texts: Some basic questions about voltage and lithium power pack

texts:
Well, I've been stuck at home and since I've run out of things to do, I've started thinking about creating a simple cheap backup for my modem, router, and desktop fan.

Since I've got several lithium powerbanks that output at 5v 2.1A (max) I was interested to see if I would be able to use these to backup the modem and router. A few videos on youtube show that this can be done as long as the amperage of modem or router is really low. My router is rated 9v at 0.6A. If this is legitimate can I just connect a 5.5mm x 2.1 DC plug to the end of a USB cable to connect the power bank to the router?

I also read that a better way to accomplish this would be to use a 5V to 9V step-up adapter which will supposedly allow me to power slightly higher amperage devices which might be better as a backup for my modem (12V at 1A).

Another option I have to maybe power the modem is using my portable 20000mAh 12V lithium battery jump starter. It has a type C USB (5v/3A) output and a DC 15V/10A outout. It came with a 5.5mm to female cigarette lighter adapter for use with the 15V/10A output.

My first question related to this device is why the unit is listed as 15V and not 12V which is the type of battery it is designed to jump start? Secondly, because of this 15V spec, would it be safe to still use this to power the modem?

If it is safe, can I just make a male 5.5mm to male 5.5mm cable by joining two 5.5mm cable ends and use this to go from the jump starter pack direct to the modem?

Another option would be for me to buy a 200W or 300W inverter (200W is under $20) then could connect the jump starter power bank to the inverter with the cigarette lighter adapter. Then all I would need to do is plug the modem and the router into the inverter. I understand this option is not very efficient as I'd be losing energy converting to AC and then back to DC.... but since the combined power requirements of the modem and router is low, this doesn't appear to be an issue?

Lastly, I would like a backup option that would run my AC 120V 0.5A desk fan for a few hours. It is variable speed so I think it draws far less than the 0.5A at the low setting which is all I would need. By my calculation this means it is using 60W at most. My jump starter outputs 12V at a max of 10A, which means it should be capable of powering a 120W device so even if I lose some energy through an inverter, I should still be able to power the fan with the power bank - does this sound right?

I have also read that a 300W inverter with a cigarette adapter is limited to 150W because of its wiring. So should I just buy a 150W or 200W inverter instead? The problem with some of the 150W adapters is that they most have one AC plug so maybe its best to stick with the 300W and just be careful to keep total watts low?


texts:
I want to know how to calculate the output of the below op amp. I know this is supposed be an inverting amplifier with offset but I have never seen the connection of the offset to the negative side of op amp.

simulate this circuit – Schematic created using CircuitLab

I have come up with this formula:

$$V_{\text{out}} =  V_{\text{in}} \times \frac{R_2}{R_1} + \frac{R_2}{R_4+R_7}V_\text{p}$$

Is it correct? \$V_\text{p}\$ is the voltage out of the potentiometer.


texts:
I am speaking, here, not in the more usual sense of a gap in the continuity of the core material.  I mean, in reference to a rod of core material, that the outside diameter of the rod is sufficiently smaller than the inside diameter of the coil, that a uniform separation exists between the core and the coil.

The question is, does such a gap affect the inductance of such a system.  I suppose a more general question would be how inductance would be affected if the coil were wound directly on a core whose permeability varies with diameter -  that is, would such a system exhibit inductance different from a system of the same dimensions but with a core whose permeability is an average of the variable one.

To give a practical example, suppose I wind a coil on the outside of a piece of (nominal) 1/2 inch pvc pipe, whose outside diameter is 0.84 inches.  I insert a rod of given permeability with an outside diameter of 0.622 inches (the inside diameter of nominal 1/2 inch pvc pipe).

Clearly, the inductance of such a system will be different than the case in which the coil is wound directly on such a core (smaller diameter coil, lower inductance), or in the case of a larger diameter rod (&c).

I have not found any material referencing such a system (possibly because the effects of such a system are so negligible as to be of no interest).

A further question might be of a system in which a layer of impermeable material fills the gap between the coil and a core of permeable material.


texts: I'm powering an attiny45 from a lithium ion battery; using these batteries the voltage cannot get below 3volts or it will damage the cell. How should I go about cutting the voltage out? Software, or hardware? I'm not sure!?


texts:
I came through this schematic for powering a 3g module (SIM800L).

What is this diode connected with the bypass capacitors? By googling 5.1V 500mW I came to conclusion that it is probably a Zener diode(however the symbol does not seem like a zener diode) Is that true?
What is the use of it?


texts: Can capacitors in speakers (Yamaha) be replaced by slightly different ones?

texts:
Now, I know that people used replacement capacitors which has a Capacity of 22nF, 250V ac and 630V dc +/-5%

The Capacitor was labeled C515 on the board it is soldered on.

I was wondering how flexible those values are. Does it have to be 22nF and those exact voltages? People have been using overspeced ones but I'm kinda scared it will destroy even more.

I mean, best-case would be that some of you know the exact capacitor, but why not use one that is a bit different, if it works just as well?

How different can it be? I feel like the capacity has to be the same, but the voltage can be higher. Is there a limit to that though, where there is too little flow?


texts: How to make a circuit that will turn on a light for only a few seconds when closed

texts:
simulate this circuit – Schematic created using CircuitLab

I am very new to electronics and circuits and stuff but I found an old electronic playground in my attic and I've been playing around with it and trying to figure out how to do things for a project that I've been wanting to make for a while. The one part that I am stuck on is that it will need a latch to open when a button is pressed and I can't figure out how to only power the latch when the button is pressed. I've been trying to use not gates and capacitors but I can't get it to work properly. I got the not gate working but when I try to run the output through a capacitor the light that is representing the switch either turns off instantly or slowly turns off and nothing els, depending on where connected to the negative/positive. Please help in any way I can and am sorry if I'm making no sense. I don't really know proper terminology. Thanks


texts: What's the simplest way at low speeds (sub 100 Hz) to shift 0-5V to ±2.5V? I was thinking of using a comparator or op-amp, but there must be a simpler / cheaper way. I wanted to avoid a dedicated chip, unless it is cheaper than a discrete solution. Any ideas?


texts: I am trying to use a nand gate from a 4093BE chip with a digital sensor which is supposed to output 5 V when an obstruction is detected and 0 when not. I am setting both inputs of gate to the output of the sensor. When not obstructed I should obtain a 5 V on the output of the gate, however I do not get this but a 0V. I tested the chip putting to ground both inputs of the gate, and I obtained the 5V expected, then the gate is working. I measured the sensor's voltage output and it gives 4.78 V when obstructed and 0.21V when not, then it also should work. I don't know what is wrong, what can I do?


texts: What misconception about telephone circuits are they trying to address?

texts:
I'm reading a book called "Telephony" published in 1905  (Miller,Mcmeen).
The book starts with this quote:

  To properly understand the manner in which sound is transmitted from one end of an electric circuit to the other, it will be necessary to entirely get rid of a popular idea, and to fix clearly in mind, that the sound produced at one end of a circuit actually travels over that circuit, in order to be heard at the other end.That is erroneous; in reality the actual sound produced at one end of the circuit, travels no farther than it would if the telephone apparatus were not present. What actually take palce instead may be described as follows:
  The sound energy produced in the presence of the telephone apparatus is transformed by the apparatus in electric energy, which, traveling to the distant end of the line, is again retransformed by the distant apparatus into sound energy.

I don't understand the point.
What is the misconception they're trying to address?


texts:
This is a schematic diagram of the circuit.

Is it possible to take  the voltage difference between AB as  E? I have learned that the potential difference in parallel circuits are the same, Therefore I did  assume  the potential difference across AB as E. But I want to know whether I am correct or wrong?

Because I hope this concept is a crucial factor when solving circuits, since I am beginner I would like to know it.


texts: I'm new at the circuit design biz.  I'm designing a battery powered device around the TI TPS61025 boost converter, and I'm rather confused about the proper range for the low-ESR output capacitor.  The data sheet says says With the calculated minimum value of 24 μF and load transient considerations the recommended output capacitance value is in a 47 to 100 μF range. For economical reasons, this is usually a tantalum capacitor. Therefore, the control loop has been optimized for using output capacitors with an ESR of above 30 mΩ.  So I understand I want a cap in the 47-100 μF range with an ESR of at least 30 mΩ.  But what's a reasonable upper limit for the ESR?  Is there an upper limit?


texts:
I am currently working on a project that uses an IR LED and a photodiode in a proximity sensor configuration (shown below). My question is, I have read some sites that state that your human body reflects IR light transmitted by the IR LED hence when you touch or move your hand close to the proximity sensor the circuit will activate. But other sources say that the human body does not reflect IR light but rather refracts it. So which is correct does the IR light emitted by the IR LED gets reflected or refracted towards the photodiode when your finger or hand moves closer to the sensor?

The second part I noticed is that even if the IR LED is removed the sensor still activates because our bodies do also emit radiation which the photodiode can detect. Provided the threshold voltage is low enough. So then what's the point of having an IR LED in the circuit if the circuit already activates when a finger gets closer to the circuit, or am I understanding this wrong?

N.B
The circuit I built is going to be used to detect when a finger or hand gets closer to the sensor.


texts: Saleae logic analyzer, exporting data to .csv file

texts: I have bought Saleae Logic Analyzer, everything is good except the fact that when I try to export data to .csv file and then open it using MS Excel I get all data in one column. I would like to get Time, Data ,Read/Write, etc. in separate columns to further process it.


texts: When generating PWM wave, shall I minimize switching or maximizing it?

texts: For instance, for a 50% duty cycle, what's the advantage/disadvantage of using 01010101 rather than 00001111?


texts:
My laptop charger is a 110-220V AC to 18.5V DC. Of late, or maybe I just heard it now, it makes a beeping noise. The noise is very very low. I have to put my ear to it to hear it.
The charger works just fine, and the proof is that I am posting this question while using the laptop on pure AC.
I did my research on the internet and people say that this noise comes and their laptop stops working and the charger won't charge. My initial guess is that it is the step-down transformer inside that maybe the cause.
I use the laptop for light use.
 Is this beeping harmful?
 What could cause the beeping?


texts: Momentary use of mixed AH batteries in series?

texts: Obviously a circuit using mixed batteries in series is a bad idea. My question is for momentary use is it that bad? I have a starter on a dirt bike that I would like to push 24V through (it's capable). The main battery instead of going to the starter relay would go to another battery first and then the starter relay. The secondary battery is not part of the charging circuit.


texts: Calculating Thevenin's circuit using KCL or node analysis

texts:
I am calculating parameters of the Thevenin's equivalent circuit as seen from the terminals A and B, for this circuit:

So I am following two steps.

