
$$\alpha=\frac{\beta}{1+\beta} \textrm{ and } \beta=\frac{\alpha}{1-\alpha}$$
But am unsure what Δα / α really means. I tried assuming that it was a linear approximation, but after lengthy scribbling, that led me nowhere:
$$\alpha'=\alpha\left(1+\frac{\Delta\alpha}{\alpha}\right)$$


texts: Does a voltage source/diode in a circuit act as an open or a short circuit?

texts:
This question originates from a diode question in which we modelled diodes using the simple piece-wise linear model. According to the lecture notes, the diode acts as a battery after attaining Vf(forward bias voltage). This creates a seemingly paradoxical relation.

becomes

In the battery-equivalent circuit above, quick circuit analysis shows that if unknown= unknown1 = 6V, there should be 4A flowing upwards from the 5V source. However this is impossible in the diode circuit since no current can flow through the diode from - to +(In the model that we are using at least).

So this creates a very confusing situation, is there actually current flowing through the diode or not? If so, how can this be explained?

EDIT: So I understand that I made a wrong assumption which led to the inconsistency. However, a new question arises, if I had unknown = 10V, that reaches the minimum requirement to activate the diode, but KCL shows that no current flows through the diode. I'd like to know why this is? More specifically in terms of intuition, what makes the resistor path more prefered for the current to travel through?


texts:
If two independent noise sources are added together, their noise adds up like so:

$$RMS_{sum} = \sqrt{RMS_1^2 + RMS_2^2}$$

Am I correct to assume that this only holds if the noise sources are independent?

simulate this circuit – Schematic created using CircuitLab

For example in this circuit (assume that R1 is the only noise source), the noise is buffered by OA1 and then inverted by OA2. The resistors R5 and R6 sum the two signals together. In this case, the noise of R1 should not appear at the output, correct?

That is, I cannot calculate the noise of the output of the two op amps independently and then add them up with \$RMS_{out} = \sqrt{RMS_{OA1}^2 + RMS_{OA2}^2}\$.


texts: Clock : CPU clock vs Pipeline Clock Vs Memory Access Clock

texts:
A few days ago, I implemented a multi-cycle unpipelined soft-core on a FPGA. It worked like a charm. The FSM beautifully orchestrated FETCH->DECODE->OPER1->OPER2->OPER3->ALU->MEMORY->REG WB->PC UPDATE->FETCH->DECODE->......

I now wish to transform it into a pipelined cpu.

While am aware of the principles such as splitting up the data path into smaller stages and littering it with pipeline latches, the timing topics have caught me off-guard, especially those concerning load/store instructions.

The MEMORY stage is clearly the slowest stage. If it takes 100 ns to complete either Read/Write, I will simply ensure every other stage takes 100 ns to complete (although they could complete much faster) to balance the pipeline.

And now the question.

Will I be right in simply ticking each stage at 10 MHz including the Memory Stage AND ticking the memory interface (Memory controller and SRAM) at 50 Mhz? The 50Mhz ensures that the MEMORY stage is able to finish its activities before the next 10 Mhz stage tick arrives.

The memory interface (controller) resides inside the CPU. So the CPU must receive 50 Mhz as input further scaled down internally to 10Mhz for clocking the stages. And of course, the 50Mhz goes to the memory controller.

In this case, what should I document as the CPU clock? 10 Mhz or 50 Mhz? I do understand that the throughput and overall pipeline latency have 10 Mhz as the base, but the input clock to the CPU as seen by the user is 50 Mhz!!


texts: Is Power Factor Correction required in China?  I am designing a high power, >3kW power supply and need to know to what power factor it needs to meet.


texts: What is "average recieved signal power over bandwidth"?

texts:
I came across to Shannon’s formula for calculating channel capacity and I don’t quite understand why we calculate average signal power… “over bandwidth”. Why over that "domain of interest"?

Here is my interpretation why but I’m not sure if I understood it right.

Imagine we are sending some signal f(t) from point A to point B. We take FT (Fourier transform) of signal f(t) at point A, and we get ourselves all the sinusoid components of that signal. For every component of that signal in frequency domain we have particular value of amplitude. Now, I’m not sure if this can be done but here is my interpretation of “power over bandwidth”: “Inside frequency domain” we calculate avg. power of signal in such fashion that we calculate power of every component of signal and by doing some manipulations with all those calculated “powers” (sum of them equals power of signal in time domain?) we can calculate average power of the signal in frequency domain.

