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  1. duke37

    Speakers amplifier stopped working

    To check the diode, switch to the diode position and take a reading both ways round. One way should be open circuit and the other would probably show 0.7V. I think the overvoltage has damaged things, possibly blown the led. The amp may be all right, with luck, just make sure that it is not run...
  2. duke37

    Resistance of double sided adhesive conductive carbon tape

    It does mean something. Take square of 1 unit giving 1Ω If you now take 100 such squares, put them into a square you have 10 in series giving 10Ω and 10 rows in parallel getting back to 1Ω. The size of the squares is not relevant. Where do you get square apples?
  3. duke37

    Project for the diasbled

    Ask your doctor or local hospital if you can help.
  4. duke37

    Project for the diasbled

    In the UK there is an organisation called REMAP, they have branches throughout the country. The Derby branch has a number of retired Rolls Royce engineers so some superb solutions are made. I did some work for them for a time since they wanted someone with electronics knowledge. Of course, I was...
  5. duke37

    Speakers amplifier stopped working

    Are you using a AC or DC supply? The circuit looks quite simple, just a diode to protect the input from wrong polarity, a smoothing capacitor and a resistor to feed the led. Check the diode and see where the the voltage stops getting to the led. You could use a 100Ω resistor in the supply if...
  6. duke37

    Speakers amplifier stopped working

    The supply is labelled AC/DC so there should not be a problem with the power supply connected the wrong way round. If the rectifier has died, perhaps the TDA 7297 has the wrong polarity and will get hot and the led will not light.
  7. duke37

    Rest in Peace, Kris

    What a tragedy. I considered Kris as a mentor and friend. He always used my real name. Trevor
  8. duke37

    Where is a good location to connect a 3-Volt relay?

    You might have been measuring DC when the output is AC with an average voltage of 0.09V. A DC relay will be reluctant to respond to AC. I would try a resistor feeding the base of a transistor with the relay between the collector and the + supply. A diode must be connected across the relay as a...
  9. duke37

    DC to High Frequency AC

    You will need to find a supplier in your area to get a suitable fet, there are many. In the UK Maplin have shops in many towns and have in stock IRF540A in TO220 style. 100V 20A R=0.052Ω 500pF input The switching speed will depend on how fast you can charge and discharge the gate...
  10. duke37

    DC to High Frequency AC

    Why should I have to look up the IRFP460 specification? Could you do this? The IRFP460 is a high power high current power transistor. 500V 20A 0.27Ω resistance, input capacitance 4200pF. This is much too beefy for your purpose. A lower voltage fet could have a lower resistance and lower input...
  11. duke37

    DC to High Frequency AC

    It would help if you said what you intended the 100kHz (not 100KHz) was for. I have a dead low power fluorescent light bulb which seems to do what you say. It has one p channel fet and one n channel fet in series to switch the 340V rectified mains. You do not need a H bridge and fets can be...
  12. duke37

    Back EMF protection

    A capacitor can also be used, it will need to be sized to accept the inductive energy without giving too high a voltage. This is the method used in old car ignition systems where the points needed to open without a spark.
  13. duke37

    An interesting experimental phenomenon related to electric field

    I do not think I can comment further. You need an expert on elecro-optical science to analyse the effect of beam bending with two cases of current and voltage. I used early SEMs fitted with x-ray detectors for analysis. Very fine spacial resolution was not important.
  14. duke37

    An interesting experimental phenomenon related to electric field

    The beam will be produced with very high voltage, tens of kV. Electrostatic deflection can occur and non conducting specimens are coated with aluminium or gold to give uniform potential at the surface. Magnetic fields can deflect the beam. How do you focus the SEM? Try a magnet near to a...
  15. duke37

    I can't see how this will work

    I think not, if there is no resistor in the LED chain, then the current from the supply will be unlimited.
  16. duke37

    An interesting experimental phenomenon related to electric field

    The electron beam will be deflected by the magnetic field, that is in fact how the beam is focussed. I would think that there will be little effect of potential differences, you will be using about 20kV and an odd volt may not do much. Disconnecting the circuit will stop the current and stop...
  17. duke37

    Ohms to trigger a switch

    The comparator must have a power supply, 5V is good, positive to P5, ground to P2. The inputs should not be outside the power supply range i.e. between 0V and 5V. If the inputs are outside this range, you may damage the device, depending how the input is designed. Sometimes exceeding the supply...
  18. duke37

    Ohms to trigger a switch

    If all else fails, read the instructions ! The comparator must have a power supply, not exceeding 5.5V not less than 0.85V. The output is push/pull so does not need a pull up resistor. The inputs can go between ground and the power supply. If you have run the comparator without a power supply...
  19. duke37

    Best solder to use

    There are many kinds of solder. The traditional composition for electronics was 60% tin and 40% lead, often shown as 60/40. The traditional composition for plumbing was 60% lead and 40% tin so confusion could easily occur. Plumbers' solder is not suitable because it freezes over a range of...
  20. duke37

    Ohms to trigger a switch

    You should fit a pull-up resistor, try 4k7. To find out where the +12V is coming from, disconnect R2 and R3. Connect the input to 1.5V. Does it switch when you twiddle? The correct operation depends on the trigger input, a high impedance at the input will let R2 override the input. Does the...
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