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  1. duke37

    Differential amplifiers - why amplify the difference?

    Suppose you have a microphone which produces a voltage at its output. Connect it to an amplifier with a cable which picks up interference on both wires. Connect the wires to a differential amplifier and what is amplified would be the signal from the microphone and the common mode interference...
  2. duke37

    Voltage multiplier

    You can generate the high voltage at high frequency (100kHz) so using a smaller transformer. This would need to charge a capacitor which would be switched to the output. A rough calculation, possibly wrong, would require a 10μF 100V capacitor to hold 50mJ. The size of the pulse transformer you...
  3. duke37

    Making a battery

    "All steel food cans are galvanized steel" Surely not, They are called tin cans and are plated with tin. They solder easily!:)
  4. duke37

    constant current LED driver without PWM (and flicker)

    Are you sure about this? The mechanism I thought was that a photon was emitted when an electron and hole combined and the photon produced had an energy dependant on the band gap.
  5. duke37

    constant current LED driver without PWM (and flicker)

    A DC PWM supply can be smoothed to reduce any flicker. It will be much more efficient than a linear supply. The driver you show looks like a high frequency PWM circuit to me.
  6. duke37

    PWM as driver for electric fence

    Most fencers I have seen use a flyback high voltage generator. This charges a capacitor to 200 to 300V which is then discharged through a 1:20 transformer. Boost convertors can be obtained which generate up to 80V limited by the transistor switch using an inductance. If this is changed to a...
  7. duke37

    Need help using Nichrome wire for a foam cutter

    @mgrass I have been a contributor to this forum for several years and have had a certain amount of criticism but have learned to accept it and try not to exceed my knowledge. I keep away from computers, it is 40 years since I programmed one. Most contributors are polite and knowledgible and help...
  8. duke37

    Need help using Nichrome wire for a foam cutter

    For the same resistance, 3.5 times the current will give 12.25 the power. P = I*I*R In fact extending the length does not alter the current density required so the current should stay the same but the voltage will be higher. Putting several strands in parallel to lower the resistance will work...
  9. duke37

    Power Supply Woes

    When I said that R2 was not necessary, I should have said that it should be removed. Then there would be no connection between base and emitter. A pnp transistor has the arrow pointing towards the base. A npn has the arrow pointing awy from the base. I would think that the 0.7Ω resistor in...
  10. duke37

    Driving 3V motor on low voltage AA batteries to close a valve?

    If you look at the data for the pmv130enea you need about 3V gate to source to get a low series resistance (fig 9). The motor current has to pass through two fets, the supply is not straight to the motor. If you use a voltage booster with a low voltage input, then more current will be drawn...
  11. duke37

    Driving 3V motor on low voltage AA batteries to close a valve?

    There are two possibilities. 1. There is not enough voltage to turn the fets fully on. 2. There is not enough voltage to drive the motor. I do not see where there is a 2.5V supply. Stepping up the voltage is the way to go.
  12. duke37

    Power Supply Woes

    Look up the data sheet for the 317, it normally gives details of how to boost the output. R2 is not necessary in your circuit. Q1 just works as an emitter follower. If you use a pnp transistor, then R2 should come before the 317 and the collector should be connected to the 317 output. You can...
  13. duke37

    Need help using Nichrome wire for a foam cutter

    I assembled a cutter using a dimmer and battery charger. I also fitted a 100W bulb in the primary in case the dimmer was not balanced. We tried several wires, Nichrome, stainless (guitar string) and suture wire. The very high temperature capability of Nichrome or Kanthal is not necessary. The...
  14. duke37

    AC generator

    What about a stepper motor or a synchronous motor out of a tape recorder?
  15. duke37

    Power Supply Woes

    If you use a boost transistor, it needs to be a pnp transistor such as a 2N2955. The circuit you show has the pass transistor permanently turned off so I do not see how it should get hot.
  16. duke37

    Bent microcontroller legs... how can I repair it?

    If you do break a leg, a new one can be soldered on with luck! I did this with a computer maths chip which was thrown out at work.
  17. duke37

    x72 Ceramic Capacitor

    Back to the power supply! There are 5 diodes think I see. Four are in the little round black block next to the green connectors. One is on the board next to the transistor. Looks as if this diode could be a Zener to set a stable output voltage. Since the gubbins exploded, it may have allowed...
  18. duke37

    My 13 year old son

    Some radio clubs provide training for the amateur radio examinations. They start at the very beginning so suitable for your son. I think he is too old to qualify as the youngest amateur. Look at RSGB.org, they give a method of finding a Foundation course within a certain distance from your...
  19. duke37

    LED Fade Circuit

    It depends on the current that the leds take but it may be possible to use a resistor and capacitor to give a slow rise and fall then, if the current is considerable, a voltage follower could be sufficient. Thinking again! You need to control current not voltage.
  20. duke37

    Conditioning signal circuits damaged

    It looks as if the opa551 inputs need to be within 2.5V of the power supply. Thus without a supply they are being damaged with excessive input voltage. Some proection should be added to stop or limit an input until power is applied.
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