texts: Killed two Teensy 4.0s with this circuit - looking for help diagnosing

texts:
I have created a circuit for my Senior Design project at my uni. This circuit is meant to receive a signal from a contact microphone attached to a brass instrument, pre-amplify it, and analyze to find the pitch of the note played on the horn. Once the frequency is found, the board then does two things:

Control an H-Bridge consisting of IRF3205s and a HIP4080AIBZ full-bridge gate driver
Send frequency data over Bluetooth using a DSD HM-19 bluetooth module

When testing the circuit, we programmed the Teensy 4.0 to do a PWM signal sweep on two pins: PWM_A and PWM_B, with PWM_A being a non-inverting input for the HIP4080AIBZ and PWM_B being an inverting input.
When the board was turned on, the Teensy booted up and began driving the motor. It got maybe a half second into the sweep and then died. The motor started turning during that half second, but stopped once the teensy died.
This circuit is powered by a 3S LiPo Battery.
Here are some screenshots of the schematic and the PCB. Do you guys see any glaring issues here? What could have killed the teensy? Did >3.3v get applied to one of the output pins somehow? Could the voltage regulator have failed somehow?
NOTE: Originally, the voltage regulator used was an LM317T, but after finding that the regulator was not regulating to 5V, we changed to an LM1086IT-5.0. 2oz copper was used, and the motor is a BaneBots 550 motor.


texts: Is it possible to charge/discharge this cap fast enough?

texts:
What I have, is a common 12-pulse rectifier with its bridges in series and I included a snubber between DC-link and rectifier output. Is important to note that all inductances before the rectifier are small in order to minimize its impact on this snubber performance. Also, I cleaned the circuit from scopes and control of IGBTs in order to visualize in a better way this system.

The main Idea of this snubber is to give a semi-triangular shape to the current by following a reference (each snubber has it reference which is the same shape but shifted in 30°). The background theory and reason for obtaining this currents, is that doing so, I should have sinusoidal currents at the transformer's primary winding or the AC busbar which is connected this rectifier.

Now, the snubber is supposed to work like this: If output current from snubber is greater than reference, then IGBTs must be turned OFF in order to charge this capacitor and lower output current. Otherwise, if output current is less than reference IGBTs must be turned on, discharging this capacitor and increasing this current. Until now, I can only get this working using DC voltage sources instead of rectifiers  (250kV each bridge) as you can see in this picture:

And when using a proper 12-pulse rectifier I get this.

Here the tracking of the reference (green) is really great but for some reason the voltage across the capacitor increases until my simulation crashes. The main idea of this snubber is to turn off both IGBTs when voltage across capacitor is aprox 1V in order to reduce losses while switching, however, if I add that condition in both cases (with DC Voltage Sources and 12-pulse rectifier) the output current from snubber (red) takes a long time to discharge when the snubber have to track the lower sections of this triangular reference.

Any suggestion or recommendation would be truly appreciated as I don't really know what to do instead of changing values of my system without knowing why.

EDIT: I'm using PLECS 3.5.2, if you think something in the logic control should be wrong then I can upload pictures of it too.


texts: What frequency did wireless telegraphs operate at?

texts:
What frequency did wireless telegraphs send and receive telegraphs at? Were there multiple frequencies?

For instance, this comment says Titanic operated around 1 MHz. Was there a range of frequencies available for use, or could operators choose any frequency and others would still be able to receive the signals?

I also read on some websites (for example, this one and this one) that wireless telegraphs spam the entire electromagnetic spectrum which is why they are illegal. Somehow, this seems hard to believe. I don't believe telegraphs are illegal, or that they spam the entire spectrum. Is there any truth in this?


texts: Confusion in understanding the relation between permittivity and capacitance

texts:
The insulating medium between the capacitor plates is called dielectric. This appears in the Coulomb's law:

$$F = \frac{q_1 q_2}{4 \pi ɛ r^2}$$

ɛ is the "permittivity" constant which depends on the medium. This can be written as:

ɛ = \$ɛ_0×ɛ_r\$

where ɛr is also called "dielectric constant" and ɛ0 is the vacuum/space permittivity.

So when I look at the Coulomb's law equation I can see that as ɛ decreases which means as ɛr decreases the force increases and this means the electric field increases.

So the equation tells me that if the relative permittivity decreases the electric field increases. It also means if I use a more insulating material I would obtain a stronger electric field.

Isn't "permittivity" a counterintuitive term here? So "permittivity increases" should mean "the material should permit more". But in this case increasing the permittivity decreases the Force and the electric field E.

Now let's look at another equation(capacitance equation) where ɛ appears:

C =  ɛ×(A/d)

Now if the relative permittivity increases the capacitance increases. But this is also counterintuitive. Metals have almost infinite permittivity but in capacitors they use insulating material which means low relative permittivity. I would think to increase C the material between the capacitor plates would be more insulating(more insulating material, smaller ɛ). But the equation says the opposite.

Where am I getting things wrong here? I would appreciate any clarification.


texts:
Today I was in Tesco in my city and I saw something quite interesting, that was electronic price tag:

I don't know how it happend, but on a parking I found this price tag in my basket beneath some old papers and leaflets... It was very late, so I decided to take it home and give them back to Tesco tomorrow or the day after tomorrow...

Now it lays on my desk and I'm wondering how this device works?

There are some printings on a sticker. A producer: Samsung, model SLT-EM005 and something very interesting: a MAC address.

When opened, there's a battery and PCB with two integrated circuits.

Larger one SSD1623L2/W232BU and smaller SAMSUNG ZBS242QRF/1234 (or Z8S242QRF... very small printings).

On PCB there's also a DYnamic NDO-VO text, a QR code and display that looks for me like E-INK, still displays price even when battery is away...

The problem is, that I couldn't found any datasheet of that IC. That are only my thoughts, but there must be some wireless network of this devices around the store.
Does someone know anything more about this interesting thing?


texts:
I have the following (badly formulated) problem.

A passive first order lowpass filter gets cascaded with a passive first order highpass filter to form a bandpass as the following circuit diagram shows.

By how many percent does the lowpass behavior (upper pole frequency) of the resulting filter move with respect to the frequency of the pole of the original lowpass filter?

I tried to solve this problem using LT-spice, because I couldn't find a way to solve it algebraically.
Here is the lowpass filter simulated. I found the -3db gain to be at \$f=4.10\$MHz. And that must mean that the pole for this filter is at 4.10MHz, right?

I also tried to simulate the bandpass filter, but it turns out that it never reaches -3db gain.
So if I can't find the pole for the bandpass filter, I can't solve the problem. I hope someone can help me with this, either algebraically and or with LT-spice.
EDIT
Trying to solve this problem algebraically with a lot of help from VerbalKint.
Using the transfer function he provided, I tried to solve this with Maple.

As you can see I get the pole frequencies to be at: \$f=444180 \text{MHz} \$ and \$f=5.47141 \text{MHz} \$.
These frequencies are very close to what VerbalKint provided, but there is still a difference. I wonder what have gone wrong in my calculations.


texts: Why is it desired to divert the surplus PV power into a resistive load?

texts:
From wikipedia/Maximum_power_point_tracking:

  When the batteries in an off-grid system are fully charged and PV production exceeds local loads, an MPPT can no longer operate the panel at its maximum power point as the excess power has no load to absorb it. The MPPT must then shift the PV panel operating point away from the peak power point until production exactly matches demand. (An alternative approach commonly used in spacecraft is to divert surplus PV power into a resistive load, allowing the panel to operate continuously at its peak power point.)

I can't imagine why is it desired to divert the surplus power into a resistive load instead of simply ignoring it. What is the advantage of keeping PV module operate at its maximum power point at all times?


texts: What is the type of AC power in Power supply/Adaptor rating?

texts:
Most of times, Power Supply or Adapter has an annotation related to the power rating such as in this figure

For the red underlined value, I understand that it is the actual delivered DC power, and the current is the maximum current. But for the AC part, is it true power or total power?
If it is total power, Could I get the power factor from rated DC power and AC total power?
Thank you


texts: Wiring a 1920s intercom to a contemporary door-entry phone

texts:
I have recently purchased a 1920s wall-mounted intercom:

I would like to connect this unit to our existing "4+n" door entry phone system, replacing the cheap plastic handset that we currently use (which is an LT Terraneo 603n):

As a replacement, it can already provide all of the required functionality: an earphone, a microphone, an activation switch (on lifting the receiver from its arm), a bell and a lock-release button (on the right of the unit, formerly used for transmitting a call signal so that the counterpart intercom would ring).

My (probably incorrect) attempt to follow the crude wiring inside the unit suggests that it  is currently connected as shown below, where the left-hand switch is operated by lifting the receiver from its arm and the right-hand switch is operated by depressing the push-button on the right of the unit; and the lettered diamonds indicate the terminals atop the unit.

Note that I think the component seen at the top of the unit is an inductor, as drawn in the diagram above.  However, it actually has four terminals: two at one end connecting to the switch, and two at the other end (one to the microphone as shown, and the other to the earphone/terminal D).

By connecting the "call" and "common" wires from the existing handset to terminals B and D respectively, the bell rings when someone presses the doorbell; and I assume that the lock release will work if the "lock" wire is connected to terminal C.  So far, so good.

Sadly, that's as far as I can get; I can't see how the circuit maps onto the separate speech in/out wires of the existing handset (and trial-and-error has borne no fruit); would they both be carried down the same wire?  Any thoughts on how one might proceed?


texts: Is there such thing as a 'capacitor socket'?

texts:
Or will I have to make one?

Something like a 2kV mount for a cap like this (but obviously higher voltage);

So you can switch a bunch of different ones in and out, if not, I might have to design one.


texts: How to find the distance between two arms of a hairpin resonator?

texts: In this picture I want to find the value of W_cap(the distance between two arms of hairpin resonator). I have the length, width, quality factor and coupling co-efficient of the resonator.


texts:
I'm quite new to this. I have just basic background in electronics. So I would appreciate an advice from someone more experienced.

I would like to connect an i2c display to my tp-link wr703n (ar9331) router gpios. Router is running linux and uses kernel module to simulate i2c interface using gpios. The display is hd44780 connected to the pcf8574 i2c expander.

The display operates at 5V while gpios are probably 2.5v+-10% tolerant. I checked the datasheet of ar9331 but not sure what is maximal voltage for high level. There some reports of people having gpio pin pulled up to 3.3V and running it just fine. So I'm not sure about the pullup voltage on the gpio.

But anyway I probably need some level shifter. I tought I could do something like this.

