texts: How to measure temperature of a syrofoam cutter hot wire?

texts:
I would like to create a hot wire foam cutter device. The wire material is nichrome, diameter 0.9mm, resistance is about 1.7 Ohm/meter. For best cutting results, I would like to control the temperature electronically. This will be a 4 axis CNC system where the wire length between the mounting points changes while the axes move. Planned length of the wire is abount 1.5m. Another extra (non-heating) wire is added, that is able to change its length to ensure the tension of the wire while the axes move. So the length of the heated part of the wire would not change, but it would be hard to measure the contraction caused by the heat.

The main question is this: how can I measure the temperature of the wire? I was first thinking about a thermistor, but then I realized that the hot wire itself could be acting as a thermistor. When temperature goes up, then probably the resistance will also go up. However, I have no idea how to create a circuit that measures the current flowing through (it can be 10A), and how to calculate the temperature from that. Another problem is that the hot wire will be heated with a 24V 200W transformator, unregulated AC power. My idea for power control was to use a diode bridge, a high power fet for switching (e.g. IRF44N or similar) and PWM signal to control the temperature. But this would make temperature measurement impossible - PWM controlled AC cannot be used together with the other idea.

The workaround I have in mind is this: use regulated DC and a simple A/D converter to measure the resistance of the wire in every (say) 1 second. Heating would be turned off completely during resistance measurement. This would take just a few msec. Use the PWM controlled driver to heat the wire in the remaining time. Would that work? How can I separate the heating circuit from the measurement circuit? (E.g. to protect the A/D converter safely.)

The secondary question is this: do any of you have an idea about how much power and voltage I need to heat the wire? I thought that 200W would be enough. That is about 8 amps at 24V. But don't have any experience. Also, even if I can measure the resistance of the wire, I have no idea how to convert it to a temperature value. (It would be nice to display the absolute temperature value, but it is not important - all I care is to adjust and maintain a constant temperature that has the best cutting results.) I have a 24V 210W transformator for heating, but the power may not be enough.

Or maybe you have an easier solution in mind - please don't hesistate to share.

Mechanical part:

Heating goes through the green lines and the red wire. Tension is provided by the gray cable (which is not heated).


texts: Floating Inductor Simulation Using Only BJTs?

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I know it is possible to replace large-ish floating inductors (~ 5mH) with
a gyrator, typically using two opamps:

What I've unsuccessfully tried to solve is : can we build something equivalent
to the circuit above, but using only caps, resistors and BJT's ?

I guess it is theoretically possible, given that an OpAmp can in practice
be built out of caps, resistors and BJT's, but I guess the question becomes:
is there a simple circuit, made only of BJTs caps and resistors that
can properly simulate a floating 5mH inductor ?


texts:
I've recently seen a homemade AC stick welder that was using 8 AWG wire for the stinger (the electrode holder) and the ground clamp. The voltage and amperage was around 30V at 200A. According to various websites, the maximum capacity for 8 AWG wire is around 40A to 55A (Source: http://www.cerrowire.com/ampacity-charts)

Granted, he only used it for a single weld, but how did it not burn up almost instantly? The video later showed him using it at 200A for an electric arc furnace and he was drawing current for over a minute.


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I have heard people say you shouldn’t Megger test transformers because the high voltages used might cause insulation between windings and between windings and the core to breakdown.  Is this true?

Suspect it will depend on the voltage actually used.

Assuming you should Megger test transformers, what kind of resistance should you see between windings and windings and the core, for the transformer to be deemed safe?


texts: Designing MOSFET bridge rectifiers for high voltages

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I've been looking into MOSFET bridge rectifiers, also known as "zero IQ" rectifiers, as a replacement for traditional diode-based bridge rectifiers.

Here's a simple example:

The benefit, of course, is that the MOSFETs don't exhibit a forward voltage drop like a regular diode does, allowing for significantly higher efficiency in cases where the current is high or the voltage is low.

The major limiting factor for higher power designs seems to be that you can't get MOSFETs with a Vgs(max) high enough to rectify voltages exceeding 80V or so. There are some control ICs that are designed to help with higher voltage rectification (e.g. LT4320, LM74670) but they too are limited to around 75V continuous.

My first thought to solve this issue was to clamp the voltage with zeners, but I ran into the issue that you can clamp the voltage on two of the transistors just fine, but when you try to do all four you just get shoot-through because the diodes provide a path directly across the AC input.

I also thought about using IGBTs instead, but they appear to also have fairly limited gate voltages.

Is there a way to solve this issue, either by designing around the gate voltage limit somehow, or by changing the topology?


texts:
Typically fast charging reduces backup time and life. Now a days almost all handsets are coming up with different fast charging capabilities. I'm currently using Galaxy Note9 which has fast charging features as well.
When I connect the supplied charger it starts charging with fast charging always. Fast charging is really helpful. But when I charge my phone at night while sleeping, it also uses fast charging. My question is during night time, fast charging is not required and normal charging is beneficial. So, why the manufacturer doesn't keep normal charging mode so that it can be used at night time  for getting better backup time and better battery life.


texts: Ladder LC Filter - why are they minimum phase?

texts:
Ladder LC filters are well-known to be minimum phase filters.

simulate this circuit – Schematic created using CircuitLab

Above: The ladder LC filter I'm thinking of, though ladder filters are more general, and so far I know, the question stays valid for general ladder filters.

Is there a explanation/demonstration or simply a intuitive explanation of this property of ladder filters?

Bonus question for those interested: What I find strange is that the analysis of lossless delay-line equation (telegraph equation) is done by "approximating" the delay-line by a LC ladder, that is to say, a minimum phase filter, though delay-line are the archetyp of the no minimum phase filter.

EDIT  (18 June 2017)
I restrict the question to lowpass filters only.

EDIT  (19 June 2017)
This question is in standby for a few days because I'm invesgating the problem.
Lastest news :

What I mean by "minimum phase filter" is a filter where the phase response can be derived from the magnitude response according to the BODE`s relationship. That's a concept that arises in Automatics and filter synthesis (here I'm only interested in analog filtering with capacitor and selfs (and resistors), a rather outdated science).
Allpass filter are evidently not minimum phase filter (because they have all the same magnitude response : 0dB whatever the frequency, so we can't deduce the phase from the magnitude response)
For rational transfert functions, minimum phase filters are the ones that have their zeros in the left half complex plan.
It seems that the ladders such as the one represented above don't have any zeros (whatever the values of the components, and assuming the driving impedance and the load impedance are purely resistive). In that case it is evident that it's a minimum phase filter.
Next problem : finally what is the general accepted definition of a ladder filter.


texts: How to convert readings from a DIY capacitive liquid level sensor to a level?

texts:
Background
I have made a tubular capacitive liquid level sensor (This is a professional one, for example). A 555 circuit outputs a frequency that is inversely proportional to the capacitance. This is read into the microcontroller (Arduino Nano clone).
The sensor will be used for monitoring our water tanks that supply our house.
There will be this one for the tank that gets municipal water, and another one for the tanks that collect rain water.
It is communicated with (and powered) over a Cat5 cable acting as a Modbus trunk.
The sensor consists of a DIY probe, made of aluminum and PVC pipes, and a custom board (made with stripboard).
The main components of the custom board are:

Arduino Nano
NE555
ISL81487LIPZ (MAX485 replacement; DigiKey)
DC-DC buck-converter

The problem
I have taken readings and put them into an Excel spreadsheet, along with the depth of water when they were taken. They seem to be logarithmic, but they are not. I have taken the natural logarithm and normalized the values, and plotted this versus the percentage of submersion of the sensor.
This is the graph:

X is percentage submerged, Y is reading. "Log Normalized" is the plot of the normalized logarithm values. "Linear" is the plot of the wanted values. "Diff" is the difference between the "Log Normalized" value and the "Linear" value for each pair of those values.
In the final application, I will have a reading, and will need to find the depth of the water the sensor is in.
Summed up,
I need a way to translate a reading to a level.
I need it it to be

easy to implement (I am not a master mathematician ;) )
work with 32-bit floating point numbers
fast

The reason it needs to be fast is because of other compensation algorithms that will need to be added, e.g. when the water level drops, the reading doesn't change immediately, it changes as the probe dries. These algorithms will need to call the level calculating one quite often.
What I Am Using at the Moment
I am currently using the formula described in my answer.
It gives acceptable accuracy (for the purpose of the sensor), is simple, is fast, and just "feels right".
Other Stuff
The spreadsheet is here. Note: I am still actively using it. There are formulas in place (which my answer here is based on), and some other experiments off to the side.
Images of the Fritzing Breadboard, the electronics, and are here.
The Fritzing file is here.
(I couldn't get Fritzing to comply with editing the schematic. It crashed whenever I moved more than one component at a time, or any large component.)
Cross-posted on math.stackexchange.com.


texts: Is it a good idea to connect PC to a non-isolated DC supply

texts:
I am working on an AC Voltmeter. The supply to the microcontroller is not isolated. Only a bridge rectifier is used convert AC to DC. To get 5V, resistors are used to drop down the voltage.

Is it a good idea to connect the debugger to a PC and microcontroller when AC is present? I want to debug my code, and without the presence of AC supply, I can't sense the voltage and I'm unable to debug the problem.

Will connecting non-isolated 5V and Ground to the PC have any effect on PC? Will it give shock while connecting?


texts: Termination between driver and transceiver

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I have the following line driver and  line transceiver

driver: 74VHC244

transceiver: 74VHC245

They're connected via a 0.5m long ribbon cable with an impedance of 100Ohm.
The digital signals have a maximum switching frequency of 16MHz at 3.3V through the cable. The order in the ribbon cable is always [signal - ground - signal - ground]. All signals are single ended.

Do I need additional termination? If so, how would you do it? Just add 100Ohm resistors in series after the outputs of the driver?


texts:
I'm using a freescale PowerPC microcontroller. In the flash memory module in the datasheet, the number of "wait states of the flash memory access" is configurable.

The following is the part of the datasheet raised my question, it's taken from the register description of the PFlash module registers :

  This field must be set to a value corresponding to the operating frequency of the PFlash and the actual read access time of the PFlash. Higher operating frequencies require non-zero settings for
  this field for proper Flash operation.
  0  MHz, < 23 MHz, wait states required = 0 ---
  23 MHz, < 45 MHz, wait states required = 1 ---
  45 MHz, < 68 MHz, wait states required = 2 ---
  68 MHz, < 90 MHz, wait states required = 3 ---

(PFlash is Platform Flash controller module)

I understand that the processor is faster than the flash, that's why wait states are introduced. What I don't understand, is : if processor is faster than flash, then the processor is the one that needs to be slowed down not the flash, but the paragraph above says the opposite (or did I not understand this?), it says that in case the Pflash is operated with high frequencies, then we need to slow it down by adding to it additional wait states !!