Step 1

Calculate Thevenin's equivalent impedance Z_AB. Remove load, short all voltage sources and open circuit current sources. We get simplified circuit whith R3 removed and R1 and R2 connected in series. Therefore:

Z_AB = (R1 + R2) = 12

Step 2

Calculate Thevenin's equivalent voltage across A and B terminals using original circuit. Here's where I have some questions. I can calculate the voltage using KCL for center node (blue pixel, the only node in fact) and get

Step 2 : solution 1

Mark the voltage at the center node (blue pixel) by V1 and voltage source as E = 12. Applying KCL for this node gives:

(E - V1) / R1 + I1 = 0

(12 - V1) / 6 + 2 = 0

V1 = 24

Which seems to be the right result, confirmed by simulating this circuit in LTSpice:

Based on that voltage at terminal A can be calculated as V1 * R3 / (Z_AB + R3) = 24 * 4 / (12 + 4) = 6

Step 2 : solution 2

But if I try to apply complete Node analysis I cannot get correct result. I know it must work, so apparently I am doing something wrong. I would like to know where do I fail in my node analysis. My calculation:

YV = I

V = voltage at nodes matrix = [ V1 ]

Y = admittance matrix = [ 1/R1 + 1/(R2 + R3) ]

I = [ (E - V1) / R1 + I1 - V1 / (R2  + R3) ]

This gives:

V1/R1 + V1 / (R2 + R3) = (E - V1) / R1 + I1 - V1 / (R2  + R3)

Which would agree with previous result only if

V1/R1 + V1 / (R2 + R3) = 0

which is not the case.

Where is an error in my proper node analysis? I can see that I would get right answer if Y = 0 but why should I set admittance matrix to be 0?

EDIT:

Found it (think so...). We need to include only independent current sources in I matrix, so the equation system is:

Y = [ 1/R1 ]

V = [ V1 ]

I = [ I1 + E/R1 ]

Then it gives the same:

YV = I  so  V1/R1 = I1 + E/R1

But I would be very thankful to anyone for confirming that or providing different explanation.


texts: Soft-power MOSFET circuit leaks - what to do?

texts:
Full schematic is at https://cdn.hackaday.io/files/1667667134916544/Evil%20Simon%20v1_3_1.pdf

This system has a pair of AA batteries, a P MOSFET for soft power and a boost converter to make 3.3v. The problem is that with the system ostensibly "off" the gate of the MOSFET is still being pulled down by... something... Presumably the microcontroller. It's enough that the gate is something like 2.1v even if the pull-up resistor is reduced to 1 kΩ.

The microcontroller's BOD has been programmed to hit at 2.7v (which is the minimum safe supply voltage for it's clock speed), so you'd think that it would be held in RESET if it had enough juice to even notice.

When the firmware starts (after someone presses one of the buttons, which causes the power MOSFET gate to be brought low), that pin is immediately brought low and held there until it's time to power off, whereupon it is made hi-Z (by turning it into an input). None of the pull-up or pull-down options are selected for that pin.

So if that pin is leaking, what's there to do? The smaller I make the power MOSFET's gate pull-up, the more power it's going to waste when turned on. What else might I try? I'm tempted to use a BJT in front of the MOSFET so that some sort of current flow (presumably leakage wouldn't be enough) would be required to positively turn on the power MOSFET, but I'd like an actual plan before I spin another board.


texts:
I want to take FCC  certification for my product which comes under "Part 15" (Unintentional Product). What tests are necessary for that?

Please suggest me some document so that I can refer it and take care of passing test on first attempt.


texts: With a constant-current, constant-voltage power supply, does the total length of the wire affect the heat produced per metre?

texts:
This seems like it should be obvious, but I can't seem to get my head around it.
If I have a length of wire 7 metres long and it has a total resistance across its whole length of 2 ohms, and I connect it across the terminals of a CC/CV power supply limited to 3A at 5V, then the wire would have to dissipate ~15W of power as heat. That would be ~2.14W/metre. If I now cut the wire in half and connect it to the same power supply, does that mean the wire would dissipate the same power but across half the length and therefore focus the heat into a smaller area? I calculate that it would then be producing ~4.29W/metre of heat.
If I'm understanding this correctly, with this setup, the resistance of the wire should have no effect on heat dissipation as long as it's low enough that the current flow is being limited by the power supply, right?
In case this is an XY question, I'm considering how I might create heated clothing. I want to avoid the possibility that if some insulation breaks and the wire shorts on itself that it might suddenly get hot enough to burn me or catch fire.
In this example case the power supply would be running in CV mode. I now realise that in the real world it's running in CC due to different values.


texts: Why does a radio still work inside a metal box?

texts:
I've put a small battery powered commercial radio inside a Quality Street tin.  The tin is all metal with rolled joints and the lid is a tight fit.  I'd be willing to bet that there are no holes greater than 0.1mm around the lid's closure.  It's a fairly common Sony ICFS22 FM/AM Pocket Radio with a telescopic aerial, and the tin is approximately 300mm in diameter.

Why does the radio work when receiving an AM station (1 MHz), but only produces static when switched to FM (100 MHz)?

Some further details of things I've done...

The tin IS magnetic, attracting a magnet well

The walls are 0.25mm thick (including paint)

The inside of the tin is unpainted

I grounded the tin to the earth wire from a UK mains electrical socket, and repeated the reception test. I filed off the paint where the wire touched the tin. Results:-

FM: Total static. No discernible change with /without earth wire.

AM: Tinny but recognisable radio station. No, repeat no discernible change in pitch or volume with /without earth wire. Surprised.

The tin with the ground wire...


texts: Two semiconductor physics problems with similar data but different solution methods

texts:
Prob 1: Find the conductivity of n-type Ge at room temperature. Assuming one donor atom in each 108 atoms. The density of Ge is 5.32 x 103 kg/m3 and the atomic weight is 72.66 kg/k-mol. Given e=1.6 x 10-19 C, μe=0.38 m2/V-s and μh=0.18 m2/V-s.Hint: No of Ge atoms per cm3 = 6.023 x 1023 x (atoms/mole) x (1 mole/72.6 g) x (5.32g/cm3) = 4.41 x 1022.

Prob 2: A specimen of germanium at 300 K for which the density of carriers is 2.5 x 1013, is doped with impurity atoms such that there is one impurity atom for 106 germanium atoms. All the impurity atoms may be assumed ionized. The resistivity of doped material is 0.039 Ω-cm. Carreir mobility for germanium at 300 K is 3600 cm2/V-s. For the doped material find the electron and hole concentration.

.....................................................................................

In order to solve these two problems, we need to get the donor atom concentration. Please tell me how should I find the value of donor concentration in each problem.


texts: ADC input software multiplexed between current/voltage input

texts:
Problem

I need to design an isolated analog front end to a Raspberry Pi which needs to work with either a 4-20mA or 0-10V transmitter. I've been studying existing analog input modules from major PLC manufacturers for inspiration.

Existing products

Allen Bradley Micro850 analog I/O module (datasheet) has for each input channel, a separate Vin, Iin and COM pins.
Wago 750 offers current input modules and voltage input modules. I didn't find any modules with analog channels having both current/voltage inputs for the same channel.
Industruino Ind.I/O seems to offer both 0-20mA/0-10V in the same pin on every channel, selectable in software as shown in the following image
UniPi S10x (datasheet), also seems to offer both 0-20mA/0-10V in the same pin.

Solution Attempts

With an ADC span of 2V, I know how to make either

a current receiver with a 100Ω resistor
a voltage receiver with a passive attenuator with source impedance >100kΩ

Precision in either is not required since I can do a software calibration with a calibrated current/voltage source.

I tried to understand how Industruino was able to software select between current and voltage input since voltage input requires high impedance while current input requires low impedance.

Their Indio I2C library tells me the following

MCP3424 is the 4-ch 18-bit ADC
2xMCP4726 are the 1-ch 12-bit DAC
PCA9555 is a 16-bit I2C GPIO extender
8 channels of the PCA9555 go to the 24V I/O through high side drivers
4 channels of the PCA9555 are toggled HIGH for current input and LOW for voltage input by the analogReadMode() function; one for each analog input channel
2 channels of the PCA9555 are toggled HIGH for current output and LOW for voltage output by the analogWriteMode() function; one for each analog output channel

Since it is a open hardware project, I tried to find the schematics on their website. It is neither there nor on any other website I came across. Their GitHub repository doesn't list it either. I tried emailing them with the query but they haven't responded.

I would be very grateful if anyone could shine a light on the solution.


texts: Why are the pads different for THT / SMT components in Eagle?

texts:
I am learning Cadsoft Eagle and have noticed that the pads for SMT devices are on the 'top'/'bottom' display layer, whereas the pads for THT components are on the 'pads' layer. Why is this?

I have enlarged the pads for the SMT device so that I don't commit Seppuku with my iron during hand production. Looking at the soldermask 'stop' layer, it appears that all is well, as the SMT pads are not covered. I just want to check that this difference between SMT/THT pads is correct before making my first batch of coffee coasters.


texts: I want to build an interactive LED Table. What are my options for a controller?

texts:
I have seen a couple of videos and instructables where people have created a matrix of LEDs controlled by photodiodes/photoresistors inside coffee tables, so that when you put your hand over the table or put a mug down, the lights under the object light up.

I want to take this to the next level by controlling the matrix with a microcontroller. Reason being: I can do even more with the matrix, maybe turn it into a VU meter or do cool light shows.

Here is what I was thinking:
A 9x5 matrix of LEDs (blue) with a 8x4 matrix of sensors (photoresistors):

I have a couple of PIC microcontrollers with 36 I/O pins lying around plus some other smaller ones.
I haven't used PIC MCs before so I thought this might be a good project to use them for.

Do you have any recommendations for the controller design? Maybe I could use 2 MCs, one for the LEDs and one for sensors? Maybe just use one MC and use demultiplexers to switch in the many sensors?

Lay it on me fellas!


texts: Cheap homebrew lab PS; need verification of magnetics for toroid

texts:
A sixteen state state machine made with an sram and max7004 cpld is a 200khz osc that drives the FETs for the chopper in four switchers.
A low end PIC can modify the contents of the SRAM to change output voltage or foldback limit.

**Need to verify T2. Making this cheap revolves around winding T2.

Using Pri multi wound L=0.8(rN)(rN)/6r+9l+10b
      Sec single wound L=(rN)(rN)/9r+10l  r radius l length b depth
Pri 4 layers 800 turns/layer 26 gauge magnet wire
Sec 1 layer 16 turns 14 gauge magnet wire
Fair Rite 5943000911 toroid form**

Since pic chips and cplds are free at school (within limits), A lab grade bench PS can be had for cheap if I wind a transformer.
Plan is to initially make only 16 states in state machine to drive four separate switchers.
Once basic PS functional, add extra inputs to state machine to get feedback inputs for adjustable voltage and short circuit folback limit.
Since state machine is implemented with SRAM instead of eprom, pic chip can change state machine values to tweak performance.
4Mhz clock from micro divided in cpld to make 200khz.
A-D outputs drive the chopper FETs to energize PRI on T2
Ultimate goal is 4 variable  0-30V 0-3 A with adj foldback current limit.
A lot of trouble but should be comparable to PS costing hundreds.....

