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  1. AnalogKid

    3v from a 5v power supply

    What is the allowed voltage range for powering the device? ak
  2. AnalogKid

    3v from a 5v power supply

    If the 5 V thing is actually a power supply that converts AC mains into a regulated 5 V DC, that is an entirely different question. For that, a couple of 1N4002 diodes in series with the 5 V output will reduce it by approx 0,7 V per diode. Or not. What is the peak current being drawn by the...
  3. AnalogKid

    Help with Transformer Theory

    What you are missing is that the transformer core is, both in theory and in practice, an energy limiter. When the 10 V is transformed up to 20 V, the available max current is transformed down to 1 A. When calculating the current through a resistor, Ohm's Law assumes a theoretically perfect...
  4. AnalogKid

    Inject sound to a phone landline (electric boogaloo)

    For a standard phone line, the phone signal is on the center two pins of an RJ-11 connector. In the cable, the wires are red and green. Since you know nothing about the interface circuits for the modem and the Sega, start with a coupling transformer. Typically these are designed for an...
  5. AnalogKid

    Hello, I want to reduce 12 volts to 7 volts, how many ohms do I need using a resistor?

    3.
  6. AnalogKid

    Hello, I want to reduce 12 volts to 7 volts, how many ohms do I need using a resistor?

    This question is so blazingly incompetent, it smells like a troll. ak
  7. AnalogKid

    LED not working

    The original bulbs were incandescent. If the new ones are simple LEDs with no internal current limiting, they will burn up. Please post a link to the LEDs you are using. ak
  8. AnalogKid

    LED not working

    Shouldn't that be L-E-D - ? ak
  9. AnalogKid

    Relay LED Optocoupler Circuit

    Both sides of the opto couplers are referenced to the same GND. Because of this, the optos can be replaced with simple 2-resistor voltage dividers. ak
  10. AnalogKid

    LED 1 input 2 output

    After the second LED is on, what happens if the switch is toggled again in under 5 seconds? Does the circuit revert to LED #1, or does it stay on LED #2? ak
  11. AnalogKid

    Looking for an old Motorola IC OpAmp SC9533P (7308)

    Why? Those parts have absolutely nothing to do with this thread. am
  12. AnalogKid

    How to use low voltage switch for 110V circuit

    Too bad. The switch is rated for a max. of 30 V, so you will need a low voltage supply. Simple and cheap - an old USB wall wart / phone charger / camera charger / etc. That, plus a solid state relay rated for at least 50% more than your 110 V load current. Most SSR's have a current-limiting...
  13. AnalogKid

    RCA 45J Problem

    Any photos? Make and model number of the device? I know what you are talking about, but my guess is that half the people on this forum don't. ak
  14. AnalogKid

    Looking for an old Motorola IC OpAmp SC9533P (7308)

    That is an early audio power amplifier, probably rated for 2-5 W. GE made similar parts in the PA2xx series. In the 1970's, Sprague made the ULN2280 / 2281; they have the same package and probably the same pinout. Also, National made a variation of the LM380 in that package, plus the LM384...
  15. AnalogKid

    Adding an audio output to an old answering machine

    Yes. ak
  16. AnalogKid

    Using a DC voltage to drive a relay to interrupt a power supply

    You need a DPDT (Double Pole Double Throw) relay with a 24 Vdc coil. The relay contacts must be rated for more than 24 V, and the current rating for the contacts should be at least twice the power supply output current that is being interrupted. Connect the power supply output to the relay...
  17. AnalogKid

    Help To Determine Resistor To Dim Incandescent Light Bulbs

    Don't see why not. Two say LED because that's what most people are searching for. One says motor because that is another popular product. To be clear, I do not have any experience with any of these specific products. But a simple PWM circuit with a big enough power transistor should have no...
  18. AnalogKid

    Help To Determine Resistor To Dim Incandescent Light Bulbs

    If you want to buy rather than build, my first stop is ebay...
  19. AnalogKid

    circuit breaker alarm

    Here is a first pass at a schematic. The PIR signal at P1pin2 drives Q1 to control the beeper. When power is applied there is 0 V across C1, so the Q2 gate is at 9 V and it pulls the Q1 base to GND no matter the state of the PIR signal. After about 1 minute, C1 has charged up (down?) to...
  20. AnalogKid

    circuit breaker alarm

    How long a delay? The datasheet says the module can take up to 60 seconds after power-on to stabilize. The sensor output can drive a 2N2222 directly, so what is needed is a circuit to inhibit this for 1 minute, then get out of the way and let the PIR have direct control of the beeper. First...
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