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  1. duke37

    Help With Calculations

    Resistors in parallel. How do you get the right answer when using the wrong equation? As Bob says, the driving voltage is the battery voltage minus the led voltage. This is given near the bottom of the table. Calculate the current from the total resistance with this voltage. Calculate the...
  2. duke37

    math problem, I lost my marbles it seems

    You are doing well:) It is normal to put a full stop between letters to act as a multiplication sign. i.e. BX is written as B.X Step 4 B.Y=X-B.X take out X so B.Y=X(1-B) Step 5 Divide both sides by (1-B) to get X Q.E.D At school we didn't do latin so the maths teacher said it was 'quite easy...
  3. duke37

    I Need Help With My 555 Monostable Circuit Please

    Show us the schematic and data on the load. You seem to have a transistor lurking there.
  4. duke37

    Ant Detecting Sensors

    Try a white board and look at the reflection when an ant walks over it.
  5. duke37

    Negative Voltage

    A valve amplifier will need the grid negative to the cathode which is used as the reference to determine the valve current. Radio output valves usually have a resistor in the cathode to ground connection to raise the cathode above the grid which is referenced to ground. This has the...
  6. duke37

    Soldering High Amperage Transistors

    I do not know on what you base the current limit of a wire. A watt or two dissipation should not be a problem in free air. Make sure the transistor is heat sinked properly. I do not have pictures of my bodging.
  7. duke37

    DIY power supply...no output

    Yes, that is what a Variac is for.
  8. duke37

    Morse buzzer

    You can get buzzers which buzz whenever power is applied.
  9. duke37

    Soldering High Amperage Transistors

    You You want thick copper to conduct the heat. I have used central heating copper pipe, slit down the side and opened up. A job for my big hammer.:) I have also used copper sheet from a leaking hot water cylinder, less thumping necessary. The transistor tag which is bolted down is connected to...
  10. duke37

    Soldering High Amperage Transistors

    I would suggest bending up the current carrying pins and solder them to some sheet copper. Connect your fat wire to the copper sheet first. Cut the copper to give strips which can be bent from each other to improve the heat transfer. The collector will be connected to the tag and a heat sink...
  11. duke37

    Replace a Transformer With a Battery

    Just break a few windows, you will soon find one:) They come up every now and again at my radio club junk sale. The batteries are often dead. The charger is usually a low voltage transformer driving a LM317T regulator. I have combined two to provide 24V for an antique railway station clock.
  12. duke37

    math problem, I lost my marbles it seems

    Remember You can multiply both sides of an equation with the same factor. You can add or subtract the same amount from each side of the equation. You cannot get the right answer if you start with the wrong equation you have to be very picky.
  13. duke37

    Looking for specific variable resistor

    If you are wanting more brightness at higher engine speed, then I would suggest that each input pulse should put an output pulse into the leds. Some smoothing may be needed if the visual pulsing is objectionable.
  14. duke37

    Replace a Transformer With a Battery

    The burgler alarms which I have seen have had a lead acid battery connected to the detector system and a small 1A charger connected to the battery, set to 13.8 or 14V. Thus when power is demanded it comes from the battery and the battery is recharged over a considerable time when mains is...
  15. duke37

    Replace a Transformer With a Battery

    A 12V lead acid battery will be easier to deal with than a lithium battery. Just charge it to 14V and take output from the battery. Remember to use a fuse for safety, batteries can put out very high currents. Batteries which are used in electric scooters or golf buggies would be suitable. You...
  16. duke37

    How can I make a robust capacitive wire?

    Welcome to the forum. The resistance of human skin will be less than that of sea water so will be swamped by water. Give it a try with a VOM meter without the Arduino complication. I believe that there are cables which are sensitive to pressure, used on alarms. I have never dealt with these.
  17. duke37

    math problem, I lost my marbles it seems

    Your original equation is wrong. You print B= R2/R1 + R2 It should be B= R2/(R1 + R2)
  18. duke37

    Clean 20Mhz square wave at 45 volts ... possible???

    I do not think this is possible. You need several harmonics to get anything near a square wave so will need to amplify at least 100MHz.
  19. duke37

    High pass filter

    An accuracy of three figures is plenty. Components of better than 1% can cost the earth. Multiple capacitors can be used. You will need to put them in parallel, If you put them in series,you will be throwing capacitance away at some cost. 800μF bipolar will be very large and expensive. For low...
  20. duke37

    magnetic switch/connector

    Tou may not need a second magnet. A lump of old iron will shunt the magnetic field and release the reed switch.
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