texts: Operational Amplifier Output Stage Biasing

texts:
I am trying to bias my op-amp output stage using diodes. I am using a current source for the bias current but later I will replace it with BJT current source.
However, it doesn't seem to work. Whatever the value of the Ibias, Q7 is never in active mode. I am not sure what I am doing wrong here.
Any help is appreciated. Thanks!


texts:
Ipad doesn't charge while in use and connected to the usb port. It definitely charges when connected to the supplied 10 watt power adapter.

The USB port, as far as I know, supplies 5 watts. Can we modify it by simply adding an extra usb adapter to the cable of ipad to draw the extra 5 watt? something which the older external hard-drives used to do?


texts: How to replace a 50 ohm speaker with 25 ohm speaker?

texts:
I'm repairing an electronic device at home. Actually it has a non functional speaker. So I've to change it. This speaker is a 50 Ohm, 0.2 Watt. But I didn't find this one on the market, what I could find is a 25 Ohm, 0.3 Watt.

I searched on the net, I found that replacing a 50 Ohm speaker with 25 Ohm may cause some damage.

The system seems that is designed to work with 50 Ohm speaker. So to meet this condition, can I connect the 25 Ohm speaker in the system and add 25 Ohm independent resistor (25+25=50)?


texts: Automatic Switch to Battery Backup when Power fails

texts:
OK. So I am developing a simple stand alone device. It has a sensor module that takes in 12V and another PCB that takes in anywhere from 5V to 12V.

Now, I am running this entire device using Mains supply. My Question is, is there a way, wherein, the device will automatically Switch to a battery supply when the Mains supply fails?

I have read on this topic a little bit and have come across devices called Power Path Controllers.

Will a simple Relay also do? I attach the Common terminal to the Input of my circuit. Like the diagram shown below.

Might that work? Any advises?

I need this switching to happen automatically. Without any human interference. Also, it would be an additional positive if my microprocessor could tell which supply is giving power.


texts:
I'm doing a practice problem and I'm unsure how my approach did not receive the same result as the solution. Any help would be appreciated.
Below is the Figure along with the solution as well as my hand written approach. I hope it is readable. Thank you..


texts: Using 12 V 2A supply unit for higher amp value

texts: I recently purchased a Meanwell RS 25 12 which outputs 12V 2A and i want to use this to supply power to a blower fan. However, my blower fan requires 12V 8A. So what I want to do is to increase the power supply current such that I can conveniently power the blower fan. I know this can be achieved using full wave rectification but have little idea of the ratings of resistors and capacitors to employ. I can solder and can work with a good diagram if anyone can assist.


texts:
I'm trying to build a tunable bandpass filter for 140 to 1500 Mhz, and the design requires that I move the signal from a PCB with an SMA connector to another mounted about 3mm above it. I'm using board to board connectors for the other connections, but I wasn't sure whether it was possible to match 50 ohm impedance (or to get close enough) with a connector like that.

My question is, how should I move the signal from one pcb to the other with 50 ohm impedance? Is such a connection even possible in that little space, or is my approach fundamentally flawed?


texts: (Infrared LED Circuit) Can i use this circuit with 3.3v logic?

texts:
I made this circuit for a 5v logic. I plan to use it as a remote control. So pulses. i hope that with this circuit i achieve more range as with the default remote. I already made it but now i have some doubts.

IR LED Datasheet

NPN Transistor (2N3904) Datasheet

As there is a voltage drop of 0.7v because of thee transistor i simply used 4.3v to do the math

For the signal/base resistor i used 330ohm 1/4Watt just to be sure that it saturates the transistor properly.(should be around 13mA, arduino handles 20mA)

The max forvard voltage of the ir led is 1.6v it and should work with 100mA.

As the ir led resistor needs to be 1/2 Watt i used 2 resistors 68ohm+56ohm in paralell which i measured and give me 31ohm (math suggests 27ohm 1/2).

1. Would you change something?

simulate this circuit – Schematic created using CircuitLab

2. Can i use this circuit with a 3.3v logic as signal but feed the led with 5v?

simulate this circuit

I'm new to electronics and the more i learn the more doubts i have.


texts: Why isn't this a right expression for FM?

texts:
Like AM that can be represented as:

$$\bigl(A_c+Km(t)\bigr)cos\bigl(2\pi f_ct\bigr)$$

Here, simply the amplitude is being varied by a sinusoid.

Therefore similarly, why can't FM be written as:

$$A_ccos\Bigl(2\pi\bigl(f_c+Km(t)\bigr)t\Bigr)$$

Obviously the constants are such that the frequency doesn't go negative.

Isn't the above equation intuitively correct? The frequency is being varied by a sinusoid again.


texts:
I am working with CAN Bus on the Nucleo H743ZI2 (STM32), I have set up the times for a clock souce of 10 Mhz, and can baud rate of 1 Mbps. Everything seems to work correctly until the motor is turn on with its power  supply.
In the CAN net I have connected:
Devices :
Nucleo + transceiver
Teensy + transceiver
Motor NANOTEC CANopen
USBtin CAN2USB
When the motor is off I can send messages and see them on the CAN lines with no problem.
WHen the motor is on I can send messages from the teensy with no problems and I can see them on the oscilloscope and the usbtin.
But when I try to send messages with the motor on with the Nucleo board with a transceiver (the transceiver is another board of the same type as the one with the teensy) some frames are corrupted.
I saw them in the oscilloscope and I attach some images, do you have any idea how I can solve it ?
TL;DR:
Motor off - Nucleo CAN messages fine, teensy CAN messages fine.
Motor on  - Nucleo CAN messages bad, teensy CAN messages fine.
CHANNEL 1 IS CANtx STM32, CHANNEL 2 IS CANRx STM32, CHANNEL 3 is CANH ,   CHANNEL 4 is CANL of the oscilloscope, B1 is the protocol decoding of the oscilloscope.
Screenshots


texts: How do I choose a twisted pair shielded cable?

texts:
The charging/discharging of a battery (1u to 30 mA) and remote voltage measurement is to be performed over 2 pairs of 2 m cable. In order to reduce picked up common mode noise I intend to use shielded twisted pair cable.

But I don't know which one to choose. There are several properties to consider.

The first is the gauge. This one is clear: the thicker, the better.

Somewhat more obscure are the types that listed i. e on Mouser: what is the real difference beetween those types?

Then there is insulation and jacket material. I am not sure whether I need to consider it in the first place?

And the last and most difficult is the shield itself.

I know that there are braided shield, which has lower resistance, and foil which has better coverage. But I can't decide what of that is more important (?)

Is there perhaps something else that has to be taken in account?

I would like to get anwsers disregarding whether you think I need shielding or not.

EDIT:
this what I see if I attach oscilloscope probe to a 1.8 m unconnected unshielded cable:

Full signal:

Bandlimited to see low frequency more clearly:

First picture zoomed in time:


texts: Equivalent resistance with specific resistors

texts:
Suppose I have a resistor R with resistance of 6 ohms and maximum power dissipation of 0.125W. My current over that resistor is 667.6mA. So the power over resistor R is 2.765W which is over the limit of 0.125W.

I tried to equate that resistor(R) with some resistors in parallel or series but I failed because I can't choose any resistor I want(that would be easy). I only have that resistors: 0.47, 1, 4.7, 10, 22, 33, 51, 68, 82, 100, 150, 220, 330, 470, 510, 680, 820, 910, 1k. All these resistors have the maximum power dissipation of 0.125W.

My idea was to put 20 resistors of 100ohms in parallel and then add one resistors of 1ohm, in series. That means I have R = 1/(20/100)ohms + 1ohm = 6 ohms, but there are too many resistors because I have to implement that circuit on a board that has only 3x3cm. And beside that resistor R, I have plenty of transistors, other resistors and capacitors. So there isn't enough space.

So my question is: how can I equate that resistor, efficiently, with other resistors in series or parallel without overcoming the limit of 0.125W(0.1W would be perfect).

PS: this is not a homework. It is a project of mine. A voltage regulator.

I have limited space. 3x3cm and also i have other components on my PCB.


texts: How much current does a typical multimeter draw to measure resistance?

texts:
Assuming it's running on a 9V battery like most multimeters are, and the setting is on MegaOhms.

How much current will be drawn from the internal battery?


texts: Powering a Servo: Do I need a separate power source?

texts:
I have a project that utilizes two strong digital, coreless servo motors.  Whenever I use DC motors, I usually need to have separate power sources for both the microcontroller and the motors (due to noise and such).  I don't have as much experience with servos, is this still the case?  I'd really like to get away with using just one battery, are there any precautions I can take for this?

Thanks.


texts: Rating 1.5V 50mA (MAX) what does it means?

texts:
I have an optic mouse that has in its specifications this:
1.5V -- 50mA (MAX).

What does it means? Does it means it consumes 50 miliamps an hour? or the maximum consumption would be 50mA depending on usage?

Thank you,

Matias.


texts: Protecting laser diode that is transmitting an audio signal

texts:
I would like to first state that I do not really know anything about circuit design- I am very much a beginner.

That being said, I am working on a project where I am using a laser to play music. I have the audio source (my iPod) going through an audio transformer (do not know the specifications, the circuit was given to me by my professor). I am powering the circuit with 4.5V and I have two LEDs that absorb excess voltage. The laser I am using is a 650nm 5mW laser. I measured the current through the laser diode and got 14mA.
(I would like to add that I have tested this and at 4.5V, the laser is at its brightest and I have run it for over two hours, but I need a very robust circuit that can last forever essentially).

For some reason, the laser diodes keep burning out and I do not know why. I have done research and I found that a heat sink would help and so would a constant current source.

I want to operate the laser at the highest power without burning it out, so how do I do this? And when they say use a 'constant current source' what does that actually mean? When I look them up, I either find really large power sources where the lowest they go is 1A (I need 14mA). Or I find these small components that clearly need something else to them (like the LM317). What would you suggest for my problem?

Also, because the laser is transmitting the audio signal, the voltage fluctuates ever so slightly to create the signal- will this affect the solution?


texts: Help finding maximum power transferred to load RL

texts:
This isn't homework, it's just a review problem.  The answer is 4mW.  I tried working the problem and came up with the wrong answer.  What did I do wrong, and how can I solve this correctly?

My steps:

Remove \$R_L\$ and create an open in its place
Find the voltage  at the open, this is the open circuit voltage
I applied KCL at node 2 (what I labeled V2)

6/3k amps in, 2mA out, 2mA in, and thus the current going out through the 6k ohm resistor (center branch) is 2mA. 2mA * 6kohms = 12 V across the 6kohm resistor.
Also, there is 4V going across the 2kohm resistor.
12 + 4 = 16, so the open circuit voltage is 16V.

