texts: What are line-of-sight limitations of UHF RFID readers?

texts:
I am looking at some UHF RFID readers for a project and I have a few questions about the overall concept of detecting passive RFID tags.

The system is concerned with keeping track of people passing through a specific point (doorway, staircase, etc.). This is not an access-control application; ideally the people walking through a certain checkpoint would have RFID tags on them but wouldn't take them out for scanning. Sort of like a car passing through an automated barrier after RFID tag detection, only in this case there is no barrier involved.

Think of it as a passive personnel locating system. The system would only keep track of "Person A was last seen walking through stairwell 4, half an hour ago", that's about it.

(Image source)

I have looked at readers like this one with circular polarization antenna and a range of 3-5 meters. I'll be using passive RFID cards. My questions are:

My assumption is that the readers like this work only in a straight line-of-sight. If that is correct, on what factor does the "width" of the scannable area depend? If my assumption is incorrect, does the range of 5 meters mean it's actually the radius of the area that is covered by this reader?
If a scanner like this were to be placed on the ceiling above a door, would it effectively be able to scan the tags passing below it through that door? How big a problem would "shadowing" be in this case (when a person has the tag in their pocket or two people walk next to each other so that the one in front is blocked by the one in back)?


texts:
I read some of Electromagnetic Compatibilty Engineering book and it advices 4 layer stack as signal-ground-power-signal.

I allocated layer 2 as continuous ground nothing else. And since i will drive 4 motors i allocated layer 3 as lipo battery voltage's copper pour. Layer 1 and 4 are for signals and 5v, 3.3v connections that are necessary for mcu type components.

1) Since motors draw too much current 12 amps max each, would this affect ic components and can layer 3 handle this much current for 5-5cm board.Calculator says 50A with 0.7mil copper require around 340mm thickness (If i could use same pcb for power distrubiton to motors it would be nice)

2) Also i need to draw only one 0.5mm trace line for 1.8v from layer 3 is it okey?

Any advice is appriciated.


texts: Does electrical current flow from positive to negative or negative to positive?

texts:
When you listen to people wiring up a DC circuit they seem to mumble about the electricity flowing from positive to negative. However in school I was always taught that DC electricity flowed from negative to positive.

I was googling for this and didn't see the definitive Stack Exchange post. Anything I read either isn't clear about this or is too complicated for me to understand.

Can someone please explain this to me like I'm 5? It seems like one of those things where both sides are right but there is a subtle difference that is difficult to communicate.


texts: Designing a Peristaltic Pump Driver with IRFZ44n Mosfet

texts:
I'm making a peristaltic pump controlled by an arduino. The pump is controlled by a PWM from arduino to a IRFZ44N Mosfet. I have added a pulldown resistor for the gate, and also diode and capacitor for the pump in paralell Here is my schematics, I think it will explains better:

But the problem is, after I have turned on the pump on high PWM (i.e: analogWrite(outputPin, 200)) after sometime the pump would turn on continuously for a while and the arduino would resets. Any idea why does this happens?
The peristaltic pump is 12V 5W, and here the VCC in the schematics is 12V


texts:
I'm trying to build a 555 timer with a 50% duty cycle.

I followed the instructions given here (pg 12).

I used a 470 microfarad capacitor, 150 ohm resistor and a kohm resistor. The output voltage is always low.

I've attached an image of my current circuit and would appreciate it if someone could pinpoint what I'm doing wrong.


texts:
I've been trying to make a voltage regulator using a zener diode.

I used the BZX79 3.3V Zener diode.
I connected the diode as the following:

Data Sheet. I assumed that as as most of them it operates at around 1mA to 10mA safely in the break down region.

I connected my supply which was 5V. The resistance was chosen to be 220 ohms. This will make the max current of the zener around 7mA. Which should be safe.

Now, when the zener was unloaded, I got a smooth 3.3V as an output.

But, when I loaded the zener diode, the voltage across the diode dropped to 2.4V.

Why did that happen?

My assumption is the following:

The load which should operate at 3.3V, is consuming way too much current that the zener current is below the min current. This caused the zener to get out of the break down region.

Is my deduction correct? And what are available solutions, taking in note that I've used probably the smallest resistance possible that is 220 ohms. (At least of what I have).

I also have a supply of 8.4V. Will it work if I connected it directly to the supply?
At the end I will have more current available to the zener even after loading it.

Edit:

The data sheet states that the zener is fine for 6 Amps. That is a huge and weird number isn't it?


texts: Identifying bad LED in series configuration

texts: I have a panel of LEDs. They are arranged in sets of three. Some have burned out, and I can easily find the offending LED with a voltmeter. But some of them are only on the verge of failing - when the intensity is lower, they work fine. Only when the intensity is turned up do they misbehave, and they don't just go out, they blink, several times per second. My (digital) voltmeter is not capable of capturing that. Is there some simple way of identifying the bad LED in such a set? I would rather not do a trial-and-error desoldering of all three.


texts: Laser audio transmitter - need substitutes

texts:
I'm building a laser audio transmitter that uses amplitude modulation to transmit audio via a 5mW laser beam.

The transmitter uses a microphone, an operational amplifier (to modulate the signal if I'm not wrong) and a 5mW laser diode.

The receiver uses a phototransistor and a one watt amplifier along with a 8 ohm speaker to play the audio.

Schematic diagrams are attached. I earlier planned to make the transmitter using a 1000:8 audio output transformer instead of the Op-Amp, but couldn't find it anywhere in India, so I switched to this circuit.

Now the problem is, I am still unable to find the two most critical components - the 7611 CMOS Operational Amplifier and the TDA7205 1W Amplifier.

India has some quite good online component stores, and though they have most of the components, unfortunately  these two are not available.

So this is what I need help with:

-Can I replace the 1W amplifier and the Op-Amp with some other model number (like 547 and 548 transistors are generally interchangeable) available here?

These are the Op-Amps available in India: 741 IC, ICL7650S IC, LF412 IC, LM346N, MC3403, NE5532, OP177, TL082.

These are the amplifier ICs available in India: A7840, AD620, AD623, CA3102E, CD4440, LF398, LF412, LM380N.

-Can you guys suggest me something cool and maybe useful to build? If I won't be able to make this due to lack of components, maybe I can build some other cool circuit. Any ideas?

I'm pretty new to electronics and I'm really excited for this project. Thank you everyone.

PS: Mouser, Digikey etc are not an option to get the components as the component price is $2-3 and their shipping and handling charge is $50+!


texts: Question about straightening the pins of a resettable polyfuse

texts:
I have resettable polyfuses like the picture below.

I am working on some PCB boards where I solder the wires myself on the PCB. Because it is very hard/cumbersome work to solder very small wires, I use the  leads of components to make a path to a nearby component, preventing small wires or tin to be soldered.

However, I am wondering about the specific shape of the leads of polyfuses. Why do they have the bent in the leads(unlike resistors, capacitors and other components)?

Is it that the fuses need to 'stand off' a bit from the PCB, or can I make the leads straight to push the orange part very close to the PCB, to get some extra length of the leads if needed?


texts: Programming microcontrollers: JTAG, SPI, USB oh my!?

texts:
I've noticed, with regards to microcontrollers, there are several way to program them. I am sorta familiar with USB as my Arduino's can be programmed via USB.

What is a JTAG or SPI interface?

Ultimately I know that these interfaces provide a means to flash the chip with new instructions but how do they differ? Are there any advantages of one over another?


texts: MOSFET Gate Saturation Voltage Threshold?

texts:
I would like to turn on a IRF510 MOSFET using a logical "1" @ 3.3V.

According to it's datasheet, the "Gate to Threshold Voltage" is 2-4V...  Does that mean I'll be able to completely turn on the MOSFET using a logical "1" @ 3.3V?

Here is the datasheet for more info:  https://www.jameco.com/Jameco/Products/ProdDS/209234FSC.pdf


texts: Transistor as a switch, what does the inductor do?

texts:
I dont understand what the inductor in this circuit is actually doing. Is there a current flowing through the coil when my input is 0 ? If so, it should be DC so the coil isnt really doing anything special while the transistor BE diode is blocking, so if I increase the base current (with a rectangle voltage source at input) , the current through the inductor changes, inducing a very high voltage since Ul=L*di/dt which flows through the diode as a safety precaution.

What is this ciruit used for ?


texts: What's the current through the 2Ω resistance? The question requires me to find the answer by using Thevenin's theorem

texts:
This is the circuit. I have found Thevenin equivalent resistance to be 5 ohm. Is that correct?
I am not able to find the Thevenin equivalent voltage across the load resistance.

These are the steps that I took to get the Thevenin equivalent resistance:

I removed the load resistance
I calculated the remaining resistances: [(4+6)||(6+4)] = 5 ohm


texts: I took apart an old microwave oven and found the relay the computer chip closes to activate the magnetron. The relay is a DEC DU1PU, made in China. Does anyone have a datasheet for it? I'm mostly looking for the pin-out. I'm wishing to control the relay with an Arduino, if possible.


texts: Reversed universal universal motor sparks and shows arcing even though brushes are completely perpendicular to the commutator

texts:
I need to reverse the rotation of the universal motor in question so I swapped the wires leading to the brushes and that successfully reversed the rotation, but now the commutator is arcing and is producing a significant amount of sparks. It's worth noting that the arcing completes half a circle almost touching both brushes simultaneously.
I tried rotating the brushes 180° because I suspected they were worn out "asymmetrically" despite looking straight (still concave but not unevenly worn) and without a slope but the sparking continued.
Then I sanded carefully the brushes so that they were squared again to sort of resetting them to their factory position so to speak but the arcing still persisted.
The only variable left is that the commutator is not perfectly worn and is making an undesired contact with the brushes.
I want to make clear that the housing of the brushes are not angled in any way to favour any direction of spin and to my understanding, it should be very feasible to reverse the direction.
I also tried sanding the commutator to clean it with fine-grit sandpaper but didn't want to go any further without consulting.
This is the stock configuration:

Stock configuration with commutator more visible:

Brushes view:

"Custom" cables configuration:

Windings closeup:


texts: Safety concerns using metal switches near 300V (low current) lines?

texts:
I am building a nixie tube clock whose power supply in the best (or worst) case scenario will put out ~300V. This is obviously quite hazardous if not handled correctly. I need to use at least 1 spdt switch to configure the clock/switch it on off. Shopping around for switches, I see pretty much all the small flipping type switches are metal.

I managed to get a generic one. When I check for continuity using a multimeter, I can see that the terminals are isolated from the "switch" part which could touch the user, but how can I find out by how much? More importantly, why isn't this sort of thing more defined? Why isn't using metal switches such a big concern? For me it seems like a very big concern. What happens if some wire inside accidentally makes contact with the metal switch case? Why would you take the risk? On the switch it says 250Vac 2A, 120Vac 5A, but I'm thinking this is more to do with the resistance of the switch itself? I.e. how much can pass through it before it can get too hot, cause arcing between the terminals etc? (Correct me if I'm wrong).