What's wrong with my understanding ?

Thanks


texts: How to remove "green" feature and recycle power supply?

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I have a power supply from broken DVD player (if I remember correctly), and would like to make a new case for it and reuse as a power source for my hobby projects.

I have some experience building 220v AC to 1-24 v DC power sources (including making transformer myself), but it was long time ago. However, nowadays power sources have "green" feature, meaning, that there is some kind of feedback from the device, which switches off the power. The original monitor also used ON/OFF button.

The question is, how can I find a place to make the power source always on?
I think, for experienced person this question is not a problem.

My own guess is, that one possible place is to replace photocoupler U2 (just besides the transformer) (not sure, should I replace it with a diode and resistor on "high voltage side" or just remove). Another idea is to plug into smaller connector (smaller one on the right). Connectors have voltages and GNDs, but also pins called "F+" and "F-"
(not sure, what for they are, but maybe they are to control the power supply?)

TNY268P integrated circuit is used, if its not visible from the image. PCB817 photocoupler.

Maybe, its stupid idea...

UPDATE: Problem has been solved so far (as I about it wrote in the comment of disappeared answer) and PSU provides all voltages on power on. I will do further checks to see if the problem re-arises.

UPDATE 2: I've found datasheet for TNY268P, and it claims to have "Simple ON/OFF control – no loop compensation needed", and "High bandwidth provides fast turn on with no overshoot". Does it mean, that TNY268P is the one, which senses load and switches ON/OFF?

The question is not any more about removing eco-feature (as it means too big change), but rather have I understood PSU operation right?

UPDATE 3: TNY268P connected almost typically (like recommended in datasheet here http://mkpochtoi.narod.ru/TNY268_ds.pdf ) in the PSU, but in addition BP (bypass) has connection to the outmost transformer pin like this:

(cant recognize what kind of diode is D6)

Does this gives any further ideas?

UPDATE 4: this is what the funny PSU gives on one of the taps at transformer secondary. At least explains annoying high-freq noice it is
making.


texts: How to simplify a circuit with ideal current source and ideal voltage source?

texts:
I'm currently trying to gain an understanding of Thévenin and Norton equivalent circuits and I've run into a circuit I simply don't understand. I've been researching online, but I've just run into contradictory information that often isn't helpful to begin with.

Here's the circuit:

I could simplify this circuit, but that ideal current source is my big roadblock. I'm currently trying to find the voltage between A and B.

I don't even know where to start. If someone could show me the right direction, that would be great! Thanks


texts: Need help selecting a transformer for an AC/DC converter

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I'm working on a pinball project that requires a 50VDC voltage to drive solenoids. The biggest load comes from the flippers (which both could be activated simultaneously) however it's possible for additional coils to fire at the same time (multiple balls on the playfield at the same time). This voltage can be unregulated, and the exact voltage isn't critical.

I could use some help in selecting a transformer as I find a lot of conflicting anecdotal statements for other DIY builders that does not make sense to me.

For background to understand the circuit, in a pinball game the flippers are controlled by a solenoid that has two windings. A high power for the kick, and then another goes in series to hold the flipper up. This is done mechanically by an end of stroke (EOS) switch being opened to tie in the second coil.

Now, the power coil is only 4 ohms giving a current of 12.5A which is pretty hefty, and as I mentioned there is a possibility of both flippers being engaged at the same time for 25A total. This would be momentary, milliseconds. However also repetitive.

From what I understand, transformers are rated at RMS and this would be in the US (120V, 60 Hz). So a 40V transformer would give me about 40 * 1.414 = 56.56 volts. The bridge rectifier would eat up another ~2V giving me 54V. I think I could get away with a 35V transformer giving me ~47.5 volts after the bridge rectifier. A lower voltage should give me a higher current at the same VA rating correct?

What I'm having trouble with though is what VA rating to go for. It seems like a 35V RMS transformer at 25A I should need around 875VA of power available. Is that correct? The contradictory information I have found is people using much smaller power supplies, do they just get less force out of the solenoids? A supplier of toroidal transformers I've found with reasonable prices offers 800VA ($84), 1000VA ($100), and 1500VA ($155) options. They're not exactly cheap though so I want to make sure I get it right while not going overboard to keep the budget down.

Thanks!

simulate this circuit – Schematic created using CircuitLab


texts: Reactive Power in Inductor and Capacitor

texts: Suppose a RLC circuit with AC source. Why the net reactive power in the circuit is the difference of reactive power in the inductor and the reactive power in the capacitor ? As both of them store power then why the reactive power in them is not added instead of subtraction.


texts: What are the main ways to generate a pwm?

texts:
Let's suppose to use PWM (e.g.  to control the 'speed' of a motor)

What would be the possible way to generate a PWM signal?

On the one extreme, there is pure software techniques where 'a programmer typically writes a value to a memory-mapped register to set the duty cycle' [Lee & Seshia, Introduction to Embedded Systems]. On the other extreme, there is dedicated PWM Peripheral. What are the other ways to genrate a PWM?


texts: power micro controller with 7.4V 400mah battery

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I want o control a servo with a micro controller and I need more torque so I chose a 7.4V battery. Power my micro controller requires only 3.3V and obvious if I try to power it straight from this battery it will fry.
Is there a way I can get the 3.3V to the micro controller and the 7.4 to the servo all from this same battery?


texts: Where should I start troubleshooting a CC1310 radio design?

texts:
I have designed a custom PCB using a CC1310 radio, based on the reference design for the CC1310 LaunchPad.

The uC is programming, and running code, when I attempt to send data through the radio, the software reports a successful transmit, but I am not able to get any data received from my LaunchPad, which I have programmed as the receiver.

I'm really not an RF expert, but I positioned the RF front end components as similarly as possible to those on the reference design, and requested that the board stackup be the same as that from the reference design.

After re-reviewing the BOM, I realise that for C21 in the reference schematic, the capacitor that connects RX_TX to ground, I requested a 0.1uF instead of a 100pF capacitor.  I guess that will have a pretty severe impact.

I also realise that when providing my manufacturer with a BOM, I only specified the part type and value, e.g. Inductor 7.5nH, but I now see that in the TI BOM, there is much more detail, specifying RF inductor, non-magnetic core.

Please can someone tell me which components in the RF front end are likely to be the culprit of my non-functional radio? I don't mind re-soldering the whole front end if needs be, but I'd like to only change the parts that I need.

Which are the most likely causes of my problem? What can I do to get it working? and how much can I test this, all I have is a scope.

Addition:
I used SmartRF Studio to set my custom board into continuous Tx mode, and to set a LaunchPad for continuous Rx. With ~1m seperation, the receiver was seeing between -35dBm and -60dBm, and then when I powered the Tx down, the Rx dropped to -100dBm. This means the custom board is transmitting something. Does this provide any extra insight?

Addition:
I have tested two custom PCBs trying to communicate with each other, and they work. Using custom boards with SmatRF Studio, I get a much more stable RSSI of ~-20dBm, as shown

So, I know that the custom boards are functional, but will not communicate with a COTS development board.

I used a Software Defined Radio (SDR) dongle as a spectrum analyser, and tested the results of the LaunchPad transmitting, and the custom board, and here are my results.

LaunchPad as Tx

Custom PCB as Tx

I have tried swapping the incorrect value capacitor C21 for one of the correct value, and it makes virtually no difference to the results.

My only thought on what to do next is to change the other components in the front-end to more closely match that in the BOM.

Please can someone explain the reason for the behaviour I have seen, and provide some information about the difference between the custom PCB and the LaunchPad based on the graphs above?

Anything to improve my understanding would be greatly appreciated.

Addition:

Now I've figured out how to work my SDR, here is a better resolution graph for each device.

The LaunchPad seems to peak at ~867.935MHz:

Where as my custom boards seem to be more at ~868.053MHz

So whatever I have done has caused a sufficient difference in frequency. Is this really likely to be from the RF front end, or is it likely to be from something else? E.g. The oscillator being slightly off, the PCB copper being slightly different? Small differences in stack up?

I didn't think that a discrete Balun could shift frequency, am I wrong? can the matching circuitry after the Balun cause a frequency shift? What is likely to be responsible for this?

Many Thanks.


texts: Safety when using ATX power supply as benchtop supply

texts:
I found many pages where people convert an ATX power supply to a benchtop power supply to give 12, 5, 3.3V.

However the current output can be very high (several amps).

When using this and you NEED high current, that is great. However, when using this for typical benchtop hobbyist needs (e.g. supply 5V to a microcontroller) the current supply needs are small. I understand that it will draw as much current as it needs -- but my question is one of safety. Since the current "compliance" is essentially set to several amps, what happens if I accidentally touch + and -? Or what about if something in my circuit suddenly blows up and shorts + to -? Then I suddenly have several amps running thru my circuit. I believe then an internal fuse in the ATX unit will probably blow (right?) but at least for some short length of time there were several amps running thru my resistor  right? or Wrong?Would anybody have a simple adjustable current limit circuit that I could build and add to my PSU?


texts:
My end goal here is to launch a camera strapped to outside of the payload of a High Altitude Balloon to take pictures at 5 second intervals during ascent and descent. Trying out a few ideas, I've bought a trail camera (link). It's triggered by a PIR sensor, which isn't really what I want, and I'd rather it just take a picture ever 5 seconds period. The whole situation has to last for about 3-5 hours on batteries.
So having provided that context, and to reduce my question to the simplest form I can think of, is there a well-known way to induce a PIR sensor to trigger "constantly"? First prize goes to "non-invasive" techniques for doing this. I have an Arduino in system but I'm trying to make the camera function of this little project, to the extent possible, independent and off-the-shelf.


texts: Enabling extra routing layers in Eagle (paid version) PCB design

texts:
I started a PCB design in the freeware version of Eagle, now I have the full version, but it won't let me route tracks to the extra route layers (i.e: only top and bottom). Starting a new design in the paid version gives 5 extra routing layers.

Any ideas how to enable these layers on designs that were started in the freeware version?

