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  1. BobK

    Very simple electronic projects for beginner

    This is more complicated than you think. A Hall effect sensor will not, by itself, give you the rotation angle. It will tell you whenever a magnet passes over it. If the wheel goes in only one direction, and you know the initial angle, you can count pulses to determine the new angle. But...
  2. BobK

    ISO a particular switch. Don't know what it's called/to look for

    A switch can either make (normally opened) or break (normally closed) a contact. The ones with three terminals with do both. The common terminal is common to both the make and break terminals. Contrary to what bluejets said, you need a normally open switch. This means, in the normal position...
  3. BobK

    Wireless key fob and USB receiver. Advice sought

    Very good analysis, ChosunOne. When I worked at Intel (now retired) off hour access was through a floor to ceiling turnstile that looked more like a torture device than an entryway. This was more to prevent tailgating than accurate determination of who was in the building, but, coupled with a...
  4. BobK

    Optical Pickup

    Jimi rules! Bob
  5. BobK

    Optical Pickup

    What do you hope to achieve by faithfully reproducing the motion of the string in a an electrical signal? Musical instruments, like an acoustic guitar for example, do not do this. The sound box resonates and filters, greatly modifying the wave produced by the string, making it sound far...
  6. BobK

    Wearable bus card

    I am struggling to understand what you are proposing. Presumably, the bus card is inserted into a slot to be read when you board the bus. How does you wearable version work? Bob
  7. BobK

    Wiring together LED lighting for a display

    The internal resistance of these cells starts at about 10Ω rising to 30Ω as they deplete. At 10mA current, 20Ω (for two batteries in series) the voltage loss is only 0.2V. So it is unlikely that the LED strings have no resistor and are surviving 5.8V. Bob
  8. BobK

    Battery - Charge or be Charged?

    Which you can buy cheaper than you can make. Bob
  9. BobK

    Battery - Charge or be Charged?

    My advice would be to get a commercial Lithium Ion battery charger. These batteries are tricky to charge and can catch fire or even explode if it is not done right, as Samsung learned recently. Bob
  10. BobK

    Attiny85 and unrecognized HIGH levels

    It makes perfect sense to me. The battery voltage might be anywhere between 4.8 and 8.4V so he is using a low dropout regulator to get a known voltage for his ATTINY, probably 3.3V since you cant get 5V from 4.8 with a low dropout regulator. Bob
  11. BobK

    Industrial voltage divider

    How much current do you need at 5V? If it is 1A, then the regulator would dissipate 19W of power and need a massive heat sink and probably a fan. On the other hand, a DC to DC converter (buck converter) would be much more efficient and produce far less heat. I would not use a linear regulator...
  12. BobK

    can IR sensor be changed?

    Add up the current requirements and make sure the new controller can handle the whole amount + 25% so that it is not straining. Bob
  13. BobK

    LED in a circuit with alternating polarities

    You could put the switch between the battery + and the motor controller instead of after it. or You could use a two pole switch. or You could use a second switch for the LED. Bob
  14. BobK

    Transistor Question

    What you need depends on how you want to control the motor. If the motor only needs to run in one direction, a single MOSFET is all you need. If you need to run it in both directions, you need an H-bridge, which has 4 transistors. Bob
  15. BobK

    Optical Pickup

    Yes, but read this paragraph: A normal pickup does not "detect frequencies" or require "decoding" to produce an audible tone "identical" to the vibrating string. Only the OP can clarify it, but it does not look like he is coming back. Perhaps I am reading too much into his inaccurate...
  16. BobK

    can IR sensor be changed?

    Audioguro: unless you are rather unusual, you probably have and audio video setup using multiple remotes, and probably they all work at 38KHz. They don't interfere because different digital coding is used on all of them and they respond only to the valid codes for the device. I think the...
  17. BobK

    Optical Pickup

    I think all of you are misinterpreting what the poster wants. He says he wants to detect the frequency of vibration and decode it. I think this means he will use the frequency to set the frequency of some kind of synthesizer that produces the actual sound. bob
  18. BobK

    Display prototype

    Wow, I did not know those existed. Seems like exactly what the OP needs. Bob
  19. BobK

    Choosing resistor value

    Calculate the current drawn from pins that are outputs and high and add them up. Extra credit: Calculate the max current drawn from all pins that might be high as the same time. Bob
  20. BobK

    Display prototype

    I find many people selling this OLED display: https://www.amazon.com/HiLetgo-Serial-Display-SSD1306-Arduino/dp/B01N1LZQA8/ref=sr_1_1?s=industrial&ie=UTF8&qid=1495909355&sr=1-1&keywords=oled+display It is 27mm x 27mm x 4mm, so, to make your 3cm x 3cm spec you would have to stack it on top of...
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