I am only planning to switch ~5V for a uC digital signal, and I am planning on integrating a relay to switch the power supply on. Since I want to give this to someone who has minimal electronics knowledge, the last thing I would want to happen is for it to become a hazard. So I want it to make it as safe as possible.

So, my question is quite a general one, what sort of design safety steps do you guys take when you design something like this? Any tips? Why are metal switches so ubiquitous? Because they are more robust? Why isn't the maximum handling voltages clearly stated? How does it deal with sudden voltage spikes?


texts: What happens when the current fed to a device is higher than the specified value?

texts:
I have a solar panel which provides the output of up to 500mA with 6v potential difference. .5A is the maximum current output, and the usual output will be around 300-350mA. Can I use it as a power source to run a computer-fan which is specified to draw 0.1-0.3A with 5v? If it is not, can I use it to run 2 fans in parallel, so that the currents will be split to each?

What happens when the source produces more current than the specified input value of a device?


texts: Interface a 5v pressure sensor with a 3.3v ADC

texts:
I'm trying to interface a pressure sensor (MPXV6115vc6u) with a 3.3v ADC. My board is providing a 3.3v (it's a XBee power regulated board, via a Li-Po battery).

To wire the MPX sensor, I need to:

Step-up the 3.3v to 5v to power up the sensor
Convert the 0-5v analog signal to a 0-3.3v to read the pressure value.

What's the best approach, considering that pressure sensor are noise-sensitive and that my board is low-power?

For 1, I can probably use a circuit like this.

For 2, what should I do to keep the full range? What's the best way to minimize the number of components (~combine 1 and 2).

Thanks!


texts:
I have a system that involves two boards and i2c communication between them.  One of the boards uses 2.8V for i/o (including i2c) and the other 3.3.  The 3.3V board is always the master and the 2.8V is always the slave.  It will never be the case that the 2.8V part initiates a transaction.  There are two board to board connectors between the boards.  The relevant signals passed are +3.3V, sda (either 3.3V or 2.8V), and scl (either 3.3V or 2.8V).  The 2.8V board uses an LDO to generate it's 2.8V locally from the 3.3V.

The obvious solution is two fets and 4 pull-ups, but I'm very space constrained.  I have room for this on the 3.3V board, but not the 2.8V board (even when using 0402 resistors and a small array package for the two fets).  The 3.3V board doesn't have any 2.8V (see above) and I cannot add anymore board to board connectors.

As a result I need to do something else.  I thought about doing the "ugly" thing and putting the fets/pull-ups on the 3.3 board and generating the 2.8V with either a biased zener from the 3.3 or dropping the 3.3 over a shotkey.  That's not super elegant, but would probably work OK (I don't want to add another LDO to the 3.3V board).

Any other suggestions?  Sort of feel like I'm scratching my ear with my toe instead of my finger, but the design is pretty constrained.


texts: Capacitor protection in transformerless power supply

texts:
I am designing a capacitor based transformerless power supply for a WiFi-based device which will be on for 24x7, with an input of 230VAC at 50Hz.
For almost 80% of the time, the device would consume 10-20mA or lower & in peak condition will consume 100 -150mA. This circuit is giving me the desired voltage & power. My goal is that this circuit should have a mean life of 5 years with 24x7 operation.
My concern is regarding C1 & C2 because I don't see any other components getting damaged apart from the MOV & the fuse. I have connected the MOV & a clamping resister to make sure the voltage is within limits. C1 rating is 400V somewhat similar to this & C2 rating 16V. D3 is 1.5KE15A
There are 2 things that concern me.

I am not able to connect any resistor at the return path of the circuit which is shown in most of the schematics. A 100E 5W resistor quickly gets heated to probably 100 C or more, if I connect a resistor with the higher value it works, but I get lower power. I kept this circuit on for ~30mA load & C1 got mildly heated ( ~10C). I was looking for NTC to connect here. Please suggest what can be done to protect C1.
Do I need to consider a capacitor with ~600V rating so that it can have a longer life?


texts: Triggering flashing light from multiple sources

texts:
I'm trying to figure out the best way to approach this;
I have a 120V flashing light which I want to activate whenever one of multiple sources sends a signal. I also want to have a small panel mount LED light signal which source the activation is coming from.
My original plan was to use a 24VDC circuit to and from each source to trigger a relay to send the 120V to the flashing light. The issue I found was that when one source sends 24VDC to the relay (also powering small panel mount LED) it will backfeed to the other panel mount LEDs.
Is this the best approach to the circuit, and if so I'm assuming diodes on each "activation" 24VDC line would solve the issue. Is there a good mounting solution to including stand alone diodes in an electrical enclosure?


texts: Will providing line-level signals into a mic input damage the recording device?

texts:
I've got a cell phone, gopro, and DSLR that I want to record audio into. I don't want to record audio into a separate device.

The problem with analog mic-level (millivolt) signals is that they require amplification inside the recording device before being converted to digital and recorded. The preamp inside the aforementioned devices are all very noisy and all introduce a background hiss into the audio (not difficult when the mic input signals are in the millivolts).

I have a device that can take a microphone and output clean line-level signals of what the mic picks up.

I can rewire an AUX cable so that the mic contacts on the plug output line-level signals from the device above, which means the mic input on the camera would receive line-level signals from the AUX cable.

Would this allow me to then set the camera's internal microphone gain to zero, thus utilizing the noisy preamp to a lesser degree, and result in a cleaner recorded audio? Or do I have a high risk of overloading and damaging the circuitry of the camera?


texts:
I'd like to make a circuit that switches between two inputs. When the control input is active I'd like the circuit to use the second input but when the control input isn't active I'd like it to use the first input.

Basically what I'm trying to do is use a channel of an RC quad-copter controller to allowing remote switching of quad-copter control between a gimbal controller and a flight controller.


texts: (How) can IEC-specification miniature circuit breakers be interlocked?

texts:
A relatively common way of implementing a transfer or bypass/isolation function in North American electrical practice is to use mechanical means to interlock the handles of multiple circuit breakers or molded case switches so that they can't be both on at the same time.  This can be done using a piece of metal retrofitted to a panelboard/loadcenter, or as part of a factory transfer switch assembly that uses circuit breakers or molded case switches as the electrical switching means.

However, the devices used to do this are designed around the North American busbar-mounted types of breakers.  Breakers designed to the IEC standards typically mount to DIN rail instead, using a cable-in/cable-out construction, with a single row of breakers vs. the opposing-columns construction typical in North America.  Is it possible to mechanically interlock this style of breaker (i.e. breaker A and breaker B cannot be on at the same time) without violating its approvals?  If so, how is it done in practice?


texts:
I'm looking for a battery solution for the Beagleboard XM, which requires a 5V power supply. I currently have a simple 4x1.2V AA battery pack, but I'm not particularly satisfied with it:

1) It gets overcharged (~5.2V) and activates the overvoltage detector of the machine.

2) I have to remove the batteries from the pack to put them on a charger every time I need to charge them. I'd much prefer a solution that with no separate parts and one in which you don't need to move the batteries around.

The BeagleJuice is the closest thing I've found to what I'm looking for, but there's no version out for XM yet.

I'm embarrassingly electronics-illiterate, so I don't really know how to go about this. Any help?


texts: Difference between tri-state buffer and inverting tri-state buffer

texts: Is there any significant architectural difference between non-inverting and inverting tri-state buffers? In what cases would it be advantageous to use one over the other? To me they seem like the same thing just differing by an inverter.


texts: What does the recommended values on a motor mean?

texts:
If a motor has a voltage and amperage on it, what do those values mean? (Is voltage how much voltage the battery must be rated? Is amperage how much amperage the motor will use ['pull' from the battery], or how much the battery must produce?)

Does voltage correlate to speed or torque?

Does amperage correlate to speed or torque?

I'm new to electrical engineering, so please don't use complicated terms; assume I don't know. Thank you.


texts:
I ordered 5 nRF24L01+ chips for 2.4 GHz RF. I have not done tests with them, but doing tests with my current 433 MHz results in a low speed, few meters maximum range.

So I expect with my 2.4 GHz RF's I also will need something better.

What I would like is to built these into an enclosure, to communicate about max 10 meters, but with low latency/fairly fast speeds (like 250 kbps). These 10 meters will not have walls, but musical instruments, possibly many mobile phones from audience (also 2.4 GHz I believe), (music) power amplifiers and speakers, wireless microphones, mostly < 1 GHz etc.

My questions:
- Below I put some examples, but there are so many types, which of the types below would be sufficient for about 10 meters (noisy environment) range?
- Did I miss other types which might be more suitable?

2.4GHz (simple ones)
These are the ones I will get soon

2.4 GHz with PA+LNA
These have PA+LNA and an antenna

nRF24L01+PA+LNA YJ-13039
These do not have antenna but have PA+LNA

See Link

E01-ML01DP5 based on nRF24L01P, shielded, builtin antenna?
These do not have a clearly visible antenna (but shielded)

See link


texts: Difference between compensation and using a PID contoller?

texts:
I have a hard time understanding the differnce between the two techniques that are introduces in my textbook, a PID controller and Lead/Lag compensation.

Ultimately we add a new box to our "loop" and change the transfer function of our system(by multiplying the new box's transfer function with the old). And then tune the parameters to get the properties we want.

Are there examples of things that we can accomplish with a PID which we cant with a  Lead or Lag or vise versa? To me it looks like not.