Vc1 2.5V? ---------------       ------------ Vc2 5V
                 |      |       |
                 X      |       X
            4k7R X      |  4k7R X
                 X      |       X
                 |      |       |
 gpio-7 --------------[FET]------------------ pcf8574

same for gpio-29

I'm not sure which N-FET to use for this. Usually people use 2n7000 which has typical Vgs threshold 2.1V but maximum is 3V. So I guess this one could not work properly if the threshold of used FET would be 2.5V or more.

And is this good thing to do anyway?

EDIT2: I've added better picture of the circuit.

simulate this circuit – Schematic created using CircuitLab


texts: Unidentified component on heating element

texts:
Clueless DIYer here, apologies in advance. I'm hoping someone can tell me (approximately, I don't need an exact part) what the circled component it is / what it's for, in order to help me diagnose repeated failures.

Mystery component in context (a dishwasher inline heating element)

Same part removed from a different element, showing scorching

Many thanks


texts: Interface with touch screen using arduino

texts:
Basically I am trying to stimulate a touch screen with an arduino board. I know this has been asked several times and Ive spent a long time looking at solutions, namely some kind of foil stuck to a touch screen being pulled to phones ground, or USB shield, or arduino earth, or a fruit or your body etc. I have tried all of this and more, using a transistor, MOSFET, optocoupler, and even a relay. All while holding the phone, or on the table or on top of a foil sheet or a grounded foil sheet etc... I have had varying success with all of them but nothing reliable and repeatable long term.

The relay has been the most successful, connecting foil via the armeture switch to the phones ground. If I set the arduino to pulse the relay closed for 100ms every 2000ms in this case, Interestingly I find a consistent result: when I place the foil a touch occurs and isn't released, the foil and wire are enough to do it. After between 30 seconds to a minute, the touch is released and touch events start pulsing with the arduinos input via the relay, and after 30 seconds to a minute or so longer, the screen stops responding all together, even to finger touches on the back of the foil - where this produced a touch event beforehand.

So I figure the screen is adapting to the environment. Just as it would need to if you were using your phone standing on a flag pole vs leaning against the steel wall of a truck. For some reason it decides the foil is environmental noise and 'numbs' that area of the screen to it.

So my question is, is there a way to reset the capacitive field image between each touch, or is there a different method to achieve touch events using the arduino?

EDIT
Attached is a basic schematic of the circuit. Pin 2 is switching from LOW to HIGH for 100ms, then to LOW, for 2 seconds, and the relay clicks closed accordingly. The wire labeled 'Wire A' has been tried a variety of ways. To iPhone Gnd like it is, to Arduino Gnd, to my fingers, to a piece of foil laid under the iPhone. Additionally I have tried all these combinations with a 1000k resistor in series, and capacitors varying from 100pf to 100nf, separately and together with the resistor.

The underlying problem is the piece of foil stuck to the screen. The iPhone sensor seems to be able to determine its proximity is not changing, even if its electrical characteristics are.


texts: Would the Bluegigga WT12 be suitable for a battery powered application?

texts: I understand that the Bluegigga WT12 requires RS232 when using UART which is what I'm planning to do and thus it requires high voltages? Would that make it unsuitable for a battery powered application? If not what alternative Bluetooth module could I use that supports SPP and has a robust API like iWrap?


texts: Low Battery Indicator Schematic Question

texts:
I have a question about this low battery indicator circuit:

I have already built the circuit, I just have a question about setting the potentiometer (R4). I want the LED to turn on at 6.1v, so how do I set the pot to do that? It's a stupid question, I've just never known how to do this properly. Thanks


texts: Selection of Frequency in Switching Regulator

texts:
The AD ADP5070 for feeding a low noise amplifier and a 24 bit ADC, can be regulated at two pin selectable frequencies: 1.2MHz or 2.4MHz, accepting an external oscillator in the range 1 MHz to 2.6MHz.

This regulator should work from +15V into +-16V 50mA.

In order to probably reduce the noise, which one of these selection should I pick?

Or is this selection not particularly relevant?


texts: Switch transistor with a low voltage and current

texts:
I'm designing a circuit that will use a combination of switches and resistors to allow a microcontroller to identify which switch was pressed based on the voltage read and perform a switch-specific action.  The design that I've come up with involves using a transistor to activate a relay, which powers the microcontroller.  When the microcontroller is powered, it pulls a pin high to take over powering the relay.  When the action is finished the microcontroller pulls the pin low, deactivating the relay and cutting power to the microcontroller.

I've tested the circuit with one switch and a voltage divider to simulate the largest resistor/lowest voltage combination from my switch array.  The voltage that I've calculated at the transistor is 1.6 V, and the current is 0.017 mA.  The high resistor values are necessary since I need approximately 0.2 V differential between switches.  The problem is that the transistor is not being activated (it works if I feed it 5V directly).

My question: Is this because the current is too low?  How would I go about rectifying this (other than decreasing resistances)?  If there is a better approach to this problem, I'd love to hear it also.

Edit

The diagram omits the 15 other switches and resistors for simplicity sake.

This is a circuit for a picture frame that will do specific actions depending on the button that is pressed.  This will be battery-operated using 6 D-cell batteries, mounted on the wall.  I'd like to get months if not years of operation out of it before having to replace the unit.  My Arduino with an attached shield (with using a MAX667 power supply rather than the stock one) consumes 45 mA at low power.  The stock Arduino doesn't go into low power mode although with a programmer the chip can be modified to go into low power mode and consume nA of current.  At 45 mA, the batteries will last about 11 days (266 hours for a 12000 mAh battery).  Hence the requirement that the resistive ladder turn on the device.


texts:
(I am new in this era, so go easy on me :) )

I am working on a project that involves weight filling of powdered material into capsules (Fill sizes, 400 , 600 & 800 mg). . Now for the design of weight part of the machine, we need to employ load sensors with a resolution of 1mg. I have tried locating sensors according to my needs and couldn't locate it. The sensors are either very high resolution (0.1 mg and downwards) or too low resolution (1 g and onwards). The problem is that the sensors with high resolutions (0.1 mg and lower) are extremely expensive. I also dug out the idea that the already existing weighing machines with resolution of 1 mg are available in the market and can be hacked into doing my job (and they are cheap, around 10 $). Does sensors with such resolution exist in the same price range (so we dont have to deal with the weighing machine circuitry) ?

Now as this is a totally new field for me, any guidance towards the right direction would be useful. I am not particularly looking for recommendations, but if anyone has a good experience working with such parts, it would be very helpful.


texts: How is volume not affected by signal strength in AM radio?

texts:
I was wondering how the range of the volume is transmitted in AM radio.
With amplitude modulation, the volume is directly linked to the amplitude of the radio signal. But this would mean that the overall volume of the radio receiver would decrease quadratically with the distance to the emitting antenna (or linearly due to atmospheric refraction and earth reflection)


texts:
After reading this post (3rd answer):

(https://electronics.stackexchange.com/a/129423/54580)

I almost got it why the saturation regions of BJTs and MOSFETs are in different regions of their diagrams. The differences were explained, but it remained unclear for me why the same name is used for two quite different analysis.

Other posts I found focused on one of the transistor types so it remained obscure for me: why the saturation region of the MOSFETs has this name?

Since we put the load line in the "flat region" of both graphs for amplifier design, it's strange to call it active in BJTs and saturation for the MOSFETs.

Edit: in the mean time I've found a nice footnote in another book (Foundations.. from Agarwal and Lang) which I reproduce here.

"The saturation region in BJTs is completely unrelated to the saturation region in MOSFETS [...]. This duplication of terms [...] can be source of confusion, but, unfortunately, has become the norm in circuit parlance".

It's something like: I know, it's odd, live with it.

Like two answers below show very well: look at the internals, forget "inputs" and "outputs" and stick with the (quite different) physics of both devices.

Thanks to all!


texts: Can the TFT in LCD displays be made in the nanometer range?

texts: Can the TFT elements and hence the pixels in an LCD display be made in the nanometer range? Say 10nm x 10nm?


texts: QuestaSim/ModelSim simulation gives me unkown value in wave window. However I get them as X and x, what is the difference between the two?

texts: What is the difference between big X and small x when we get red (unknown) signals in QuestaSim? I would assume it to be the same in ModelSim simulation as well.


texts: are these the standard headers for i2c and ISP?


texts: The best way to get rid off common mode noise for remote measurement

texts:
I measure DC pseudo-differentially over 1-2 m wires. In order to avoid any voltage drop in wires  the built in  ADC input buffers  are used, thus there almost no current flow.  I expect the wires to catch a lot of common mode noise from RF to 50 Hz power grid.

Most materials about common mode noise that I found, consider it in the context of power line that involve common-mode chokes. Howver, I am not sure if this is suitable for my measurement.

Another way is the vanilla common mode filter

But again, I am not sure if it would be good enough and provide adequate level of filtering.

Moreover, there might be more methods that I am not aware of.

What possibilities are there to suppress common mode noise, and what is the best method for a measurement application?

In addition, how much the application of a shielded twisted pair cable would help to ease the problem?


texts: How does a MOSFET gate resistor reduce ringing?

texts:
I desiged P-MOSFET for reverse voltage protection, without gate resistor.
The reason that I tend to use it is protect from reverse DC voltage when
someone connects the battery.  Do I need a gate resistor?
(When someone connects the battery correctly it will be in the ON state, otherwise the PMOS will be OFF.)
Second question:
How does a gate resistor reduce ringing?


texts: Loop inside a loop, where is the mutual inductance greatest?

texts:
I had a question while working a problem as to where the mutual inductance of a circular loop inside a rectangular loop is greatest.
Is it at the center, because the magnetic field of all four wire segments converge on it,or is it at an edge or corner, making it closer to the magnetic fields?
Here is a picture of the loops in question:


texts:
I would like to know what could be typical cost difference of :

Through hole via (say x $)
Blind Via
Buried Via in a high dense PCB.

Which is costlier & Why?


texts:
I considering doing an electric Go-Kart project with two direct drive rear 48v motors (considering two of these). I plan to control it using Arduino PWM pins. However, I am not sure of the route to go as far as motor controllers. Could I build a motor controller myself that will take Arduino PWM input? Or should I be looking into pre made motor controllers? Is there a particularly good IC for 48v motor control?

Thanks!


texts:
I have 3 logic input called: I1, I2, I3 and 1 ouput logic call OP.
I need:

1/ When I3 set Low, OP is High, not depend on I1, I2 's state which mean even I1 or I2 state is Low or High, OP keep High.

2/ When I3 set High, I1 or I2 Low -> OP is High, I1 or I2 High -> OP is Low

Any IC with small footprint suggested or transistor's setup can do it?

