Search results

Search Forums New Posts
  1. Alec_t

    Have 3,3V need 15V

    A single 'normal LED ' has a forward voltage of about 2V if it is red/green/yellow or about 3V if it is blue/white. Anything rated higher means it is either a series string of LEDs or else a single LED combined with a series current-limiting resistor. I have never searched for off-the-shelf...
  2. Alec_t

    Why do some devices turn on with the mains before the "On" button is pressed?

    Many domestic appliances these days never switch off fully: they only go into a deep sleep from which they can be woken with a button press or screen touch.
  3. Alec_t

    Have 3,3V need 15V

    You can use a level-shifter as a driver for a LED, based on this principle :- The component types/values will depend on how much current the 'LED' draws. Rx represents the current-limiting resistor in series with the 'LED' (which is presumably a LED module rather than a single LED, if it is...
  4. Alec_t

    Sennheiser HD429 Earphones. Cable broken.

    I repaired a headphone set (not the brand you have) with a similar broken cable problem. I found about 30Ω from wire A to wire B, the same from wire C to wire B, so concluded that B was a common ground and that A and B were the Left and Right channels (though which was L or R remained a...
  5. Alec_t

    Sennheiser HD429 Earphones. Cable broken.

    Do you have an Ohm-meter with you on hol? If so, measuring resistance between the wires should give a clue as to function. With that sort of wire I've found putting the ends briefly in a small flame was necessary to burn off an insulating layer which prevented soldering.
  6. Alec_t

    Replacing tiny IR LED

    Sounds as though one of those pins might be causing the problem, perhaps by shorting something? Or else the pcb has a trace with a micro-crack which opens when the pcb is flexed/stressed in a certain way?
  7. Alec_t

    Replacing tiny IR LED

    How did you measure that? If the diode is being pulsed then a DMM would give a misleading 'sort of average' reading. Do you get the same measurement at a working diode?
  8. Alec_t

    Practical, simple circuit and method in make our own oscillating volt meter

    It rather depends on what oscillation frequencies and voltages are involved. Hz, MHz? Volts? Hundreds of Volts? ......?
  9. Alec_t

    Ps4 dualshock 4 controller thumbstick goes from analog to "digital" signal

    Does the web-site now have the option to select analog or digital controllers? Sounds like it might be assuming a digital controller is being tested.
  10. Alec_t

    Laptop Short causing weird symptoms

    Resize it to <300k and upload it here.
  11. Alec_t

    how to identify max forward current in an infrared LED with no spec sheet

    I'd go with 80%, or even less. It's never a good idea to run components at their maximum rating if you want them to have a long and happy life.
  12. Alec_t

    Astable multivibrator circuit making me astable

    A completely symmetrical circuit, as in the case of a classic multivibrator, can confuse LTspice sometimes, and it helps if slight asymmetry is introduced so that oscillations can get started. Alternatively, the .uic directive can be used to specify a starting voltage/current for a particular node.
  13. Alec_t

    Increasing the output voltage of a step-down transformer by reducing the number of coils

    Most appliances designed to run from mains will tolerate a considerable variation in the mains voltage.
  14. Alec_t

    Astable multivibrator circuit making me astable

    Depending on the transistor gains and other circuit component values that may be a stable position.
  15. Alec_t

    Increasing the output voltage of a step-down transformer by reducing the number of coils

    In general, no. There would be a risk of saturating the transformer core and the transformer could overheat. If there is space to do so you could wind extra turns on the secondary. Yes, definitely. But never run components at their rated maximum values if you want them to have a long and happy...
  16. Alec_t

    Astable multivibrator circuit making me astable

    Most NPN transistors will work if the C and E connections are reversed, but the current gain differs for the two directions.
  17. Alec_t

    Opto Coupled Tunable Coil Circuit - Comments Please

    Simulation of your circuit (albeit with guestimated component values) with the value of that cap changed by a factor of 100, suggests the cap value has no detectable effect when the cap is in series with the primary, but increasing the value reduces the output from the secondary when the cap is...
  18. Alec_t

    Opto Coupled Tunable Coil Circuit - Comments Please

    I don't see how, if the opto-coupler is a standard type, which has a LED as the input device.
  19. Alec_t

    Opto Coupled Tunable Coil Circuit - Comments Please

    How? The schematic shows it in parallel with one coil only.
  20. Alec_t

    Electric circuit problem

    ... or if you run a sim and left-click the transistor's emitter or collector you can plot the current into that node.
Top