So we have avg. power of “clear/undistorted signal” of value for example 40[W] “over bandwidth” that interest us (bandwidth of our signal).

Signal traveling from point A to receiver side B gets distorted. At point B we take FT of that distorted signal. Now, maybe we have some components of signal that are added within our signal, so all those components represent “noise signal”. We “separate” noise components and our signal components (in our head). Since signal is distorted maybe some of the amplitudes of signal’s components are now changed, so we again calculate (in a same fashion as one above) average power of that components and get… maybe some different average power which for example might be less than one at point A.

So, based on this interpretation do we by that mean average signal power “over bandwidth” (“over bandwidth of something that interests us, over our signal bandwidth to see if something has changed”)?


texts:
Following on from my last question Cascaded BJT Amplifier Load - I'm trying to understand what it is (via math or otherwise) that causes the input signal to appear malformed when the output of the signal starts 'clipping'
Looking at my circuit:

Am I right in saying that for the output at the collector (V(n002)):

The clipping at the high end is because it cannot swing above Vcc?
the clipping at the low end is because the voltage at the collector (V(n002)) cannot go below the voltage at the transistors emitter (3.18V)?

Then my main question is - Why is it that the limits of the biasing/BJT cause a change to the input signal when measured at the base of the BJT (V(n005)?
Many Thanks


texts: Is it possible that I fried an MCU pin by performing a continuity test

texts:
I have a microcontroller (dsPIC33EP64GS506, 64-pin, TQFP, link to its datasheet), which doesn't seem to work on 2 GPIO pins (pins 4:RC0 and 11:RC11), whereas all other pins are functional. The problem with these two pins is that they are directly connected to GND, even when the MCU is not powered. I tested all neighboring pins with continuity check to check for possible short circuits (bridges between pins), using a Fluke 179 multimeter. None of the neighboring pins are short-circuited.

Now, MCU pins are 3.3 V tolerant, and some of them are 5 V tolerant. In the multimeter's User manual, it says that the open circuit test voltage is <8.0 V DC, and the short circuit current is <1.1 mA. Is it possible that I fried the two MCU pins using this continuity test? I have two equal boards, the other one seems to work just fine.

Is it possible that I fried these pins while soldering? I've soldered the MCU on 300 °C with a 2.2 mm tip.

I found the error. It was due to the bad PCB manufacturing - via is connected to the ground plane, and it shouldn't be. See attached image. I've fixed this by cutting the ground plane around the problematic via.


texts: One Digital Logic Question in Previous Exam?

texts:
I Prepare for Entrance Exam on PhD, CS Filed. I ran into a previous question with following options (A to D from one to forth lines):

The question is:

if the input is always has valid values (no invalid inputs),  the the second line is True, How Can help me how this will be reached ?!


texts:
I have an automotive application where I would need a 12V relay/circuit that can be toggled with single button between on/off. But it should reset itself back to when input voltage drops to zero.

I found this: https://www.the12volt.com/installbay/uploads/E33_Latching_Relay_2.gif
but it seems to require two buttons.

Edit: I am controlling 12V 6A max.

Edit 2: I found promising looking one button two relay circuit: http://www.homofaciens.de/technics-base-circuits-relay_en.htm and there figures 32-41. Any comments on that?


texts: Why is my red LED dimmer without a resistor than with a 100 Ohm resistor?

texts:
Complete newb here; sorry this may be a basic question but trying to learn.  I made a simple circuit with nothing except an Arduino power source a 100 Ohm resistor in series with a 10mm red LED.  Weirdly it gets dimmer if I remove the resistor and my question is why is that occurring?  I thought reducing resistors would brighten the LED.  The datasheet is attached.  The max current is 80mA and the LED worked fine after and this phenomena is repeatable so I don't think I burned the LED out.  This phenomena doesn't happen if the power source is 3.3V in which case I don't notice much brightness difference between the two.  This phenomena also doesn't occur with a same sized blue LED by the same manufacturer.  FYI, there's no code, I am running the power direct from the Arduino Uno's 5V and 3.3V pin and gnd pin.  I read the Sparkfun tutorial on resistors and am confused.
https://www.sparkfun.com/products/8862

simulate this circuit – Schematic created using CircuitLab


texts: European Cooktop for use in US split phase

texts:
I was wondering if someone could give me some advice. I'm an architect so I only know so much about electrical engineering.