If they are really different could someone try to explain the difference between these control techniques?


texts: Is my calculated capacitor sign correct?

texts:
I have the following circuit where I would like to obtain an analytic expressions for the value of \$Cs\$ and \$Rs\$ only kowning the phasors \$\bar Vina\$ and \$\bar Vinb\$ there displayed, I don't know the value of current \$ \bar I\$

Therefore, applying KNL on the circuit I obtained the following  equations

$$\ \bar I = \bar Vina * \left(\frac{1}{Y}+\frac{1}{Y_{ss}} \right)^{-1}  $$
$$\ \bar I = \bar Vinb * \left(Y_{ss} \right)  $$

where
$$\ Y_{ss} = \frac{1}{R_s}+C_ss   $$
$$\ Y = \frac{1}{R}   $$
$$\ \bar Vina = Vina *e^{-j * \phi_a} $$
$$\ \bar Vinb = Vinb *e^{-j * \phi_b} $$

From the current, since it is the same for both nodes, I can get the ratio between \$\bar Vinb \$ and \$\bar Vina \$ as
$$ \frac{\bar Vinb}{\bar Vina} = \frac{Vinb *e^{-j * \phi_b}}{Vina *e^{-j * \phi_a}} = \frac{\frac{1}{Y_{ss}}} {\frac{1}{Y}+\frac{1}{Y_{ss}}} \Rightarrow\frac{1}{\frac{Y_{ss}}{Y}+1}  = \frac{Vinb}{Vina} e^{j*\left(\phi_a -\phi_b \right)} $$

Given that I am interested in \$Cs\$ and \$Rs\$, using above equation I can replace their admittance as follows

$$ \frac{1}{\frac{Y_{ss}}{Y}+1}  = \frac{Vinb}{Vina} e^{j*\left(\phi_a -\phi_b \right)} \Rightarrow  $$
$$ \frac{{Y_{ss}}}{Y}+1 = \frac{Vina}{Vinb} e^{-j*\left(\phi_a -\phi_b \right)} \Rightarrow $$
$$ R *\left(\frac{1}{R_s}+C_ss \right) +1= \frac{Vina}{Vinb} e^{-j*\left(\phi_a -\phi_b \right)}$$

Expressing the polar complex into its cartesian value would lead to

$$ s=j*\omega \Rightarrow \frac{R}{R_s}+1 +j\omega RC_s= \frac{Vina}{Vinb} \bigl( {cos\left(\phi_a -\phi_b \right)-j*sin\left(\phi_a -\phi_b \right) } \bigr)  $$

And finally equalizing real parts and imaginary parts I come up with

$$\frac{R}{R_s}+1 = \frac{Vina}{Vinb}cos\left(\phi_a -\phi_b \right) \Rightarrow R_s = \frac{R}{\frac{Vina}{Vinb}cos\left(\phi_a -\phi_b \right)-1} $$
$$ \omega RC_s= \frac{Vina}{Vinb}\bigl(-sin\left(\phi_a -\phi_b \right)\bigr) \Rightarrow C_s = \frac{1}{\omega R}\frac{Vina}{Vinb}\bigl(-sin\left(\phi_a -\phi_b \right)\bigr)$$

So my questions are two these two

-Are these expression correct? if so,

-What does mean the negative value ( coming from the term \$-sin\left(\phi_a -\phi_b \right)\$) that affetct to  the capacitor, since I know that a capacitor should be positive

Thanks in advance,


texts: PIC18F14K50 with 8Mhz crystal and 50Hz PWM

texts:
I'm looking to generate between 50Hz to 150Hz square waves with a PIC18F14K50, which is running with an 8MHz external crystal (XT).

Apart reading an analogue value for the frequency from a pot and displaying the value on a 7-seg display, the PIC doesn't do anything except the square wave.

My options are to either use the PWM module or just write code that alternates the relevant pin between 0 and 1. I don't necessarily mind doing the latter, except there will be a slight interruption when I periodically (maybe a couple of times per second) fetch the potentiometer value from the ADC.

I've never done PWM before so I looked it up. There is one place where you can type in your MCU's frequency and your desired frequency, and it'll give you the corresponding XC8 code. When I tried this, it seems 8MHz might actually be too fast, and I cannot produce a 50-150Hz square wave with the PWM module. My only option is to move down to 500kHz or to use the manual method.

Is this correct? Can I really not produce a 50-150Hz square wave using the PWM module if my MCU is running at 8MHz? Is there any better way to achieve this square wave?


texts: V-meter's value is stabilizing when measuring

texts:
I am curious about my V-meter behaviour. Sometimes when I measure voltage the voltage showed by V-meter is slowly dropping until it stabilizes after few seconds. And same for current, except current is slowly rising. But not always, just sometimes. I heard that when measuring bias conditions of MOSFETs with V-meter (gate voltage is a good example, or the voltage divider in front of it) has similar effects on V-meter, when voltage is measured.

I think there is nothing wrong with my multimeter since this effect occurs occasionally.

Questions:

Do these effects occur in V/A-meter due to high resistance of the circuit to be measured?
Should I wait until the value stabilizes and then take notes (for calculation, circuit understanding, etc.)?


texts: Can anyone identify what this smd component is?

texts: It’s on a Pentax camera lens. I know it’s made by Murata. Believe there are six terminals.


texts: I have a 5 pin trim pot I desoldered from an old board. I am assuming maybe it is a dual gang poteniometer or something with a common ground pin. Does anyone have any ideas what the actual pinouts could be and how I can test it to check? There is number on the side that says 2889, but I am not sure what that means (I doubt its a part number). Here are some images of it:


texts: What are voltages at these points in this opamp circuit equal?

texts:
I know V1 is equal to V2 because my professor  said there is no current flowing between the two points, because there is infinite resistance. But if there is really large resisitance, shouldn't the volage also be very large?

Second, I don't know why V2 is Vs. I know there is a ground symbol, but it's not on the branch where the battery is.


texts: why use of 1uf capacitors in max232 ic, why does not use 10uf capacitor in max232 ic.?

texts:
I have use 1uf capacitor in max232 circuit
c1=1uf (pin 1 and 3)
c2=1uf (pin 4 and 5)
c3=1uf (pin 2 and vcc)
c4=1uf (pin 6 and gnd)
c5=0.1uf (pin vcc and gnd)

why this type of values used?


texts: I found these triangular solder joints in a 24v power supply. Why are they made as triangles? This is the first time I have seen it and I was unable to google anything about it.


texts:
I watched an interesting video in which the caster reverse engineers a modern 850W computer PSU. From this teardown one can see that 90% of the bulk of the PSU is devoted to synchronous conversion of the 120V input to the ultimate output which is a 12V flyback transformer. Once this 12V DC source is obtained, the outputs are generated using either direct output from the transformer or the output from two different synchronous buck regulators (one for 5.5V and 3.3V). In general, once the 12V is obtained, the only things downstream in the power supply are the following:

5V buck regulator
3.3 buck regulator
voltage sensing circuit board (sends "power good" signal to motherboard)
-12V inverter, which is another buck regulator (non-synchronous)

These components compose less than 10% of the mass of the PSU.
So, what I don't understand is, given the relatively small size of these components, why are DC-DC ATX converters so big? For example, PowerStream sells a 650W DC-DC ATX PSU which is just as big as the 850W PSU in the teardown video. But since the PowerStream is taking a 12V input, why does it need to be so big?  Since it would only seem to need the 4 components listed above, couldn't it be much smaller?
One possible clue is that there is a reference to 1500V AC "isolation" in the specs. So, does that mean they are converting the input to 1500V AC, then downconverting again? If so, that would explain the bulk. If this "isolation" is indeed the reason, why would they need to do that? If the PSU is getting 12V power from a battery, the power will be smooth, so why go to all the trouble to take to 1500V AC and back again to 12V DC?


texts:
I am using a Omron relay for DC voltage control circuit. The rated coil voltage is 48 V DC whereas the max tolerance is 110%.

However at site I just realized the measured voltage is 54 V DC, i.e. 1 V DC higher than the max coil voltage. Will it burn the relay? The relay is not used in continuous and is for synchronizing application where it is used once every few months. I am running out of lead time to purchase another relay.


texts: serially connected current source and resistor

texts: In source conversion we can simplify circuit by shorting resistor in case of resistor and current source are serially connected and open resistor in case of voltage source and resistance are parallel y connected. But in case of mesh analysis how I calculate the voltage drop in resistor if the resistor and current source is serially connected? do I short the resistance like we do in source conversion or just multiply the current source value with resistance to calculate voltage drop? e.g: mesh analysis in loop 1 where 4 amp current and R4 resistor are serially connected.


texts:
The recommended power schematics for Atmel's AT32UC3C (figure 6-1) shows the use of 2 decoupling capacitors from the power supply to the digital circuitry, CIN1 and CIN2. These are meant to decouple VDDIO1, VDDIO2, VDDIO3, and VDDIN_5. However, the pin layout of the chip has these pins on different sides of the IC, each with their individual grounds.

The IC is 16mm*16mm so it seems to me that the traces connecting all the pins to a common decoupling capacitor set might get quite long (somewhere I found a recommendation that decoupling capacitors should be within 1/2" of the pins).

Should I duplicate CIN1/CIN2 for each VDDIOx/GNDIOx combination? Why or why not? If not, which pins should I place the decoupling capacitors closest to, if it even matters?


texts: Implementation of a 8-to-256 decoder using BJTs

texts:
I'm designing an 8-to-256 decoder for an SRAM module I'm building for an home-made 8-bit BJT computer.

This is what I've got, which is the straightforward and trivial way:

However, the design requires more than 2000 transistors and about 300 resistors, assuming the use of a common resistor for each BITx and BITx_NOT output.

That's almost 7000 pins to solder, and would require an immense amount of space and time to do.

What are some ways I can optimize the design to require less transistors?

(By the way, I'm aware that the implementation of the actual RAM will require just as many transistors. What I'm trying to do is to only do that once. :)


texts: Connector Problem. How to conveniently connect with cell-phone LiPo batteries

texts:
Using a LiPo battery from sparkfun is easy as it comes with a molex connector on it.

But how to conveniently connect to a LiPo battery taken from a cellphone?

Soldering doesn't work on the exposed terminals of the battery.
I've tried to tie up with sticky tape and thread and glue, but its very unstable/unusable, a slight vibration ruins the connection.

Does anyone here know a better/convenient/stable way of connecting such battery to a circuit?

INFO: I wish to use this battery to power up my breadboard circuits.


texts: ST Motor Profiler and STEVAL-ESC001V1 + ST-Link Connection Error

texts:
I am new to the ST ecosystem.  I have a STEVAL-ESC001V1 demo board and the firmware STSW-ESC001V1 (via STSW-STM32100 which includes Motor Control Workbench v5.4.5).  I also have the ST-LINK v2 debugger and have installed the current firmware on the device via ST-Link Utility (V2.J34.S7).
When I open the project "SDK43x-STM32F303-STEVAL_ESC001V1.stmcx" in ST Motor Control Workbench, I can connect to the demo board via USART (baud set at 115200).  However, when I try and use the Motor Profiler, ST-Link refuses to connect stating "communication error".  The debugger is connected to Windows 10 (VMWare on mac OSX 10.13.6) but no communication activity.  I have ensured my connection via SWD is correct with the demo board per the schematics available for the demo board and ST's user manual UM1075.  The debugger LED is solid red indicating a connection via USB to the PC exists.
I won't sit here complaining about ST's crappy documentation (though I just have), but what am I missing?  I have tried my best to follow the instructions laid before me to use their tools (UM2200, UM1075, UM2197...etc), but I am just banging my head against the wall.  How do I connect and use the ST Motor Profiler?  What am I missing in order to get ST-Link to work with this demo board?  Is the demo board not plug-and-play, do I need to configure something in ST-Link Utilities?
As an aside, I can run a small motor with the demo board while supplying a 490Hz PWM signal from another mcu.


texts: Can I bypass a trace from the diode to the solder point with wire?

texts:
I'm working on the button/power motherboard of an X-Box one's controller - the menu (start) button doesn't work.
I think there might be damage to the trace when I followed the trace to the solder point.
If it is just the trace, can I bypass it from the diode to the solder point with wire, or what would be the best simple fix?
The trace I suspect is broken follows SW5 down and I suspect it is broken after the diode:


texts: Controlling a PWM'ed DC fan from 24v instead of 12V source

texts:
I have a tiny 12V which consumes ~0.07A and i was wondering if i can PWM the 12V fan with a 24V source at a 50% duty cycle through a ardunio and a mosfet. Would that work or fry the fan as the voltage is still 0 to 24v peak to peak.