Can someone verify that the description of T2 will be adequate for a 200 khz switcher for outputs of 0-30v at up to 3A?
Thanks


texts: Does a coaxial cable have any advantages in transmitting lower frequencies? If it does, what are those advantages?


texts:
Is it possible to use a mini USB Bluetooth dongle like in the following picture in order to improve my Arduino Uno, so it can comunicate with other Bluetooth devices?

If it is, how can I do that?


texts: Using a 16MHz crystal with an atmega328, it works only if I remove the two capacitors connected to the crystal

texts:
I am using a 16MHz crystal with an atmega328. I added two capacitors to the crystal as usual. Everytime the capacitors are attached, avrdudee does not recognize the atmega. Once I remove the capacitors it's recognized.
I've tried using different capacitor values from 22pf to 47uf and the results are the same.
How come avrdudee fails to recognize the microcontroller when the capacitors are attached to the crystal?


texts: by default are component thru hole pads in Via style in Eagle software?

texts: If I go in to Display / Layers, I can see the bottom and top routes, and if I click on Pads, I can see the pads, and because I have Top and Bottom routes, and not using surface mount components, I assume the Pads are on both sides, however I can't find any indication that the hole pads are Via style - Is this just a standard for the machine shops?


texts: How to provide separate voltages from a common power source

texts:
Assuming the input voltage is regulated, how do I provide two different, specific voltages to the below devices? I specifically want 4[V] in the left part and 3[V] in the right part of the parallel sub-circuit on the right.

I thought a voltage-divider circuit would help me get 4[V] after the first resistor, but all the components in the middle have got me doubting myself.

simulate this circuit – Schematic created using CircuitLab

The devices are an analog temperature sensor (such as LM35) with an operating voltage in the rage 4~35[V], and a microcontroller, with an operating voltage in the range 2~4[V]. The sensor output is to be connected to one of the pins of the microcontroller. The sensor is on the left and the controller is on the right.


texts:
PCB:

My name is Ertuğrul. I made a regulation board with an LM2678 but I have a problem: I provide 12V input but I can not get 5V output.
I only get 5V with the on/off pin enabled, but the datasheet says that I can get a 5V output with the on/off pin not active.
I have to give 1.4-6V to the on/off pin because otherwise it does not work.
I tried it on a breadboard but it did not change. I used Webench schematic design.
Do you know about LM2678? Can you help me ?


texts: Connect SIM800L with other GPIO pins in Raspberry PI 3B+

texts:
I have a SIM800L module and a keypad module that I want to connect to the raspberry pi 3B+ but then when I had all my modules and stuff I found out that the raspberry pi had only 1 UART (1RX & 1TX) pin I have 2 devices that I want to connect to that...
so my question is: Is it possible to connect SIM800L to another GPIO pin? to use serial communication? or is there any other platform like I2C & SPI can I use with SIM800L?


texts: Area vs Operating Frequency in asic synthesis

texts:
I am trying Synopsys dc tool for synthesizing my design. I tried different operating frequencies and observed the design area. Normally area should increase with increasing operating frequency but in my case design area for 220 MHz is somewhat greater than the area at 240 MHz. How is it possible??

Combinational area for 240 MHz is greater than 220 MHz but non combinational area for 220 MHz is greater.

Thanks in advance!

PS: Design area doesn't include net area.


texts: Just wanted to ask how the GBW of an op-amp affects its operation. If I am given a 2 Op-Amps with different GBWs, do I choose the one with higher or lower and why?


texts:
I'm looking for a Lecroy 9354 on ebay and found that there are a number of different models A, AM, L, CM, etc...

I though this was simple but having searched around for a while I still don't know what the letters describe.


texts: What are the temporal dynamics for the temperature change in a resistor driven by a current source? I am hoping that there is a simple equation that works well for most resistors so that I don't have to do something like solving the heat equation for a cylindrical conductor.


texts: As I understand it, the field coils and armature windings in a DC motor are insulated and this insulation can 'burn off' if the motor overheats, causing a short circuit to develop. What is the material coating the windings and coils in a DC motor? In the examples of the insides of DC motors that I have seen, the windings still retained the look of copper wire - does this mean that the coating is transparent? If so, is this always the case or are there winding coatings that are not transparent?


texts:
I'm trying to determine what a "minimal" circuit is to get an STM32F411 processor running and able to blink an LED. I wish to use the internal PLL and no external crystal at this point.

I've looked at some documentation and I'm just confused as to what is really needed.

Anybody have a minimal schematic from which I can build upon?

Edit: I'm attempting to pick out the most minimal circuit using the schematic provided in this STM Nucleo Board PDF. This schematic has some extra bits not needed, and I'm not quite sure what to do with all the solder bridges.

Edit: I've managed to solder the LQFP64 part to a breakout board for prototyping. I'm not a EE, just a software engineer, and I've always used development boards. This is the first time I'm attempting to create my own board. I've looked at several documents including schematics of the Nucleo board(s) and STM reference design but picking out what is the minimum that is needed eludes me.


texts: How does a split rail supply work and how to design one?

texts:
I need a split supply for a project I am working on and there's no way around it, however this is very unknown to me.

How does one even design one and how does it work? I find it confusing to do a KCL on it just so I can see the analysis but I am failing on that as well

The goal is use a 12VDC wall wart and split it into +/-6 V I would be really happy with that. It will not be driving anything heavy besides OP-AMPS and buffers.

Sample:

simulate this circuit – Schematic created using CircuitLab

This is the current problem Iam facing:

simulate this circuit

This is what I believe is the solution:

simulate this circuit

EDIT:

I am sorry the confusion I have laid on to people but here is my XY problem I am having.

Goal Design:    To create an amplifier with auto gain control using the Arduino and a rheostat to achieve this.

How I achieved it:    Firstly I had my audio signal going into the INPUT of the precision rectifier to convert the audio signal in a "DC Line" with a magnitude of the peak of the audio signal. From there I took the output of the precision rectifier and put it into A0 (Analog pin) of the Ardunio so it can read the value. From there I have the code that the Arduino executes that finds the suitable R2 value from the feedback equation of: (Gain = 1+ (R2/R1)), where Vout can be adjusted via code and Vin(Vp) was measured on the A0 line. Once found a R2 I do some basic R2/RS, where RS is the steps I had on the rheostat and then do some SPI stuff. The code then tells the rheostat (Which is in the NFB loop of the amplifier) To change the rheostat resistance and get the desired Vo regradless of Vin. All in terms of Voltage peaks

The flaw:   I found a big flaw recently when I was doing some input/output Impedance stuff for some filtering for the output of the amp. I realized Depending on the Rs( Output impedance) of the output source (iphone or laptop) the Vin that the op - amp sees is a different Vin from the ardunio sees. I realized I should capture the Vs from the V+ terminal and not from the audio source. But the V+ node has a DC offset that is unwanted for the ardunio to read I guess.

Theoretical if this works, this can defy the source resistance and can be disregarded due to the rheostat compensating for the voltage loss due to the loading of the stages from the input.

simulate this circuit

EDIT: EDIT: My solution ? Will this work? Should Make node A the same voltage as Node B assuming 1khz at 0dB.

simulate this circuit


texts:
All I can find online is explanations like this:

When a power supply with current sink capability is programmed to a
voltage level less than that actually at the output terminals it will
automatically begin to sink current. The down-programmer can be thought
of as an internal load across the power supply's output terminals that
helps bring the output voltage down quickly.

But how does it actually work? is there a mosfet as a load? what about the current this "load" is drawing, is it being nulled by the ammeter?
Can someone please open this up a little with an schematic and/or working principles?


texts: Help in analysing circuit to show which resistor controls the differential gain

texts:
I understand the circuit to be a summing circuit but I am struggling to analyse past this point: Vout = R5 (((-R2/R1 * V2)/R4) * (V1 / R3)). can anyone analyse this further to prove that R5 is the controlling resistor?

simulate this circuit – Schematic created using CircuitLab


texts: what exactly prevents my smartphone from being used as an SDR without a dedicated dongle

texts:
The answer seems obvious (frequencies restricted by chips) but I'm looking for a clear and accurate explanation. Several examples of SDR projects connecting an SDR dongle to a smartphone are available on the web, such as here or here etc. Thing is, the SDR dongle is not required to demodulate, otherwise I could not listen to my favorite FM station using nothing more than my headphones as an antenna (without mentioning the actual GSM/4G... bands), as I've done myself. Another webpage explores the possibility of converting smartphones for radio communications, while suggesting the smartphone limitations:

"Despite the progress, the smartphones still could not communicate
with handheld devices running the frequencies because the phones
support different bands"

A short SO post indeed suggests the frequencies supported by a smartphone are very limited by the chips within it:

" a device manufacturer has those, and none of those will have
anything to do with changing the frequency, as those are fixed by the
chipset manufacture"

Therefore I ask the question: what exactly limits the possibilities of using my smartphone as an SDR, for example with my headphones as an antenna, to listen to other frequencies than FM radio stations (typically CB, VHF 144-146 MHz, PMR 446 MHz) ? Would the setup theoretically work but not well enough ? What would limit the demodulation capabilities of my smartphone, when not helped by an SDR dongle ? What are the limits exactly ? There is a lot of information available on SDR online but I'm still a little confused, hence my question here (not sure if this belongs here or should rather be posted on SO/signal processing stack exchange Q&A).


texts:
As I was designing a split voltage supply for an opamp supply, I thought that cutting one rail if the other rail wasn't at it's nominal voltage would be a good idea if I wanted a "good" output signal. Turns out it isn't that useful (at least in my particular case). BUT I'm still wondering how to do that. So for my curiosity:
How would one do that?
I have a split voltage (in my case it was +/-30 V and a load of about 25 mA. Although this post is hypothetical so not sure it's useful).
My idea was to use some comparator and the output would activate or deactivate a switch. Maybe a BJT or a MOSFET with a MOSFET driver.
If I use a comparator like the LT1017, in it's datasheet the absolute maximum rating for the input voltage is -0.3 V to 40 V. So how can I monitor the negative rail with that? In one application example, V+ and V- are "switched". But can I use a negative Vref on INA- or INA+? And if it's the case, can the output of the negative rail comparator drive a switch (MOSFET or BJT)? Or MOSFET driver?
LT1017 datasheet


texts: 74LVC1G125 on the arduino wireless shield?

texts:
What does the 74LVC1G125 do on the Arduino wireless sheild?
Its just a buffer, but is it really necessary, or is it only necessary if you stack a lot of shields? (ie: collectively increasing input impedance)

Its this shield:
http://arduino.cc/en/Main/ArduinoWirelessProtoShield


texts: Why do my 3 custom voltage pulses stop working as soon as I plug in the A1362 Hall-Effect sensor?

texts:
Why does the Vout pin in the diagram below receive 8 volts with Vcc = 0 volts, but becomes 2 volts when Vcc=5 volts. If switch SW9 is closed, circuit theory says Vout should always stay at 15 volts regardless of whether I am powering the hall-effect sensor with Vcc or not.

