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  1. Alec_t

    Water detector with NE555

    Try this add-on. Success depends on the added transistor Q1 having a high gain, since R8 needs to have a high value to ensure the 555 can be kept in a reset state when there is no water. If the LED doesn't light you may have to replace Q1 with a Darlington transistor or a P-MOSFET.
  2. Alec_t

    Water detector with NE555

    Welcome to EP. A LED in series with a 1.2k resistor, connected between pin 3 and pin 8 of the 555, would be one option. Assuming the usual situation is no water, then the added LED will draw ~5mA nearly continuously. If your 9V supply is a PP3 battery it won't last long. Is that ok?
  3. Alec_t

    Power Amplifier for thermoelectic cooler with Op-Amp and Power MOSFET PROBLEM

    Perhaps the controller providing the 0-10V input can only source a low current, so requires a high impedance load. Probably easier to source a standard E12 series value.
  4. Alec_t

    555 on/off circuit for 5v motor (w/ schematic)

    The 555 output stage includes push-pull transistors which can pull pin 3 (Out) up to within a volt or so of Vcc, or pull it down fairly close to Gnd. An additional internal transistor connected to pin7 (Dis) optionally assists the pull-down if it's necessary to get close to Gnd as quickly as...
  5. Alec_t

    555 on/off circuit for 5v motor (w/ schematic)

    The electrolytic cap seems to be connected directly across the power rails; not as per the schematic.
  6. Alec_t

    NPN circuit isn't switching after power change

    Your schematic shows the transistor collector connected via a resistor to the negative pin of the sensor instead of to the positive pin.
  7. Alec_t

    555 on/off circuit for 5v motor (w/ schematic)

    The only resistor going to the NPN base should be a 470 Ohm if you're using the post #2 circuit. This resistor should be connected between the base and pin 3.
  8. Alec_t

    555 on/off circuit for 5v motor (w/ schematic)

    Try this modification. Separate pots are provided for the on and off time adjustments. D3 is a back-emf spike-suppressor. C1 needs to have low leakage if you want fairly consistent time periods. A 555 is not ideal for accurate long periods, especially where electrolytic capacitors are involved.
  9. Alec_t

    Build a 120 vac to 18vdc Power Supply for DC Tool

    Welcome to EP. It will be cheaper, simpler and quicker to buy an off-the-shelf switch-mode power supply than to build one.
  10. Alec_t

    If I have a Li-Po battery connected to four quadricopter motors...

    That's certainly simpler than a gyro :) .
  11. Alec_t

    Greetings Electronics World :)

    Welcome to EP. We all have our problems :) . What's yours?
  12. Alec_t

    If I have a Li-Po battery connected to four quadricopter motors...

    To make it hover hands-free you will need a control circuit which gets feedback from a 3-axis gyro, otherwise slight differences in power output from the motors will cause the drone to drift up or down or even tip over.
  13. Alec_t

    How to trigger solenoid with very low current?

    Difficult to say from the write-up for that switch. If it's too sensitive you may find that 1.5 metres of wire makes a good enough antenna to pick up sufficient interference to give false triggers.
  14. Alec_t

    Need help building a circuit for low voltage alarm with bi color LED with flasher

    For lipo you need to monitor individual cells, to prevent any one discharging too far. Do the cells have individual protection circuits already?
  15. Alec_t

    Electromagnet project

    Welcome to EP. I'm sure the forum members can provide a schematic without you having to hire anyone, once you've decided whether you wish to use off-the-shelf modules as far as possible or go for a more component-level approach.
  16. Alec_t

    Need help building a circuit for low voltage alarm with bi color LED with flasher

    That would be more easily doable. I question the chosen voltage thresholds, though. Assumig you are monitoring a lead acid battery, it's my understanding that battery damage can occur if the voltage drops below 10.8V?
  17. Alec_t

    Can i repair my graphic card?

    Welcome to EP. Unless you can easily identify all the dead parts and can cheaply source replacements, have an infinite amount of free time and the skills to remove and solder SMD parts, just buy a new one :) .
  18. Alec_t

    Need help building a circuit for low voltage alarm with bi color LED with flasher

    Welcome to EP. While it would be theoretically possible to do what you want using discrete components, the sheer number of voltage thresholds and timed periods involved would require a bucket-load of parts. Have you considered using a microcontroller instead?
  19. Alec_t

    Microwave acts wrongly not working properly!

    Yes. It accounts for the origin of the phrase "computer bug".
  20. Alec_t

    How to trigger solenoid with very low current?

    Welcome to EP. How much current does the solenoid draw when supplied with 9V? Can you post a link to the solenoid spec?
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