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  1. BobK

    Having trouble visualizing Voltage = Joules / Coulombs

    I guess I did not make it clear. I was showing how it would result in an absurdity if Q was in the numerator in the original equation. So this eq. was supposed to be wrong. Bob
  2. BobK

    Self-made transistor RAM

    Yes, Intel, NVIDIA and AMD, do this quite well. Bob
  3. BobK

    help for lm324

    Why do think it would be on? You are putting the same voltage on both the + and - inputs. This could cause the output to be anything. Did you expect the 2 different resistors to create different voltages at the inputs? Will, they will, but the typical current drawn by the inputs is 20nA...
  4. BobK

    Design question on microcontroller and TIP122

    That is not the way to use an NPN transistor as a switch. The load should be between the + voltage and collector of the transitor, and the emitter should be connected to ground. Bob
  5. BobK

    Having trouble visualizing Voltage = Joules / Coulombs

    V = Joules / Coulomb, is not an equation is a defintion of the unit of voltage. The equivalant equations would be: V = E / Q Where E is energy in Joules and Q is change in Coulombs. Now, rewrite this as: E = V * Q The energy is the product of the charge and the voltage. Which...
  6. BobK

    I would appreciate any input

    Sorry, but if the only connection between the two probes is the skin, and you have 2m A going through the probes, you also have 2 mA going through the skin. Bob
  7. BobK

    Difference between polarised and non polarised capacitor.

    You can use a polarized capacitor when one side is always at a higher potential then the other. Connect the + lead to the side that is higher. Otherwise, use a non-polarized capacitor. Exception: if there is only a few millivolts max across the capacitor, a polarized one is okay. Bob
  8. BobK

    I would appreciate any input

    You are going to need a LOT more than 5V to get 2ma through skin. I just tried this on myself. At 10V the most I could get is 20uA by squeezing the probes very hard, one in each hand. Placing the two probes nearby on my leg, I could not get more than 1uA. So, 500K to 10Meg for my skin...
  9. BobK

    What do I need make this flash pattern?

    A 555 can alternate between 2 LEDs or set of LEDs by simply connecting one set between pin 3 and ground and the other set between pin 3 and V+. If you need more than 200 mA, for either set though, you will have to use MOSFET switches. A P channel for one set and N channel for the other. Bob
  10. BobK

    What do I need make this flash pattern?

    Your pattern has one set off and one set on at the any time. This can be done by a 555 with no additional circuitry. Bob
  11. BobK

    De-soldering wick, pump, or gun type?

    Both have their uses, and I use both. The pump is required to get solder out of holes in through-hole boards. The wick is great for cleaning up after drag soldering. In the pump I have, you end up with little tubes of hardened solder which are easily removed. Bob
  12. BobK

    What do I need make this flash pattern?

    You only showed us 1 type of flash pattern. What is it that you think a 555 cannot do? Bob
  13. BobK

    Can capacitor be made with 2 pennies + paper?

    Here is a link to the system on units in which capacitance is measured in centimeters: http://en.wikipedia.org/wiki/Centimetre%E2%80%93gram%E2%80%93second_system_of_units 1F = (10**-9 * c**2) cm The system of units is called cgs for cm / gram / seconds. All units are expressed only in...
  14. BobK

    Need help with 555 timer circuit

    Each LED needs a separate resistor. Bob
  15. BobK

    help in a project

    Simply have a capacitor that is charged when power is on and discharges through a resistor when power is off. If, when power is supplied, the capacitor is above a threshold, the device is held in the off until the cap discharges. Bob
  16. BobK

    Can capacitor be made with 2 pennies + paper?

    When I took physics in college, the unit of capacitance was cm, which, I thought sounded funny. That would be a 100000 cm capacitor. (i.e. 10000 cm sqared / 0.1 cm) Bob
  17. BobK

    Help identifying chip

    Nope: Bob
  18. BobK

    My first circuit

    I can't believe I missed that the polarity was still wrong. Bob
  19. BobK

    My first circuit

    Much better! That will work, assuming your power supply can supply 200mA. Bob
  20. BobK

    My first circuit

    No, it means you cannot put them in series. They have to be in parallel and have a reistors in series with each one. Did you bother reading the tutorial I pointed you to? Bob
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