texts:
I have a few questions regarding battery packs.

Is it OK to mix 2 sets of old batteries together, ie 2 are 75Ah and other 2 are 70Ah, they all came out of a mobility scooter and weren't getting the range anymore, the 70Ah ones are heavy and larger

Is the max draw currant the same as max charge currant as that's all information I have. Does it refer to 1 battery in a bank in parallel

If so does that mean the lowest batteries max charge current


texts:
I have an LED power supply - constant current with output 1.4A/96W/23-69VDC.  I want to buy a number of LEDs and connect these in series.
What do I need to calculate to know how many of the following LEDs I can add to this power supply?
Can I just do it all by Ohm's law?
https://www.led-tech.de/en/CREE-XM-L2-T4-on-Star-PCB
My calculation results in approximately 48 LEDss (though I would only want to push the power supply to say 80% which gives more like 38.)
Just wanted to see if I made this right here since it was a while I did this.


texts: What's the simplest way to store 1 bit after a device has been turned off?

texts: Is there a simple way to store a boolean value that persists when power has been turned off?


texts: Buck boost converter for lipo 6s charge info request

texts:
I need to dimension a Buck boost converter to charge two LiPo battery packs 6s 20ah starting from a variable input voltage. Both packs have their own PCB BMS board. This one:
http://bestechpower.com/222v6spcmbmspcbforli-ionli-polymerbatterypack/PCB-D165.html

So I just need  to charge them at 25.2 volts—being able to adjust the charging current automatically based on the input voltage.  And I would like to charge them at 10 amps maximum.

I have a voltage input that may vary between 12 and 25 volts. Usually is fixed to 25 volts.

What I know is that Lipo batteries need constant current and constant voltage to be charged safely but I didn't find many Information about charging them or designing a charger for bigger packs than 2s.

My questions are:

Do I need to limit progressively the current during the charge? If yes, how do I do that?
Do I need a microcontroller to cut the power automatically when the battery voltage  reach 25.2 volts?
Are there any control IC's that simplify the design of a 6s Lipo charger?


texts: Bridge Local Mosquitto MQTT broker installed on RPi with cloud MQTT broker

texts:
I was trying creating a bridge between the cloud broker (io.adafruit) and mosquitto broker which runs on my Raspberry Pi.
I have successfully tested the local mqtt connection whereas connecting to a cloud broker, I am unable to publish or subscribe to any topic.
I have made the following changes to mosquitto.conf file
connection adafruit
address io.adafruit.com:1883
remote_username xxxxxx
remote_password xxxxxx
start_type automatic
bridge_protocol_version mqttv311
notifications false
try_private true
bridge_insecure false
cleansession false
topic # both 0

pid_file /var/run/mosquitto.pid

persistence true
persistence_location /var/lib/mosquitto/

log_dest file /var/log/mosquitto/mosquitto.log

include_dir /etc/mosquitto/conf.d

Logs during subscription using command mosquitto_sub -d -t mytopic

Client mosqsub|4306-raspberryp sending CONNECT
Client mosqsub|4306-raspberryp received CONNACK (0)
Client mosqsub|4306-raspberryp sending SUBSCRIBE (Mid: 1, Topic: mytopic, QoS: 0)
Client mosqsub|4306-raspberryp received SUBACK
Subscribed (mid: 1): 0

Logs during subscription using command mosquitto_pub -d -t mytopic -m 'Hello'

Client mosqpub|4333-raspberryp sending CONNECT
Client mosqpub|4333-raspberryp received CONNACK (0)
Client mosqpub|4333-raspberryp sending PUBLISH (d0, q0, r0, m1, 'mytopic', ... (5 bytes))
Client mosqpub|4333-raspberryp sending DISCONNECT

Please suggest where I am going wrong.


texts:
In "Fundamentals of Microelectronics" textbook. The question number 25 of chapter 3 is:

This is part c of the question:

And this is the solution of part c from the solution manual:

For the blue circle: Is it correct to add the two voltage sources before voltage division as it is done here ? Isn't there any restriction ?
For the red circle: Shouldn't it be: Vin > VB + VD,on ? where did he get (R1+R2)/R1 from ?
How did he draw this graph ? How to calculate the slope here ??

Please answer even for some of those three questions.


texts:
Hi electrical engineers!
This is my first time posting, and I am really just beginning to explore basic concepts in EE.
That said, my project right now is putting a raspberry pi zero into a ti 83. I expect it to be pretty easy, but I'm not sure how to make the keyboard work with the pi. The ti 83 has a pretty normal capacative keyboard, and I was wondering what the best solution would be to get it working as a keyboard for the pi. I have access to my universitys pcb printer, soldering station etc.


texts: Can part of Integrated Circuit be damaged from heat gun usage?

texts:
I tried to re-use a costly Integrated circuit which includes dual port ram inside.
I removed it from unused previous board by carefully using heat gun.

The problem is that the other part of the ram works fine, but the dual-port ram part always reads as 0x00. The interface is SPI and other part of the ASIC works just as fine, and the same firmware on the other board that was build from new IC works fine.

Is it possible that only that part of IC damaged from using heat?


texts: Are electrical properties measured using the International system of units (SI)?

texts:
What measurement system is used to measure electrical properties such as voltage, current, etc.?
I understand the units are defined by SI (at least according to this article), but is that considered the measurement system used to measure properties of electricity?

It is confusing me because I have some people telling me that scientific notation is required for it to be considered part of the SI system, and that engineering notation is not part of the SI system.

So I am unclear if I am indeed using the SI system when measuring electrical properties. If not, then what system am I using?

To clear up ambiguity, the old definition of "the metric system" is not intended to be the topic of the question. I aim to clarify that any statements I make that refer to "the metric system" in comments refer to the modern  International System of Units (SI).


texts: Can anyone explain why a B-H curve with Hysteresis doesn't result in a highly non-linear input-output transfer function for a transformer?

texts:
See the attached picture of a typical hysteresis loop, it is clearly highly non-linear even if you keep the signal small enough to stay out of the saturation region (beyond points b,e). So my question is why does this not result in a non-linear transfer function through the transformer from primary to secondary? Ampere's Law dictates that the H field generated is proportional to the current in the primary, so if I have a sinusoidal current as the input the graph below suggests that this will result in a B field which is a (non-linearly) distorted sinusoid and then the induced voltage in the secondary will be proportional to dB/dt, so it cannot be a sinusoid either, so an input sinusoid doesn't result in an output sinusoid and => the system is not linear. Yet transformers are routinely used in applications like audio where linearity is critical. So it seems that in general transformer transfer functions are linear but I just cant understand how they manage this given the Hysteresis effect, can anyone explain this ?

Thanks,


texts:
I'm trying to build a proximity sensor that triggers on nearness of the sensor to a perimeter antenna, sort of like an underground invisible fence.  I want to feed that input into a microcontroller which will respond when it approaches the perimeter.  Most of what I'm finding online is dealing with RFID, which is not exactly what I'm looking for.

Are there components that I can use that will transmit/receive simple signals?  If I need to build this with discrete components, are there schematics?  The sensor should be sensitive only over a short range (~1m)?  Ideally this could be configured by increasing or decreasing the power of the transmitter.

I understand that the question is a bit vague, but I'm not looking for super detailed responses, just a nudge in the right direction.


texts: Designing a circuit that converts rage of currents to a range of voltages

texts:
Using only resistors, ideal op amps, ideal sources... convert current of range \$4-20\:mA\$  to \$0-10V\$ voltage.

This is a homework question and I'm not quite sure what's the task. One way I could solve this is by using an ideal op amp and setting the rail voltages to \$0V\$ and \$10V\$. Can you suggest, or give an example of a better solution?

simulate this circuit – Schematic created using CircuitLab


texts: What is the formula for how long a capacitor can power a circuit

texts:
I was thinking of implementing a feature for my circuit that protects it from loosing power after a 1 - 2 seconds power outage. Although a battery would do the trick, i would like to go with the capacitor route as its easy to implement to circuit, i will just add it to +/- of the circuit.

further question, how does a capacitor work in storing a charge is it like a battery? Where is starts at 0v then gradually goes up to 5v when full (assuming the circuit is 5v). and upon discharging does it gradually looses voltage too until it reaches 0? If so, how is current affected? Or is it like you power bank stays a constant 5v when charged and can dish out a constant current until its "drained"

based on observations of how a capacitor is affecting the leds i would say voltage goes slowly down, but i am not definitive.


texts: Which among the circuit is the most efficient for battery backed up systems?

texts:
Which among the circuit is the most efficient one for a battery backed up solution. Would be helpful if you can state the reasons as well.

simulate this circuit – Schematic created using CircuitLab

Notes

Power Supply - 15V, 1.4Amps (SMPS)
Battery - 12V, 11.2Ah (SLA)
Load - 3.3V, 250mA
Charger - Float Charging (13.6V Max)
Voltage Regulator - DC to DC buck (4.5 ~ 50V input)
Some components are not shown since they are not relevant


texts: NPN Transistor Switching 12V - grounds with different potential

texts:
I'm struggling with a NPN transistor switching problem, and in the process I've burned out a board elsewhere in my machine. Electronics is not my strong suit. I want to use a 5V signal to switch 12V. Problem is that the grounds between the 5V and 12V are not close in potential. They are about 7V apart, so I cannot connect them. I have the circuit configured like this:

Which, based off of my research on this site - should work right? And it did work for a period of time! A board that I'm drawing my variable voltage from got fried somehow down the line though.

Are there any dangers to setting the circuit up as such? I feel like some excess current/voltage got drained into the variable return - messing something up down the line. Or maybe it was that I'm only using the high line from the power into the circuit (return line not attached to anything?).

When I get my board back from repair, I want to retest this configuration but with some sort of safeguard installed to protect the other components in the machine. What suggestions are there for this?

I'm very concerned about the potential difference (about 7V) between the negative line on the power, and the negative line on the variable. On most examples I've seen recommended (necessary maybe?) that the grounds be connected somewhere in the circuit.

Could be that this is indeed correct! And that I burned my board while going through the experimentation process that led me to this haha.

NOTE: diagram is wrong. I'm using R1 = 500 Ohm, R2 = 1k Ohm


texts: dsPic33f : How to interface ECAN with CAN High/Low Signal

texts:
I want to start communication between (dsPic33f) ECAN_Module & PCAN-USB ADAPTER

I have downloaded a demo code AN1249 from microchip website.

I am using Explorer-16 board for Testing.

Now the Issue I am facing is connecting PCAN-USB ADAPTER with Explorer-16 board or dsPic33fj256GP710A ??

dsPic33f has two CAN pin C1RX (CAN_Receiver) & C1TX (CAN_Transmitter).

While PCAN-USB Adapter has CAN_HI & CAN_LOW.