However, when I measure (with a multimeter) what Vout pin is getting it's never 15 volts, however if I individually measure "VpM" below (with the hall-effect sensor unplugged from breadboard) I correctly get 15 volts.  As soon as I plug the hall-effect sensor back in I either get 8 volts (with Vcc=0 volts) or 2 volts (with Vcc=5).

I reason (I think) why I get 2 volts on VOUT pin when VCC=5 volts is because according to this data sheet on pg. 4 in the row marked "Pre-Programming Quiescent Voltage Output" it says it is supposed to be 2.0V.

But this still does not explain why the programming pulses I'm sending (HIGH,MID,LOW) are not at their correct values.

Per Brian's suggestion I have lowered impedances as shown below and ran a simulation from on  circuitlab.com and here are the current readings I am getting:

 In above image R1=R6=10K Ohms, R5=R2=90K Ohms, and R3=R4=20K Ohms.  The current between [R1, R2] and [R5, R6] is -300 micro amps, whereas the current between [R3,R4] is -750 micro amps.

 In above image R1=R6=1K Ohms, R5=R2=9K Ohms, and R3=R4=1K Ohms. The current between [R1, R2] and [R5, R6] is -3.0 milli amps, whereas the current between [R3,R4] is -15 milli amps.

Is there a particular range of current I need to be in? Is this specified anywhere in the data sheet? The only thing I see is on pg. 2 under the "Absolute Maximum Ratings" table  for "Output Source Current" and "Output Sink Current" should be 3 and 10 milliAmps respectively.

Since all the currents I listed below are negative, this should satisfy the requirement, correct?


texts: Is there a standard PCB Array Size for PCB Assembly?

texts:
I am planning on use various PCB assembly houses to get my boards PCB assembled. To minimize process costs, I am told it is best to panelize/array the PCB such that there is multiple boards per array, so the pick and place machine can populate more efficiently.

I am planning on getting my boards manufactured from Company A, and getting them assembled from Companies B, C, and D.  Companies B, C, and D can assemble on individually routed boards, but obviously the cost is higher.

When I get my board fabricated from Company A, is there a standard size for the PCB Array that would be most compatible with the PCBA companies?

I've watched various YouTube videos on PCBA pick and place and it seems the conveyor belt has a certain width.  What is this width, and is there a standard?  Most PCBA use the MYDATA pick and place machines.

Is there also a standard or most commonly used array template showing where the fudicials and tooling holes should be?

My PCB is rectangular, size 2.5" x 6.2".  Trying to see how I should create the array when I order my PCB.  I am planning on using v-scoring because I don't like the rough edges and I have no components near the edges.


texts: Drawing too much power vs not supplying enough power

texts: Why in some cases a device draws more power than the source is capable of supplying thus damaging it, and in other cases the device will work under-powered?


texts: What is this keyboard connector and how to connect it to MCU?

texts:
I have a 1991 laptop keyboard w/o the motherboard. It was attached to the main board with two flexible cables. The keyboard feels awesome and I would like to make use of it. The issue is that I can't identify what connector this is (see pic. attached) and I don't know what keyboard controller was used to drive it. The flexible connectors are 0.59'' (~1.5 cm) and 0.43'' (~1.1 cm) in width.

My questions are:

What's the common name of this flexible cable connector, if any?
How to turn the keyboard into a usable one with an MCU (i.e. how to connect it to Arduino or Raspberry Pi, or any other micro controller/board)?

If it's hard to tell, I'd appreciate an advice on how to reverse engineer the keyboard to connect it to any modern controller (AVR, RPi, what not).

More pics:

Keyboard innards
Cables close-up

PS: The Part No. on the back of the keyboard says SU54TM017DK but googling returns zero hits.


texts: Using the core of a toroidal inductor as the core for a toroidal transformer?

texts: As the title says, I have quite a few toroidal cores that I have gathered over time, and would like to reuse them, do they also work as transformer cores?


texts: Are commonly available microcontrollers hardwired or microcoded?

texts:
This question sprung out as a curiosity while I was trying to understand CPUs. But I could not find a good answer on the internet. So, I am asking here: Are the commonly used uC's like PIC 10f200, PIC 12f683, PIC 16f87, the ATmega one's used in Arduino and the STC 8051 microcoded or hardwired?

I am guessing they all are hardwired. But seeing that the PIC execute 1 instruction in 4 cycles, they feel a bit CISCy and have me wondering.

Thanks for all answers.


texts: Amplify PWM Signal from exactly 0-3.3V to 0-5V

texts:
I am converting a chinese lasercutter to be controlled using a Smoothieboard. The PSU is controlled by a TTL High / Low to "arm" the laser as well as several safety measures.

When the laser is armed, the power is controlled by a PWM signal. This PWM signal from the Smoothieboard is output at 3.3V, and then converted to a 5V PWM signal using the recommended Logic Level Converter (From SparkFun, we soldered our own circuit because we couldn't wait for delivery).

This all works like a charm apart from one little detail. The circuit on the logic level converters' signal side always has around 0.4 volts when not active. This means that when our laser cutter is travelling with a G0-command, it is still armed, thus burning with around 7mA (compared to 28mA full-power). It has to be 0 volt when travelling.

We already measured the signal from the Smoothieboard using a picoscope, and it shows 0 volt when low, 3.3v when high: without the LLC connected. So issue is supposedly to be found in the circuit.
In the name of "Logic" level converter, I kind of understand that 0.4 volts is a binary low, but this is not what I desire in my project.
The problem is temporarily solved by disarming and arming between G0-moves, but this seems like a bad way.

What kind of circuit can I use to solve this problem?
Thank you in advance.


texts: Input impedance of inverting amplifier clarification

texts:
Take a standard inverting amplifier:

I'm unclear on what the input impedance is. At first I thought it was the equivalent resistance from the inverting input to the ground, which would be Rin || Rf, because there's a ground on the other side of Vin and Vout as well as inside the output of the opamp. However, most sources on the internet seem to claim that the input impedance is Vi/Ii, thus making it Rin. This appears to ignore the fact that the feedback wire connects to other grounds. Then there are answers like this that mention that input impedance is infinity. I'm hoping to figure out a clear definition of what the input impedance represents and a [brief] general approach to calculating it in a more complicated circuit. Thank you!

I read tons of pages like this answer and others, but at my beginner level it was hard to extract a clear answer.


texts:
Please see attached image. I've become confused if the answer to this question, which uses Miller's Theorem is correct as it should not be a minus, rather it should be a plus. Please see my working out.

Thanks


texts:
I am working on a datalogger that writes positions from GPS to serial flash W25Q64FV. I plan to write GPS data every second. I have couple of questions:

With this flash memory it is possible to write to any position from 1 to 256 bytes at once (page). Specification says the memory has 100,000 write/erase cycles. Is it counted per page or per byte? So if I write one byte at address X and then later another one at address X + 1 (but the same page) does it mean that I have only 99.998 writes left to that page? I would say no, but for sure I am asking. What if writing one byte internally rewrites complete page?
How to persistently keep address of last written byte? I could write it to Arduino's EEPROM on every update, but it also has "only" 100,000 write cycles so this would be reached much sooner. Other possibility could be to scan all written memory and look for empty byte(s) but this can probably take a while. Or maybe just to have some bitmap in the flash header marking full pages and I would only scan the last one. Any other suggestion?
Is there any special purpose of erasing blocks or complete flash memory? Can't I just write to memory in round-robin way? If I delete file on my HDD it won't write zeroes to all its bytes so couldn't it be same with flash?


texts: Boost converter as high-side MOSFET driver

texts:
I have a circuit where microcontroller drives a H-bridge which is powered from 12V. I am having a problem with driving the high-side MOSFETs. I will be turning the H-bridge on/off only couple of times a day for up to 5 minutes at once.

I've designed a boost converter that is capable of converting 12V to 24V in hope of driving the high-side MOSFETs. However I am currently stuck with connecting microcontroller to boost converter for driving the gates.

This is how I am thinking of wiring it up:

simulate this circuit – Schematic created using CircuitLab

But...
Boost converter is working in continous current mode. And if I were to leave boost converter working on forever, if I wont drive H-brdige, the voltage output from the boost converter would rise untill something would fail.

And if I were to enable the gate driver IC only when I would want to turn the H-bdrige on, same thing would happen, because I would need to power it for up to 5 minutes.

Does anyone have any idea on how drive high-side MOSFETs without blowing something up?


texts: Gyroscope's Output Data Rate (ODR) vs. Program Loop Frequency (L3G4200D, Arduino)?

texts:
I configure a L3G4200D gyroscope with an Output Data Rate of 100 Hz and a program reads the raw values from the registers (X, Y, Z axis) every 5 ms.

But if the program runs at 200 Hz (i.e. loops every 5 ms) and the gyroscope outputs new values at 100 Hz, then does it that mean that the program (always) reads the very same values every 2 program loops?


texts: Trouble designing compensation network for TEC Controller using Analog ADN8831

texts:
I am designing a circuit to control a TEC using Analog's ADN8831 as the TEC Controller chip. My application requires more TEC current than the ADN8831 eval board can supply so I built a test board to experiment with.
The ADN8831 offers two amplifiers.  The first is used to normalize the NTC to produce a linear voltage with temperature. This is working fine for me.  The second amplifier is used to take the set temp and diff it with the NTC temp to produce a control voltage for the TEC MOSFET driver. This is also working fine for me -- when the set and read temperatures match, the ADN8831 temperature lock line is signaled. The TEC heats and cools appropriately.
But here's my issue.  According to the Datasheet, the equation for the output of the second op amp is:
$$
Vout2 = Vtempset - \frac{Z2}{Z1}(Vout1 - Vtempset)
$$
Where Vout1 is the output of the first op-amp, Z1 is the impedance between Vout1 and the second op-amp's negating input and Z2 is the negative feedback for op-amp 2.
Note that when the the set point is reached the output of the second op amp should be Vtempset. I've verified this, and this also triggers the chip to signal its temp lock line.
However, the MOSFET driver uses this voltage range graph:

So the bias on the output is intended to have equilibrium at 1.25v. But I'm seeing that Vout2 matches the equation above, so shortly after I reach temperature lock I lose it because the TEC is still being driven. I've also verified that when I set the setpoint temperature to be 1.25v the TEC does power down when the setpoint is reached. So it works perfectly but only at this temperature.
Vout2 is internally connected to the TEC driver.  Neither the data sheet or the eval board have anything special here other than a standard PID network so I'm at a loss how the is supposed to generate the voltages shown in the graph. I've tried a full PID network using default values from the eval board schematic and I've also simplified this down to just a "P" network to better read what's going on.  I've also tried simulating several networks in Spice to try to get that elusive 1.25v offset to no avail.
There's got to be something I'm missing and I'm hoping someone here can educate me.
Full schematic of my TEC section here.  There is a full PID network in the schematic with values taken from the eval board defaults. I've removed it while I experiment but when present the behavior was the same:

Thanks for looking.


texts: Implement cryptography algorithms in an ARM microcontroller

texts:
Assume a situation in which you want do some encryption procedures in your ARM microcontroller. (Receive a file, encrypt with 3DES and some hash functions and returning it, for example.)

