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  1. AnalogKid

    Low frequency adjustable but stable oscillator

    That's not how it works. If you assume an infinitely accurate and precise crystal with zero drift/aging/whatever, and use it in a circuit where the output frequency can be modified by a pot, then the stability of the pot completely overrides the stability of the crystal. In worst case round...
  2. AnalogKid

    Low frequency adjustable but stable oscillator

    Agree. If the motor is running exactly 10% fast, that sounds like a 50 Hz motor running on 60 Hz.
  3. AnalogKid

    Low frequency adjustable but stable oscillator

    A crystal circuit with that adjustment range is not simple. Two methods that come to mind are phase-locked loop and direct digital syntheses. Since a squarewave signal is acceptable to you, a starting point might be a CD4060 oscillator/divider with 1% capacitor, a 0.1% resistor, and a trimpot...
  4. AnalogKid

    Help requested to identify common emitter, collector base bjt circuits

    I skimmed through the thread and did not see this: Back to the original post, #5 is incorrect. #5 is common collector, just like #2. There are pedantic, semantic, and qualifying issues with each statement, but I see the kind of truth table you are trying to construct. All of the subtleties...
  5. AnalogKid

    ECG circuit digram with AD620 and 741 op amp as a gain differentiator

    After 8 years, I don't think the OP is completely invested in a solution. In case anyone else is, here is one common way to do this. ak
  6. AnalogKid

    Using AC/AC wall adapter and converting to DC

    Maybe quality is a contributing factor, but a minor one. All transformer outputs decrease with load. Separate from that, and even without R25 and R26 in the circuit, the two output voltages are completely unregulated. This means that the AC ripple voltage component of the output voltage is...
  7. AnalogKid

    Siren circuit

    Paraphrasing Rear Admiral Joshua Painter, "Engineers don't take a dump, son, without a schematic."
  8. AnalogKid

    clock movement battery

    If your DVM does not have a Diode mode, try this. Put the diode in series with a 1 K resistor, connect the string to a 9 V battery, and measure the voltage across the diode. With the battery connected one way you will read 9 V. with the battery connected the other way you will read the...
  9. AnalogKid

    clock movement battery

    Yes, it is a special kind of diode. The color has nothing to do with the diode type. Most signal-level and low power level diodes are either black epoxy or clear glass. The stripe, or band, is an indicator of the cathode end of the diode, Without diving into the device physics, generally...
  10. AnalogKid

    Split Power Supply using xformer w/o CT

    IOW, in the #2 schematic, delete C1, C2, D2, and D4. Tie the D3 anode and D4 cathode to the upper transformer point. Leave the lower transformer point connected as is. ak
  11. AnalogKid

    clock movement battery

    Yes. A normal alkaline battery is *not* rechargeable. Put a small Shottkey diode in series with it. This prevents current from the buck converter going "backwards" through the battery. Next, adjust the output of the buck converter so that it is approx. 1.8 V. This is the 1.6 V of a fresh...
  12. AnalogKid

    Audio signal conversion

    If that was a response to my question, you misunderstood. I have some familiarity with what a VU meter is (and a copy of Howard Chinn's book). My question was for the TS, to see exactly what he is working with. There are many things out there that are called a VU meter, but do not meet most...
  13. AnalogKid

    clock movement battery

    I think Kiwi has the right idea. A simple alkaline cell will provide years of intermittent backup service. If you really want a rechargeable in there, go with a nickel-cadmium (NiCd) cell rather than a lithium. A single resistor can trickle-charge it forever. It may take a day or two to come...
  14. AnalogKid

    Basic Announciator

    Leaving out parts to reduce clutter, improve clarity, and focus on the unknown parts of a circuit is fine, as long as you state what you are doing so we all don't jump on what look like newbie mistakes. Is this part correct? The one-second beeper monostable is triggered by the leading edge of...
  15. AnalogKid

    Audio signal conversion

    Can you post any information or links to the VU meter and its board? ak
  16. AnalogKid

    Decade counter to Momentary relay?

    That is exactly what I had in mind. The 2N7000 can handle easily a -5 V gate voltage. Still do not know the required minimum recovery time. If the TS does not need a short recovery time between activations, D1 can be removed. ak
  17. AnalogKid

    Basic Announciator

    True, the circuit as shown needs work, but it might me more of a concept drawing than an actual schematic. Still waiting on a TS response. ak
  18. AnalogKid

    Basic Announciator

    This sounds like a retriggerable monostable. A little switch bounce fur at the end of its input signal is not going to have a large effect on a 3 minute period. ak
  19. AnalogKid

    Basic Announciator

    It sounds like what you want to do is add a 1 second monostable to the output of the 3 minute timer. The output of this monostable drives the beeper. Because the 3 minute timer is stable for much linger than 1 second, you can get away with a "boxcar" circuit, basically a differentiator, that...
  20. AnalogKid

    Need help in converting a 12VDC 16.5A PSU to +-17.5VDC 2A PSU

    To expand on post #2 - Most boost converters, certainly most modules on ebay, are non-isolated; the input GND is tied directly to the output GND. If you start with two "normal" positive boost converters, there is a conflict where the output grounds are connected. If you want to stay with this...
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