I have this cooktop I ordered from Italy, it's an induction cooktop that's from Elica. This cooktop supports 220v-240v ~ 50Hz/60Hz, 380v-415 ~ 2N ~ 50Hz/60Hz, and 380v-415v ~ 3N ~ 50Hz/60Hz. See below the diagrams of how the instructions show how I should wire it.
enter image description here

I have a typical 200amp split phase service. Since I don't have a single-phase 240v I am not sure how I should wire the cooktop? Should I attach one 120v wire to "#3" on the diagram and then bridge "#3" to "#2", then wire the other 120v wire on "#1"? Also, should I install the neutral wire on "N"?

If someone could help me with this, I would greatly appreciate it!!


texts: How to distinguish between a read and a write in a Harmony USART BufferEventHandler?

texts:
I would like to use the Harmony USART driver on a PIC32MX695F512H using interrupts and with buffer support. After setting the appropriate settings in the MPLAB Harmony Configurator, the system has generated the ISR for me (system_interrupt.c):

void __ISR(_UART_2_VECTOR, ipl1AUTO) _IntHandlerDrvUsartInstance0(void) {
    DRV_USART_TasksTransmit(sysObj.drvUsart0);
    DRV_USART_TasksReceive(sysObj.drvUsart0);
    DRV_USART_TasksError(sysObj.drvUsart0);
}

Since this is a generated file, I assume I'm not supposed to edit it. But if this is the ISR, how can I make sure my code will be executed on an RX interrupt. I want to receive the received data in a function that I am supposed to edit.

As I understand it, that is what the buffer event handler is for. So I can do the following (this code is highly simplified):

void APP_BufferEventHandler(DRV_USART_BUFFER_EVENT bufferEvent,
        DRV_USART_BUFFER_HANDLE bufferHandle, uintptr_t context) {
    switch (bufferEvent) {
        case DRV_USART_BUFFER_EVENT_COMPLETE:
            // @todo
            break;
        case DRV_USART_BUFFER_EVENT_ERROR:
            appData.state = APP_ERROR;
            break;
        case DRV_USART_BUFFER_EVENT_ABORT:
            appData.state = APP_ERROR;
            break;
    }
}

//... in APP_Tasks somewhere:

    appData.usartHandle = DRV_USART_Open(DRV_USART_INDEX_0,
            DRV_IO_INTENT_READWRITE | DRV_IO_INTENT_NONBLOCKING);
    DRV_USART_BufferEventHandlerSet(appData.usartHandle,
            APP_BufferEventHandler, 0);

My questions are:

Is this actually the right way to make sure APP_BufferEventHandler is called on an RX interrupt?
How can I distinguish between an RX and a TX event in the event handler, if the event is one of COMPLETE, ERROR and ABORT?


texts: Why are there high frequency components from an LC oscillator

texts:
I simulated an LC colpit oscillator. In time domain it oscillates no problem. When i check fft, it looks like this

where are the high-frequency parts coming from?


texts:
I have an old PS-303D from Conrad in use at home. Recently it showed a problem.

If I measure with my multi from V- to V+, the voltage reading is correct, current and voltage regulation seems to work fine. But when I connect V- with GND the supply turns off. Connecting V+ with GND is no problem. So I opened the case and did a little check ups. Soldering looks so far ok, and no visible damage has occurred. The GND is only connected to the case and via 2 ceramic capacitors to V+ and V- which seem ok. I looked at the schematic and I understand what each section is doing, but after a day of measuring I can't seem to find the error.

Can anyone point me to the right direction on how to approach the problem? Help would be greatly appreciated.

Schematic:


texts: How to protect mcu pins from reverse voltage [edited]?

texts:
I am asked to build a 5 V /24 V circuit interface using an ATMEGA328P.For that i built a little comparator circuit to get  a 5 volt level on a I/O pin  .
My problem is that   the output of the comparator can be high while the I/O pin can be configured as a 5 volt output .
  I thought a little then decided to add a 4.8 zener diode as below.[Edited]

Is this circuit safe to use?


texts:
i am trying to control bldc motor (sinusoidal commutation). I am somewhat controlling bldc motor, by applying sinusoidal voltage with 120 phase shifted to the phases.

Now my issues is i cant able to vary the speed, i runs at the max speed.

At a maximum speed, For 120 phase shifted it sucks around 2 amp but for 130 phase shift it sucks only 1 amp. Why so?
Then bu noticing the phase to phase waveform, the output phase to phase is not good. But phase to gnd is probably good.