As far as I know we have two option here:

Reinventing the wheel! i.e. writing some functions to do described cryptography algorithms.
Adding already-written libraries in our project and using their methods simply.

Now I want to benefit from the second solution using OpenSSL libraries. But I'm not sure about it! Is it possible to add these libraries to the IAR IDE? Shall I recompile the OpenSSL source code before adding to my program?

I really appreciate a step-by-step solution.


texts:
Hopefully I don't get torn apart for such a noobie question (but how else do you learn right?). I got a Raspberry Pi to hopefully learn a bit about electronics (and because it was 35 dollars). I asked a question on another Stack Exchange site:

https://raspberrypi.stackexchange.com/questions/32012/electronics-of-a-water-pump/32014#32014

I got a great detailed answer but in turn had questions about that answer.

The answer mentions that I need a relay to switch the pump. To my understanding a relay is a device that opens and closes an electrical circuit.

I dont know enough about electronics to know why I need a relay, but here is my sad attempt at a guess:

The Raspberry Pi's GPIO pins do not provide enough current for the water pump, so I need an alternate power supply to provide enough current to the pump. So in order to turn the pump on or off I need a relay (which I assume would be toggled by a GPIO pin) to open or close the circuit which turns the pump on or off.

If this is correct, wouldn't everything stop getting power? Once the relay opens the circuit, wouldn't the GPIO lose control of the relay... since the circuit is open...???


texts:
I wish to drive a 12V stepper motor with a USB port as the source of power. However, the USB port only outputs only 5V as output. This will obviously not work.

I had thought up of several ways to overcome this. 1. chain multiple USB ports in serial to bump up voltage. 2. Use some sort of circuit ("booster") to increase the 5V to 12V

I have tried searching this issue up online, however I have seen very differing answers. Some people say that using 2 USB ports in serial will create a short circuit while other people say that this will work and is the basis of Y cables. Could someone clarify and suggest the best option to increase a 5V supply to 12V?


texts: I'm not really sure why an inverting buck-boost might be disadvantageous compared to a non-inverting converter. If the load has a particular polarity, then can't you just connect it backwards to achieve the same effect?


texts:
I've calculated the area of product needed for transformer, it's 71cm^4, but in core datasheets there is not value with cm^4 unit for example: https://www.tdk-electronics.tdk.com/inf/80/db/fer/e_65_32_27.pdf,
am I missing something here? How can I choose a core for calculated area of product in cm^4

https://www.ti.com/lit/ml/slup126/slup126.pdf


texts:
I am trying to drive an electrical vacuum pump from a car directly from 12 VDC.

Earlier, I succeeded with a different pump just by connecting them to DC power, the other pump (different brand) used around 10 A at 13.8 V.

But now I got a new pump (different manufacturer) which does not rotate when I plug the power. It just moves small steps each time I connect it.

It might be an AC pump, which seems strange to me for using it in a car.
Can someone help me understand how to drive it?

I attach the image of the circuit inside after opening the cap in the electric side, next to the two leads.

The model of the pump is 59220-J5000. It looks exactly like this.. The resistance between the leads is about 0.2 ohm.


texts: Problem with calculating high frequency response of a CE amp

texts:
I have this amp:

The parameters of the transistor are hfe=120, Cje=40pF and Cjc=4pF. I am also told to assume Cpi = Cje = 40pF and Cmu = Cjc= 4 pF.
From that I should calculate fh and compare it with the simulation.

Here's the output of the simulation. It shows -3db point around 2 MHz, which is according to the design constraints. However when I compute fh by hand I get completely different results. I use following reasoning:

fH = 1/2πCinR’sig

Cin=Cπ + Cµ(1+gmR’L) = 40pF + 4pF(1+0.06A/V*3680Ω) = 927 pF

R’L= ro||RC||RL = 3680 Ω

R’sig = rπ||(rπ + (RB||Rsig)) = 7300Ω

From this fh is about 23 kHz, which is way off. I have no idea where I am making a mistake. Can anyone help? Thanks.


texts:
The data sheet for the CD4013 specifies a "setup time" value, but when you look at the included waveforms, that value describes the timing between the "data" input and the leading clock edge.
What specification do I use to determine the minimum time from a SET
or RESET falling edge til the leading clock edge?
There must be enough "daylight" between the falling edge of the SET or
RESET input and the clock's rising edge so that these two inputs won't
override the clocks ability to "latch" the data on the input.
I like to know how much time is needed between the deactivation of SET or RESET and the first active clock edge to safely latch the data. The t(SETUP) in the data sheet is only shown in the waveforms as the time between the center of the leading edge of the DATA input (either rising or falling) and the center of the rising edge of the clock. At a 5MHz clock (100nSec high, 100nSec low), I need to ensure that the reset signal has "completely" disappeared before the clock leading edge arrives.


texts:
For the operation of emitter-coupled logic and sedra smith book,

1) Compared to CMOS, why ECL is the faster logic family given that it requires so many transistors to propagate to output Y (T5 emitter node) ?

2) Why current drawn from the power supply remains constant during switching and regardless of which input logical state the ECL is in ?

3) How is the reference voltage Vr made insensitive to temperature and PSRR according to calculation made below ?


texts: Supercapacitor Discharging - Strange Behaviour

texts:
So i have a bank of Vishay "196 HVC ENYCAP" supercapacitors and I am witnessing strange behaviour when discharging them that I cannot explain.

The bank has an equivalent capacitance of 60F. I have charged the bank to 6V (all supcaps in bank are rated for 7V) and placed a 100 ohm resistor across the bank and monitored the fall off in voltage.

The results were as follows:
Voltage after 5 minutes: 2.4V,
Voltage after 10 minutes: 1.16V,
Voltage after 15 minutes: 1.16V,
Voltage after 20 minutes: 1.02V.

Based on the voltage decay formula of Vt=Voe^(-t/RC), the voltage should only have dropped to 4.91V after 20 minutes.

However then after removing the 100 ohm resistor, the voltage immediately recovered to 1.97V. After 15 minutes the voltage had recovered to 3.38V, and after 30 minutes to 4.2V.

I have checked all connections and they are fine.

Is there something I am missing here? Is the voltage expected to drop off as much as it has before recovering over time?


texts:
I'm an audio beginner.

I'm required to design a box with a jack for a headset and connector for an unknown cable going to a Windows desktop PC.

Headset has the standard 3.5mm plug for microphone, r speaker, l speaker, and ground.

Intention is there's a user at desktop PC who will communicate with user of the headset.

Questions:

the box is only pass-through. what's the best cable I can use to pass these low-level signals between headset and Windows desktop PC? distance is 15 meters.
at desktop PC side, what's the best hardware I can use so Windows desktop PC can receive/process these signals? I'm thinking USB link to PC but not sure what's available out there.


texts: What is the point of this resistor network?

texts:
What is the purpose of this resistor network? Why not just use one resistor? or connect the cathode of RA93 diode directly to the mosfet drain (this mosfet is high side of the h-bridge).

It seems to me that pin 30 of the relay is connected to pin 87 through diode and the resistor network.
I just am not able to figure out why? The diode is probably to preventing the circuit in case someone plugs in the battery terminals backwards, is this right?

Thanks.

simulate this circuit – Schematic created using CircuitLab

simulate this circuit

Alternate schematic (by @Transistor) emphasising bulk capacitor and relay bypass of soft-start. Purpose of D3 is unclear. Operator to review.


texts:
I am somewhat new to DIY electronics, and I am having a go at Arduino.

Having succesfully made a simple door alarm using a PIR sensor and some parts of my old car, I am now trying to create the classical clap-on clap-off contraption. However I am having trouble tuning the microphone.
The setup is fairly simple, having the electret microphone routing it's analog output to the Arduino's analog input - which is reading the voltage. The arduino maps input voltages between 0 and 5 volts into integer values between 0 and 1023.

The problem is that the input signal when literary NO sound (even when I disconnect the microphone all by itself) is always reading values between 850 and 860. Having the microphone connected may differ these values from 1 to 3 integers, where 1 is simply when the microphone is ON, and 3 is me tapping the membrane with my finger(!).

Needless to say, this is not particulary good. I have tried with another Arduino clone, and another electret microphone - with no luck.

QUESTION: Is the general quality of cheap electronics parts of for example eBay, really that bad compared to the genuine more expensive parts? Eg.: My Arduino clones each went for 3 dollars, compared to the genuine product approximately 20 dollars.

PS: I am also relatively new to this forum, so I am hoping this is an okay question to ask.


texts: What's the importance of source impedance termination?

texts:
Given a circuit like this:

simulate this circuit – Schematic created using CircuitLab

What's the importance of R1? One can guess that it's to make the output impedance of BUF1 equal to the impedance of the transmission line, but why is this important? What happens if R1 is omitted? How does what's on the other end affect this? Maybe it's a matched load, open, or short. Maybe it's a transmission line with discontinuities in it.


texts: 32.768 kHz crystal for RTC, should the case be soldered to GND?

texts:
I've seen this on a few boards, but I don't know if it's the right thing to do. Should the case be soldered to GND?

It is the common cylindrical package:


texts:
I'm trying to regulate the voltage of 9 volts battery to DC motor but didn't work. This is my scheme:

The original scheme is for led and just wondering why it didn't work for DC motor.

Here is the image of DC motor with 104 capacitor.

Please give me an idea why it is not working.


texts: Measuring Solar Cell Short-Circuit Current with INA219

texts:
I'm currently trying to characterize a solar cell i.e measure its open-circuit voltage and short-circuit current over time. I have an INA219 current sensor lying around I'd like to use. The former case (Open-Circuit voltage) is no problem. However, the INA219 datasheet  states that the shunt resistor (I have a 0.1 Ohm shunt) should not have more than 320mV dropped across it. However, wiring the solar cell to the INA219 to measure the short circuit current would result in the full solar cell voltage (~4-6V) dropped across the resistor...Can anyone kindly tell me how to go about measuring the short-circuit current with the INA219?