Opening the voltage source and shorting the current source, the internal resistance is 6k ohms (2k ohm is ignored, no current flow, and 3kohm is ignored, no current flow)
The Thevenin equivalent circuit has a 16V source, 6kohm internal resistance, and 6kohm load R_L.  The voltage divides evenly.  So, 8V/6kohms = 1.3mA through RL
P=IV, 1.3mA * 8V = 10.667 mW

What did I do wrong?


texts:
I need a capacitor to charge using 5V in 1 seconds and discharge at 30 mA 3 Volts for 10 seconds. How do I calculate the capacitor needed.

I am sorry I don't have electrical background.

Actually in my Arduino, I am not using interrupts, it becomes unstable and I am sleeping for 8 seconds, but I want to know whether any interrupt/ high voltage occurred at analog pins.

Any help would be appreciated.

EDIT:
Ok let me explain, a little bit more about my Arduino program. Using Interrupts, you can find out if the PIR motion sensor sends a pulse, when someone crosses in front of the sensor. Now consider my problem, I am not using Interrupts, as my program is already very large and interrupts make my program unstable due to less free RAM. I am anyway reading the sensors after each 8 seconds using watchdog timer. Now the problem is that the microcontroller is in sleep mode for 8 seconds, and won't poll the pins, so I was thinking of putting a correct capacitor, that can be charged by the PIR sensor and then the capacitor can keep the input pins of the microcontroller high for 8 seconds. Sorry, I don't know much about electronics, so may be this is stupid, but if this can be doable, please share your opinion.


texts: What are SD/SS, delay, and flag pins on LM2596?

texts:
I'm studying the TI datasheet for an LM2596.

On page 4, at the top left in section 7.1 Absolute Maximum Ratings, it mentions:

\$\overline{\mathrm{SD}}/\mathrm{SS}\$ pin input voltage (6V)
Delay pin voltage (1.5V)
Flag pin voltage (-0.3 - 45V)

..without definition.

Googling on 'sd/ss pin' and 'flag pin' produce unusual results that don't help in this case :)

The chip has an enable pin, labeled \$\overline{\mathrm{ON}}/\mathrm{OFF}\$ in the schematic and elsewhere. The others are \$V_{IN}\$, \${Output}\$, \${Ground}\$, and \${Feedback}\$ (it is a 5-pin device).

Can anyone explain what these three pins are and why they're named that way? I have to assume they are each either an alternate name or a different use for one of the pins because there just aren't enough pins to go around otherwise :)


texts: What is the battery weight of the Nissan Leaf 62 kWh?

texts:
I found many websites as this one where all details regarding battery packs for 24, 30 and 40 kWh batteries of Nissan Leaf models are stated, while I could not find information regarding the battery weight of 62 kWh model.

Battery weight of 40 kWh model is done according to the battery module weight and number of modules, which is 8.7 kg x 24 = 208 kg. Since number of modules is different regarding newer Leaf model, does anyone know how to properly scale its weight?


texts: Li-ion Battery Shelf Life Calculation (Including Temperature)

texts:
Long time reader, first time poster...

I have encountered an potential issue in regards to shipping Lithium-ion batteries in products over from China to the United Kingdom.

I have always factored in the standby battery consumption when calculating a products shelf life, but it has come to my attention that during transit in containers, these products can undergo heats of 60°C (140°F) for up to 28 days.

After this period the products will then be returned to "ambient" temperature and stored normally.

How can I factor this extreme temperature period into my calculation when calculating product shelf life?

Thanks in advance!


texts: When is VHDL code considdered compile time

texts:
EDIT:

I am working with a lookup table which is generated in compile time.

Is this compile time code:

because sinus_table is a constant
or because any computation before begin is compile time.

Or maybe both?

ARCHITECTURE Behavioral OF set_output IS

----------------------------------------------------------------------
-- Begin - Generate the lookup table
------------------------------------------------------------------------

  -- Elements per Signal
  CONSTANT table_length : integer := 2**sinus_width;

  IMPURE FUNCTION createSamples RETURN output_sinus IS
    VARIABLE result : output_sinus(0 TO table_length - 1);
    VARIABLE table_step : real := 2.0 * math_pi / real(table_length);
    VARIABLE sinus_result : real;
  BEGIN
    FOR i IN 0 TO table_length - 1 LOOP
      sinus_result := sin((real(i)) * table_step) / 2.0;
      result(i) := std_logic_vector(to_signed(integer(sinus_result * real(table_length - 1)), sinus_width));
    END LOOP;
    RETURN result;
  END FUNCTION createSamples;

  CONSTANT sinus_table : output_sinus := createSamples;

------------------------------------------------------------------------
-- End - Generate the lookup table
------------------------------------------------------------------------
------------------------------------------------------------------------
-- Begin - Manage the address and return the sine wave
------------------------------------------------------------------------

BEGIN

PS: Do you know of any literature that I can cite about this?

(Most of the literature that I found explains synthesis/elaboration)...


texts:
I know VHDL and I understand the syntax but I never programmed an FPGA before. I am going to write soon my first VHDL code and then upload my code to Xilinx FPGA. When writing VHDL code we have entity. On the examples I saw, signals in UCF file are always related to the top level file not others. Is this correct? Because when I write my own code, Im confused about mapping which signal to which file, vector signals and their differences from others and how the files are connected with each other etc. Since this is not Java/Cpp I feel really weak. Is there a tutorial/link which can give me a fine start for my first project?

I know what clock divider is, it divides the clock ... but why dont we use the system clock 50 Mhz for example? What is clock divider good for? What is the advantage? Do we need it at all? How do I use clock divider in my codes?


texts: Can the location of the inductor on the board affect the operation of the microcontroller?

texts:
I have a voltage regulator, based on LM2596, in its circuit there is an inductor on 33uH.

The question is, can this inductor be a source of interference? Next to him, I plan to place the Atmega328P chip and the AVRISP connector, with which I will program the board.


texts: solving pipelining data hazards using stalls

texts: I have a question about fixing data hazards in a pipelined datapath using stalls. I have read slightly varying things on this. Some lectures I have found put the instruction decode (ID) in the same step as the write back and some put it in the next step. From what ive read, in the first example the write can be done in the first half of the step and the ID in the second half. If this is possible why is the second example needed, or are there specific occasions where both need to be used.


texts: Conformal coating of UHF (radio frequency) circuitry 400 - 1000 MHz

texts:
Do you have experience applying conformal coating on UHF circuitry (ISM band)?

Are there known issues (e.g. degradation of UHF performance) which arise when coating UHF components like filters and matching networks or even Chip-Antennas?

Would be glad to hear about your experience.

edit:
I wanted to provide some results from my investigation. The Smith-Chart shows the impedance looking into the matching network (from transceivers point of view), before and after coating was applied. In particular both smith charts are overlapped. The orange arrow shows how marker 1, the center frequency is beeing affected.

Question: does that mean, that coating acts as a series inductor? Would I need to counteract that with an equvalent series capacitor or by choosing a lower value for the existing series inductor?


texts: Is this Mealy representation correct for 011?

texts: I am practicing on moore and mealy machine sequence detectors and I want to make sure if the mealy 011 sequence detector is correct.


texts: How do large power supplies work? (VFD's etc.)

texts:
I've looked at the designs of switching power supplies (buck/boost/buck-boost) and I basically understand how they work. But is this the same thing used in large power supplies such as those in the VFD of a tower crane (etc.)? Like the larger of the two hoist winches offered for the Liebherr 710 HCL 25/50 tower crane, which uses a 220 kW (294 H.P.) AC motor. How does the power supply maintain DC output while the motor is bogged out to ~18% of full speed?** Do large VFD's and whatnot still use a conventional buck (boost) switching converter to get the required "rail voltage"?

Note that 480 Vrms coming in gets you approx. 680 VDC through the rectifier and reservoir capacitors.

**Here's part of the performance data if anyone wants to know:

0 - 3450 kg*** at 0 - 238 m/min (0 - 6900 kg at 0 - 119 m/min)

0 - 25000 kg at 0 - 43 m/min (0 - 50000 kg at 0 - 22 m/min)

***238 m/min only goes up to 1800 kg on 1-part line if the reduced speed curve is used.


texts:
Can some please suggest if I am doing this right ?
The intended circuit is to used with opamp (TL072)

Have I understood the decoupling right ?


texts: Is there a way to import a PCB layout from one "sheet" into a multisheet in KiCad?

texts:
I am making a multisheet schematic and I'm appending schematics from other projects into the multisheet. They take their netlist along with them which is great but,
is there a way to take their PCB layout with them from their respective projects so I don't have to layout the appended schematics again?


texts: Can one voltage output from OpAmp read with two ADC inputs?

texts:
this might be a little silly question, but please advise me. I am trying to use two photodiodes (one for the absorbance measurement and one for the source of the light as a reference) and the voltage from the transimpedance amplifier from each photodiode connected output pin of OpAmps will be connected to the differential amplifier input to improve the SNR.

Here is my question.
Let's say the output voltage from the 1st PD is V1 and the voltage output from the 2nd PD is V2. VD is V2 - V1.
I want to measure VD and V2 simultaneously. So VD is the voltage difference between V2 - V1 and V2 is simply single end measurement (relative to the ground reference).

If I use two ADC (microcontroller) channels to measure those two voltages, can I connect
1) V1 - V2 as inputs to one differential amplifier and
2) V1 - ground as inputs to the other differential amplifier?

Say figure below is a dual differential ADC IC from Analogdevices.

Can I use that IC to measure those voltages without any problems? Thank you in advance for your advice.


texts: Change space between Routs and copper pours in Altium PCB designer

texts:
How Can I change the distance between Polygon pours and routs in Altium PCB designer?

Update 1:
Actually I'm newbie on Altium so posted the PCB with default clearance value (0.245 mm) and larger value (0.345 mm) respectively. I think it conflicts with routs through U1 and U2, which routs are so close to pads.