Here are the waveforms....

Phase 130 degree shifted

Phase 120 shifted

phase to phase

Phase to gnd

Why phase to phase is looking so horrible i don't know. Guide me frds where i am wrong.....


texts: RS485: What is the difference between RO and D_OUT?

texts:
I have an RS485 transceiver (datasheet here). Page 8 explains the various pins. I do not appreciate why there are two output pins, namely D_OUT (pin A1) and RO (pin A6).

The first is a "General Purpose Logic Output", the second is the "Receiver Output".

Why are there two different outputs, and what are they respective roles?


texts: Choosing a Switchmode Converter for a Battery Powered Project

texts:
I'm currently designing a battery powered, 2xAA in this case, project. The problem that I have is very simple, I want to power a DS1307 (the only part in my circuit which requires 5V). I've looked into similar parts like the DS1337 and the MCP7940, which operate under 3V, but they don't have a battery backup pin like the DS1307, which is something I want.

So, the first thing that I thought was to build a step-up DC/DC converter circuit to power the RTC (that's the first thing I thought, so I'm open for suggestions). Since I never used a switchmode converter before I decided to watch Dave's video about the MC34063, but the problem with it is that its minimum input voltage is 3V. So I would like to know some tips on how to choose a suitable switchmode converter for this kind of project.


texts: Unnecessary pull down resistors on BJT and FET transistors?

texts:
I commonly see weak pull down resistors at the base of NPN transistors.  Many electronic sites even recommend doing such things, usually specifying the value as something like 10x the base current limiting resistor.

Bipolar transistors are current driven, so if the base is left floating, I see no need to pull it to ground.

Also, I commonly see gate current limiting resistors on FETs.

They are voltage driven and there is no need to limit current feeding the gate.

Are these two situations examples of people confusing the rules between transistors (which need base limiting resistors) and FETs (which need pull down resistors) or combining the rules or something...

or am I missing something here?


texts: Is there a difference between using a built in SPI module and bit-banging?

texts: Is there a difference between the two, or is it just a matter of abstraction? My intuition says there's no difference but I'd love to be wrong.


texts: Thyristor Voltage Waveform in a Full Wave Bridge Controlled Rectifier at Discontinuous Mode

texts:
I'm having some trouble to understand the thyristor voltage waveform for the full wave bridge controlled rectifier. I plotted the Voltage at the secondary, the current at the load, the voltage at the load and the voltage at the thyristor T1.

When the current at the load drops to zero, there's no voltage drop at the load. So why the voltage at the thyristor 1 (T1) is half the source voltage before the thyristor T2 and T3 are fired (red circles)?


texts: Generating a sine wave from a square wave, for a large frequency range

texts:
I have a PWM output from a micro controller.  I want to turn this into a sine wave.

The typical way to do this is a low pass filter.  Unfortunately, I want to change the PWM frequency, and the corresponding sine wave frequency, over more than a couple decades (say, 10Hz to 100kHz).  Are there any simple ways to do this?


texts: What's google's balloon estimated LTE radiated power at ground ?

texts:
Google loon, google's internet balloon project , is transmitting from a height of 20km , and has a cell radius of 40km, and uses LTE.

What would be the EIRP ? would be one such that EIRP at near ground level just below the satellite is equal the EIRP of regular LTE ? Or some other regulation ?


texts: What is the function of multiplexer boolean expression?

texts:
Here is the image of multiplexer:

May I know, what is the output form of Boolean expression, how it is working function?

Can anyone help me to guide me?

Any help would be highly appreciated,


texts: Diode circuit analysis using ideal diodes exam problem

texts:
I've been reviewing some past exam and stumbled across this question

So I need to find the current I through the middle diode and the voltage across the bottom left 10KΩ resistor.

To try solve this problem i used the technique, "assumed states for analysis of ideal switch model diode circuits" (not sure if thats the actual name of the technique).

So for my first state, i assumed that both D1 and D2 are on

Since the current are not negative for both diodes, the assumption for both diodes being on must be correct. Thus the required current across the diode is:

(15V - 11.25V)/10KΩ = 0.000375A

However upon looking the answers, it says that the current across the diode is 0A. This means that the diode is actually "off" (while the other diode is on), and thus my analysis is wrong.

Is there a problem with my reasoning or am i missing something crucial?