How to make connections to start Communication ???

Do i need any CAN IC to complete the interface ??

I tried to study ECAN reference Manual. But could'nt trace out about connections.

This is my very First CAN communication testing code.

So please share me some knowledge/links so that I can proceed further.

Thanks in advance.


texts:
I'm working on the following homework problem. (Yes, this is homework. :p ) I'm supposed to find the current through L1 as a function of time.

simulate this circuit – Schematic created using CircuitLab

Using current division I've identified the current at zero time.

$$ I_L (0) = 0.01(15/(47+15)) = 2.42mA$$

However, I'm a little confused on how to find the equivalent resistance (since the Time Constant = Inductance/Equivalent Resistance.) Are they in parallel with each other? I guess the reason I'm confused is that my textbook said to find the equivalent resistance from the view of the inductor.

Note: The empty wire parallel to the inductor had a switch that was closed at t=0.


texts: Recently I bought a ready PCB that is basically a power bank when 18650 batteries are connected This. It has a micro USB port to charge the 18650s and two USB type A one of which output is 1A and the other 2A. I also bought a USB Type C breakout board The female one. Now, I try to convert that power bank to support Type C. I want it to be bidirectional. So when it detects external voltage at the Type C port to switch to charging mode and apply that voltage to the micro USB connections. But when there is no external voltage at the Type C port it will output voltage from the 2A Type A port. Can that be done with the use of simple electronic parts? If not what components sould I search for? I tried to find documentations on USB Type C on the Internet on that topic but I cannot find what I want.


texts: Taking into account the advantages of triphase current in relation to monophase current, I keep wondering if a multi-phase current such as heptaphase would be more advantageous than triphase. Does anybody know if this has been tried or proven?


texts: Finding Values of Rd and Rs to satisfy the N-MOSFET design

texts:
I've been stuck on this design problem for a while and I am just filled with a lot of equations and unknowns and not getting anywhere with it. Here's a picture of the problem with the problem statement below

(1) Constant Current Region : id = k/2 (Vgs - Vt)^2

(2) via KVL:  Vgs = 1 V - idRs

(3) via KCL:  1 V - idRd - idRs -Vds + 1V = 0

(4) Rd = (1v - Vd)/id

(5) Rs = (Vs - (-1 V))/id


texts: Need help extracting line out signal from car radio

texts:
I'm trying to extract audio signal from my car stereo and use it as an input to my external amp. The place I want to get it from is marked in red in this picture:

I used the IC31-34 pin12 to get the signal, but when I connected it to my external amp line in inputs it went to protective mode. I measured the voltage and it was 4V dc.
Will it work if I put some resistors to lower the voltage?

My external amp has these pre-in parameters:

Pre-In sensitivity: 0.3 ÷ 5 V RMS
Pre-In impedance: 15 kΩ

Here is the full service manual of the stereo.


texts:
I have a device (an energy meter) that sends data via RS-485 (Modbus protocol). And I want to collect it with MCU. The important thing is that I'm trying to design a board and I want it to be scalable. That means I might have 1 device connected, or maybe 2 or 3 devices connected (with different Slave IDs). I have the following questions:

I think that I need MCU with an UART and then I need to add RS-485 driver (like this one) and I'm fine? I mean Modbus is just a protocol, so on the design stage I shouldn't worry about that?
Should I consider a MCU with 1 UART or I need more? Is MCU with a signle UART is capable of communicating with multiple devices? I mean one UART will provide only Rx and Tx lines, so it is easy to connect to one device. But how to handle more?
Do I need to handle all the Modbus stuff manually? It can be done easily with PC, but how I can do it with my MCU? I will need to define function codes, data arrangement and all this stuff from scratch? Or there are available libraries for some MCUs?

Thanks in advance!


texts: What is thermal resistance of SMD7530 LED

texts:
What is thermal resistance of SMD7530 similar to this photo (Or typical LED in this type):

With this datasheet:

Datasheet for SMD7530

I cannot find any thermal resistance in it's datasheet.


texts: Improving an existing half wave rectifier circuit on generator

texts:
Background: Just upgraded my old Generac portable generator by replacing the rectifier which had gone bad. Here is the schematic. The old style rectifier that this unit used is no longer made or available. Replaced it with a Fairchild GBPC3510 as best replacement I could determine. Now I'm in business again with 120 VAC through my two outlets.  Yay! Generator also has a "battery charge" circuit offering "12 VDC, 10 Amps."

The challenge: Would like to review the battery charge circuit and see if it can be improved. Specifically: Would adding a capacitor as shown in this half-wave circuit offer any benefit along with the existing rectifier described below?
If so, what is the benefit?
If so, what capacitance would I need? (How would I calculate this?)

Currently, is a very basic half-wave rectified circuit with no capacitor. The 'diode' is a Motorola 1N3492R 8550W "Medium Current Silicon Rectifier" (reversed polarity version with cathode to terminal lead, anode to case). The anode connects directly to the battery negative terminal post which is also the common chassis ground.
The behavior of the circuit is, at no load: 16.3 VAC coming from the generator windings (55, 66 in schematic) showing 7.1 VDC at battery terminal posts. When a DC load is placed DC voltage will scale up. Measured 10.8 volts with a small 12 volt blower (for air mattresses) and up to 12.5 volts with a high-pressure air compressor.

This is an older generator so no technical information or support available from the company beyond the schematic already attached.


texts: How can I change the standard .jft .bjt .dio .cap files in LT spice XVII

texts: I tried adding a model to one of the standard.jft located at C:\Program Files\LTC\LTspiceXVII\lib\cmp (actually I was updating the standard.jft files from LT spice wiki, if you haven't done this you should check it out). But I get no change when loading LTspice XVII when I look for the models in the drop down list of the Jfet. How do I add a model to the standard model files in LTspice XVII?


texts: Is there any way to programmatically reset the BWP bit on a PIC32

texts:
We have a product using the PIC32MX795F512L out in the field that has firmware in both the boot and program sections.

The boot flash is write protected using the BWP bit 24 = 0 in DEVCFG0.  The firmware is not Code Protected (CP bit 28 in  DEVFG0).  The program section is also unprotected and writable.

We find ourselves in a situation where we need to update the boot flash.  Since these units are overseas, we have no physical access to them, thus we cannot hook up a laptop and Microchip programmer like the ICD3 or RealICE and reprogram them (which would give us access to both the boot and program areas0.

We are able to update the program section via a firmware update through our cellular modem.

Is there any way to programmatically set the BWP bit in DEVCFG0, so we can overwrite the boot flash with new code?


texts: Using Beaglebone Black to prototype commercial product

texts:
I am designing a system and it's safe to say I am a little out of my depth. The requirements of the project are as follows;

drive 7" WVGA touch screen and generate graphics

4-20mA input

3 x 4-20mA outputs

2 Analogue inputs

4 Digital Outputs

2 Digital Inputs

Spi Bus (5 x CS)

I2C

PWM for LED controller

Eeprom for data storage

I have designed most of the system under the impression we would be using BBB as the main processor for the system but the BBB has been called into question over its suitability for use in a commercial project.

I was thinking of using the BBB for the 1st iteration of the board design. Once  we have established a working system to then redesign the board with the Cortex-A8 and any other components needed from the BBB. Seeing as the BBB is all open-source this should be possible right?

Is there a better/easier solution for this using a microprocessor or something like that? Product longevity has been flagged as one of the problems of using BBB as the product needs t o have a lifetime of 15-20 years.

I should also add that I will be doing most of the programming for the system and only really have slight experience with C++ any help/advice would be appreciated!


texts: Compensation of custom high voltage power supply

texts:
To test an offline switching PSU I decided to build a custom isolated high voltage variable PSU. The idea was to build a nice, small, low power equivalent of a variac and isolation transformer that is commonly used in this scenario.

The idea was to use two stock transformers 'back to back' with a variable voltage load in the middle to simply waste the excess power. As the design only called for a few Watt's power this is not much heat to get rid of. The concept is similar to the helix regulator in Luis Cupido's TWT PSU.

The variable load circuit I came up with worked nicely on the bench when dropping a constant DC current but when combined with the transformers it oscillates wildly. This seems obvious in hindsight as the transformers are an inductive load and there is AC ripple across the variable load circuit which will get into the feedback network and wreak havoc.

As feedback compensation is not my strongest point I was hoping for some advice about what to try to stabilise the circuit or if it is even possible. The unit could be useful for safely (relatively) testing of low power circuits that need higher voltage. A simple rectifier, filter cap and bleeder resistor could turn this into a 0 - 340 VDC isolated PSU.

The schematic is simplified slightly, not shown are the internal 12 VDC supply or any protection / switching of the mains. The LM358 also has the second op-amp input grounded and it has bypass caps.

.


texts:
A book I am reading has this sentence explaining capacitors:

  Capacitors are passive components in which current leads voltage by
  nearly 90° over a wide range of frequencies.

I am not well-versed in electronics.  What does it mean for current to lead voltage?


texts: How to 'spoof' (switch) a photodiode electrically - rather than with light

texts:
I bought a paid of LCD welding goggles in the hope that I could re-purpose the switchable light filter for another project. Unfotunately, the circuit driving the LCD filter is way above my ability to understand ..
However, I did notice that the unit has two photodiodes that are used to detect the arc-light and trigger the filter. I was wondering if there might be some way to 'spoof' the diode so that it switched the filter .. i.e. shorting each of them out .. or injecting current at the input or output.
Any suggestions would be gratefully recieved.


texts: While selecting resistors most often if standard values aren't present , the closest standard values are used which might be a kilo ohm or two away from the design requirements . I want to know how much leeway is there while choosing an inductor or capacitor .I couldn't find a 0.6nH for L1 in the below interfacing circuit and the ones I have ordered are about a week or two  away from being delivered and I was sort of wondering if I could use another ballpark value (say 9.9nH) in its place. L1 in combination with C2 is used as some sort of LPF I think to remove ripples from supply voltage to the low noise amplifier SKY65404.


texts: I'm trying to wrap my head around the 20m and the 2000µ setting. On 20m I see 0.01 but on the 2000µ setting I see 005. Does this mean my circuit is using 5µA of current? Why the discrepancy?


texts: Suggestions for an ultra-low leakage diode

texts:
I'm looking for a diode-like component with a "resistance" (when linearized about V=0) of at least 20 Mohms at 75 deg C.  The behaviour for larger voltages doesn't really matter so long as the diode is able to conduct about 50 uA by 2.5V. The capacitance must be no more than a few pF.

