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  1. K

    Problem understanding an answer given to a question in 'Complete Electronics Self-Teaching Guide'.

    I don't get where they get 1A from, when the question specifically says a max of 20 mA. I think it's a typo. Maybe the question was originally worded 1A and changed to 20 mA and the answer wasn't modified accordingly. I would say the correct answer is 5K ohms as well.
  2. K

    Mistakes You Can Avoid

    To amend #10, get a variable power supply that also has adjustable current limiting. Then you can reduce the chances of releasing magic smoke by powering up with limited current at first, until you're sure nothing is shorted or miswired.
  3. K

    3 Phase Motor - 3 Individual Circuit Breakers - Detect if 1 Breaker Tripped And Shut Down Motor

    How about connecting the coils of 3 relays, one to each phase, then wire the contacts in series so all 3 relays (phases) have to be energized for current to pass. Then run the control signal for your main motor relay (the 3 pole one) through the 3 series relay contacts. Bingo, the motor only...
  4. K

    Harman Kardon AVR 330 Receiver

    Optical inputs don't light up since they're receiving an optical signal via a photodiode, not sending one via a LED. Can you post a pic of the CUP 11581-3 board? Maybe some bad capacitors on it. You did verify the settings were correct, selecting the correct optical input for your source? If...
  5. K

    Lessons Learned and When the Chips Are Down

    "Capacitors shorted to ground"... do you mean a capacitor connected between some part of the circuit and ground? Like C5, C6 and C7 in the schematic Audioguru posted above? (I'll be referencing that schematic in my post below for convenience) C6 and C7 are power supply decoupling capacitors...
  6. K

    Led driver of constant current - is it really constant ?

    I don't know what the application for your circuit is (what is it being used for) but maybe look at circuits used in solar garden lights, like these (there are 2 different circuits described on this site): http://www.talkingelectronics.com/projects/SolarLight/SolarLight.html These circuits...
  7. K

    Sony discman not turning on

    Have you opened it up to take a look? It could be something as simple as a broken wire between the battery terminals and the main PCB. Or it could be a bad capacitor or voltage regulator.
  8. K

    Epson Artisan 835 power issue

    Thanks for your reply. I haven't done anything further yet... printer is still in the same state of partial disassembly on my desk. Obviously not a huge priority LOL. Good point on load testing. I'll have to see what I have for power resistors in my pile of junk. Option B would to be...
  9. K

    FAAC XT4 868 SLH remote control frequency emission

    Is it possible to change the code on your gate? Most remote systems use changeable codes to prevent this very thing from happening... also for those with 2 or more garage doors wanting individual control of each. It also makes it harder for burglars to clone your remote and open your gate/garage.
  10. K

    Video over laser

    What's the purpose? Can't you use WiFi or Bluetooth?
  11. K

    25 PF Capacitor sub

    Ditto, the difference will be negligible if any. I think it's just to prevent the 741 from oscillating at high frequencies, by damping them. Basically a low-pass filter, with a high cutoff judging by the small capacitor being used.
  12. K

    25 PF Capacitor sub

    What's the smallest capacitor you have? The smallest in the kits you linked (your 1st link) are 100pF. If you have a couple 12pFs you could parallel them. In a pinch you could connect 4 100pF caps in series to get 25pF but that's a kludge. Maybe find some locally (if you have any electronics...
  13. K

    How to protect battery from a power adapter?

    A switched DC jack is ideal as mentioned. If you use diodes, you'd need one on the DC power input as well as on the battery. One to prevent the battery feeding into the DC jack (if the adapter is connected but unplugged), and another to prevent the DC input from feeding into the battery...
  14. K

    Led driver of constant current - is it really constant ?

    A LED, like all diodes, don't act like a resistive load. You can't reliably use voltage to control current through a diode. The Vf of a LED isn't always consistent across samples, or at different currents or temperatures. Without a resistor or some other form of current limiting, the LED will...
  15. K

    Led driver of constant current - is it really constant ?

    You could simply use a series resistor with a 3+V supply though a switching IC will be more efficient, thus better battery life.
  16. K

    Led driver of constant current - is it really constant ?

    You want constant current, not voltage for driving LEDs. Voltage just has to exceed the forward voltage of the LED, which the chip you listed will provide even from a single cell. What's your application? That chip appears to be geared toward smaller LEDs at low mA usage, so something like...
  17. K

    Led driver of constant current - is it really constant ?

    To me that isn't really a "constant" current source, since the current varies with supply voltage. It's not a regulated current source in other words. It's sort of like a fancy, efficient resistor. Its purpose in life is to boost the supply voltage and allow LEDs to be driven from a single...
  18. K

    I need a relay HJR-3FF-S-Z 24v coil

    There was no "nib" that I noticed. The "S" in HJR-3FF-S-Z indicates it's a "sealed" relay, and there were no holes, nibs, or even a seam to crack it open without breaking it. I think the contacts just welded over time and got stuck. It's working again for now, if it fails again I'll replace...
  19. K

    I need a relay HJR-3FF-S-Z 24v coil

    Update: I unsoldered the relay and tested it. Coil had resistance, and when I put a 9V battery across it, I could hear the contacts "try" to pull in, so I hit it with a 12V power supply I had, and after a couple hits the contacts started clicking again, and working properly. They must have...
  20. K

    I need a relay HJR-3FF-S-Z 24v coil

    The relay isn't clicking, even though I confirmed the coil is receiving 24V DC when I press the forward button. This weekend I'll unsolder it from the PCB and check the coil and contacts for continuity out of circuit.
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