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  1. AnalogKid

    24VDC Relay Driver switching 240VAC 10A Load

    With proper attention to trace width and copper thickness (weight), a pc board design can handle your voltage and current easily. After all, they are common in many power supplies. Since a relay has true galvanic isolation, why do you have an optocoupler between it and the PLC? Very few optos...
  2. AnalogKid

    Negative Voltage

    The thing to remember is that there are very few absolutes in physics, and this ain't any of them. Positive and negative are 1) completely arbitrary terms, just like up and down; 2) they are relative terms, and are meaningless without a reference point. A voltage is not positive or negative...
  3. AnalogKid

    Quiz buzzer system

    The ultra-ultra-simplest circuit uses neon bulbs as both the latch element and indicator. I've lost it somewhere. ak
  4. AnalogKid

    Quiz buzzer system

    OK, second pass at a minimal game show circuit. Same basic logic description as post #7. Note that the OR-ing diodes are LEDs, with a Vf of around 2 V. To meet CMOS AC logic levels, best to run the circuit on 9 V or more. It should work on 6 V, but this is untested. ak
  5. AnalogKid

    Quiz buzzer system

    U2A is an inverting-input OR gate (if any input goes low, the output goes high) which is turned into a NOR by U2B. An OR function of some kind is a central element of all game show circuits. It doesn't form a latch with the 7475 in the normal sense, but it does drive essentially drive a...
  6. AnalogKid

    Quiz buzzer system

    It is the same logic as in post #2. U1 is a transparent latch. When LE is low, it sits there as, effectively, eight non-inverting buffers. When any input goes high, it goes through to its LED and R1. This pulls LE high, clocking all latches and freezing the system. OOPS - got the LE...
  7. AnalogKid

    Quiz buzzer system

    First pass at a reduced component count game show circuit. This is an extension of the circuit in post #2. By changing the logic polarity of the inputs and outputs, the LEDs act as an OR-ing diode array into R1, with the correct logic polarity to drive the latch input. SW9 is the moderator's...
  8. AnalogKid

    Quiz buzzer system

    The first schematic will work, but expanding it to 8 inputs gets a bit messy growing an 8-input OR gate. I've done this without doing that by using a 74AC573 octal transparent latch with a resistor network and one transistor forming a NOR gate. I can post that if anyone is interested. The...
  9. AnalogKid

    High Current DC Switching

    Referring to the schematic in post #1, you can solve the turn-off problem with a 1K resistor from the emitter of Q1 to GND. This preserves the logic polarity of the original design. The current through Q1 is only 12 mA, so the fact that the voltage drop across an emitter follower is slightly...
  10. AnalogKid

    What is this???

    You show no images of the other side of the part, so it is impossible to tell. Hi-pot testing usually is between a transformer's primary and secondaries, but it could be from a single inductor to the frame. If you are sure it a) is undamaged, and b) has no other electrical connections, then it...
  11. AnalogKid

    Brake light flasher (555 - based) circuit works on breadboard, but not PCB

    If the pcb layout is correct, simply removing Q1 with no other changes will turn the circuit into a continuous oscillator. If not, the problem is in the 555 oscillator circuit (or a bad 555). C2 does not have to be polarized; it could be a ceramic or foil capacitor. But if it is polarized...
  12. AnalogKid

    Brake light flasher (555 - based) circuit works on breadboard, but not PCB

    If the time the board is not blinking is the same as the time the prototype is blinking, then the 555 reset circuit (Q1 et al) might be ok. Next is why the 555 is not oscillating. Remove Q1. The output should blink continuously. Let us know. ak
  13. AnalogKid

    Darlington pair false triggering.....

    As a test. ground the inputs rather than leave them floating. The TIP122 has built-in resistors across both base-emitter junctions. The odds are 99% that you have the transistors connected incorrectly. Check the pinout. ak
  14. AnalogKid

    Problem with 555 timer

    First, since you are a whiz, post a schematic. Be sure to have a reference designator for each component so we can discuss them clearly. ak
  15. AnalogKid

    How does the sallen key filter work?

    Since the mixer is driven by a square wave on one input, it might be functioning as a full-wave rectifier. But it isn't a diode, so there would still need to be one before whatever kind of filter. This is assuming that the DC level he wants represents the peak value. If the RMS value would be...
  16. AnalogKid

    value of learning vs value of meter

    Modifying a hobby kit (not the most accurate meter in the first place) to extend its range by 50x (to reach 10,000 uF, a reasonable top end for hobby circuits) is not trivial (even if we had the kit schematic, which you did not share), and you won't be able to trust the results because you will...
  17. AnalogKid

    Need help building a roulette game

    One of the schematics in that link triggered an old thought. Here it is from another forum. On yet another forum there was an incorrect discussion of how the oscillator works. https://forum.allaboutcircuits.com/threads/wheel-of-fortune-circuit.115524/ Here is an older version of the same...
  18. AnalogKid

    Need help building a roulette game

    This is sometimes called a Wheel Of Fortune circuit. https://images.search.yahoo.com/search/images;_ylt=A0LEVxTkWOhYH50AIB1XNyoA;_ylu=X3oDMTE1OG9zYTB2BGNvbG8DYmYxBHBvcwMxBHZ0aWQDVUkwMkM0XzEEc2VjA3BpdnM-?p=wheel+of+fortune+circuit&fr2=piv-web The better circuits will have an exponentially...
  19. AnalogKid

    Questions resect plastic of electronics

    Standard big 40 W fluorescent bulbs make a fair amount of UV, and can yellow the plastic case of a monitor in an office in just a few years. Same with white LEDs, but my guess is that the UV production per lumen of visible light is lower than for fluorescents. ak
  20. AnalogKid

    Some Help With Volt Scale Reversal Needed For An Idiot.

    Only if the load resistance is low enough to pass the current. With a high value resistors load, a 3914 output will try to sink the programmed current to the point of saturating. At that point it looks like a saturated switch. For example, with a 10 V Vcc and a 1 K load, the max possible...
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