A regular signal diode like a 1N4048 has a linearized resistance of about 5 Mohms at room temperature, and much lower resistance at 75 deg C, so this obviously won't work.  I've found a few "ultra-low leakage diodes" that could work but are quite pricey and not in the form-factor I'd like:

https://www.digikey.ca/product-detail/en/on-semiconductor/FJH1100/FJH1100-ND/1058005

https://www.centralsemi.com/content/product/bare-die/select/diodes/Ultra_Low_LeakageDiodes.php

I also found this thread suggesting that using the base-emitter junction of a BJT may be preferable:

transistor as low-leakage diode

The ideal solution would cost less than $1 in QTY=10,000 and take up no more space than an 0603 or 0805 component (so putting 10 diodes in series is probably not feasible).

Any advise?


texts:
I'm looking for a motor to produce 11V. I'm a little confused about which type of motor should I use. The shaft of the motor is connected to the nitro engine and it will rotate the shaft of the motor.

I'm actually designing a generator. I'm not sure what type of motor should I use.  Brushless? Brushed? Permanent magnet?

I just need to produce only 11V to produce electricity.

I'm actually designing a generator to charge a LiPo battery. I'm using a 3 cell LiPo battery. The 3 cell LiPo battery is equaled to 11V. So I have to work the reverse engineering way.

How can I produce 11 V from the most suitable motor and nitro engine?

That's what I'm figuring it out. Like what are the best motor and engine to produce 11V.


texts: I have a 16 amp 230V supply and wish to auto disconnect heating when using a kettle using a relay,

texts:
I have a limited wattage supply and rather than remembering to switch of the heating for a couple of minutes to boil the kettle would like to fit a relay in order to "break" the feed to the heater and remake the feed after the kettle has boiled using the plug on/off switch.what type and rating of relay should I use?
input 230 volts 16 amp RCD approx 3680 watts.
Heating max 2000 watts and kettle 3000 watts.
Thank you


texts: Is it safe to run a 220v "Split-Phase" piece of equipment on 220v "single-phase"?

texts:
EDIT:

Let me re-phrase the question, as I did a terrible job the first time.

I have a mill that can definitely run at 220v, with two legs of 110v, (split phase, as commenters have informed me). I've run it from both a drier plug (split phase 110v in canada), and a variac (split phase 110v.). The nameplate also says 240v.

I bought a 2kw transformer (perhaps an autotransformer?) that provides 240v, single phase.

Is it safe to connect these?


texts: Automatically opening and closing a door

texts:
I'm working on an automatic door that runs like this:

Receives an input trigger, probably a voltage input
DC motor runs in one direction for x seconds to open the door
Same DC motor reverses direction for x seconds to close the door
Standby for another trigger

The challenge here is that I can't use any microcontrollers (I'm too reliant on those things) and that everything is automated. I've done some research, so I've figured that I can control the motor direction with a H-bridge IC like an L298N, but I'm pretty confused with the timing control.

So far, I've found capacitor and 555 timing control circuits, but they are timing to ON and OFF circuits, which I'm not sure how to fit in here. I've also found a couple of time delay relays, but I don't know how those work.

Any help would be appreciated, thanks!


texts: zero-crossing detection: to optocouple or not to optocouple?

texts:
That is the question.

Most of the diagrams I have seen on the interwebs are of the opto-coupling school of thought:

But the AVR182: Zero Cross Detector application note just throws in the resistors like so:

I am headed for simplicity. Will this MCU directly plugged into mains stand any chance of surviving longer than a couple of uses in the real world ?


texts: Expected behavior for damaged transistor

texts:
The generic question I have is what's the "expected" behavior for a damaged BJT. Let me add more color..
I was trying to fix my kid's toy where a motor would run even when it wasn't supposed to (no matter if the switch was on or off, it would always run). I tried to reverse-engineer the schematic driving the motor and here's what I think they had on the PCB:

The motor is represented by an inductor (ignore its value). What I think is damaged is the transistor Q3 because when the motor was running there were ~8V at the base of Q3 (so it should have been off) and yet I could measure ~1V at the gate of Q4, enough to keep it on. Q4 didn't seem to be broken because if I drove 0V to its gate, the motor would stop running.
Is my analysis correct or the problem of them motor always on could be elsewhere? I guess my question is: is this an expected behavior for a damaged PNP? If not, what is? I'm asking because I'd rather expect a burned BJT not to conduct when it's on, not the other way around (i.e. conduct even when it's off). And if that's the case, what might have caused it? Some specific incident (spikes in current or similar) or do transistor wear out over time anyway?
Thanks
EDIT
So I opened it up again and there was indeed a diode across the motor as Spehro suggested (just not on the PCB). And as andre314 suggested, I measured the voltage across R4: it was 0V. So it looks like Spehro was right: the transistor that's damaged is Q4, not Q3. Now I need to learn how to replace it...
Thanks everyone for your help and suggestions


texts: What exactly does a 10-transistor XOR gate look like?

texts: I need a schematic for a 10-transistor xor gate, I have searched everywhere and I see 8, 12, 6, but I can't see 10. What does it look like in a transistor like picture?


texts: Low power rectification of AC component of modulated current signal

texts:
I have a current source consisting of a 100Hz sine plus a DC offset: \$I=I_{DC}+I_{AC}\cdot\sin(2\cdot\pi\cdot 100Hz\cdot t)\$ with \$ I_{DC}\approx100uA\$ and \$I_{AC}\approx 1uA\$.

I would like to extract the AC signal and rectify it to get a digital output (rectangle) signal with a frequency equal to the modulated current. The phase may be shifted, but the shift should be constant. The circuit should consume as little power as possible and work from a single supply rail of \$ V_{SUP}\geq 1.8\$.

My idea was to have a shunt resistor (R_SHT) between the current source and GND to convert the current to a voltage. This voltage is then high-pass filtered to remove the DC component. Finally, an OPAMP comparator rectifies the AC voltage. I used a low power rail-to-rail OPAMP with low offset voltage (TI LPV821). Here's the schematics:

simulate this circuit – Schematic created using CircuitLab

After soldering the circuit, I don't see the expected rectangular output voltage. Instead, the output is drifting slowly between the supply rails, occasionally exhibiting the 100Hz input signal.

Is the proposed circuit generally suitable to achieve my goal of converting the modulated current to a digital signal?

Are there any obvious problems with the circuit, that may lead to the observed drifting behavior?

Are there better alternatives to achieve my goal while consuming similarly little power (\$ \approx1uW \$)?

Thanks for your input.


texts: Programming CC3200 Microcontroller and Separate Flash Without a Development Board

texts:
I have an "Alfie" device which has wifi and USB, but I never
use this device, so would like to change its function.
It uses the CC3200 microcontroller (which has a little ROM)
and a separate flash chip.  At first, I thought I could just
reprogram the flash chip alone and make it more useful, but
it seems to have encryption forcing the reprogramming to
go through the CC3200, so now I am hoping I can use a
SPI (or UART) programmer applied to the CC3200 with some
jumpers to reprogram it (I'm guessing the original developers
would reprogram this chip with just an SPI programmer, or
even simpler with the USB port, and a few jumpers, right?).
Can I do this with just a generic programmer?  All the instructions
online seem to do this with a particular development board;
I don't understand why Texas Instruments would not publish
a bare-minimum programming spec.
So, how can I most easily get a new compiled "mcuimg.bin" onto this device?
By the way, I also looked for back doors, but my computer sees
no USB connection and, though the wifi gateway listens on port 80,
every page I asked for returns "404 Not Found".
Here are some photos:
https://fccid.io/document.php?id=2971294


texts: What is the most efficient way of charging an AGM battery using a car alternator? I have a 12V plug connected to alligator clips which can be used in the 12V sockets inside the vehicle. Is this the best option or is it best to use jump start cables to connect directly from car battery to AGM terminals (positive to positive and negative to negative)? How many amps of current would be achieved with each of these methods?


texts: How do I detect revision of a particular PIC microcontroller?

texts:
I have a PIC18F4680. After reading the datasheet, it's still no clear to me how can I determine which revision the chip is.

So how do I determine the revision of the microcontroller other than asking the supplier to provide that information to me?

Answers relevant to other PIC series are welcome too.


texts: MB85RC256V for data logger sensor project?

texts:
Please. I need somebody can tell me if I can replace a SD card module of arduino to use instead a MB85RC256V fram module 32KB.
I want to save power of 3.7 battery, but I am not sure if I can use a fram to store sensor data. the datasheet of MB85RC256V says :

  it is suitable for the log management and the storage of the resume data, etc.

My idea is to read pressure/temperature each 15min and maybe send the data to server twice in a day. After send the data I want to clear the fram memory to can store more sensor data.

The format of each line to store could be:

yyyy-mm-dd,hh-mm-ss,pressure-value,temperature-value,some-id

I think 1000 lines of this is 32KB. If I measure each 5min I got in one day 288 lines (maybe 10KB)..?

Is it possible to do?


texts:
Im trying to flash an LED to music.
I have tried to follow this article and calculate values but cannot get it to go.
Basically what i think i need is:

audio in
through a low pass filter (isolate frquencies <200hz)
output to a peak detector or Schmidt trigger of some sort
trigger a pulse monostable (eg 555) for duration.

My trouble is i cannot work out a useful low pass and peak circuit. surely this has been done before!


texts:
I am from a computer science background, I need some help with some electrical engineering problem.

Electricity consumption for a home in the last 56 days is 7561 kWh.

There are two floors. The combined area is 300 square meters.

Can I use this information to get watts per m² for this house?


texts: Converting Pulses to Analog Input for Mic

texts:
A continuation of this question.

I am attempting to read two flow meters through the mic port of a phone/tablet. The flow meters' pulse pins toggle between +0V and +5V as their pinwheels rotate. I use an R-2R to combine the pulses from the flow meters. My first attempt was to simply send the digital output from the R-2R straight into to mic port like so:

This worked great on my PC. I was able to look for edges in the signal and (based on the magnitude of the amplitude change) determine which flow meter the pulse was sent from. Here is a screenshot of my program detecting pulses on my PC:

Raw signal read from PC mic port:

(source: awesomebox.net)

Program highlighting detected flow meter state changes:

As you can see, the program is successfully identifying flow meter state changes; smaller amplitude changes are caused by flow meter 1 and larger amplitude changes are caused by flow meter 2.

The problems start when sending the same signal to my Galaxy Note 8 Android tablet. This is what the signal looks like when one of the flow meters is spinning and changing state, read through my PC's mic port:

(source: awesomebox.net)

Here is what the same signal looks like when read through the tablet's mic port:

(source: awesomebox.net)

Because of the (stronger?) AC-coupling in the tablet's sound card and the noise cancellation and other processing done to the signal, it is not possible to use the same edge detection method.

