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  1. duke37

    Need advise on controlling the speed of a drill motor.

    The drill you show has a speed control, 0 to 2800 rpm, so you do not need an external control. With powers such as this, a triac light dimmer will do. These come in a fitting for a standard box so the thing can be made safe.
  2. duke37

    solar

    "The other way you could go a further distance is if you change the DC from the panel to AC, send it to the controller, then turn it back to dc before it enters the controller. There would be some losses in this though, so you'd have to look at how long you charge line in carefully. On that...
  3. duke37

    Theoretical Problem

    The specification of the task and the requiremnts are somewhat lacking. A resistor feeding a zener diode will limit the voltage but will need another diode in series with it to stop it conducting on the negative part of the cycle. This will give a clipped waveform. A 20V rms source will go...
  4. duke37

    nokia E72 charger

    Seems as if you have had an attack of the dreaded tin whiskers. These have caused trouble in certain transistors and affected the space shuttle.
  5. duke37

    Transformer Design

    I think you should get information from the lamination manufactures, 1000Hz could give a lot of loss using laminations intended for 50Hz.
  6. duke37

    Questions from someone just getting into electronics, and DIY

    Perhaps you are trying to run before you can walk. The best way of learning about electronics is to build and understand kits and then to move onto repair. Repairing equipment forces one to be logical and to understand what is happening. Then, when you know your capabilities, you can devise...
  7. duke37

    Motor control diy

    The exercise would do me good! If you want a drive with limit switches, you could investigate how a car window winder works. As fitted to a car, it would perhaps be too slow but it may be possible to gear it up. Visit you local scrap yard but take someone with you to stop you getting addicted.
  8. duke37

    How to find short on PCB

    If the rectifier has gone short and blow a fuse, then it should show on the meter as a short not open circuit. If you have a diode and an analogue meter, use the 20k range and see what happens in each direction of the test leads. With a bridge rectifier, measure between an AC input and the...
  9. duke37

    what is negative voltage/power supply ?

    Yes but the two supplies need to be independant with the positive output of one connected to the negative of the other.
  10. duke37

    op amp question

    You cannot find voltage where there is non. With a 6V supply, you would be lucky to get 4V maximum output. You could use some kind of voltage multiplier (boost converter) to generate a 15V supply. It all depends on the currents involved.
  11. duke37

    spring/plate reverb

    The signal is sent down the spring which gives a delay before it gets to the other end. The transducers on the delay lines I have seen are like little speakers i.e. electromagnetic devices. You will need to drive the spring with an appropriate amplifier and receive the voltage with an...
  12. duke37

    PWM modulation on a AM transmitter

    Pehaps you mean 2MHz not 2mHz. PWM produces a signal with a high frequency component, it can be attenuated for say an audio amplifier and does not cause trouble. In the case of an AM transmitter, any high frequency component will generate a very high bandwidth signal. Spark transmitters...
  13. duke37

    Home Made Batteries

    I thought voltage was dependant on the chemical reaction and the concentration would affect the cell resistance. For details of the potentials available in batteries you could look up a book written by my brother-in-law. 'Specific energies of galvanic reactions, and related thermodynamic data'...
  14. duke37

    How can I drop 12V to about 8.4V?

    The motor can have considerable inductance which could generate high voltages with a rough switched supply. Perhaps this is what affected your capacitor. You could try:- 1. Putting a diode across the motor. 2. Putting a large capacitor across the motor. 3. Putting a resistor across the motor...
  15. duke37

    Need some help applying the voltage divider rule in this circuit.

    You know the current through the loop. Start at the ground, R4 will need to drop 20v, R3 12v and R2 36V. R1 will be needed to be a resistance to get 16mA through the loop (drop 100-68V).
  16. duke37

    possibly a simple problem!

    The problem with a one shot is that it will need to produce a short pulse at high frequencies and this will produce a very unsymmetric signal at low frequencies. A CMOS 4046 phase lock loop with a divide by two flip flop could do the job, the 'CMOS COOKBOOK' by Don Lancaster says that a...
  17. duke37

    Loading a blinker relay.

    CocaCola Where do you find omega? Duke
  18. duke37

    DIY turntable build

    I think that roller/ball bearings are noisier than plain bearings because any slight defect will produce a bump. Plain bearings average out the position due to the large contact area. Have you thought about a stepper motor? This can be made to have a very highly accurate rotation rate and...
  19. duke37

    Application of 7805

    The maximum base/emitter voltage of the 2N3055 is with the base negative to the emitter. In this circuit, there is no negative voltage. When the 2N3055 is turned on, the base will be approximately 0.7V positive (one diode voltage drop). If you have a supply more than this you will need a...
  20. duke37

    Is high resistance good or bad in an alternator?

    The size of your alternator will determine the power output. You have the choice of a lot of turns giving a high voltage and a low current or a few turns giving a low voltage and a lot of current. I think you should wind a coil and see how many turns/volt you get.
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