Update2: I was changing the clearance between track and polygon so it didn't work. I changed clearance between polygon and other parameters and it's working.


texts:
I would like to use an arduino system to control a heating pad that I will be using in my system.

http://www.amazon.com/Signswise-200x200mm-Silicone-Heating-Printer/dp/B00ZP3XCS4/ref=sr_1_fkmr1_1?ie=UTF8&qid=1447442029&sr=8-1-fkmr1&keywords=400+200+silicone+heater+24v

Although it says 24 v in the link when I click it says 12 v so I don't know whether the heater I got 12 v or 24v. Perfect :)
Now the question is...
How do I turn this thing on and off so that it stays at 37C in my system. I have seen various mosfets but I couldn't find any that support 150W. I also don't know how to set up the mosfet system but I can look up the diagrams online so that's not a big issue...
I have seen some logic level mosfets but people raised concerns about some "charging" and "protecting the pin" and all that... so idk. I am a biochemistry student trying to build a nice arduino system and not completely clueless but fairly inexperienced with these systems. so if anyone can explain how can I use mosfets/relays (i think relays only work with ac not like my heater (dc)), I would be really happy.
Thanks a lot.
Have a great day.


texts: Absolute value circuit around a non-zero value

texts:
I have searched for a few hours on the internet and in some circuit design books, but have been thusfar unable to find a circuit that produces absolute value around a number other than zero. Does anyone here know of such a circuit? An example IO would be:
At Vin = 10, Vo = 10
At Vin = 9, Vo = 11
At Vin = 11, Vo = 11

I'm hoping to accomplish this with a single absolute value circuit, rather than subtracting 10 beforehand, taking the absolute value, and adding 10 or offsetting the result.

Thanks for any help


texts: Zigbee low power mode when both devices are battery-powered

texts:
Does Zigbee allow low power mode when the communication is between 2 battery powered devices so that both can last longer on the batteries?

I suppose typically there's a mains-powered host that would be listening for transmissions from battery powered devices that would wake-up and transmit occasionally which would make it low power on the battery-powered side.

But what about a communication between 2 battery powered devices? Whould it require a synchronized clocks between the 2 for them to synchronously wake up for communication?


texts: TPS65233 LNB Circuit is drawing more current from supply

texts:
I have used LNB controller TPS65233 in my design. Input is 5.5V and Output: 13/18V. I am seeing access current drawn by the circuit when I give 5.5V input to the circuit and no load is connected to the output. Manually I have checked and there is no short seen on the circuit.
Also, When I connect the input supply and remove. Input supply rail is showing short with the ground for some time.


texts: I need to translate 0-5V analog signal from CASR 50-NP to 0-3.3V analog signal for the MCU's ADC. I came along Microchip's tip #16 solution. Is this a good practice? Can someone verify my design?


texts: How to keep a stable output voltage from changing input voltage

texts: I'm learning about solar panels and bought a 6V panel and a 3.7V Li-Ion battery as well as a solar battery charger, all from adafruit. I also got a boost converter thinking that the output of the circuit would be 3.7V but actually it outputs from 3.7 up to 6.8V depending on the sun. This was my mistake for not reading carefully. I need 5V at the output for a microcontroller and other components. I was looking around and found a 5V precision voltage reference REF02, but it takes a minimum of 8V input and upto 40V. So my question is, can I use a boost converter at the output of the solar charger set it up to where it won't go below 8V at the worst condition and use the REF02 to have the stable 5V? Is this a reasonable circuit or is there a better idea or better way of doing this? Thank you.


texts: Exercise question about Thévenin theorem

texts:
I'm new to Thevenin's theorem and I'm trying to figure out this simple one.

I did what's on the next figure. I'm wondering If I can join the cables as I did and I could say that the voltage across \$R_{1}\$ is also \$V_{th}\$ since they are in parallel.  The answer says \$R_{eq}=R_{1}\$. But I'm getting \$R_{eq}=R_{1}+R_2\$.

Thank you for your time!


texts: Altium - How to disable white (polygon?) outlines during interactive routing

texts: I seemed to have pressed some hotkey activating a white outline around same layer objects during interactive routing. See image below. It seems to slow down FPS quite a bit, so I'd like to disable it. Can someone tell me (1) What the white outline means / what it's for (2) How to disable it?


texts: Will connecting Vcc and enable together cause problems

texts:
The following chip seems to be acting funny.

http://www.ti.com/lit/ds/symlink/sn754410.pdf

I have one DC motor hooked up to 1Y and 2Y and the other to 3Y and 4Y.

Could the behavior be because I connected the VCC1 (logic supply voltage) and 1,2EN and 3,4EN all together? NB. No resistor between them either (see page 6 of link). What might happen?

The weird behavior is the following:

When driving a DC motor in one direction (1A = 5V, 2A =0V), I'd expect 1Y to be VCC2 (output supply voltage) and 2Y to be 0V. Instead with  a VCC2 of 9V, 1Y is around 7V and 2Y is over 1V. Making the voltage drop between the DC motors leads only 7-1 = 6V. What is happening here?
When activating two motors at the same time. They start to drive as normally and then slow down to a stop and twitch. This might be a software issue, but I'm not sure...
Also is it normal that the inputs of the H-bridge chip are floating values. Up to 1.3V-ish if I don't hook them up to the controller and set them to zero from there. I would expect them to take the 0 from ground
Finally, what is the purpose of all the diodes on the page 6 graph? I have the outputs hooked up directly to the DC motor.

Page 6 graph:


texts: Charging and discharging Ultracaps with a 12v DC Brushed Motor

texts:
I am trying to store small amounts of energy from a 12v motor with an ultracap. I'm thinking of a 3000F 2.7v cell from Maxwell.
I am trying to find out info on charging ultracaps, specifically the current required/advisable, as in my situation it may fluctuate.
I also need to boost the voltage to 12v on discharge, but with a motor stall current of 60A (although I do wish to put a PWM in to control it to about 30A), I fear that combined with the near 5x boost, I'm drawing some serious current (270A worse case without PWM) over the 30 seconds it's active. Will the ultracap take it? I read some can output up to 1000A safely, provided I make the wiring thick enough it doesn't melt. Or do I take the capacitance hit and put 2 in series?(For cost I don't really wish to buy 4 and put another 2 in parallel)
Thanks,


texts: Is electric voltage fade in and fade out?

texts:
Consider theres a LED through switch with power from DC power supply. It will on when switch is close and off when switch is open.
From closed switch we open the switch, so the LED will turned off. But was LED instantly turned off? Or theres time it's still ON after switch closed?
And the question is vice versa when we close the switch from the opened switch.
If LED not instantly,
Is it happen because capacitor from power supply? If true, Consider the power supply doesnt have capacitor at all like battery AA 1.5v will it be same?
Who the fade in/out? Current or voltage or both?


texts: How does the CPU handle XCHG internally?

texts:
While designing my own 16-bit CPU I wonder how the register-register XCHG instruction is executed internally. From computer science I know the DLX which doesn't provide XCHG and therefore doesn't need to access two registers in write-back (would this even be possible?), but only the destination register.
I guess this isn't done in one cycle, right?

Thx in advance


texts:
I made a circuit which selects one of 4 sensors and determines if a valid data stream is present on that sensor and counts the number of times data is valid. I narrowed my problems to hardware.

In the original circuit, I did not include the LED and 100 ohm resistor in series (see thick wire in schematic) because I thought I didn't need it. Then I started adding it temporarily and everything seems to run more smoothly with it in.

So at this point with the resistor and LED in, I can detect light status on any sensor of my choice at a rate of 1 every 2 ms. Ideally, I want to detect at a rate of 1 every 125 us.

I believe my problem exists because of some delay caused by the math resulting from the internal resistor on the micro's RXD pin plus the 1k resistor plus a capacitor somewhere in any of the IC's?

The reason I added the 1k resistor is because if by fat chance I ground the RXD pin via software and output W is high and I didn't have any resistor then I'd have a short circuit which I do not want.

But what baffles me is that I get success with the diode and LED circuit even though output W would return a high or low since the part is a 151 not a 251 or does that chip output still have a resistor in series?

My other thought is to replace the AT89C2051 with an AT89LP4051 but that's asking for more money and another programmer.

Anyways, other than my thoughts, Can I configure this setup hardware wise to allow a signal to pass through from the photo transistor to the micro via a multiplexer at a rate of 1 bit per 125us? (like change resistor values and/or add/remove resistors)? etc.

Currently I have the entire circuit minus the LED+resistor in series mounted on a PCB with tracks at least 12 mils wide and power tracks at least 40 mils wide.

The supply voltage averages at 4.8V.

UPDATE

I have tried all of the following without success:

Replaced the series LED+resistor combo in original circuit with just a 1K resistor and used 220 ohm for series resistor
Removed the series LED+resistor combo and instead connected the GPIO pin to ground via 22K resistor and again used the 220 ohm for series resistor

Now I haven't gone as low as 75 ohms for series resistance that someone pointed in their diagram but I'm still a little fuzzy. Maybe there's an entry in a datasheet I need.

Now I'm curious, considering this micro has (based on literature I read) GPIO pins in open drain format only, could I get away with removing the resistors and LED and replacing the series resistor with only one reverse-based diode (so anode connects to GPIO and cathode connects to multiplexer output)? If so, can I get away with a standard 1n4148/1n914 diode?


texts: Measure the maximum value of an exponential analog signal and provide a constant supply having that same value

texts:
I need to detect the exact time for which an exponentially decreasing analog signal is equal to the half of its maximum value. I'm using for that a digital-output comparator but I have a big problem of how to provide a constant signal equal to 0.5*Vmax on one of the comparator input. Do you have any idea that may help?
Thanks a lot.

Best regards,
Emna.


texts: How to change the reading from an ADC of 10 bits to the timer 0 registers using a PIC18f4550?

texts:
I a reading an anlogue value using the 10 bits ADC from the Channel 0. I have implemented an interruption using timer 0, where I set some value for the registers of timer 0 (TMR0H and TMR0L - 8 bits) and wait for the over flow.

Refergin to the question, I want to use the reading of 10 bits from the ADC for the 2 8 bits registers of timer 0. I came up with the idea of multiplying the reading from the ADC by 64(16bits reading approximately), then some how transfer that value to TMR0H and TMR0L. I know that by making the multiplication I am lossing some data.

I havent found a way of accomplish the change between the 16 bits register to the 2 8 bits registers. I tried using bit masking with shift operators.

void interrupt ISR(){
    //Check if it is TMR0 Overflow ISR
    if(INTCONbits.TMR0IE && INTCONbits.TMR0IF){//TMR0 Overflow ISR
            if(giro){
                    if(aux && PORTD == aux){
                        PORTD = 0x01;
                    }else{
                        PORTD <<=1;
                    }
                }else{
                    if(PORTD == 0x01){
                        PORTD = aux;
                    }else{
                        PORTD >>= 1;
                        }
                }

        TMR0H  = (auxADC && 0xFF00) >> 8;
        TMR0L  = auxADC && 0xFF;
        INTCONbits.TMR0IF = 0;
    }
}

There is no problem compiling the code, but when debuggin the code with the pickit 3 the values of TMR0H and TMR0L dont change properly, they dont update with the low and high part of auxADC.

