Search results

Search Forums New Posts
  1. duke37

    Trying to create rotating device/minimum speed. Could use some advice!

    You could consider intermittent operation, say 1 second every 10 seconds.
  2. duke37

    Replace vacuum headlight covers

    I have had another think. You must have had something to activate your previous device, what was this? If you wish to active the solenoid when the light comes on, just connect to the light supply. If yoy wish to activate when either one of two filaments is energised, then you will need a...
  3. duke37

    12 volt electric car speed

    If it has proportional control i.e. goes faster with more pressure then a resistor in series with the comtrol should do the job. If it is just a simple on/off switch, it will be much more difficult.
  4. duke37

    AM receiver

    A battery is normally connected in the collector circuit, not the emitter and in any case the polarity is such that it turns the transistor off. The diode is not necessary, the emitter/base connection of the transistor will do this. You will need 0.7V to turn on the transistor and 1.4V to...
  5. duke37

    Replace vacuum headlight covers

    G'day and welcome. It looks like they would be OK. You would need a switch to turn them on and they would take 17W (1.5A) when activated so should only be used when the engine is running.
  6. duke37

    Replacing film with electrolytic capacitor?

    And electrolytic capacitors leak, this may or may not be important depending on the circuit.
  7. duke37

    Current through a coil in a DC circuit

    A better description of what you have is an inductor, made as a torroid. The voltage on the input of the inductor switches between 12V and ground. The average voltage across the inductor will be much, much less than this so trying to get the current using voltage drop will not be possible. The...
  8. duke37

    Antenna design

    I dissagree. The resistance of an antenna is not a problem for most receivers since the set has gain to make up the losses. In the case of the crystal set, the output power all comes from the antenna and so losses are catastrophic. A long wire will have low losses but a loop will have high...
  9. duke37

    Current through a coil in a DC circuit

    If it is in a buck converter, it is unlikely to be DC but a mixture of AC and DC. It is likely to be an inductor to smooth the current flow. If it is a torroid, there will be little exterior magnetic field.
  10. duke37

    Anyone played with rubidium frequency standards?

    If the stadard is temperature stabilised, then surely it should be at an even temperature. Do you have a 10MHz radio frequency standard available WWV or WWVH?
  11. duke37

    Current through a coil in a DC circuit

    I have never used a Hall effect device so I cannot recommend. Ebay have A1301 chip advertised which is a linear device and is in a similar package to a small transistor. You will need to specify the accuracy you need and the magnetic field that the device will detect.
  12. duke37

    Current through a coil in a DC circuit

    You could measure the voltage across the coil but the current will depend on the coil resistance which will change with temperature. If the coil fails, the voltage will be high but the current zero. You could use a Hall effect device to measure the magnetic field of the coil.
  13. duke37

    Antenna design

    To capture a lot of energy you need a big antenna and a minimum amount of wire to keep resistance down. There is obviously a compromise here. Any transformer will absorb energy. I suggest you look up 'pi match' to see how an antenna can be efficiently coupled to your receiver. There is a...
  14. duke37

    where to get blank circuit boards

    You could try going to a PCB maker and ask for some scrap boards. You can get copper clad board (not cheap) and can etch it yourself if you are happy to handle nasty chemicals. You could get populated boards from the local recyling centre but these will contain solder with a poisonous lead...
  15. duke37

    forward and reverse variable motor circuit

    Electric wheel chairs have a joystick which contains two potentiometers to control the two wheel motors. The sum of the voltages comming out gives the speed and the difference gives the turn. I forget the actual circuitry. A similar control is used to steer planes. In the original design of...
  16. duke37

    Wanted: Mosfet P-CH AND N-CH

    Mosfets are supposed to be capable of running in parallel but I have never tried it myself. Thus two or three lower current devices may do the job.
  17. duke37

    Sky Remote

    It is a Sky (not sky) remote to control the Sky satellite box. My remote is set to operate the TV as well as the Sky box and it is a pain to enter the TV coding required if the memory is lost. I do not see how any damage could be caused by taking the batteries out for a while.
  18. duke37

    Rectifier, what am I looking at here

    I do not see the advantage of germanium diodes and they are much more sensitive to heat. As to what shop sells diode bridges, it all depends on where you live. I get my parts from Bob Potts in Derby, UK. Try the internet for information.
  19. duke37

    current division in circuit

    Its not what I get. The three resistors in parallel have a resistance of 1.92R. Add 1R for the source gives total resistance 2.92R. Current =1/2.92
  20. duke37

    current division in circuit

    In a practical circuit, there will be resistance in the voltage supply and resistance in the wire. The voltage across the resistors will depend on the values of these.
Top