Thanks

P/S: This is my setup
I1, I2 put in a OR Gate IC and ouput come with I3 into a AND Gate IC, but the final output OP is invert, I need 1 more Invert IC, so any IC can do it instead of 3 ICs?

Table 1. (For OP to edit. - Edited - Thanks Transistor)

I1  I2  I3   Out
-----------+----
 0   0   0 |  1
 0   0   1 |  1
 0   1   0 |  1
 0   1   1 |  0
 1   0   0 |  1
 1   0   1 |  0
 1   1   0 |  1
 1   1   1 |  0


texts: Please explain MOSFET output characteristics and load line when used as a switch

texts:
My end goal is to switch a 9V-12V LED strip with an STM-microcontroller (3,3V level logic). So, I'm reading about MOSFETS (n-channel enhancement type in particular), but I'm very confused about the output characteristics and load line graphs.

In what region should MOSFET operate in "on" state? Linear or saturation?
What is the point of the load line in the output characteristic? We build a load line with 2 points: Vd=0, I=Vsupply/Rload and Vd=Vsupply, Id=0. Then we find an operating point at our Vg (Vg=3,3V in my case). But what is the point of this if maximum current is at Vd=0? And there is no graph part that corresponds to Vd=0. If Vd=0, Id=0.
How do I find a MOSFET with a low enough threshold voltage to turn fully on at 3,3V?
Thank you!


texts: MOSFET ORing behaving differently with fast slew rate on one of the Input rails

texts:
I am giving more details about the problem . pls read patiently.

we are using p-MOSFET's ORing to do automatic switchover b/w @ 12V_External (comes from PCIE edge) and emergency battery.

The circuit is as follows.

We have testing with different slew rates on 12V_External (@ CIN - comes from PCIe edge). at slower slew rates(~ ms) this works as intended.
But when we tried with 35us ramp-up rate on 12V. we are seeing ~11V spike on Battery (presently we used DC power supply for battery) during turn ON of 12V_External.

This spike is not seen with other slower ramp-up rates.

I will explain little more details on this.

When 12V_EXT power ON, VBATT ON --> 12V_PLOSS will be LOW & 12V_SLOSSN will be HIGH - power feeds from 12V_External

When Power off on 12V_External, @ 7.015V of 12V_External, 12V_PLOSS becomes HIGH (at this 12V_SLOSSN is still HIGH) so, no power is goes to 12V. when 12V_External reduces 6.715 12V_SLOSSN starts swicthing and becomes LOW Turns ON VBATT MOSFETs (M2) - which then powers the 12V.

Now, when power came back,
when 12V_External reaches 6.715V 12V_SLOSSN becomes HIGH( at this 12V_PLOSS is HIGH) so, again no power goes to 12V. when 12V_external reaches 7.015 12V_PLOSS switches LOW now power comes from 12V_External to 12V.

Above is the regular scenario.

Now the problem is>>>>

When Power comes up 12V_External with faster slew rate, there is path from 12V_External to VBATT because of that VBATT is increasing --> as 12V_SLOSSN,12V_PLOSS thresholds are depend on Battery voltage , 12V_SLOSSN,12V_PLOSS are switching @ higher 12V_External voltage.

One more thing, when M1 OFF & M2A,M2B ON - there is a path from 12V_External to Battery through Body diode of M1. But Vf of body diode is 0.8 to 1.2V, Since 12V_SLOSSN siwtches @ 6.715V, Vf of Body diode won't reach as per design.

any help will be useful.

Edit :

any thoughts on this?

I doubt dv/dt false Turn ON on M1 - But not sure how to find it.


texts: Is the efficiency of (Qi) wireless charging affected by a metal surface?

texts:
I recently picked up a Galaxy S7 Edge and love it.  I've also gone "all in" on wireless charging, now owning three chargers: a third party standard charger, a third party QC 2.0 (15W) Adaptive Fast Charger, and an OEM Samsung fast charger.  The standard wireless charger is slow, and the Samsung quick charger is fast.  The third party quick charger, however, measures a healthy 720-950mA, but never fully charges the phone after eight hours overnight.

I have a replacement charger on order, but was wondering if perhaps the surface under the inductive wireless charger would make any difference.  The charger that fails to produce a complete charge is sitting on a large, heavy gauge steel box (safe).  My question for the EEs is, could the "ground plane" from this big steel surface cause the third party quick charger to somehow be less efficient?  Could some of the inductive energy be getting absorbed, perhaps due to eddy current losses, by the large steel surface?

Thanks!

Dave


texts: Compact Voltage-Controlled Current Source Array

texts:
I'll start by asking what it seems to me a trivial but I don't know what is the most efficient solution. Electronics is not my main occupation, so I may need some indication to proceed:
I need to produce a voltage-controlled current source array. My problem is not making one current source by itself, but doing many independent current sources (16, 32, 64 channels) in the most compact package possible.
Essentially, it would be very similar to a LED array driver, where each LED is driven independently.
This is work-related, not for hobby use: I have access to a cleanroom facility to fabricate a PCB, and I can order any IC or discrete component I need. Specs are:

Current output from 0 to 30 mA (desirable, to 50 mA)
Min. 16 channels (desirable, up to 64)
No requirement on the frequency (DC is enough at the moment)
Current monitor is required (no requirement on accuracy at the moment, but in the hundreds of uA range)

I couldn't find anything on the web, if you could indicate me any resource I'll be very thankful!
At the moment, I have this LTC2668 16-bit 16-channel DAC. This is meant to provide the voltage (by software) to control the current source using SPI protocol.
Then I was thinking about using two of the ULN2803A, which is an array of 8 NPN Darlington transistors. Each emitter would be connected to a resistor (for sensing) and the load (which is another resistor basically).
What do you think about this implementation? Do you have better suggestions?


texts: What factors affect the read distance of NFC chips, and how?

texts:
I'm trying to understand how to improve the reading distance of an NFC system. So far, my understanding is that there are a few main factors in the read distance:

Size/shape of the antenna on the NFC reader
Size/shape of the antenna on the NFC chip
Power output of the reader
Power draw of the NFC chip

What I don't understand is how much I can expect to improve the read range by varying which of these parameters. If I have an NFC sticker/reader combination* that's showing a very poor read range, what should I try to do to improve it?

For instance:

some sources claim that the chip antenna size doesn't matter after a point while others say that bigger is always better.
some sources say that a very large reader coil could achieve long distance reads whereas others say that the reader coil should be similarly sized to the tag coil.

What's fact and what's fiction here?


texts:
I can't seem to find decent information on this topic as all articles only explain general concepts of pull-ups and pull-downs or only cover pull-ups in greater depth.

I understand the general concept of pull-up/pull-down resistors. I understand the working of a pull-up resistor and how to calculate its value. It's the concept of voltage drops considered when calculating R for a pull-down resistor that confuses me.

I will start with a pull-up (ignoring the 100 Ohm resistor):

Switch open: digital input acts as a current sink in a HIGH state. It has a leakage current of ~20uA and Vhigh(min) = 2V. Therefore, the circuit simplifies to +5V -> 10k resistor -> GND.

Rmax = (5.0 - 2.0)/(20*10^-6) = 150k

So with a switch closed and R = 150k, we will have a V = 2V at the junction, which is the minimum voltage required to register as logic HIGH. By picking a smaller resistor value we can ensure the voltage drop across R is smaller so the voltage at the junction is closer to +5V. For example, a 10k resistor would only have a voltage drop of 0.2V, leaving us with 4.8V at the junction when the switch is open.

Switch closed: digital input acts as a current source in a LOW state. That current is pulled straight to ground. So we can simplify this to two separate circuits: Vin -> GND and +5V -> 150k -> GND.

So essentially the pull-up resistor value has to be high enough to prevent a short circuit when the switch is open and low enough not to cause a high enough voltage drop.

Now, I am failing to come up with same logical conclusions when applying the same method for the pull-down (again, ignoring the 100 Ohm resistor):

Switch open: digital input as a current source in a LOW state. It has a leakage current of 400uA and Vlow(max) = 0.8V. How do I use this information?

In my eyes I see it like this: The input is connected directly to GND, the drop across R will always be 5V no matter what, giving us exactly 0V.

Switch closed: most of current bypasses R, thus a large amount of current at 5V is going straight into input (bad thing?).

So why do people always talk about voltage drops across R when it comes to pull-downs? It doesn't make any sense to me, it's been bugging me for a while now, any help is greatly appreciated!


texts: What is best sources for learning and practising AVR microcontrollers?

texts: I am computers and systems engineering student and I am very interested in microcontrollers so What is best sources for learning and practising AVR microcontrollers ?


texts: I need help in rewiring a chicken coop pop door

texts:
4 years ago I purchased an automatic chicken pop door for my coop. It is 12 volts and the door opens at dawn and shuts at dusk by means of a photosensor. It is a home built device that works quite well. It stopped working recently. Of course, I took it apart to diagnose the problem and made a sketch where all the wires went (they are all either red or white) and promptly lost the sketch. I need help in correctly wiring the linear actuator to the relay. Can someone tell me how to wire this? Sorry for the primitive sketch. The linear actuator is from a hospital bed and stops when it is fully extended or fully retracted. When the polarity is reversed the actuator travels in the opposite direction. The microswitch is at the bottom of the door to stop travel when an obstruction is hit and signals that the next direction of travel is in the opposite direction. The relay is an Omron LY2N-J DPDT on a PTF08A base. The wiring shown I KNOW to be correct. I just do not know where to attach the switch (possibly 1 and 4) or the actuator.

It is important to me - I know I look like a rube - I'm not electronically oriented but can handle the wiring.


texts: How does this inductive musical-keyboard function?

texts:
I've been looking to interface with a keyboard that I've removed from a non-functional system, specifically an Ensoniq EPS-16. As luck would have it, I managed to find schematics for the controller board, which handles the output of inductive sensors underneath the keys, and hands it on to the main controller.

I have reason to believe the controller board may be faulty (or at least, I am having a lot of trouble getting input or output from the MC68HC11 micro controller on the board) and I can not find any documentation about the proprietary IC (Motorola branded S38BC010PS01) used, processes the key output signals.

My plan is therefore to read the data directly from the keyboard signals which is where I'm having trouble. I can so far deduce that there are 4 input select lines and 4 data output lines, the input lines, CS0 to 3, drive a set of 4 to 8 demux ICs (74LS138) which select the key/bank of keys to poll data from.