Thanks a lot!


texts: Ramp up voltage on a small AC train motor

texts:
I am looking to start older electric trains that run off an AC transformer at a gradual ramp up of the voltage when coming out of a block signal area instead of starting at the last voltage set on the transformer.
I have a circuit that does exactly what I want to do but it only works with DC

I have been experimenting over a year now with different configurations of circuits I had sent to me and have found but none of them have worked.
Any help would be appreciated.


texts: Is there a minimum current drain to use LM25011 of TI?

texts:
Using LM25011 as switching voltage regulator to power a board with wide range of current drain rates.

Input of 24v;
Output of 5V;
Drain current between 5mA and 1A.

Is this component suitable to this purposes?

I'm asking this becouse I'd like to use this module to power also another device with a 10mA drain at 5v. On datasheet I see that efficiency drastically go down at 300mA and no information on less than this value.

Additional question, is this IC able to operate under 300mA load, so at 10mA?


texts:
I've a device (An old NES cart, actually) that I've fitted with a USB port and a flash drive. I'm using it in a NES to Raspberry Pi conversion. My idea was to have a port on the side for connecting to the computer to upload data (movies, ROMs, music, etc.) and use the original 72 pin connector to connect to the Pi (using the original slot loader from the NES).

Obviously 5v and Ground are soldered in parallel.

When I soldered up the USB port (basically just a USB extension cable), it works fine. However, when I add the data wires to open pins on the connector, the drive ceases to function.

I have no idea why this is happening. Any clues?


texts: Do you need a Pull down resistor when the line has an LED connected?

texts:
basically, since the LED is a diode that is tied to GND via a Resitor, does that mean it can double as Pull-down resitor for that line?

simulate this circuit – Schematic created using CircuitLab


texts:
I'm trying to replace my tablet li po batteries and am trying to understand the connections.
The following figure shows the 2 3.7v batteries connected in series. Most replacement batteries I've seen have just 2 wires coming out of them. I understand I connect them to the +ve and -ve contacts on the PCB. However, I'm wondering where do the black wires coming from the PCB connect on the battery and what is their purpose.
Also what is the whitish gluish like substance that covers the black wire connections on the PCB
The tablet is Fujitsu Stylistic M532 and the battery part number is FPCBP388

Below is the back side where the battery tabs connect to the PCB

Closeup of where the black wires go into the battery.


texts:
In case of BJT for example, the input characteristics can be described with \$I_B=f(V_{BE})\$ and output characteristics with \$I_C=f(V_{CE})\$.
How can the input and output characteristics be described in case of TTL gates?


texts:
is there any transistor or some module else than relays able to switch the given current digitally between two wires? I would need 4 switches in my circuit, the next 4 channel module of relays would work fine, I guess:

But I'm looking for something smaller, also these modules handle up to 220v and I only need 5v 2A, which I consider a waste of capability.

So, is there a better option or should I just use this module?


texts:
http://mantravlsi.blogspot.tw/2014/08/wire-load-model-wlm_1.html
From the link, there is an instance of snapshot of a WLM.I　can not figure out the number "1" in fanout_length("1",0.002) of the instance.Is it meaning length unit?Or output number of fanout?Why is it different with different with length of wire?


texts: 36x LED 5730 in series: diodes burnt when LED driver (based on BP9833A or MT7854BD) powered up

texts:
Background:

I have 18W, 36 LED lamp fixture which I cannot change.
Originally it has 2x parallel 18off 5730 LEDs and 300mA driver. It works for some time, but diodes starts burning. I thought that the problem is 300mA when one of the LED strings gets faulty - remaining parallel string cannot handle 300mA and it ends up with both branches destroyed. Below table describes 5730 LED which I bought to replace burnt diodes:

Solution which turns into problem:

I manage to re-wire all 36 LEDs in series (=3.3Vx36=118,8V, 120mA) & renew faulty diodes.
I bought driver based on BP9833A and assembly everything altogether. Please see below picture of my BP9833A driver:
After re-installation of fixture two LEDs get burnt during power-on. I repeat previous steps and got another few LEDs burnt (not only those which I renew). Finally I install 3x in series 390 varistor parallel to the LEDs. It allows me to start-up the driver without harm to the diodes. With UT203 multimeter I have: 115-120mA, 117Vdc. Driver idle voltage is ca. 180Vdc. When loaded it is switching off around 120Vdc. Nearly perfect except this idle voltage which I suppose should be not the case as I have the load connected.

ROVP has 10kOhm, resistor on pin CS seems to be fine as driver stabilises around 120mA.
I thought my bad experience is a flaw of BP9833A. I bought driver based on MT7854BD with lower maximum voltage. Please see below picture:

I reduce string to 24 LEDs (=3.3Vx24=79,2V, 120mA) as it cannot handle more than that - it simply stays in safe mode. Current stays around 120mA, loaded voltage 75Vdc. Surprisingly same fault happens without varistors. Few LEDs are damaged again during power-up phase. It seems to be worse when single pole wall switch is in use. They survive few starts when switched by Schuko type plug with round pins on my bench.

Question:

Why do I burn 150mA diodes with 120mA driver during power-up phase?
What can I do to limit excessive initial voltage/current in both BUCK converter designs during start?


texts: Wall following Robot without MicroController

texts: I am trying to develop a Wall Following robot without using a micro controller. Is there any way I can maintain a fixed distance from the wall using Ultrasonic Sensor HC-SR04 without using Arduino.


texts: How to design and build intelligent controller for a power pack made of recycled lead-acid batteries?

texts:
I am quite ignorant in electronics, but I am now building a small off-the-grid installation to be freely cloned (CC-BY) in rural areas of Eastern Poland (and perhaps Ukraine). The vital part of it is the battery bank, which will be built from recycled car batteries etc. So we need some intelligent charger/regenerator/desulphator/monitor/controller to take care of them.

What I am looking is pointing to some low-cost DIY solutions and perhaps some support in prototyping.

The concept is to set up a matrix of batteries (mostly recycled, in various levels of wear) and provide them highly controlled environment - separate chargers, monitoring, on-the-fly desulphation, separate discharge controllers etc. etc. People who will use this design cannot afford buying new batteries, lest replacing whole parallel banks once one unit breaks down. So we shall be dealing with a variety of batteries and the challenge is to make them work efficiently, long term and happily. :-)


texts:
I know this might sound a little bit easy for some of you but i do really need a clarification on this.

I have a question about the operation modes of the Bi-Polar Junction Transistor.

In the graph below (bjt characteristics) we all do agree that there are four regions for a transistor to operate :

Forward Active
Saturation
Cut-off
Reverse Active

Most of the refrences I have looked into said that in order for a transistor to operate in the "Reverse Active" The biasing voltage on the Base-Emitter-Junction must be in Reverse, which makes sense to my understanding of the BJT.

Unfortunately, my Professor at the University has another approach and he said that if the Voltage of the Collector-Emitter-Junction is negative (Reverse) the transitor is Reverse in general, therefore we must swap the Collector with the emitter and then we keep solving currents in order to know if the Transistor is in (Rev SAT/ or /Reverse Act)

Can anyone explain that to me?

Also is there is any method to detect when a BJT is operating in the Reverse Active mode?

Any help will be appreciated

Thanks in advance


texts: LM317 power regulator ajust is affected by MAX485 chip

texts:
Ok, I'm completely puzzled by what is happening to my LM317 power regulator adjust pin voltage. Here is the schematic of the power supply section of my PCB that distribute the 3.3v (VDD) to the microcontroller while other components use the 5.0v (VCC) directly from the connector (J14 and J13 are test pins on the PCB).

So far so good. I get 3.3v distributed to my microcontroller no problem and 5v to my leds and LCD.

Trouble arise when I connect a MAX 485 chip to VDD or VCC:

When connected to VDD point, the LM317 outputs about 1.6v and gets super hot.
When connected to VCC point, the LM317 outputs about 3.8v not getting hot but not either returning the proper 3.3v.

Here is the part of the schematic that handles the MAX485 chip:

The 10k pull up resistor aren't soldered so I crossed them out. As soon as the pins 5-6-7-8 are soldered in place, the LM317 gets out of wack according to my previous stated observation. Please note that the DMX in and out plug aren't connected at this point.

What I think I understand is that the MAX chip circuit introduces new resistance path on the adjust pin of the LM317 through VCC and GND but I that's just a gut feeling. Anyone has any idea on why this MAX chip seems to affect my power supply section?


texts: Phase shift of the signal with grid frequency

texts:
I have to deal with a signal with grid frequency. And I have two channels, one channel should shift 90 with the other. Now, I have two ideas:

Use an AC integrator (actually it can only approximate 90 degree infinitely).
Use a one-order all-pass filter.

As known, the grid frequency may have some fluctuation, so which one is more insensitive to that? And are there any better solutions?


texts: EEPROM Values Corruption - Only Some times

texts:
I am using 25LC640A EEPROM with a 32 bit Micro controller. This EEPROM can store 8kb of data, with SPI serial Communication.

In my case during every power down sequence MCU will write some block of data into EEPROM and then it will shut down. And also its working fine. I have tested as many time as possible. No issues with EEPROM Data

Issue :
But, Some times the EEPROM values got corrupted. My code throwing checksum error after turn on the MCU. i have checked code thoroughly, i am not able to find the bug since its working fine for so long time.

So any one here please suggest me what is the cause of this corruption of data. I have attached schematics also.


texts: How to get equivalent behaviour of NOR and Nand gates, by making changes on the input side, when their inputs are attached

texts: I have two input NAND and NOR gates, I have attached their inputs and they both give the same result as the NOT gate, that is the inverter. Now i want to make further changes at the input side, so that their result is equivalent. I have tried alot making changes in the input side, adding gates and inverters, but I am not getting the same output. Can anyone suggest something?


texts:
I have a  question about potential current wastage.

I am looking at connecting the output of a low power 2 input XOR chip to a GPIO on a microcontroller. The input to the XOR chip will be connected to a switch delivering 3.3V from a button battery. The circuit below will produce the pulse.

So, my question which is perhaps a silly question, is this. In the following diagram

I will be applying either 0V or 3.3 V to the input line through a switch. Once the XOR gate sends the pulse to the microcontroller,  will the XOR chip then dissipate the 3.3V to ground, as the switch is closed, through an internal set of resistors, or not?

i.e. when the switch is closed and 3.3V is applied, after the pulse is sent by the XOR gate, is there an appreciable ongoing current?

The reason I ask is that I have a 220mAh battery and the switch could be closed for quite some time. I need a solution that pulses the uC through the output of the XOR gate, but does not continue to appreciably drain the battery once the pulse is sent.

