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  1. duke37

    Caustic Corrosion on Water Level Sensor

    Or use a floating magnet and a reed switch.
  2. duke37

    Problem Power Supply

    This is an ustabilised supply, it will be designed to have a high voltage when unloaded and the voltage will come down to the rated value when loaded at its maximum. 7V seems very high, 3V AC rectified is 3*sqrt(2) peak = 4.2V and you have to take off the rectifier drop. You could use a higher...
  3. duke37

    Tri-level composite signal from microcontroller

    The wikipedia article says there is no DC, perhaps a capacitor in the line would be sufficient. There are integrated circuits which can give a low current negative supply, I have never used one.
  4. duke37

    Amplify signal from piezoeletric

    I think the charge amplifier should work, I used one on a scanning electron microscope 40 years ago to detect radiation. What are the values of R and Cf? What input specification does the amp have? A fet input amp would be preferred. What is the capacitance of the detector. I would try Cf of...
  5. duke37

    Replacing light bulbs with LED's for illuminating a radio's scale

    I have had a brain storm and decided to do some calculus. 65 years is too long to leave it dormant. Take a supply of 10V, peak of 14.1V. Take drop of two leds totaling 6.4V. Work out when the voltage is high enough to pass current. 0.476 to 2.67 radians. Integrate sine wave between these...
  6. duke37

    Relay

    You need a npn transistor (2N2222) or n channel fet.(2N7000) Edit. Nothing like saying the same thing twice:)
  7. duke37

    Experimental Repair

    A coil needs insulated wire, if you used bare copper, you introduced shorted turns and will get nothing out.
  8. duke37

    Replacing light bulbs with LED's for illuminating a radio's scale

    If you want to calculate properly, then work out the time of the peak of the sine wave above 6.4V. Integrate the voltage during this time to calculate the average voltage to use to calculate the resistance. Perhaps you went to school.:) I would do it by trial and error.
  9. duke37

    Replacing light bulbs with LED's for illuminating a radio's scale

    The leds may be similar but they will not be identical and will be at different temperatures. I would try two inverse parallel pairs in series and a single resistance. At a rough guess (10-6.4)/0.0020 = 180 See how the brightness compares with 20mA on DC. Use the circuit as in #10 but delete...
  10. duke37

    Replacing light bulbs with LED's for illuminating a radio's scale

    That diagram would work if all leds were identical. It would be better to put them into pairs so that one led does not have to take all the reverse voltage. R = (10- 9.6) / 0.012 = 33 This however is too low to define the current with voltage or temperature variations. The resistor will set...
  11. duke37

    Coil Question

    Look up ludens transformer.
  12. duke37

    Converting an electronic cooling fan to battery operated

    No. The fan is designed to run on AC. A battery supplies DC. You will need to get or make an inverter to up the voltage with 60Hz. It would be easier to change to a DC motor.
  13. duke37

    LED Circuit

    You should have no backfeed if you use a change over switch. Also, perhaps the power supply is not up to the job.
  14. duke37

    Replacing light bulbs with LED's for illuminating a radio's scale

    Instead of a series diode, use two leds in inverse parallel, each will protect its butty from excess reverse voltage. With 10V AC you could use two pairs in series.
  15. duke37

    Calculate Op Amp Gain

    Are you sure? (I am 76.5) I have just passed 80 and seem to be travelling faster and faster. The 37 in duke37 is my date of birth. I will have to decide what I should do when I grow up. I am training to be a 'silly old fool' Trevor
  16. duke37

    Help finding unusual power supply

    I have two power supplies which you are welcome to. 1. +/-18V in steel case 153*102*44, 650g with standard mains input socket and mains switch. This has broken mains fuse holder. It is just smoothed with emitter followers but there is room in the box for 3812 and 3912 regulators. 2. Amplicon...
  17. duke37

    Help finding unusual power supply

    I might have something here but you will need to know whether you need 10mA or 10A:) Common is the reference for the 12V supply. I presume that Gnd is ground or the case. How far are you from Matlock?
  18. duke37

    Help finding unusual power supply

    A computer ATX PSU can do this with other outputs. My neigbour has just taken one to the tip:(. What is the load, Op-amps usually go up to 18V and run on 15V. You should be able to find one of these and drop the voltage a little if necessary.
  19. duke37

    HELP: need to get away from 9v spdt relays!

    You can get spdt relays in a TO5 can. If you give your circuit with power supply and load, I am sure someone can recommend a transistor circuit.
  20. duke37

    Calculate Op Amp Gain

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