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  1. KrisBlueNZ

    reverse engineering help

    I'm very glad to hear that you're using a system where the control circuitry is all isolated from the mains. Sounds like back EMF from the inductive loads that you're switching with the relay contacts. For each output, add a resistor and capacitor in series across the contacts of your first...
  2. KrisBlueNZ

    Rewiring 7-band EQ

    LOL :-) If the existing cables are shielded, I doubt that using newer ones will help, but you can try. Another possibility is that the chassis of the record player is NOT earthed. Try the same experiment, but instead of touching the chassis of the record player, touch something else, which...
  3. KrisBlueNZ

    Rewiring 7-band EQ

    The hum was just affected by your body's proximity? May be hum picked up by your body and capacitively coupled into a signal that isn't properly screened/shielded... It's not magnetic pick-up because your body is not magnetic (unless you have false limbs :-) The next time you notice it, try...
  4. KrisBlueNZ

    Rewiring 7-band EQ

    Right, two 6V lantern batteries in series is perfect for testing. Filters on audio signals are usually implemented using op-amps like the dual op-amp in the buffer circuit, with capacitors only. Inductors have real-world issues that can be problematic - they are susceptible to magnetic fields...
  5. KrisBlueNZ

    Rewiring 7-band EQ

    It can be hard to know how the hum is getting into the signal path. It's most likely coming from the power supply; if you can find a 12V battery to test with, you can find out for sure. You'll need a battery made from C-cells or D-cells. Don't use AA cells; they can't supply enough current...
  6. KrisBlueNZ

    Which Switching Transistor?

    Where does the 12V for the Peltier cooler come from? If it's a switching power supply, it's probably simplest to shut the power supply down when the temperature is low, and enable it when the temperature is high. As Laplace says, you'll need a comparator with hysteresis. The hysteresis is...
  7. KrisBlueNZ

    reverse engineering help

    To clarify. I'm not sure what you (the OP) mean by a "5V transformer". If you mean a simple transformer, rather than a complete power supply, then the transformer secondary should be specified at around 7V AC. You feed that through a bridge rectifier and to a smoothing capacitor of around 1000...
  8. KrisBlueNZ

    Could do with a hand...

    Yes, you can use batteries to power a motor to turn Meccano wheels. I'd suggest using two or four Alkaline D cells; two cells give you 3V DC and four cells give you 6V DC. D cells will last a reasonable length of time; smaller cells may not. You will need a DC motor that operates at the...
  9. KrisBlueNZ

    Should be simple to answer.

    It's very hard to answer this question because so much important information is missing. The term "photo sensor" has many meanings, depending on context, but your question doesn't have much context. What is the part number or model number of the "photo sensor"? If this "photo sensor" is a...
  10. KrisBlueNZ

    delay circuit

    I would be more concerned about the whole 4093 being splatted by load dump voltage coming in on the +12V supply. I wouldn't use CMOS in an automotive application without plenty of protection; this function could be easily performed by some simple discrete circuitry (a transistor and a MOSFET...
  11. KrisBlueNZ

    reverse engineering help

    The transformer is probably a good idea. The whole circuit is already connected to the Neutral mains wire so it's all potentially live. Adding a transformer won't affect this; it will just increase the current capability of the low-voltage supply for the MCU and any other parts that the OP...
  12. KrisBlueNZ

    Op-amp based current sensing

    The general idea is that you insert a low-value resistor (called a current shunt) in series with the charge path and use a differential amplifier to measure the voltage across that resistor. Generally you want this current to produce a voltage that is relative to the 0V rail, so you can easily...
  13. KrisBlueNZ

    7 Transistors Triangle Wave Generator (650Khz)

    I can't promise that I will build the circuit. I'm interested in it, but probably not THAT interested! I'm glad that you've built it up. Interesting that the waveform is wrong. I'm sure you understand the design better than I do, but I have a few suggestions for you to consider. 1. Use a...
  14. KrisBlueNZ

    RC Transmitter Wont turn on

    The mark on the crystal would have been made from outside. Without any technical information it's hard to know where to start. I would first suspect any areas where you've done work on it. I would do a careful visual inspection of those areas and the whole unit. If you can post all the...
  15. KrisBlueNZ

    Buck converter getting started ?

    The MC34063 is a very old device and uses a Darlington emitter follower which isn't rated for 1.5A. I doubt very much that you can get 5V out of it with only 6.5V input. You would have to use an external PNP or P-channel MOSFET. I've used them before and I don't like them much; there are much...
  16. KrisBlueNZ

    Buck converter getting started ?

    I would look on Digikey - they have a very wide range in the section "Integrated Circuits (ICs) > PMIC - Voltage Regulators - DC DC Switching Regulators". Unfortunately they don't have a minimum dropout voltage figure in their selection guide so you will have to download the data sheets of...
  17. KrisBlueNZ

    Old capacitor broken and needs to be replaced

    Yes, that one looks good. Just look at the big line of safety organisation approvals on it! The 0.1 µF version of the same part is http://www.conrad.be/ce/nl/product/450208/MKP-condensator-X2-Rastermaat-15-mm-01-F-275-V126-10-;jsessionid=F085F9C5C44DAFF4BDA5D3D15D1CF819.ASTPCEN24 Size isn't...
  18. KrisBlueNZ

    ELECTROMAGNETS

    I think it's simpler to think like this: "Over-unity" devices are currently considered impossible by definition. If you can demonstrate that the current scientific understanding of the nature of reality is wrong, and you have collected your Nobel prize and worldwide fame and fortune, you can...
  19. KrisBlueNZ

    Voltage to current amplifier

    Any circuit that accepts a voltage signal and outputs a proportional current signal can be called a transconductance amplifier. A voltage amplifier is defined, in basic terms, by the formula Vout = Vin * G, where G is the voltage gain of the amplifier. A transconductance amplifier is defined...
  20. KrisBlueNZ

    ELECTROMAGNETS

    Just a heads up, ScienceBorn, if you're trying (again) to work towards a "perpetual motion" / "over-unity" system: (a) No such device or system has ever worked in the past, despite people's best efforts; (b) Devices and systems that have claimed to do this either have been shown to be scams...
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