Any suggestions on the best low power 2 input XOR chip to consider, if this is a solution that will work, is gratefully received.

Thanks

SteadyD


texts: How to trigger reset at long press of button

texts:
I am trying to make a button control on/off and reset all in one, but I can't quite get my head around how to design it.

It should basically function like a PC power button. If short press it's either on or off, depending on state, and a long press is the reset that works when something completely locks up the computer. The on/off is easy as that's software controlled, but the reset has to be in hardware somehow as it has to ALWAYS work, no matter the state of the software or MCU.

The reset functionality should kick in after a long press of about 5~10 s. Once the reset signal goes low it should stay low for >10ms. How to do this?

I can find dedicated IC's that can set a signal low for x ms, which would work, but how do I trigger them in a good way? RC and then a comperator to trigger at a set voltage or...? And how do I avoid triggering the reset when starting up if using the RC approach?

Any help would be appriciated.


texts: Raspberry PI Zero - 5VDC output current?

texts:
I was planing on using a Raspberry PI Zero W for å smart lamp project with WS2812b LEDs, to avoid separate power supply for the LEDs, my plan was to power the LEDs from +5VDC on the RPI ZW. The lamp is going to have 18 WS2812b leds, so total power consumption is going to be 1080mA(*) at full brightness.

I have read that the RPI has a fuse at 750mA @ +5VDC, so the question is, can I power opp 540mA @ +5VDC with LEDs from the RPI? I do not need USB ports or anything else than 1 I/O-port to data for WS2812b and WiFi connection.

(*) Corrected my math mistake from 540mA to 1080mA

UPDATE:

I have decided to only use 16 WS2812b LEDs and by software set it to half brightness (128,128,128) so the maximum current only is 480mA.


texts: Understanding the slayer exciter circuit base voltage

texts:
I am quite new to electronics and I have a bit of trouble understanding part of the slayer exciter circuit.

If we take this schematic from electroboom here:

I don't understand how the secondary would send a negative voltage to Q1. From the flow of current through the primary, it would seem to me like it would actually send positive current; I don't see at what point Q1 is interrupted.

How does the secondary create a negative voltage?


texts: Why are the dead-time in IRF boot-strap gate driver ICs relatively long?

texts:
Why are the dead-time in IRF gate-driver ICs like IR2109 relatively long?1 I can be interpreting the data-sheet wrong too.

The IR2109 has a dead-time of 540ns. For IGBTs that dead-time are not relatively long. But if you take into consideration the driving currents of this IC (+120mA/-250mA) this seems more acceptable for MOSFETs, in my case a IRF740 that has specified switching times of less than 100ns.

So, what I'm getting wrong?

1 Yes, you can generate the dead-time in the controller and use dual input like IR2110 (that has so much driving current compared to the IR2109), but I want reduced space (8PDIP), and I have only one signal per half-bridge leg, so I want drivers that can generate the dead-time and other switch signal.


texts: How does a ps2 mouse send data to a computer?

texts:
I want to read data from a mouse with the help of Arduino.
I want to calculate relative motion between two objects.
My questions are

1) Is it possible?

2) How is mouse interfaced with Arduino?


texts: AD8131 Single Ended to Differential Problem

texts:
I am attempting to convert a single ended signal (0-5V) to a differential signal (+/- 5V about 0V) using an AD8131ARZ. I have it wired as per the attached schematic. When I supply +5V to the positive input DIN+ of the AD8131, the output behaves correctly with +/- 5V. However, if I ground the DIN+ input the outputs hold at or near 0V instead of inverting. So, it halfway works.

Experimenting, if I disconnect DIN- from ground and apply a voltage slightly more positive than zero to it while grounding DIN+ I begin to get the desired effect of the signals inverting. However, the amplitude is not correct. The amplitude appears to be the difference only (gain of 1).

How can I achieve my stated goal with this IC?

.


texts: Can I use a resistor in place of a transformer?

texts: Why is a step-down transformer used instead of a resistor for reducing high voltage?  For example: If input voltage is 230V and I have step down the voltage, can I use a resistor instead of transformer? If I cant, can any one explain the drawbacks?


texts: What are some examples of MSI (Medium-Scale Integration) circuits that are used for doing arithmetic?

texts: Just looking for some examples of MSI circuits used for doing arithmetic.  I understand MSI circuits have more than 10 but less than 100 gates, or less than 500 components.


texts:
I'm considering using a IR3315 as a replacement for a PTC fuse. I dont need current sensing nor logic control of it. I just want it to shut down if a given current is reached, and need it to come back if I unplug power and plug back in.

I read the datasheet and this app note but it wasn't clear to me if I can just ground the IN pin to achieve this goal.


texts:
I just started studying about batteries and battery chargers. I have this simple query so please help me out.

I am trying to charge my 3000mah li-ion battery. The battery voltage is around 3.6v and the charger regulates the 5v from the source to 4.2v. I connect the battery to the charger. Now what is the voltage at the output should I expect?
Shouldn't the output voltage be at 4.2v so that the battery gradually charges to 4.2v ? I ask this because I am using Bq2057 IC and once I connect to the battery to the charger the output voltage is dropping to 3.63v.

My assumptions were,
1. I considered the charger as voltage source
2. Battery also as a voltage source

I experimented this buy connecting two DC voltage sources(5 and 3.3v) in parallel and measured the voltage at the node and it was 5v. So I was expecting the charger output to be 4.2v even when I connected my battery to it.

Thanks


texts: Why is the output of a high-pass filter not 0 when the input is 0?

texts:
I'm trying to design a 5th order Butterworth high-pass filter built on the Sallen-key topology with a cut-off frequency at 100Hz. For some reason, the output has a DC offset of around 5mV when the frequency of the input is less than the cut-off frequency even when the input is grounded.
I am using the Op-Amp LT1498 on LTspice and all the capacitor values through all three stages (first order, second order, second order) are 100nF. I'm guessing that its from the output of the op-amp but I'm not really sure.
Link to LT1498 Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/14989fg.pdf
The output is as follows from a 10Hz input:

Any help would be appreciated!


texts: mosfet as a switch on arduino pin and xbee explorer board 5v

texts:
I have looked at various examples of MOSFET switches but I am not knowledgeable enough to adapt what I see to what I would like....
I want to have a pin on my 5 volt Arduino Micro board turn on or off power to the Sparkfun Xbee Explorer Regulated Board.
I don't think I can connect it directly to the Arduino pins because with the Xbee hooked-up and transmitting I think I will exceed the allowed current (20mA) on the Arduino pins. All I read about MOSFETs is using low voltage to control 12v or more... is it possible to use it to just turn the explorer board on or off as required ??  I would have a button press wake up my arduino board and then code to take the controlling pin to high (or low) as required to turn on the explorer board via MOSFET.

Thanks


texts: Are there any true direct-current motors?

texts:
The "DC motors" that I'm aware of use a DC power source, but they have a current running through a coil that changes direction based on the angle of the motor.  Therefore, they current inside actually alternates as the motor rotates by switching the current (electromechanically with a brushed motor, or electronically with a brushless motor).

But are there any motors which are trully direct-current?  By this I mean that the internal currents never change direction.


texts:
I have two microwave signals (0.2 and 2.3 GHz) and I have to join these signals in a common channel (microstrip TXline).
I've decided to use two BP filters and a power combiner hybrid.
I've already designed the filters, but I don't know which power combiners' (like Wilkinson, Rat-race hybrid, etc.) bandwidth is big enough for them.
Which type of structure would be ideal?


texts:
I am participating in a robotics competition that requires colour detection  using discrete components.

The aim is to detect red and green lights of traffic signals.

I have tried making a sensor using photo transistors, but unfortunately they don't work very well, they are heavily dependant on the brightness and distance from the light source. And slightest of misalignment throws off the entire calibration.

Is there a better way of making a colour sensor, cost is not the issue? How can I make photo transistors work better?

EDIT: More Detail. The robot needs to navigate it's way through the arena following the traffic rules, throw a ball to knock down bowling pins and navigate back through another route. Off the shelf colour sensors are not allowed, ICs are allowed.

Major Edit: I contacted the organizers, apparently this is not just my problem, everybody is having issues sensing color using photosensor, off the shelf color sensors are allowed.


texts:
I'm wanting to control a 6V Solenoid valve from an Arduino using only a single power supply. To do this I was planning to use an external 9V power supply.

There are a few issues I am not quite sure how to resolve

1) Providing power to both components via a single power supply. Whilst the Arduino can accept up to 11V input it is not able to power "high" voltage external components. What would be the recommended route for this scenario? I have taken a look at the Motor Shield v2 however it does not appear suitable for this scenario.

2) Confirmation of Solenoid power requirements, the specification for the Solenoid valve only mentions a voltage and power consumption.

Solenoid Specifications:

Voltage: 6VDC (continuous), 6-12VDC subject to duty cycle
Power Consumption: 1.6 Watts - at 6VDC

Using the above specification I've calculated that a current of 267mA should be supplied to the Solenoid, using a 23 Ohm resistor (or whichever is nearest commercially available) would give the desired outputs.

3) Apart from a MOSFET used to control the on/off signal to the solenoid and a flyback Diode to reduce the change of voltage spikes reaching the Arduino. Are there any other components I would be missing?

Thanks,


texts: Mechanical or Solid State Switch for 48V DC and 2 Amps current

texts: I've been looking for a SPDT switch that can support 48VDC and 2 Amps current but so far I haven't had any luck.  It can be mechanical or solid state it doesn't matter. Is there such a thing?


texts: Identify this component? Temperature-related?

texts:
Can anyone tell me what this is?

I have nothing else, sorry - just the part. No markings or labels on it.

Came out of a Brother laser printer- I was clever enough to salvage neat-looking parts from it, but not clever enough to document where each was taken from...

There was a heating element inside one of the rollers. Near that roller were:

1) a thermostat (CH-152-35),

2) this thing,

3) a G16C Thermistor in an amber sheet housing with a black base similar to the one on the posted item.

Exact locations unknown, I didn't document it. But all near the heated roller.

Black marks are toner residue not burn marks. Wiped them off the outside of the amber plastic.

A better look at the side not shown well in the last pic.

The thermostat. I love part numbers, makes newbie research easier.

The thermistor. Again, I love it when they print useful part numbers on stuff that you can Google!


texts: How to determine the center frequency of a photodiode?

texts:
I'm using IR LEDs to blast away at a bunch of photodiodes, which I then latch into a shift-register and read into a PIC.

While reading/browsing about the topic I found an article that stated that the best way to ensure the conduction in the photodiodes would be to blast them with the LED radiation generated by a PWM signal at the center frequency of the modulated light sensor.

