Search results

Search Forums New Posts
  1. duke37

    Need help for building a noise filter

    You already have a low pass filter with the electrolytic capacitors. These are not too good at high frequencies but can be paralleled with something like 10nF to deal with high frequencies. Any low pass filter should have cut off well below the troublesome frequency, say 10kHz, there will then...
  2. duke37

    what is bleeder current? n how to find it out?

    I get 1.96mA through R2. I obtained this by first calculating the output voltage. It would then seem that the bleeder current is the wasted current through R2
  3. duke37

    Varistor+Diodes as transient suppressor

    The relay will take 6A and this will be passed by the diodes for a little while when the fet turns off. What is the rating of the diodes? I presume that two are used because one cannot pass sufficient current. How many times/sec do the diodes have to pass these pulses?
  4. duke37

    Temperature Sensor help

    The LM135 gives an output depending on its temperature. It does not need to be electrically connected to the human body and in fact any such connection could pick up electrical noise and give a faulty reading. To measure the temperature accurately you will need to sleeve the LM135 and press it...
  5. duke37

    Temperature Sensor help

    The output of the sensors is 10mV/degC, your amplifier has a gain of 10 so you now have 0.1V/degC, is this better for your display? If you use a gain of 100 then you will get 1V/degC, a voltmeter with a range of +/-10V will then show the temperature directly with the decimal point in the right...
  6. duke37

    Temperature Sensor help

    That looks like it will work. The meter is connected in a differential way, that is, it is measuring the voltage between the two sensors. The sensors give 10mV/degC and the meter should be capable of showing this as a sensible number, if it is not sensitive enough, then an amplifier should be...
  7. duke37

    Temperature Sensor help

    I have looked up the data for the LM35 and LM335. It appears that they give an output of 10mV/degC so if you want a range of 10deg, you will need a meter to measure the resulting 0.1V, connected as in your diagram #1. If you can measure the 0.1V then you will not need an amplifier.
  8. duke37

    Temperature Sensor help

    Thermocouples produce a voltage between a cold and hot junction. A chromel/alumel junction will produce 41μV/degC. If you can measure this, you will not need amplification. I do not understand what you mean by what circuit would be after amplification, you will get a voltage to deal with as you...
  9. duke37

    Variable resistor question

    Wikipedia has a page on reactance but I will try to explain a little. Resistance - R A resistor needs a voltage across it in order for it to pass current either AC or DC. Ohms law describes this V = I * R. Reactance - Xc and Xl A capacitor will pass AC current but not DC. The equation is...
  10. duke37

    Temperature Sensor help

    The meter in your circuit is connected in a differential way. This is where a differential amplifier should be connected if you wish to provide an output referenced to ground. Two thermocouples connected back to back will provide a differential output but may need considerable amplification to...
  11. duke37

    Variable resistor question

    When connected to AC, a capacitor will pass current. This is out of phase with the applied voltage and the energy going into the capacitor is returned to the supply so no net power is consumed. The current level is determined by the reactance (see #14) and the voltage across it. In your case...
  12. duke37

    making a tiny heat element

    Hot copper will oxidise so will not be suitable for repeated use.
  13. duke37

    making a tiny heat element

    You will want a thin wire, try a stainless violin E string or a steel wire from a geetah. You could use a copper wire which would be easy to solder. Getting the size right would cut the nylon and then fuse to turn off the battery.
  14. duke37

    Variable resistor question

    The capacitor will need to be sized to pass the correct current I suggested that you measure the current required and you seemed to understand this. The reactance is 1/(2*pi*f*C). The capacitor should be of the type (X or Y?) intended to be connected across the mains so that if it fails, it...
  15. duke37

    Variable resistor question

    The size of the resistor will not affect the heat generated but a bigger resistor will run cooler. The current into the motor can be controlled with a capacitor in one of the mains supply lines. The motor will not be isolated so if not insulated properly there will be risk of shock. The...
  16. duke37

    Question for site manager

    If you do not like what I write, just ignore me, I get very grouchy on times. If someone says you are wrong, find out why and take it in good part. Everyone I have dealt with here has been most considerate and helpful and the knowledge base is exceptionally good. I trust you will have a happy time.
  17. duke37

    Wireless lightbulb from Tesla coil

    A fluorescent tube contains low pressure gas which emits radiation when it is ionised. This radiation then activates the fluorescent coating. You do not need to connect to the tube terminals, it is only necessary to put the tube into a strong enough field to ionise the gas. The Tesla coil will...
  18. duke37

    Variable resistor question

    Sorry about the typo, Kris is right as always. I should have put 30V not 35V. This is the maximum voltage which should be across the pot when it is at full resistance. You can use it at higher voltages as long as the rest of the voltage is dropped across the load. The current is the critical...
  19. duke37

    Variable resistor question

    The 'pot' will be made of resistance wire which can stand 0.845A before being damaged. The voltage across the pot will be determined by how much of the wire is in action. Thus the voltage will be near zero when little wire is used and 35V when all the wire is used (at 0.845A). The maximum power...
  20. duke37

    Current detection

    Is this correct? I thought more turns will give more voltage and less current?
Top