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  1. duke37

    How to increase range of IR Emitter

    I was just commenting on the limits of distance which could be obtained. I have not studied the effect of reflection but much work has been done on reflection of radio waves from the moon, it can be done with a high gain aerial for transmission and reflection. To measure distance using...
  2. duke37

    Electromagnetic Quiz Confusion.

    I use lots of microwaves to cook my dinner, perhaps that was what the questioner was thinking.
  3. duke37

    How to increase range of IR Emitter

    To increase distance, you will need to concentrate the light in one direction. You can use a parabolic mirror or a Frenel lens. The mirror can come out of a torch and the lens can be bought cheaply. Using a lens at each end and coded signals, distances of several km have been obtained.
  4. duke37

    Led's to be programmed for Swiss locos

    A 1N4007 should be plenty good enough but if it is leaking, then it has been zapped. The train can produce high inductive voltages. A pair of Zener diodes, about 20 or 30V back to back across the input would trim the pulses. Do you control speed with pulse width modulation? If so, an...
  5. duke37

    Car batteries in // with charge controller

    Say you have a voltage difference between the batteries and a 1k resistance, that means 1mA of current which will be less than the self discharge of the battery so the voltage drops. You could connect the two batteries in parallel, depending of what you want. An inverter to add a couple of...
  6. duke37

    micro seconds

    It could help if you spaced the numbers in groups of three so 40μs = 0.000 040 40ms = 0.040
  7. duke37

    Need professionally made circuits to control heaters using PWM and MOSFET

    Since the heaters have a time constant of several seconds then the switching does not have to be rapid. I think that the best solution would be to run the heaters on 110V AC and switch with a solid state relay. There will be no massive currents on your PCB and no large power transformer or...
  8. duke37

    Need professionally made circuits to control heaters using PWM and MOSFET

    Give us some more information. 1000W at 1kV = 1A 1000W at 10V = 100A The catch diode needs to be able to pass the load current for a short time. If this drives a heater, then 1kHz seems to be plenty fast enough, what is the thermal time constant? You could parallel several MOSFETs to lower the...
  9. duke37

    Wiring pot as voltage divider across polarities

    If you reduce the current, the voltage will reduce. The gubbins will take the current it requires. Make sure the voltage does not exceed what it can cope with.
  10. duke37

    A few questions about coils from someone with no knowledge

    A transformer has the core bent round on itself to constrain the magnetic field. The best configuration is the torroid but E I cores or pot cores are more commonly used. To get a magnetic field further away, then use a linear core with open ends. An example of this, used for reception rather...
  11. duke37

    Is it my transformer or rectifier?

    If you have a dead short, it is difficult to measure things when power is applied. A bulb (lamp) in series will let some supply be applied without the fuse blowing. The transformer could have failed due to the core saturating and excessive current being taken. The rectifier could have failed...
  12. duke37

    Electric fan Capacitor Connection

    There is no such thing as positive and negative wire with AC. Just connect the new capacitor as the old one was connected. The multiple wires may be due to connecting more than one winding in the motor.
  13. duke37

    Activate transistor with piezo disc

    You could try a low voltage zener diode. I think the transistor junction is prefered since it has a lower capacitance and so will output at higher frequencies. Here you only want audio frequencies.
  14. duke37

    LED FLASH/ON

    Welcome to the forum, what country are you in, it is nice to see the country flag and gives information about mains supplies and local suppliers. I suggest making an oscillator with a 555 to flash the LED, then to use a comparator to switch an extra current to the LED when the LDR resistance...
  15. duke37

    Help me to chose the proper photodetector

    In RadComm a few months ago, there were some articles on using LEDs to communicate. They managed several kilometers and used the same LEDs (Cree) for transmission and reception.
  16. duke37

    Chatting about stepper motors and their control

    Hi Helmut I have never used a stepping motor but do not see how the principles of physics should be different for them. Question 1 The torque drops off as speed rises due to the inductance limiting the rate of rise of the current. Question 2 If you have a motor with one turn on each pole, it...
  17. duke37

    RF noise from a chip dc-dc step up module, fix?

    The frequency you want to suppress is 315MHz which is quite high. To get the resonant frequency of a bypass capacitor sufficiently high, you need a small capacitor and very short leads. An electrolytic capacitor is of no use. Try 100pF disc ceramic across the two big input and output capacitors
  18. duke37

    Pull Down Resistors

    If the transistors take no current, then the base voltage of Q1 will be 5*1.5/8 = 0.94V The voltage shown of 0.41V indicates that the transistor is taking base current. The normal rule of 0.6V or 0.7V is only a very approximate value based on considerable current draw. The relation between...
  19. duke37

    RF noise from a chip dc-dc step up module, fix?

    I doubt if wrapping the device with foil will do much. You will not be able to seal it properly. A gap of a few mm will be a gaping hole at 315MHz. An aluminium box with bolt-in feed through capacitors or a copper box made from PCB board with solder-in feedthrough capacitors may do the job...
  20. duke37

    How does opening a car door work?

    A radio wave is an electromagnetic wave. The key contains a radio transmitter which is activated when a button is pressed. The car contains a radio receiver, probably in the dash board which will unlock the doors when it gets the right code. The radio wave does not activate the door directly.
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