Any help is appreciated

Tom


texts: Brushless DC motor problems at high velocities

texts:
For a project we use a brushless DC (BLDC) motor. Everything works fine until we tried to reach high velocities. I will first explain my setup, and than explain our problems using some graphs. Unfortunately I don't have enough points to put al my images in separate links, so they can be found here.
1.0 Setup
The following hardware is used in the setup:

BLDC motor: Tiger motor U8 (135kV)
Motion controller: SOMANET DC 1K
Encoder: RM08 12 bit absolute encoder

An overview of the setup can be found in image (1)

1.1 Requirements and Parameters
We need about 4800 [RPM] from the motor. The Tiger motor has a kv value of 135 [RPM/V], connecting it to a 48 [V] supply means it theoretically should be able to go up to 6500 [RPM]. The specsheat includes a scenario where it reaches 5000 [RPM] while a propeller is connected to it, so 4800 [RPM] with no load should not be a problem.
2.0 Problem
We are not even getting close to the 4800RPM, a plot of the motor velocity vs phase current is shown in image (2). We can identify 2 problems from this plot.
2.1 Inefficient commutation
The first thing which was remarkable from the test is that about 10 [A] was already required to turn at 3200 [RPM] without any load connected. This seems to be caused by inefficient commutation, we figured there are two main possible causes for this.
2.1.1 Phase offset error
Their might be an error in the phase offset used, this will cause an linear increase in required current with velocity. This can be best solved by finetuning the offset at a high velocity. However our curve does not seem linear, thus this does not seem to be the case.
2.1.2 Delay error
There is a certain amount of delay in between requesting the position from the RM08 and applying the new voltage. This delay can cause the current to exponential increase with motor velocity, which is true in our case.
By adding up al delays we found a total delay of ~0.1 ms in the system (see image (3)). Spinning at 3000RPM = 50Hz and using 21 pole pairs means that the electrical turning frequency is 1050Hz, than a delay of 0.1 ms would cause a 37.8 electrical degree error, This likely causes the inefficiency!
2.2 Control going crazy
if we try to go above ~3200 RPM, the motor starts pulling a lot of current and makes a lot of noise. This means the motor is not operational above 3000RPM, this seems to be the most urgent problem at the moment.
Voltage dependency
Normally the motor velocity is limited by back-EMF, if the back EMF would be causing this issue the problem would be voltage dependent. Therefore some measurements where done at different voltage levels, see image (4) and 卌.
The moment where the motor stops following the velocity sweep seems to increase linearly with voltage. Another interesting outcome is that at 30V the motor just stops following the velocity sweep, while at the higher voltages (40V and 43V) the motor suddenly dropped to a lower velocity. Note that the 46V test stopped before this moment because to high current peaks were flowing trough the SOMANET (35A).
However it seems unlikely the back-EMF is the problem since Tiger has been able to reach 5000RPM themselves.
Solutions
For the first problem we thought we could use something like:
Pcorr = Penc + t_delay * Vel.
With:

Vel: angular velocity
t_delay: the delay compensation gain
Penc: the encoder position for the rotor
Pcor: the delay compensated position

However this didn't save the problem at all. Do you have any other suggestions?
For the second problem we can't think of any cause, can you think of any?


texts:
How can we find the topology of an amplifier's feedback?
I was asked to find the feedback topology of the following circuit,
The following observation is made by me:

Since the o/p voltage is connected with the feedback directly i.e R1, it will reduce the overall o/p impedance of the amplifier and hence we can say that the circuit is shunt sampling
Similarly the i/p impedance is reducing due to R3 connected directly to the I/p.

So it must be shunt-shunt feedback, But the answer given is shunt series feedback, so where I get wrong?


texts: What happens if the input voltage of a low dropout regulator is under the rated minimum voltage?

texts:
I am not that familiar with regulators, so, I want to know what happens if the input voltage is under the rated minimum voltage? Does it give zero volts or something under the rated voltage? If it's not zero volts, is there any type that gives 0v or acts like an open circuit in that case ?

there is another similar question but it's not that specific. what I want here is a mention of any type that goes open circuit when the input voltage is under the rated minimum voltage


texts:
I am designing a PCB that has will hold an Arduino Micro, as well as other components.  One of the electrical engineer mentors that are overseeing the board development has told me to increase the copper pad size/decrease the hole size for the pin headers in order to have an overall larger pad surface area.  He told me to do this because it lowers the risk of the pads coming off in the event that we have to desolder the Arduino from the PCB (dead board, etc.).

Currently, the holes and pads are circular, with the total edge-to-edge exposed copper diameter at 2mm, and the hole size diameter at 1mm (picture below).

We are planning on ordering our board from OSH Park with their 2 Layer 2oz 0.8mm Service instead of the standard copper.

Is there a need to make the copper pads larger in the case of a desolder, or will keeping the pads their current size be fine after a desoldering?

NOTE: I cannot make the pin header hole much smaller, as they are square headers with a 0.65mm side length (corner to corner length is just under .92mm), but I can make the pads slightly larger if absolutely needed.

-Ben

Pin header hole and pad with measurement:


texts: Maximising DC motor torque within parameters - and stuck on terminology

texts:
Mandatory components:
24v DC supply,
No-name PWM speed controller (originally packaged with 24v 250w DC motor)

Existing but replaceable:
24V DC, 14A, 250W, 2750RPM motor.

Need:
The most torque I can get at 24V and 15-20A, while remaining under or at 300w. RPMs are not very relevant as I can gear up for rpms as long as I have enough torque to get things moving.

Purpose:
Repurpose a 12" wheel scooter drive system for use on a bicycle with 20" wheels, while also improving stop-from-start and uphill performance. Original motor-to-wheel gear ratio of 5.91 will be improved to 11.73 to lessen torque need and to compensate for wheel size difference.

Caveat:
I am horrible with the nomenclature of both electronics and motors. My search efforts are restricted by this, and I apologise for my lack of proper terms.

Questions:
1) Can the existing 250W motor be modified to generate more torque at the existing voltage and max Amps?

2) If a new motor is needed, what do I need to look for when these motors do not list torque as a spec? (Even google won't help, since I don't know what to search for)

3) What approach to this would work if my hoped-for approach will not?


texts: How to protect a MAX232 from PIC programming high voltages?

texts:
This question is derived from this Board review thread, I thought it would be preferable to make it a standalone question.

I want to be able to reset a PIC remotely using the only communication port of the board, the RS232. But I also want to be able to program it using a ICD3 (no bootloader), and this programmer apparently applies high voltage (0-13V?) to /MCLR which will certainly kill the MAX232 (MAX233 in fact).

Would a schottky between R2out of the MAX233 and 5V be the way to go? The datasheet says that the absolute maximum voltage on that pin is 5.3V, I find it a bit tight for a schottky. Any more robust suggestions? I don't want to use a jumper as this could be forgotten...

Schematic:

Thanks

Edit:

Will this work?

simulate this circuit – Schematic created using CircuitLab

The Zener is a ON SEMI BZX84B5V1LT1G that has 5-5.2V tolerance at 5mA and I'm allowing 4.4mA max. The MAX233 will drive the /MCLR pin at 0.41V where up to 1V is a low level. The 20kOhm pull up comes from one of Olin's answers here.


texts: Why can't electrons leave the surface of a conductor?

texts:
At room temperature, no free electrons can ever leave the surface of the metal. A free electron cannot escape the coulomb (electric) attractive forces presented by the positive metal ions in the lattice. (We'll see later that under special conditions using unique mechanisms, it is possible for electrons to escape)

Source: http://www.amazon.ca/Practical-Electronics-Inventors-Third-Edition/dp/0071771336

I don't understand why the electrons can't leave the surface. Even though there is an attractive force from the positive ions there is an almost equal repulsive force from the other free electrons. So the net force should be almost zero, so even a small voltage should be enough to get the free electrons to leave the surface right? What am I missing?

Please keep answers relatively simple. I only have a basic understanding of physics and chemistry.


texts:
I am working on a project that requires an IR receiver module to detect particular buttons pressed from a SONY Stereo Remote. I have a regular kind IR receiver that looks like this:

The problem with this is it can only detect 0v or 5v. Could anyone help me find an IR receiver that will be able to tell me what button was pressed on the remote? A link to an online vendor would be much appreciated.


texts: Sophisticated order to connect the poles for a jump start of the car battery

texts:
How to connect or jump start a car battery. So in what order to connect the poles and why?
I read so much (different) explanations and I would like to have a final generally accepted/recognized answer to mark this question.

This is (also) related to human safety.


texts: Impedance matching with only capacitors?

texts:
I need to do impedance matching for 33 + j32 ohm source and 16.5 + j0 ohm load. The copper traces adds 99 ohm impedance and 20 degree electrical length.

According to smith Chart below, I need to use one shunt cap and one cap in series. I wonder if it is a legal circuit?

As I have seen on various documents, L-C or C-L are always used that has also a function as a high pass or low pass filter. Would it cause a problem if I only use C - C (or L - L for a different case) although the impedance is matched?


texts:
I got a WINOMO LM2596 DC-DC 1.23-30V converter which I want to use to regulate the speed of an old PC fan.

I did not find a schematic for my specific converter, but I think this one should be close to it.

https://www.youtube.com/watch?v=9vMNa-H_PRg

I exchanged the potentiometer (top, blue)

http://www.ebay.de/itm/112589926880?clk_rvr_id=1415775361179&rmvSB=true

with this one

https://bilder5.eazyauction.de/ebaye70/auktionsbilder/2568_0NS_4881_1000x1000_0dc7819a.jpg

shows the cables that now go to the new potentiometer.

My setup works as intended only if I hold the converter in a specific position. When I wiggle/move the converter a little bit the fan speeds up with max. voltage, although the potentiometer is set in a position where it should not power on the fan.
If I hold / fix the setup in the "right" position, I can regulate the fan speed as intended (and even turn off the fan when the voltage drops too much).

This leads me to believe that somehow the potentiometer gets bypassed due to poor connections somewhere or another effect I haven't figured out.

I added some pictures below, no cables are visible touching as far as I'm concerned.

I know that I did an extremely poor soldering job, desoldering the old potentiometer was a real piece of work due to my poor desoldering skills and then I just wanted to quickly connect everything to see if it works.

edit
I completely redid the question as I'm under the impression that it was hard to get what I actually did / what the problem is.

edit2
I disconnected the poti completely and the fan also spins with max voltage.


texts: Can the reference plane for reducing crosstalk within a PCB be a power plane?

texts:
One of the most effective ways to reduce the coupling between PCB traces (to reduce crosstalk) is to put the reference plane close to the traces.

I have always used a ground plane as the reference plane.

Could a power plane be the reference plane and would it still be effective?


texts:
My intention is to drive a MOSFET (say, a IRF840 or some logic-level) from a low-current (<10mA) SoC output pin.

Using appropriate resistors from gate to pin and ground, this works... but the gate voltage change could be faster.

