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  1. BobK

    Help With Potentiometers

    Potentiometers are not for controlling power directly. In a PWM controller they provide a variable voltage that controls the percentage of time the power is on. The current to run the motor or LEDs does not go through the potentiometer. Why? It would heat up and burn out if you did that :D Bob
  2. BobK

    Noob needs help with batteries

    It is not only safe, it is impossible. The current cannot be flowing into and out of the battery at the same time, so the battery is always either charging or discharging. Bob
  3. BobK

    Supply for 30 LEDs

    A 6V supply and a 1K resistor should not damage any LED. Are you sure you connected it right. Bob
  4. BobK

    Query relating voltages in circuit

    You can't use a 24 and a 12 to get ±12 because the 12V supply would have to sink current from the 24V supply. What you want is a buck-boost converter, which puts out a negative voltage. Or, better yet, get one of the many thousands of amps designed to work on an auto electrical system. Bob
  5. BobK

    Peltier

    Why don't you tell us what it is you are trying to do? The temperature you need to keep the device at, and the ambient air temperature, for starters. Bob
  6. BobK

    Trying to buy the right sockets for my PICs

    The PIC microcontrollers do not get hot unless you have done something wrong. ICSP uses two pins, but you can, with a little forethought, use these same pins in the circuit. Just don't use the pins as outputs that control something you do not want to have a signal on while programming. If...
  7. BobK

    Peltier

    Davenn is right, all the Peltier is doing is adding heat that you must remove because it is not 100% efficient. The hot side of the Peltier produces more heat than the cool side removes. So cooling the liquid directly is more efficient. Bob
  8. BobK

    Measurement -2.5 +2.5 with ADC

    Here you go. The opamp must be have rail to rail inputs and outputs, and the power supply must be precision regulated to 5V for this to work well. Even then, there will be some bending of the line at the top and bottom of the range. The graph shows the output for input sweeping from -2.5V to...
  9. BobK

    Peltier

    But you still have to remove the heat from the liquid. Bob
  10. BobK

    Trying to buy the right sockets for my PICs

    Why would you use a socket for your final projects? I always solder mine in. I needed to replace on once and I did so by desoldering it and soldering a new one. Also, you don't want to be moving them from a programmer to the final board. The time it takes is truly annoying and you will break...
  11. BobK

    Peltier

    The point of liquid cooling is to move the heat away from the device so that it can be dissipated somewhere else, presumably where there is more space for a heat sink. Your Peltier device just moves it again. You still have the same heat to get rid of, plus the extra heat created by operating...
  12. BobK

    Peltier

    This kind of question is what Google is for. Bob
  13. BobK

    Power Relay needed

    Here is a circuit that would work. It uses Linear Technologies parts, but that is because I use their simulator (LTSPICE) and was too lazy to try to add more standard parts. The very common TL431 can be used in place of the LT1009 voltage reference. Just connect the ref pin to the cathode and...
  14. BobK

    TEGs

    I hope it is very cold when you are riding! The energy you can produce depends on the difference in temperature between your hand and the heat sink. If is is 30C outside, you are not going to have much of a temperature difference. Like Harald, I think this project is not feasible. You might...
  15. BobK

    Powering 104 LED's from Molex connector, possible?

    You need to go to 3 LEDs in a string to make this work. Assuming 20mA LEDs, that would be 101/3 = 34 strings x 0.02A = 0.68A. Quite doable. I calculate 150Ω for the resistor. Bob
  16. BobK

    Is It A Transformer 220vac-110vac ?

    Yep, I think Dave nailed it. I cannot be sure of the size since there is nothing to compare to, but it looks like maybe the transformer is 4 cm across. If it is this size, the power it can handle is pretty low, maybe 100W at most. What is it rated for? Bob
  17. BobK

    Creating logic AND gate with 2N222 Transistor

    Okay, I read you question too quickly. I was giving the acceptable low (< 0.8) and high (>2.5) levels, and I got that wrong, the high is 2.0. I have never heard of a threshold voltage, I have always thought anything between 0.8 and 2.0 gave undefined results. Bob
  18. BobK

    Motor Discussion

    Steppers are typically 1.8 degrees, but with gearing you can get any step size you want. I.e. gear it down by a factor of 9 and then 5 steps is one degree. Bob
  19. BobK

    Motor Discussion

    Steppers are typically 1.8 degrees, but with gearing you can get any step size you want. Bob
  20. BobK

    Can I Connect Same Speakers To 3 Players?

    There are MP3 modules out there that let you select one of 9 tracks to play via 9 inputs. 1 player, and 2 flip-flops and a couple of random gates to sequence through the 3 tracks. Or, simpler still, a microcontroller. Bob
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