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  1. KrisBlueNZ

    Best type(s) of capacitor

    Dave, in the circuits I have mostly dealt with (audio-frequency analogue, interfacing, digital) each individual capacitor is usually used for one purpose or the other, but a capacitor can do both for different frequencies, and that's a clever use of resources. :-)
  2. KrisBlueNZ

    Help with Under Water Sony Remote?

    Excellent advice from CocaCola, and Steve as usual. I have heard that the carbon pads in the rubber key overlay that make contact with the gold plated contacts on the PCB when the button is pushed down can be rejuvenated with graphite (or powdered 6B pencil "lead" which is nearly the same). I...
  3. KrisBlueNZ

    Best type(s) of capacitor

    Thanks bishop01 :-)
  4. KrisBlueNZ

    transistor circuit for counting wheel rotations

    I imagine the most important feature of the rotation detector is robustness. These derby cars will be bouncing around and shaking like crazy, won't they? My first thought would be a bump on the axle and a low-force microswitch with a metal arm that the bump pushes. I was about to suggest a cam...
  5. KrisBlueNZ

    What value of resistors do I need and a sanity check

    I had a quick look at that page. The spelling and grammar are awful. Admittedly it's written by a non-English speaker but that level of carelessness does not inspire confidence - not that I had much confidence in this TCDS stuff to start with! Perhaps I'm just being cynical. I would also...
  6. KrisBlueNZ

    LED FORWARD CURRENT & VOLTAGE

    BobK is right, you can't determine the LED's power rating through measurement. You could measure the temperature rise and use that as a guide. You're measuring the parameters the right way. You need to understand that LEDs are primarily current-driven devices. The voltage you measure across the...
  7. KrisBlueNZ

    Best type(s) of capacitor

    Decoupling and coupling are different things. Have a read of my long posting in this thread: https://www.electronicspoint.com/newbie-questions-t248766.html Ignore the part from the LED onwards. I think some people didn't like it because of the strange analogy I used :-) In it, I model a...
  8. KrisBlueNZ

    Problems substituting a relay

    That one looks good, apart from the tolerance (20%). It might be your best bet though. FYI here's the schematic and some traces from a simulation to detect the average (mean) zener current. In the schematic I have replaced the zener with a reverse-connected diode (which takes the "negative"...
  9. KrisBlueNZ

    Best type(s) of capacitor

    Yeah, buying unbranded Chinese components is like a bawx of chawcolates - you never know what you're going to get :-) Yes, if you have a sinewave of 5V p-p with a centre voltage of zero, it goes between -2.5V and +2.5V. If you add 1V DC to it, you get a 5V p-p sinewave that varies from -1.5V...
  10. KrisBlueNZ

    Problems substituting a relay

    No, a cap rated for 300 VAC will be fine. The AC rating is an RMS rating, not a peak voltage rating. Also, you don't need a very large safety margin on the value to allow for disturbances on the mains. Most disturbances are at very high frequencies, and the capacitance is so high that...
  11. KrisBlueNZ

    Best type(s) of capacitor

    MLCCs are fine for the applications where they're normally used - decoupling, mostly, where the important factors are high capacitance per volume, low ESR and ESL, and low cost, and in non-critical timing circuits perhaps. But most MLCCs are Class II and Class III and have poor capacitance...
  12. KrisBlueNZ

    Transistor to switch power supply

    Nice work Electrobrains. I have the parasitic diode included in my schematic symbol. I've been caught out once before when I used one in the feedback path of an op-amp. It took me a while to figure out why the output was clipped on one side but not the other! Since then I made sure I could...
  13. KrisBlueNZ

    Transistor to switch power supply

    Electrobrains, I suggest you show the parasitic diode in the P-channel FET to make it clear that your circuit will feed the internal 5V rail back onto the USB connector with one diode drop. I don't think that will necessarily be a problem, but it would be helpful to show the diode, to make it...
  14. KrisBlueNZ

    potentiometer replacement

    First you need to understand how the temperature is controlled. As Electrobrains said, the three wires connected to your potentiometer are probably a +2.4V reference voltage (on the clockwise terminal), a microcontroller ADC input (the wiper terminal) and probably ground (on the anticlockwise...
  15. KrisBlueNZ

    Best type(s) of capacitor

    Re capacitor types. Some self-described audiophiles claim that particular types "sound" better, but AFAIK no one has ever done controlled tests to eliminate psychological bias, i.e. the people listening have always known what type of capacitor they are listening to, so the results are not...
  16. KrisBlueNZ

    Help finding somewhere to buy a component

    I don't know where you would find a ready-wired plug. You can probably find the necessary bits at Digikey though. You need to buy the "housing" and the pins separately. The pins normally are connected to the wires using a crimping tool but you can bend or cut off the crimp "wings" and solder...
  17. KrisBlueNZ

    Problems substituting a relay

    Most capacitors aren't designed to be charged and discharged continuously like this. You need a capacitor that is specifically rated for AC operation. That's 2.7 nF not 2.7 uF. And it's mylar. You need something rated for continuous AC mains operation. That looks better. 400VAC and 2.5 uF...
  18. KrisBlueNZ

    Problems substituting a relay

    I can't find any posts from you that show the effect of varying the input capacitor. The ones I can find relate to changing the smoothing capacitor, C2. Varying the smoothing capacitor will affect how long the rail takes to reach full voltage when AC power is first applied, and how much ripple...
  19. KrisBlueNZ

    Problems substituting a relay

    That shouldn't be a problem. The peak and trough voltages are both well within the minimum pull-in voltage and the maximum allowable voltage. The principle is sound, as I said many times, but the component values are clearly not appropriate for that amount of load (about 20 mA with the relay...
  20. KrisBlueNZ

    Problems substituting a relay

    Not a good idea, there will be slight differences between zeners (even from the same batch) that will cause one to take the majority of the current. You CAN put two or more zeners in SERIES, though.
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