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  1. Alec_t

    Circuit validation & improvement

    The MJ11028 is rated for 50A, not 80A! No wonder it gets hot :). I can't recommend a particular MOSFET, but other members here probably can.
  2. Alec_t

    555 timer to turn on 2nd 555 timer

    Ok. Assuming you can get a 555 circuit to work satisfactorily on the 3.7V supply and that your servo is happy with that, here is the suggested modification to Circuit B. Diode D2 keeps the oscillator 'off' until the Circuit A delay ends. The trimmer allows adjustment of the servo pulse width...
  3. Alec_t

    Circuit validation & improvement

    Isn't it the ESC which handles the high current? Yes.
  4. Alec_t

    Interfering circuits

    Good to know it now works.
  5. Alec_t

    Interfering circuits

    So you still haven't decoupled the supply to the mic? You could try ~1k between the 2k2 resistor and the +5V rail, and add 100uF or so from the junction of the two resistors to ground. Do you have a star ground arrangement so that the oscillator ground currents aren't affecting the mic amp?
  6. Alec_t

    Error in electric linear actuators and limit switches

    ..... provided the in/out drive polarity is correct. There's a 50% chance you may need to reverse it (unless the actuator datasheet removes any ambiguity).
  7. Alec_t

    AC adapter not working, strong burning smell

    As long as the voltage is correct you can use any adapter which can provide at least 1.2A. I see plenty of 10V 2A adapters advertised.
  8. Alec_t

    555 timer to turn on 2nd 555 timer

    This would be my approach. U1 is a (cheap) CMOS hex Schmitt inverter package. Inverter U1a provides the delay from switch-on (adjustable from ~2S to >10S with the components shown). The other inverters are strapped in parallel to boost the drive current available for the servo signal and form an...
  9. Alec_t

    555 timer to turn on 2nd 555 timer

    Hmm, that throws up a couple of problems: 1) the bipolar version of the 555 is not specified for a supply voltage less than 5V and 2) if you used a CMOS version instead it might not have the drive capability for a servo. Are you sure your servo will run from 3.7V and its control signal input...
  10. Alec_t

    Error in electric linear actuators and limit switches

    You could overcome the problem by including a respective power diode in series with each limit-switch. Like this :-
  11. Alec_t

    555 timer to turn on 2nd 555 timer

    Your interpretation of my instructions is correct; however, without having seen the schematic for B my interpretation of "turn on B" may have been a wrong guess. I assumed you meant trigger B. Sorry. Can you explain what "turn on B" means? Does B have a continuous power supply or do you want A...
  12. Alec_t

    555 timer to turn on 2nd 555 timer

    Connect pin 3 of the first 555 via a (e.g 33nF to100nF) capacitor to pin2 of the second 555. Connect that pin 2 via a ~47k resistor to the +ve supply rail. Connect a diode in parallel with the resistor (anode to pin 2, cathode to +ve rail).
  13. Alec_t

    Amplifier Potentiometer Replacement

    That would work, if you are happy without the detents. Perhaps you could Mcgyver some externally?
  14. Alec_t

    Circuit validation & improvement

    The LM358 output voltage can only get to within ~1.3V of the +ve rail. With that, and the voltage drops in Q1, Q2 and Q3 you are dropping around 3V in total. Have you considered replacing those transistors with a single p-channel MOSFET?
  15. Alec_t

    Amplifier Potentiometer Replacement

    So, it's R72. I reckon 10kk means 10k. On the schematic the text appears to read "10kA". Whether or not the "A" means logarithmic or linear is debatable, since A/B have not been used consistently by all manufacturers. Logarithmic would seem more appropriate in this application. As it's not a...
  16. Alec_t

    Amplifier Potentiometer Replacement

    Welcome to EP! The only gain controls shown in the schematic are normal (audio taper?) pots, not multi-way switched ones. The 12 positions are presumably defined by detents. Can you determine if those are internal or external? Pots with internal detents are available.
  17. Alec_t

    Interfering circuits

    I agree that decoupling of the power supply to the opamps and microphone is needed, and that the 555 should be replaced by a CMOS version.
  18. Alec_t

    Heater repair - mystery switch

    Try lubricating the bearings of the fan motor. Ensure neither the air inlet nor air outlet are obstructed.
  19. Alec_t

    Voltage across LEDs in series

    The anode of D2 is connected directly to the battery and should therefore have exactly the same voltage as the battery. If it doesn't, then there must be a poor connection (high resistance) between the anode and battery. For ordinary LEDs, 270Ω seems a rather low value.
  20. Alec_t

    LTspice to Hspice problem

    Welcome to EP! Does the sim run without error in LTspice? I don't know Hspice, but according to an Hspice guide, a behavioural voltage source has the syntax : Exxx n+ n- VOL=’equation’ + <MAX=val> <MIN=val>
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