From there, the output of the demux lines is fed through a strange network of transistors and the individual key inductors, and then into a bizarre use of inverter gates which are then directed to 4 output lines F0 to 3. I have no idea what kind of output signal I should be expecting. At rest, all of the output lines sit at 2.5 volts does not change if I press anything.

Everything I've described is shown in full in the schematics KBD-LOWER with the rest of the keys in KBD-UPPER. The main input/output header leads into the KPC Controller board where the micro controller and the other proprietary chip process the information.

Someone else with a similar mission to mine posted here that the output signal is a 3MHz rectangle that adjusts with key presses but I'm not seeing how it could be produced, and my only analog scope is low frequency and doesn't detect any worthwhile changes in the 2.5 volt signal


texts: The SPH0645LM4H-B microphone seems to output all negative values via I2S

texts:
Attached is an image from the analyzer. I am afraid that the I2S is shifted one bit, because as it stands, the MSB bit is always high, all samples come back 0x3nnnn (18-bits, so MSB bit is on the left). 2's complements format would indicate they are all negative.
Analyzer is set up per microphone documentation, sampling at clock falling edge. By the way, the PIC, which I am using, is getting the same data in RAM buffer, as the analyzer. Yes, maybe I set them both same wrong. But this question is not about PIC, it is about understanding this specific microphone data format.


texts:
I am working on the question in the image attached. As shown, I have gotten the first question right, although with a bit of trial and error. I was able to solve circuit one on my own, but from there on.

For example:

In circuit two, I found that the impedance is: 1/jwC +R.
For w=0, the size of the impedance I think is R, = 10000 ohms, (substituting w=0 into the overall impedance equation I just wrote.) However, the answer is actually infinity, and I do not understand why this is.

I appreciate any help. Thank you for your time.


texts: Why is my linear taper potentiometer nonlinear at the end points?

texts:
I purchased a rotary potentiometer with a linear taper.  I assumed that this meant that from its lowest position to its highest it is linear in its resistance change.  However, I've found that this only holds for approximately 180 degrees, after which the resistance is nonlinear.  I've attached a figure below:

Here's the datasheet. It doesn't contain any resistance data other than to say it is linear (unless I'm totally missing it).

Interestingly enough, this is for a 1st year circuits lab, so it's actually better if this behaviour is typical.  I could, for instance, as them to analyze their data and choose the range for which the linear relationship holds.  However, if my pot is broken then I'm obviously not going to do that.

So, is it my potentiometer that's the problem, or is this a normal thing?


texts: Soldering problem when changing component on tablet board

texts:
I needed to change demaged Schottky SMD diode (2.2x1.2mm) at chineese tablet board. But I was not able to melt solder even I used hot gun at 400°C or soldering tip at 480°C. Finally I more or less "unstick" diode (solder was not liquid), put there lead solder and soldered new diode. But the quality of connection is rather poor but working.

What solder is used at these boards, is there some covering lacquer, resin or is there so huge heat sink via PCB I'm not able to melt it without preheating? I don't think the pads has reason to have huge heat sick as it's low current step-up converter for display (tiny power choke). And seems neither component solder was not affected too.


texts: Is it possible to add up DC DC converters in series to create 36V output from 5V input?

texts:
I am trying to step up my voltage from 5 volts to 36 volts.

The only way that I am seeing this is to have a DC DC Converter. I am planning to use a DC converter which steps up 5 volts to 12 volts each and by using three of them and then later on connecting them in series assuming the voltage would add up.

Would this be possible?

DC/DC converter, semi reg, 3W 12V specifications:

DC / DC Converter Type: Isolated POL
DC / DC Converter Output Type: Fixed
Input Voltage DC Max: 5V
No. of Outputs: 1
Output Voltage Nom.: 12V
Output Current Max: 250mA
Output Power Max: 3W
Depth: 19.5mm
Width: 7.2mm
Height: 10mm
Isolation Voltage: 1kV
Output Current: 250mA
Output Voltage: 12V
Power Rating: 3W
SVHC: No SVHC (19-Dec-2012)
Supply Voltage: 5V


texts: Relay not switching immediately from switching power supply to battery backup

texts:
WARNING

This project as currently described is badly flawed in a number of ways that are liable to lead to complete failure of the equipment. As it is stated that it is intended to be used in a life support system, equipment failures could result in fatalities.

It must be understood that advice given here is by way of comment and, even if followed,  is in no way certain to be adequate to ensure that lives are not endangered.

The poster should seek competent professional assistance before implementing any system for this purpose. - RM

Added: Dude8604 has indicated that this system is for a respirator for his own use. That makes the concerns just as valid BUT the risks are up to him to judge.

I'm building a 12V UPS system to run some critical medical equipment without power interruption. The power noeds to switch over immediately so the equipment won't shut off. I have it finished except for one problem - the relay takes about 5 seconds to switch over. I've traced the problem to the 13.8V switched mode power supply, which is connected to the relay coil and the normally open terminal. The output of the power supply stays at a voltage high enough to keep the relay closed, but too low to keep the equipment running for those 5 seconds.

I have 2 1N914 diodes in series with the relay coil to reduce the voltage to the coil to closer to 12V coil spec. Do I just need to put in a Zener diode with the right voltage to keep the relay barely closed? This doesn't seem like the best way to do it since the power supply's output capacitor won't discharge for a long time.

Or is there a way I can rapidly discharge the power supply's output capacitor low enough to switch the relay without wasting a lot of power through a resistor in parallel?

Here's a link to:
the power supply

the relay

On a related note, I'm considering switching from relays to transistors.  To get a "normally closed" position, I think I'd have to use a depletion mode P FET (with Vth=0? does that exist?), but they're nearly impossible to find, especially for a decent price.  Or a P JFET, but the ones I've seen can only handle a few mA, unless I use it to drive the gate of an enhancement mode FET, but I'd prefer a single transistor solution.

Thanks!

edit: Here's the circuit diagram.  My question is about the relay towards the bottom right. The rest is for charging and might not be the best way, but that's a separate issue for now.

edit 2: Simplified version:


texts: VHDL -- When is a process block too long?

texts:
There is a great free (gratis and libre) VHDL book called Free-Range VHDL which is quick starter.
As a neophyte, I am having difficulties judging the relative rules of thumb when it comes to process blocks.

From the book:

  In VHDL, the best approach is to keep your process statements centered arounda  single  function  and  have  several  process  statements  that  communicate  with  each
  other. The bad approach is to have one massive process statement that does everything for you. [p. 49]

I'm not sure how long exactly it too long. For instance, while trying to designing a simple 4-bit counter with enable, reset and load value functions, my process statement exceeds 40 lines of code. Since we're targeting actual hardware, we were able to synthesize it without a problem.


texts: Moore vs mealy, why the output is delayed in the former?

texts:
I am not an engineer (software developer myself) but would like to understand why moore machine output is delayed.

I know that in Moore's machine, output depends only on the state, while in Mealy's machine, it depends on both the current input and the state.

But to me it does not explain why it is said to be delayed (or as one source puts it "the change in the input will manifest on the output in the next status".

But why? If the Moore input is entered, the state changes and the output is generated. So what is this delay?


texts: RC-circuit with one input terminal and many outputs with different integration time

texts:
What is the simplest way to create an RC-integrator with one input terminal and several output terminals which differ their times of integration (see schematics below).

simulate this circuit – Schematic created using CircuitLab

NOTE: It is intended to plug-in only one output at a time.

I think the following circuit would work. But think that calculation for three and more output terminals would be messy. Though I don't know if any desired times of integration could be obtained by this schematics.

simulate this circuit


texts: DC Coaxial Power Connector Rated for 20A

texts: I have a 12V 20A power adapter seen here (https://www.ledwholesalers.com/v2/index.php?route=product/product&path=40_117&product_id=999). I would like to connect to this power supply, but my issue is that it ends with a coaxial connector and I can't find a compatible item. I've found something close to what I want (https://powerwerx.com/21mm-coaxial-socket-powerpole-adapter), but this is only 18awg whereas I'm looking for 12awg. Is there something better suited for the job or something I'm missing?


texts:
I want to use some DC-DC LM2596 stepdown power converters available from EBAY. They have a pot used to set the output voltage.

Several questions arise.....

First, is related to adjusting the voltage to the desired levels. Is the output voltage dependant on the input voltage? The input voltage may vary from 12 to 18 volts or so when connected to different systems, so having to adjust for this manually is a non-starter.

Second, assuming these are usable, what input filtering is needed for correct function? The input will be from a rectified square wave that's about 16v created from an H-bridge which is reversing polarity of the signal. Basically a 50% duty cycle square wave around a ground reference.

I initially used an LM317 regulator, but the thermal requirements to supply 400MA dropping the voltage to 6VDC is excessive.


texts:
Hi I am building a motor controller and I decided to use PSMC instead of CCP to create my PWM, my decision was based on the fact that I dont have enough CCP ports on my pic 16f1788 for the project. I am using the PSMCdesigner module provided by Microchip. I went through it and generated my code but unfortunately the code doesn't work. I know how to program CCP but never worked with PSMC before I would like to get some help here is the code I generated through the program.

#include <xc.h>
// Config word

// CONFIG1
#pragma config FOSC = INTOSC    // Oscillator Selection (INTOSC oscillator: I/O function on CLKIN pin)
#pragma config WDTE = ON        // Watchdog Timer Enable (WDT enabled)
#pragma config PWRTE = OFF      // Power-up Timer Enable (PWRT disabled)
#pragma config MCLRE = ON       // MCLR Pin Function Select (MCLR/VPP pin function is MCLR)
#pragma config CP = OFF         // Flash Program Memory Code Protection (Program memory code protection is disabled)
#pragma config CPD = OFF        // Data Memory Code Protection (Data memory code protection is disabled)
#pragma config BOREN = ON       // Brown-out Reset Enable (Brown-out Reset enabled)
#pragma config CLKOUTEN = OFF   // Clock Out Enable (CLKOUT function is disabled. I/O or oscillator function on the CLKOUT pin)
#pragma config IESO = ON        // Internal/External Switchover (Internal/External Switchover mode is enabled)
#pragma config FCMEN = ON       // Fail-Safe Clock Monitor Enable (Fail-Safe Clock Monitor is enabled)

// CONFIG2
#pragma config WRT = OFF        // Flash Memory Self-Write Protection (Write protection off)
#pragma config VCAPEN = OFF     // Voltage Regulator Capacitor Enable bit (Vcap functionality is disabled on RA6.)
 #pragma config PLLEN = ON       // PLL Enable (4x PLL enabled)
 #pragma config STVREN = ON      // Stack Overflow/Underflow Reset Enable (Stack Overflow or Underflow will cause a Reset)
 #pragma config BORV = LO        // Brown-out Reset Voltage Selection (Brown-out Reset Voltage (Vbor), low trip point selected.)
 #pragma config LPBOR = OFF      // Low Power Brown-Out Reset Enable Bit (Low power brown-out is disabled)
 #pragma config LVP = ON         // Low-Voltage Programming Enable (Low-voltage programming enabled)

  void main(void)

