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  1. duke37

    RF switch transmitter pls help

    Menu - diode detector. Take a fast diode, connect one side to ground. Connect a small capacitor (100pF) to the free side. This is the input. Connect a high value resistor (1M) to this junction Connect a small capacitor (100pF) from the other end of the resistor to ground. This is the output...
  2. duke37

    I can't see how this will work

    If P3 out is high there will be no current limit for the lower LED - POP. Add another 470Ω resistor.
  3. duke37

    I can't see how this will work

    I do not see why the amplified LDR should not work. We need information to see what is happening. Measure the resistance of the LDR at zero light, at the level where you want the LED to change and the resistance at maximum light.
  4. duke37

    Hyper Sensible Touch Lamp

    Keep your fingers well away from the internal circuit unless you want to curl your hair. I have one that does the same as yours, I just give it a flick so that there is no input after the wanted step has passed.
  5. duke37

    Coax Collinear Antenna

    To get an antenna gain all the parts of the antenna should pass current in phase so that when looked at from a distance, the radiation from the whole length adds up. Stacking a half wavelength on top of another gives a null since the currents in each part will be in antiphase. The coax antenna...
  6. duke37

    anyone help me?

    If the input is around 120V AC, then I would use a 400V bridge to give a bit of spare capability. You could try a resistor such as a 100W bulb at the output of the dimmer to give it a more stable reference voltage.
  7. duke37

    RF switch transmitter pls help

    Will the scope respond to a frequency as high as 300MHz? You could build a simple diode detector, using a fast diode such as a 1N4148 to detect if the oscillator is working.
  8. duke37

    Ohms to trigger a switch

    You will need enough base current to turn Q1 hard on so you will need a pull-up resistor if the comparator does not pull up. If you wish to look at several different levels of voltage, then you could investigate the LM3914 which has 10 comparators on board.
  9. duke37

    Ohms to trigger a switch

    A comparator normally needs a pull-up resistor on its output.
  10. duke37

    Solar Panels for Hydrogen?

    You will need to lubricate the turbines with snake oil.
  11. duke37

    0 to 3 volt variable a\c signal generator

    Presumably the trigger pulse will be shorter at high speeds so you should have a circuit which will change the repetition rate and pulse width. Al my data is put away at the moment but I suggest that you should look at a 555 oscillator. There are many people here who love these venerable chips...
  12. duke37

    Help with detecting open switch

    I had a look at a three pole 230V AC changeover relay some time ago and it would pull in and drop out at the same AC voltage but when driven with DC, it would hold right down to 8V.
  13. duke37

    Voltage offset shifting

    Show us your circuit. If all you wish to do is to make the waveform symmetrical about zero, then feed it through a capacitor with a high resistor to ground.
  14. duke37

    Changing The Current Direction inside the Peltier for temperature regulation

    A Peltier device will have a significant thermal time constant so there is no point in switching the polarity quickly so a two pole change over relay may be adequate. Mosfets are easy to drive but need quite a high voltage so you will want a 10V supply. Use two N channel and two P channel...
  15. duke37

    Help with detecting open switch

    You will need a diode in inverse parallel with the led to shunt the 34 peak reverse volts. Also, the load must need enough current to NOT operate on the led current.
  16. duke37

    Changing The Current Direction inside the Peltier for temperature regulation

    You will need four devices not two. Look up H bridge.
  17. duke37

    Help with some old fairy lights

    As a resistance you could place a 40W bulb in series with the string and if this a bit dim, go up to 60W.
  18. duke37

    Help with some old fairy lights

    A 3A fuse should be big enough to run 20 strings. To protect the flex I would put in a 1A fuse if you can find one. A plug-in lamp dimmer is the easiest and safest way to reduce the string voltage. A diode in series with the string will pass only half the waveform so will reduce the...
  19. duke37

    Please help with replacing electromagnetic buzzer

    If the sound takes too long to die away, then the 100μF capacitor is too large. If you are happy to use a separate power supply, then the transistor switch as suggested by Bob is the way to go. You could use 5V but why not use 12V without extra circuitry? Get a siren to suit. Measure the...
  20. duke37

    RC Toy Car

    So, was it damaged instantly or after 30 minutes?
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