I was suggested by @DwayneReid to not try to force a digital signal through. Instead, I should convert the digital signal to an analog one and pass that through. He suggested this schematic for converting the digital signal into an analog one:

I combined this schematic with mine and came up with:

As far as I understand it, a constant analog signal should be generated by the 555 timer and sent to the mic port. Voltage changes caused by flow meter state changes should cause frequency changes in the analog signal. I will then be able to read the frequency changes of the analog signal and know when a pulse occurs, and based on the change in frequency, which flow meter the pulse came from.

This is what the signal now looks like when one of the flow meters is spinning and changing state, read through my PC's mic port:

(source: awesomebox.net)

As you can see, there is a now a slight oscillation present in the signal. However, the overall signal is unchanged and none of my expectations are met. The constant analog signal is so slight it could be considered noise. Changes in voltage seem to effect the signal no differently than before.

Where is my schematic wrong? How can I get a generate a constant analog signal that changes in either amplitude or frequency when the combined voltage from the flow meters changes?

Thanks,
 - Mike


texts:
Last weekend and the weekend before, I have been trying very hard to get a good small 8 ohm speaker amp with a preamp for a dynamic mic to work with no luck. It seems like every design I try has problems like this weird oscillation I got changing pitch if I touched different wires.

I even half-broke my left output from my iPod with one design It now will not play music quiet (scratchy sound), but oddly works above 80% audio level to the output jack. I will have to try to build an external POT volume control I guess :(  .

So I have a dynamic mic , or a telephone pickup coil. How can I amplify this with the least distortion, and highest efficiency to drive an 8 ohm small speaker with a volume adequate enough to hear in a semi-quiet room (maybe a small fan running) up to 8 feet away from the human ear.

I also have one more question:

How can you learn from experience if you can't identify the problem and just hope the circuit works the next time you attemt to build it.


texts: Voltage drops when load connected to ld1117a

texts:
Package: LD1117A (package sot223)

Power: USB adapter( mobile charger ) 5.3 V 2 A

When these is not r1 resistor present and adj is connected to ground, Vout is 4.9 V for Vin 5.3 V.

r1 is 120 ohm and r2 is adjusted with 20 k potentiometer to get 3.46 V at output. Then load (essentially esp8266 01) is connected, voltage drops to 0.6v and even on adjusting potentiometer to full 20 k, vout just reaches 0.71 V.

Why is this happening?

How to resolve so that ESP8266-01 gets power up?

Datasheet  See page 12


texts: PIC16F1704 strange DAC output on DAC1OUT2 - it seems some other peripheral loads the pin down

texts:
I'm trying to get the DAC of the PIC16F1704 to work, specifically I want it to output on pin RA2/DAC1OUT2.
There's nothing connected to that pin, and I've reduced the test code to this:

#define _XTAL_FREQ 4000000
#define FCY 4000000ULL
#include <htc.h>
__CONFIG (FOSC_INTOSC & CP_OFF & MCLRE_OFF & BOREN_OFF & WDTE_OFF);
__CONFIG (PLLEN_OFF & LVP_OFF & ZCDDIS_ON);

void main(void)
{
    WPUA = WPUC = 0;       // disable weak pull-ups
    nWPUEN = 1;
    ZCD1CON = 0;           // disable Zero-cross detect module

    SLRCONA = SLRCONC = 0; // disable slew-rate limiting
    ANSELA = 0xff;         // all analog
    TRISA  = 0b00111111;   // all inputs

    OSCCON = 0b01101011;   // 4 MHz internal oscillator, no PLL

    DAC1CON0 = 0b10010000; // DAC on, Vref+ = Vdd, Vref- = Vss, output on DAC1OUT2
    DAC1CON1 = 0;          // Tap #0: output 0.0V on DAC1OUT2
    while (1) {
        __delay_ms(10);
        DAC1CON1++;
    }
}

This should output a ramp 0..Vdd in about 2.56 seconds, but instead what I see is this:

My Vdd is 3.3V. The skewed and inverted ramp is from 1.0 down to 0.4 V, with a plateau around 0.8V.

The problem seems to be with that particular pin, not the DAC itself. If I change the DAC config to

DAC1CON0 = 0b10100000;

I.e., output on DAC1OUT1 instead (RA0), I can read the ramp on that pin, it is perfectly linear, and not inverted.

It seems there is some peripheral that tries to keep pin RA2 on 0.8 volts, and does it in a weird non-linear fashion.

Any ideas what might this be? For completeness, here's what this pin is multiplexed with:

The Zero-cross detect circuitry fits the bill quite well, but as you can see, I've explicitly disabled it (btw changing the ZCDDIS_ON to ZCDDIS_OFF doesn't change anything).

The compiler is XC8 (1.31 I think) and I'm programming the chip with PicKit2.


texts: Simple circuit to fade in / fade out LEDs randomly

texts:
I have a group of 8 blue LEDs (Vf 3.2V @ 20 mA) currently powered up in parallel by a resistors (one for LED) and a 4.5V power source (3xAA batteries). I've been playing with fade in/out effects and 555 circuits.

What would be a simple circuit to randomly (or-pseudo randomly) fade in and out them independently? I mean, when some LEDs are increasing in intensity others could be decreasing following no specific pattern (the fade in/out cycle time could be different as well).

Ideally, I'd like the fade-out effect not to be complete. In other words, more than a fade in/out effect what I'm looking for is a circuit that can slightly affect the light intensity if each LED randomly (e.g. fluctuating the current from 3mA to 20mA).

I would appreciate any hints or pointers. A detailed explanation or circuit diagram is now necessary (but it would be awesome!).


texts: Measuring Li-Ion Battery voltage during charging/discharging

texts:
I am supposed to measure a Li-Ion Battery cell's energy efficiency. For this purpose i have built up the apparatus setup which charges and discharges the battery cell to calculate its energy.

One thing that i studied before, and also noted while experimenting is that the cell's voltage is higher than the open circuit voltage during the charging process, and is lower during the discharging process. For e.g during charging when it was showing to be 3.9 volts, when i disconnected the charger, the cell voltage showed to be approx 3.7 volts (OCV). (i know the reason for this voltage difference is the drop across internal resistance of the battery cell)

My question is that if i charge and discharge the cell, without doing any extra calculations (compensation) for this thing, and i calculate the energy efficiency based on charging and discharging current and voltage values straight away, will i be getting the right results for energy efficiency ? Or do i have to do some kind of compensation for this thing (the difference between charging/discharging voltage and OCV) in order to calculate the right energy efficiency of the cell ?

Also, disregarding the energy calculation of the cell, when we have to fully charge the cell for normal use for e.g, do we compensate for this thing ? As i am guessing that the open circuit voltage becomes equal to the charging voltage in the CV region, so may be its not necessary to do the compensation. Which means that one can disregard this thing and simply charge and discharge the battery cell for normal use. Am i right ?

EDIT :

After posting my question, i just read @Russell McMahon ' s reply to this post:
Maximum *charging* voltage for Li-Ion battery

And by reading it I'm assuming that i dont need to worry about this thing, i.e i should just keep a check in my software (like ive already did) "if(Vread >= 4.2) then go to constant voltage CV cycle" during charging, and  "if(Vread <= 2.75) then stop the discharging" during discharging.

Still i would like to ask  @Russell McMahon to verify my assumption, and also tell me about its validity in case of energy efficiency calculation.

Your helpful comments and suggestions would be appreciated.

Thankyou.


texts: How would I hook up this load cell to work with an HX711 amplifier?

texts:
I’m trying to build a scale using this load cell which is different than the similar looking load cells in that it these are rated for 100kg, whereas the typical load cells are rated for 50kg.  More importantly, this load cell has four wires instead of three.  I have used four of the 50kg/3 wire cells with an HX711 amplifier by following this diagram:

My question is how can I hook four of these 100kg/four wire cells so I can weigh things up to 400kg?


texts: Implementing a low cost battery backup circuit for internal RTC in STM32F030R8

texts:
Extension of this question.

Datasheet: http://www.st.com/resource/en/datasheet/stm32f030f4.pdf

The micro-controller in question has an internal RTC module but no VBAT pin. As such, the only way RTC can be given power backup is to use a battery for whole microcontroller, sense the absence of main 3.3V power supply and shut down the micro-controller leaving only RTC running. However there will be external LEDs and other elements present which might draw current from the battery draining it quickly.

Top answerer of that post hinted towards a minimal circuit using diodes. However I couldn't come up with a simple solution. If the circuit is too complicated and/or costly, it might be worthwhile to select another microcontroller which has a VBAT pin.

Is there anything that I can do in this regard?

Edit:

I am looking at CR2032 battery for this purpose. However I am also leaning towards using a supercapacitor for the same purpose. Max duration of power outage will be 6 hours and I think I can easily find supercaps which will provide power that long. If I fail, CR2032 is the way to go.


texts:
I am part of a project that is implementing a power storage system. The storage device voltage must be monitored in order to direct power. The storage device voltage should remain between 12 and 36 V. The project uses a TI TMS320F28027 MCU which operates at 3.3 V. How can the 12 to 36 V be mapped onto 0 to 3.3 V for the MCU.

I posted a similar question here but it specified that the voltage would range from 0 to 60 V. The difference for this question is how to bias the voltage appropriately.

I also posted another question about biasing the output of a current sensor for an ADC, but it involved biasing a balanced voltage around 0 V. I am having trouble adapting the answer to this problem. Diagram from answer:

 Figure 1. Diagram from previous answer

An attempt to emulate the design methodology would be:

24 V maps to 1.65 V
38 V maps to 3.3 V
10 V maps to 0 V

The most basic circuit model:

How to design the  bias?


texts: How does the led fade circuit with the NE555 timer work?

texts: I searched about this and each explanation did not make any sense,my explanation is that when the OUT pin is HIGH the transistor turns on and the capacitor charges,also the led turns on gradually because the capacitor voltage rises,but when the OUT pin is off ,the capacitor discharges(trough the transistor) and the transistor stays on until the capacitor is fully discharged and when the OUT pin is HIGH it repeats all over again.Am I wrong?


texts: Secondary Power Distribution Unit (SPDU) vs DC DC converter?

texts:
While I was searching DC-DC converters, I have seen something as "Secondary Power Distribution Unit (SPDU)" according to the person this unit is mainly used in armored vehicles. I have made a research over internet but I couldn't find what is it and why do they use it. So I have some questions about it:

what is SPDU and why it is being used in armored vehicles?
What is the difference between SPDU and a regular DC-DC converter?

Here is one product that is called as SPDU, but page itself does not contain any useful information:
SPDU product


texts: Correctly measure L7805ACT regulator output

texts:
I am trying to measure the output of a L7805ACT voltage regulator (datasheet) with a multimeter, without any additional parts (no caps, etc, just the regulator). I'm using a regulated wall adapter power supply with settable output (5-12VDC). The adapter's connector can be inversed so + becomes -, but I paid attention to connect it the right way.