{

PSMC1CON  = 0x00;
PSMC1MDL  = 0x00;
PSMC1SYNC = 0x00;
PSMC1CLK  = 0x30;
PSMC1POL  = 0x00;
PSMC1BLNK = 0x00;
PSMC1REBS = 0x00;
PSMC1FEBS = 0x00;
PSMC1PHS  = 0x00;
PSMC1DCS  = 0x00;
PSMC1PRS  = 0x00;
PSMC1ASDC = 0x00;
PSMC1ASDL = 0x00;
PSMC1ASDS = 0x00;
PSMC1PHH  = 0x00;
PSMC1PHL  = 0x14;
PSMC1DCH  = 0x00;
PSMC1DCL  = 0x00;
PSMC1PRH  = 0x00;
PSMC1PRL  = 0xC7;
PSMC1DBR  = 0x00;
PSMC1DBF  = 0x00;
PSMC1FFA  = 0x00;
PSMC1BLKR = 0x04;
PSMC1BLKF = 0x02;
PSMC1STR0 = 0x3F;
PSMC1STR1 = 0x80;
PSMC1INT  = 0x00;
PSMC1OEN  = 0x05;
PSMC1CON  = 0x80;
PIE4     &= 0xEE;
PIE4     |= 0x00;

   }


texts: What is a good PCB that you can fit with 8AWG wires?

texts: Me and a couple of other students are working on a school project that is using voltage up to 100v and 40amps.  So I figured the that 8AWG wires are the ones to to use for this. They are pretty thick wires compared to the wires I would use for an Arduino. So since they are pretty thick, it does not look like they can be fitted onto regular PCB.  Anyone know where I can find PCBs to that can fit them?


texts: Is 150mW a lot to dissipate from a TO-92 in 50°C free air without heat sink?

texts:
I'm designing a circuit in which a 2N3096 PNP BJT in a TO-92 package will drop 15V with \$I_C\$ of 10mA worst case, for 150mW heat dissipation. Unfortunately, the worst case is when the circuit is idle, which could happen for long stretches if left on continuously, overnight, etc. The internal case air temperature can get to 50°C and there is no fan or case vents. Cooling is through conduction via the aluminum enclosure. The equipment is designed for use in living areas, like a lab bench, so it's unlikely to see external air temperatures above say 35°C

The thermal resistance, Junction-to-Ambient, \$R_\text{$\theta$JA}\$, stated on the datasheet is 200°C/W. I'm taking that to mean the device could get to \$50 + (200*0.15) = 50 + 30 = 80°C = 176°F\$, which is definitely hotter than I want to touch with my finger.

This strikes me as a bit hot to be running a TO-92 package on a fairly extended basis.

Am I being over-conservative or should I really think about making a change here, either to the current or the package?


texts: Direction of current flow in resistor networks

texts:
We have a simple resistor network \$g\$ with \$5\$ nodes and \$6\$ edges (resistors) as given below:

We assume all resistors have the same resistance (say \$1\$ Ohm, so homogeneously distributed resistances). Now suppose we want to know which edges would carry a non-zero current if
we applied a \$1\$ Volt potential difference across the nodes \$1\$ and \$4.\$ Once we apply this constant potential difference, there will be current flowing either from node \$1\$ towards \$4\$
or the other way around. Assuming so far I haven't made a mistake in my description (from circuit theory point of view), if we adopt a "positive" direction for the current (I guess it doesn't matter which way is chosen),
how do we determine the current direction along each edge? In other words, having now induced a current flow through the resistor network, my originally undirected graph will become a directed one, but I don't know how
the edge directionality ought to be defined consistently.

One hypothetical situation of current flow once a voltage is applied between nodes \$1\$ to \$4\$ could be: (intuitively I don't expect there to be current flowing between 4 -> 5 because probably the potential difference
between those nodes is 0 given the difference was applied across 1 and 4.)

Once I can determine the direction of flow across each edge then I can write down the incidence matrix \$A\$ where then for an edge that goes from node \$x\$ to node \$y\$, the row corresponding to that edge has
\$−1\$ in column \$x\$ and \$1\$ in column \$y\$ with all other entries in that row being \$0.\$
Having the matrix \$A,\$ to answer my original question (namely which edges are carrying non-zero current), for the current vector \$\mathbf{i}\$, I invoke the Kirchhoff's law, namely that:

$$A^T \mathbf{i} = \mathbf{0},$$

where the current vector has a dimension equal to number of edges in \$g,\$ then finding an eigen-basis for the nullspace of \$A^T,\$ I would know which entries of \$\mathbf{i}\$ are non-zero. I admit
I am not entirely sure about this approach, as in whether it's really the way to find an answer to my original question.

Summary of questions:

How do I determine the direction of edges, in other words direction of current flow along each resistor, as described in the first paragraph?
Given the original question of: "which edges will carry a non-zero current once a potential difference is applied across nodes \$1\$ and \$4,\$," is my approach as described in the last paragraph at all sound?

I've specifically chosen a very small and relatively simple network in this question for the purpose of illustration.


texts: Routing of multiple impedance controlled tracks

texts:
I am designing a board with 50 and 75 ohm tracks on the same layer.My board receives SDI video via RG179 coax. The board has an SMA connector that receives the said input. The track is 75Ω track.

This is given to an LMH0344 chip that converts it into differential pair. The said chip is an adaptive filter chip which accepts either differential pair or 50Ω signal. So I am using an impedance matching pad - Link.

The differential signal is sent to an LMH0346 reclocker chip. The output of which is sent to an LMH0307 chip. The output is split RG179 video which means the 2 signals are 75Ω.

Now, the same layer has 75,50 and differential 100Ω. I am using a 4 layer stack-up Top->Gnd layer->Vcc layer->Bottom layer. Any tips in layout and routing of these signals ?


texts: I am using tl494 to drive the buck converter because I want to drive the MOSFET so I using the Transformer to enlarge the PWM signal. Ds is the TL494 output signal and Vcc is 15V. the transformer ratio is 1:1. I am using the PSIM to model the circuit, but the result is not right. the Vp1 still the DC value not AC I don't know why, can someone tell me what's wrong with this circuit?


texts: Missing footprint dimensions in Datasheet

texts:
I am preparing to start work on designing a board that uses a component in a PowerFLAT 5x6 package (the component is a power Schottky rectifier, part STPS30M100DJF from STMicroelectronics). The datasheet is here: http://www.st.com/web/en/resource/technical/document/datasheet/CD00255467.pdf

Altium Designer (the software I am using to design the board) does not have a land pattern for the PowerFLAT 5x6 package so I am having to create it from scratch. However, looking at the footprint in the datasheet I am still missing a few critical dimensions. I contacted STMicroelectronics but have not received a response. I'm wondering if anyone has the information shown in red in the below image?

Most of the land pattern is done, I'm just missing the information needed to put on the side tabs. Thanks!


texts: Safe microcontroller input from 8.4V circuit

texts:
I have an airsoft rifle which uses an 8.4V battery to drive a motor when the trigger is pulled. The circuit is that simple, just a battery, motor and switch - there's also a 15A fuse.

I want my microcontroller to detect when the trigger is pulled, but I don't want to have to dismantle or extensively modify the replica gun. The only wiring I can get to is the battery terminals.

My first thought was to just put in a relay on one side of the battery, but I'd prefer to avoid the noise and reliability issues. (I'm willing to be persuaded otherwise)

Now I'm considering using opto-isolator. I haven't picked a particular model yet.

I can't risk the microcontroller being damaged. Its digital input is pulled up to 3.3V by a 22k resistor.

I apologise for my total lack of skill at electronics, but I don't know how to put the opto-isolator in circuit, at the right voltage etc. (Other than just putting it in series, with a resistor, which would presumably slow down the motor - no good.)

I'd appreciate any relevant example you can provide - or completely different approaches.

Thanks!


texts: Instead of using a $25 Li-Poly battery with a $10 charger, I was going to use one of these- https://hackaday.io/project/46436-3-cell-rc-battery-pack-made-with-18650-batteries What I was wondering Is how it would compare? It seems safer than a Li-Po, and cheaper, seeing how I have a bunch of those batteries sitting around, but performance wise, I'm clueless.


texts: Determining jitter for Vivado clocking wizard?

texts:
I have an Artix-7 FPGA AC701 board. In the documentation, it says that it has a 2.5V LVDS differential 200 MHz oscillator (model name: SiT9102AI-243N25E200.00000). I went into SiT9102 datasheet and it says on page 7 that 2.5V LVDS model at 200 MHz has a typical RMS jitter of 2.4ps and maximum RMS jitter of 3.5ps.
Now, to input the value into Vivado's clocking wizard, it says inside the clocking wizard documentation on page 37 to input the peak-to-peak jitter.
Based on this paper from Maxim Integrated, I should multiply the value of the RMS period by 14 to glitch once every 10^12 cycles (>1 hour stable).

Is it at most one glitch every 10^12 cycles or is it highly likely to glitch every 10^12? I am guessing the later.
Should I use the typical RMS jitter value or maximum RMS jitter value for the RMS value?
Is typical for when it will usually glitch and maximum RMS is when it is guaranteed to glitch?
Can someone confirm what I am doing is correct?


texts: Determine direction of RS485 communication

texts: I got two devices communication serially with RS485. I got a serial analyzer with which I am able to listen to the whole communication but I am unable to determine which bytes come from which device. Is it possible that I can somehow split up the line while still letting the devices communicate with each other, so I can determine the direction of the communication?


texts: Why would I use a transformer instead of one inductor in a crystal set?

texts:
I'm reading up on A Simple Radio Receiver. I have a question about this image:

The signal from the antenna (perhaps a few tens of microvolts, or hundreds for a nearby transmitting station) is introduced to the LC circuit either through a small capacitance, or, as in this case, by means of a second coil L2 wound on top of L1, with its other end connected to earth.  This behaves like a transformer - currents flowing in L2 generate a changing magnetic flux which cuts L1 and induces an emf in it.