Edit: I'm expecting a maximum current of around 260mA from the cell


texts: Is using floor plan tool during FPGA design ever actually useful or required?

texts:
I have used Intel Quartus and Microsemi Libero. Both of these tools contain a method whereby we are able to view the floorplan of the FPGA, hover the mouse around to see what parts of netlist have been mapped to different locations on the FPGA floorplan.
The tool is called Chip Editor in Intel Quartus & Chip Planner in Microsemi Libero. The purpose is the same for both.
One feature of these tools is whereby we are able to lock certain part of our design to specific region of the FPGA. This is done via logic lock regions in Quartus and via Floor Planner constaints in Microsemi Libero.
Usually we just click on the compile button and let the tool do synthesis and fitting and this usually gives a netlist that meets timing. The fitter will figure out how to fit the design.
This brings me to my questions:

Why would one ever need to use these floor plan tools to lock design logic into specific regions? Is there any benefit to doing this? Is this ever really required?

Also, if we have done this logic locking to specific regions, what if we want to add debug logic e.g SignalTap II (Quartus) instance into that logic or an Identify Instance (Libero)?

If one wants to use this tool then,

How does one decide what part of design should be locked into what part of the FPGA floor plan? For complex designs, it will certainly be very difficult to make a decision on this by human. This is why I don't understand the point of these tools.


texts:
I'm currently trying to install some IR sensors on an Arduino robot and am having issues with the sensor readings anytime the motors (2 of them) turn on.

I'm using an Arduino Uno connected to an Arduino Motor Shield. The IR sensors are Vishay IR detector modules powered from the regulated supply rail (5V) on the Arduino.

Anytime the motors are powered off, everything works just fine; that is when it detects IR  the output of the sensor goes to GND.

But as soon as the motors turn on, the output keeps dropping to GND regardless. I used an oscilloscope to confirm that indeed there is high frequency (~10 MHz) noise. I'm assuming this is noise introduced into the supply by the motor/Motor Shield PWM control signal?

But isn't the whole point of a regulated 5V supply to provide a stable voltage?

I even tried connecting the sensors straight to the Battery (3300 MAh NiMh cells, so current draw isn't a problem) and it made no difference. I've also tried putting capacitors across the motor terminals, across the IR sensor Vin and GND, and also tried them across the Output and GND. No dice. So are the motors actually causing ripples on the Battery voltage?

Any insights?

EDIT:

This is the IR detector: http://www.pololu.com/file/0J19/TSOP34156.pdf


texts: I would like to light a very tiny light (led?) using RF

texts:
I would like to light something very tiny like these hobbylinc.com/model_railroad_light_bulbs without running wires for my wife's dollhouses.  I was thinking RF to power them.  The houses are VERY small - 3 inches or so ( http://victorian-dollhouses.com/scale.html ).

Technically I have a BSEE but frankly I am more of a Comp Sci Guy.


texts: Electrical current's role in a processor?

texts:
I am curious of what role electrical current plays in a processor. When I asked this back in school a couple years ago, my teacher only replied that the processor executes instructions in response to a series of 0:s and 1:s. However, I cannot grasp how something as seemingly random and unpredictable as an electrical current can be used to execute instructions in a processor that is used for deterministic and predictable operations.

How is electrical current used by a processor?


texts: 26MHz crystal not oscillating - strange capacitor behavior

texts:
I am using this 26MHz crystal from NDK. The specified load capacitance is 10pF, I am using two 18pF capacitors in series accordingly. The circuit is shown in figure below. The problem is that the crystal is not oscillating. I observe a constant 2.4V at OSCP and GND at OSCN [VDD for U1, which is an RF transceiver, is 3.3V].

I have an evaluation board for U1, where the same crystal (and 18pF caps) is oscillating OK - the average voltage at OSCP is 0.5V in this case. I tried replacing the crystal and the capacitors (C1,C2) on my PCB to make sure the problem is not due to defective parts - but with the same result.

Finally, the observation that is currently puzzling me is that out of desperation, I tried checking for short on C1, C2 using a digital multimeter - when the part was powered up. While C2 did not report a short, C1 did - I also noticed that the reported resistance was (negative) -600 ohm when the red probe was at point B and black probe at point A (points A, B shown in figure below). I understand that this might be due to the capacitor discharging in to the multimeter - but the problem is I do not see the same behaviour with C1 on the evaluation board where crystal is oscillating OK.

What might explain the difference in behaviour for C1 b/w the
evaluation board and my PCB - i.e., why don't I see a negative
resistance between points B and A on the evaluation board?
[For people who have experience debugging crystals] What can I try next to debug why my crystal is not oscillating?

simulate this circuit – Schematic created using CircuitLab


texts:
Recently,my research will focus on DCM flybck but I don't have any theory on DCM. I don't know how to start I want to model the small signal model.
Do you guys can suggest me some paper or book let me can learn form it. I will be appreciate it.
I have searched some papers but it doesn't teach me the basic so I have no idea.


texts: It is an image of a squirrel cage rotor. \$\textbf{B}_{S}\$ is the rotating magnetic field created by the stator. It creates an induced voltage \$\textbf{E}_{S}\$(not shown in the image) in the bars of the rotor. The plane of maximum \$E_{S}\$ is the plane containing \$\textbf{B}_{S}\$. \$\textbf{E}_{S}\$ creates the rotor current \$\textbf{I}_{R}\$ which produces another magnetic field \$\textbf{B}_{R}\$. The net magnetic field \$\textbf{B}_{net}\$ induces a voltage \$\textbf{E}_{R}\$.Will \$\textbf{E}_{R}\$ produce another current which will add with \$\textbf{I}_{R}\$? How does this process end?


texts: Importance of laser numerical aperture in selecting photo diode

texts:
I want to design a  circuit in which the laser light will be detected by a photodiode. I just wanted to know how the laser numerical aperture will affect the photodiode selection.

Am I have to concern about the Numerical aperture and other things like acceptance angle, the divergence angle of the laser, for selecting the photodiode. Please share your experience it will be a great help. (Sorry for my bad English :( )
Thank you.


texts: LCD clears itself when potentiometer contrast is too low

texts:
I'm making a project that requires an LCD, and the project was working fine on my breadboard for testing.
I moved it to my final product, but now my LCD stops displaying text after a few minutes, or when the potentiometer value is too low.
One thing that really gets my attention is that if the potentiometer is fully high, the LCD doesn't clear by itself. When I lower it, it happens again. I have a refresh rate in this project as well for about every 250 milliseconds. Here is the code for my project along with its schematic.
Schematic:


texts: Please see the circuit diagram below and under the assumption that VBE = 0.7 V, what are VB,IB, IE, IC, VC, β?

texts: Ve= 1V and Vbe=0.7V how to approach this problem and solve it with the basic transistor knowledge?


texts: Shunt resistor after MOSFET and op amp to amplify voltage

texts:
I'm trying to figurate out how to measure current in circuit. I have idea to use shunt resistor but after connecting op amp on shunt I have some unpredicted measurements on output of op amp. I want to measure amps of leds. Is this good idea to measure current? I can control led intensity with pwm that works fine and I can measure small voltage on shunt and after using Omh law I got current in circuit and I want to amplify that voltage because MCU need to read voltage. Is voltage on shunt dc or we have there some ripples which can look likes sin(pwm) signals? Here is schematic:

Any idea and comment is welcomed


texts: Can't control RB10 (and RB12) of the PIC32MZ2048ECG064 as a 'normal' GPIO

texts:
This is an excerpt from the datasheet of the PIC32MZ EC Family concerning peripheral pin select output mapping:

I'm using the PIC32MZ2048ECG064. My question concerns RPB10. I would like to use RB10 as a general purpose IO port, and control it with TRISB10, LATB10 and PORTB10. However, nowhere in the right list I see a possibility to do this. All options are either 'reserved', 'no connect' or really a peripheral. At first I thought 0x0, the default value, would let me use the pin normally, but section 12.3.5 says:

  A null output is associated with the output register reset value of '0'. This is done to ensure that remappable outputs remain disconnected from all output pins by default.

So if I understand correctly the default value is that the pin is unusable. Yet, the LATB10 bit exists, so there must be a way to use it.

How do I use a remappable pin as a 'normal' GPIO?

Here are my configuration bits:

#pragma config DEBUG =      OFF
#pragma config JTAGEN =     OFF
#pragma config ICESEL =     ICS_PGx1
#pragma config TRCEN =      ON
#pragma config BOOTISA =    MIPS32
#pragma config FECCCON =    OFF_UNLOCKED
#pragma config FSLEEP =     OFF
#pragma config DBGPER =     PG_ALL
#pragma config EJTAGBEN =   NORMAL
#pragma config CP =         OFF

/*** DEVCFG1 ***/

#pragma config FNOSC =      SPLL
#pragma config DMTINTV =    WIN_127_128
#pragma config FSOSCEN =    ON
#pragma config IESO =       ON
#pragma config POSCMOD =    OFF
#pragma config OSCIOFNC =   OFF
#pragma config FCKSM =      CSECME
#pragma config WDTPS =      PS1048576
#pragma config WDTSPGM =    STOP
#pragma config FWDTEN =     ON
#pragma config WINDIS =     NORMAL
#pragma config FWDTWINSZ =  WINSZ_25
#pragma config DMTCNT =     DMT31
#pragma config FDMTEN =     ON

/*** DEVCFG2 ***/

#pragma config FPLLIDIV =   DIV_8
#pragma config FPLLRNG =    RANGE_5_10_MHZ
#pragma config FPLLICLK =   PLL_FRC
#pragma config FPLLMULT =   MUL_44
#pragma config FPLLODIV =   DIV_32
#pragma config UPLLFSEL =   FREQ_24MHZ
#pragma config UPLLEN =     ON

/*** DEVCFG3 ***/

#pragma config USERID =     0xffff
#pragma config FMIIEN =     ON
#pragma config FETHIO =     ON
#pragma config PGL1WAY =    ON
#pragma config PMDL1WAY =   ON
#pragma config IOL1WAY =    ON
#pragma config FUSBIDIO =   ON

/*** BF1SEQ0 ***/

#pragma config TSEQ =       0xffff
#pragma config CSEQ =       0xffff


texts: Auto-switching Power Mux with High Current Output for 5V Power Sources

texts:
I'm trying to find a power mux or design a circuit to supply 5V to a load that draws approximately 6A. The power supply should have a back-up power which is why a battery will be used alongside an AC-DC converter; should the converter fail, the battery will take over. The setup looks something like this:

simulate this circuit – Schematic created using CircuitLab

So, both converters output 5 Volts and both are capable of outputting the amount of current I need. The crux of the system is the power multiplexer. Although it was pointed out to me that I can use TPS211x as power mux, they're limited in terms of current rating and output only 1.25 or 2 A depending on the version.

