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  1. KrisBlueNZ

    Amplifier circuit for speakers

    I guess he just wants to MAKE something. Making things is fun, interesting, educational and rewarding, especially for beginners. That's why kitsets have always been popular.
  2. KrisBlueNZ

    Amplifier circuit for speakers

    Sparkfun have a kit based on the STA540 that could be good. It's pretty grunty. https://www.sparkfun.com/products/9612 I wouldn't use the preamplifier stage though. You won't need any extra gain and the LM358 is not good for audio IMO. You'll also need a dual ganged log potentiometer for the...
  3. KrisBlueNZ

    Pink noise generator circuit mod

    culomax and I have been working on this project via Skype. The circuit I designed earlier seems to work but there's a problem during the ramp-up - the noise starts up as spits and pops during the ramp-up. We haven't investigated this problem, because I had a better idea for how to do the...
  4. KrisBlueNZ

    Wood for the Trees

    That's brilliant! You're very resourceful. I (and I expect many others here) would be interested to see your hardware design, and maybe a flowchart or brief firmware description, once you've got something you can show us.
  5. KrisBlueNZ

    On/Off Voltmeter

    That doesn't take into account nonlinearity in the ADC, variations due to temperature and variations over time. I don't think it will even give an initial accuracy of 0.2% anyway. But there aren't many options for improving the accuracy, so you will get what you get, I suppose. I prefer to say...
  6. KrisBlueNZ

    On/Off Voltmeter

    BTW I suspect you won't be able to achieve 5 kHz switching rate without losing a lot of accuracy. The high voltages and high resistances you want to use mean that any capacitance slows things down, and capacitance is hard to avoid. The faster you go, the more effect the capacitance will...
  7. KrisBlueNZ

    On/Off Voltmeter

    Your ADC has a RESOLUTION of about 0.1% but that's not the same as ACCURACY. There are many sources of error. Check the data sheet for your voltage reference for the initial accuracy and the temperature coefficient. The ADC has a parameter called differential non-linearity. You can get resistors...
  8. KrisBlueNZ

    On/Off Voltmeter

    Accuracy of 1V in 500V is 0.2% which can actually be difficult to achieve. A P-channel MOSFET, just like an N-channel MOSFET, responds to the voltage between gate and source. In the case of a P-channel device, polarities are reversed, so the gate must be driven negative with respect to the...
  9. KrisBlueNZ

    Problems substituting a relay

    Actually I was suggesting putting the bridge between the feed capacitor and the zener. Since the feed capacitor would be in the Phase side, and the combination of the bridge and the zener would limit the voltage across the bridge to 30V, the ground rail of the circuit would only jump between 0V...
  10. KrisBlueNZ

    On/Off Voltmeter

    Thanks for the description of your project. It still leaves a lot of questions though. Are these capacitors fully isolated from the voltmeter circuit, is that the issue? So you want to be able to measure the voltage across each one using the same DAC. And you want to avoid loading the capacitors...
  11. KrisBlueNZ

    Problems substituting a relay

    Thanks Steve. I think my comment about needing to halve the 72 mA current (which I calculated based on the mains voltage and the reactance of the feed capacitor) was right. Regarding the bridge rectifier idea, I suggested that earlier, and CDRIVE disagreed, because the negative rail of the...
  12. KrisBlueNZ

    On/Off Voltmeter

    Could you go into more detail about what you're doing? You say you're measuring a "voltage of up to 500V" and that you need both sides of that voltage disconnected from your measuring circuit, but that doesn't really give us any idea of what you want to do.
  13. KrisBlueNZ

    Problems substituting a relay

    Yes, good. The behaviour of the power input circuit is determined by a combination of factors. The mains voltage and frequency can't be changed. Other factors are the input coupling capacitor (the 1 uF one), the zener voltage, the smoothing capacitance, and the load current. You aren't going...
  14. KrisBlueNZ

    Problems substituting a relay

    Hi Paul, That schematic doesn't make much sense to me. I think you must have made several errors reverse-engineering it. Here are a few specific points, but this may not be a full list of problems. You should show the power path to 4093. I know you explained it in the comments but it...
  15. KrisBlueNZ

    12V Relay from a .2mA LED

    Assuming the mains voltage is nominally 230V RMS, the peak voltage is RMS * sqrt(2) which is 325V. The average (mean) voltage for each hump of sinewave is 2 Vpeak / pi which is 207V. Assuming that the circuit uses half-wave rectification (one diode visible on the board), every second hump is...
  16. KrisBlueNZ

    12V Relay from a .2mA LED

    No, it's right to use the DC current range because you want to measure the mean (average) DC current.
  17. KrisBlueNZ

    12V Relay from a .2mA LED

    Thanks for the pic. It looks like there are two 100K resistors, one diode, and two LEDs on the board. The "water is hot" signal presumably comes from a thermostat, and is probably a mains-voltage signal. Most likely, the resistors drop the mains voltage and limit the current to quantities...
  18. KrisBlueNZ

    12V Relay from a .2mA LED

    That's not the right way to measure current. Current is a FLOW, not a potential DIFFERENCE (like voltage). You measure it by breaking the circuit at some point and inserting the meter across the break. You would have to disconnect one wire from the LED and connect the meter between that wire and...
  19. KrisBlueNZ

    Common Emitter Transistor

    BobK, I think the LM324 output will swing quite close to the positive rail when the load is towards VCC. The specification for pulling to VCC-1.5V applies when the load current is in the other direction (it is specified with a resistive load to GND in the data sheet). But you would have to test...
  20. KrisBlueNZ

    SPI Chip Select Interference

    Oh it's a PIC. I doubt it will have DMA. For information on interrupts, probably best to look on PIC-specific sites. What language are you programming in? Search for "timer interrupt" on a site that relates to that language and that architecture, i.e. PIC.
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