So I considered putting a NPN (to VCC) & PNP (to GND) BJT between the pin and FET

simulate this circuit – Schematic created using CircuitLab

and at that point I thought I'd ask if that setup has a name and/or any known problems to avoid (feedback, etc).


texts:
Hello there here i want to calculate average power dissipation of radar

My question is here

i tried to solve it this way

Average power = peak power*Duty cycle

here transmitted power is 300kW and efficiency of radar transmitter is 60 %.
so my power is 180W and i calculate it with duty cycle. so i am getting 18 kW.

but my expected answer is 20.9kW. can anyone tell me why I am wrong??

thanks!


texts: Why does adding this low pass-filter to a monostable multivibrator prevent triggering?

texts:
A 24 VDC sinking sensor is tied to an SSR.  The SSR converts the signal from 24 VDC to 5 VDC.

The output of the SSR goes directly to input B of a 74121 One-shot. (The diagram has a resistor and capacitor in between that were not there originally). This one-shot generates a 155ns pulse that is less than an encoder width in time. It is used to reset a set of encoder driven counters.

Most of the time this works very well. But on one of the machines we have an issue. There is an occasional "motor" noise when the system stops that causes the one-shot to fire. I'm assuming there is a short duration negative spike on the sensor line. It is very intermittent and I have been unable to track down the source.

I modified the circuit to add a low pass filter. The normal duration the sensor is about 60 ms, the components I chose should be able to filter out the spikes.

My test version, without the one shot, looked really good. The curves looked just like the books, and my time seemed to be right on track.

When I added it to my original design, as shown in the schematic, it no longer  trigger the one-shot.

The curve started well, but the downward part clipped at about 1.7V and not zero, before curving nicely back to almost 5 V. Popping out the multivibrator 74121 revealed that the signal would go to zero cleanly. It appears the one-shot is holding th level higher.

Further testing by leaving R1 and removing the capacitor, C1, shows that the voltage never reaches close to the 0.4 VDC required. Trying various other resistors such as 10K and 1K, I found the 1K got closer to 0, around 1.4 and seemed to work, but this is really out of spec for TTL.

I thought about putting the RC in front of the SSR instead, but it has similar TTL input characteristics.

Why would the 74121 prevent the signal from going to 0 V? Without
the RC it did.
What should I do to get a low pass filter working
with the one-shot.
Should I add a non-inverting Schmitt trigger
between the filter and one-shot input?

simulate this circuit – Schematic created using CircuitLab

Update: Not directly related to the question, but was the solution to my issue. I ended up not being able to use the delay in the circuit. The spike totally overrode the one-shot causing a trigger and the delay provided no relief to this.

Each of these reduced the occurrence of the issue after testing, but none of them alone solved the problem.

Tying 0 VDC to Earth ground in my cabinet
Running a ground wire from the external enclosure to the machine, both frames were already grounded through their power cords, but this greatly reduced the problem.
Added varistors to the machines 24 VAC relay and contactor control coils. Specifically the run latch relay seemed to be the noisiest.

The weird thing was that after the last item was in place, I could still see noise in the 5 VDC section through my scope, that I would have thought would be enough to cause a trigger, but it didn't.


texts:
For audio I can use just sound card, plus OS api to record any signal from 20 hz (below that's blocked via capacitor) to 96khz(that's half of max samplerate).

But what if I just want to go higher? As high as it possible!

How far could I go and what PC hardware should I use, in order to sample that signals?

For example, I want to record broadband signal, and do FFT, to see "what's happenin here?"

how this was even recorded?


texts: How does radiation produce transient bit errors in DRAM?

texts:
Ionizing radiation can produce transient bit errors in volatile RAM.  What is the exact mechanism by which this occurs?
E.g., is there a threshold energy level for a single photon or neutron to corrupt a bit?  Or is this a result of larger amounts of lower-energy radiation over some critical period of time?  Is that threshold a function of the RAM circuit feature sizes and/or voltage?


texts:
I would like to use my soundcard as osciloscope to measure low voltage analog signal (between 0 and 5v).

I would like to insert a circuit between the sound card input and what is measured

The goal of this circuit is to provide:
1) high impedance input to not interfere on the measured circuit
2) be able to change the ratio: 1x, 0,5x and 1/10x
3) limit the value that goes to the sound card to less than 1V

Here is the solution I would like to know if it's correct
1) 1 opamp in folowing mode
2) a resitor bridge divisor + 1 opamp in folowing mode
3) a diode a 0,6-0,8v is fine

If I only mesure positive current do I need the AC coupling part descibed in the folowing diagram link
http://xoscope.sourceforge.net/hardware/buff.gif

Is it necessary to have also 1M R1 in the input to have 1M input impedance instead of an infinite one ?

Thanks
Franck

What is the goal of capacitor that can be seen on the input of probes as

simulate this circuit – Schematic created using CircuitLab


texts:
I need advice on powering a STN-display module. I am confused on getting the correct power source for the backlight.

The backlight of old module (SP12N002) contained CCFL and new (SP12N01L6ALCZ) is LED. The input voltage for driving the old CCFL circuit was 12V (inverter INVC828 for LMD7420PLFC-X). The new LED display module needs  5V/84mA. Should I use a simple DC-DC convertor (IL1205S)? Otherwise, I was also wondering if I can take a simple DC power supply (mobile phone charger with 5V/500mA) and power it.

Many thanks for your help.

PS: A DC-DC convertor from the company exists with circuit diagram here: https://www.koe-europe.com/doc/AN13005-upgrading-CCFL-to-LED.pdf


texts: Contact ESD protection vs Air gap ESD protection

texts:
There many ESD diodes available in market for ESD protection from connectors or 'touch surfaces' of product.
But how about air gap ESD attack? What if I have large PCB with connectors at the end, ESD happens through air in the middle of PCB. What kind of protection can be implemented in the circuit design or in PCB layout for this attack?
Does it matter if IC is at the edge(Upper or lower) of PCB or in the center? Air gap ESD attack can also happen from Z direction.


texts:
This is the second part of the problem which I try to solve from textbook.
I wrote the truth table. Z is 1 only if A, B and C are 0.

I've found a boolean equation like that :

\$ \large Z = \bar {A} \bar {B} \bar {C} \$

But according to the solution manual the answer is :

\$ \large Z = \bar {A} {B} {C} \$

Which one is correct?

Citation :

  Agarwal, Anant, Lang, Jeffrey. Foundations of Analog and Digital
  Electronic Circuits


texts: How to combine H-bridge with high current pwm smoothing filter

texts:
I would like to drive a peltier (rated max 12V, 5A) with three considerations:

i want to control the voltage absolute value with a PWM signal from an arduino (30kHz),
the voltage across the peltier needs to be smooth and not a square wave and,
I also want to control the voltage direction across it, to choose between a "heating" and a "cooling" mode.

I know the 1) and 2) are nicely solved with a buck-mode step-down converter to smooth a high current PWM signal (Smoothing a High Current PWM). I also know that 3) is typically solved with an H-bridge (
PWM controlled H-Bridge).
But, how can I combine both? Is it possible? I guess that the H-bridge goes in place of the FET (M1), but will the smoothing filter work appropriately with the H-bridge in forward and reverse mode? Or do I need to place two "filters" one for each mode? Are there any ICs that do this? And if not, which FETs do you recommend for the H-bridge, would IRF1405 (and their P counterpart) be good enough?
Thank you very much!


texts: Why is my PIC microcontroller pic16f683 resetting after 2.4 seconds?

texts:
I have written the LED flashing light program for a 16F683 microcontroller.

I expected the LED to have a 50:50 mark space ratio. i.e. on exactly half the time. In fact, it is spending longer on than off.

I connected the output to the storage scope and can see that there is a glitch exactly 2.4 seconds after the first switch on. It appears the output is going low, then before getting quite to 0v, is going tristate before going back to +Vcc.

I have checked the #pragma config WDT=OFF which all looks correct.  I have tried re - compiling with WDT set to on and off and can see a bit difference in the compiled HEX file.

I am using a MiniPro TL866 programmer.


texts: I was measuring the voltage across a 12v VRLM battery when I noticed something : the battery had 11.7 volts without the load and when the load was added, the voltage dropped to 11.4. I don't want to have to disconnect my battery just to get a low battery indicator to work properly. How can I know if my battery is low when I have it "in use"?


texts: How come charging a phone with less current is just slower?

texts:
I am wondering how charging circuits works; obviously there is some misunderstanding on my side. For example, a mobile phone is sold with a 1.5 A adapter. One can assume that charging and powering the phone can load up to 1.5 A. How is it possible that no malfunction occurs when a less powerful adapter/USB port is connected to the phone?

First adapter: It should behave as a perfect voltage source up to some specific current. So if I have a 5 V, 0.5 A adapter, until the load is less than 500 mA, it will provide the 5 V. With a bigger load either the voltage will drop or it will burn or malfunction in some way. So => the load of the charging circuit must be somehow max. 0.5 A even if in other cases it can load much more.

Second charging circuit: As I understand it, it should have some specific load, for instance 1 A. It is obviously not so, but I do not understand how this is achieved. How can it be 0.5 A in one case and 1.5 A in another?

How can the charging circuit 'decide' how much current to use based on the source?


texts: How to convert current source to voltage source when to current sources are in parallel?

texts:
I've been given the following diagram with two current sources:

I have to calculate the current shown by the ampermeter (A) which is quite easy once I'm done with the conversion.
The theory says the following (current source to voltage source):

This is my attempt but I' think I've done something wrong (made in Paint)


texts: Running a DC motor with too high voltage

texts:
I am proposing to run a nominal 12 volt DC motor using a LiPo battery providing a maximum voltage of 16.8 volts. The motor will be controlled by PWM so my understanding is that I do not need to regulate the input voltage to 12 volts provided I monitor the input voltage and set the maximum duty cycle to the equivalent of 12 volts. Is this correct?
I am also intending to monitor the input current. The motor has a 5 A stall current so I am intending to set a trigger voltage of say 3 volts where I will do something! The question is what to do. My hazy understanding of back EMF suggests that if I simply stop the motor or drastically reduce the duty cycle I could actually make the problem worse in the short term. What is the best action to take?
Thanks.


texts:
I have to control a temperature, with a 3.5 kW under 230 V AC resistor.

I have a regulator with this OUT : 4 A / 240 V AC.

I found this relay to commute my circuit.

My question is : can I use it ?
It's 4 kVA and my circuit is only resistive. The coil resistance is 38500 Ohms, so I =...0,006 A ? But as specified in the doc' : "rated operational current" is 8 A or 16 A (changes according to the cabling, isn't ?).

That's my problem. What amount of ampers will the relay take from the regulator ? Is it 6e-3 A or 8, 16 A ? Does this "rated operational current" refer to the current in the command or power side ?