I don't understand why L2 is needed. It forms a transformer with L1, to "cut L1 and induce an EMF in it". What is meant by 'cutting' in this case? And, when they need EMF in L1, why not just connect it to the antenna input directly? Like this:

simulate this circuit – Schematic created using CircuitLab
Sorry for the ugly schematic, it would've be too large otherwise.
Anyway, why is a transformer needed in this crystal radio set? I actually built a crystal set without a transformer, with this circuit:

I also added a 100n capacitor parallel to the crystal earphone.
Why would or should I use a transformer instead of going into the LC circuit immediately?


texts: I have a motor that only runs in one direction.  I currently use a fqp30n06L logic level MOSFET to control the motor.  Once the MOSFET gate is grounded, the motor does stop but it freewheels.  I also have on hand some p channel MOSFETS, FQP27P06.  The motor is a 12v motor.  Is it possible to use two of the N channel logic MOSFETS or a combination of the N channel and P channel that i have on hand to construct a circuit that also has braking in an H bridge layout?  If so, would anyone be willing to supply a schematic using the two for me to learn by?


texts: I want to run run two different 2.4 GHz radio cards off of the same antenna. Is this possible? I was thinking of running both into a splitter and running a single cable to the antenna. The two radio cards are operating on different channels. Is this possible or no?


texts: Difference Amplifier to retrieve sine wave

texts:
I have built the following summing amplifier circuit from a Fourier approximation of x(t)= 0.143 +  4/π ∑((sin(2π(2k-1)ft)/(2k-1)). I am now trying to retrieve a sine wave from the output of the summing amplifier circuit by using a difference amplifier.
The sine wave must have an amplitude of 1V and a frequency of 100Hz.
I thought using the terms of the Fourier approximation with a frequency higher than 100Hz as input into the difference amplifier would do the job but I end up with the no change to the summing amplifier output.  How do I go about retrieving the sine wave?
Summing Amplifier circuit and Output


texts:
If we get 220V from outlet, would it be possible to tell the maximum power (wattage)?

Since,

Power = Voltage (V) x Current (I)

Also, Is it possible to get the maximum amount from current (I) from 220V? Assuming any type of standard wire with resistance used?


texts: maximum clock frequency for a sequential circuit

texts:
This is the all question.

I thought that because Tcq>Th we will only count Tcq. If we need to know the minimum clock period, we should calculate the duration from the beginning to the output of DFF1. It makes TpdX+Tsu+Tcq+TpdA+TpdX+Tsu+Tcq = 51ns. Is that right?

I didn't get how the minimum clock period will occur when there are 2 flip flops. Because second flip flop depends on output of the first flip flop. Will we count Tcq twice?


texts: what is the meaning of BLE data rate 1Mbps?

texts:
I am using BLE HM10 module which is BLE 4.0 1Mbps

assume I have 1000000 data bits to send within a second, so I need 1Mbps bandwidth,

Is 1Mbps only for Data bits?

or 1Mbps means complete Bluetooth packet bits + data bits?


texts: In ADCs, what is the number of conversions per sequence?

texts: I'm dealing with a microcontroller's Analog to Digital Converter (ATD_10B8C) that has a control register who's bit values determine the "number of conversions per sequence". What exactly does this parameter refer to?


texts:
When using film capacitors for high frequency (100's kHz) applications, is one type better then the other? Historically it seems like axial capacitors were used in audio etc. where frequency characteristics were important. I am assuming that is because axial was just easier to make back then vs now...

For instance, is it better to use a Radial or Axial capacitor for a half bridge?  What about decoupling ringing due to high frequency switching? Does one have less internal inductance? Or does it really not matter?


texts:
I am currently working on a project to amplify a very small signal (about 10 millivolts) using a vacuum tube. I understand vacuum tubes were used as amplifiers and transistors back in the day, but I can't figure out how they were used to power anything with the tiny amount of current they can deliver through the anode/cathode.
I'm looking to power a small relay with the amplified pulse.
I'm obviously missing something.
Can someone explain to me just how these were wired to perform the same function as transistors?


texts: Phase shift problems with ICL7611 op-amp

texts:
Update: This problem has been solved, the error was in another circuit that was providing the current and not with this. Note to everyone (and self): ACS712 is direction sensitive, even for AC currents. Connecting in the opposite way gives a 180 degree phase shift in the current.

I am using the ICL7611 op-amp to add DC to an AC signal. In a non-inverting amplifier configuration. The output looks good on magnitude, but is shifted by nearly 90 degrees in phase.

simulate this circuit – Schematic created using CircuitLab

This is how my output is looking (Red is Voltage, Green is current). Normalized in magnitude.

While reading the datasheet of ICL7611, I found this piece of information.

Does it mean, the IC is adding a phase shift? If yes, how do I compensate it? If no, Why am I getting this phase shift?  Thanks.


texts: Here is a typical diagram of a bjt amplifier. so whenever we talk about output impedance (unloaded)do we mean the impedance (AC) between the point V_0 and ground? and also we say "loaded impedance" that just means we have now just added the load R_L;  in this case what are those two point we are considering between we are suppose to measure the impedance? how about the term "loaded output impedance"? which is R_C||R_L, this impedance appears between the point X and ground. seems like now we are considering the point X and ground as our output port, which is not. so what does it mean to have a loaded output impedance? and where to measure it?


texts:
What is the proper non-contact way to monitor the temperature of an surface area? In the picture below, I divided a square into 36 little squares. The goal is to get the temperature of each and everyone of little squares. What technique do you recommend?

The most obvious one is to attach 36 laser thermometers, but this approach doesn't scale well, if the number of squares becomes larger, or the size of them smaller.

Edit:

Each square's area is about 0.25cm2
Material isn't fixed. It ranges from metals to organic.
I have no clue of the emissivity of the materials in question and it would also be hard to predict all of them.
Desired sampling frequency is 1Hz for the whole surface so read time I guess is < 1s/36 per square for the particular image and more like 10ms for each of 100 minisquares, but the exact value doesn't matter
Desired temperature range falls within 300K and 600K


texts:
There is a problem I have been dealing with for hours.
In my Electronic 1 lecture, small signal analysis was like this:

The small signal equivalent of this circuit in my lecture notes was this:

When they calculate the no load voltage gain Av they do not remove the Rc. To me, Rc is the load but they do not accept.

In this semester in Electronic 2 lecture, the topic is feedback of amplifier circuit and this time they accept Rc is load (effective load this time) and when they calculate the no load open-loop gain they remove the Rc.
Why? Which one is correct?

(I am sorry for my bad  english)


texts: Why aren't latch based designs common these days?

texts:
Almost every ASIC out there if flip-flop based. In summary, DFF is two latches pushed closely together. While in a latch based design you can "separate" these two latches apart and squeeze logic in-between them. There are several advantages to  a latch-based design:

Time borrowing: can relax timing a lot
Reduced area and power consumption: you get the same logic with half of the registers

Disadvantages:

Two-phase clocks with dead-time are necessary
Hard to wrap your head around the concept
Tools don't support the concept easily
Hard to prototype. Every FPGA out there has a DFF in their cell, not a latch
Hard to do a scan-chain

Are these disadvantages so severe that the latch designs were abandoned? I mean, if we had proper EDA tools and FPGAs we could still do it, right? Or am I missing something really important here?


texts: IEEE802.3af, 802.3at @ 2 x 30 Watt. But now @ 2 x 75 Watts

texts:
I have built large networks with IEEE802.3af & IEEE802.3at in PoE midspan and endspan style.

I favor 48VDC, because it is the only standard used world-wide. AC can be anything depending the continent... Each serious telecom equipment manufacturer has them in their portfolio.

We can power phones, fixed and PTZ camera's and IoT devices over cat 5/6 UTP cabling, but when you say that you want to power a serious server, everybody starts shaking there head. No can do..

Research shows that UTP cabling when using 4 pairs can support 160 Watts up to 20 meters. In the case of GB ethernet, you need two 1on1 separation transformers for each pair (so 4 times) to be able to inject and extract the superimposed 48 VDC.

But nobody builds transformers for > 30 Watts... Simply because there is no standard supporting 2 x 75 Watts...

Forget separate power cables. Want to save copper. Superimposing an Ethernet signal on a DC source is as old as Alexander G. Bell, so I guess it should be possible.

Anyone on designing new IEEE802.3a(z)?

Fred


texts: Why/when would you use a light to frequency converter?

texts: I have looked at the TSL235 light to frequency converter and for measuring ambient light it seems expensive (~$1.50). What application would you have for using a light to frequency converter vs a standard light sensor (CDS/LDR/diode) to measure the light?


texts: Simple Logic Circuit Not Behaving As Expected (TinkerCad)

texts:
I need to build the following cicruit: F = (A AND B) OR (A XOR B) and I came up with the circuit in the image above. The bulb is only turning on when both A and B are OFF. The expected behavior is for the bulb to turn on if (A OR B).
I tested all the gates and bulb seperately and they all work as expected but the switch inputs don't, so I'm thinking it has something to do with the switch.


texts:
I just read in Phillips led datasheet that led has 200.000 switching cycles. Would that count PWM cycles too? Because it would mean only few minutes of operation.
Also - is it ok for all DC led bulbs to be controlled by pwm?


texts: Fuse design for taking in account real-world very small transients

texts:
A bit of context

I came up with this question after someone suggested that two fuses are better than a main one in the below configuration. The converters are SMPSs which regulate output voltage.

simulate this circuit – Schematic created using CircuitLab

Now someone justified that F1 and F2 are a better implementation through the following example: both converters are functioning within normal limits, each drawing 1A (and F1 and F2 are both designed to trip at 2A). If Converter 1 would fail open and Converter 2 would continue working normally, then during the finite instant when the aforementioned conditions start applying, as current cannot change instantly and has only one path to follow from supply to ground, the 2A will flow through Converter 2 and potentially damage it. Since F2 is there, it would protect against the over-current condition. If converters reverse roles in the same scenario, F1 will be there to open the circuit.

The justification basically says that the fuses are there to protect against an open-circuit event...instead of a short-circuit.

That's as much context as I can give. Current can't change instantly, because that's just how the real-world works. I agree it's a weak reasoning, as the "why?" is missing, but I would like to prove it wrong or right to myself (with your help). To help answerers, I would like to know both if the parasitic inductance or anything else (other than parasitic inductance) could recreate the effects described.

Main part

Now, remove the converters and the loads and place two real-world resistors between each fuse and ground, both (resistors) drawing 1A normally. Again, the total current drawn from the power supply would be 2 A.

The questions are:

1) If one removes a resistor (ceteris paribus), will the remaining other experience the 2A through for a very short, but finite amount of time? If it does, can it be due to something else, other than parasitic inductance (and can parasitic inductance also affect things)?

2) Does 1) mean, if true, that ohm's law only applies if the time-step (or time scale) is large enough?

