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  1. AnalogKid

    Schematic Help

    Obviously a wiring error, probably at least two. Without a decent photo of the bottom side of the board, what do you expect from us? Make a sketch of the physical component layout, with a rectangle for each resistor. Based on your wired connections to the 4017, label each rectangle with the...
  2. AnalogKid

    Help Modifying Constant Current LED Driver from 700mA to 400mA

    The board has so many through-hole components that I'm surprised that they went with SMT for the current shunt. A 1 W wirewound would be smaller than the fuseistor at the top of the board and would fit in the space. Whatever - Glad it worked out. ak
  3. AnalogKid

    Help Modifying Constant Current LED Driver from 700mA to 400mA

    Image #3, right center, the 4 power resistors in parallel probably are sensing switch current, not output current. FR1 is a fuseable resistor, and VR1 looks like a transient protector, not a voltage reference. I don't see an optocoupler, but feedback could be run backwards through the...
  4. AnalogKid

    Auto shut off circuit

    First pass . . . Replace Q1 with a 2N4401 / 2N3904. Be **very** careful with the pinout Drain > Collector Gate > Base Source > Emitter Add a 10K resistor in series with the base to limit its current when the circuit turns on an the capacitor snaps up to 12 V. This will affect the...
  5. AnalogKid

    Auto shut off circuit

    As shown, Q1 *is* a transistor. If you are asking about changing the circuit to use a bipolar transistor instead of a MOSFET, that will require some changes. Is that what you are asking? ak
  6. AnalogKid

    Help to measure 10K sub amplifier voltage output with 20:1 voltage divider and envelope follower circuit fed into an arduino

    Diodes are not only large and small, but also fast and slow. What is the "flat" bandwidth you want to measure? Also, what is an acceptable minimum voltage to be measured. A bridge rectifier yields a smoother and more accurate waveform to be sampled and calculated, but adds a second diode drop...
  7. AnalogKid

    What types of LEDs

    My GUESS is that this is a reflective sensor. The clear part is an infrared LED emitter, and the "black" part is an IR-sensitive photo-transistor or photodiode. There are way too many different parts in these packages to guess at a specific part number. A guess at a circuit, the tab nearest...
  8. AnalogKid

    A Phony Question

    And the telco didn't try to find out why there was an almost 24/7, 5 mA fault current on a line? ak
  9. AnalogKid

    A Phony Question

    Yes. Does not matter. Diodes D1-D4 form a bridge that adapts either line connection polarity to the polarity of the circuit. This is common in many phone line circuits. If you have an extension phone, answering machine, or whatever, that is sensitive to the phone line polarity, it is an...
  10. AnalogKid

    A Phony Question

    Unofficial data from the 60's-70's: In the US, the standard cable from the pole and running around a house is 4-conductor, with only t conductors used for normal residential service. The inside stuff is called J-K (reason unknown) with a grey or olive-grey outer jacket (although I have a spool...
  11. AnalogKid

    Minimize Ripple in Rectifier by Waveform, Polarity, Bridge-Type, Inductor, Trafo?

    You want a full-wave output from the rectifiers. This can be done either with a non-center-tapped secondary and a full bridge, or a center-tapped secondary and only two diodes. The latter is slightly more efficient, but a center-tapped transformer (and yours almost certainly will be a custom...
  12. AnalogKid

    Homework

    It could stand to have a little more clarity, but it's a cute little puzzle. C ak
  13. AnalogKid

    Fool-Proof 5V charging circuit design

    Lithium batteries, even small ones, must be charged correctly. This involves both voltage and current monitoring. At your power level, there is no way you can build one for less than you can buy one. ebay is your friend. ak
  14. AnalogKid

    Target Shooting Game: A LED moves back and forth on a strip. Players press a push button to "shoot" when the LED is at a specific target position.

    True, but a non-uC approach covers a variety of digital design concepts. ak
  15. AnalogKid

    Target Shooting Game: A LED moves back and forth on a strip. Players press a push button to "shoot" when the LED is at a specific target position.

    WE NEED for you to show us your work so far; this is not a free homework service. Please post your schematic and parts list. Be sure to have a unique reference designator for each component so we can discuss them individually. Also, include details about the power sources, how fast you want...
  16. AnalogKid

    Alternating L/R 4-way flashers

    SPST - On / Off SPDT - Either / Or ak
  17. AnalogKid

    Alternating L/R 4-way flashers

    I like the #14 approach, but I would move D3 and D4 to the U3 NC contact. Other than that - Doesn't this approach require that the "normal" wiring from the brake and turn circuits to those lights be diode- or relay-isolated? I would prefer diodes, but a 4PDT relay would eliminate all 8...
  18. AnalogKid

    Can an audio amplifier be used to transmit or receive radio signals?

    Your professor was paraphrasing Confucius. CHAP. XVII. The Master said, 'Yu, shall I teach you what knowledge is? When you know a thing, to hold that you know it; and when you do not know a thing, to allow that you do not know it;-- this is knowledge. Confucius (September 28, 551 – 479 BC)...
  19. AnalogKid

    Help with a simple circuit

    If the 12 V bulb also is being powered through the regulator IC, that is 120 mA for the relay coil and 120 mA for the bulb. Increase C1 in the schematic to 1000 uF, and increase the size of the heatsink. ak
  20. AnalogKid

    Help with a simple circuit

    Just a coincidence, the component values in post #2 should be ok for your application. Assuming your AC source is 17 Vrms (as opposed to peak or peak-to-peak), the regulator will dissipate over 1.25 W and should have a small heatsink. ak
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