Thx, and sorry for my english (not my native-tongue...),

F36.


texts:
1.open-circuit test determine the electrical conductance and susceptance,not impedance

2.close-circuit test determine the  impedance ,not  electrical conductance and susceptance

First,i want to ask that we know the  difference between open-circuit and close-circuit  is that secondary of the transformer is open-circuited or close-circuited,and as we know conductance =1/resistance,that is ,i should know the impedance ,resistance, conductance and susceptance  no matter circuit i used.so why can i only know conductance and susceptance,not impedance from open-circuit test?


texts: Find the largest value of \$K_1\$ and \$K_2\$ for instability of the system

texts:
A cascade control system with proportional controller is shown below

  Theroritically the largest values of the gain K1,and K2 that can be set withot causing instability of the closed loop sytem are

  Given \$G1=\frac{1}{(s+1)(2s+1)}\$ and \$G_2=\frac{1}{(3s+1)}\$

  \$(A)\$10 and 100 \$(B)\$100 AND 10 \$(C)\$10 AND 10\$(D)\$\$\infty\$ and \$\infty\$

The closed loop T.F will be

\$\frac{C(s)}{R(s)}=\frac{K_1K_2}{(s+1)(2s+1)(3s+1)+K_2(3s+1)+K_1K_2}\$

Now C.E will be
$$6s^3+11s^2+(6+3K_2)s+1+K_2+K_1K_2=0$$

Now after applying R.H criteria I got two conditon for stability

that is $$20+9K_2-2K_1K_2>0$$ and $$1+K_2(1+K_1)>0$$

Now after satifying Options one by one all options becoming unstable for this equations.

Is the options are wrong or I am doing it wrong?


texts: circuit for converting in 0-5v to 4-20mA current source

texts:
basically is want to make a circuit that takes 0-5v input and converts it in and corresponding output current of 4-20mA using opamp , i have seen reference circuit from this pdf https://www.analog.com/media/en/technical-documentation/technical-articles/D61_EN-Convert.pdf
but it has converted from 1-5v to 4-20mA current source
but i want to make a circuit that converts 0-5 to 4-20mA current source


texts: I am building board with Atmega328p, in total energy usage is 40mA, now I need to focus on power suplay, on the board is standard V regulator to 5V, what is better baterry configuration, 4 AA which gives me 6V, or 6 AA which gives 9V ? I need optimize space so 4AA would be better, but 6A gives more energy, will the board with 6AA live 33% longer ?


texts: Need a protection diode if only connected by common ground?

texts:
I have many solenoids running on 25VDC.  Some are controlled by MOSFETs which are powered by a 5VDC circuit, and others are controlled by physical switches in the 25V lines. The 5V and 25V circuits have a common ground.  I put protection diodes on the solenoids that are MOSFET controlled, but I'm not sure if I need them on the switch controlled solenoids?  I've been running into a weird phenomenon where if I activate the switch controlled solenoids enough then the MOSFET controlled ones will start randomly firing in unison, and the only reasoning I can come up with is that the surge from the solenoids is going over the common ground or something and messing with the MOSFETs.  If I do need a protection diode on the switch controlled solenoids, would it be possible to just put one in parallel with their busses to protect all of them?

(ignore the upper switch connected to the transistor, that's not what I meant by switch controlled.  the upper switch is actually an arduino out with a 10k pulldown resistor)


texts: Is it compulsory to use ext oscillator in designing arduino circuit?

texts: I am designing a circuit for arduino. I will be using Atmega328p, and will connect few male header for pin access and 6 male headers for programming (MOSI,MISO,SCK,RST,Vcc,GND). So is it compulsory to use ext oscillator. I know MCU can also work using int oscillator but not sure that while programming it through USBasp it will work or not. I heard somewhere that while programming it using USBasp ext osciallator is required. So ext oscillator is required or not.?


texts:
I need to connect a bunch of Mass Flow Controllers on a RS485 (TIA-485-A) multipoint bus. I will use Modbus protocol to communicate with the devices.

As specified on modbus.org (Specification and Implementation guidelines), the serial bus infrastructure in a multipoint Serial Line system is like this:

In my project, I would need only the Passive TAP (no Active TAP), because the length of my cables are around 10 cm.

From the mechanical point of view, 2 types of connectors are specified. The RJ45, and the D-shell 9-pin, as depicted below.

My question is, what can I found on the market as Passive TAP with either RJ45 or D-Shell 9-pin connectors?

Something like this with RJ45/D-Shell instead M12 would be nice.


texts: This is my first time making pcb layout. I am also quite unfamiliar with datasheets. I am using DS90LV019 (the figure is attached below). What is the actual length of this IC. Does (0.335-0.344)/(8.509-8.738) mean the length is 0.0393 inches?


texts: Serial communication with microcontrollers AT89S52

texts:
I have a problem, I need to connect two microcontrollers and programming one of those as a transmitter and the other as a receiver, I've tried to do this but it's not working, and I don't know why.

The serial communication need to be in Mode 0. The transmitter microcontroller has a dip-switch where I enter the data (a number) and I need to be displaying in Led's connected in the receiver microcontroller.

Here is the code for both, I hope you can help me, thanks.

.................Transmitter.................

       MOV     SCON, #00H;    MODE 0 AS A TRANSMITTER
HERE:  MOV     A, P1;         MOVE THE DATA ON P1(DIP-SWITCH) TO ACCUMULATOR
       CLR     TI;            CLEAR THE BIT TI
       MOV     SBUF, A;       MOVE THE DATA TO SBUF
       JNB     TI,$ ;         PAUSE UNTIL THE TI BIT IS SET
       SJMP    HERE

..................Receiver...................

        MOV    SCON, #10H;    MODE O AS A RECEIVER
WAIT:   JNB    RI, WAIT;      PAUSE UNTIL THE RI BIT IS SET
        CLR    RI
        MOV    A, SBUF;       MOVE THE DATA SEND TO ACC
        MOV    P1, A;         MOVE ACC TO P1 (LED'S)
        SJMP   WAIT


texts: What kind of power management circuit do I need to embedded a rechargeable battery in my electronics project?

texts:
I am doing a project where my electronics runs on 5V which I wanted to power from a 7.2v lipo regulated down to that voltage. I'd really like to include the opportunity to charge the lipo without removing it from the project. What kind of circuit/components do I need to do it properly?
Say, would putting a battery charging ic at the battery's terminals in parallel to my system be enough to achieve what I need?


texts: what happens in a seperately excited DC generator when load increased

texts:
A book about electrical machines states as below

what happens in a generator of this sort when the load is increased? When
the load supplied by the generator is increased, IL (and therefore IA) increases. As
the armature current increases, the lARA drop increases, so the terminal voltage of
the generator falls.

What I don't understand is what is meant by increasing the load? If the load is increased shouldn't the current through it (IL) decrease? How can IL increase when the load is increased?


texts: XBee needs reset for every action I do in X-CTU

texts:
I am setting up my XBee radio using the official X-CTU tool. The XBee is connected to a USB XBee explorer. The first time I did it was a few weeks ago, and I kept getting errors (see below), but however not constantly. Today, I have not been able to make a single piece of communication with the modem without needing a reset.

I open X-CTU, pick the correct COM-port, and click "Test / Query". I get this error message:

I then reset the XBee by short-wiring pin 5 and 10 (my Arduino does not have a reset button). Instantly the error message disappears, and I get the expected result.

If I click Retry, I get the first error message again. Every time, out of at least ten trials, the error message appeared after clicking Retry, and every time, the correct infobox appears after resetting by short-wiring.

Is my XBee simply broken, or what is going on here?


texts: PWM frequency and sine waveform generation

texts:
I am trying to follow some guides (for instance this) to generate some analog signals (for instance a sine wave of 50 Hz) with Arduino (but my questions are general).

But I have two basic questions:

1) The author of the guide chooses to generate that sine wave starting from a PWM signal of 31372Hz. As I understood, it is possible to choose an arbitrary frequency (with some limits obviously) since it is determined by some settings on the MCU internal timers. How do we choose it? Does its choice depend on the low - pass filter we decide to apply?

2) The guide shows the procedure for generating the first half wave on a pin, and the second half wave on another pin. Then, the voltage difference between them is taken, with a circuit called "H bridge". Is there any method to generate the full waveform directly on a single pin?


texts:
I'm working on this circuit below:

What is the functionality of R2 here? Stabilizing the input voltage? (If it was, it would've been connected in series, right?)


texts: Multiple 4-Digit 7 Segment Displays with Arduino

texts:
I have 3, 4-Digit 7-Segment Displays from Adafruit, and the included docs/ libraries say I should connect the display to pins A4 & A5.  However, I have three of the displays, so I am looking for a way to connect one to pins A1 & A2, another to A2 & A3, and the 3rd to A4 & A5.  I've looked through the included docs/libraries, but I can't seem to figure out what to change in my code or the libraries.

Here is the code I use to initalize them:

Adafruit_7segment matrix = Adafruit_7segment();

I'm hoping for a solution in the form of:

    Adafruit_7segment matrix1 = Adafruit_7segment(1);
    Adafruit_7segment matrix2 = Adafruit_7segment(2);

or something similar.


texts: Why Webench power tool suggested using this Hot-Swap Controller (TPS2420) for my design?

texts:
I was trying to build dc to dc converter that has one input which is anywhere between 9V-20V and has 4 outputs: 5v @ 2.5A, 3.3V @ 2.5A, 3.3 @ 1.5A, and 1.5V @ 1.5A. So, I sequenced the outputs and checked the Hot-Swap box and clicked next, then I noticed that my generated circuit has the TPS2420 as a Hot-Swap Controller which can have 4A as a maximum output current while the total of needed currents through the 4 outputs should be around 8A !!!!

Kindly, what is the thing that I'm misunderstanding here?!

Image-1

Image-2

Image-3


texts: TL16C550 UART doesn't transmit, baudout is permanently high

texts:
I've got a TL16C550CIFN UART wired up to a MC68000 softcore in an FPGA.

The UART seems to be working correctly in that I can write the registers (I'm toggling OUT1 and OUT2 etc) but the baudout pin is constantly high and the transmitter empty flag never clears. I guess the baud generator isn't working or I'm missing something else. I have tried a few external crystals and they seem to oscillate correctly (I can see the clock via my logic analyser) and I've tried hooking up the clock input to a clock generated from the FPGA. In both cases baudout is constantly high, the transmitter empty flag never clears and nothing seems to get transmitted.

I have tried about 8 different chips.. so unless I have a really bad batch I don't think it's an issue with the UART itself. I thought it could be that the UART disables the baud generator when the carrier detect etc signals aren't right so I wired everything on the board to look like a null modem. Still no joy. :(


texts:
I have a workstation that's becoming a little long in the tooth, as it were.  It's a rock solid system, but about a year ago it had a faulty power supply that I replaced.  During the past 11 or so months, it's run just fine, but recently it again had a "hiccup" where it just died (no panic) and then rebooted.  I suspect the power supply again, but I just don't know.
 (Unfortunately the power supplies are not cheap for this server.)