3) If 1) is true, is it worth taking into account this effect from an engineering perspective-i.e. during that short finite time, the 2A could damage the remaining resistor?


texts: TL072 based circuit generates loud noise

texts: This circuit, designed as a bass scream, keeps generating a low noise about the same loudness as the guitar signal on the output.


texts: Why coil at high frequency pass lower current?

texts:
I am currently working on a project that uses an H-bridge to output different direction current.
I use 2 P-channel MOSFETs (IRF4905), and 2 N-channel MOSFETs (IRF3710) to build my H-bridge.
*reference circuit:
https://www.homemade-circuits.com/how-to-implement-p-channel-mosfet-in-h-bridge-applications/

(The figure title is "Using P and N-channel MOSFETs", and I input signal which label as MCU)
I use an Arduino to give two different square waves between 5Hz~50Hz, 0~5V signals.
I found that the higher the frequency I give to the H-bridge, the lower current through the H-bridge (under same resistance connect to output and voltage power supply.)
Why does this will happen?
//
2020-04-22 edit
Thanks for your comments. Those really help me a lot!
Because the h-bridge output I connect to the coil(around 1000 turns)
So coil may become bigger resistance at high frequency
Could anyone give some keywords that I can do more search about this?


texts: Communications issues between Ardupilot and Computer

texts:
The Issue and Project:

I have been at a standstill with my autopilot because I cannot communicate with it using my high powered transmitter: the Ubiquity Rocket M5. But the whole communications issue is not as simple as breaking it down to just one component, it succeeds through various sections for various reasons as I will discuss in the section below. But before I go any further, this is the end goal and current setup for by project:

Ardupilot with custom software (communications via serial)
Arduino Ethernet to convert Serial to Ethernet [static: 192.168.2.30]
On-Plane Switch
Ubiquity Rocket, this is in the plane as the "router/access point" [static: 192.168.2.1]
Ubiquity Rocket, this is on the ground ad the "bridge/station" [static: 192.168.2.21]
Laptop with custom user interface [static: 192.168.2.10]

The packets are sent on port 8888 via UDP. The ground reads the packets via python piped as xml via CherryPy to a webpage on the same computer. The plane also contains a network camera attached to the on-board switch (3). It has an IP of 192.168.2.20.

My Trials:

What happens with everything plugged in appropriately:

The network camera provides a live stream
I can ping the arduino ethernet module
I send packets to the ardupilot, but no response

Ok, I then thought that I broke something somewhere. So I skipped the wireless link and plugged my laptop connection directly into the switch (skipping connections 4 & 5):

Everything works appropriately

I was baffled, I have never had anything bad happen between my ubiquity rockets. So after a while I figured out a way to test the connection. I disconnected my autopilot from the Arduino ethernet to hook up a FTDI cable to my computer and opened up serail monitor to verify the packets.

Packets get sent though and display serial monitor just fine
I opened up a testing program on my computer to read packets for port 8888. I sent some packets from the Arduino Ethernet to my computer and they worked just fine.

I am flush out of ideas at this point. If you have an idea you would like to test, let me know and I will post the results.


texts: Context switching and systick handling on the STM32F series

texts:
I am using a STM32F407 board to build my own tiny RTOS and I have some questions.

How can I define my own stack in different memory location, so I can have one stack for each queue of tasks?
How do I push and pop to those stacks in my systick handler, what registers?
Systick handler works fine for me, but when I put a function in an infinite while loop it stops working, why is this?

Example code for 1 and 2 would be very appreciated.

My current code is below:

#ifdef __cplusplus
extern "C" {
#endif
void SysTick_Handler(void) {
    /*1-Mask all interrupts except for E programs dependency*/
    OSD_maskUnE_Interuppts();
    OSD_SystimerISR();
}
#ifdef __cplusplus
}
#endif

int main(void) {
    SystemCoreClockUpdate();
    SysTick_Config(SystemCoreClock / 100);

    while (1) {}

    return 0;
}


texts:
Apologies if this question is too vague. I have incomplete information and I'm asking because I'm not sufficiently knowledgeable to answer this myself!

I have ten USB LED units and I have a 12v power supply (that is the only power supply I have available, no mains). I also have a number of LM340T 5 volt regulators. Given the components I have to hand, I want to figure out the best way to wire them up, or whether there is no best way to wire them up and I should do it differently.

There is very little info on the LED units, except that they're rated 5 Volts. I don't know the current rating. Inside are two pairs of tiny J3 transistors and resistors. I can't see the tracks, but I could work it out the circuit with a continuity tester. I imagine we're talking a few tens of mA but I don't know.

Do you think it would be a good/bad idea to use one LM340T per LED to drop the power from 12v to 5?

Do you think that the LED units (and their internal regulator circuit) would behave nicely in series to form a potential divider, three to a circuit to give 4v each?

Should I just get a proper Buck converter?


texts:
I am trying to increase the working range of cheap arduino 433 mhz RF link modules like these https://www.sparkfun.com/products/10534.

The page says they have range of 500 feet in perfect conditions however in my case it's more like several feet.

So I know I can extend the range by simply applying more powerful power supply, but I thought if I can take the Tx output and feed it into some sort of high frequency amplifier.

I can't buy any here so I'll have to make my own. I am interested if it is even worth trying or will it be so complicated I am better of doing something else?


texts: Contact pad size for microprobe coaxial to planar waveguide transition

texts:
http://www.ggb.com/t-4.html

Can someone explain what size one should choose at minimum/maximum for the pads and what role the pitch plays (besides impedance matching)? If I order a 100 micron tip diameter Ground Signal Ground GSG probe for contacting a coplanar waveguide where I do via lithography big contact pads and then taper the this large structure to the final wished geometry (signal ground line width some few microns), how big has the contact pad to be? Is 200-300 micron edge length enough assuming I can hit the pads with the probe tips by using a micromanipulator and optical microscope. So mainly for reasons of adjustment, or does a too low size of the pads effect negatively the electromagnetic wave propagation? In software like HFSS, CST, Sonnet the ports are mostly modeled as areas perpendicular to the signal and ground lines, does this really compare to picoprobe transition correctly?

Thanks for any tips or pointing me towards some literature


texts:
I don't know if I'm at the right place to ask this question but here is my trouble :

I'm trying to find a good way of calibrating a electronic device used to measure small torques (0 -> 25 mNm).

Device adjustment :
Our current way of adjusting our measuring device is by hanging measurement standards to it and adjusting the way it measures.

Calibration :
Our current way of calibrating this device is again by hanging the measurement standards and checking if the device measures properly.

Being new to the process of calibrating a device, is there a standard way of proceeding ? Are there good documentations on the calibration problem ?


texts: Tried to measure current with red lead in voltage socket - bad for multimeter?

texts: I just tried to measure the current that my circuit draws when powered by 2xAAA batteries (3 V) using my Fluke 87-V. I connected the leads in series with the battery, but I accidentally left the red lead in the voltage socket instead of the mA/uA socket. Is this bad for the multimeter or could I have damaged it somehow?


texts: When eqvivalent transfer function of two systems in series is a product of two transfer functions that describe these systems?

texts: In control systems theory when two systems with transfer functions \$ H_1(s)\$ and \$H_2(s)\$ are in series, equivalent transfer function is given as \$H(s)=H_1(s)H_2(s)\$. However if we have two RC filter in series, the equivalent transfer function is not a product of the two transfer functions of RC filter. It is indicated here Can you find the transfer function of two cascaded networks if you know their individual transfer functions?. My question is, does this means that transfer function  \$ H_1(s)\$ and \$ H_2(s)\$ are calculated and these systems are always made such that input and/or output resistance of the other connected system doesn't make any influence on its performance? Or I am missing something? Or, when is it possible to do simple multiplication of the transfer functions?


texts:
I am designing 4-layered PCB for the first time.

Searching web, I learned that normally we place layers in following way

TOP
|
GND
|
VCC
|
BOTTOM

Will there be problem if i place GND at the bottom? So that it works as below

TOP | VCC | BOT | GND

?


texts:
I am trying to implement Smart Card Reader( MFRC523 Reader) using Controller LPC2138 interface.

Link for datasheet:
http://www.nxp.com/documents/data_sheet/MFRC523.pdf

I have interfaced MFRC523 smart card reader to LPC2138 using I2C protocol. For I2C interface, IC datasheet suggests NRSTPD pin to controller interface.

But due to shortage of I/O pin ( all I/Os used for other application ),  I have hardwired NRSTPD pin to Logic High state.

As per datasheet,

NRSTPD ( Input ): ( reset and power-down input )
reset: enabled by a positive edge
power-down: enabled when LOW; internal current sinks are switched off, the oscillator
is inhibited and the input pins are disconnected from the outside world

So Can I hardwired NRSTPD pin to Logic High.

Please guide and thanks in advance.


texts: Do 74HCxx chips require a linear voltage generator?

texts:
Recently I've read a book that says it's absolutely necessary to use a linear voltage regulator like LM7805 in circuits that use any of 74HCxx chips (CMOS logical gates). I thought that this advice is kind of odd (LM7805 requires 9V instead of 5V I most frequently use, 4V are used just to heat an air) and decided to re-check.

I didn't find this requirement in any of 74HCxx specs, at least in specs from Texas Instruments which made chips I use. This requirement is also not mentioned in Wikipedia or any other source. All circuits I tried work just fine without LM7805, with only 100 uF capacitor as a filter. So I'm thinking, maybe this advice is outdated (the book was published in 2010) or maybe author just needed an excuse to give an example of linear voltage generator usage?

In your opinion is LM7805 required to use 74HCxx? Do you use it in your circuits?


texts: Where are registers and what do they look like?

texts:
I racked my brain through my comp-arch class and reread wiki’s article on hardware registers (they’re flip-flops, I get that), but one year later and I still don’t understand what a register physically is, other than that detail. Where on a processor is it? What do they look like? How big are they?

Tentatively (assuming this isn’t worthy of a second question), I also ask: how does a datum from the rest of the system make its way to the register?


texts: Identifying mystery dual channel opto detector?

texts:
How do I identify if a component is a photo diode or photo transistor? I have a three lead component removed from an old mouse where it was used to do quadrature encoding of the scroll wheel (a normal side facing IR LED was illuminating other side of the wheel) - presumably it houses two photo detectors side by side to distinguish which direction the wheel was being turned. What tests can I do to determine if it is a photo-transistor or photo-diode and appropriate parameters to drive it? I would like to re-purpose this for a micro-controller project I'm working on.

Only markings on the package is "H6.26" on the back and 'EL' on the top.