The multimeter I'm using is an EXTECH EX330.

Here's the regulator's pin layout:

Steps:

set multimeter to VDC setting
attach COM probe to regulator's GND (middle pin)
attach red probe to output pin (3rd)
connect wall adapter to input pins (1 and 2)
switch the wall adapter on

Diagram:

simulate this circuit – Schematic created using CircuitLab

With the first regulator I tried, the multimeter displays the input voltage and the regulator quickly heats. No voltage drop whatsoever.

At first I thought 12V input is too much, 7V have to be dissipated as heat and that the overheating is normal, so I set the input to 7.5V, but the results were the same.

Changed the wall adapter, same thing. Measured the adapter's output power with the same multimeter, 7.5V exactly as set.

Tried with another regulator, 7.5V input, and now the measured output voltage starts from about 7V and rapidly drops to 0 (didn't really waited to get to 0, don't want to see the regulator burning).

Although the multimeter shouldn't be the problem, as even without connecting it the regulator still heats, I thought to change the multimeter batteries. Low battery indicator was showing on the multimeter, although the batteries were only half discharged. I changed them anyway. Same result.

So what am I doing wrong? Does the regulator need a load on the output, like a resistor? This might sound stupid, but does the multimeter draw too much current from the regulator?

I know this is a basic task, but it got me a little frustrated after possibly destroying 2 brand new regulators.


texts: Isn't the term RAM technically incorrect?

texts:
I know that RAM is a word used to describe a type of memory that is volatile and more importantly doesn't have a speed difference when accessing different parts of the "memory grid". Isn't the last characteristic of RAM(no speed difference between accessing different areas of the memory)  technically not possible because it depends on the length of the wires going to that intersection of the grid from the two decoders?I know that some of my terms are incorrect and may be misleading so here is an example diagram of a RAM chip(on the first page there is an architectural diagram):

http://users.ece.utexas.edu/~valvano/Datasheets/6264.pdf

On the datasheet the "memory grid" is called the array, and two decoders are used with the address input so that one "intersection" can only be "active" at once.


texts: Repairing burned PCB traces for 220V. Is it safe if I don't know why they burned?

texts:
I'm trying to fix the cooker hood of my kitchen and I found that the problem is in the controller. The PCB has two burned traces, respectively to the electric source of 220V (neutral and phase... picture below). I think it is very simple to fix with some solder on the broken traces, but since I don't know the reason why they brake, I'm not sure it's safe to adjust the PCB with this simple intervention.

Any advise?

LAST UPDATE:

I remade the broken traces of board and mounted back in its place, the result is:

The halogen light works (one of them, the other is broken). The corresponding button id the last on the right side.
The second button from the left side (lowest speed of the aspirator) turns the LED on, but the aspirator doesn't start.
Third and Forth buttons from the left side (intermediate and highest speed of the aspirator) trigger the home safety switch. (I guess in English can be translated in "electrical leakage"...)


texts: Honeywell TH1100DH1004 - temperature signal

texts:
Is it possible to have this (non programmable ) thermostat communicate only a constant temperature reading regardless of what the sensor senses?

My understanding is that it communicates a value set by user lets say 66 F once, and it compares that value to the temperature sensor readings. sends a "turn on heater" command if the temperature drops below the user set.  It stores the user set value until it is changed again.

Is it possible to somehow block this signal? such as taping a pin or cutting a wire inside? The installation manual doesn't describe which pin does this


texts:
I want to find the output voltage of a circuit like this:

and this is my Matlab code to solve it:

function find_x
t = 0:0.001:10;
x0 = 0;
R1 = 90000;
R2 = 1000;
C = 0.001;
[t,x]=ode45(@rhs, t , x0);

plot(t,x);

    function dxdt = rhs(t,x)
        dxdt = -(C/R1 + C/R2)*x + C/R1*abs(sin(100*pi*t)) ;
    end
end

but it gives me the wrong answer, because the right answer is nearly a DC voltage.

Can anybody help me?


texts:
simulate this circuit – Schematic created using CircuitLab

The schematic shows an attempt to amplify the signal coming from my chip to help fully saturate the base of the TIP29. All in all, the voltage I get when everything is running, is perfect across the board.
;However, the motors are finicky. Though they receive all the voltage, the current going to them is very poor. The motors have virtually no resistance so they need to pull almost all the current to get to full power.

Increased voltage to the amp was far more helpful than increased voltage to the motors. Naturally I would think to increase the voltage for the amp. The problem is this is a quadcopter. I cant just slap 2 9v batteries in series.

I'm still a student, so my familiarity with part models is not the best. I'm merely using the parts they taught us with. Any help for this would be excellent. I have been wrestling with this problem for months and need some help.

PS: I couldn't find the motor icon in the schematic editor.


texts: Why is voltage properly siphoned off in this circuit?

texts:
This comes from the Raspberry Pi "fart detector" project. It says to place a 47k Ohm resistor connected to ground in order to siphon off a certain amount of voltage so that the voltage read from the GPIO pin is less.

Given that the row in a breadboard is connected by the same metallic element (thereby electrically common), why doesn't the majority of current flow through to the GPIO pin? Is this because the GPIO pin is acting as voltmeter and thus providing very high resistance? If this logic is true then could the resistor theoretically be placed at J1 and have the same effect?

EDIT:
Experimenting with this configuration I found that modifying the arrangement of the resistor relative to the GPIO input didn't make a difference which fundamentally makes sense. When completing everything even moving the resistor ladder around didn't matter as well. The best way I can explain this to myself is that the voltage is present in the same form as long as you are on a common ground.

I wasn't able to find out much about how the input of a GPIO actually works but it seems like it basically draws barely any current and acts as a voltmeter. This allows all 5 resistors to do their job to regulate the current.

(source: raspberrypi.org)

(source: raspberrypi.org)


texts:
I want to construct a voltage divider according to this schematic. I want to set the R1, R2, and R3 voltages to power a LED with a forward voltage of 3,5V and a forward current of 25mA. How should I think?
Updated to add:
The full question is the following:

You want to show that a motor is running by lighting an LED. The motor
drives at 12 V and 0.8A, while the LED drives at a forward voltage of
Udiod = 3.5 V and an Idiode = 25 mA according to the data below. To
get the right voltage across the LED, a voltage divider is used. A
rule of thumb is that the current through the voltage divider is 10
times as large as that which passes over the consumer (LED)


texts: Can this Noise Suppression Filter/ RF Inductor be used in buck/boost converter instead?

texts:
Say I have a buck/boost converter operating at 100Mhz. Would this inductor be a good choice if I needed larger inductance, over other fixed inductors? (considering I do not surpass its current limit)
I am asking this, because I see the label "Noise Suppression Filter/ RF Inductor" in the datasheet and in the mouser buying page
So I do not know if there is any disadvantage using this inductor on buck/boost, over others that are just 'fixed inductors'. I also see that it has greater current capability compared to the simpler 'fixed inductors' I see in mouser.


texts:
As part of a test i was given the following question:

My attempt gave an incorrect answer. The "correct" answer is 1000 ohm but i am having trouble figuring out why. My interpretation; min value is:
$$
R_p = (V_{dd}-V_{OL})/I_{max} = 9.67 ohm
$$
$$
R_p = (3.3-0.4)/0.3 = 9.67 ohm
$$
This will give the fastest rise time but max current, question asks to minimise current so i should aim for the slowest allowable rise time.
$$
T = 1/f = 1/100k = 10us
$$
minimum hold time is the minimum time during a period that the signal must be held high to correctly trigger the logic level. Therefore \$t_2\$ from the graph is:
$$
t_2 = T - t_{hold} = 10us - 300ns = 9.7us
$$
using the value given in the graph for logical high threshold:
$$
V_{IH} = 0.8V_{dd} = 0.8*3.3 = 2.64V
$$
substituting these values into the given equation to find R
$$
v(t) = V_{dd}(1-e^{-t/RC})
$$
$$
2.64 = 3.3(1-e^{-9.7u/R(200p)})
$$
$$
R = 30.13k
$$
closest E24 value being 30k (rounded down as 30.13k is the maximum) This is a great deal different from their answer of 1k, my question is where have i gone wrong? i feel like i have misintepretted the hold time or need to use the \$V_{IL}\$ value somewhere?


texts: Why is an Enhancement P-Channel MOSFET Used?

texts:
I'm trying to design the power circuit for my project. I wanted to implement both USB and a LiPo battery to power it. I came across this circuit online but I'm struggling to understand how it works.

The VBUS is the 5V USB input, and the VBAT the LiPo. What I don't understand is the chosen MOSFET is a P-Channel Enhancement MOSFET which from my understanding means when there is a voltage applied to the gate, only then will it conduct.

However wouldn't you want a P-Channel Depletion MOSFET, as when there is no USB plugged in then you want to conduct to power the circuit? Otherwise wont you just have two power supplies operating at the same time?

Also what is the functionality of the Schottky Barrier Diode in this as well?


texts:
I want to replace a battery, which has a load of LEDs and a temperature sensor, with a super capacitor.

How can I calculate the specifications of the super capacitor?

Thanks!


texts: Which voltage is lower, 0V or -1V for connecting a MOSFET's source terminal?

texts:
In an NMOS transistor the source should always be connected to the lowest voltage. Does this mean that if the source was originally grounded, but then the drain was connected to -1V that the source and drain would flip? This would lead to the source being connected to -1V and the drain connected to 0V. Please correct me if I am wrong, I am not sure my understanding is correct.
Thank you!


texts: Why use an opamp for the variable Q feedback in a Twin-T notch filter?

texts:
In the following circuit, for a Twin-T notch filter, the author is using an additional inverting op-amp for the T-filter "feedback", that is connected to a potentiometer (pot).

Image credit: here

Why are they using this extra opamp instead of just the pot or fixed voltage divider circuit?

UPDATE:

I see there are some good info from the answers of this question:

Twin-T Active Notch Filter Analysis


texts: Multiple DTMF circuit interfaced to one microcontroller, will it work?

texts:
I already tested this circuit with only one modification, I changed the R2 to 300kOhms which worked in my case.

I interfaced this circuit to a microcontroller where they shared a common ground. I successfully read the telephone number of the caller as shown in this figure. Apparently, I received the code number (10 2) and the 7 digit phone number. The frame was encapsulated with byte 0 and byte 15.

Now, I wanted to create a circuit that contains 3 channels for 3 different phone lines which are then to be interfaced into one microcontroller..

If I'm going to share a common ground for them all (3 DTMF circuits and microcontroller circuit), will it work?

On the sidenote, based on the datasheet, the circuit is in single-ended configuration.

EDIT: I added the entire circuit shown below.


texts: Low current divider for battery voltage monitoring

texts:
I’m working on a low power sensor and would like to measure its battery voltage.