I was thinking of using them in parallel to output higher current, but am not sure about any consequences resulting from that. One thing I'd like to point out to is that the load can be divided into 3 parts each of which would need 5V, 2A to operate. I'd appreciate any comments on that.

Is there any breakout board that I can use to do this switching? I'm open to using diodes, but only concerned with the voltage drop. Any suggestions?
UPDATEAfter getting in touch with the technical support, it was pointed out to me that using 2 units of TPS211x in parallel can be risky if the switching time in the two components is different.


texts: What is the difference between the Hopkinson's test and the Swinburne's test for a DC motor/generator?

texts: If both are used to calculate the efficiency for a DC motor/generator, then why don't we just use the Swinburne's test? For example it has a easier circuit. Is there (maybe) an advantage of one test over the other?


texts: How to build a larger ROM using smaller parts?

texts:
How can i build a 1024-bit ROM using 512-bit and smaller ROM's?
Is it good idea to use a 2:1 MUX and that selects on of 2 512-bit ROM's?


texts:
I am looking for a simple circuit to invert a tristate output from a microcontroller, hopefully using only BJTs. What I mean by this is that the truth table would look like:

IN   OUT
H    L
L    H
Z    Z

An ordinary inverter circuit / NOT gate will not do, because I don't want current to flow through the output if it isn't flowing through the input.


texts: How can I be sure to supply enough current without increasing the voltage?

texts: I have been trying to supply 5V into parallel-connected components which require a certain amount of current in total. If I wanted to increase the current from my supply, can I increase its current output without increasing the voltage?


texts: What are Peripheral Interface and Host Interface?

texts:
For this bluetooth smart module, the specification says

UART and USB host interface
SPI, I2C, PWM, UART, GPIO peripheral interfaces

what is a host interface and what is a peripheral interface?


texts:
I have the next signal

$$x_1[n]= 1 \ |n|\leq N_1; \ 0 \ otherwise$$.

Now I am given some points of sampling of the frequency of the fourier transform of the above signal. \$\omega_0 =\frac{2\pi}{5}\$, and \$\omega=k\omega_0\$ for \$k=-2,-1,0,1,2\$.

Now I am defining a periodic signal \$x_2[n]\$, which is given by:

$$x_2[n]=\sum_{k=-2}^{2} a_k e^{jk 2\pi n /5}$$

Where \$a_k\$ is given by the synthesis formula:

$$a_k=\frac{1}{5} \sum_{-2}^{2} x_1[n] \exp(-jk\frac{2\pi}{5}n)$$

I want to plot \$x_2[n]\$  in the \$n\$ space, but I don't want to calculate the \$a_k\$'s by hand, is there a way to do this by matlab, I mean without writing the full expression in paper and then typing it in matlab?

Is there such functionality?

Thanks in advance.


texts: Calculating differential PCB traces - Edge-Coupled Microstrip

texts:
I finally have the microstrip characteristic impedance thing figured out.  But now, of course, I need to learn about differential signalling on PCB traces.

I've spent some time researching.  Here is my understanding.  Please tell me if I have anything wrong!  I have a few specific questions at the end :)

As the two microstrips get closer together their coupling increases, and their ODD characteristic impedance gets smaller.  In addition to the "standard" benefits of differential signalling (noise immunity, signal quality, etc), this allows you to use significantly smaller traces than if you were using two non-coupled, single microstrips.

My board has a UWB transceiver in the 6.5 GHz range.  Its RF pins are \$100\Omega\$ differential, which will run to a balun.

My questions:

It appears that I should solve for odd characteristic impedances of \$50\Omega\$ each.  Is this true?
Using the TNT Field Solver mentioned by @RolfOstergaard, I find that 8.3 mil traces with 5.3 mil space between them (13.6 mil center-to-center) gives me \$Z_{odd} = 50.05\Omega\$.  My board house can do 5/5 mil trace/space.  Is there any reason not to use these values?
How much of an effect will soldermask have on the circuit?  Should I keep the differential traces uncovered?

Thanks!  Here's the pcb stackup:

Top: 1-oz copper.
   6.7 mil FR-408 prepreg (Er = 3.66 @ 1 GHz).
Ground: 1/2-oz copper.
   47 mil FR-408 core.
Power: 1/2-oz copper.
   6.7 mil FR-408 prepreg.
Bottom: 1-oz copper.


texts: How to use 24V 100Ah battery to run 12V motors?

texts:
How can I run 12V motors with the current of 30A together with 24V 100Ah battery? Should I modified my circuit to change 24V to 12V and connect to motors? or

Should I find a battery which can change 24V to 12V directly?

Thank you all.


texts: Modeling phase delay in high frequency resonantly coupled inductors

texts:
I am interested in simulating resonant wireless power transfer circuits similar to the ones developed by MIT and others. So far, I have been able to successfully create a basic simulation model of a set of resonantly coupled inductors with a k of 0.1 or less. However, I'm interested in exploring the behavior of the system at high frequencies where the distance between coils becomes a significant fraction of the transmission wavelength.

When I say significant, I mean within a quarter wavelength, as I am still interested in near-field coupling. However, even within this regime, I am interested in exploring the effects that the propagation/phase delay of the field from the receiver has on the transmitter.

Is there any way to model the effects of delayed phase of two resonantly coupled inductors in LTSpice? I imagine it would be something like a wireless transmission line but I have no idea how I would even start to model this. Again, the phase delay range I'm interested in is only 10-20 degrees max from the source. Any pointers in the right direction greatly appreciated!

Also, as a reference, here's a paper I've been reviewing that discusses the subject a bit more.

http://www.physics.princeton.edu/~mcdonald/examples/wireless.pdf

Thank you,
Jason O


texts: The effects of frequency resolution in FFT on the frequency spectrum

texts:
This is a section for the parameter study of my thesis (basically: why and how I did what I did in the experiments). Currently, I have to choose the fit bandwidth and FFT lines combination for the experiment (for the parameter study, it is just giving an impulse for the generator, or hitting the metal specimen with a hammer). Investigations (actual measurement) say that with frequency resolution under 0.1 Hz, the spectrum obtained would be very squishy. For example, right below is 12800 FFT lines (or 12800 FFT bins) with different bandwidths (0.5, 1, 2, 5, 10 and 20 kHz) and different frequency resolutions (39.1, 78.1, 156.3, 390.6, 781.3 and 1562.5 mHz respectively)

The spectrum with 39.1 and 78.1 mHz frequency resolution (blue and orange) are very "squishy"...
Question 1: Why do we have such squishy spectrum?
For reference: this is non-squishy spectrum

Question 2: At low-frequency range (<50 Hz), smaller FFT bin shows peak better (more data point on the same range of frequency, thus easier to spot the peaks). But why at high-frequency, smaller FFT bins lead to lower peaks (at 300 and 330 Hz)?
Question 3: Is there a "critical point" for frequency resolution? Or the trade-off between frequency resolution vs spectral/time resolution? If yes, is there any source you can point towards for me, or is this more like a rule of thumb?
Thank you for your support


texts: How to calculate the rise time and fall time of a flip-flop?

texts:
This is an effort to find the rise and fall time of the following circuit.

I have calculated the rise time and requesting confirmation from expert’s end. There are some assumed values like trace impedance parasitic capacitance, kindly note that is for the sake of calculation purpose. I am much interested how the calculations need to be done than the numerical values. But values can be updated if it is not at all close to real values.

See the details,
D Flip-flop (SN74LVC1G80)  is powered with 3.3 V and logic levels are  0 V (Logic LOW) and 3.3 V (logic high).

Assumed parasitic capacitance = 3 pF

Assumed trace impedance = 10 Ohm

Data switching at a rate of 500 kHz

Following method used to calculate the rise time:

\begin{align}
3.3 \cdot 0.1 &= 3.3 \left(1- e^{-\frac{t_1}{RC}}\right) &\implies t1 &= 3.1608\text{ ps}\\
3.3 \cdot 0.9 &= 3.3 \left(1- e ^{-\frac{t_2}{RC}}\right) &\implies t2 &= 69.078\text{ ps}
\end{align}
So the net rise time is = 69.078 – 3.1608 = 65.9172 ps

Observations

Rise and fall time is independent of the data signal switching frequency
Rise or fall time can be increased by adding series resistor and parallel capacitor to the each output stage of the FF ( that is pin Q ).

Kindly confirm or point out my mistakes.


texts: How do universal IR remote "codes" work?

texts:
It is easy to find this kind of reference when searching for IR protocols and codes for specific equipment. The actual IR transmission contains far more data than these small codes can hold.

What exactly do these codes represent?
How can four digits represent all the commands a device can receive?
Are these "codes" references to some standard protocol?
How do the universal remote knows the protocol and all the codes the product understands from this small configuration code?

I would love to understand more about this technology. For me it seems that every remote is different, and you would have to reverse engineer every message to identify which bit/byte does what.


texts:
I was trying to build a 16x9 LED matrix with an MCU with a limited amount of pins. The Anodes of the LEDs are driven by P-channel MOSFETs which gates are driven by a 74HC595 8 bit shift register. the cathodes of the LEDs are sunk by the TLC5940 LED PWM driver IC. The circuit around the MOSFETs looks like this:

The Source is connected to 5 V and the Gate is pulled up to 5 V through the 1 kΩ resistor. Drain is connected to the anodes of 16 LEDs in parallel and the gate to the 74HC595. Now my observation on a logic analyzer (as well as on an oscilloscope):

The red channel is just the constant 5 V supply at the source. The brown channel is the switching signal coming from the 74HC595 and the black channel the voltage at the drain. Isn't the MOSFET supposed to shut off immediately after the gate gets pulled high again? The turn off delay is described as about 80 ns which is clearly passed on the output of the logic analyzer. Is this the expected behavior or am I doing something wrong here? Since the TLC5940 can only sink current on the cathodes of the LEDs I could not get around high side switching, but I was under the impression that this circuit should work...

EDIT:

After finally having some time, I recreated a simpler version of the circuit and tested it on a prototyping board with an Arduino to isolate the problem. This is my schematic, the unconnected nets connect to the control pins from the Arduino:

As p-channel MOSFETs I tried both, the FQP27P06 and the IRF9540N which both have similar specs. My readings were in both cases almost the same:

We see that the MOSFET is only supposed to conduct for 0.27ms according to the gate reading but it remains for another 0.86 ms which really causes harm to my application when all 9 led rows are connected in the end. It caused trouble, because one column with all 16 LEDs lit was drawing 320mA. With this behavior on all the MOSFETs though and all LEDs activated in my matrix, 3-4 MOSFETs were conducting at the same time which at least tripled the current draw and since my board was not specced for this the voltage was braking down and the MCU ended up halting. Also my package of the TLC5940 was not rated for the amount of heat dissipation and it occasionally went into the temperature error mode.
Anyone having an idea why this problem might occur? Every answer is greatly appreciated!


texts: What mean two dots on same transformer winding

texts:
I know the dot mean the start of the winding, but on this schematic the same winding have two dots, i can't find info regard this on internet so i come ask what that means.
I meassure the 7 and 5 and give infinite resistance.
That's from a TV PSU, not outputing any DC safe voltage, secondary coils are all 0V.

