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  1. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    No, I haven't prototyped it, and I don't plan to. You're welcome :-) Good luck! Hope to hear from you soon. P.S. I forgot to mention. The 3-position switch part number on the schematic is the cheapest 3-position switch I could find on Digikey. The manufacturer is "E-Switch" or something. But...
  2. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Here's an improved design. The changes from the previous design relate to the ON/OFF control and low-voltage shutdown. Here's a description of the new circuitry. SW1 is a three-position switch. A centre-OFF switch can be used, because the middle position, "AUTO", doesn't need a connection...
  3. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    OK, I get the idea. I'm not clear on a few things though. 1. I don't see how D1 "prevents the IRF7319 from shutting down due to the capacitance in the circuit" 2. Q2 seems to have its source and drain reversed and there's no need for R14. 3. D3 is either backwards or connected to the wrong rail...
  4. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Thanks Chris :-) Actually that one's been in the slow cooker for a few days and I'm still not happy with it at all. And I don't have kids!
  5. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Hi Greg, Thanks for that diagram. I mostly understand what you're doing there but I'm confused about a few things. For a start, are the batteries connected with the wrong polarity? And is one side of them supposed to be connected to GND? Perhaps you could write up a circuit description for me...
  6. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Hi Greg, I haven't forgotten you! I'm still working on ideas. I don't know what you mean about using a presettable divide-by-n counter in an analogue circuit, but I agree with the specifications in your post #5. I really wanted to arrange the circuit so it could be powered from the voltage...
  7. KrisBlueNZ

    Transistor instead of relay

    You're right, the Darlington won't saturate. Typical Darlington Vbe at moderate current would be 1.5V; add a few hundred mV for the optocoupler's transistor, and a bit more for the voltage dropped across the series resistor. I'd say the voltage drop would be 2~3V. That's why I said that the...
  8. KrisBlueNZ

    Transistor instead of relay

    OK, I see. Thanks for that diagram. Yes, your modified schematic is what I was suggesting, to convert a normally open circuit to normally closed. Using an optocoupler driving a transistor is not a perfect solution. As Harald just pointed out, you will have some voltage dropped across the...
  9. KrisBlueNZ

    Transistor instead of relay

    You've used all English words there, but I can't make head or tail of it. Can you post a diagram of the circuitry that you want to connect to the output of the relay? Re converting the design to normally closed, there may be ways to do this. For example, instead of connecting the optocoupler's...
  10. KrisBlueNZ

    Transistor instead of relay

    It might work. It depends. What are the "contacts" being used for? Show the circuit that you will be connecting them to. How are the "relays" controlled? I don't see any input to the circuit.
  11. KrisBlueNZ

    Op-Amp with bjt Design

    Click here for a good idea!
  12. KrisBlueNZ

    Simple off/on circuit help

    You can connect a two-coil latching relay so that it toggles each time a contact (e.g. a pushbutton) closes. I showed a design for this in https://www.electronicspoint.com/need-help-needed-circuit-t254020.html#post1505380. The relay contacts are wired as a reversing switch; you can modify that...
  13. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    I was assuming that the whole circuit would be powered from the battery that you're discharging (or whatever it is). The meters would need to run while the circuit is active, but when the target voltage is reached, they could turn off, right? The problem is the power supply voltage they need...
  14. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    Hi Greg, I'm interested in this project and I want to help. BTW thanks for posting such a thorough and clear description of what you want to do. You are one of the very few! I designed something similar a while ago but I want to start again and design something with better performance and...
  15. KrisBlueNZ

    Trapezoidal Wave Generator Circuit

    OK. Can you post a diagram of how you've connected the signal generator to the rest of the circuit. I've never done this before, but I've decided that I won't post again on this thread until you have THOROUGHLY EXPLAINED the purpose of all of this experimentation. THOROUGHLY.
  16. KrisBlueNZ

    Knight Rider K.I.T.T. Scanner

    Ditto Bob. And good suggestions there. I don't necessarily "like doing it the hard way"; I prefer to have the complexity in the firmware, where there's no per-unit cost, than in hardware.
  17. KrisBlueNZ

    Trapezoidal Wave Generator Circuit

    Re-read my circuit description, and look up some of the keywords (e.g. current source, current sink). I note that you STILL HAVE NOT explained the purpose of your experimentation, after 40+ posts on this thread. I have no idea why you want to run the astable multivibrator from a 9V supply...
  18. KrisBlueNZ

    Looking for oscillator and frequency divider schematics

    Bob, thanks, I saw that. It won't be very accurate. For musical applications I think it's important to avoid any imperfections in the frequency spectrum. OTOH, if the signals will be heavily filtered, it won't matter!
  19. KrisBlueNZ

    Looking for oscillator and frequency divider schematics

    The reason why the transistor Schmitt oscillator's output won't be 50% is that the switching thresholds are not exactly the same distance away from the supply rails. So the capacitor will take longer to charge to one threshold than it takes to discharge to the other threshold. It's actually...
  20. KrisBlueNZ

    Trapezoidal Wave Generator Circuit

    I was assuming that OddOne was talking about the circuit he linked to in post #1, which I duplicated in post #16.
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