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  1. duke37

    Need to light different LEDs when polarity is reversed

    You can use a diode in series with the led to allow it to light if the polarity is correct. You can use a pair of leds in reverse parallel, one will light with one polarity and the other will light when the polarity is reversed. Each led protects the other from excess reverse voltage.
  2. duke37

    Extreme High Temperature Measurment

    Many, many years ago I used an ORP12 photoresistor looking down a ceramic tube to control temperature. Chromel/alumel (K type) thermocouples will work at the temperatures you want. Have you thought about using charcoal as a more consistent fuel?
  3. duke37

    Speed Restrictor

    You need to find out the type of motor fitted to the bike. If it is an AC motor, then the frequency of the supply will yield a measure of speed. If it is a universal motor with brushes, then you will have to devise some speed measure. If it is a DC motor, then motor voltage could be used. The...
  4. duke37

    Voltage Regulation Using Diodes Problem

    The picture is not clear, use a fatter pen. The question asks for a sketch of a sine wave of peak voltage 5V so start with the voltage on a vertical axis and time on the horizontal axis. You seem to have plotted the forward/backward characteristics of a diode. This was not asked for.
  5. duke37

    Voltage Regulation Using Diodes Problem

    The diodes drop 0.7V each so 1.4V total. When D1,D2 conduct you have the input voltage minus the diode drop across the 5k resistor so you can sketch the resulting voltage. Have a go at this and then we can move on to D3,D4.
  6. duke37

    Project for exam please help...

    The three coil device is often called a LVDT. Linear variable differential transformer. With phase sensitive detection they can be very sensitive.
  7. duke37

    How to drop 18.5V 6A DC to 15V 6A DC

    I suggested using the LM317T as a substitute for the big resistor and big zener. It will only take the base current of the output emitter follower. You will need about three volts more than the output, Two for the 317 and one for the 3055. If you wish to use a pass transistor, then a PNP...
  8. duke37

    Lenco 600 Transformer identification

    The voltage table goes up to 30V so a 24V transformer would probably do. This is a much bigger and powerful device than I first thought, a picture would have helped, there must be big heat sinks.
  9. duke37

    Lenco 600 Transformer identification

    I was mistaken! The 6V bulb has a series resistance so the transformer voltage is much higher than I thought. It is only a guess as to the current consumption of the set. You could look up the current capability of the output transistors. The fuse needs to be strong enough to charge the...
  10. duke37

    How to drop 18.5V 6A DC to 15V 6A DC

    The LM317T is the same size as a TIP3055 and very little different to two diodes. A couple of very small resistors would be needed. It could be made very small, Manhatten style.
  11. duke37

    Photo upload problem

    FuZZ1LOGIC My problem adding a file was that the attachment button was on the bottom of the screen, below where I was working. Scrolling down found the button. The paper clip is usually at the top. I am not going to get any image editiors. I am too old to learn new tricks and often have to...
  12. duke37

    Total Newbie Question: Using a relay as a switch?

    It may do but will only drive 70mA. It seems to be fussy with control voltage of 1 to 1.3V. Decide on the light you wish to use, find its voltage and current requirements, find a power supply with ample spare capacity. The switch can be a MOSFET, junction transistor (prefered) or Darlington...
  13. duke37

    Industrial voltage divider

    I do not know about industrial devices. Whatever, you will need more specifications on what you require. A 7805 or LM317T regulator will be able to supply 1A with a stable output. A couple of resistors will not do this.
  14. duke37

    Total Newbie Question: Using a relay as a switch?

    A junction transistor or MOSFET will be able to drive a more powerful light. A suitable power supply will be required.
  15. duke37

    How to drop 18.5V 6A DC to 15V 6A DC

    If you wish to go with a voltage follower you could consider a LM317T instead of a zener. This would dissipate less power and could be easily set to the voltage required. Investigate whether 6A in one 2N3055 will be reliable.
  16. duke37

    LED in a circuit with alternating polarities

    I think you could dispense with the relay and use two LEDs connected in antiparallel where the relay is connected. Alternatively you could use a bridge rectifier with one LED but this will drop about 2V which may not be suitable when running at slow speed. By adding some amplification it should...
  17. duke37

    Fan speed control

    I have never seen capacitors connected that way. Show us a schematic from an official web site. A capacitor connected across the input close to the LM317 is used to stop oscillation. A capacitor connected to the adj pin to ground can be used but I have never used one, the performance is good...
  18. duke37

    usb carry 12v for quick rgb extention

    I do not know what you want to do but I would suggest that you do not put 12V on a USB cable, that is a recipe for disaster.
  19. duke37

    Fan speed control

    Connect the capacitor as in the data sheets. Check whether oscillation is occuring with a fast oscilloscope. If all you want to do is to slow the fan speed a little, then chose a suitable series resistor.
  20. duke37

    breakers and power

    And find the earth leakage before you get shocked. Sounds very dodgy to me.
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