Close up of the component - sorry, best I can do with 4am shed lighting

In situ view - placed back from whence it came

Managed to trace the two outer pins directly to separate pins on an unidentifiable micro-controller - (each trace is well below 1 Ohm). As for the middle pin it connects through a 10 Ohm resistor to I don't know where


texts:
I was studying about currents in an injected semiconductor (by illumination) from Integrated Electronics by Millman and Halkias. They consider the diffusion hole current in an injected n-type open-circuit uniformly doped semiconductor, assuming that hole concentration is negligible compared to electron concentration, and hence, the hole drift current can be neglected as it is proportional to the hole concentration.

Since the semiconductor does not have any external potential difference, drift current due either charge carrier should be zero. But it is said that the diffusion current density of the holes causes an internal electric field leading to the drift current of electrons, and the relation
$$J=\sigma E$$ is used to calculate the field (which is non-uniform) where \$E\$ is the electric field caused by the diffusion current density, \$\sigma\$ is the conductivity and \$J\$ is the diffusion current density which is not constant as it depends on distance from illumination. The net current (which is the sum of hole diffusion current, electron diffusion current and electron drift current) is zero as it is an open circuit. How, physically, does the current density cause an internal electric field?


texts: Transmitter design methods using 0201 SMD

texts:
I have some experience designing an IOT transmitter (315MHz/345MHz/433MHz) using 0603 SMD parts, but am considering building a transmitter for production using 0201 parts. My question is, what is a good work flow using 0201 parts, especially for the antenna matching/filter network? I am used to swapping out dozens of parts in the matching network while tuning and getting spurious emissions below the minimums. But I'm guessing 0201 parts take the process to a new level.

Thoughts?


texts:
Our professor asked us to name the pins of the gates as below based on a chip pinout diagram he provided which includes only NAND and NOR but in the circuit diagram, there's a negative OR gate.

Can someone please explain how to include pin numbers for it?


texts:
I'm working on a phased array radar design, and I'm trying to work out the best way to combine the different receive signals from various antenna. I'm also trying to reduce cost as much as possible, so reducing the number of RF switches, active components etc is important.

The frequency range of interest is 2-3GHz, and the signal will be narrow band (that sweeps 2-3GHz).

Each element is a transmit and receive module (TRM) and can be switched from one to the other by serial control. This means I need to be able to selectively combine any number of RX signals from the total (for the sake of argument 16).

Simply connecting all signals into large combiner or cascade of combiners is going to lead to the situation where some of the input ports are driven and some are floating, connected to a length of copper that is unterminated at the end. Will this cause issues and am I likely to loose power up the floating track of the unused input port? Will the port-port isolation help alleviate this?

Is there a particular type of combiner that is most suitable to this kind of scenario? Something that can be realized by PCB etch and passives would be absolutely ideal.

I can add in a switch to a short terminated stub so that unused input ports are terminated, but that's a lot of extra RF switches that I'd rather avoid if possible.

Thoughts?


texts:
I'm looking at options to detect forces applied to a car door. An accelerometer seems by far like the most popular option, but I was also considering placing several piezo elements inside the car door, because they appear to sense impact as well and they also seem to be easier to work with.

Is there a reason why using piezo elements is a bad idea? I can't find an example where they are used for sensing, for example, car crashes or the door hitting another object.


texts: How stable are digital multimeters' parameters?

texts:
I live in a region where standard mains voltage is 220 volts. Recently I tried to measure it using a digital multimeter. The multimeter specs say that it has maximum error of 1,2 percent of the displayed value plus 3 units (volts in my case).

So I measured and got 241 volts which kind of scared me. According to the specs maximum error would be

241 * 1,2 / 100 + 3 = 5,892

which is about 6 volts, so the real value is in range 235..247 volts which scares me even more.

The spec further says that the maximum error is only guaranteed for the first year of the multimeter lifetime which implies that the error might be even greater as the multimeter gets older.

My question is - how much worse will the error become? The multimeter is something like 5 years old now - what measurement errors should I expect?


texts: concept for true random number generators

texts:
I have an idea. Lets say we have an unpowered TTL set-reset flip flop with both inputs tied to 5v(logic high). When we apply power to the flip flop, it goes into a quiescent state, so there is no telling what the output would be. Basically, we have a one bit random number generator.

Now for my question. Modern processors and microcontrollers have the ability to generate pseudo-random numbers. Of course, these aren't truly random. But if my flip flop scenario generates true-random numbers, then why don't designers use this concept, but with more flip flops?


texts: Sending "larger than 8-bit" quantities over an 8-bit link

texts:
I have data that I logically manipulate in 12-bit quantities which I need to move over an UART link. (actually soft-serial from Mbed to PC over USB cable, but that's irrelevant)

I was thinking about using the common 8N1 (8 data bits, no parity, 1 stop bit) UART setup, which just leaves me with the question of how to "chop up" my 12-bit values in to two 8-bit "packets".

I could of course implement something trivial myself like sending the 8 lowest bits first and then sending the 4 highest bits in the second packet, with the other 4 bits of the second packet not used. Or I could chop it up in to two 6-bit pieces, with the other 2 bits of each packet either unused or designated for meta-information (like whether the current packet is the first or second half of a 12-bit quantity).

Before doing that I wanted to see if there was any standard or a "standard industry practice" way of chopping up data larger then 8 bits in to 8 bit quantities?

Link speed should is not a issue since my requirements are about 3 kbps.

(In the absence of a "low level communications protocol"-Stack-Exchange I feel this is the most suitable platform for this type of question, per various discussions on Meta.)

EDIT: All answers were valid and good. I marked Olin's answer as correct since it's the way I went with my project.


texts: Steady state response and transfer function

texts:
For an LTI system in frequency domain, Y(s) = H(s)X(s), where symbols have their usual meanings. I am confused in what this represents, i.e., is it true only in steady state (in other words is it only the forced response) or is it true for all times including the transient time (forced plus the natural response).
Because when we take the sinusoidal response of a system we calculate the steady state response by calculating the magnitude of the transfer function H(s) and multiplying it by the input sine.
But when we calculate the inverse laplace transform we get the total output of the system.


texts: RF - changing a trace slightly from original design...?

texts:
I am trying to make a new PCB for my self just for experimenting.

I found a document on TI website that suggests using a single chip 50Ohm Balun

That is fantastic as it saves anybody faffing about with calibrations and all that..

I have made a PCB before using a symmetrical PCB antenna with no balun and it worked fine in close range. TI always uses the Inverted F antenna as they say it performs the best..

I want to extend the range but i want to keep the PCB as compact as possible.
I found this SMD 2.4 Antenna

and I just wondered if i can connect it directly to the Balun?

The catch is that i need to change TI's recommend trace, add a 90degree bend to it.. otherwise the footprint is the same.

The original HOT wire is greyed out.. and all i want to do is put a kink into it.

I know RF is very temperamental to the slightest design change and I have no spectrum analysers or even experience to detect what this change could cause in the signal.

Can I .. just do this?

EDIT
I re read the pdf a few hundred times and realised it says this monopole antenna requires simple stripline matching on the PCB without the need for discrete components.

So am I correct in assuming that it is fine to put the bend in the place that I want?I do not really understand what that means.

EDIT 2

Do you think if i place it at 45 degrees.. it should be ok as its omnidirectional..

EDIT 3

THe mos logical way, as commented would be shifting it over. I think I will go with this..


texts: Understanding Phone Service from Cable Companies

texts:
Since communication technology is considered part of EE, I thought I would pose this question here - hopefully it is on-topic.

Cable companies like Comcast have been offering home phone service for some time now, and they claim their phone service has the "highest clarity".

Questions:
1. Is the phone service provided cable companies simply VOIP?
2. Since the voice signals are eventually routed to the PSTN, how can cable phone service surpass the quality of traditional phone service provided (by companies like AT&T) through the phone jack?

In response to comment
I believe the how and why's of engineering needs to be understood before an answer is formulated.


texts: output filter capacitor of a buck regulator behaves as an inductor at the switching frequency. Will the ripples get filtered out?

texts: I'm using LTC3533 buck-boost regulator. The output capacitor is 100uF ceramic based. After checking the manufacturer's datasheet ,it turns out that at the switching frequency( 1MHz) the capacitor behaves as an inductor. Equivalent capacitance at the DC bias is around 48uF but will it continue to serve my purpose as a capacitor and filter out the high frequency ripples and how does it affect the design of compensation network?


texts: How does ground affect a battery? (Nodal Analysis)

texts:
I began solving this question with nodal analysis, but I ran into 2 problems while solving the question:

V_A has to be equal to zero to solve the question (and get R_1). I get 40V... I think that ground is affecting my battery?... Why is this?
I got a negative value for R_3. Does this mean the current is in the wrong direction that I assumed?


texts: Induction Motor - Reactances and Leakages

texts:
In the induction motor equivalent circuit (either Thevenin or otherwise), the rotor, and stator leakages and reactances are necessary for any useful calculations.

How does one estimate leakages and reactances?

Without computational electromagnetics and
Without building the motor

What relations are there to do this?

In studying this genetic optimization paper for induction motors, and they reference one paper and one book for doing this, so there must be a way!

Thanks in advance!


texts:
I'm designing a simple diode ring mixer for down-conversion from 1.5G to 200k. I want a band-pass LC pi-filter on the mixer IF output.

I've designed the filter for 50R source and load impedance by using a low-pass butterworth prototype and used the usual equations to scale and transform into a band-pass at my center frequency of 200k.

My LTSpice simulation shows the input impedance is only 50R at the center frequency, dropping to 0R in the stop band.

Should I be concerned that the filter wont absorb mixer spurs and harmonics in the stop band and will instead reflect them back into the mixer?

What is best practice for terminating an IF output with a narrow bandwidth?


texts: Using LED bike lights with a dynamo instead of batteries

texts:
Today, I stayed too long chatting at a friend's house which caused me to ride home in the dark.
Unfortunately the batteries on the lights were quite drained so the lights barely worked.
Then I noticed that I still had my old dynamo attached. Couldn't that be used to power the lights? After some research I found out that it was possible according to this page.
Disclaimer: it is in Dutch but here is the schematic:

This schematic shows that I need a rectifier to turn the AC of the bike dynamo into usable DC.
For safety I also would like to add a capacitor which keeps the lights on for 5 minutes maximum so you won't sit in the dark near a busy crossing or a light stop.
So this brings me to the following problems.

Is there a rectifier available that works on a bike dynamo?
Isn't the changing voltage of the dynamo going to cause issues?
How many microfarads would you need to power it all?