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  1. AnalogKid

    BJT Basics questions

    1. In the transistor diode model of an NPN transistor, both anodes are connected to the base. Therefore, in normal operation with collector current flowing, the base-emitter junction is forward boased and the base-collector junction is reverse biased. This is why when a transistor is talked...
  2. AnalogKid

    BJT Basics questions

    With the addition of two resistors to limit base currents to safe values it will work exactly like an SCR. Really. ak
  3. AnalogKid

    voltmeter on bridge rectifier

    When 24 Vac is full-wave rectified by a diode bridge, the result is not 24 Vdc - it is closer to 32 V which is an overrange for a 29.99V DC meter. 32 V comes from the secondary AC voltage times the square root of 2, minus the forward voltage drop across two power diodes. Of course, since we...
  4. AnalogKid

    BJT Basics questions

    In the latched (on) state, both junctions are forward biased. In the off state, neither junction is biased at all. When Vb = Ve, the transistor is off but the base-emitter junction is not reverse-biased. Also, Q1 should have a resistor from base to emitter for reliable operation. ak
  5. AnalogKid

    Modernise old rotary telephone

    Good idea. Fortunately, the MT8880 *is* a DTMF transceiver. ak
  6. AnalogKid

    Come & get yer watts!!!

    Here's one from 1840: https://en.wikipedia.org/wiki/Maximum_power_transfer_theorem ak
  7. AnalogKid

    Mic detection circuit

    They are very common in conference rooms with long tables, where each element picks up its side of the table, and in depositions where the questioner and deposee wind up semi-isolated on the two stereo channels. ak
  8. AnalogKid

    Mic detection circuit

    If you are talking about active noise cancellation, I've never seen that at the microphone level. Microphone noise cancelling and response shaping is done acoustically, with vent shaping and placement. ak
  9. AnalogKid

    Modernise old rotary telephone

    Both the arduino and PIC have trouble doing touch tones well because servicing the D/A and its update rate suck up so much CPU time. The 8880 is overkill for the project, but should work. 8880 app notes have interface circuits. Also, search for "telephone hybrid schematic" to find many more. ak
  10. AnalogKid

    Mic detection circuit

    A single microphone can have two independent elements mounted back to back internally. But those do not have a standard round ball; it is far more obvious where the two elements are pointed. ak
  11. AnalogKid

    Car Battery Powered House Ideas, Questions

    Given that you have to charge up the batteries somehow, and then convert the DC back to AC to run the household devices, the overall energy efficiency will be about 50% of just using an AC outlet directly. What is the point of the project? ak
  12. AnalogKid

    Mic detection circuit

    As with most of the OP's responses, I don't thing that one translated well. I doubt that the adapter is for connecting a mono microphone to a stereo input. Given the mocrophones shape and the location of the switch, I'll stick with an SM58 clone with a transformer output. ak
  13. AnalogKid

    What capacitors to purchase?

    If you are talking about buying a "complete" set of capacitor values like you did for resistors, many distributors have kits that are less expensive than a long list of individual part numbers. If that isn;t an option, here are my suggestions. For values, follow the series 1, 2.2, 3.3, 4.7...
  14. AnalogKid

    Mic detection circuit

    It's amazing how information slips away after only 30 years of not using it. Many dynamic microphones have an impedance matching transformer built in. The mic element is a high impedance low current generator, and the transformer steps the voltage and impedance down to drive a long cable. The...
  15. AnalogKid

    Can changing wire gauge affect EMI certification

    Certs requirements vary significantly among countries. For US military projects, changing the wire gague would require a recert. Changing the manufacturer to an identical wire with a different UL registration file number would require at least an audit. ak
  16. AnalogKid

    Mic detection circuit

    Part of the measurement problem might be the cable. Lets go back to basics. Unplug the cable from the microphone. The base of the mic has a 3 pin XLR connector. If you squint, you can see the pin numbers molded into the connector. With the mic switch ON, measure the resistance between pins...
  17. AnalogKid

    Mic detection circuit

    The resistance across the balanced output pins should be different in the on and off positions. This *might* be detectable with what is basically a very low current ohmmeter circuit/comparator. A potential problem is that many microphone input circuits have a low input resistance, and this...
  18. AnalogKid

    Mic detection circuit

    What is the resistance of the microphone output pins with the switch in both positions? ak
  19. AnalogKid

    Daylight-turn off

    http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=photoelectric+light+switch&_sop=15
  20. AnalogKid

    Car Power Inverter

    That is a "modified sinewave" inverter, and is *not* the same as plugging a consumer stereo product into a domestic wall outlet. don't be surprised if there is a constant buzz out of the speakers. ak
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