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  1. KrisBlueNZ

    Trapezoidal Wave Generator Circuit

    There are actually three factors that affect the shape of the output waveform: 1. The frequency generated by the astable multivibrator at the left side of the diagram; 2. The rate of voltage change across C, which is determined by the value of C and the currents drawn/provided by the current...
  2. KrisBlueNZ

    Looking for oscillator and frequency divider schematics

    The value of R3 isn't critical. I would choose a value that gives a current of around 1~10 mA, unless there's some reason not to. So if your power supply is 9V, a value between about 1k and 10k will be fine. For example, 3k3. The frequency divider circuit doesn't draw much current. And it's...
  3. KrisBlueNZ

    2 stage switch design using mono-stable multivibrator circuit. HELP!

    A discrete solution is very unlikely to be cheaper. Possibly could be more reliable. Most importantly though, the microcontroller solution will be far more compact than any discrete solution. (I'm assuming you're using SMT micros.) Microcontrollers are no more sensitive to heat than any other...
  4. KrisBlueNZ

    Knight Rider K.I.T.T. Scanner

    Just because all the calculations for pulse-width-modulating 30-plus LEDs would be far too slow in an interpreted language. If you're talking about compiled BASIC, I would agree. I was really referring to the BASIC Stamp and the like as being impractical. The overhead for pulse-width-modulating...
  5. KrisBlueNZ

    Knight Rider K.I.T.T. Scanner

    As long as the code isn't written in BASIC or something like that, the dimming effect can be done easily enough with PWM. Even if you're using 74HC595s and bit-banging the SPI, PWM is feasible. True, it adds a fair bit of complexity to the firmware.
  6. KrisBlueNZ

    I would like the LED to turn off when beam is broken

    Here's a circuit that will do roughly what you want. This circuit is based on a common two-transistor Schmitt trigger. A Schmitt trigger is normally used when dealing with real-world signals because a fixed threshold causes problems when there is noise on the signal - as the voltage crosses...
  7. KrisBlueNZ

    2 stage switch design using mono-stable multivibrator circuit. HELP!

    Yes my name is Kris. Thanks for the links. For others' information, the CR123 is a 3V Lithium cell used in cameras. It's shorter and slightly fatter than an AA cell. I understand the control method. You've explained it very clearly. Turning the flashlight ON enables the LED at low brightness...
  8. KrisBlueNZ

    2 stage switch design using mono-stable multivibrator circuit. HELP!

    It can be tricky to design circuitry to operate from a 3V supply. Low Vgs(th) MOSFETs are available, and transistors are always an option. The other difficulty is the requirement for the circuit to be powered off completely between activations. This requires the circuit to have a timeout...
  9. KrisBlueNZ

    Problem - Triangle Wave Generator

    That circuit should work. What are you connecting to the two voltage input points (top end of R5, and pin 8 of the op-amp)? They should both be connected to your +12V supply. If you can't get the circuit working, post the voltages on all pins of the op-amp.
  10. KrisBlueNZ

    Looking for oscillator and frequency divider schematics

    As duke37 already suggested, you can use a CD4024 to generate seven lower octaves from each oscillator. (I'm assuming you will have twelve oscillators, one for each note, so you will need twelve CD4024s.) If you really mean discrete, i.e. no ICs, look at the schematic for the transistorised...
  11. KrisBlueNZ

    220v LED DIMMER??

    Do you mean that you would modify every LED light bulb that you buy, to remove the capacitor and bridge rectifier?
  12. KrisBlueNZ

    220v LED DIMMER??

    Steve, the problem is that he wants to drive LED light bulbs, which contain a series capacitor and bridge rectifier as well as the LED string (and a small smoothing capacitor). You can't drive them with DC. He wants to use a circuit in post #26 on this thread, which puts the current source...
  13. KrisBlueNZ

    220v LED DIMMER??

    A switched-mode current source? There may be such a thing but I haven't heard of it.
  14. KrisBlueNZ

    220v LED DIMMER??

    Yeah, what CDRIVE said. A commercial linear regulator (needs to be a current source/sink) will have better linearity but it won't have lower dissipation. A certain amount of power needs to be dissipated, i.e. converted into heat. Any linear regulator will have to dissipate this heat.
  15. KrisBlueNZ

    220v LED DIMMER??

    Ah, I see what you mean. That's a good way to simplify the design - use the mains itself as the frequency source. If repeatability or control aren't good, you can change your poorly defined variable resistance element to be a current source. Just adding a source resistor will help. And of...
  16. KrisBlueNZ

    220v LED DIMMER??

    You went ahead and tried your circuit? What circuit is that? I ask because as far as I can tell, you do actually need a current generator with alternating polarity, like the circuit I designed. A simple linear regulator won't work because of the capacitor in the LED light bulb. As BobK says...
  17. KrisBlueNZ

    Touch switch help!

    OK, good. That circuit should have a diode across (in parallel with) the relay coil. A 1N4001 or similar will be fine. Connect the anode to the grounded end, and the cathode to the top end of the coil (= the cathode of D1). This diode is needed to suppress the "back EMF" or "inductive kickback"...
  18. KrisBlueNZ

    220v LED DIMMER??

    Well, I've had a go at designing something. The circuit simulates OK but it's pretty large. Also I don't know whether it would comply with any electrical requirements - in your area, or anywhere else. I've drawn it up in LTSpice. I don't have models for the high-voltage transistors I specified...
  19. KrisBlueNZ

    220v LED DIMMER??

    I guess a triac type dimmer would be worth a try. You might not even need to remove the 4.7 uF cap in the light bulb circuit. It doesn't provide much hold-up time. There might be a problem with insufficient current to keep the triac turned on, and because the load current and voltage are out...
  20. KrisBlueNZ

    Question about MOSFET

    No. I think the problem is that you don't really understand voltage and current, and how they interact. You should probably Google for basic electronics tutorials that explain these quantities. Re the schematic diagrams I post, see...
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