Thanks,


texts: Attenuation curve of the twisted pair cable

texts:
I'm searching an image of attenuation of twisted pair utp and stp for school report. I googled and I found only utp this curve!

any help?


texts: What kind of radio transmitter would be used on an data collection unit to transmit telemetry over long distances? For example a weather station in a remote location, or in a buoy just off the coast collecting information on currents.


texts: What is the parameter of the power source that satisfies the inrush current of the load?

texts:
Power supplies (more specifically, the SMPS') have voltage and current rating on its label. However, the inrush current supplement capability will depend from supply to supply.

What is the unit of inrush current?

Is it Joules?
Is it Coulombs?
Is it Amperes along with the duration (which is Coulombs actually, with split parameters)?

How can we identify (thus test) the inrush current provision of a power supply?


texts: 555 to debounce comparator output for PIR circuit

texts:
I'm trying to create a circuit that takes an input from a PIR and outputs a high signal when movement is detected. My circuit currently looks like the schematic below (VCC is 5V).

The circuit works and the output goes high when movement is detected however it oscillates (it also only goes from 1.6V to 3.4V rather than 0V to 5V but I don't think this is a big issue - simple transistor would fix I think). I have shown this in the sketch below.

I would like to condition the signal more so that I can put it into an interrupt on my microcontroller to count the number of seperate movements detected (the aim is to count people through a door way, maybe one person every couple of seconds).

I could do this in code by:

Countdown = maximum possible bounce time.
Input from PIR sensor circuit is normally low.
When input from PIR sensor goes high it starts a countdown or resets currently running countdown.
If countdown reaches 0 we have 1 detection.

However I would prefer do do it in hardware so I was thinking that a watchdog timer built around a 555 does a very similar job. Something like:

Countdown = maximum possible bounce time.
Watchdog output is normally low.
Input from PIR sensor circuit is normally low.
When the input from PIR sensor goes high (start watchdog + kick) the watchdog output goes high and starts a countdown (charging a cap).
Every time the input from PIR sensor goes high either: if countdown has not finished (kick) which restarts the countdown (output stays high) or if countdown has finished start watchdog + kick.
When countdown has ended the output goes low (stop watchdog).

QUESTIONS

I know I would need to calculate the correct resistor and cap values but I wanted to know if this is feasible first?
Can anyone give me a quick diagram of how this would be connected up?
If a watchdog circuit is not the right solution what other circuits would you recommend?

Thanks in advance


texts: Thermal noise voltage measured by an impedance matched ADC

texts:
I have a question regarding the thermal noise voltage measured by an impedance matched ADC.

In the figure above, I have a simplified circuit with a source impedance (on the left) and an ADC (on the right). I have modeled the ADC as a matched load resistance along with an ideal voltmeter (this is perhaps oversimplified to the point of being inaccurate, but I'm trying to break down the problem to the minimum complexity. Please let me know if there is a better model.).

I fully understand the typical thermal noise treatment of this problem.

In the figure above, the source impedance is replaced by an ideal resistor in series with an ideal thermal noise voltage source, with  \$\langle V_{th}^2\rangle=4kTRdf\$. In the typical treatment, the noise from the load is ignored, and the question is, how much noise power is dropped across the load from the source? (The answer of course is \$kTdf\$).

However, this is not the question I am after. My question is, what voltage is measured by the ADC? If only thermal noise from the source is included, then we have \$\langle V_{ADC}^2\rangle=kTRdf\$. But, in reality, we also have thermal noise from the load resistance.

In the figure above, the thermal noise from both source and load are included. In this case, the noise voltages should RSS, so that the voltage measured by the ADC should be \$\langle V_{ADC}^2\rangle=2kTRdf\$.

Is this a correct conclusion? If so, I would interpret this result as the ADC having a noise factor of 2, or noise figure of 3dB, since the measured noise power is twice \$kTdf\$. Does this mean that an impedance matched ADC fundamentally has a minimum noise figure of 3dB?


texts: I am trying to build a solar light for my yard using a 6volt,200ma solar panel and 3-1.2 volt rechargeable batteries. I have 8 red leds in parallel each having its own 33 ohm resistor. I am using a bc547 transistor to switch on at night. The collector attaches to the negative side of the parallel leds/ resistors. The emitter goes to negative between battery and solar negative. there is a resistor from the positive side before the leds to the base. also I have a diode 4007 to block current from going backward when not in charging mode. The problem I have is what size resistor goes to the base of the transistor.Please help


texts:
I'm looking at this light sensor:

What exactly is the point of having an LM358 (a Dual Op-Amp I believe) for a Light Sensor?
Maybe I'm missing something....but what exactly purpose does it serve?

I know this is probably a simple and stupid question. But why can't you just read the Analog data out from the Light Sensor?


texts:
I have a wireless keyboard that uses rechargeable Lithium-ion battery, the battery is flat and it won't recharge, instead the circuit becomes very hot. I checked the coponents on the circuit for any sign of burns or faults but every thing seems to be fine, the only peice that's heating up is a 6 pins IC labelled 017tL, i think that it is the battery charge IC, However i couldn't find it on the interent.

This is the circuit and the red line points to the 017tL IC:

I couldn't find any schematics for this device and the 017tL component is not available on Amazon or Ebay, Is there an equivalent replacement part that i can buy?


texts:
I am in a measurement systems class at school, and we have a project to design a measurement system.  I was reading my text book when a diagram caught my fancy, and I thought I would try to build it.  I have a few questions regarding it.

Bipolar Transistor PTAT Cell:
http://i.imgur.com/Slkftk4.png

The governing relationship is that the difference between the two emitter voltages is equal to the thermal voltage times the log of the proportion of the currents

Vptat = Vt*ln(I/Is)

The first question I have is how to do a constant current source to bias the BJT's.  I was thinking along the lines of using a Widlar Current source like so.  http://www.ami.ac.uk/courses/ami4409_amsicd/u01/images/amsicd_btccsd_img08.gif

Secondly, the temperature that this setup measures is the absolute temperature of the transistor because that is what effects the voltage to current relationship.  So, if I wanted to make this cell measure ambient temperature, could I just stick a heat sink over the top of the transistors so the sink would help keep the transistor close to ambient temp?

Thanks,
Jon


texts:
Is it possible to debug an I2C bus effectivaly with a two channel (plus an external trigger) oscilloscope?
I've been trying to do it, to catch a single transaction starting from the start until the end, but I find it hard to set a trigger properly on the scope.

Is it possible to build some kind of logic AND gate with SCL & SDA as inputs, and feed the output to the external trigger ?

Note: I have a simple 2 channels digital scope, with no extra features.


texts: Synthesizable Leading Bits Detector in System Verilog

texts:
My goal is to design a synthesizable leading bit detector in System Verilog. I want it to count either the number of leading ones or leading zeroes ( Dependant on the MSB ).
For that I wrote a function:
/*
Input vs output examples:
"01110" shall return 1.
"11101" shall return 3.
"11111" shall return 5.
"00000" shall return 5.
"10101" shall return 1.
*/

function automatic integer find_leading_bits
(
    logic [ WIDTH_DATA - 1 : 0 ] data
) ;
automatic integer counter = 0 ;
for ( int index = $high ( data ) ; index >= $low ( data ) ; index -- )
begin
    if ( data [ index ] != data [ $high ( data ) ] ) begin
        break ;
    end else begin
        counter ++ ;
    end
end
return counter ;
endfunction

Will the above synthesize ( I worry about the "break" statement ) ?
Will it yield any transparent latches ?


texts:
I read this book called Practical Electronics for Invetors,and it says that one of the ways to increase magnetic field strenght of solenoid is to increase the current or increase the number of turns.

That got me thinking,why do induction heaters and induction coupled plasma use small number of turns and high current? Why not increase the number of turns and then decrease the current so there is less problem with coil overheating?

I played with online solenoid magnetic field strenght calculator,and as I kept increasing number of turns it kept giving stronger magnetic field without increasing current.So logicaly that extra energy must come by voltage right? I mean energy doesnt just magicaly appear out of nowhere,and since the current stays the same,it must mean that solenoid with more turns needs higher voltage,is that correct?

Can I avoid heat problems by using solenoid that have large number of turns so I can power it with high voltage low current instead of low voltage high current that conventional solenoid with small number of turns would require?

edit : I want to say big thanks for all of you who came here to help me,I didnt expect so much help so fast,this ElectronicsEngineering section seems friendliest of all stackexchange sections I tried,I love you all <3


texts: LM317 Get Stable Output voltage at 1,25 V

texts:
I am currently trying to use the LM317 with a stable output voltage of 1,25 V.
The general formula is
$$
Vo = Vref\cdot\left(1+\frac{R2}{R1}\right) + Iadj\cdot R2
$$

I used this circuit to create the 1,25 V output voltage:

simulate this circuit – Schematic created using CircuitLab

This circuit is directly according to the formula. R1 is infinitely high, R2 is zero. In general I measure the 1,25 V output voltage. But when the load is drawing current, everything gets unstable. Then I measure voltages higher and lower than 1,25 V...

I read some things regarding the minimum current in Adj Terminal. Therefore I thought about calculating R1 to create Iadj at ~50µA (according to ST LM317 datasheet). But whats with R2, should it be shortened to ground in this case?

I also thought about inserting a series resistor at the output, just to create a small load of ~1mA. Maybe the LM317 needs a minimum load...
Are there any suggestions? Thanks for your help.


texts: My question is about a rotel rt 226 1978 radio, it takes three 6.3v 250ma to light the display. What would happen if I put 6.3 300ma fuse bulbs in instead? Will it work just not glow as bright.


texts: How to reduce guard gap of a component in Proteus

texts:
I need to reduce the guard gap on a connector of Proteus but I can't find the option. I think it is possible to modify that by modifying it as a property of the package footprint but I don't know how to do that.

