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  1. KrisBlueNZ

    Help with a battery powered tube preamp

    Hi Cernnunos5 and welcome to the Electronics Point forums :-) I'm surprised you chose the 12AJ6. It contains two diodes, which would not be useful, and one triode, and is not a common component. Valve (tube) audio preamps usually use the ECC83/12AX7, which has two triodes, which can be cascaded...
  2. KrisBlueNZ

    Why are Turntables not Grounded?

    Turntables should be grounded. Normally the preamp will have a terminal post on the back which should be connected to the metalwork of the turntable using a separate wire. The signal wires from the pickup to the preamp are screened and the pickup is grounded through the screens. The turntable...
  3. KrisBlueNZ

    Will this circuit work for a 3A load?

    As Duke points out, the 1N4007 input diode is only rated for 1A. A 1N5407 is rated for 3A maximum current. Schottky diodes are available with higher ratings and have lower forward voltage drops but can be damaged by reverse voltage spikes. Look on Digikey, Mouser etc. Another approach to...
  4. KrisBlueNZ

    connection of a thermal sensor TC1047AVNBTR to the microcontroller MSP430F4618

    All the information you need can be found in the TC1047 data sheet. The TC1047Axxxxx requires a power supply between 2.5V and 5.5V DC and draws up to 60 uA from that power supply. It generates an output voltage that varies by nominally 10 mV per degree Celsius and is nominally 500 mV at 0...
  5. KrisBlueNZ

    Working with micro connectors

    Start by counting the pins and determining the pin pitch. Measure the distance from one end pin to the other and divide that by one less than the number of pins to get the pin pitch. Also look for any markings that might indicate the manufacturer. Often there will be a manufacturer's logo...
  6. KrisBlueNZ

    Car Parking Sensors Help Needed

    There are lots of ways. The way I would do it is: record the tone using the voice recorder feature of a smartphone, transfer the recording to a computer, view it using a waveform editor (e.g. Audacity), measure the duration of, say, 20 (for accuracy) consecutive cycles, divide the duration by...
  7. KrisBlueNZ

    Solution by Explanation

    Cool story Steve!
  8. KrisBlueNZ

    Op amp configuration with 1 resistor ?

    There's probably a large capacitor (something like 1000 uF) across the output terminals of the power supply. This is commonly done to improve the effective series resistance and transient response of the power supply and it's helpful when the power supply is in voltage regulation mode, but it...
  9. KrisBlueNZ

    Car Parking Sensors Help Needed

    You're welcome. Don't worry if you don't use my design; it's searchable now so someone else may use it. Duke's idea might be workable. If the circuit responds to only the frequency that's emitted by the unit, with a very tight filter, it could be placed anywhere in the car. You would still need...
  10. KrisBlueNZ

    Solution by Explanation

    Sleeping on problems often works for me too. I think while you sleep, your brain is busy organising the memories of the thoughts and events that happened since the last time you had a long sleep. When you wake up, problems no longer have the immediacy they had the day before; your brain has put...
  11. KrisBlueNZ

    Op amp configuration with 1 resistor ?

    Yes, you can use that circuit without an input resistor, and feed a current into it from an LM317 wired as a current source, and see what happens. Remember that all the current you feed into the circuit has to flow through the feedback resistor and into the output of the op-amp, and the op-amp...
  12. KrisBlueNZ

    Op amp configuration with 1 resistor ?

    Gorgon has explained it pretty well. You can't apply a voltage to the input. That will simply force the op-amp to slam its output against one of the supply rails and the circuit will do nothing useful. You have to apply a current to the input, which can be opposed by the current through the...
  13. KrisBlueNZ

    Car Parking Sensors Help Needed

    OK, here's a circuit that should do what you want. It's pretty straightforward, though it probably looks pretty complicated. If you're interested in understanding the circuit better, you can look up any unfamiliar words using Google or Wikipedia. The microphone on the left is an electret...
  14. KrisBlueNZ

    Laptop speaker swap - danger of burning out?

    I agree with Dave, you're very unlikely to have a problem. Ideally the impedances of the replacement speakers should match the original speakers. Impedance is measured in ohms, and they should be marked on the speakers as a number followed by the ohms symbol, the upper case omega. See...
  15. KrisBlueNZ

    Car Parking Sensors Help Needed

    I second Duke's suggestion. You should avoid modifying any part of your vehicle, if at all possible. You could build a self-contained device, powered from the car battery supply, that "listens" for the original sound (using an electret microphone or similar) and uses that signal to enable an...
  16. KrisBlueNZ

    Hot Wire Cutter Power Supply

    Your comment about a variac being dangerous because it doesn't provide electrical isolation is not relevant here; you would not power the cutter directly from the variac's output. A transformer would be needed, to step down the 0~115VAC or 0~230VAC from the variac to a lower voltage and higher...
  17. KrisBlueNZ

    Op amp configuration with 1 resistor ?

    No, the VOLTAGE at the inverting input is equal to zero, because the non-inverting input is tied to 0V. This is true for an op-amp connected with negative feedback, as long as the op-amp is operating within its specifications; that is, unless the op-amp's output is hard against its positive or...
  18. KrisBlueNZ

    Off - On - Off timed circuit.

    That's looking good. No, you can't add a resistor in series with the coil. If you do that, the resistor and the coil resistance will form a voltage divider, and you will only get a fraction of the total voltage across the coil, so the relay will not pull in. Make sure you get a relay with a 720...
  19. KrisBlueNZ

    Op amp configuration with 1 resistor ?

    That schematic is quite wrong in several ways. Obvious errors are (1) the inverting input should always be at the same voltage as the non-inverting input (this is normal for an op-amp circuit with negative feedback working within normal limits), not 1V higher, and (2) the current through the...
  20. KrisBlueNZ

    Hot Wire Cutter Power Supply

    So you wanted to use a battery charger as a power supply to power your hot wire foam cutter? I agree with Duke that using a lamp dimmer with a transformer-based circuit may not work properly and could cause damage. The important factor is the characteristics of your hot wire foam cutter. I...
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