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  1. BobK

    A light-sensitive motor

    KrisNZ - very cool circuit. Basically a form of Schmitt trigger with one of the transistors being the power switch. I've never seen it done that way. Bob
  2. BobK

    Does this Circuit make sense?

    12V incandescent bulbs can just be connected in parallel to the 12V supply. Bob
  3. BobK

    A light-sensitive motor

    At 30K the LDR is not going to supply enough base current to run the motor. You might try a darlington. A better circuit would use a comparator to discriminate light and dark and use its output to drive the base of the transistor. Bob
  4. BobK

    8 omhs-4ohms

    Well, I don't have any ideas then. The speaker will work, but it won't have the same frequency response as it did before. Have you tried just wiring it in as is? Bob
  5. BobK

    PIC16f877a interfacing with other PIC

    What kind of information are you trying to send from one to the other? That is the key. If you just need to signal a single on / off state, then you would just connect and output of one to an input of the other. So tell us what exactly what you want to communicate from one PIC to the other...
  6. BobK

    Bought a board that has an adjustable pot - how to measure ohm vals

    No, in that circuit, the pot is used as a variable resistor, i.e. only two legs are used. Let's say you have a 10K pot. And at some position, the center leg to the left leg reads 3K. The the center to the right leg would read 7K, and you could replace the pot with those two resistors wiring...
  7. BobK

    8 omhs-4ohms

    So if I understand you, you are replacing an 4 Ohm tweeter with an 8 Ohm tweeter and the crossover was designed for a 4 Ohm tweeter. You might be able to modify the crossover to use the 8 Ohm tweeter. Do you have a schematic for it? Bob
  8. BobK

    Mosfet noob

    Several reasons: 1. Motors do not run well on lowered voltage. It is better to control the speed by using PWM which varies the % of time the full voltage is applied. 2. MOSFETS are not good as linear devices, your control voltage would be a small range. 3. You are wasting energy and...
  9. BobK

    8 omhs-4ohms

    Why? Bob
  10. BobK

    Mosfet noob

    Okay, now the question is why are you using a DAC output to drive the gate? Are you planning on varying the voltage to control the speed of the motor? If so, this is not a good idea. Bob
  11. BobK

    Bought a board that has an adjustable pot - how to measure ohm vals

    Most likely you can measure it in circuit, since it would likely just be setting a voltage for a comparator, which should not draw much current. If the 3 legs all have separate connections you would need 2 resistors to replace the pot. If one of the outer legs is connected to the middle leg...
  12. BobK

    Question about 2.4 ghz receiver

    I wouldn't know becuase I don't do that kind of work, but I think I can safely say that it would be 5 figures (in U.S. dollars). Bob
  13. BobK

    Question about 2.4 ghz receiver

    I hope you are expecting to pay a LOT for it. This is not a small project. If there is a commercial solution available at any cost, it is likely cheaper than building this from scratch. Bob
  14. BobK

    Sweat monitor using electrodes.

    Whoa! Did virtual smoke come out of Tina when you fed Megavolts into an op-amp? Bob
  15. BobK

    Mosfet noob

    So you were connecting to a PWM output? If so, then it would read 5V * duty_cycle when read with a multimeter, which explains the 1.9V. Bob
  16. BobK

    Mosfet noob

    Aha, the outputs are open collector. That means you need a resistor from the output to a 5V source, it does not produce any voltage itself. And you do not need the pulldown resitor. Bob
  17. BobK

    How to select Vref?

    In PICs you can separately specify whether Vref+ and Vref- are internal or external. You would leave the Vref- internal, which connects it to ground and frees that pin for other uses. Also check the datasheet for the minimum Vref. I think 1.5V is going to be too low. Bob
  18. BobK

    Mosfet noob

    What is the 5V source then? It must be high impedance to have a 5.6K resistor pull it down to 1.9V. Bob
  19. BobK

    Chronograph for bullets

    But still most of it is transferred as kinetic energy right? That is what the swinging wood block is measuring, how much kinetic energy was transferred to the wood block. And what I was saying was that some of the bullet's kinetic energy would become heat, and the rest would become kinetic...
  20. BobK

    Simplest and cheapest possible noise generator circuit

    That should work, though you might have to change the value of the capacitor to get the sound into the right frequency range. The resistnace you get from the body will depend a lot on how much pressure you put on the electrodes, which might be a desireable effect. Bob
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