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  1. KrisBlueNZ

    Voltage Suppression

    If you're driving a large DC-coil relay from a small relay, you should still have back EMF voltage suppression across the large relay coil. If you don't, the back EMF from the large relay coil will cause arcing in the small relay contacts, and it won't last long. You should also have back EMF...
  2. KrisBlueNZ

    Building a circuit

    Chris, in many cases a discrete design (as opposed to a microcontroller-based design) is only more complex if you assume that the user already has microcontroller programming experience, and will only be more costly if you assume that the user already has the necessary programming setup. I...
  3. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    If that's the right name for that pin, your PIC seems to have an new feature that I didn't know about... I'm surprised the forum software didn't catch that and asterisk it!
  4. KrisBlueNZ

    linear mode 10A MOSFET current source

    Steve's design should do what you want. But your statement that the circuit needs to operate with an output voltage range of 10~20V makes me wonder whether you know anything about this LED at all. You know that if you feed 10A into an LED whose forward voltage is 20V, it will dissipate 240W...
  5. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    The ZXMP6A13F isn't really suitable; the Rds(on) is far too high. In fact it isn't even specified at Vgs=3V or lower. The closest specification is at Vgs=4.5V where it is 0.6 ohms; at 3V it would be more than an ohm, and you would lose significant voltage across it. When you're working at 3V you...
  6. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    Right, the boost converter will not put much load on the battery when it's not loaded by the bell's 1k resistance. You have to test with the bell active. I estimated 450 mA load on the battery while the bell driver transistor is actually ON. You want to switch the supply to the boost converter...
  7. KrisBlueNZ

    Mosfets

    I'm like that too Steve. Any information about factors to consider in electronic designs (in general) is more important than the detailed information itself; you can always look that up later, or ask an expert. The important thing is to recognise all the factors that might affect your design. As...
  8. KrisBlueNZ

    ADVREF pin current draw?

    Excellent advice Steve.
  9. KrisBlueNZ

    Tchnics ch 900 amp powering down ?

    Run it from cold, with the volume control at minimum, with a multimeter, set to the 300 mA or 10A range, connected in series with one of the speakers, and see whether the current starts to creep up before the amp shuts down. If there's no significant current, repeat the test from cold with the...
  10. KrisBlueNZ

    Mosfets

    It sounds like you have a lot of experience in this area Steve. Perhaps you might like to combine this advice into a tutorial on MOSFET driving in demanding applications. I would certainly read and save it. Advice like this can be worth its weight in gold!
  11. KrisBlueNZ

    Battery Powered Power Supply

    Did they say what was wrong with them? I assume they were damaged somehow?
  12. KrisBlueNZ

    Alternatives to LDR for audio signal.

    Yes an LDR is a good solution for amplitude modulation or variable gain. They have a fairly wide resistance range too. They have a pretty slow response though, so I don't think they'd be suitable for modulating a carrier with an audio signal. You would lose any high frequencies in the audio...
  13. KrisBlueNZ

    Alternatives to LDR for audio signal.

    OK. The "Application 3: Pan Pedal" design would work, but I don't think the panning will be very smooth. In other words the sound will appear to move at an uneven speed, and will appear to change in volume as well. See if you can find a circuit that's designed to pan smoothly, and with...
  14. KrisBlueNZ

    Modification of anti-bark control circuit - help please!

    I can't see where the base drive comes from. The track disappears under the ultrasonic transducer and I can't tell where it comes out. But luckily, Chris has suggested the answer - a crystal earpiece. Otherwise you can use a signal tracer. When you've detected which pin has the audible signal...
  15. KrisBlueNZ

    Mosfets

    I think all your calculations, and your conclusion, are correct, and you're doing everything right. Your power dissipation is way under your limit, so no heatisnk is needed. I guess you had assumed that. Make sure that your gate drive waveform has a high slew rate. In other words, don't leave...
  16. KrisBlueNZ

    4 Channel Diversity Controller

    I get it. I've been thinking about how best to do this. I'm still thinking. I'll get back to you within a few days. Regarding video switching. If all the receivers are receiving exactly the same signal, then a quick change between them shouldn't cause a problem. Ideally it would be best if...
  17. KrisBlueNZ

    Function Generator

    Good one! I'm glad things are working for you. Remember we're still here to help if you run into any problems. Good luck!
  18. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    Yes, 34 mA sounds right. It does seem pretty low, but I think that bell is designed to operate from a pretty high voltage, such as ~100VAC as used in the telephone system. The converter may be rated for 2.5A output, but you also have to consider how much current it will draw from the input...
  19. KrisBlueNZ

    Understanding NPN

    Yes, as BobK says, that statement is simply wrong. There is no way you can have 3V across a base-emitter junction (unless the transistor has failed). I can't understand why the author would say this, as it's very obviously wrong. R2 and R3 form a voltage divider that's designed to present a...
  20. KrisBlueNZ

    Alternatives to LDR for audio signal.

    Thanks Dave! I hadn't noticed! makaze, I don't see any links in your post. Anyway I can't look into it now. It will be a day or so before I check in again.
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