What I take from this is already what I intended to do, but the frequency aspects got me thinking.

Given that the PDs I'm using have an untraceable datasheet (I know that the reference is SWPD3330-16, from Sunwell), does anyone have any info that might help me figure out how to calculate the best frequency? As an alternative, is there any rule of thumb for this kind of problem? What would be a good starting point/estimate for the PWM frequency?

EDIT: After reading the comments, I would like to add the following:

I am using a photodiode. It looks like a LED and has two leads. The only thing I know about it is the aforementioned part number: SWPD3330-16.
The article does not specifically relate to my question, but on page 5 (2169), in the paragraph starting with "Step 2", you'll find what I quoted. LINK

EDIT2:

I found in a folder here at work the datasheet (in chinese) for this photodiode. It only covers mechanical aspects and (unfortunately) a few electrical specs (in parenthesis are the test conditions):

forward current: 100mA
pulse forward current (@1KHz, DC 10%): 1A
reverse voltage: 30V
power consumption: 150 mW
(some stuff about temperature)
light current (VR=5V, H=5mW/cm2): 64uA
dark current (VR=10V, H=0mW/cm2): 30nA
open voltage (H=5mW/cm2): 350mV
short current (same): 65uA
total capacity (5V; 5mW/cm2): 20pF
rise time (VR=10V; RL=1Kohm): 10ns
fall time (VR=10V; RL=1Kohm): 10ns
peak sensistivity wavelength: 940nm
sensitivity wavelength: 750~1100nm
radiation angle: 20 deg

With the hightlighted spec, is it possible to calculate/infer a educated guess for the PWM frequency I should use?


texts: How can I make an object with curved surface touch sensitive with Arduino?

texts:
Is there a way to make a "ball" (or an object with curved surface) touch sensitive? I want the ball to do something when someone touches it with their hand.

So, currently I got an object out of plastic, i.e. the surface is smooth. The object is hollow. Inside of that object there is an arduino uno with LED and a speaker.

Whenever someone touches it and as long as a person touches, I want the arduino to make a sound or blink with the LED. That object should be also freely moveable, i.e. not tied to something. Its also very light; like a small ball that can fit into your hand.

I want the whole object to be touch sensitive. I want the ball to register whether someone is currently touching the ball or not (I.e. it should also recognize when a person is not touching the ball anymore). Is there a way to accomplish it without buying multiple expensive touch sensors?

At first I was wrapping aluminium foil around the object and put voltage on it so it becomes a capacitor. The downside is that it is not reliable, i.e. sometimes it recognizes the touch sometimes it doesnt. I suspect the aluminium foil area is too big to recognize the touch reliably.

The solution doesn't have to involve with arduino uno. I could use any arduino as long as it does the job of creating a touch sensitive (curved) surface.

The reason why I want the curved is because I want people to be able to comfortable hold it in their hands. A curved surface is suitable the best for this, I think


texts: What causes the electromagnetic waves to prefer one dielectric over another?

texts:
it's known, and there are some devices that exploit this phenomenon (see the references if you want), that if an electromagnetic source (antenna) is placed between two different dielectric layers, the waves will prefer one over the other according to the  frequency.
Here you see an example from one my simulation.
Half-wavelength dipole antenna: it radiates equally in all directions of ϑ = 90° plane.

Now I put two different dielectrics (yellow = eps 20, blue = eps 2). Note that the permittivity is assumed to be constant on frequency (non-dispersive medium).

Conclusion: at such a frequency (3GHz, in which the dipole resonates), the waves prefer going towards the low permittivity medium (greater amplitude).
At other frequency the situation changes and the role of the two dielectrics may be reversed.
What I'm looking for is not a math explanation of that, but just an intuitive and physical view. If the antenna were a voltage source and the two materials were two parallel impedances, I'd say that electrons (current) will be higher in the easiest path (lowest impedance). But in this case there are not charge flowing, but just a wave. What causes physically a wave to prefer a material? Why should its electric and magnetic field be higher in one of them and why does it depend on frequency?
The electric permittivity is assumed to be constant on frequency, and the magnetic permeability is assumed to be 1. So, we can't say that the frequency - dependence is due to the material electric/magnetic polarization variation as frequency changes.
Example at 2GHz Now the waves prefer the yellow dielectric.

References: here (page 5) and here (page 3), two antennas are showed and they have both a substrate (like ordinary planar antennas) and a superstrate. The last one is used to send more power on the upper direction instead of to the lower one (where there is the substrate).


texts: Trouble with PCB design for USB3 connections

texts:
I'm struggling with making a USB3 connection work.  The PCB needs two USB3-A female receptacle, to play sort of a "man-in-the-middle" role.

I cannot provide much detail, since it is part of an ongoing research project --- however, I boiled down the issue to a minimal PCB that we actually manufactured (as a debugging test).  Here's the layout, designed with gEDA PCB:

The thin traces are 12mil wide, the thick VBUS and GND traces are 35mil wide. The through-hole connections for the receptacles' pins have a hole diameter of 28mil (minus the plating thickness), and a pad diameter of 43mil.

The idea is that I connect from the PC to this board with a male-male extension cable, and then connect the device from the other receptacle on this board (using the same cable I would use to connect the device directly from the PC).  The receptacle I used is the Amphenol 10117835-002LF.

The board was manufactured with "High Frequency" material, at 1mm thickness (the "Advanced PCB" option at Seeed Studio).  However, one detail is that I did not manufacture with impedance control  (nor did I do any calculations of trace impedances --- on the one hand, I didn't think it would be necessary --- at this point in time I'm not sure whether it is;  and on the other hand, the receptacle specifications do not include characteristic impedance).

The trouble I'm having is:  it works intermittently; or maybe I should say unreliably.  I'm testing with a USB3 logic analyzer we have, and that one seems to work well (I set up capture at the highest rate the device supports, and it does capture, without reporting any errors).  However, I try with a USB3 camera, and that one works some times, it report errors some times, the camera freezes once in a while, etc.

Any ideas on what I did wrong (specifically, things that could explain the unreliability), or suggestions to make it work more reliably?


texts: I accidentally pluged my multimeter in a 220 v 50hz power supply keeping the knob on the resistance section. Now when I rotate the knob to the resistance part it always shows 24 ohms although there is no resistance I'm mesuring. What to do now?


texts: How much does the Bias Voltage affect the NEP of a photodiode?

texts:
Look at this data sheet for example. Everything there is measured at 0V, including the NEP, if I connect that photodiode in reverse bias, how will that NEP change?.

I'm inclined to believe that it doesn't change, simply because whenever I read about it, no one mentions the voltage being relevant, for example in this Thorlabs Paper, or in the book Optoelectronic Sensors by Decoster and Harari. (Screenshot at the end).

Then again, the NEP is measured considering all sources of noise, right?, and Dark Current grows with voltage, so it seems that NEP would change with voltage as well.

If NEP does change with voltage, how can I calculate that change?.


texts: Is a resistor required between VCC and Data for my temperature sensor?

texts:
I'm using a TinyDuino with a Protoboard to measure temperature with a DS18B20. I was following this tutorial but am not getting any valuable information back on the arduino when I try to read the value on the data port.

I just started reading around and it looks like most people put a resistor between VCC and Data. I'm fairly new to electronics, so 1) I don't know why the tutorial doesn't mention this and 2) I'm not sure what putting a resistor between those two would do?

Any help or explanation appreciated.

Edit
Here's a schematic from a site which uses a resistor. The only difference is my board has VCC, one site said to connect VDD on the sensor to VCC, this one shows it connecting VDD to 5V. I'm not sure the difference


texts:
I'm making this right now - https://www.youtube.com/watch?v=qlMtakaa7u8

Each 5m roll of LED takes 60W power (http://www.ebay.com/itm/182028302443?rmvSB=true). He's using two of these rolls, so a total of 10m LED Strip.

My question is, that he's using a 19v 3.14A adapter which gives out a wattage of 60W. Isn't this lesser than what is required for the overall 10m (60w + 60w = 120w?). What's the effect of using this lower wattage on the LED output?

Instead, I thought of connecting the two rolls in parallel but the 19V adapter and connecting in parallel will probably burn the LEDs due to the fact that the LED strips are rated at 12v. Can I connect the two sets of 5m LEDs in parallel to a 12V 5A (which will result in 60W, the maximum wattage the LEDs can handle) DC Power supply? I'm assuming that then both the 5m strips are running at full brightness then. Or am I wrong and since a total of 120W is required, should I go for a 12v 10A DC SMPS Power supply? I studies Physics a long time ago in school and I'm pretty clueless here. What I'm looking for basically is the best way to extract the maximum light out of the LEDs. Thanks a lot guys!


texts: My NMOS inverter is showing negative spikes in the LTspice simulation

texts:
The red line is the input and the green line is the NMOS Output.

I am doing a 10ms transient analysis at the output, but if the capacitance is 0 then I am getting a negative spike when the input is on falling edge. Why is this?


texts:
I am working on the prototype of a circuit that does some data acquisition and preprocessing on an FPGA (Mojo Board). After preprocessing I quickly need to get the data to the PC. For that I want use an FT2232H mini module in the synchronous FIFO mode. The Mojo board and the FT2232H board are currently connected together using short wires of a ribbon cable of about 2 - 3 cm length. My problem is, that once the FT2232H is put into FIFO mode it generates a lot of noise in the ground. This noise is exactly at the 60 Mhz frequency of the CLKOUT signal of the FT2232.

Between different points of the ground plane of the FT2232H board I measure oscillations at t up to 500 mV peak to peak and between the Mojo board ground and the FT2232H board I see in excess of 1 V. The weird thing is that I also see this 1V or larger oscillation across the short grounding wire (3 cm) that connects the FT2232H board to the FPGA board.

The oscillations are also found on all the control signals ( TXE, RXF, RD, WR) and lead errors in the connection leading to a large percentage (>20%) of bytes being lost. How can I reduce the ground noise to acceptable levels?

So fare I have tried:

adding a capacitor (100 nF ceramic multilayer) in the FT2232H board between 3V3 volt and GND: no change
directly soldering the grounding wire to the board on both ends:
setting different levels of termination on the FPGA side using in_term = unbalanced_split_75, unbalanced_split_50, unbalanced_split_25 as well as pulldown in the ucf file for the FPGA. This seems to improve the amount of lost bytes significantly but does not change the height of the oscillations on my ground plane.
adjusting the output power of the FT2232H using the FTDI software: lowest power seems to be best for getting bytes through.

