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  1. KrisBlueNZ

    Rewiring 7-band EQ

    Yes, if you notice a lack of bass you should increase the four 1M resistors to 4M7. It's not ideal to have such high resistances at the input of an op-amp but it will be OK. I doubt anything will harm the speakers. The amplifier will soft-clip at a level far below that level. Maybe you do need...
  2. KrisBlueNZ

    Rewiring 7-band EQ

    OK, that sounds like it's a 5 megohm pot. That's higher than I expected. The buffer board has a 1 megohm input resistance. This may cause some loss of bass frequencies. You could change the four 1 megohm resistors on the buffer board to 4.7 megohms if you notice a problem with loss of bass.
  3. KrisBlueNZ

    Project-A SIMPLE RECEIVER/TRANSISTOR AMPLIFIER

    No, my suggestion is to add a 180k resistor from the top of the 4k7 resistor to the +6V rail and reverse the detector diode. The idea is to pre-bias the diode by about 0.15V so that it will detect signals with an amplitude less than its natural forward voltage, i.e. weak radio stations. I was...
  4. KrisBlueNZ

    24VAC power supply question about VA spec

    Yes, that one looks good.
  5. KrisBlueNZ

    Project-A SIMPLE RECEIVER/TRANSISTOR AMPLIFIER

    Ah yes, a crystal set with an audio amplifier. That will certainly work. Just out of interest, has anyone tried adding a small DC bias to counter the voltage drop in the detector diode? For example, break the ground connection between C1 and the 4k7 resistor and connect the C1 side to a voltage...
  6. KrisBlueNZ

    Two atmegas from the same oscillator?

    Personally I would use an external oscillator driving the inputs of the oscillator gates on both devices, although this could be an EMC issue. You could probably get away with using a crystal on the first device and connecting the output of the oscillator gate on the first device to the input...
  7. KrisBlueNZ

    Old capacitor broken and needs to be replaced

    Assuming these are suppression capacitors in the mains circuitry, then as Steve says, your replacements should have an X2 rating. I don't know what conradshop is; if it's conranshop, then I assume you're in the UK? In that case you'll want to buy from Farnell / Element 14 or RS Components...
  8. KrisBlueNZ

    24VAC power supply question about VA spec

    That relay has a standard 24VDC coil. Also, it is PCB-mount. You need one with a 24VAC coil. If you get one of the ones I suggested, you'll need to get a socket/base for it as well. Thanks :-) The interview went OK. I'll find out in a day or two whether they will offer me a job.
  9. KrisBlueNZ

    How to isolated a 3.3V signal

    Yes, please let us know how you get on.
  10. KrisBlueNZ

    How to isolated a 3.3V signal

    Wow! Yes, it looks like you've solved your problem! Good work! That's a neat device. It uses "chip-scale air-core transformers" operating at 180 MHz to transfer signals and power across the isolation barrier. The power isolator can supply 55 mA and the device can drive a fully loaded RS-485...
  11. KrisBlueNZ

    solar tracker

    OK, that's a pretty poorly designed solar tracker. The firmware doesn't do anything clever to track accurately, and there is no automatic adjustment for brightness changes, so when a cloud crosses the sun it will track around randomly or track way too far in one direction. Edit: Correction. I...
  12. KrisBlueNZ

    7 Transistors Triangle Wave Generator (650Khz)

    I'm impressed! I had a lot of trouble understanding your first circuit until I redrew it in a way that shows the logical progression of the signals. I also rewrote the description. I'm posting it here in case you want to do a similar re-layout of your new design. I haven't changed anything...
  13. KrisBlueNZ

    Good Bus Design

    Digital inputs DO generally need to be driven either low or high. That can be done by a push-pull output, which actively drives high and low, or an open-collector or open-drain output with a pullup resistor, in which case the pullup resistor pulls the output high when the transistor or MOSFET is...
  14. KrisBlueNZ

    amps audio jack 1/4 stereo switch

    I would guess something similar to shrtrnd. I think the right jack socket probably has a switched contact so that when nothing is plugged into it, the right input to the amplifier will connect to the ring connection on the left/stereo jack. In that case, here are the scenarios. "Tip" is the...
  15. KrisBlueNZ

    Current Mirror Disaster

    The problem may be self-heating. The "output" transistor usually dissipates a lot more power than the "input" transistor, because its collector-emitter voltage is usually a lot higher so its power dissipation is a lot higher. When the transistors are next to each other on the same piece of...
  16. KrisBlueNZ

    How to isolated a 3.3V signal

    I doubt you'll be able to transfer any significant amount of power across the isolation barrier in much less space than the RSZ-3.33.3HP. The size of the transformer is the critical factor, and going to less tightly integrated solution will just make it bigger.
  17. KrisBlueNZ

    Project-A SIMPLE RECEIVER/TRANSISTOR AMPLIFIER

    Make sure it's less than 100 kilobytes (150 kilobytes for JPG images I think). Click "Go Advanced" and click the paper clip icon to get to the Upload dialog. If the image is too large: If it's a scan of a drawing, JPG format can be used; load it into an image editor such as Paint.NET (free) and...
  18. KrisBlueNZ

    What can i do with Quartz Crystals?

    You can use a quartz crystal to combine crystal healing with acupuncture. They actually operate in the same way anyway. Just get a confident sympathetic person to jab the leads into your body until the general vague ill-feeling is alleviated.
  19. KrisBlueNZ

    Design question on microcontroller and TIP122

    I recommend always using the zener directly between the gate and source. MOSFETs are too easily damaged by gate overvoltage without it. There must be a common 0V connection between the micro and the 0V rail on the USB connection to the PC to complete the circuit. When the micro pulls its output...
  20. KrisBlueNZ

    Design question on microcontroller and TIP122

    Definitely throw it out. Semiconductors, and especially MOSFETs, can be damaged in ways that will show up later as more serious problems. For less than a dollar, it's not worth the risk. That's why I always get a few spares when buying cheap components - if you don't need them on the current...
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