It got me to thinking: Is there a way to test power supply input and output to find out if and when a power supply fails or is failing?

It seems as though there should be a way to measure both of these in/out lines (realizing that DC out on the inside is a little more involved) to monitor such issues...


texts: Problem connecting INA114 with LM331 for voltage to frequency conversion

texts:
i'm actually using a load cell and i would like to send the load cell information to an android tablet through jack audio.
Then load cell caracteristics are presented here: http://www.phidgets.com/products.php?product_id=3134

I'm using first an instrumentation amplifier, INA114 with a 1000 gain, to amplify load cell output and it works fine.

The second step is to build a voltage/frequency conversion with LM331.

When i test the V-F circuit with a variable DC supply it works fine  but when connected to INA's, the output of V-F converter saturates (directly to 5v) and i don't know why.

Did anybody have the same problem; any help would be really useful


texts: I am trying to interface JHD12864E graphic LCD with an ATmega32 controller. I simulated it in proteus using the LGM12641BS1R model. Both are KS0108 compatible so I thought it should work. I have written some code using the procyon avr library. The only change I did was to modify the code for a active high RST signal (in place of an active low signal as on LGM12641). For that I changed the function glcdreset and added a not in the if condition. Also in the proteus model I added a not gate primitive before the RST signal. So now I guess my model and the actual chip are compatible. And it works too, in simulation. But when I burn it on the ATmega32 chip I do not get anything except the LED backlight. I have double checked the wires and they are in order. What else may be the problem?


texts: Is it recommended to add external ESD protection to devices that have internal ESD protection?

texts:
I have to design a system composed of a main PCB and enclosure (with multiple interfaces - UART, RS-232, SPI, I2C, GPIO) and an external interface board without enclosure (with only connectors for external devices/sensors). The two are connected via a 64-pin ribbon cable.
I would like to ensure ESD protection and I was thinking of putting ESD protection devices on the external board. However, some of the circuits located on the main PCB (such as the RS-232 transceiver or I2C-SPI bridge) already integrate ESD protection.
So, is it really necessary to add external ESD protection in this case?


texts:
I'm (kinda) new to electronics and I have a simple question... So, I have a phone charger and I cut the wire because I wanted to connect the PWR and the GRD to another circuit. But when I connected the multimeter to the wires I get no readings. I believe this has to do with the wire (it has multiple copper wires...)

I'm used to work with simple wires on arduino (not the copper ones) and this may be a dumb question but i'm really lost here :(


texts: How to understand mosfet capacitance characteristics?

texts:
I am looking at the following capacitance characteristics of the n-mos FDS6680A (spice model):

How do I understand this graph regarding the conditions? Let's take Ciss for example.

From what I understand, Ciss = Cgs + Cgd with Cds shorted. So how can Ciss in the graph then vary as a function of Vds if Cds is shorted? Vds should by definition be 0V.
It seems for the graph Vgs is fixed at 0V. How then does the f=1MHz come into play? Which voltage is alternating and with which amplitude?


texts: Should SMB capacitors read their values after soldering onto a board?

texts:
I am doing an SMB soldering project. I Have here 3 ceramic capacitors, 100nF, I test each one after soldering to the board.

Oddly, the capacitor at the top of this image is not reading any capcitance at all when soldered. When I desolder it, it reads 100nF.

All other capacitors read 100nF when soldered.

Is this a sign of a problem, or can this be absolutely normal! Please advise.


texts: Scaling up NTC measurement through Multi-Channel Ohm meter

texts:
For a test bed, we want to measure temperatures with NTC sensors (~10kOhm at RT) for the range 10°C to 70°C. Our test machine accepts auxiliary signal through CAN-bus, so we used a Raspberry with a "CAN-hat" to prototype the temperature measurement (three-point probing) and configure the test machine.

We now want to scale it up to 80 (phase 1) then 320 (phase 2) channels. We already have all the necessary NTC sensors (recovered from previous projects).
So far we have 2 solutions which are not satisfying:

An all inclusive solution by a provider for a hefty price
Acquiring eight 10-channel Ohm meters + eight RS-232 to CAN. That's about $100 to $150 per channel. That would slash the price in 2 compared to solution 1.

In both cases, that's more than the cost of the RPi + the CAN-hat per channel. I would expect that scaling up a prototype would mean reducing the price per unit.

Is there any less resource-intensive solution(s) we are missing?
Ideally measurement with 3 or 4-point method would be wished.

Thank you.
edit: accuracy around 1K, resolution around 0.1K.


texts: Is it safe to bundle together 380V cable + 24V signal cable + network cable?

texts:
I have the following cables between two machines:

380V 3-phase power cable
24V signal cable
EtherCAT cable

I would like to create an interface using a modular connector such as the one in the picture below.
My question is it safe to put all these cables in a single connector (the cheaper option) or should I put the 380V cable in its own connector (the more expensive option)?


texts: Raspberry Pi 4 won't boot with current sensor connected

texts:
I have a problem when trying to boot my Raspberry (c03111)  with a current sensor connected.
The Joy-it COM-KY053ADC is used to translate the analog signal of the current sensor (LEM Hass 50-s) to I2C (which works fine.)
It is powered via an external power supply using the 5V-pin, so it should get enough power.
When I disconnect the sensor from the analog input of the ADC the Raspberry boots.
This is my circuit:

Do you know what could cause the problem?
Datasheets:

ADC PCB: https://joy-it.net/files/files/Produkte/COM-KY053ADC/COM-KY053ADC_Manual_2021-01-20.pdf
ADC: https://www.ti.com/lit/ds/symlink/ads1115.pdf?ts=1612705175707&ref_url=https%253A%252F%252Fwww.google.com%252F
Current Sensor: https://www.lem.com/sites/default/files/products_datasheets/hass_50-600-s.pdf


texts:
I have a few FTDI FT232H breakout boards from Adafruit. I wanted to connect multiple of them through a USB hub. I was under the impression that the serial number is unique and based on "The serial number consists of 8 characters, the first two being the manufacturer ID and the next 6 being base 36 numbers based on the date and exact time of programming." as per https://www.ftdichip.com/Support/Knowledgebase/index.html?howistheautomaticserialnu.htm.
But when I run my code to identify the devices. I see
Channel number: 0
Description: FT232H
Serial: FTKIJX5M
ID: 67330068
LocId: 13377

Channel number: 1
Description: FT232H
Serial: FT3ZQ7NY
ID: 67330068
LocId: 214084

Channel number: 2
Description: FT232H
Serial: FT3ZQ7NY
ID: 67330068
LocId: 36

Channel number: 3
Description: FT232H
Serial: FTOVSJUB
ID: 67330068
LocId: 35

Channel number: 4
Description: FT232H
Serial: FTOVSJUB
ID: 67330068
LocId: 13378

As you can see I have two FT3ZQ7NY, and two FTOVSJUB, and one FTKIJX5M, is there a way to make it unique because all my devices and attached peripherals are identical in nature. Is there any way to uniquely identify the device?


texts: Designing Excess 5 to BCD using Binary parallel adder

texts:
I've been trying to form a combinational logic circuit of converting excess 5 to BCD. I've been able to make a normal logic circuit but I do not know what a binary parallel adder is.

My attempt - formed the truth tables. Got the min terms and Drew 4 kmaps to simplify it. It gave me the normal circuit.
How do I implement binary adders to this


texts:
I have constructed a piezo-resistive sensor using graphite. I managed to obtain the output voltage of 0-5V by using the ADC of my Arduino to read the sensor. But I have no idea how to calculate its sensitivity. Any suggestions?

Some things on this post were similar to my question: Calculate G's of an Accelerometer

But I need to know how to calculate the mV/g instead of getting it from the datasheet.


texts:
simulate this circuit – Schematic created using CircuitLab

I am doing a clamper circuit as shown in the above figure, I am confused regarding its operation when diode is forward biased we have a sinusoidal output, as the circuit is clamped to V2 but what I am not getting is when diode is forward biased shouldn't the output be constant V2, as at node for 1 we get V2 when diode is short circuited.
Can you please help?


texts: 12V voltage regulator with the least drop out voltage

texts:
I have a DC adapter rating 12 V 750 mA. I broke open its case and saw that its rectified but not regulated.

I need 12 V for my design and do not want to buy a transformer. Do you know of any regulator with the least dropout voltage?

I know LM317 is adjustable and its Vdo is 1.2 V(min) but can't use that because then regulated voltage will be 10.8 V and I need 12V regulated.

I haven't tested the adapter yet, will do that tomorrow its offload voltage.


texts: How to find Z impedance if I have only S11 (db) and phase

texts:
I need to measure Z line impedance. Using VNA I measured S11 it is -53.8785 dB and phase at this point is 175.6706.
Could you explain using these numbers how to find R and jR
S11 = (Zx-Z0)/(Zx+z0) = -48.1777939889323
I calculate it and I received a negative number how could it be?
Kind regards


texts: How to compute the maximum power I can get from an optical fiber?

texts:
I'm thinking of a project which requires powering a device with an optical fiber, but I don't know how to compute the maximum amount of power it can supply at the end.

These are the parameters I know:
 - The diameter of the fiber
 - The materials used in the fiber and its properties.
 - The length of the fiber


texts:
I'm planning to use the FT232R in my USB device. The device consists of the FT232R and a dsPIC33EP64MC202 (Basically speaking, the FT232 and a microcontroller only).

On the FT232R's datasheet, at the end of page 26, section 6.4, it talks about another possible configuration, using an LDO voltage regulator, which would be supplied by the 5V of the USB bus. This LDO can be used to supply between +1.8V and +2.8V to the VCCIO pin and to the external logic.

So, I have some doubts:

Why does the LDO regulator voltage need to supply 1.8V to 2.8V? I made this question because we can connect the 3.3V pin to VCCIO either, and the 3.3V pin has 3.3V, no?
I'm planning to make PWREN# and SLEEP# available to be used by my microcontroller to verify and decide when and how to enter in low power mode. Is there a problem in doing this?
The voltage source that drives the TX_LED and the RX_LED is the 5V from USB bus, and not the 3.3V from LDO, correct?

Here is another version. In the next picture, the VCCIO pin and the external voltage supply are supplied by the 3.3V pin from the FT232.

I'm not planning to make my microcontroller follow the Low Power mode protocol, at least not for now. But, configured this way showed in the second image, the FT232 can interrupt the current to my microcontroller. Am I right?

What do you think about these schematics, I'm afraid to have some electrical mistake, because the device will need to be available on a server to be accessed by other people.

Any help would be very appreciated.