I need to to this because I need to pass a trace at full size between two pads of the connector PCB footprint but the rule checker don't allow me to pass the trace unless I pass a neck between the pads but like I said, I don't want a neck but the full size trace.

Can someone help me with that?


texts:
When choosing a split supply for an op-amp circuit, how do I determine my power supply requirements? For a single supply, this is easily determined by finding the required current - but how is power distributed in split supplies? For example, if the op-amp in question states it draws 100mA - does this mean thatt both the negative and positive power supplies should be capable of sourcing 100mA?

Thanks!


texts:
The number of capacitors and an inductor are used at the input side(forms pi-filter) for filtering, in order to reducing electrical noise, frequency noise, switching ,etc. This type of filtering technique is always good for motor type of load connected to the battery.

The given image is filtering 48v (pi filter),the image source is taken from internet. But why they use specifically 4.7uH, any mathematical calculation is there.

How do I choose a value of an inductor for a pi filter?

Thank you for your response guys. The load connected to the supply (48v) is bldc motor.
But the motor will surely runs above 10khz. But as per the calculation it shows only 3.4khz. I am bit confused, bcoz the controller going to produce 10khz pwm frequency. Sorry if I am wrong.

Eg: If we connect such supply (48v pi filter design) to micro-controller after regulating. I think the controller will produce above 10khz. Then why the design has made for 3.4khz. I am a learner, sorry I am wrong anywhere.


texts: Flyback Converter with multiple DC outputs

texts:
I am trying to understand how (step up) Flyback Converters work, since I need to design one myself. I am not at all new to electronics and I understand the fundamentals behind them, but I am totally new to circuit designing and I am having some trouble with this project.

I need to design a DC-DC flyback converter such that \$V_{I}=2.7V\$ and it has three constant outputs: \$V_{O1}=5V\$, \$V_{O2}=-15V\$, \$V_{O3}=13.4V\$. I can only use one transformer. I have though about buying one transformer with multiple inductors so that I can get multiple outputs at the same time (like this one, for example).

Am I on the right track? Is there any possibility to find the transformer I need in the market or I will have to make one myself? How should I choose the inductance of the different coils in the transformer?

Thank you in advantage.


texts: Why is the battery jumpered to a resistor in this schematic?

texts:
I am looking at a schematic for the wifi D1 mini data logger shield that I'm using right now. In this part of the schematic, a coin cell battery powers the RTC. I see R5 is jumpered across the positive and negative terminals of the battery. I identified R5 to be 2MΩ, so it obviously isn't shorting the circuit. But that leaves the question, what is its purpose?

Note: There is a sideways 1 above the battery symbol that looks like a minus sign. Don't be fooled!


texts:
i want to make this project:
https://www.instructables.com/DIY-Bare-Minimum-Arduino-Mega-2560/
but i found one of the parts is 16MHz ceramic resonator with 3pin.
i want to know :
1- what is the difference between 2 and 3 pin 16MHz ceramic resonator ?
2- can i use 2pin instead 3pin without problem ?


texts: I know it's a basic question but I want to understand how works the ePWM block from simulink ? On Matlab documentation I find just the configuration..


texts: inout port in VHDL RS232 Module from Digilent

texts:
I'm looking at the Digilent RS232 reference component available from http://www.digilentinc.com/Products/Detail.cfm?Prod=S3EBOARD for the Spartan 3E Starter Kit. I began putting together a testbench, but the VHDL code contains an 'inout' port.

I've been looking at the code for the RS232 component, and I don't see how the RDA port is ever an input port - RDA is "Read Data Available", which indicates that there is a word ready to be read; I see that as an output function. I thought it would be clear why this was 'inout' after reading the code, but I cannot see how this is an input function at all.

Any thoughts? Thanks for your help, all.


texts: boolean algebra question regarding how to simplify a 5 input circuit

texts:
Background:
I'm teaching myself computer architecture because I do not have a technical degree and want to learn this even though my finances won't ever allow me to have a formal education. I am doing all the problems in a book, but I ran into one problem where the problem seems too complicated for me. A karnaugh map won't work here since it has 5 inputs rather than 4. Also, a truth table seems a bit cumbersome since 5 bits means 32 entries.

Question:
Could someone show me how to solve this problem using the theorems of boolean algebra? and logically explain how it works? I have spent many hours trying to simplify this problem. I'm sure I'll be able to build the circuit once I determine how to simplify the algebra.

Problem:

// ` = NOT
ABC + ABD + ABE + ACD + ACE + (A+D+E)` + B`C`D + B`C`E + B`D`E` + C`D`E`


texts: help with simple thevenin circuit and filter

texts: I was trying to solve these excercises with thevnin circuits and filters but I really don't know what to do, could anybody help me?


texts: Connecting multiple series battery holder in parallel of 18650 batteries

texts: I'm pretty new to this, i understand how series and parallel work. Just want to ask if it's safe to connect multiple series battery holder in order for them to be parallel? If my battery are all the same, charged to all same level and same mah.


texts: how to calculate the maximum radiated power for the FM broadcasting?

texts:
I am trying to experiment a fm transmitter project of Raspberry Pi -
with a frequency of 88.1 MHz.

http://icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter

However, I am reading the specifications in my country -

https://gazette.govt.nz/notice/id/2010-go4604?year=2010&noticeNumber=4604

I can see that I can use the frequencies like

(1) The permitted transmitter carrier frequencies are:
87.6 MHz 87.7 MHz 87.8 MHz 87.9 MHz
88.0 MHz 88.1 MHz 88.2 MHz 88.3 MHz
106.7 MHz 106.8 MHz 106.9 MHz 107.0 MHz
107.1 MHz 107.2 MHz 107.3 MHz 107.4 MHz
107.5 MHz 107.6 MHz 107.7 MHz ''

However, I am unsure on the radiated power. How can I calculate in theory the radiated power from the FM broadcast antenna?

Also, how do I calculate the field strength in dBµV/m?


texts:
I am trying to figure out the zener voltage of 1n4742a zener diode. I constructed the following circuit:

The data sheet of the diode can be found here:
http://download.siliconexpert.com/pdfs/2016/8/24/2/35/11/334/gda_/manual/21n47xx.pdf

I measured the voltage across the diode and the current through it, and I stopped at the point where the current going through it was 67.5 mA and the voltage was 13.453 V.

The data sheet states that the zener voltage is 12 v however here I have about 12% discrepancy. Is that usual? or is there something wrong with the way I am doing it. I did not further increase the voltage source, because I am afraid it will destroy the diode, so is there a better way to measure the zener voltage?


texts:
I am using a 9-wire RS232-LVTTL device (Iridium 9602N) along with an ATMega2560. There are some PCBs / cables out there that passively convert the 9-wire signal to 3-wire TX/RX. The PCB I have that does this comes from a supplier that uses nothing but diodes, resistors, caps, inductors, and 1 IC that says "FK1" on it. I wasn't able to identify FK1, though it looks like an SOT-23 package. How is this being done without the MAX3232 chip??

Thanks!


texts: Convert power readings to energy readings

texts:
I have some electric power readings collected from a smart meter. With each reading there is energy consumed as shown in figure at link.

Some readings do not have energy values. So, I need to calculate these values manually in order to complete the data set.
 How should I calculate these missing values given the fact:

The time interval between successive readings is 30 seconds

I used the formula energy(watt-hour)= power(in watts) * time(in hours), but it is not giving correct values on applying on the readings associated with energy values. How should I calculate the energy values? Is there any other approach to calculate energy values?

My calculations: Considering second reading given in figure:

Energy= power * time  //(formula)
        = 123.4582443 * 30
        = 123.4582443 * 0.00833  //(time in hours)
        = 1.028 watt- hour
    but, correct value  is 1670763.75


texts: Is it proper to use an internal layer as a heat bed if I want to warm my multilayer PCB?

texts:
I need to design a circuit to warm my PCB. There are many ways to build up such circuit. But I learned from a post "Warming PCB in a low temperature environment" that maybe I can use traces as heater.

My first idea is to use one of the internal layer as a heat bed and place copper traces there. I have searched the Internet for a while but I can not find any application note or any discussion on this topic.

So my question is: is it good or proper to use the internal layer as a heat bed? If not, any disadvantage?

(I am not familiar with the fabrication process of PCB boards. So I am not so sure whether could I place traces in the internal layer)


texts: What is the effect of current noise in this op amp circuit?

texts:
I have modeled a non-ideal op amp as an ideal op amp with a noise current I_n flowing between its inputs:

In this circuit, I have also modeled a non-ideal voltage source as an ideal voltage source plus a non-zero source impedance R1. Finally, R2,R3 are the only real resistors in this circuit, and control the feedback of the op amp.

As an exercise in op amp noise, I will compute the theoretical rms value of noise of this circuit, and compare it to experimental values, so I HAVE to get this calculation right (please assume that the above circuit is correct, I have omitted some details in order to ask this question.).

Now here is the question: what is the rms value of the noise in V_out due to the presence of I_n in this circuit? I argue that, since I_n will flow towards lower voltage, it will run into R_2, and draw current from R1, causing an error of I_n * (R2 + R1) * gain.

However, according p.4 of this document (section header is "CURRENT NOISE"): http://www.ti.com/lit/an/sboa060/sboa060.pdf, the noise should be I_n * R3. Perhaps, along with your answer, could you demonstrate why I am wrong and this document is right?


texts: How to generate fast clock signal with MAX10 and PLL?

texts:
I'm using 10M50 FPGA to read data from a camera via MIPI-CSI2, but the clock I have on the board can't operate fast enough. So right now i'm trying to use the PLL to generate faster clock signal.

I'm using the following code to test if the clock signal generated is correct, by manually setting the v1 variable so my led blink every second. In this example the PLL (generated by the ALTPLL wizard from the Quartus IP Catalog) is set to receive a 100MHz clock signal and should display a 400MHz clock signal however nothing happens.

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

LIBRARY altera_mf;
USE altera_mf.all;

--   debut entity     --

entity test is
    port(
        CLK : in std_logic;
        LED0 : out std_logic     -- leds are ON for '0' and OFF for '1'
    );
end test;

-- debut architecture --

architecture test_led of test is
signal s_led0 : std_logic :='1';
signal c0 : std_logic;

component pll400
    port(   inclk0      : IN STD_LOGIC  := '0';
            c0      : OUT STD_LOGIC
    );
end component;

begin

clk1:pll400
    port map(inclk0 => CLK,
                c0 => c0
    );

p:process(c0,s_led0)
variable v1 : integer range 0 to 800000000 :=0;
begin
    if c0'event and c0 = '1' then
        v1 := v1 + 1;
        if v1 = 400000000 then
            s_led0 <='0';
        end if;
        if v1 = 800000000 then
            s_led0 <='1';
            v1 := 0;
        end if;
    end if;

LED0 <= s_led0;
end process;
end test_led;

I was able to use this to generate and test signal up to 320MHz , but it doesn't seem to be able to go higher, though I found in the datasheet that the VCO was able to go up to 1300MHz (I noticed that the Pfd limit is 325MHz, is that linked ?).

