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  1. AnalogKid

    Circuit Help

    If you are sure that only one LED will be on at any time, then you can eliminate all of the resistors next to the LEDs and have just one resistor in series with the entire circuit. ak
  2. AnalogKid

    EEG circuit - need help please!

    Opto couplers are not ideal for analog signal isolation. OK, they suck. The LED and phototransistor have different gammas; what could possibly go wrong??? Fortunately, both ADI and BB make isolation amps with DC recovery. ak
  3. AnalogKid

    EEG circuit - need help please!

    I've seen this circuit before, and it is a very poor piece of design. It uses 5 chips where 2 will do, is basically just some filter stages and a gain stage, and has no power decoupling. The hard part, a differential amp with the mandatory common mode rejection, isn't even shown. If you...
  4. AnalogKid

    help with voltage reducing, then amplification

    A single precision opamp configured as a difference amplifier with 0.1% resistors will have a CMRR of less than 60 dB, while the INA114 has a higher input impedance and a minimum CMRR of 96 dB, 63 times better. Both the lower input impedance and lower CMRR contribute to what appears as a gain...
  5. AnalogKid

    help with voltage reducing, then amplification

    Not. Mentioning the 741 usually brings on a flurry of childish hyperbolic borscht about how old and terrible it is. But for what you are trying to do there are in fact many better individual opamps and way better integrated instrumentation amps, parts that would have been black magic back in...
  6. AnalogKid

    help with voltage reducing, then amplification

    "A man's got to know his limitations." ak
  7. AnalogKid

    help with voltage reducing, then amplification

    Since this is your first foray into differential signals, I strongly recommend that you buy an integrated instrumentation amplifier in a chip rather than try to grow one. Growing one from scratch is all about the resistors. Even with 0.1% parts, nothing you assemble will equal the performance...
  8. AnalogKid

    Randomizer help

    What is the maximum allowed time delay between power-on and the decoded decimal output being stable? Also, are the outputs allowed to change or bounce around before he stable output, even for just a few microseconds, or do they have to snap to the stable output? ak
  9. AnalogKid

    Time Base and Crystal

    Depends on what output frequency you want. For a 1 Hz output, no. ak
  10. AnalogKid

    Time Base and Crystal

    If you can afford it, if you have room for it, and if you can afford and have room for the additional dividers to get down to 1 Hz - yup. Also, when you get away from the 32 K watch crystal and up into the realm of "real" crystals, there are many more packaging, accuracy, and stability options. ak
  11. AnalogKid

    Help regarding possibility and planning

    Note that while we can't see the bottom side of the board in your link, none of the visible components are as small as in post #2. Surface mount (SMT) parts are fundamentally more difficult to handle/solder/unsolder than through hole (PTH), but there are degrees. The device in the link is not...
  12. AnalogKid

    Push button start-stop computer psu without motherboard

    One option is a toggle switch. Flip up = on, flip down = off. If you really want a push-on/push-off button, you need an alternate action pushbutton switch. Either way, grounding the control wire (pin 16, often a green wire) enables the supply. Switch bounce is handled inside the supply...
  13. AnalogKid

    Requesting help for my project..

    We don't know you. We don't know your experience base, you're skill set, or your interests. Only you can select a project that meets your needs. After that we can help, but the first step is all yours. ak
  14. AnalogKid

    Need advice on relay. (Wiring rf transmitter into burglar alarm)

    Also, meter the PIR power supply output terminals in the armed and disarmed conditions. If they turn off PIR power when disarmed, you can use that output to drive another small relay for armed signaling. ak
  15. AnalogKid

    Digital Roulette

    Your schematics look great and will work exactly as drawn. Just fill in the rest of the components and you're good to go. ak
  16. AnalogKid

    Capacitor Question

    The capacitor combines with the pull up resistor and the thermistor value form a lowpass filter to reduce radiated noise picked up by the wires going out to the thermistor. As usual with Colin, his response is technically correct but intentionally obscure and of no value. A capacitor stores...
  17. AnalogKid

    I need some feedback on connectors

    OK except for this one. The VGA connector is a high-density D-subminiature, and the pins sometimes wiggle around enough to miss the sockets. Better to use a game port (joystick port) cable - same 15 pins in the next larger body size, with the pin spacing and ruggedness of a 9-pin serial. Note...
  18. AnalogKid

    TCXO or oven heated oscillator? Which one and why.

    I don't think there is any fixed rule of thumb about when to use which. Generally speaking, an oven device has better stability and faster warm-up to specified operation, but is larger, more power hungry, and more expensive. So it is a SWaP (Size, Weight, and Power)-and-money-vs-performance...
  19. AnalogKid

    Time Base and Crystal

    Let's not. Generally speaking, 32.768 kHz crystals are not nearly as accurate or stable as higher frequency devices. However, the are smaller than may other standard crystal packages and lower cost. So for a production product it is a cost vs. performance decision. ak
  20. AnalogKid

    Remote signal

    The description of the problem is not very clear. Can you post a sketch of a schematic or block diagram showing the signals and howthey interconnect? ak
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