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  1. Alec_t

    Design help to control 2 relays

    A CD4017 could be part of the solution. It can't provide enough current to drive the relays directly, but could be used to switch two N-type logic-level MOSFETS which, in turn, would drive the relays. Depending what the relays (current-hogging things!) are to be used for, you might even be able...
  2. Alec_t

    Tablet charging problem

    I'm guessing the tablet has a current sense resistor somewhere and monitors the voltage (only a few mV probably) across that to sense the current going into or out of the battery. If that resistor or the monitoring arrangement is faulty then the tablet may well be fooled into thinking that the...
  3. Alec_t

    Position of one device relative to another.

    What range? Millimetres? Kilometres? .... ?
  4. Alec_t

    Turning an LED Off when voltage is applied

    Good to hear it's working.
  5. Alec_t

    4 state illumination controller

    Yes, the 74AC74 looks good for this.
  6. Alec_t

    Simple Schematic - but components may not even exist! [600VDC]

    From a quick look at potentiometer specs, the usual max working voltage seems to be 350VDC. Didn't spot anything above that. A transistor rated >600V might be a better/easier-to-source current control device.
  7. Alec_t

    Reverse Color Organ

    ....and disconnect pin 4 of the opto coupler from ground.
  8. Alec_t

    Turning an LED Off when voltage is applied

    You have a choice: 1) Use a CD40106 with a 5V or 12V supply but high-brightness low-current LEDs (since standard CMOS outputs aren't intended to source/sink more than a few mA), or 2) Use a 74HC14 with a 5V supply (not 12V) and either that type of LED or the standard LED (drawing e.g. 10mA or...
  9. Alec_t

    4 state illumination controller

    If you want to do that, using weighting resistors without the switching transistors, a higher-current equivalent of the 4013 (e.g. a 74HC74) would probably be needed.
  10. Alec_t

    Voltage Amplifier Stage (VAS) design

    Ok then. In your simulation, try doing a temperature analysis, try using transistors with different current gain specs, try using DC feedback to stabilise the operating points. How much effect do these changes have? Are variations acceptable? What is the power dissipation in each component...
  11. Alec_t

    Voltage Amplifier Stage (VAS) design

    The bias currents and voltages will be very temperature dependent (which is why negative DC feedback is used conventionally, to counter that). I'm not familiar with ORCAD; do you have to specify temperature? BTW, unless Q12/15/17 are very closely matched and maintained at the same temperature it...
  12. Alec_t

    Considering viability of project: small wind turbine for 5 V camping charger

    I've no experience of trying to use stepper motors as generators, but would expect that whether or not there's a common would make little difference. Others here may not agree.
  13. Alec_t

    4 state illumination controller

    Confirmed.
  14. Alec_t

    old garage door opener circuit board

    In the second pic in post #8 it looks as though the big electrolytic cap has leaked, so would need replacing. I wonder, too, about the state of R3, which looks to have been cooking nicely.
  15. Alec_t

    Is this circuit compatible for charging my gel cell?

    I thought the battery was 7.2Ah, not 1.2Ah?
  16. Alec_t

    LM2907 output saturates with i/p signal of 90% duty cycle

    We need to see your schematic (as requested earlier).
  17. Alec_t

    Considering viability of project: small wind turbine for 5 V camping charger

    A lot would depend on the individual motor construction, e.g. magnet strength, coil pole shape, pole/rotor clearance. I think you'd have to spin the motor at a known rpm and measure the output volts.
  18. Alec_t

    DC motors and speed control

    I can't think of a non-destructive method :(.
  19. Alec_t

    DC motors and speed control

    I note that the controller markings in the pic indicate it is rated at 1000W, whereas the first motor is rated 90V 15A. Don't know what the power factor is for the motor, but if it approaches 1 then motor Watts = 90*15 = 1350. The controller may be working ok now, but could be under stress.
  20. Alec_t

    Is this circuit compatible for charging my gel cell?

    Not rubbish, Colin. AK was referring to the current-sense resistor in the post #1 circuit.
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