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  1. duke37

    IGBT symbol

    The second symbol shows a diode in parallel with the transistor. This will protect the transistor from reverse voltages and may be advatageous in some kinds of switching circuits.
  2. duke37

    What wil be the output?

    R32 will keep Q11 turned on even if the input is 0V. This may be the same for Q12 depending on the required voltages to turn it on.
  3. duke37

    What wil be the output?

    What is the voltage on the base of Q11 when the input is 3.3V and 0V? Similarly, what is the voltage on the gate of Q12 when Q11 is on or off? Will this turn Q12 on or off?
  4. duke37

    PIC + Triac motor rpm controller

    I have never used a PIC or any of its relatives so cannot help with suggestions. I wonder why you need to control the motor speed, the drills bits will be of more or less the same diameter so the speed could be preset and the motor just turned on or off. This will make the programming easier.
  5. duke37

    Delay-off switching of a 115v 2amp load

    That little dot can be seen if you type 0.9.
  6. duke37

    Heating element

    You do not want any external resistance, this will only waste energy. The way to do it is to switch the heating element on and off, quicker than it can heat up, so the average power is reduced. The battery will have to be substantial, a diddy PP3 wil not do much. The resistance will need to...
  7. duke37

    PIC + Triac motor rpm controller

    Electric drills usually have AC/DC universal motors, these are good to be controlled by a triac. The easy way is to use a lamp dimmer. DC permanent magnet brushed motors are not suitable without extra circuitry. You have not said what the purpose of the PIC is, what will the input to the...
  8. duke37

    Please help me build a device to let me hear again!

    My hearing is OK but I have tried hearing aids and find them horrible. Thus you do not want to degrade the good hearing that you have. All hearing aids in the UK have a T position to pick up magnetic signals. This is used in conjuntion with audio loops fitted to public buildings. You could...
  9. duke37

    Heating element

    I cannot find the thread either but it dealt with mains driven hot wires. This will not be suitable for you. Electric blankets have heated elements and should be scrapped after a while for safety. These could be a source of insulated heating wire to be run on low voltage.
  10. duke37

    Heating element

    There was a thread here a month or two ago on making a hot wire to cut polystyrene. The power supply can be AC or DC, it depends on what you have and the amount of control you need. The wire should be resistant to high temperatures, constantan or kanthal come to mind. Also stainless...
  11. duke37

    555 timer reverse polarity circuit

    The common is wallpak -,C1,C2,C3,P1 and const current COM. These are all at the same potential. P3 is the output of the 555 which drives the relay coil.
  12. duke37

    555 timer reverse polarity circuit

    I have not been following this thread which seems to have gone on and on. COM is short for common, in other words all these points should be connected together. It would be clearer if a line were drawn across the bottom of the diagram and all the connections went to this. I do not like lumps...
  13. duke37

    A Newbie Question on PNP Transistors

    This is how I would have drawn the circuit with the positive at the top. Taking Q1 first. When the switch is open, R3 goes to the 9V supply and provides a base current to turn on the transistor. When the switch is closed, R3 current is shorted to ground so there is no current into the base...
  14. duke37

    Electromagnet and Switch

    I am no expert in batteries, in fact I hate them. The batteries will have a specification of mAh. Divide this number by 330mA and this gives the number of hours under optimum conditions, you could divide this by two because you are draining the bateries very rapidly and divide by two again as...
  15. duke37

    Electromagnet and Switch

    The batteries will be pushed to the limit and will not last long. The switch should be able to handle the voltage but the electromagnet will be highly inductive and will draw an arc when the switch is opened. This will rapidly destroy the contacts. The solution is to go to a fatter switch or...
  16. duke37

    A Newbie Question on PNP Transistors

    There seems to be little current limiting in your circuit. Presumably the battery will be running flat out. I prefer circuits to be drawn with the positive at the top. I find this easier to understand. The austalians and new zealanders may prefer it the other way up. When the switch is...
  17. duke37

    30v DC to 27v DC

    A DC motor will vary its speed with the loading. If you need an accurate frequency with varying load, then a voltage control will be necessary. A slightly high voltage will give a slightly high frequency, this will be better than a low frequency.
  18. duke37

    Analog signal 4-20mA

    Also, I thought the 4mA was used to supply the transducer with power.
  19. duke37

    revered polarity LED

    No, the motor current goes through the led and there would unlikely to be enough current to run the motor. I attach two versions which will light the led with one polarity only. In the first version, you could use a led of different colour instead of the plain diode so you get red for...
  20. duke37

    dark activated circuit lamp

    If the LDR does not respond to light, then it is not an LDR. If the response is not sufficiently sensitive, then an amplifier will be needed. Measure the resistance of the LDR in bright light and at the light level where you need the light to come on. In the final design, the LDR should...
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