So is there something I'm missing or is it impossible to generate such signal with my current board ?

Edit : datasheet I am using as references :
MAX10 Clocking and PLL
10M50 User Guide
MAX10 Datasheet

Edit2 : I removed this post from stackoverflow to post here, where it is more suitable.

Edit : Here is a schematic of the PLL, right now i have access to the parameters N, M and K, but I can't change the post-scale C counter, located just before the output. Given the comments and answers I had, it should be what I need to stay in range of both VCO and PFD and still getting the desired output frequency (>400MHz)


texts: Can I efficiently monitor sound card line in with a vu meter?

texts:
I'm trying to monitor some audio input to my desktop pc with a vu meter.  I've connected to the line in, and it's just a bog standard on-the-motherboard sound card.  I'm having a problem understanding the various signal levels.  I haven't actually bought the meter yet as I need two antique ones at some cost, so at this stage I'm looking at the feasibility and risks involved.

From Wiki, consumer grade kit is designed for a nominal -10dB line level.  Recording via Audacity, it appears that my sound card line input actually clips at -6dB so there is very little headroom.  The typical analogue (it must be analogue) vu meter is calibrated -20dB to +3dB.  The -10 mark is only approximately 1/7th of the way up the scale.  To avoid the risk of clipping, I'd need to run at a level less than – 10dB.  That doesn't seem a very efficient use of the meter real estate.  I'm assuming that vu metering is for absolute readings and not arbitrary scales.  I only have rudimentary knowledge of this area, but have I miss understood something?


texts: Trace fork for bypass capacitor OK? Why?

texts:
I was placing some components on PCB recently, and, being relatively new to the subject, there are still things I miss out in terms of knowledge even though I try to google every question that comes to my mind in terms of how to do things right and why.
While I found a pair of really helpful posts around here about bypassing and grounding, I still have a question to which I found no answer. At least, not in a way I tried to word it.
The bypassing rule "cap right to the pin" is simple enough, but I had situation when trace would approach the chip from under the chip, meaning I couldn't place bypass cap between power source and pin itself, I kind of have to make a fork from the pin (there is a known good option of placing bypass cap on the other side of the board right against the pin, but let's say I can't.) Bypassing guidelines gave me a lot of information, but didn't really cover my question.
Now, there is a post here, that's asking, as I see, exactly my thing, and while a pair of answers discuss it, I kind of don't see a definitive and confident answer that will say "It's totally OK" or "It's not recommended". At least nothing struck me as a confident and definitive answer for me to understand it once and for all. OK or not OK. And why, of course.
Question is: is this kind of placement OK or bad? I have a feeling it's not recommended purely intuitively (intuition feels trace inductance and extra path the noise have to make to go to the ground), but I only trust some hard proof and not my guts when it comes to scientific stuff. So I would want to know for sure and listen to the opinions of more experienced and professional people.
Edit 1: I'm talking about common low frequency circuit, where most stuff is kHz or a few MHz, maybe 100MHz as an absolute maximum for MCU, nothing more


texts: For high resistance load, Battery lasts longer?

texts:
After reading this answer, I got to know that battery lasts about Total charge divided by current draw.

So, lets assume the voltage across 2 terminals of battery is constant.
by,
$$  V(Constant) = IR$$

If I apply high resistance load in series, then very low current will flow and the battery will be drained even more slowly.

My question is, Is my understanding correct(or I am missing something)?

(I have never made any circuit other than led in series,parallel)I was going to use LDR to turn on and off led lights. Earlier i used to think that high resistance produces heat$$H=I^2Rt$$
and that would consume a lot of energy wasted in heating. so battery will be drained faster. But today  i read that above linked post and my concepts changed.

(I don't know whether this question was asked before. because I don't know how do I search for it. I searched battery and resistance but irrevelant results came. so I asked question)


texts: What is the 1G Ethernet jitter requirements?

texts:
We have a Stratix V FPGA on which we want to run a 1G Ethernet PHY and MAC. Because we don't have a readily available 125MHz reference clock, we are considering using a PLL internal to the FPGA to generate a 125MHz clock from a clock of a different frequency.

PLLs internal to FPGAs are "known" to have have high jitter. Would the jitter requirements of 1G Ethernet be held if we used an internal PLL as a reference clock for our 1G PHY/MAC? What are the IEEE requirements on deterministic jitter for the reference clock of a 1G MAC?


texts: Which transistor should I use in my circuit?

texts:
I've made a rudimentary flood alarm (a circuit that rings a buzzer when the water in a reservoir is full) using a 9V battery and a cheap Chinese buzzer that came without a current rating. All I know is that it operates between 6V-12V. There's no power rating on it either, and my multimeter is broken so I can't measure the current myself. There are two parts to the circuit I'm trying to modify it into.

Connect a small low-heat capacity resistor in series with the
battery (to limit current) and put the two open ends of the circuit
as probes in the water, so that the probes are connected by the
water, the circuit is completed. I want this part to act as the
control voltage, applied to the base of the NPN transistor (since I
want the circuit to close only when the HIGH signal is applied to
the base).
I also want to supply the transistor with 9V which is passed only when the voltage at the base is also applied (i.e., circuit is complete due to the water).

Here's a basic circuit diagram of what I'm trying to create:

I'm new to this, and have no idea what transistor to use. What should be the value of the resistor? Also, do I need to use any other parts to ensure the proper behavior? Please advise.

Also, is this circuit feasible for long term use? When the battery voltage degrades, will the transistor be able to adapt? I can't use an AC source coupled with a 7809 IC as I want this to be battery operated. Please suggest a better way if need be.


texts: Measuring almost 1 volt between Raspberry Pi input pin and ground, why?

texts:
I'm trying to use a switch to to provide input to software running on the Raspberry Pi. I have software running right now that continually reads the input pin and prints the result. Problem is, even when nothing is connected to it, the voltage reading from the input pin to circuit ground reads about 0.9V. The software rapidly flickers between TRUE and FALSE.

Is this a software issue? If not, how can I avoid this?

Thanks for any advice,
- Chase


texts: Wifi - Determining the channel of a probe packet

texts: How do applications such as Airodump-ng determine the channel of probe packets they receive? To my understanding, when the receiver is scanning channel 11 it can pick up packets all the way down to channel 6 without much trouble, but these probe packets (to my knowledge) don't actually say what channel they're transmitting on, yet somehow the program knows. Is this determined by the program itself, or is it happening at a more basic level in the receiver?


texts: Calculating Phase wise Energy in Three Phase System

texts:
In three phase three wire system, is it necessary to calculate phase wise energy?

As per my knowledge, in three phase three wire system we are concerned about only total power/energy.

But does it have any meaning to calculate & show phase wise energy in three phase three wire system.

Thanks & Regards,
Nitin K.


texts: Why are input and output of I2C voltage level shifters connected?

texts:
Below is a schematic for a board from ST for testing VL53L1X sensor. It converts 3.3V to 2.8V internally because the sensor's recommended operating voltage is 2.8V.

The green lines are SCL and SDA lines for communicating with the sensor. It goes through ST2329AQTR (at the center of the image) to shift from 3.3V to 2.8V. This level shifter has the following block diagrams:

What I cannot figure out is why SDA is connected to SDA_2.8V and SCL to SCL_2.8V in the first schematic. The input and output of ST2329A is connected with the green lines. This is not presented in the level shifter's application block diagram. This does not pose a problem when either side is being pulled low, but when both are not being pulled low (i.e. both are high) then I think that there is no point in putting the level shifter there with the current configuration. The 4.7k pull-ups on both sides will make the resulting voltage 3V (2.8V and 3.3V voltage divider) regardless of what the level shifter does.

Can somebody please shed some light on the matter? Could this be a mistake?


texts: Replacing (and perhaps upgrading) bad capacitors within a speaker system?

texts:
A few months ago the volume of the left speaker of my pair of low-cost audio monitors began slowly diminishing. Every day it seemed to lose a fraction of it's normal operating volume until the speaker became nearly completely silent. Since I bought these speakers in 2010, I noticed that the left speaker tends to run very hot. So, when the speaker began to die out, I assumed that the speakers were poorly designed and weren't built to withstand their own level of heat, and after a certain amount of time they broke. However, I wasn't sure about the cause. I thought it might have been that a solder joint might have weakened and broken or something like that. However, I thought back to an experience that I had before where my PC's video card made a loud crack and upon investigation, some of the capacitors on the PCB had broken open. This was my first experience with bad capacitors.

So, with that in mind, I thought to pop open my left monitor and check around to see if something was visibly wrong. And sure enough, I saw something that looked like two capacitors that had overheated (i think) and vented some of their fluids.

[I can't post my image due to the spam filter]

I'll admit that, while I'm interested in hardware and electrical engineering, my knowledge is much more limited than I would like it to be. I would love to try this repair/upgrade, but I'm worried about messing it up and winding up with a pair of non-working speakers (which, is only slightly worse than a pair of half-working speakers...).

Now, at this point, I've been able to identify a potential cause of the problem. But, I'm not sure what to do about it, or if I can even do anything by myself.

I know that there are places online where I can get replacement capacitors (in this case, it looks like the caps that were used were 4700uF/35v caps). But is this an easy D.I.Y. job for someone who is inexperienced with electronics and soldering, but is willing to learn?

Long story short: I think that I need to replace two capacitors inside my speaker system. The caps that were in there (4700uF/35c) broke too quickly for my liking, maybe due to overheating.

Is replacing these capacitors something that is relatively easy for an inexperienced person?

Do I need a special type of soldering iron or can this be done with a cheap hardware store one?

Also, would it be possible to buy replacement capacitors that are stronger/better/durable/heat resistant, instead of simply re-buying the same type?

Should I (or do I have to) replace the bad caps with new ones that are also 4700uF/35v? Or could I/should I replace them with something else? If i can repair and improve these at the same time, I'd like to. I'm not sure if that's possible though, as I don't really understand how capacitors work...

Finally, If I manage to remove the old capacitors, do I have to do something to remove the capacitor fluids that are all over my speaker's PCB? What can I do to clean that and is there anything I should know about that stuff?


texts: What is the function of the resistor in the below circuit?

texts: What is the function of the resistor R13 in this circuit?


texts: What other ways besides using magnetic fields can we use to convert mechanical energy to electrical energy and vice versa?

texts:
I have just started to read Electric machinery fundamentals by Stephen Chapman and there is one question in my mind after reading the first paragraph.
What are the other mechanisms, besides using magnetic fields, used in motors and generators for converting energy? I'm asking this because the book uses "Almost all" at the beginning of the sentence, whereas in other places it has used more general terms like "For any given".
P.S. I would appreciate if you explain your answers in detail or provide material for further reading.


texts: How can I indicate that an IR LED is functioning without detecting its emissions?

texts:
I have salvaged, non-documented, IR LEDs. Without a datasheet I do not know how much current they can handle.

