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  1. dorke

    Fairy lights rewire ?

    Some photos may help. As well as make and model.
  2. dorke

    How to compute low noise voltage.

    Welcome to EP . Did your professor teach you about resistor thermal noise? Draw the circuit as described with all resistances and calculate the noise.
  3. dorke

    Transistor pair to switch between Voltages

    F1 and F2 are fuses to protect against malfunction(they are not a necessity but good to have). The voltages are not wired together . One diode is reversed biased(blocking)at any given time. There may be a very short neglectable transition time(order of nsec) in which both diodes may be on at...
  4. dorke

    Transistor pair to switch between Voltages

    I'm Assuming you can control the 12v and 5v being on/off separately. All you need are a couple of schottky diodes to steer the voltage to your "Peltier load". The diodes should have breakdown voltage greater than 12v,and current capability greater than the load. The diodes will drop the voltage...
  5. dorke

    digital multimeters

    I would say that every DMM works on the principal of analog to digital conversion. DMM differ from the electro-mechanical Galvanometer types which worked on the principal of mechanical movement produced by current through a coil in a magnetic field.
  6. dorke

    Calculating resolution.

    Adam, Actually you are correct my bad. The definition of resolution is "the value that 1LSB equals to". In the case of 1bit it is indeed 1. so ,subtraction of 1 is the correct way to calculate the resolution. Another value is the "error" of a converter this is 1/2 LSB no -1 here.
  7. dorke

    Distorted audio on an old transistor radio cassette

    Yes, You marked them well. I agree with Ed about the importance of collector voltages of VT9 and VT10. and would add the base voltage of VT2 and VT3.
  8. dorke

    Need help to identify this device

    It helps some. Trace the 3 pins of the TRIAC and try drawing the schematic around it. Especially pin G(see red on pic). At what voltage is this board operated on?
  9. dorke

    Calculating resolution.

    I can understand why. For 1 bit we have 2 states "0" and "1". How do we decide which state are we in? "0" if we are below 1/2 "1" if we are above 1/2 What is the resolution than? I would say 1/2 not 1...;)
  10. dorke

    Calculating resolution.

    Adam, You shouldn't subtract 1. To convince yourself check the case of 1 bit ;)
  11. dorke

    Distorted audio on an old transistor radio cassette

    It looks like the points marked on the schematics are not all present on the PCB. The GND should be connected to the "-" terminal of the speaker (blue ).
  12. dorke

    Cheapest way to get data from multiple(100s) of sensors?

    So you have: VR200=4.87-2.73= 2.14V ILED=IR200=2.14/200=10.7mA That current should be fine. You do need to calculate the total current that the full circuit consumes, as long as it is below 500mA you can use the USB alone for the 5V supply.
  13. dorke

    Cheapest way to get data from multiple(100s) of sensors?

    Look at the schematics attached in #84.(the resistor is marked in green). I think you should connect the 5V directly to your 5v power supply(may be fused) not the Arduino.
  14. dorke

    Cheapest way to get data from multiple(100s) of sensors?

    0.63V should be fine. What is the value of the resistor in green? Please measure the voltage on it. Is the Transmitter LED polarity o.k?
  15. dorke

    Distorted audio on an old transistor radio cassette

    You should look for points 13 and 14 for GND (on board A8)
  16. dorke

    Distorted audio on an old transistor radio cassette

    You do need a scope for this kind of problem. I am assuming you don't have one,so a DVM may have to do. If you have a DVM: With volume at minimum. Please measure the voltages marked in red relative to the blue point(GND). BTW, Is this a Rusky made tape?
  17. dorke

    Need help to identify this device

    The case style is TO-202. The visible (2nd ) line may be the date code 1988 week-22,makes sense? Do you have the missing piece? Could you please post clear photos of the board(both sides), so we can see the other devices near that blown one? Agree withe @TedA, you shouldn't yank out the...
  18. dorke

    Wall wart replacement

    I think a non-conductive epoxy glue should do the work.
  19. dorke

    Wall wart replacement

    Is it "broken" but still working? If so, electrical isolation tape where the plastic is broken may solve this.
  20. dorke

    Fan help

    Welcome to EP. Should be o.k The controller is PWM and can supply up to 10A The fans are 2.5A each . You can also fuse each fan(separately !) with a 5A fuse . BTW, In this kind of parallel operation the fans will work at about the same speed. If separate control is required ,you should use a...
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