The battery voltage is too high my ADC input so I have been dividing it with a pair of 1M resistors and a 100n cap so that the ADC’s input capacitance doesn’t load it too much while sampling and affect the results.

The trouble is that the resistor divider drains a few uA all the time and this is far from ideal. Is there a common solution with a low BOM cost to this problem?

I thought of switching an N channel mosfet to the base of the divider but it would allow the ADC input to float too high. Putting a P channel on the +ve rail would be difficult to drive.

Do special ADCs exist that can measure beyond the +ve supply rail?

Any suggestions welcome.


texts: How to change component values when changing tube B+ voltage

texts:
I'm starting a build a tube headphone amp from diyaudioprojects.com (the simple one: http://diyaudioprojects.com/Solid/12AU7-IRF510-LM317-Headamp/)

The projects uses a 12V supply for the tube plate voltage and states it gets decent result, although it should be run at higher voltages for better results. Considering I will build my own linear power supply for this project, I was thinking about using a higher plate voltage (say 24V, maybe more, depending on how big/expensive the input transformer will get).

Now, I assume some component values need changing, but I'm not clear on what and how to change those. I'm looking at P1, R2, R4...


texts:
I've been working on a circuit to do active noise cancellation, but I'm worried about controlling the phase.  Here are my assumptions, and I'd love some help understanding 1)what of my assumptions are wrong, and 2) what should I/should I not worry about with regards to potential problems (listed below)?

This whole ANC will be mono, to simplify things.

If I feed the output of the microphone directly into an inverting op-amp, I should get exactly (?) \$180^0\$ phase shift.  So if the microphone and the speaker were in the exact same location (and we considered nothing else in the signal path), it should be a "perfect" ANC.  That said, the microphone and the circuit will not be in the exact same place, for calculation sake we'll say they'll be 1 meter apart.  For a very low frequency, like 20hz, that's 1/15000000 of a wavelength, which probably doesn't make much difference.  For a frequency much higher, say 20khz, that's a difference of 1/15000 which is considerably higher, but I don't know if that's high enough to warrant me worrying about it.

If that IS concerning enough that I'll want to worry about it, what approach should I take - do I want to try to impose a uniform phase shift across all frequencies, or do I want a uniform time delay?  I get confused whenever I try to think through it.

Let's complicate the problem further: My speaker (singular, not mega-high-quality) probably can't produce 20hz very well - so I'll want to throw a high-pass filter on the output of the inverting op-amp.  Again, my speaker can't produce 20khz very well, so I'll want to put a low-pass filter on.  Now I've got a band-pass filter, which imposes some weird phase shifts depending on the exact selection of components.  Is THIS a big enough concern that I need to compensate for it?  If so, how do I go about it?

I've been looking at an analog solution, but if digital is easier I'm not opposed to it - I just wanted to try analog since I haven't ever approached a problem like this before.  Thanks for the input!


texts: MM5452 with 4 digit parallel 7-segment LCD display

texts:
I have a question regarding the backplane connection for the MM5452.  From this data sheet:

MM5452/MM5453 Liquid Crystal Display Drivers

It says that the backplane pins on the MM5452 connects to a BP pin on the display.  Here is my display: Varitronix VI-422

I don't see a BP pin.  Are the common pins (Pin 1 and 40) my backplane pins?


texts: Although there are lots of PSRAMs transmitting data at 16-bit bit depth, it seems almost impossible to see a 32-bit PSRAM. Is there any reason for not making such product? (I'm not asking for product recommendation, please do not mention any product No in this thread.)


texts: Would lower current cause a battery to go flat slower?

texts:
So I understand the basics of ohm's law and batteries. The electrons move from the cathode to the anode via the circuit and when the anode and the cathode have the same amount of electrons they stop flowing.

So when it comes to V=IR if the resistance in the circuit is increased the current decreases, so wouldn't this mean that the more resistance in a circuit the longer it would take the battery to become flat?


texts: Why does this current not match my multimeter?

texts:
Newbie to electronics here! I have an Arduino Uno with a 15 Ω resistor connected to the 3.3 V pin, on my multimeter, it gives me 3.2 volts.
If I use this calculator:
https://ohmslawcalculator.com/ohms-law-calculator
And place values of 3.2 volts, and 15 Ω resistance, it tells me that it should be a current of 213 approx.
But when I test this with my multimeter, I get a current of 161ma approx.
Could anyone please explain why this happening, and what I am not calculating correctly?
Thanks.


texts: Measuring small currents over a small sense resistor

texts:
I have been having some difficulty recently when trying to measure very low currents when using a small sense resistor.

I am trying to measure in the range of uA (1 - 150uA) with a supply voltage of 3.3V. Now, usually this is not too much of an issue, but the problem I am getting here is that this particular project uses a WiFi module that peaks at around 600mA.

I am needing to use a small current sense resistor (0.1R) because I just can not afford the voltage drop over higher values at peak current consumption. I tried a few different current sense amplifiers but found them to be not quite accurate enough at these small levels.
I eventually settled for a chopper stabilised amplifier (TLC2652) because even though it wasnt a specific current sense amplifier, it offered my <1uV offset which I thought was great. I set it up as a differential amplifier with a gain of 100 however, it still struggled with accuracy when getting tot he very low current range. Annoyingly, it works perfectly when using a 1R current sense resistor, but as previously mentioned, I cannot afford this voltage drop. With the 0.1R resistor, it is fine untill it gets below round about 20ish uA then it gets a bit noisy.

Does anyone have any suggestions on a good workaround for this to get it to work?

Here is the way I have it set up:

simulate this circuit – Schematic created using CircuitLab

I will say that it is not highly critical for it to be supremely accurate, this is just part of a circuit to do functionality checks, so I am fine with it being a little noisy in these very low currents, however, it does not stop my curiosity and my desire to find a way to solve it!

I hope I have worded my question alright, please let me know if I have missed any information or if there is something I have not explained correctly.

Also, as a side note, I must state I am still learning electronics so apologies if I have done something incorrectly or done something that some more experienced people may find silly!


texts:
When charging a battery I want it to turn off before it charges to the chargers full voltage.

Say the battery is 4.2v normally I want it to stop at 4.1 v say.

Forgetting the charger or whatever sensors or arduino codings and the like  can I make a circuit like a form of voltage doubler that just increases the read voltage by an exact amount .

As a diode will drop the voltage out is there a device or circuit that will increase it?


texts:
This image below is from this TI cookbook.

Please look at the red box.

Question: why large signal can make a conditionally stable system unstable?


texts: op-amp outputs supply voltage on GND Signal

texts:
I am trying to use an op-amp (first time).
I know the basic theory of its amplification circuits.
To test I am using an Arduino Nano Microcontroller to create a Signal (0-5V). I want to amplify the signal by a Factor of 3. I measured the input and the output of the opamp relative to GND with an oscilloscope.
The amplification works (5V to 15V --> factor 3), however when the signal goes to ground the opamp always reaches the supply voltage (tried with different supply voltages).

I know that an op amp amplifies to the supply voltage if there is no feedback, but i cannot explain how it can happen in my case.
How do I prevent the opamp from switching to supply voltage once the signal raches GND?

EDIT: The Op-Amp is a MC33078 (datasheet)


texts:
I wanted to perform AC analysis for a buck boost converter using SIMetrix/SIMPLIS for simulation,  using this simulator the designer does not need to the average model to get the frequency response of that SMPS, but one can use direclty the switching model. Based on that I have built the circuit below for simulation of a buck-boost converter with the following specifications:

Vin=10 to 15v.
Vout=12v,
Iout=2A max (maximum output current)
Fsw=100kHz (Switching frequency).
Crossover frequency at 5kHz
A double zero at 600Hrz
A pole à 7kHz
A pole at 50kHz

I set the maximum current through the inductor to be 7A to reset the switching at start up, it is used to set the maximum duty cycle, in this case 90% (This current is chose to be (Vin/L)x(Tswx90%)).
-My first question is: How do I chose this current and the sense resistor that will limit the current at startup ?
-What is the effect of this current limiter on the frequency response of the model?
When I simulate the model, I got the following transient response of the different probed points:

If we focus on the transient response graph, we notice that something goes wrong Vout, because the settling of different currents and output voltage is not smooth.
The Verr graph,which is the output of the Type3 compensator shows that its output is oscillating around 0.5v and it does not saturates, but it saturates at start up.
To troubleshoot my circuit, I looked to the frequency response of each bloc.
- Power Stage Frequency Response without the duty ration generator:

It seems to be good and I got the same thing from MATLAB.
- The Type 3 Frequency Response:

The frequency response is perfect which means the  model of Type 3 compensator is correct.
- Frequency response of duty cycle modulator (encyrcled in blue in the circuit above)

Here is the problem, when this gain and phase are added to the power stage, I do not get a nice frequency response of the whole power stage. Because mathematically speaking, this part of circuit is included in the power stage model (transfer function)
What have tried to build another model using voltage controlled current source but I field.
Could anyone explain to me what is this phenomenon and how can I build a modulator without a gain and phase distortion ??


texts:
My device is powered at 12V and I have some components which need 5.5V power supply. In order to drop the voltage I have used a step down switcher (figure 13 of datasheet). That circuit works very good but as soon as I plug a load at Vout, the tensions drops of severals hundreds of mV.

Do you thing it is a good idea to decouple this step down circuit from the load using an ampli op with unitary gain? If yes do you know some example of alpi op which would do the job? Pretty much all those I have found so far (such as datasheet, note 3) have low output currents. I might need them to support currents as high as 3A (extremely worse scenario).


texts:
I want to measure a motor's load by it's current draw using Arduino, so I made this diagram:

The Motor is controlled by a L298 H-bridge.

My questions are :

The motor's rotation can be reversed, so the voltage on resistor R5 can be reversed, how the LM358 to deal with this? how to modify the diagram to implement this?
Is there any other errors on the diagram? Any suggestions are appreciated.


texts:
I started electronics recently and I'm trying to make the most basic mp3 amplifier. First I tried to make the amp myself with reused electronic parts but I didn't succeed... Amplify speaker with 9v battery and one transistor. Do you have any recommendations about it ?

So I decided to use a LM386 because it's easier. I found a module which integrates de LM386 on dx.com for 3$. This one http://www.hamgadgets.com/LM386-AMP-MOD. But I guess I can make it myself for less and probably better/stronger.

It worked pretty well with the 9v battery if I set the gain to 50%. I read it provides up to 0.3w of audio power so it uses 0.3w/9v = 0.033a max ?