I have run into this before: I confirm the LED is good with by viewing it through a camera. I set up my circuit and begin troubleshooting. Only after  eliminating all other possibilities, do I resort to a camera to discover that along the way the IR LED stopped emitting.

It would be great if I could be confident that I am using the right resistor but even then accidents happen. What I would like is a simple indicator that the IR LED is functioning without detecting its emissions.

I would prefer an "idiot" light such as a visible spectrum LED that is lit when the IR is functioning properly and can be relied on to go dark should the IR LED fail.

I was thinking that I could trigger this from a voltage drop using a transistor, pull-down resistor, and a variable pot that I could tune to toggle my visual indicator.

Is this feasible?


texts:
I'm from Germany and im not so good in English, please forgive me.
I have a little bit idea of electronics but I'm not so sure with this problem. I would like to say beforehand that I have a soldering iron and hot air gun, so I can do a clean desoldering work.
I have a dead 4901 MOSFET (link) on my vega56 and I would like to repair it. Now I have seen that the 780ti has a 4901NF MOSFET (link). My plan is to buy a dead 780ti and use it as a spare parts dispenser. So the Question is: is the 4901NF okay to replace the 4901?  From what I understand from the datasheet of the 4901NF right now, it is the same as the 4901 apart from the fact that it can give more amps, but it nevertheless works, right? A new 4901 is expensive (20€, including shipping cost, from Mouser): does there exists an alternative seller for the 4901 or another graphics card mounting the same 4901 MOSFET?
It's okay for me if the card is completely dead: I will learn to repair electronic stuff by myself and desoldering the card is a good exercise to do.
I hope that someone can help me


texts: Sizing a breaker for a 24VDC power supply

texts:
I searched through the NEC code book and can't find any sections dedicated to the protection of power supplies (that supply 24VDC to pressure transmitters, speed sensors, etc.). I don't expect to find anything as detailed as Art. 430 for motor protection, but feel like there should be some section addressing this.

Now the main components of a power supply are a control transformer and a rectifier with capacitors to reduce ripple in the DC output voltage. So should I be looking at protection rules for those components individually? Or should I just go with the 125% rule? Also, do I need to account for inrush currents due to the presence of capacitors?


texts: How do I provide a variable 4-20ma input?

texts:
I'm working on an embedded project that takes has an input that ranges from 4-20ma.  This is normally provided by an external controller, but I'm working on a test bed.

Controlling voltage is easy - just stick a potentiometer in between the power supply and the input.

My first thought is to apply ohms law:

\$I=\dfrac{V}{R}\$

So assuming a 24 volt supply, we would use the following to get 4ma:

\$.004=\dfrac{24}{R}\$

\$R=1.666667\Omega\$

Assuming the same 24 volt supply, to get to 20ma:

\$.02=\dfrac{24}{R}\$

\$R=8.333334\Omega\$

I feel like I'm ignoring some key items such as the amperage of the incoming power.  Am I anywhere close to being on track to using a potentiometer that (in combination with some other resistors) swings between 1.666667 and 8.333334?


texts: Old valves (vacuum tubes) sometimes do not come in their original boxes. Sometimes the part numbers seem impossible to read. Is there an easy way to read an apparently illegible part number? Would UV light bring up the number? Would chalk be relevant? How did the old timers deal with this problem in the day?


texts: Lumens specs when buying a flashlight/torch. Why maglite has only 680lm but cheap ones have 900,000?

texts:
I am working as a night delivery driver and when its dark and/or rainy it's almost impossible to read many of the house numbers/names I am looking for.

I've heard of Maglite and in fact my friend has a large Maglite which is 680lm and very powerful but it cost him a fair bit and uses huge batteries.

I look on auction website and see ones boasting 900,000 lumen output! (for about £5 :D) I then google 'worlds most powerful flashlight' and it seems one made by 'Wicked Lasers' is considered one of the most powerful at 4,100 lumens. (https://www.wickedlasers.com/torch)

So why on auction site are they allowed to state 900,000 lumens. And how can i trust the output specs on any advert? (is there any other spec I should be checking)?

Really need it soon, and I need to be able to see stuff that is about 20-30 metres away in heavy rain at night.

Any help would be greatly appreciated. Thanks

(Ps. I could put links showing the adverts boasting 900,000lm but didnt want to put their links anywhere in case they are a scam)

Additional Edit:-
Well I have continued looking and the specs vary massively. This one I am thinking of buying boasts 20,000 lumens and 500m range. But it only takes 1x AAA battery ??!?!? - Surely this cannot be 20x more powerful than a top Maglite? https://www.ebay.co.uk/itm/Tactical-20000LM-L2-Zoomable-LED-Flashlight-Rechargeable-battery-Torch-with-BOX/322609536378?epid=16031184130&hash=item4b1d06dd7a:g:SwQAAOSwmcNdIJWc)

Conclusion:
For what it's worth I decided not to buy a 'No-name' brand. And after finding this one at Toolstation: https://www.toolstation.com/ledlenser-tt-police-tactical-torch/p41307
I realised their pricing is  actually very competitive. It is a few quid cheaper in Toolstation than the same torch is on Amazon or ebay.
I can just go into the shop and buy it today :D

I am happy now, thanks again all you guys. PS. You have inspired me to begin learning electronics as a new hobby too


texts: STM32: Interrupt latency for serial protocol implementation

texts:
I am implementing a synchronous serial interface (SDLC) using an STM32.

My original implementation for the RX side is running on a ARM7 which uses the FIQ to set an interrupt on the clock line, in the interrupt handler the bit is sampled from the data line and a short processing is done.
The TX side is using the SPI hardware with the FIFO.

My question is: can a STM32 (F4/F7/H7) running at 168Mhz or more handle the interrupts fast enough? I have read that the interrupt latency should be around 12 cycles[1]

The current clock for the protocol is 153.6kbps but I need it to run also at 614.4kbps (4 times faster)

[1] https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/beginner-guide-on-interrupt-latency-and-interrupt-latency-of-the-arm-cortex-m-processors


texts: Combining 12v Marine batteries of unequal capacities

texts: I would like to increase my RV marine deep cycle battery capacity.  I currently have a Group 24 battery with 64 amp hours.  I would like to add a second battery to increase my capacity to the max.  As an example, I could add a group 27 battery with 88 amp hours.  That would give me 152 combined amp hours. What is the safe 50% level for depletion? 50% of 152 would be 76.  However, I think 88 is the correct value as I do not want to go below 44 amp hours on the capacity battery.


texts: Super basic Q: How to regulate voltage in this basic circuit to avoid damaging the heating plate?

texts:
simulate this circuit – Schematic created using CircuitLab
This is for a teen-level science fair type project.
Materials include this 3V-12V generator and this 5V 1W heating plate

Goal: 12V generator, turned by propeller or crank, heats a 5 V heating plate to up to 120 F.

Problem 1: What component(s) must / should be added to the circuit to regulate the voltage to prevent exceeding 5V and (presumably) damaging the heating plate?

Problem 2: The device is intended to be hand-held and mobile, and thus sometimes not grounded during power generation. Is it necessary to ground it to prevent charge build-up (and shock to someone handling it)? If so, how?

Thanks, in advance, for any guidance for these basic and fundamental questions!


texts: Identifying the cause of defects in an H-Bridge by damaged transistors

texts:
I am preparing a fishbone diagram for reactive maintenance to be used as evaluative approach and part of it is brainstorming possible causes to get contributing factors.
Consider the following H-bridge:

I am trying to identify the cause of defects in the H-bridge by pointing out damaged couple of transistors as follows:

Q1 and Q2 (or Q3 and Q4):
a. control problem.
b. one transistor is blown up and shorted causing the other to follow.

Q1 and Q4 (or Q2 and Q3):
a. load short-circuited.

Q1 and Q3 (or Q2 and Q4):
a. rare case, uknown reason.

Could you please help completing or correcting this list?


texts:
I am trying to get an understanding of white noise and how it can be filtered out, etc. For that I'd like to understand correlation.

What would the autocorrelation of white noise look like? If I am not mistaken, it should look like a delta function at t=0 since at all other values there is no correlation at all. Is this correct?

What about when this is added to a signal. Say you have a sine wave and you add white noise. What would happen if you autocorrelate this signal? Would the noise disappear or would it just stay the same or what?

And what if you simply cross-correlated a white noise signal with a sinusoid. Would the correlation always be zero? How is the phase affected?

And finally, the main question this all builds up to: How is correlation used to filter out noise from a signal? What has to be known about the signal for this method to work?


texts: What's a schematic (compared to other diagrams)?

texts:
What's the difference between a schematic, a block diagram, a wiring diagram and a PCB layout?

Why do engineers want a schematic instead of a wiring diagram?

Where does Fritzing fit into this?


texts: Do conductors age under reasonable electric load?

texts:
Construction steels are prone to fatigue failure - they get structurally weaker when exposed to repeated mechanical stress.

Is there any similar process for conductors which makes them less usable once they conduct current for long enough?

In other words, suppose I have an old transformer which has served for say 30 years. It still functions fine (didn't burn down, short or anything like that) but it is rather old already. I expect that magnet wire insulation will get weaker because of being heated for all these years. I also expect that core plates insulation will get weaker.

What about the wires themselves? Will aluminum or copper in them be any different from what I'd find in newer wires?


texts: How to verify ST Link V2 original or fake?

texts:
I need your help to identify the product is original or not?
I ordered the ST-Link V2 from one of the local and reputed online website. The product I received has an outer box that looks like original but after seeing the product I think it is not. I just want to know how to verify that the product I received is original or not?
Below are the photos of the product which I received.


texts:
I am using a Tinkerkit button as input to Arduino PORTD pin0 and expect an output on PORTC, pin0 as output.

Code:

void wait_for_button()
{

  if( (PORTD & (1<<PD0)) )
      PORTC|=(1<<PC0);
  else
      PORTC|=~(1<<PC0);

}
int main (void)
{

  DDRD=0x00;   //PORTD pin 0 as input
  PORTD=0x00;
  DDRC=0xFF;   //PORTC as output
  PORTC=0x00;

   while(1)
   {
     _delay_ms(200);
     wait_for_button();
   }

}

HW Setup:
http://ibb.co/ek6R7a

TinkerKit:
http://www.mouser.com/catalog/specsheets/TinkerKitPushButton.pdf

LED does not lightup on button push. what am i doing wrong?


texts:
What is the difference between
x=#5 a;   where a blocking statement is used

And  x<=#5 a;  where a non blocking statement is used


texts: Driving a LED from a wide ranging input voltage

texts:
I have been working on a small linear power supply, capable of regulated output between 2V to 30V, using the LM338 IC. For the most part it is a simple implementation taken straight from the datasheet.