In the end I still loose >10% of my bytes and still have > 1Vpp noise in my ground plane. What am I overlooking?

edit: The problem does not happen when the system is just connected to the PC via USB but only when the synchronous FIFO mode is started. All measurements I did were taken with an oscilloscope probe with a short (~5 cm) grounding clamp and a decent scope at either AC1MOhm or DC1MOhm coupling.

I found two sources on the web that also deal with similar problems with the same chip but their solutions do not seem to work for me. I can't post the links because of too little reputation.


texts: Some questions about a series pass transistor & op amp voltage regulator

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I have the following voltage regulator using a series pass transistor and an op amp providing the base voltage:

I have three questions:

How do you calculate the output voltage for such a regulator? I can see that it is equal to 9V but I'm wondering how you can work this out without simulating the circuit. I'm particularly interested in knowing how the op amp's negative and output terminal voltages can be calculated.
What role does the op amp play in regulating the output voltage?
What are the advantages and disadvantages of this configuration verses a single zener diode providing the base voltage?


texts:
So I was looking at the schematic of NPN and PNP transistors which basically involved layered blocks of doped material stacked.

My question is how do wires connect to these devices? I think this image is misleading as the actual width of the n segment would be on the order of 50-60ish nm as per:

https://en.wikipedia.org/wiki/65_nanometer

And it seems a molecular level of accuracy would be required to line up a copper wire on both ends. How on earth is the copper bonded to the the actual structure, without damaging it? Surely heat can't be used, but if it is just placed on then it could easily fall apart if it isn't bound chemically to the junction.


texts: Protoboard limitations when dealing with high impedance circuits?

texts:
I understand protoboards have several limitations for prototyping circuits. However, most information found deals with parasitic capacitance such as to cause problems with higher frequency circuits.

My question is what are the limitations of breadboards in regards to high impedance circuits? I'm attempting to measure the voltage drop across a basic voltage divider circuit. Vout is across a fixed 10 Mohm resistor while the other resistance is a variable resistor of a sensor (500 kohm to ~1 Gohm).


texts: Calculator Algorithmic Error (Bowmar MX140 [1974])

texts:
My senior colleague recently retired and left behind a Bowmar MX140 calculator that I've managed to repair

After playing around with it I've noticed it has some error with certain functions.
As an example, \$9*9=81\$. Where as \$9^{2}=80.9999\dot{9}\$
Numbers 10 to 19 squared display as full integers, but \$20^{2}=399.9999\dot{9}\$
It does explain there is a degree of error in the manual found here in pages 30-31.
My question is: Where does this error come from?
I would assume firmware, but are there other ways to calculate the \$Y^{X}\$ besides \$Y*Y*Y\$ etc.?
As an extra question, why does this error only happen with certain numbers? e.g 9 & 20


texts: What could be causing this GFCI trip upon fan turn off?

texts:
I have a 2-pronged fan plugged into a GFCI in my basement. Twice now, as I was turning it off (out of maybe 30 times I have turned the fan off), the GFCI tripped.

Now, I understand that GFCIs trip when they detect a current imbalance, however, I'm at a loss to figure out what could have caused that current imbalance. Here are the relevant facts:

The fan has a plastic case and buttons (except for the metal fan cage). I was not touching any metal part of the fan when turning it off.
The fan sits on a wooden pallet and has rubber feet.
The fan's cord is in good condition (it was running very close to some metal components, including the fan cage, but there are no cracks). In any case, why would a cord fault cause a GFCI trip only when the fan turns off?
The GFCI is working properly (I have a drill press plugged into the same GFCI, no problems).

Where could the current imbalance be coming from?

As requested, pictures:


texts:
I'm trying to build a state variable filter, to this circuit diagram:

All resistors are \$1k\Omega\$ and both capacitors \$1\mu F\$.

I've constructed it on a breadboard:

But the output I get, ignoring some distortion when the input is loud, is the same as the input, no filtering is done at all. I have tried powering the opamps with both a 9v battery and a +12v/-12v power supply, and still, the output is the same as the input. (I have of course done the calculations on the circuit and the output should definitely not be the same as the input). The opamps seem to be working (they're getting power and the + and - inputs are at the same voltage).

How can I diagnose this? I do not know where to start.


texts:
I would like any possible explanations/diagrams of how the waveform voltage rises at the point where the missing tooth/teeth of the reluctor wheel approach and pass the Inductive Sensor.
This is just to take the intrigue out of the Waveforms and the barebones explanation of Picoscope.
https://www.picoauto.com/library/automotive-guided-tests/crankshaft-inductive-floating-cranking/
In particular I am foxed by the last sentence of the 5th paragraph of the Further Guidance section in the above link.
"The missing tooth on the pulse wheel provides the main timing reference mark. As the gap passes through the magnetic field, there is a period of reduced disturbance and voltage. Furthermore, the trailing and leading edge of the teeth that immediately precede and follow the gap are further apart, thus they produce a larger net magnetic field disturbance and induced voltage."

Thank You for any enlightenment !


texts: Voltage increase by connecting Voltmeter

texts:
I've got this scheme. V1 and V2 are voltmeters without their own power supply. (V1 gets power from the measured circuit, V2 is powered separately, but in this case from the same power supply.)

The power supply is two batteries connected in series.

V1 alone (V2 disconnected) shows 7.7 V.
V2 alone (V1 disconnected) shows 6.9 V.
V1 and V2 (both connected) show V1=5.8V, V2=7.4V

What made me to ask this question is:

V2 alone shows 6.9 V. When V1 gets connected the V2 shows 7.4 V (voltage increases).

Baterries should be almost full, checked with another (independent) Voltmeter, with its own power supply, Both show ~4.6V.

Both Voltmeters had been ordered long time ago on ebay - no data sheets, no information. Picture of the back side of one of them:

The main point of the question:
How can voltage increase in the same measured spot, if you connect one more load (voltmeter)?


texts: Two different length antennas can cause problems?

texts: I am using two 443 MHz transceivers (FY-605 transceiver) with both having different antenna lengths. One antenna is around 12cm long and the other antenna is around 17cm long. Will this cause problems? And does it affect the range or doesn't it work at all? Also the ±12cm antenna is connected to the transceiver with a coax cable. As far as I know this doesn't cause harm. Can anyone confirm this for me?


texts: High-speed Infrared UART link with photodiode

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I need short-distance (about few centimeters) wireless IR UART link with 250k+ baud. I tried to use phototransistor (assume Q1 is phototransistor). Q3 is used to prevent inverting signal.

simulate this circuit – Schematic created using CircuitLab

With this schematic I reach 57600 baud with Arduino. Now I am looking for photodiode schematic and I hope that it can be faster.

I found out tipical application with transimpedance amplifier. Something like this:

simulate this circuit

Is this suitable for my application? What about environment light adjustment? Also, can I use this circuit with unipolar supply?

Maybe comparator will be more suitable for my application, because I need only binary signal and don't care about amplifier linearity etc, but I have no idea how to use comparator instead of op-amp in this chematics.

UPD #1:

I replace R1 with 100 Ohm and reach 115200 kbit/s
I know about IrDA, but environment light isn't a really big problem in my case. I can protect optocoupler from environment light.


texts:
I have started a design for work where I want to interface some sensors, (strain gauge, bridge, thermocouple, low voltage stuff) to a national instruments sbRIO card. This card has analog inputs built in as well as DIO. The sbRIO can measure down to +- 1v and 16 bits, but in my experience thats not quite good enough for thermocouples and strain gauges where you're looking at <100 mV. We were going to already be making a "mezzanine" card with some other interface circuitry so I was going to add on some circuitry that could handle these lower voltages.

A while ago I had found a 32 bit ADC with SPI interface and I've been looking for an excuse to play with one and thought this might be a good fit. (https://www.protocentral.com/analog-adc-boards/1005-protocentral-ads1262-32-bit-precision-adc-breakout-board-0642078949630.html). It has a built in gain amplifier, and a few other bells and whistles.

My question is for any hardware designers out there is this. Would I be better suited to using amplifiers for each individual channel rather than using this unit of an ADC? ie using thermocouple amplifiers and bridge amplifiers where appropriate? I appreciate any insight you might be able to give me. Thanks for your time!


texts: EEPROM only retaining a value for a short duration

texts:
Background
I have a product that includes an SPI EEPROM connected to a Microcontroller.
Address 0 if the EEPROM contains what we call the status word. In production the value of the status word is set to 0x2152 which indicates that the EEPROM is "alive" and the rest of the data stored in the EEPROM is sane.
If a erase/write/read/verify failure occurs we mark the status word as 0xDEAD. We also mark the status word as 0xDEAD if we detect corrupt data at boot. Note, 0xDEAD == ~0x2152
The Problem
I've noticed on small population of our units when I write a value of 0x2152 to the EEPROM's status word and read it back immediately it is still 0x2152, but if I then perform a read several seconds later the value seems to "decay" to 0x2142 or 0x2102. On a particular unit I read the value back five minutes later and it was 0x0000. All of the other locations in the EEPROM can be written to and appear to retain the proper values for long periods of time.
We do not think we write/erase to that EEPROM location frequently, nominally just once ever. We have identified a situation though where we could perform a lot of writes/erases to that location in production if some steps are not performed correctly. The endurance is a million writes and we could be hitting that.
We perform frequent reads from this location over the life of the product, we generally read every give minutes.
The Question
Previously in my career I've always seen write endurance failures look like sticking bits that seem to never take on a new value. Could this "decay" phenomenon that I am seeing also be a explained by excessive writes? Or is there another way EEPROM could become damaged that could explain this failure mode?
EDIT:
Answers to questions in the comments, and some tangential things:

I am deliberately not including the part number or data sheet because we have an open case with the vendor and I do not want to disclose too much if we end up uncovering a quality issue.
The SPI clock speed is 1MHz.
Writes are self timed by the part. We confirm the part is done with its write before attempting any other operations or powering it down (the part signals it is done on is MISO line)
We're using a hardware SPI peripheral with software control of CS.
This is a bare metal system.
We have adequate delays on power up before attempting to communicate with the part.
We always enable writes before writing.
Interrupts are not factor, we do a blocking write in the main thread.
The minimum erase/write block is one 16 bit word, this part is word addressable.
This part has a erase/write endurance or 1M cycles per word.
The power supply to the system is very stable, the system is powered by a lithium thionyl chloride battery that has tab welded leads. It is connected to the PCB with a robust connector that is potted over so vibration/contact bounce isn't possible. The system is "always on", the microcontroller is in control of when it goes to sleep.
The voltage at the VCC pin of the EEPROM is stable and within spec throughout the duration of a write. This was measured with an o'scope.


texts:
Not too long ago I acquired an old ('70/'80) German flip clock. I found out that this clock is driven by a one-phase synchronous engine.