Schemantic PDF download


texts: Solar-powered DC motor for mini fountain

texts:
I'm working on a small water fountain that's powered by solar panels, and I would love some help identifying a root cause for a water pump dying. This is my build so far:

Water pump

Solar panels

I have 4x 6V-100mA solar panels in parallel, so I can generate 6V at 400mA. Under full sun, the panels's voltage is around ~7V and under this voltage, the pump draws 240mA (it is rated for 220mA)

I get 3h of direct sunlight every day so the pump will turn on, and turn off 3h later

My first run was great, but the pump died after 3 days of usage.
I identified several possible causes:

running at 17% above the rated voltage (I didn't expect this was going to be such a problem as I'm used to 1.25 safety rating)
low quality pump (I found a very similar model on Amazon that recommended to use them for experimentation only)
Turning on and off every day, beeing worse than running continuously
[not the case] dry run burn out (the pump never worked under dry conditions

I've ordered a better pump that should be more suitable for this usage, but the size is starting to be an issue. Any thoughts on what's the most likely reason for the pump dying in the first place? (if there is hope that such fountain can run on small pumps like that one, it is great as it can fit many other projects)
Bonus question: as the light increases slowly, the pump starts drawing high current while not running as it hasn't reached its starting conditions. How much of an issue is that?


texts: PIC 24F VGA array addressing instructions

texts:
In order to make a VGA driver for a PIC 24F microcontroller, I am generating an interrupt creating a VSYNC pulse, followed by a loop that puts data to the ports. HSYNC pulses are calculated after this video loop. All timings are correct, and my CRT monitor accepts the generated signal. However, I can only write literal data for the moment, and would like to be able to write arrays filled with data to my screen. This code is currently working:

MOV     #80,W0

VID_LOOP:
    BSET    LATB,#4
    BCLR    LATB,#4
    SUB     #1,W0
BRA     NZ,VID_LOOP

The B4 port is the R part of my signal, so this loop writes vertical lines on the screen. my W0 reg is loaded with #80, this means 80 lines are written over the screen. This loop is executed 60 times and a front and back porch are added, so I get a resolution of 80*60 PX. So far so good, but this means I only have 2 instructions to load a variable from a screenbuffer array to the port. Does anyone know how I could go about doing this? Maybe my loop could be made shorter?


texts: How do I speed up transistor switching in low side power switch?

texts:
I am working on a project and want to drive a motor with a 12V PWM signal (Motor connected to 12V and the Motor- net on the diagram).

The circuit below is an idea I have, however after I built it, it turns out it has quite a slow turn on and turn of time. What are some methods of speeding that up?

Thanks in advance,

Rob

Edit 1: Adding scope plots of input and output as requested.

Plot 1 - Between R31 and U4

Plot 2 - Probe at "Motor-"

Edit 2: Adding schematic of circuit to the right (Current sensing).


texts:
How can I design a system that gives the functionality of an MCB (overload protection, operates in an AC circuit) with an electronic trigger-off.

So that once the device is in ON state, it should be able to be turned-off by

Human interaction (mechanically flipping the latch)
Over-load (MCB inherent feature)
Electronically, by using a small trigger voltage. Once this trigger is applied this switch should be mechanically flipped to off position, so that the user should see it is in OFF state.

The device is to be used to run a domestic motor (say 1HP.)


texts: Multimeter, outlet and a Spark: the question of simple Voltage measurement

texts:
So I got a TekPower TP4000ZC MultiMeter.

(Image source)

It has COM port and two red ports:

V-Ohm-etc. set at 600V Max and 500mA Max Fused
10A red fused port.

Unlike other multimeters, there are no separate red ports for Volts and Amps.
TP4000ZC MultiMeter has literally the inscription between COM and 1st red port, saying that using them is 600V MAX and 500mA max.

I want to measure voltage in the wall socket.

I presume that plugging probes into the outlet would complete the circuit, thus making the multimeter as the load of some sort.

Since my first red port has 500mA MAX, I presume that wall outlet has more amperage flowing than pathetic 500mA. (Arent they set at 15A?)

So I plug the red cable to 10A red port, black to COM. Black probe goes into larger opening, red probe into the smaller opening of the outlet, set the multimeter knob to Volt setting

AND ..... SPARK! (in the outlet)

So I disassembled the multimeter and saw that the 10A fuse connects COM and 10A Red port.

I guess I shouldn't have put red cable into 10A port, but kept it in 500mA red port V-Ohm-Amp-Hz one.

My questions:

Why the 1st red port (600 V / 500mA MAX red port V-Ohm-Amp-Hz one) is the correct one to use when measuring voltage in the outlet?
Wouldn't plugging the multimeter into the outlet complete the circuit, allowing current (under voltage potential) to flow into the multimeter (regardless of whether the multimeter is plugged in in series or in parallel)?
Thus I should have "honored" the 500mA MAX warning (or 250mA on some other multimeters) on the 1st red port and theoretically plugged into 10A port?
If the fuse that connects 2nd red port (10A) was set at 10A (F10AL250V), then could I presume that the multimeter just became a "load" in the circuit  - e.g. just like any small appliance - then why fuse broke, why it did not act as said "load"?

Thank you in advance for your time typing the answers for this.
I cannot find clear answers to this despite plethora of resources that just goes around my questions tangently.


texts: fm transmitter booster - can it even work?

texts:
In my research I ended up on jameco electronics site and they had an online course on FM transmitters located at http://www.jameco.com/Jameco/workshop/JamecoFavorites/fmtransmitter.html.

I followed the link to the schematic of the standard model then I followed the link to another transmitter. After browsing a few pages of FAQ's I came across this one from http://anarchy.translocal.jp/radio/micro/radioFAQ.html#q4. and I quote:

  Q:How to increase the output power?
   A----This main unit is so sophisticatedly designed that you can boost the power only when you add a boosting circuit to it. The model circuit is here. I didn't mention, but the transmitter ("1-3 watt") has harmonic signals such as the double and tripple of the original frequency and you need a lowpath or bandpath filter between the transmitter and the antenna. When you connect this booster, such a filter is indispensable. Otherwise, you may have interference against television and radio.

And the circuit presented to me when I clicked the word "here" is the following:

Since my transmitter uses 5V, I plan to run this circuit with 5V instead of 12V. I do however have some quick questions:

The odds of me accessing the 2SC1970 transistor are low since I'm located in Canada. I do however have Pn2222, 2n3904 and Pn3563. The Pn3563 has a higher Ft (600Mhz) than the Pn2222 and 2n3904, so I'm looking for the best transistor to replace the one in the circuit.

Since I plan to transmit at the carrier frequency of 300 to 500Mhz, shouldn't I make 33pF input capacitor lower?

Why in the circuit isn't there a super high resistor value (such as 1M) from +12v to NPN's base?

And wouldn't the transistor blow up if enough signal gets injected into the base through the capacitor? and I say this because the choke is a short circuit at DC.

and why is 33pF, 100pF and 3.5 turns of wire made as a filter, is it supposed to be of a certain frequency to filter out the input before reaching the antenna? if so, what frequency?


texts: Level transformation 0/+5 V TTL logic to +/-9V how to maximize gain and frequency range (DC to 4 MHz)

texts:
I see a lot of repeat answers and instructions how to convert dual supply levels to logic levels, but I have the inverse situation, converting 0/+5 V TTL logic to +/-9 V, and I don't see a lot of info about it. Strange, this should be very common for driving an RS232 line.
In principle for AC of a reasonable frequency range, it should be doable with just a simple transistor and decoupled with a capacitor at the base, etc.

simulate this circuit – Schematic created using CircuitLab
But in my case I need to transform a digital signal that may both change at 4 MHz frequency, but also may be in the same state for a long time, so any decoupling capacitor with a simple transistor circuit would end up not working.

simulate this circuit
I played around with an op-amp and this is working in principle for low to moderate frequencies, except I am getting into the problem of the dynamic range of the op-amp, I put it between +/- 9V and I can dial up the gain from the 5 V peak-to-peak to about 8.5 V peak to peak, but not better. That's one problem why I would rather just use a single transistor.
I don't really care about distortion, since my signal is a square wave anyway. But I care about gain and rail to rail, but I don't have, nor can I get a rail-to-rail op-amp (I can't order from Mouser or Jameco and my selection at the local store is small and the hit/miss ratio too low if I come in with the part number for some fancy R2R op-amp.)
I also don't want my signal to be integrated and reduced to a tiny triangle wave, as it is at higher frequencies.
Here are some impressions from my op-amp circuit in practice:

As the frequency doubles 3 times we start getting the triangle:

and it gets downhill from there

and this is the maximum frequency we need to support, about 2 MHz.

What might be done?

UPDATE: Michael responded and helped me try the LM393 comparator, I didn't realize I need a pull-up resistor on the output. So I tried a few values, 4.7 kΩ, 1 kΩ, 10 kΩ. And I am just leaving the scope pictures here because I found the behavior of the low very peculiar, and I suppose one needs to add some capacitor somewhere too. But anyway, it has a bit better frequency response but not good enough. I just hope that 75188 line driver chip will meet the frequency response requirement.

Further update: I could get this instability fairly well in check, but still the LM393 is just too slow. It has a nice gain, but at 2 MHz the square wave reduces to a tiny triangle also. Here is how that looked, but this was about the last frequency where it was useful, I think this was at 125 kHz or so, really not great at all.

while this here is at 2 MHz. And don't be fooled by the scaling, the triangle there is tiny and super amplified on the scope.

FINAL UPDATE: Bruce Abbot's circuit rocks! And I want to show the scope pictures of it. Here is at 250 kHz:

and this is at 2 MHz:

and at 4 MHz. We can see that it's getting a little sluggish with switching down to full negative, but hey, this is about solving my problem for now so that I can focus on other things.

I will report back on how this compares with the 75188 line buffer when it arrives in the mail.
FINAL UPDATE: The jury is out folks and the 75188 came in the mail. Here I present to you a head to head comparison between it and Bruce Abbott's simple two transistor level shifter.

You can see that in terms of maxing out the available range from he power supply (same pair of 9V batteries) they both are equivalent. The little ripple on the roof of the square wave gives away the IC. But it is at the high frequency that the simple (and probably more power-hungry) design of Bruce Abbott is shining as it still performs at the full amplitude and only slightly rounds off the falling edges. Remember that this is on a breadboard, so capacitance is an issue, but this time I measured with x10 probes as Bruce suggested.
Now I am sitting on those 25 chips of 75188 I bought for cheap in bulk, not going to use them.