On the module it says 5 to 12v and I read that a battery provide the amps depending on the voltage and the resistance. But then I decided to try connecting it to an outlet. I retrieved an old transformer : 9V - 300mA - 2.7w. The LM386 chip on the module fastly became very hot so I disconnected it. When I tried again with the 9V battery, the led still lighted up but the sound didn't pass through.

I know home current is AC and a battery is DC but I don't fully understand it. The AC current works on cycles (is it up only during short periods ?) and DC is a horizontal straight line (in a graph). Doesn't AC provides the amperage like a battery and the 300mA value is the maximum amperage ? Why did my circuit burn ?


texts: Practical current limit for TO-220 package

texts:
I see a lot of MOSFET transistors with suprisingly high continuos currents in TO-220 packages. To make matters more magic open ressistance is very low.
For example I want to use IRFB7545PbF N-MOSFET transistor. In datasheet, there's stated that maximum continuos current is 67A and RdON is lower than 5,9mOhm.
I don't believe, that this is possible.
Tiny legs of TO-220 package will have far bigger resistance that few mOhms at this conditions, it'll heat up and unsolder.

Where am I wrong?

I believe that semicunductor inside is capable of such currents, but I don't believe, that TO-220 package can deliver...


texts: Given desired overshoot graphically find k from the root locus (Scilab)

texts:
I want to find \$k_1\$ that leads to the feedbakc system having poles in the 53º line (to have overshoot \$\leq 10\%\$). From the root locus, the poles move along the vertical asymptote centered on -1. How can I find \$k_1\$ using Scilab and how can I draw diagonal lines representing the 53º line in which I want my poles to be at?

So far, I made this graph in Scilab,

Code:

s=%s;
num=2;
den=s*(s+2)
t=syslin('c',num/den);
clf;
evans(t);
mtlb_axis([-10 10 -2 2]);

Obtained graph:

Desired graph:


texts: Transistor is getting hot on low duty pwm cycle

texts: I have a circuit which is used to control dc motor. PWM is configured to work with 10 kHz frequency. Each time when the duty cycle is set to 100%, the transitor is rather cold, but any other configurations like duty cycle set to e.g. 80% makes transistor very hot. I'm wondering is it something usual and using radiator will be enough to dispate heat? Or maybe I'm doing something wrong?


texts: Deciphering Thin Copper and Fabric Wires in Cable

texts:
I'm planning on connecting a Nintendo Wii Classic controller directly to IC2 input on a RP2 board.

The controller I'd like to use is a Black Wii Classic Controller.

Here's some photos of the Controller cable. I need to figure out which of the smaller cables will need to be connected.

http://i.imgur.com/2sZci14.jpg

http://i.imgur.com/uSXGl7x.jpg

Which of the above cables will need to be utilized? I'm not sure what the thin (copper?) wires surrounding the coloured cables are for, or the central copper wire. My guess is it's a ground connection and the thin wires are for protection.  Also not sure about the fabric wire (it's either nylon or polyester).

I'll probably have to open up the controller to see what the Red, White, Yellow, and Green cable control. I don't have the controller in front of me ATM but I don't recall if it has screws on the body so I'll have to try to pry it open carefully.

If anyone can give me a hand in identifying these wires that would be a big help.When I connect the colored cables can I just cut off the thin copper wires? What about the central copper wire and the fabric?


texts: Help identify "0GSV" or "OGSV" SMD Integrated Circuit

texts: This IC is part of a malfunctioning LCD LED backlight control circuit built around the D60A60. Maybe it's a voltage regulator? Couldn't find after many tries. The marking is either OGSV or 0GSV.


texts: I am designing  a power system and I have to use a stepdown trafo to change the voltage from 380 kV to 110 kV.  I want to know  what is the rated power in the trafo 'Sn'. How can I know that ?


texts: What are the advantages of including mounting holes in a schematic?

texts:
I've seen some designs which have mounting hole included in the schematic. Are there any good reasons of doing that?

I can see one advantage of doing so when you want to connect your mounting holes to some nets (e.g. GND). But what if the holes aren't supposed to be connected to any net?


texts: Find an amplifier voltage output to match my subwoofer rating

texts:
I have two amplifiers with a subwoofer connected to each one and I was wondering how to check what the output wattage to make sure I don't blow my subs.  Since they are two exact same pairs, I'll just use one for the example and do the same for both when I get an answer.
My amplifier is a SSL EVO4000.1 which can output 750W RMS @ 4 Ohm
My sub is a Psi  with 750W RMS DVC(Dual Voice Coil) and 2 ohm option. The voice coils are connected in series for 750W RMS @ 4 Ohm
Thing is, I have no idea how to make sure I don't blow either of them. So I was hoping there's a way to check the output of the amplifier with my meter and convert it to know the wattage output.
EDIT: If anyone can help but need more details about anything (that is not in the products page) just tell me in comments, I'll do my best to find the infos.


texts:
I'm reading a relay's datasheet from OMRON, it mentioned this

I haven't got the relay yet. So, what does 'charged terminals' mean?
I guess the shaded area may be where the coils located.
I think it mean the copper on all layers, which facing the shadow (not only the copper on the same layer with relay) should be removed, right?


texts:
I am trying to write a 1 bit shift register with this code

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

entity simple_one_bit_serial_shift_register is
   port(
      clk      : in  std_logic;
      reset      : in  std_logic;
      shiftin : in std_logic;
      shiftout : out std_logic_vector(1 downto 0)
      );

end simple_one_bit_serial_shift_register;

architecture simple_one_bit_serial_shift_register_behavior of simple_one_bit_serial_shift_register is

    signal shiftreg : std_logic_vector(31 downto 0);

begin
process (clk,reset)
    begin
        if rising_edge(clk) then
            shiftreg <= shiftreg(30 downto 0) & shiftin;
        end if;
end process;
shiftout <= shiftreg(31);
end simple_one_bit_serial_shift_register_behavior;

but when simulating I get the errors

ERROR: [VRFC 10-925] indexed name is not a std_logic_vector [C:/Users/Darren/Desktop/project_6_1_3/project_6_1_3.srcs/sources_1/new/1Bit_delay_register.vhd:28]

but they both are vectors and I cant seem to find much on this problem

Edit : Testbench

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

Entity one_bit_shift_tb is
end one_bit_shift_tb;

architecture behaviour of one_bit_shift_tb is
    component simple_one_bit_serial_shift_register
   port(
          clk      : in  std_logic;
          shiftin : in std_logic;
          shiftout : out std_logic
          );
    end component;

    signal clk: STD_LOGIC;
    signal shiftreg : std_logic_vector(31 downto 0);
    signal shiftin : std_logic;
    signal shiftout : std_logic;

begin
    u_shifter: simple_one_bit_serial_shift_register
    port map (clk =>clk, shiftin => shiftin, shiftout => shiftout);
    process
    begin
        clk <='0';
        wait for 5 ns;
        clk <='1';
        wait for 5 ns;
    end process;
    process
    begin
        shiftin <='0';
        wait for 50 ns;
        shiftin <='1';
        wait for 50 ns;
        shiftin <='0';
        wait for 50 ns;
        shiftin <= '1';
        wait;
    end process;
end behaviour;


texts: Designing a 4-bit ALU to compute various functions

texts: I've been working on designing an ALU that calculates various functions but I don't really know how to separate each function from one another.  The inputs are 4-bit numbers A and B.  I have a decoder that selects which function to use, but I don't know how to implement the functions from the decoder.  The ALU needs to do arithmetic operations and also logical operations.  If anyone knows how to go about structuring an ALU that has 2 4-bit inputs and 1 4-bit output, any guidance would be appreciated.  Thanks.


texts: PIC12F ADC conversion has an unwanted offset

texts:
The current setup is shown below. PIC12F1822 with a 10-bit ADC.

I'm using a 250R 0.05% precision resistor to get a nice 0-5V input to the analogue pin (AN2 if it matters). As far as I can tell I have the software side of things correct but I'll show the relevant parts of the code at the bottom.

I'm pushing the conversion results (ADRESH and ADRESL) straight to the SPI SDO pin which I know is correctly functioning.

The issue is that for a 0mA input (both input terminals grounded) I get an output of 00 0011 0011 (51 dec). With my current source connected and set as low as possible - about 34.6mV across the resistor - I get a result of 00 0011 1010 (58 dec). A value of 58 decimal should correspond to an input voltage of 0.283V giving quite a large

I'm struggling to see why there is an offset of around 5.6%. Is the internal setup a potential cause?

It is configured to use Vdd and Vss as the reference voltages, have conversion clock of Fosc/2 (250kHz) and the ADC module is switched on during a start-up routine.

Relevant code:

ADC_CONV
            banksel     ADCDATAH
            clrf        ADCDATAH
            banksel     ADCDATAL
            clrf        ADCDATAL
            banksel     ADCON0                  ;
            bsf         ADCON0,ADGO             ;Set ADGO conversion start bit
CONVTEST    clrwdt                              ;Clear Watchdog Timer
            call        DELAY                   ;Short delay
            btfsc       ADCON0,ADGO             ;If conversion finished skip next instr
            goto        CONVTEST                ;Conversion not yet finished
            call        DELAY
            banksel     ADRESH                  ;
            movf        ADRESH,0                ;Move the upper bits of conversion to W
            banksel     ADCDATAH
            movwf       ADCDATAH                ;W to ADCDATAH
            banksel     ADRESL                  ;
            movf        ADRESL,0                ;Move the lower bits of conversion to W
            banksel     ADCDATAL
            movwf       ADCDATAL                ;W to ADCDATAL
            return

SPI_ADC_TRANSMIT
            banksel     PORTA
            bcf         CS                      ;Select DAC slave to receive data (16 bits)
            banksel     ADCDATAH
            movf        ADCDATAH,0              ;Move SPIDATAH data to W
            banksel     SSP1BUF
            movwf       SSP1BUF                 ;W to SSP1BUF
            call        DELAY                   ;Call delay (must be >8 inst cycles)
;
            banksel     ADCDATAL
            movf        ADCDATAL,0              ;Move SPIDATAL data to W
            banksel     SSP1BUF
            movwf       SSP1BUF
            call        DELAY
            banksel     PORTA
            bsf         CS
            return

Should I only be turning the ADC module on when performing a conversion? Its only purpose is as an ADC so I didn't see any point in switching it off seeing as power usage isn't an issue.


texts: How does ISP cut the customer's internet access technically?

texts:
We know that if we fail to pay our internet bill then our internet access will be cut. But how does the ISP technically cut the access?
For wired internet, do they just shut down the port where the other end of the customer router is connected to? If yes, then that must be automated -- but how do they automate that? What is the technology or protocol behind it?
But what about wireless internet, especially prepaid sim card? When you top up your prepaid sim how does it get access technically and when the credit expires how does it get cut technically? Is it somewhat similar to wifi voucher? What is the technology behind prepaid sim top up?
In what layer do they cut the access? Layer 1? Layer 2? Application layer?


texts: Calculating the self resonance frequency of coil

texts:
If I have a coil of diameter D (in mm), using wire that is d mm in diameter, having N turns over a total height of L mm, assuming that it is just a single layer, and has an air core, is it possible to calculate what the self resonance frequency should be (approximately) of such a coil?  If so, what would the formula for the frequency be?  If not, what additional information needs to be known?

