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  1. duke37

    Transistor markings

    I don't have spots on a leg, just on my body.:)
  2. duke37

    Transistor markings

    The first transistors I used were red spot (audio) and white spot (a bit faster). These were surplus transistors which did not fully comply with the spec. The spot was by the collector and they were emitter/base/collector.
  3. duke37

    Needing a sealing resin

    Some silicone sealants give off acetic acid, this will devour the circuit.
  4. duke37

    Filter Choke for power supply

    Four 22.5V batteries will give 90V.
  5. duke37

    Beehive scale

    I would measure the weight of the hive each midnight when the bees are all tucked up in bed. You could make your own scales with a spring and potentiometer. If a tone was generated, a micro at base could translate this to weight.
  6. duke37

    Multi location thermostat

    A thermostat measures the temperature at one location only. You could use two thermostats and some logic to give the action you want.
  7. duke37

    Filter Choke for power supply

    Colin There are things that I know and things that I do not know and things that I don't know I know. I only know that my transmitter kits had expensive chokes in them so they were not free. Going back to the question I have assumed that the load is 100mA or 6KΩ and the choke is 10H. The...
  8. duke37

    Filter Choke for power supply

    This is rubbish. Inductors are much more expensive than resistors and the stability of the output is less. The power loss is also expensive and deleterious to adjacent components which are heated. The advent of very large electrolytic capacitors has shifted circuitry towards resistive smoothing...
  9. duke37

    Filter Choke for power supply

    The 'Electronic Designers Handbook' by Landee, Davis and Albrecht (1957) gives graphs of filter attenuation for various types of filter and rectifier toobs. It even compares an LC filter with an LC, LC, LC filter using components of one third the value. One of the practical problems is that...
  10. duke37

    Zener Diode

    PIV is the peak inverse voltage. This is the voltage that the diode can withstand. It is wise to have a diode which can withstand higher voltages than normally obtained in order to cater for transients which may occur.
  11. duke37

    Diode Power and Heat Sink

    To find out the current that can be used without a heat sink, you need to experiment and ensure that the case never gets above 150C. It is easy to test if the diode is above 100C. Remember that when installed the heat will be conducted from the case to the base it is bolted to and the tail...
  12. duke37

    Diode Power and Heat Sink

    If the diode is conducting for half the time, then the dissipation will be 100W. With a case temperature of 150C and ambient 50C then the heat sink needs to dissipate 1W/K. I guess that 10W would be OK without a heat sink, you will need to measure it.
  13. duke37

    a circuit equivalent to function generator

    There are many ways of making an oscillator. The simplest I have made uses a CMOS 4093, one resistor and one capacitor. You could also use a blocking oscillator (one transistor and an inductance), a bistable (two transistors) or Wein bridge oscillator (one op-amp). I am not up to the latest in...
  14. duke37

    Connecting a powersource directly to a SLA Battery

    Yes ! Overcharging a Pb/H2SO4 battery will boil off the water and make the acid far too strong. I do not know how much overcharging a SLA battery can stand. In my early motoring days, a battery would last two years if you were lucky. When dynamos gave way to alternators with accurate voltage...
  15. duke37

    PWM to DC

    You will still need the LPF but the circuit as shown will give an upside down output. Either take the output across R4 with a low pass filter or add a transistor to invert the signal. 47k to base, 1k to 5V, emitter to ground.
  16. duke37

    motor reverse

    The sewing machine motors I have seen are mains AC motors and I would not advise a novice to play with them for safety reasons. A DC motor with permanent magnet field can be reversed without getting into the motor just by swapping the wires over. I have used motors from car radiator cooling...
  17. duke37

    PWM to DC

    Is the output correct if you measure across R4?
  18. duke37

    Connecting a powersource directly to a SLA Battery

    Car batteries are charged between 13.8 and 14.4V. For continuous charge with no load I would think 14.0V would be best. The burglar alarms I have seen use a simple voltage stabiliser such as a 7812 or 317T raised to 14V. An input of about 16V would be necessary unless a low drop out (LDO)...
  19. duke37

    dc generator

    The field winding is of high resistance so is not suitable for series connection. A magnetic field is required and if the field circuit is used to provide this, it will need a constant current which will deplete the battery. If you go for shunt wound, then the stronger the field the more torque...
  20. duke37

    Theoretical Half-Bridge Inverter Explainantion

    Show us your circuit (schematic).
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