I can't get the motor to run. I (carefully!) connected the motor to the mains (220V 50Hz). The results was a chaotic buzzing and the motor oscillating.
The motor look like this:

I have no idea what 'Type 5' or 'BT 1200' signifies (I googled it extensively). The coil has 4 wires running from it. Counting from top to bottom, or from green to yellow, the resistance between:

1 and 4 (green and yellow) is 460 Ohm
2 and 3 are shorted (0 Ohm), not in the coil but the blue and black wire
1 and 3, 2 and 4 is 230 Ohm

With the coil removed the axis becomes visible:

One turn of the axle moves the clock forward 1 minute (I am able to turn it by hand). This is also weird. What I understood of synchronous motors is that they rotate at the same frequency as the mains it is connected to, in this case 50Hz. In other words 50 times to fast.

I can easily remove the axle as well:

Behind it is the gearbox. The motor is obviously not a Shaded-pole motor.

So how does it start? Perhaps it needs a different voltage (the clock was recovered from an industrial complex)? 120V, 480V? Is there a (start) component removed? On the second image there are some protrusions visible on the left side of the axis with no obvious function.

And how to explain the difference between the expected rotational speed of the motor (50 rpm) and the required 1 rotation per minute for the clock?


texts: Why do I still get some voltage at the load when the regulator supposedly is turned off?

texts:
As I rolled my simpleified (removed the overload protection circuit) home-built PMOS LDO circuit on a breadboard, I found out something strange is going on.

simulate this circuit – Schematic created using CircuitLab

Now what is going on? Why am I seeing 0.01 V across my 1 kΩ load? Also, why is the sampling voltage divider emitting 0.04 V? Or is it because of the OPA2134 amplifier? Did I get a fake one from the Shenzhen supplier?

Am I treading the waters of leakage currents of semiconductors?


texts: Calculating Differential equation RLC Circuit

texts:
Hi,
I tried to find the voltage on the capacitor as a function of time, Vc(t).
In the initial condition (t<0) the switch was closed and the current source was open circuit, so I found the initial conditions for the capacitor and the inductor ( VC(0)=65v, and IL(0)=1A).
At t=0, the switch will open and the current source connect to circuit like the picture here.
I'd tried to write the differential equation of the circuit and got something weird:

I know that the equation of RLC circuit 2d must be positive, otherwise, I will get one of the roots positive which is impossible.
Please, I need your help, what is important to me is to proof the equation so I can show the lecturer that he was wrong, but I'm not sure if what I did was right.
Here is the solution of the lecturer:
(A1 and A2 easy to find)

the decition of current in the inductor is true:


texts: Why does customer see high voltage on my PNP sensor output?

texts:
I have designed a capacitive sensor with a PNP output. The output stage is a Sziklai pair, as follows:

simulate this circuit – Schematic created using CircuitLab
While the circuit works OK, one of my customers have measured the DC voltage on the output node (the multimeter works well) as 40V when the output is off, and 80V when the output is on. (He touches the output probe while doing so) I am fully assured that this is noise, and this will flow when the output is connected to a load, but it is hard to convince the customer which will connect this to a sensitive input. We didn't notice this effect during our tests in our noise free laboratory.
The customer has access to terminals VDD, GND and PNP_OUT.
My questions are:

What causes this effect?
Can this really cause damage to the connected devices?
What can I do to prevent this from happening, without breaking the reverse polarity protection on the output?


texts: What can the ohms of a DC motor tell me about itself?

texts:
I have a lot of motors and all type of size but mainly they are all small to mid size adult hand size or so , I took out my multimeter and switch to ohms settings and grabbed the ground and power wires of each motor to see what type of reading I would get, what  confused me is that, I found that most bigger ones had high ohms of 1.5 to 2.5 ohms while the smaller ones had higher ohms of 4.5 to 14 ohms.

Can someone break it down for me?


texts: I have a few of these relays and I was looking at the data sheet.  It states that the max inductive load is 7amp(3 on form C).  Does this mean when I am using an LED light or motor that the max load is actually 7 amps instead of 3? I just want to make sure I fully understand and am safely staying within the currents the relays are rated for.


texts:
I am trying to switch a small water pump (for a pet fountain) according to the output of a PIR sensor. A couple of years ago I setup a circuit on a breadboard and tested it with the pump - it worked! Unfortunately, I don't have schematics or photos of the circuit anymore.

The circuit is powered by the power adaptor of the water pump (12VAC output). Using the L7805CV it should regulate to 5VDC (for the PIR sensor). The PIR sensor activates a transistor which uses the same 5VDC to activate a relay. The relay should then switch the original 12VAC.

I am a bit confused why that worked back then. I tried a similar setup now and the L7805CV gets hot, but there is no power output.

Can I source the L7805CV with AC power? (without using a diode bridge)

If not, is it correct that I could use a diode bridge to convert the 12VAC to 12VDC and use that as an input for the L7805CV?

Update:

After reading your comments/answers, it came back to me that in the working circuit I had been using a 9V battery as an input for the L7805. Sorry
My current (wrong!) circuit is attached:


texts: Is it safer to use multiple RS-485 point to point connections compared to a daisy chain?

texts:
When wiring multiple RS485 slaves to a master equipped with a RS232/RS422/RS485 interface*: is it safer to wire multiple point to point connections from the hub with their own termination resistor, compared to using one socket on the hub and daisy chaining them all terminating with a single resistor? The spec seems to say daisy chaining is a "dumb" parallel hard-wire, and I wonder if one receiver couldn't freeze the bus or even damage it (meaning the interfaces) if a failure occurs.

*: the interface is a 8 or 16 ports industrial USB to RS232/RS422/RS485 converter, to be selected


texts:
I'm going to buy some IR sensors for gas detection measure. As soon as I need lights on specific waves length for measure specific gas, I have opted for a black body IR emitter, specifically this one

I've understood that this type of emitter uses a resistive element connected between two pins.

My questions is that I can't understand how to make it operate. As soon as there are three pins, I can't understand how to connect it to the power supply.

On the datasheet I've read that to

  ensure that anytime RH does not exceed the representative limit as
  shown in this diagram with respect to these conditions: a. f ≥ 5 Hz b.
  on-time (pulse duration) ≥ 8 ms

Does it mean I need to use a PWM modulation, with a microcontroller (Arduino) for example?


texts: One particularly irritating variety of bug in a microprocessor-controlled system is for the microprocessor to unexpectedly reset. An important tool for debugging this kind of problem is a list of possible causes. What could cause a microcontroller to unexpectedly reset?


texts: Bending insensitive connection or highly flexible/thin cable

texts:
I want to attach several accelerometer data loggers to different parts of the human body (i.e. my own, it's not gonna be a commercial product). The individual units save their data to sd card so they are mostly autonomous. Nevertheless I want to wire them, in order to centralize power supply (a commercial portable power bank mounted to my waistbelt) and probably to be able to synchronize them regularly if the individual clocks drift too much. So most probably 2 or 3, but never more than 4 wires.

Since the limbs move a lot (like when I am running) the cables will also be bent a lot. So if the cables have all but the most minute bending stiffness, they will exert additional forces to the accelerometers, which distort the measurements. I am also worried because if I end up doing the experiment very often, the wires will break in no time. Any finally I am worried about the cabling being very uncomfortable and cumbersome to use if the cables are stiff (for example attaching 2-3 stiff cables to one leg alone doesn't sound much fun).

So are there any common applications which require multi-wire cables with very small diameter (with very small I mean less than 2mm for a 3 or 4 wire cable) or high mechanical compliance, which I could abuse for my purpose? Is there another well-established way to make cable connections to electronic devices which have to be insensitive to frequent bending (probably sounds funny, but: wiper contacts or something?)

Side notes:

There are several reasons why I don't want to power the units individually:
1) LiPo batteries are small, but are an inherent safety risk when mounted to the human body (multiplied times the number of batteries times the measurement time); I don't want to perform as burning man...
2) the individual units should be as light as possible so that their own inertia doesn't spoil the measurements (I can't nail the units to the bones...)
3) with small sized LiPo batteries the operating time is rather limited.

The capacitance of the cables don't play a dominant role because (infrequent) synchronization in the range of milliseconds is totally sufficient. Also resistance of the wires is not so much important because the data loggers only consume very little current.

My design of the data loggers is already finished (and first prototype boards etched), so I would hesitate to change it. Nevertheless if any alternative suggestions with extraordinary advantages show up, I might change my mind as to changing the design.


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I did a simple 6 LEDs parallel circuit but I am a bit confused. I must remark that I am a total NOOB but I made some research on LEDs, Voltage and Resitor calculations before weld the circuit.

The circuit is already welded and works, but I would like to know if I did it well, or if it is an other or better solution.

Here are the mockups I did before welding, finaly, I decided to do the Option A.

Wich option would you consider to be the optimal?

Components I used:

4 batteries of 1.5 volts
6 Leds of 3.7v at 20mA
6 Resistors of 120 ohms

For the last example:

Resistor of 33 ohms

EXAMPLES


texts: Total changing flux in Faraday's law of induction

texts:
To clarify my question, I made the illustration below, assuming I understood the Faraday-Lenz law:

Above a copper loop theoretically stays in parallel between the plates A and B.

The magnetic field B hence the flux between the plates A and B is continuously increased.

The copper loop circulates a current such that to oppose the increasing flux.

Above I showed the directions of increasing flux and self generated opposing flux.

My question is, will the total changing flux always be zero no matter the conductor is perfect or not?

If the applied flux was constant(not varying by time) the total flux would be non zero.

But in case the flux is increasing, will the total changing flux be zero?


texts: Alternative to double dabble for binary to BCD conversions in FPGA?

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I want to design a binary to BCD converter. While the double dabble algorithm is easy, it also takes a long time to execute because you can't do the whole calculation in parallel.

Are there any alternatives to double dabble that also don't require multiplication/division?

I'm looking for a generic algorithm that can work on any size.


texts:
I’m trying to replicate something I got a few years ago for practical use and I found every component except for this one. It says WL BD on the package and measures 2.58x1.53mm (LxW) and around 1.3mm tall. It has a line towards the 100 ohm resistor leading me to believe it is a diode. I measured the voltage with the diode function on my meter and found it to be 0.352V. Any clue what component it could be?

Thanks!


texts: Current Transformer Question. Usage:Solar Panel v grid electricity aas measured at meter

texts: How to make a CT detect current flowing along a conductor in 1 direction only.  So if the CT were clamped on the conductor reverse, or the conductor current flows the other way then no current will flow in CT output to sensor?