Thank you for your time!


texts: Isolating two op amp amplifiers from each other

texts:
My circuit consists of two oscillators: one VCO in audio range and an LFO (low frequency oscillator - below the audio range). The signals from the two oscillators are amplified with two non-inverting op amp amplifiers. The two amps (LM358) share the same split voltage supply/virtual ground source. Because of that the LFO effects the frequency of the VCO. The two oscillators should be entirely independent. How can I avoid the two oscillators effecting each other?

simulate this circuit – Schematic created using CircuitLab


texts:
Somewhere I've read:

  Current (I) is given by 1 Coulomb per second. One ampere of
  current is a flow rate of 6,250,000,000,000,000,000 electrons passing a given point per
  second.

If it is correct then my question is what is this given point? Like point A to point B?
Just saying, 1Amp = 1 Coulomb per second isn't making any sense to me.


texts: In an AC supply why does two single phase 110V wires connected to hot and neutral produces 220V

texts:
I have seen people connect 110V to the hot end and 110V to the neutral end of the socket to give a 220V to appliances like refrigerators.
My understanding is that current flows, whenever there is a voltage difference between wires like a 110V hot wire and 0V neutral wire, giving 110V supply to a device.

But how is it possible where two 110V wires are supplying being at the same voltage able to run a device?

Also, how does 110V + 110V produce 220V mathematically?


texts: Reading a 5 Band resistor with Gold as a middle band?

texts: Can anyone read the resistor that the arrow is pointing to?  From what I know you can not have a gold band as a number and if I am reading it correctly it has a tolerance of 0 which does not seem right.


texts:
Is there anything special (like set fuses or register values) I have to do to be able to the following pins as digital IO on the ATTiny84?

PA0 to PA3
PA7
PB2

I thought I could use the RESET pin but after reading the datasheet I found out I couldn't, so I'm trying to avoid any other gotchas that I might have missed in the datasheet. Thanks!


texts: How might you use a LiPo battery as backup for mains power loss?

texts:
Many people seem to run their projects off the mains (e.g. with a wall wart) or from a battery, but there doesn't seem to be too much discussion about how to run a device off the mains, charging a battery, but then switching over to the battery in the event of a power outage.

I imagine that with NiCD/NiMH batteries you could just hook them up in parallel with the power supply (more or less), however since LiPo batteries hold more power for their size I would like to use them instead in a project like this - but they don't seem quite so simple to use in this way!

Can anyone offer some pointers as to how LiPo batteries might be used for backup power?  I imagine you would need some logic to power a charger and switch over to the batteries when the mains disappears, but I'm not sure how this might work.  I imagine you'd also need a large capacitor to avoid a momentary dropout during the switch over as well.  Or perhaps there's some cheap IC that can do all this for me?

Thanks for any suggestions!


texts: Why does music synthesizer built from chain of astable multivibrator circuits get "out-of-tune" after a few hours?

texts:
I built a prototype keyboard/sound synthesizer using a chain of 13 astable multivibrator circuits whose outputs are connected to an audio amplifier chip (LM386) and speaker, all powered off a 9V DC battery.

Each individual circuit gets tuned to one of the 13 frequencies in a musical octave (C5, C#, D, etc. up to C6) by varying a fine-tune trimpot that is in series with specific resistor values and which get the oscillation into the ballpark frequency.

The oscillation is the classic BJT astable multivibrator you can see in Figure 1 here and which is explained in this article.

The prototype stays correctly in tune for a short period (up to a day).

You can hear what it sounds like here. (Safe to start at 0:49s -- Wadsworth's constant ;) )

What I can't figure out is why the circuit appears to get spontaneously detuned, i.e. one or more of the individual circuits end up with frequencies that are different from what they were tuned to (checked against an o'scope and a reference piano).

The frequency deviation of the detuning is typically 2-5%, which is audibly noticeable (e.g. C5 at 523Hz might wander to 540Hz or 510Hz).  Interestingly, the detuning never occurs while playing.  But several hours afterwards, the keys no longer sound the same.

I had originally thought maybe the trimmer pots were mechanically relaxing by themselves.  To eliminate this I replaced the trimmer pots to try to "lock in" the specific frequencies based on resistor values alone so that no variability was left in the design.

But the de-tuning problem persists even after replacing the trimpots with fixed resistor values.

Before: 13-key analog synthesizer with fixed resistor values

Resolution: Thanks all for the useful feedback, digital design ideas, and historical context to better understand the challenges of a pure analog design.  All the answers were excellent.  I've accepted ToddWilcox's answer as I get from it that (a) detuning is an expected part of pure analog designs, (b) the artistry lies in how to establish a slick way of tuning the instrument quickly.