From tips and alerts made by Maple, I made some corrections, I came to this solution:

The LEDs RX_LED and TX_LED are not necessary, so I took them out


texts: How ICBO gets amplified to ICEO in BJT when base is open

texts:
I have been doing some reading  about ICEO and ICBO, but couldn't really understand how ICBO is getting amplified (1+ beta) times to reach ICEO, in the open base condition.

This is my understanding so far.... The ICBO flows from collector to base. You talk of ICEO when the base terminal is open. The ICBO will actually have to flow through the emitter to reach back the collector.The textbooks say, now the ICBO also gets amplified "just like IB", to get a bigger value : ICEO.

But our transistor now has only 2 terminals.. how does the transistor amplifies the ICBO to ICEO with just two terminals?


texts:
Good morning/afternoon/evening everyone

This is my first time posting, so please excuse if the format is not 100%

I'm trying to build a circuit, that has logic pulses from a gap sensor as input. The circuit has to output a logic pulse once the count has reached 20.

So far I have successfully created a circuit that displays the count of logic pulses by using two seven segment displays. The displays also successfully reset once the counter has reached twenty, however there are two issues I'm struggling with:

Instead of using a gap sensor, I have used an Ac voltage source, coupled with a diode, where I have adjusted the frequency, to essentially act as a source of logic pulses. Is this correct, or should I directly try to implement the gap sensor.
I'm struggling to implement an output that outputs a logic pulse once the counters reached twenty.

I have included a simulation of the circuit. The top seven segment display counts the "ones" and the bottom one counts the "tens".

Thanks for your time.


texts: Does a MAX485 need decoupling capacitors?

texts:
I am designing a small device with two MAX485 chips.

Do they need the decoupling capacitors on the 5V power?


texts: dead car battery charged using solar panel?

texts:
I have 12v calcuim+ battery was on my car but now it is almost dead (8.9v) I bough solar panel and charge controller to charge it.
i put it in the sun for two days and now it is 10.5 volts but still dead as it didn't charge yet.
i am not sure is it effective way to keep it for another few days or it is not even possible to charge it?
i have seen the questions here and over the internet all the batteries were not dead and also i didn't see the calcuim + battery
The solar panel is 50W
thank you all.


texts: Overlapping GND and PGND on different layers of a PCB

texts:
I have a 6 layer PCB that is populated on both sides. The PCB mainly consists of power supplies (PoE, battery charger, buck converter) and a uC and a controller. The Layer stackup is: TOP Signal - GND - Power - Signal - GND/Signal - Signal Bottom.
At some areas, the GND, PGND and BATGND are overlapping on different layers (mid-layer 1 and 4). However, I made sure that the components directly above the ground layer are corresponding to the correct ground.
Do you think this could be much of an issue?


texts:
I calculated R thevenin to be 5.322 ohms, but I don't know how to get a voltage after this step. I tried to use node voltage equations since V thevenin is he voltage across the terminals, but it didn't work out... I had:

va-vb=-I1[the current in the loop with V source, clockwise]*8ohms +55V=59.4V

I1 was gotten from mesh current analysis and I1=-.55


texts: AVR interrupt setup seems to stop program execution

texts:
On ATMEGA168PA I have problems with interrupt-driven character reception over UART. When I include the line setup_interrupt() it seems that program execution stops after one iteration in the while-loop (one blink and one "HOWDY"). Optionally it executes continuous interrupts.

The uC stops in the sense that it appears not to be doing anything. No blink. No "HOWDY" sent out on the UART.

The UART works. I have verified that it can send and receive characters (receive using polling).

Same interrupt-driven reception worked well on ATMEGA64.

What can possibly cause the program to stop execution? Any help appreciated.

#include "project.h"
#include "drivers.h"
#include <stdlib.h>
#include <avr/io.h>
#include <avr/interrupt.h>

#include "uart.h"
#include "util.h"
#include "leds.h"

// Parameters for serial port
#define BAUD            2400
#define MYUBRR          F_CPU/16/BAUD-1

// Parameters for menu
volatile char action             = 0;

// Global debug flag
uint8_t           debug_global   = 1;

int main(void)
{
   setup_portb();
   green_off();
   cli();
   uart_init( MYUBRR );
   setup_interrupt();
   while ( 1 )
   {
      blink_025_sec();
      UART_sendLine("HOWDY!");
   }
}

ISR( USART_RX_vect )
{
   blink_05_sec();
   char receivedByte;
   receivedByte = UDR0;           // Fetch the received byte value into the variable "ByteReceived"
   if ( debug_global )
   {
      UART_sendChar( receivedByte ); // Echo the received byte back to the computer
   }
   action = receivedByte;
}

void setup_interrupt()
{
   //EIMSK |= _BV(INT0);  // Enable INT0
   // Set Global interrupt ENABLE flag
   sei();
}

My UART init looks like this:

#include <avr/io.h>
#include "drivers.h"

void uart_init(unsigned int ubrr)
{
   // Set baud rate
   UBRR0H = (unsigned char)(ubrr>>8);
   UBRR0L = (unsigned char)ubrr;
   // Enable receiver and transmitter; enable RX interrupt
   UCSR0B = (1 << RXEN0) | (1 << TXEN0) | (1 << RXCIE0);
}

  The execution stops even if there are no data on the UART RX line (no interrupt is triggered)? – Bence Kaulics 5 hours ago

-Yes. It does not react to incoming chars from the serial port.

UPDATE:
The comment from "user57709" was the key: I commented out the line EIMSK |= _BV(INT0);  // Enable INT0

That made the program work as expected. If I understand the data sheet correctly, there is no need to enable any external interrupts like this one when using the RXCIE flag in the UART. The specific pin is not connected to anything.

Apparently the uC got stuck executing continuous interrupts because of this.

Thanks for the help, "user57709"


texts: Non intrusive controlling & monitoring system

texts: I have read and researched online about electric monitoring systems like the kill a watt and wattspn and i have observed something in vpmmon, they do reuire intrusive devices like sockets as means of controlling (on or off the devices) and monitoring mechanism. Now  is there a diffent way or idea in order to control and monitor electric appliances in a non intrusive way (without using additional sockets to be placed on each load)? I know non intrusive mechanism can do monitor stuff like what is on or off through voltage variations, but it cant control the loads like turning them on or off. Thanks


texts: Op Amp Integrator not working with DC Source

texts: I am creating an Op-Amp Integrator circuit in Multisim. It seems to work for sinusoidal voltage inputs, square wave inputs, etc but when I connect it to a DC source the output voltage (channel A in the diagram below) just immediately goes to -11V. Based on the integrator equation (-1/RC)*integral(v(t)dt), the output voltage should be equal to -0.4t (-0.4 volts per second). I have tried using a bunch of different values for R, C and Vin. The Op-Amp is a 741 Op- Amp. Thank you for any advice.


texts:
simulate this circuit – Schematic created using CircuitLab

Hi,
I am trying to build a 5VDC from my 220VAC (Switched-mode power supply). The first step is to convert AC-DC. Above is my schematic

V1 is 220VAC, the peak is about 300V.
C1 and C2 are the same, each has 200V voltage max rating.
Thermistor is MF72-5D9 Surge Current Limiting.

When I turn on the power, F1 blows immediately. I do not know why. I check them out, no shortcut. Can someone help and tell me why?
Thank you very much!

EDIT: I found the rating of F1, it's 5A 250V.


texts: Measuring soil resistivity and estimating soil equivalent resistance in a long distance

texts:
I'm trying to size the Neutral to Ground resistor (NGR) in the Wye of a 138 KV to 4160 V Delta-Wye Transformer. In order to find the proper value I have estimated the charging current of the system by following the instructions in this page section “Estimating”. And later reading the article "Charging Current Data for Guesswork-Free Design of High-Resistance Grounded Systems" supplied as reference in that page. After my study I realized that in case a fault to ground occurs in any of the 4160 phases (2400 V phase to neutral) a lot of current will flow through ground (soil) back to the star point of the Wye and this will be limited by the NGR. Let's say I will allow 150 A (low resistance grounding) to flow. At 2400 V that is a 16 Ohm NGR.

Now reading the standard CSA M421-16 Use of Electricity in Mines they say "In resistance-grounded systems, it is standard practice to assume zero-impedance fault paths and consider only the neutral-grounding resistors to calculate prospective ground-fault currents."

By reading this, anyone may think that earth(soil) has no resistance to the pass of current. So I started to study that. First I selected my worst case scenario, a fault on my furthest point, which is 1.2 miles (1931 m) from the transformer. And then I tried to find out earth resistivity. Turns out it varies depending on many things (mineral composition of the rocks, humidity, salinity, temperature, the mood of the guy making the measurements, etc ).

For instance a couple of the articles explaining soil resistivity can be found here and here. Let's assume for an example that the soil is composed of sand with a resistivity of at least 100 Ohm per meter. The soil equivalent resistance would be 1931*100 = 193100 ~= 200 kOhm. That is not something to ignore compared to a 16 Ohm NGR!!! Earth will stop charging current much more that the NGR.

Why isn't this considered?

Maybe my assumption about earth(soil) is wrong, I kind of see that with distance earth is a series conductor but also many parallel conductors, so maybe the 2 effects will compensate and resistance value will tend to a constant value (a friend of mine named this Remote Earth model)

Is there a mathematical way to model my remote earth and to know in practice how much resistance will my soil have at such a distance? If I assume my soil is sea water that is still 1 Ohm/meter. I guess that it may affect my decision of which NGR to select.

Update: It is always easier (and the standard does this) to skip such a complicated measurement (the equivalent resistance of the soil). Even more when its value changes depending on so many factors and rely only on the NGR for limiting the current. Anyway this is the worst case and you can never go wrong if you are protected against the worst case. But, am I wrong by thinking that without an NGR when a ground fault occurs, thousands of amps will flow through ground? If this is the case then the soil itself must not be of such high resistance value. Has anyone seen such thing as a study saying how many ohms a mile of dirt is equivalent to? I would die to see such thing.

Update 2: checking this document it says :

The ground electrode is surrounded by earth which conceptually is made up of concentric shells all having the same thickness. Those shells closest to the ground electrode have the smallest amount of area resulting in the greatest degree of resistance. Each subsequent shell incorporates a greater area
resulting in lower resistance. This finally reaches a point where the additional shells offer little resistance to the ground surrounding the ground electrode.

They don't quote any reference for claiming this. Does anybody know where they got this from and if I can make this same assumption for very long distances ?


texts: Electric Tester light up on secondary side of Ground

texts:
I have assembled a PCB, which takes mains input 240VAC line and Neutral (my system enclosed in plastic case , so no ground/earth is provided) , and it use on board SMPS module(https://www.meanwell.com/Upload/PDF/IRM-10/IRM-10-SPEC.PDF ) , there are also some DC to DC regulator which convert SMPS 15V to 5V and 3.3V.

