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  1. duke37

    XOR gate using only diodes

    Sorry. I was wrong, will have to get my brain cell connected. I thought the diodes were chasing their tails.
  2. duke37

    Help in wiper motor circuit

    A simple oscillator can be made with a cmos Scmitt NAND gate (4093). With a capacitor to ground on the input and a resistor fom output to input, a frequency of oscillation is 2.7/(R*C). For a frequency of 0.25 and 100uF cap you will need a resistor of 110k. The output should go to the H bridge...
  3. duke37

    Basic beginners mistake?

    The 270k feedback resistor in your circuit makes it a Schmitt trigger. If you have a DVM. measure the voltage at the + input, it should be half the supply. Measure the voltage at the - input and warm up the thermistor and see if the voltage gets to half the supply and from what direction. If...
  4. duke37

    XOR gate using only diodes

    That is not a bridge rectifier, it is a diode ring and you can only get 1.2V across it. The diode ring is often used as a frequency mixer in better radios with a two windings, connected across the ring for the two inputs and the output taken from the centre taps of the windings
  5. duke37

    very shocking ceiling fan install

    I always check with my magic screwdriver.
  6. duke37

    Portable Electric Grill Shorting?

    You do not need to open it up to check for leaks. Take a resistance measurement between the earth pin of the plug and one of the current carrying pins. There should be no connection, if so, heat it up and try again when hot. But you know this already because the earth trip goes.
  7. duke37

    Portable Electric Grill Shorting?

    I believe that Pyrotenax make cable with copper wires inside a copper sheath. The wires are insulated with magnesium oxide (magnesia) and the cable ends need to be sealed to prevent moisture getting in. The cable will withstand high temperatures so is used in critical applications. I do not...
  8. duke37

    Portable Electric Grill Shorting?

    Seems to be the same thing as I have. The obvious way of powering this is by an isolating transformer, however, the case will be live and I would not know where to find a sufficiently powerful transformer. Site transformers (110V centre tapped) could perhaps do the job but I think the centre...
  9. duke37

    Portable Electric Grill Shorting?

    Which breaker blew? Did you get over current or earth leakage? Hot plates and some heaters have ceramic insulation which can get damp over time so that there is a leakage to earth. The leakage increases with temperature. I have a old cooker top in my shed with four solid hot plates, only one of...
  10. duke37

    Cooling several LM350s

    Quite correct, but your current source can do up to 3A. What current does the led take? Surely resistors would do.
  11. duke37

    Cooling several LM350s

    Sorry, I did not read the requirement correctly, I interpreted the TO220 as a transistor so my second sentance was rubbish
  12. duke37

    Cooling several LM350s

    You can get insulating kits which consist of a mica or plastic sheet and a plastic bush to go in the TO220 hole. Heat sink compound should be used with the minimum possible thickness, just enough to eliminate any air gaps. Could you modify your circuit so that the collectors are all at the...
  13. duke37

    Need help identifying wire

    Resistors generate heat, so if you want to make a high power resistor, you will need to strip the insulation. Measure the resistance of say one meter and calculate the length you need. If it is going to get hot, it will need to be wound on an insulating, high temperature former.
  14. duke37

    Problem fixing an Amplifier - replacing electrolitic capacitors

    Resistors will fail if they dissipate too much power. In the case of capacitors, the dissipation depends on the ripple current which will vary with the output power that is demanded by the amp. You need to check that one of your amps has not failed short circuit.
  15. duke37

    Problem fixing an Amplifier - replacing electrolitic capacitors

    From the value of the capacitors, I assume that it is a transistor amplifier so it can not be old! If the fault occurred on one channel only. then the power supply was not the trouble. You may well have a PSU problem now. Have you checked the rectifier, the capacitors will not like AC and...
  16. duke37

    LT Spice Model file for ideal switch

    I have not used LT Spice but could you use a resistor, changing from 1E-10R to 1E10R? Not ideal but near enough perhaps.
  17. duke37

    vibration sensor magnetic

    You could try a diddy earphone with a weight glued to the diaphram. This will give you a coil and magnet set up optimally. The output impedance will be low and could go into the base of an amplifying transistor.
  18. duke37

    smooth range variable transformer?

    You can use a train of relays to add votage or resistance and get the computer to select the ones you want. One relay two voltages/resistances Two relays four voltages/resistances Three relays eight voltages/resistances that should be enough. The voltages/resistances should be in the...
  19. duke37

    smooth range variable transformer?

    The two controllers that you list are nothing to do with a Variac which is a variable auto transformer using a sliding carbon brush. One of the controllers is a triac phase controller and the other is an autotransformer with five taps. The later DC fan is controllable externally but there is...
  20. duke37

    smooth range variable transformer?

    You could use a DC motor, but 200W or so at 12V would need quite a large current. Have you got the fan? Do you have a scrap yard nearby where you can get automobile radiator fans? Do you need to use a thermostat, other electronic methods can be used to provide many steps or stepless control...
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