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Hero999

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Posts posted by Hero999

  1. force limit a motor

    in Theory articles

    Posted

    It's fairly straightforward with a DC motor or AC motor. The motor's impedance reduces (therefore drawing more current) as the mechanical load increases. A current limit could be used to restrict the torque or detect the shaft being jammed.

    I don't know about a stepper motor. I think using a DC or AC motor with an encoder, forming a servo system, is the best route to take. It's also possible to measure the back EMF from a DC motor or synchronous AC motor to monitor the speed so an encoder won't be necessary for speed regulation, unless you need to know the exact position of the shaft.

  3. Full sound bar schmatic/BOM

    in Electronic Projects Design/Ideas

    Posted

    If you want to attach a file, please upload it here, rather than over there.

    Don't worry too much about viruses, audioguru. Opening a zip file is a fairly low risk activity, far safer than installing software or even viewing a Word document. Even if it does contain a virus which isn't detected by your security software, it's unlikely to run unless you tell it to, i.e. you open the zip file and load an .exe file stored within the .zip.

    I'll do the following myself, when I have the time:

    • Download the .zip
    • Check it really does have a .zip extension and isn't executable i.e. it isn't really files.zip.exe
    • Scan it with antivirus software.
    • Open it with 7-zip.
    • Check that none of the files are executable before extracting the files.
    • Scan the extracted files with anti-virus software, just in case the scannercouldn't read the zip.


    Following those steps will greatly reduce the risk of viruses.

    If all is good, I'll attach the file here.

  5. Personal Project With Lights & Settings

    in Electronic Projects Design/Ideas

    Posted


    It's actually reServe energy, because normally when you "tab" on a light switch, you would see the light illuminate for as long as you "poke" (press for 1 sec, and you'll see 1 sec of light). But I need it to flash for 4 secs with just 1 sec of poking the switch.

    Oh I misread it.

    What  mean I mean is why do you need to store energy?

    The 12V battery is still there right? All that  needs to be done is not switch the light directly. The light could be connected via the control system (microcontroller and transistor/relays) which is permanently connected to the battery. The control system would then be programmed to respond to the switch's status.

  6. Adding led brake lights

    in Electronic Projects Design/Ideas

    Posted

    Forgive me for butting in, I've not had time to read the entire thread.

    I notice there are lots of LEDs connected in parallel; why? It's more efficient to connect them as three strings of five or even five of three.

    If all this does is buffer the PWM signal then why use an op-amp IC? A comparator such as the LM311 or LM393 would be a far better option.

  7. Personal Project With Lights & Settings

    in Electronic Projects Design/Ideas

    Posted

    What do you mean by reverse energy?

    It can be done with a simple microcontroller, which is basically a very simple computer on a single chip, that can be programmed to do a variety of different tasks. There are other ways of doing it with logic gates, transistors and relays but by the time you've done that, you might as well have invested the time and money in learning about microcontrollers.

  11. What is the function of this circuit?

    in Theory articles

    Posted

    That circuit is wrong, the transistor is configured as an emitter follower with no gain so there'll be no oscillation. Here's a link to the correct version, with a better explanation:
    http://users.silenceisdefeat.net/~lgtngstk/Sites/Circuits/Buzzer/Buzzer.html

    It can be made louder by replacing the collector resistor with an inductor:
    http://homemadecircuitsandschematics.blogspot.co.uk/2011/12/how-to-make-simple-piezo-buzzer-circuit.html


  13. help with circuit simulation

    in Spice Simulation - PCB design

    Posted

    You haven't been provided with enough information to answer the question: without knowing the line frequency, it's not possible to solve the problem.

    You need to break the loads down into their inductive, reactive and resistive components:

    To calculate the resistance of the lighting circuit just use Ohm's law.

    You can calculate the capacitor's value using Ohm's law to get the reactance and transposing the formula for the impedance.

    The resistance and inductance of the motor can be found by transposing the power factor formula, to get the resistive and reactive components, then transposing the impedance formula to give the inductance.

    All of the above requires the line frequency, which is unknown.

  16. Current through a coil in a DC circuit

    in Electronic Projects Design/Ideas

    Posted

    Another way would be to derive the current by the number of turns of the coil. Deriving the current by the resistance is not possible you guys say? due to the AC current. I have a spare motherboar with the same coil that i can unsolder. I can use it to measure the characteristics if needed.

    But I thought you were talking about DC current?

    Deriving the DC current is easy: you need to know the resistance and voltage and use Ohm's law.

    Calculating the AC current is also not difficult but you need to know the inductance too.

    The only option I have is to use a Hall Effect sensor I think, but thats my last solution because i have to place it inside a computer. THere is a great chance that interference will occur.

    A Hall effect sensor will work but for AC it'll need to work up to the frequency being measured.

    But why do it the hard way? It's DC so measure the resistance of the coil, the voltage across it and calculate the current.

  17. Choosing a Mosfet to switch an Electric Match

    in Electronic Projects Design/Ideas

    Posted


    Hi Guys,

    I have a couple of questions but I know you might be busy, I would appreciate ANY answer even for 1 question.  :-*

    I have a situation where I would like to switch an electric match. The typical trigger power for such a device is 12v 800mA - 1A. I have three questions for this.

    1. I was told that Mosfets are better than Transistors for this situation. Why? Is this true?

    http://www.google.co.uk/search?client=opera&rls=en-GB&q=MOSFET+BJT+advantages+disadvantages&sourceid=opera&ie=utf-8&oe=utf-8&channel=suggest


    2. I need to choose a Mosfet which is fast and reliable. I need it to turn on fast but its only going to turn on once in an hour's time, and its only going to be used for a few mS until the match is lit.

    Going from your previous posts, you need a logic level MOSFET.


    3. Lets say I connect 12V DIRECTLY to Drain/Collector, and Ground DIRECTLY to Source/Emitter and when I switch the Gate/Base an 'infinite' amount of current passes to the match however it takes mS to burn and once it burns the current flow is not possible anymore. Would you recommend such a design? I calculated that to put a resistor to limit the current to 1A, it needs to be at least 12W which is huge and expensive. I need to switch around 300 of these... imagine having 300 resistors of 12W each ...  :-\ Any other Ideas?

    You don't need a 12W resistor, as the power dissipation will only 12W for a few ms, a lower power resistor (try 1W or 2W) will be fine as the power won't be applied for long enough to overheat the resistor.

    With no resistor to limit the current, all of the power will be dissipated in the transistor which will have a lower resistance than 12R so will dissipate much more power, possibly enough to overheat it.
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