To dispel any concerns about doing someone's homework for them in advance, be assured that this is not a homework question.  I'm just curious how this kind of thing can be calculated.  Thanks.

So... for clarification purposes I have the following parameters:

1) Diameter of the coil (D) in mm
2) Diameter of the wire (d) in mm
3) Overall height of the coil (L) in mm
4) Number of turns (N)

I also know the material in the conductor of the wire, although I do not think that would be relevant to solving the problem unless the material was not a good conductor.

One thing we categorically cannot assume is that I will have any way to measure any properties of the coil with tools such as a meter or scope... I am asking how to calculate this on paper only.


texts:
Suppose I have a simple RL-circuit with known resistance R and, inductance L with a voltage source where I can apply any input voltage (via an arbitrary waveform generator).
What I want now is a specific shaped current through the coil (I need the b-field), for example the convolution of a rectangle signal with a cosine (i.e. half cycle of a cosine). What voltage do I have to apply to get the desired current through the coil.

I'm pretty sure it is possible to calculate it with the response function and several Fourier-transformations, but I'm unfortunately not an expert in this area.


texts: How to model Nernst equation for numeric solution?

texts:
I want to write a program (this is not programming question!!) that numerically solves voltage across virtual battery-resistor circuit over time. But sometimes explanations is too overcomplicated, not using simple terms. This approach favors short length, but slowers understanding alot (requires years practicing math, to get clear vision of "what is going on", just seeing math notation). Let me please explain on example that I can understand.

For a RC cirtuit, its very easy. When solving ODE numerically you have some bunch of changing values, measured at fixed snapshots of time t. To know voltage you may do V(t) = V(t-1) + dV(t-1)*dT. That is a main calculus loop of a solution program. You know V(t-1), dT is fixed. And dV(t) = -V(t)/RC. So far so good, this resource is a bad explanation example. Because solver does not require exp, it arises from solution. It does not require integral, so on.. No simple formula dv/dt = .... At least they have graph (reversed, for charging) from where you may get simple intuition:
Now I want to simulate chemical battery (accumulator), google said I need Nernst equation. But wiki guys again start with Ox,  arrows ->, kind of some other fancy symbols, that should occasionally get to Red?.. Oh, I was just about writing a sim program within 5 minutes, but they dont get answer. All that I want is "to simulate it in digital ODE solver do this equation, where parameters are..". So, finally, my question is - can you help me to rephrase in simple words? Or how to calculate dV(t)=? for a battery?
PS. A battery starts at t=0, with known V(0) = V0, conneted to resistance R again, so on.. and i want kind of simple model that would draw me something like


texts: Linear vs Logarithmic Potentiometer for Meter-Sensitivity

texts: Why would a linear-taper potentiometer be used in a meter-sensitivity control in a test instrument over a logarithmic-taper potentiometer?


texts: Best practice for documenting ports / peripherals?

texts:
I've recently taken an interest in embedded development and am wondering how most people document their projects. For example:

  Each pin on PORTE is wired to an LED and is aliased as LEDPORT.
  Methods related to the LED functionality is located in led.h.
  Timer/Counter 0 on PORTC controls the blink rate of the LEDS.

etc.

I can certainly use a bullet list like this while the project is small, but I have a feeling that it will become unwieldy as the project grows into something more complex. How is this typically done? Is there a preferred format for this kind of documentation in the professional embedded development world?

After receiving some feedback, I'm thinking of something like this, does it seem reasonable?

|Port|Pin|Peripheral|Desc
|----|---|----------|----
|E   |0  |Led0      |
|E   |1  |Led1      |
|... |...|...       |
|C   |0  |Timer     |Controls the Led blink rate


texts:
We are designing a circuit which should be powered directly from mains (230VAC), and have in the previous design used a normal transformer.

But in the next design we would like to use an AC-DC converter, since this could make our design more flexible with possible input of 120VAC to 230VAC 50/60Hz.

The output of the converter is preferred to be 5VDC but could be higher.

I have found the bp5048-15 from ROHM, which would do the job.

www.rohm.com/products/databook/pm/pdf/bp5048-15.pdf

Does anyone have a better or cheaper solution?

EDIT: wall adaptor is not an option, we need to supply the product directly with mains.


texts: Where the ICM20948 DMP memory is stored?

texts:
In Invensense ICM20948 motion sensor
they mention

The DMP in ICM-20948, therefore, has higher memory for code storage
Hence, the AP/MCU must accommodate higher memory required to hold the DMP image
AP/MCU must be able to store more code to accommodate expanded DMP code size. However, if Application does not use DMP functions, then this code size can be avoided.

DMP code size 16kB

Does it means if Arduino nano is used to get data from this sensor, and DMP is being used, Arduino nano has to store memory 16kB extra related to DMP of ICM20948 sensor?


texts: Is it safe to connect two MCU pins directly to each other?

texts:
I am working on an MSP430 project that requires me to route the output of one peripheral into the input of another peripheral. Thus, I have two MCU pins connected directly to each other. This looks suspicious to me since there is the possibility of a programming error causing both to be (possibly conflicting) outputs. Also, there is the issue of startup and programming states.

In the worst case, if one pin is driving HI, the other is driving LO, the GPIO pins generally have way more sink capability than source capability... so it'll be somewhat like taking a HI output and shorting it to near-ground. Which is bad... but how bad is it? Is it likely to cause damage to the MCU?

I often see examples on the web of people using Arduinos to light an LED between two pins without a resistor, and I haven't heard of any stories of anyone frying anything but the LED. Clearly you wouldn't want to do this in a product, but do manufacturers generally try to protect the MCU from GPIO pins being overloaded anyway?

Thinking about it in retrospect, putting a current-limiting resistor between the two pins would have prevented any worries, but even a minor hardware change is a very difficult thing to do at this point.

For future reference and the benefit of posterity, does anyone have any other ideas about the proper way of minimizing the risks of connecting two MCU pins together, and more generally, minimizing the risks that come from the possibility of overloading a GPIO pin?


texts: Switching USB data lines with SSR doable?

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I have a computer and raspberry and I want to share my USB HardDrive to both and control the direction from raspberry.

I think it's possible to that with SSR (Solid State Relay) ? If a use 4 channels SSR for both (data+ / data-) ? HardDrive GND/VCC powered from Raspberry.

I tought that because is only way I know, but this can working great ?

SSR model : http://p.luckyretail.com/Uploadfile/20160721/073211/073211.jpg


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I've been given 12 arduinos (Mega) and 12 breakout boards (custom built. they pump up the output of the digital pins to 12v @120mA) to control around 300 LEDs. I'm using a pseudo PWM library to fade the LEDs.

This could have been achieved with a much, much cheaper setup. Open to suggestions, but time is of the essence.

My quandary is getting all these micro controllers synced. I've never been involved in a project where timing was so significant; I would usually use the TX/RX serial pins to just relay commands out, but I'd sleep better at night if there was some kind of heartbeat from a master to 11 slaves. Is I2C the way to go in this case, or do I look at alternatives?

tl;dr
Whats the best way to keep 12 arduinos in sync?


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Is it possible to format an SPI EEPROM (such as AT24C128) to be used as an SD card?
So format it with FAT 32 and have a 16MB drive appear in windows?

Thanks


texts: Write to multiple I2C devices at the same time

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I have two OV5640 images sensors that I need to configure using I2C. Both have the same I2C address and are on the same I2C bus and both will be configured identically.

As the configuration profiles for these cameras are quite large, I was wondering if it would be possible to write the configuration from the MCU to both cameras at the same time? I do not need to read from the cameras via I2C.

The OV cameras use the SCCB interface, which is similar to I2C but with some slight differences (I think the main one being the lack of the ACK signal).

I am almost certain the answer is "no" but I would like to understand why.


texts: What exactly IS voltage and its difference to other measurements of electricity?

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I apologize if this is a stupid question, but I cannot find any answers online, so I feel I must ask here.

I do not quite understand exactly what voltage is. I see on batteries, "X Volts", but I do not quite know what that means. I looked online and read sources on volts, amperes, and watts, and it has only confused me more. What exactly is voltage? If it isn't a measure of the electric current, then why is it used on batteries as a measure of their electric power? Why aren't amperes used?


texts:
In an NMOS, does current flow from source to drain or vice-versa?

This Wikipedia page is confusing me: http://en.wikipedia.org/wiki/MOSFET

The above image confuses me.  For the N-channel, it shows the diode's polarity going towards source in some, but away from the source in others.

I'm wondering which terminal should be connected to the power source (i.e. the positive battery terminal) and which should be connected to the power user (i.e. electric motor).


texts:
I am designing a buck boost converter with a 12v output, and 50A current output.
The input range is 8v-14v from a supercapacitor. However based on the Texas Instrument buck boost design sheet Basic Calculation of an Inverting Buck-Boost Power Stage that the average inductor current formula is

The max duty cycle is 58 % which will make the average current of the inductor to be 120 A.
Do I need to find an inductor with rated current of 120A?


texts:
I have problem with solving this rlc circuit, which we should detemine i for t>0.
I have written kvl law and got this equations:`

0.04i'' + 1.21 i' + 4i = -50
which has this characterstic equation:
0.04s^2  + 30.25s + 100 = 0

s = -3.7, s= -26.4.

Are these equations correct?
Unfortunately the solution only has the final answer which is different than mine. I'm currently self-studying so i couldn't ask anywhere else. would you please solve this circuit and determine i?

`


texts: How does the frequency increase and decrease in a FM transmitter circuit?

texts: i still dont understand how fm transmitter circuit works, from what i understand the transistor acts like a switch or a valve when the output voltage increases and decreases wont it affect the amplitude of the wave? And whats the use of C2?. I saw some fm signal images i dont understand how it increase and decrease the frequency by controlling the voltage!


texts: What is the benefit of driving the HV5622 chip to the recommended operating voltage?

texts: I am a beginner in electronics. I want to use HV5622 serial-to-parallel converter to drive nixie tubes. However, there are two types of datasheets: Recommended condition and absolute maximum ratings. I want to operate the chip with 5VDC like this. However, for recommended operating conditions, the Vdd voltage is shown as 10.8V to 13.2V. What is the benefit of driving the chip to the recommended operating voltage? What are the limitations of driving a chip with a voltage outside the recommended operating voltage (for example, 5V)?