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  1. hevans1944

    Use a PIR Sensor to detect a movement of a paper

    Maybe, but probably not. A PIR or Passive Infra-Red sensor is based on sensing the difference in infrared radiation from a warmer object against a cooler background (or vice versa, sensing a cooler object against a warmer background) using a pyroelectric sensor (or detector). The pyroelectric...
  2. hevans1944

    Missing battery connection on Magnetic Exercise Bike

    The thingy with the spring and the flat contact, joined together with a wire, is used on one end to tie the two AA cells in series. A similar thingy, without a wire joining the spring and the flat contact, is needed at the opposite end to make contact with the + terminal of one AA cell using the...
  3. hevans1944

    Looking for a nice small project!

    @AndreeU17 before we provide project ideas it would help to know your goals and limitations: How old are you? How much time do you have to complete your project? Do you have (or are you allowed to have) someone to help you? Do you have a budget to purchase parts? Have you written (or...
  4. hevans1944

    biasing this op amp

    It would be a big help if you would label the pin numbers and the type of op-amp you are using. If that 9 V battery is intended to be a "split supply" then you need two of them: one to provide +9 V to the positive supply rail of the op-amp and one to provide -9 V to the negative supply rail of...
  5. hevans1944

    Need a little help on circuit for 120VAC to 12VDC

    I was only suggesting using a car battery as a temporary source while you track down what is "blowing up" the CA Chinese converters. There isn't much inside these things: an IC to drive a MOSFET switch, an inductor to store energy, a couple of capacitors, a resistor or two, maybe a Schottky...
  6. hevans1944

    Need a little help on circuit for 120VAC to 12VDC

    Well, it looks like you have everything you need except for a reliable 12 V DC power supply! Have you tried substituting an ordinary lead-acid automobile battery for the transformer and Asian converter, just to see if it all works okay? I assume the object mounted on the finned circular heat...
  7. hevans1944

    Carbon Monoxide detector circuit

    This image may help with wiring that puppy up: Visit this page for more information. And this page too!
  8. hevans1944

    Mountain bike rear suspension motor controller

    Well, that's the price you pay to be on the "bleeding edge" of technology. In response to rider experience, Lapierre has launched a new model that features... wait for it.. MANUAL CONTROL! Maybe you can purchase a retro-fit kit to add this "feature" to your bike.
  9. hevans1944

    Need a little help on circuit for 120VAC to 12VDC

    Sure, just answer the questions I asked above and I will see what I can dig up on the Internet. Current and voltage regulation on the output matters.
  10. hevans1944

    Need a little help on circuit for 120VAC to 12VDC

    Nice Tesla coil. I've always wanted to throw one of these together but never found the patience (or purchased enough wire) to wind the high-voltage secondary. I have several neon sign transformers laying around the basement, and have toyed with the idea of building a rotary spark gap for the...
  11. hevans1944

    isolation transformer

    @pete g you only need the isolation transformer on the o'scope. Its only purpose is to prevent the oscilloscope chassis ground from interfering with the television chassis ground through a mechanism known as a "ground loop." Do not defeat the safety prong on the line input side of the isolation...
  12. hevans1944

    I'm a little bit lost with transistors... need help

    It sounds like you are well on your way with the Arduino! I would recommend purchasing a "beginners kit" such as this one that I bought at Radio Shack, but also available on-line. You will probably want to eventually purchase a few Arduino Shields and these are also available from Seeed Studios...
  13. hevans1944

    I'm a little bit lost with transistors... need help

    It appears from your list that you may have already found that Google is your friend. See image below. This chart of typical small-signal transistors, all available in bulk packages at very reasonable cost, gives you most of the information you need to select a particular transistor for your...
  14. hevans1944

    5V short circuit protection

    Are you trying to protect your laptop power supply, or the one dollar step-down converter? Why not place a circuit-breaker or fuse in series with the laptop supply?
  15. hevans1944

    Synchronization of pulses

    @Harald Kapp has already told you that it is impossible to synchronize the pulses from independent astable multivibrators even if all have the same RC timing components. Moreover, your "triggering" inputs appear to be asynchronous, so why would you expect the output pulses to be synchronized...
  16. hevans1944

    isolation transformer

    As @Harald Kapp reminded me, it is dangerous. Neither of us said it was impractical. Electricity is dangerous, but that doesn't mean we can't use it safely. Defeating the green-wire safety ground means you are then responsible for the safety it provided. Not everyone, especially beginners, are...
  17. hevans1944

    isolation transformer

    I agree, it is "bad advice" to even suggest this to a beginner who is unaware of the problems it can create. So, I went back and edited to color in red that part where I said you do this at your own risk. I should perhaps mention that the first time I did this I was working on line-powered...
  18. hevans1944

    isolation transformer

    @pete g, you must either be very patient or have other resources! I see you joined the forum almost five years ago, waited almost three years to post one pretty simple question about voltage and current metering but did not receive a satisfactory follow-up answer... and now here you are again...
  19. hevans1944

    15V 5A - Font

    We can better help you when you provide specific information about your problem. A schematic with parts designations is a good start.
  20. hevans1944

    Need a little help on circuit for 120VAC to 12VDC

    It is soooo much more satisfying to blow up something you have built rather than something cheap that you bought, especially if you don't have a clue why the cheap ones keep blowing up. Good luck trying to power up that laser diode with a 12 V 5A DC power supply. You are going to need a lot of...
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