I power up the board i check all Voltages are OK. I observe one thing here whenever i touch digital ground (mostly) i feel kind a very little shock, I took electric tester and put it on the Digital ground pin on PCB , I saw the bulb in tester glow.

I checked SMPS datasheet (link mentioned above) , has leakage has 250uA only at 240VAC , they why electric tester glow on this little current and why i getting little shock when touching PCB digital ground, Wondering SMPS has UL mark.


texts:
I am working on a flight control board inspired in this Sparkfun board:

http://cdn.sparkfun.com/datasheets/Dev/Arduino/Boards/RedBoard-v21.pdf

It is basically an Arduino UNO with a FTDI chip instead Atmega8u2 as USB-UART bridge. It manages power stage in order to allow both USB and Jack connector at same time. In my device I want to allow both USB and ESC power options. My question is, can I replace the Jack connector and the LDO and just connect the 5V output of my ESC in the 5V wires of that schematic?

Something like this:

I actually don't know how smooth ESC's output voltage is. Maybe it is a good idea to let the LDO and connect the ESC over the jack input.


texts: Why is it desirable in an amplifier to have high input impedance and low output impedance?

texts:
I've learned that it's desirable in an ideal amplifier to have high input impedance and low output impedance. Why exactly? What are the implications an amplifier has the opposite- low input impedance and high output impedance.

I don't exactly understand how impedance input and output.


texts:
First post! Please bear with me...

I am an electrical tech and EE student with no design experience. This is the first circuit I've been asked to design. I have been given the task to take the input from the existing circuit to switch the inputs of the PLC. The PLC has ground switching inputs with the "0" state being 18-30V. I need SW1 to provide a low to the PLC input when closed, and nominally 24V when open.

I ran a SPICE simulation of this circuit, and it appears as if it will work. However, I'd like to know if I am taking the right approach. There will be a total of 60 such circuits on a single PCB.

The darlington array is part of an octal IC so I could get my 24V 'off' state at the PLC. I am using an octal inverting buffer IC so that the input of the existing circuit is not inverted at the PLC. R6 is to pull up the voltage to 5V at the input of the inverter.  I am using R2, R3, D2, D3 for input protection based off the information I read here:

http://www.digikey.com/en/articles/techzone/2012/apr/protecting-inputs-in-digital-electronics

I believe I was using the SN74ALS540 as the inverter. Is the external input protection necessary here? Since I am doing a board layout of 60 circuits, it would make my life much easier if I could omit it. I chose D1 as a schottky for the low forward voltage, so I am well below the V_IL of the inverter.

I appreciate any suggestions/constructive criticism.


texts: TPS541620 Buck converter IC - Feedback loop

texts:
I've been designing a POL supply using TI's new TPS541620. This seemed to be a good choice but it being new, it's quite hard to get more support than the datasheet can provide. And unfortunately some things are missing from it...
Looking at the Dual Independent Outputs application information, there is a 49.9kohm resistor called \$R_{inj}\$ in series with the \$R_{fbt}\$ resistor in the feedback loop.
There is no mention of the \$R_{inj}\$ resistor in the datasheet, and having it here doesn't make sense. According to the datasheet, to select the output voltage, you need to put a voltage divider with a 10k bottom resistor. The top resistor value can be chosen with the following equation (where \$V_{fb} = 0.5V\$ is the reference voltage) :
$$
R = 10k * \frac{V_{out} - V_{fb}}{V_{fb}}
$$
In their example, \$V_{out}=1V\$, so they take a value of \$R=10k\$ which makes sense. But if you add the 49.9kohm to it, then the output voltage would be \$V_{out}=3.495V\$.
I am far from being an expert in designing power supplies, so I'm listening if anyone has an explanation.
Thanks !
PS: I would have asked on the E2E forum but apparently my account doesn't allow me to do so.
EDIT:
I've just realized that \$R_{inj}\$ is 49.9 ohms and not 49.9kohms, so it is indeed negligeable.


texts: PIC16F877A : How to keep controller awake?

texts:
I am using Pic16f877a for a Serial Communication. I have a PC-based application which sends data to Microcontroller. Microcontroller receives the data and transmit it over I2C.

But, I am facing an issue. After every transmission, I have to reset the microcontroller for next transmission. I am using ISR (Interrupt Service Routine) for receiving Serial Data. But even ISR is not been called for the next available data. And I have to end up reseting the device.

Part of my Code for reference :

int main()
{
    UARTInit();
    idmInitI2C();

    TRISB7 = 0;
    bool toggleBit = false;
    while (1)
    {
        RB7 = toggleBit;
//        __delay_us(10);

        if ( UART_GetRecvByteStatus() ) {
            UART_SetRecvByteStatus(false);              // Set Received flag False
            receiveDataPkt();                           // Receive Incoming data
        }

        if ( isDataPktReceived ) {
            initIDComm();
            isDataPktReceived = false;
        }

        toggleBit != toggleBit;
    }
    return 0;
}

void receiveDataPkt()
{
    char buffer = NULL;                             // Load character receive to output buffer
    int i = 0, j = 0;
    int buf_count = 0;                              // Count character received
    int dly = 50;                                   // Initialize delay duration local to this section

    initBuffers();

    while ( !TXSTAbits.TRMT );                      // Wait until Transmit shift Register is not Empty,
                                                // a transmission is in   progress or queued in the transmit buffer

    while ( buf_count != MAX_PKT_SIZE ){

        buffer = UART_Read();                             // Read Data

        if ( buffer == 0x00 ){
             break;
        }

        if ( buf_count < MAX_BUF_SIZE ) {
            data_Pkt_1[ i ] = buffer;               // Store data to Char Array
            i++;
        } else {
            data_Pkt_2[ j ] = buffer;               // Store data to Char Array
            j++;
        }

        if ( ( data_Pkt_1[ 1 ] == READ ) && ( data_Pkt_1[ 4 ] == ETX ) ){
            break;
        }
        buf_count++;                                // Increase Count
    }

    while (dly){                                    // delay
        dly--;
     }

    if (OERR){
        CREN = 0;
        CREN = 1;
    }
    RCIE = 1;                                       // Enable Receive Interrupt

    isDataPktReceived = true;
    }

 void interrupt ISR(void)
 {
     if (RCIF)
     {
         RCIE = 0;
         if ( OERR ){
            CREN = 0;
            CREN = 1;
         }

        UART_SetRecvByteStatus( true );         // Signal for Received Byte
    }
}

What can be done to resolve the issue ?? I want to keep it always awake so that ISR can be called for each incoming data.

EDIT:

function UART_Read() for reference:

char UART_Read()
{
    int count = 0;
    char data = 0x00;

    while ( !RCIF ){
        if ( count >= 10 ){
            break;
        }
        __delay_ms(10);
        count++;
    }

    if ( RCIF ){
        data = RCREG;
    }

    return data;
}

( Also I am receiving Max 133 Bytes in one Transaction. )


texts:
I have a custom board with a new platform which does not have any tool to configure the DDR setup( I asked). I have the Source code for the uboot.config (CONFIG_DDR.c, CONFIG_DDR.h etc). So I have to manually find the correct values to start the Linux Kernel. I have the original Uboot-file
EMR
EMR2
ZQPROG
etc
The platform consist of NOR-flash, eMMC, DDR3 and the CPU (with integrated DDR-controller)
I can run the Uboot and upload the OS to the eMMC through a serial interface and ethernet (TFTP). But when it(eMMC) is trying to upload the OS to RAM it fails.
I guess it has to do with the setup of the DDR3 different parameters.
I have tried to modify the Impedance levels and DDR-clock, but without results.
Right now it stops at:

Starting kernel ...

[    3.949129] blk_update_request: I/O error, dev mmcblk0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[    4.483700] blk_update_request: I/O error, dev mmcblk0, sector 1 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[    5.018260] blk_update_request: I/O error, dev mmcblk0, sector 2 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[    5.552826] blk_update_request: I/O error, dev mmcblk0, sector 3 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[    6.087385] blk_update_request: I/O error, dev mmcblk0, sector 4 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[    6.621942] blk_update_request: I/O error, dev mmcblk0, sector 5 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[    7.156531] blk_update_request: I/O error, dev mmcblk0, sector 6 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[    7.691104] blk_update_request: I/O error, dev mmcblk0, sector 7 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[    7.701324] Buffer I/O error on dev mmcblk0, logical block 0, async page read
[    9.281759] blk_update_request: I/O error, dev mmcblk0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[    9.816328] blk_update_request: I/O error, dev mmcblk0, sector 1 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[   10.350884] blk_update_request: I/O error, dev mmcblk0, sector 2 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[   10.885446] blk_update_request: I/O error, dev mmcblk0, sector 3 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[   11.420005] blk_update_request: I/O error, dev mmcblk0, sector 4 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[   11.954561] blk_update_request: I/O error, dev mmcblk0, sector 5 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[   12.489121] blk_update_request: I/O error, dev mmcblk0, sector 6 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[   13.023675] blk_update_request: I/O error, dev mmcblk0, sector 7 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0
[   13.033900] Buffer I/O error on dev mmcblk0, logical block 0, async page read
00:00:16 Timeout. Device /dev/mmcblk0p1 not found
00:00:16
00:00:16 Devices found:
    .
    ..
    mmcblk0boot0
    mmcblk0boot1
    mmcblk0
    ubi_ctrl
    i2c-155
    i2c-154
    i2c-153
    i2c-152
    i2c[   16.357555] reboot: Restarting system

Do you have any suggestions on how to proceed (I am really stuck) or any suggestions on a generic(free) DDR software?


texts: Why is an op amp's bandwidth higher at lower gains?

texts: If I build a resistor network where the op amp has a lower gain, it is able to maintain its gain for a larger bandwidth. Why?


texts: 7809 Linear Voltage Regulator Outputs in Series

texts:
I'm building a linear power supply that converts 120VAC mains voltage into multiple 9VDC, isolated outputs. I'm using this transformer that has the proper primary winding and 8 secondaries that I'll use for the 9VDC outputs. Each channel will look like this:

simulate this circuit – Schematic created using CircuitLab

However, I'll be making a couple of these, and I want one of them to have an 18V output. My first instinct was to wire two of the secondaries in series and use an LM317 to get the 18V like this:

simulate this circuit

Then, I thought in order to avoid designing two PCBs and dividing my order (only making a few), I could just connect to of the 7809 outputs together to get 18V like this:

simulate this circuit

At first glance, this seems ok. Am I overlooking anything? Are there any nuances with the 7809s that would keep this from working? Am I forgetting something stupid?