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  1. duke37

    Bridge Rectifiers to repair battery charger

    You could fire up the circuit and measure the output at the diodes. You could disconnect the wires and test each diode for integrity - conduct one way, non conduct the other. One pair of diodes may be of different polarity to the other - possibly not. Draw the circuit, it looks as if...
  2. duke37

    Simple Phototransistor switch circuit

    Here is the idea, when the fet turns on it turns on the pnp which provides current to turn on the fet, there is therefore a tendancy to latch. The amount of feedback is controlled by the variable resistance, this will need to be found by experiment without data on the output of the detector.
  3. duke37

    Capacitor value ?

    No, but 0.1microF is.
  4. duke37

    Simple Phototransistor switch circuit

    1. You do not have anything to limit the current through the leds. 2. You do not have anything to distribute the current to each led. A resistor in series with each led will do the job. 3. The convention is that lines at a cross do NOT connect. Use two Ts. 4. An added transistor could...
  5. duke37

    Photoelectric Switch controlling a 12V DC Motor.

    What battery are you using? Is it fully charged? Have you measured the voltage on load? If it worked for a while, then stopped, it appears the battery ran out of breath! What is an ice cube relay? What is the voltage rating of the coil and its resistance or current consumption at 12V.
  6. duke37

    Starting from scratch

    You need three filters. A low pass filter for under 1kHz A band pass filter for 1kHz to 5kHz A high pass filter for above 5kHz The band pass filter will be the most difficult with a 5:1 frequency ratio but you may be able to assume the signal is between 1kHz and 5kHz if the upper or lower...
  7. duke37

    10 led circuit help(white and red)

    With 3V/led, three leds = 9V To get 20mA and a voltage drop of the extra 3V, a series resistor R = V/I = 3/0.02 = 150 ohm. The three leds should be connected in series with the resistor. Three strings will allow nine leds and the current drain will be 3 * 20mA = 60mA You can work out the...
  8. duke37

    Wow, this is where the US is

    I have just seen a review of "The Future" by Al Gore. I will have to read it, it seems to agree with my sentiments.
  9. duke37

    Op Amp - what am I missing

    The non-inverting op-amp does not have a vertical ground. The + input must be biassed somewhere between the power supply inputs. Take some DC measurements to make sure the op-amp is biassed properly. Show us the circuit.
  10. duke37

    Switch mode power supply. Help!

    Try two 12V car bulbs in series. They will take quite a large current when cold but if they are 36W, they should run at 3A.
  11. duke37

    Bug zapper Q

    I use a rough estimate of 3mm/kV when testing electric fencers.
  12. duke37

    Whats this Weird Circuit Symbol?

    These look like a bidirectional insulated gate fet. They operate as switches, one on, the other off in sychronism with the switching input signal. I could not find data. A 4066 would probably do the same job and maybe replace Q1012 and Q1013 as well.
  13. duke37

    Comparator inputs

    Kris, I am no expert on current transformers. The circuit looks pretty good to me, the only thing I would question is that the hysteresis control is linked to the set point. Thus there will some interaction. Would it be better to put a variable resistor across the comparator. Duke37
  14. duke37

    Amplified Difference op-amp configuration questions

    How accurate do you need to be? Resistors are fairly cheap so you could buy a handful of 1% resistors and sort them. If they all come from the same batch they will be similar and have a similar temperature coefficient. You will need some high class measurement to do this.
  15. duke37

    Comparator inputs

    The basic idea as Kris says was to rectify the two signals and subtract one from the other. If the bridge rectifier is placed between the transformer and the resistor, then the effect of the diode voltage drops will be minimised since the output impedance of the transformer will be hgjh.
  16. duke37

    protection for short circuit

    The battery negative lead should go to the fet and all the buzzers and sensors. Do not short anythig! The negative lead goes round in a loop, this is not a problem if things work but if they do not, you do not know which way round the current is coming.
  17. duke37

    protection for short circuit

    You have 16 leds all in series. If each one needs 2 or 3V then a 12V battery will not drive them. A piezo is driven with a high voltage, this may be more than the fet can stand. Put a 12V zener gate to source to limit the voltage. A capacitor gate to source may be advantageous to lengthen the...
  18. duke37

    555 timer using a transistor to drive a 12 v. 30 amp relay

    You may be able to use a fet instead of the relay, you do not say what the resistance or the current drain of your heater is. Big fets can have a very low on resistance.
  19. duke37

    protection for short circuit

    You do not have any current limit through the leds. The input voltage is not specified, if the signal produces high voltage pulses, you might have popped off the fet. Please show the entire circuit.
  20. duke37

    Op Amp - what am I missing

    The virtual ground is the - terminal. You would be better to use two 9V batteries with the + connected to the junction.
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