To solve the immediate problem, I've put trimmer pots (1-2K ohms) back in the design to give 2-5% tuneability to each key.  It takes a couple of minutes at the start of playing to tune up the 13 oscillators, after which they stay in tune for several hours at a time. See new image below.

Will post the results of the experiments using wall-wart, fresh batteries.  The digital designs (using digital divider and/or 555 timer chips) are interesting, and would potentially compress the size significantly.  Future updates can be found at the project page here.

After: 13-key analog synthesizer with trimmer pots (1-2k ohm) for tune-ability


texts: Over voltage, over current and surge testing

texts: I used a TI reference designto prototype a 120VAC to 5VDC 2A power supply on a PCB and it's been working fine for a couple of months. I want to run some basic tests to see if the PCB is safe under over voltage and over current scenarios. Is there a cheap way to go about doing that? I came across Hipot testers, but they were pretty expensive.


texts: Comparing accelerated ageing with "real" ageing

texts:
In the electronics industry (and many others fields, but I'm interested in electronics here), it is common to submit electronic components and boards to accelerated ageing processes. The aim is to detect early-life failures and avoid putting the concerned product on the market in order to improve overall reliability. And also, it can be used to assess long-term reliability of the product.

My question is : on which scientific basis can we affirm that accelerated ageing is "similar" or "comparable" to "real" ageing ?
How is an electronic board that spent 100 hours in an oven at 90°C "similarly aged" than the same board that spent 10 years under operation ?


texts: Can I use a different voltage / amp to what the device is rated?

texts:
Please bear with me as my knowledge on electrical is very limited.

Background

Question relates to a driving simulator product = Thrustmaster T500
Product uses a 24v / 6.67a 4 pin power supply (factory supplied)

Context

I intend to purchase one but it does not come with a power supply
I can source one on Amazon / Ebay but it is extremely expensive ($100AUD)
The product will be used in Australia.
There is someone who has used a 19v / 7.1a laptop power supply and simply cut the wires (male from power unit / femal in the base) and connected the positive and negatives back together in order to power the unit.
They claim everything works, and been using it for over a year with no problems

Concerns

I understand if I do this I will lose any warranty on the base
Unsure if not using recommended volt/amp is a wise decision
Asthetically it will look ugly as its hard to hide all the wires
The only Pro is that the cost will be very minimal, especially if I can find a 2nd hand laptop PSU

Question

Is doing it the "cheap" way possible and logical ?
What are the implications of using the non recommended volt/amp

BTW - I tried to find an answer to no avail. Thanks heaps for reading up this far and your feedback will be greatly appreciated :)

Kind regards

Gary


texts:
I found an IC ( SST27SF020 ) from old CD player. On searching it's data sheet I found that it's a 256K x8 CMOS, MTP(Many-Time Programmable) and can be electrically erased and programmed at least 1000 times using an external programmer with a 12 volt power supply. Can anyone suggest, how to program these IC..?

  I don't have PICkit or any other device other than Arduino UNO. :-(

SST27SF020 data sheet


texts: How to use tcl script to generate Qsys system inside Quartus?

texts:
When I change .vhd files I need to regenerate Qsys and then compile the design. How can I use tcl commands inside Quartus to regenerate the Qsys and then compile the project as well?

Is there a way to automatically generate the Qsys systems when project is compiled? Why is this not done automatically? The problem arises since Qsys keeps local copies of the HDL source files.


texts:
The SMD jumper. One of the most basic devices on any board using SMD technology.

Yet, considering devices from various sources and looking into the hints of designing it, I get differing techniques and points of view.

The properties under consideration:

Size of the pads. Some designers point to the device size being comparable to standard 0 Ohm resistor size to put in place - e.g. 0603, 0805. This gives good reference for the device design, but it leaves question open on what must be a gap between the pads.
Solder mask. This one is actually why I started to investigate the matters. People say you won't want having solder mask between the jumper pads. Yet I have these designs in standard EAGLE library:

The first device, called SJ, is having tStop (mask stop) area in between the pads, others do not. These are from standard EAGLE library called jumper.lbr.

Number of pads. The simplest one at the very top has 2 pads, thus single jumping area. But what's about 3 pads jumper, with 2 jumping areas? Need to have mask in between? What its properties must be in order to have the most effective removal and insertion of solder jumpers?