I want to include a "power" LED on the board indicating when the board is live. The LM338 requires the input voltage to be ~5V above the output voltage. This means that the input power may vary depending on usage scenario from approx. 5V to 35V. I'm not sure what the best way to drive a power LED on the board given this wide ranging input voltage.

Apparently the 7805 5V regulator can tolerate up to 35V input, which would provide a 'known' voltage to drive an LED from. However this seems a little overkill/expensive and would probably have heat issues. I don't think I can use a large resistor either as at lower voltages the LED would not illuminate or be very dim? I did wonder about a constant current LED driver but could not find a suitable part.

I would appreciate some design suggestions on how to include a 'power on' LED in my design bearing in mind the wide input voltage range. Thanks

Clarification Edit: My power supply board has a three way header and 2-pin jumper to change the operating mode from either (A) fixed voltage or (B) adjustable voltage. For the fixed voltages, such as 3.33V, 5V, 12V, a piano DIP switch is used in conjunction with various 0.1% or 1% resistors. For the adjustable voltage operation, the jumper connects the LM338 ADJ pin through a 5K linear potentiometer.


texts: Capacitors for AMS1117 for 5V to 3.3V regulation

texts:
I would like to convert regulated 5V (from USB port) to regulated 3.3V using AMS1117 regulator. Since input voltage is already regulated, are any capacitors needed for the circuit? If so, what kind should I use? What problems should I expect when I won't use them? Could output voltage be less stable than input one?

The datasheet doesn't provide much information about the capacitors but it suggests using 22uF tantalum output capacitor (one of two datasheets I've seen does not tell anything about input capacitor). But I believe that my conditions are just much simpler than usual and I should probably get away with much smaller one and maybe of other type (like ceramic?) or maybe without it at all?

I did see those regulators in use in few cheap voltage converting modules and I'm pretty sure none of them used tantalum capacitors. One of them, for example, uses two 104 and two 106 (probably one of each type for input and one for output) which seems quite arbitrary. Is this bad engineering or it's just OK for most cases? How are does capacitors chosen if not by following datasheet recommendations, empirically?


texts: How to explain and possibly avoid undervoltage on I2C bus?

texts:
I've been testing different sensors for the I²C bus with two host devices: Raspberry Pi 3B (3.3V), and Sitec S4 (5.0V).

Since one of them, namely the Sensirion SCD30, had communication problems every few seconds, I looked at the bus with a scope and found that the voltage both on SDA and SCL drops below ground level to about -0.3V at the beginning of each communication.
Here is what the scope showed:

There is no difference when all devices and cables are diconnected from the I²C bus, except for the obvious fact the the host does not receive an answer when using i2cdetect.

The I²C specification allows the low level voltage to drop to -0.5V, so this undervoltage should not be a problem.
The SCD30 only accepts a low level voltage above -0.3V, so this is most presumably what is causing trouble.

[EDIT] I have experimented a bit with series resistors in the bus lines (22R and 100R). 100R rounden the signals too much, but with 22R series resistance both in SDA and SCL, it looks a bit better:

[EDIT2] The communication problem seems to be caused by clock stretching, not by the undervoltage. This is what a regular transmission looks in detail:

When clock stretching has not been enabled as described here, there are communication failures. Undervoltage does not seem to be the cause.

My problem is probably solved, but the original questions are open:

What causes the undervoltage? (Inductance?)
Is it possible (though not necessary) the make sure that the I²C bus voltage does not drop below a certain level, e.g. be adding a diode between each bus line and ground with a low enough forward voltage? Such devices seem to be difficult to find...


texts:
I have a project with LEDs which are switched on/off with MOSFETs. But there is this "off mode" slowly reducing voltage period which takes 12ms to go truly to 0 V. I have this Vishay Intertech SI4477DY-T1-GE3 P-Channel MOSFET. Is it possible to reduce this off period to go down faster? Is this MOSFET too slow to do that?
This is my shematic, and the processor is an Arduino Nano.

simulate this circuit – Schematic created using CircuitLab


texts: Calculating Power of a Non-Continuous Signal

texts:
I have to find the power of the following signal and would like to know if I'm doing this right or, if I'm doing it wrong, how to do it.

The equation for power in my textbook is \$\overline{m^2(t)} = \lim_{T\to\infty} \frac{1}{T} \int_{\frac{-T}{2}}^{\frac{T}{2}} m^2(t) dt\$

This signal periodically has the equation \$m(t) = \frac{t}{\pi/4} \$

From the picture, \$T=\pi\$

Therefore, this can be simplified to: \$\overline{m^2(t)} = \lim_{T\to\infty} \frac{1}{\pi} \int_{\frac{-\pi}{4}}^{\frac{\pi}{4}} (\frac{t}{\pi/4})^2 dt\$, right?

If the above is correct, then \$\overline{m^2(t)} = \frac{1}{6}\$

I believe this is correct, but only for the part of the signal that exists.  Since half of the signal has no value or is zero, does this mean I have to divide the answer I just got by 2? So that \$\overline{m^2(t)} = \frac{1}{12}\$?


texts:
I have built quite some buck converters for ~3A@3-5V (~1MHz, 24V Input) and I always used schottky diodes due to their low forward voltage drop (and therefore low power dissipation during free wheeling). Now I naively replaced the converter‘s feedback divider to regulate an output voltage of 12V. After a short time the regulator failed and soon I found out that it was the shottky diode that was destroyed.

I think I understand the Problem: schottky diodes don‘t only have a low forward drop (which is desirable), but they also have a relevant reverse leakage current which rises significantly with die temperature. While that wasn’t a problem in the 3-5V versions, at a reverse voltage of 12V the power dissipation (12V*100mA=1.2W) is too high for the device. I replaced the diode with a common silicon diode for experiment and it failed as well, but (as I assume) for a different reason: the ~0.7V forward drop at 2A causes at least 1.4W of dissipation.

How do I choose a suitable diode for such a buck converter (high current and high voltage) where schottky diodes don‘t appear to be a good candidate?
Is there a class of diodes which has a low forward drop and low reverse leakage or should I use a bunch of schottky diodes to share the Power?
Someone told me I could use a transistor instead of a diode, but I have no idea about that; does it make sense?

Edit: this is the schottky diode that failed in my case

Edit2:
I'm using the TPS54240 regulator and I need the converter to provide at least 2A.


texts:
I am using the below input circuit which has this SM6T36CAY 36V TVS diode.

The input voltage range is 12-36V and the output is the same only dropping the diode forward voltage.

Typical load current is around 80mA.

My case :

I applied around 130V at the input side by mistake which resulted in the magic smoke.
After turning off the power supply and adjusting it to the nominal voltage range, the typical current draw increased from the usual 80mA to 500mA.

Upon debugging, I checked the individual power rails. This 12-36V is converted to 5V by the LDO which is fed to the microcontroller. I found that the 5V rail was showing short (continuity) and therefore, I replaced the microcontroller thinking that it might be damaged. But After replacing the microcontroller also, same result of 500mA current draw.

Later, I checked the resistance across the TVS diode. It was showing some 10-50Ohms only.

After changing the TVS Diode, the current draw reduced to 80mA nominal.

I thought TVS was to handle transient voltages. And I applied that 130V for some 30seconds.

My questions :

TVS diodes are not capable of handling some hundreds of volts for 30-45seconds but they can handle kV range for few micro or milliseconds. Why is that?
And why did the current draw was high till I replaced the TVS? The TVS was a short circuit impedance path for the current?
If the TVS diode was the only problem, why did my LDO output (5V) also show a short circuit?


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I have an old piece of instrument that suppose to connect with a Windows XP machine. I keep getting "Framing Error" messages on the instrument panel while the PC side shows that the instrument could not be found.

The instrument uses RS232C in a 9 pin serial port to connect to the PC. If I understand correctly, RS232C is the same as the prevailing RS232 on Windows XP. I have tested the serial port on the XP machine with Hyper Terminal, and made sure I use the proper "straight through" type of cable. The cable has been used on the same location with other instrument and worked properly.

In order to connect the instrument with an XP machine, I have set the following parameters to be the same on both sides:

    Baud rate 9600
    Data Bits 8
    Parity    None
    Stop Bits 1
    Handshake None

However, on the instrument side, there is an item called "terminator" with CR, LF, and CR+LF settings, which is not available on the serial port settings for Windows XP. I tries all three settings but none worked.

What should I do next?

Edit:

According to the service manual:

  An RS232C format serial port is available at the DE-9 connector J3. U8 provides voltage level translation from +5 volts and ground to ± 12 volts. Direct I/O control lines are used for all signals because of the timing critical nature of the communications protocol. Two data lines (TXD/RXD) are used and two
  control lines (RTS/CTS) are available for hardware handshaking if enabled by the software. ....

What are "direct I/O control lines"?


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texts:
I want to know what methods are used for microstepping stepper motors, and their pro's and cons

For example, I presume, to hold the motor between two steps, PWM would be most efficient; simple circuit and lowest power wastage; a simple FET H-bridge. Would this work well? And if so, what phase should the pulses to the two relevant coils be? E.g should the mark (and space) overlap? Or be inverted 180° to each other? And what frequency? (Obviously higher than step rate, and probably microstepping rate, but by how much?)


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I have the following circuit, the gate is driven by a pwm pin on a raspberry pi zero.

The LED, successfully light when my program commands it to.

However, the LEDs flicker occasionally when the duty cycle is set to anything less than 100.

What can I do to stop the LEDs from flickering?

simulate this circuit – Schematic created using CircuitLab


texts: I would like to know what this circuit is

texts: I'm a engineer of embedded systems and I'm studying a 4G modem. The circuit has a component that I want to identify but the reference  is apparently wrong. The reference printed in the circuit is H51RFA but I couldn't find this in any place. You can see a picture below.


texts:
I'm using Realtek's ethernet PHY RTL8211E, but can't figure out what's the purpose of pin 'RSET', and how to connect it. The only datasheet I can find is
here.

It's wired I can't get that datasheet from the official web page about RTL8211E/EG.

So, anyone can give some informations?


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texts:
For an artistic installation, I need to use 20 TV remote controls. So I would like to replace their batteries (1.5V * 2 = 3V) with a single power supply.

How to connect the remotes controls? In series?
How to calculate the power supply needed for these 20 remotes?