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  1. BobK

    Basic question about charges

    Because we can move it close to a known positive or negative charge and see if it attracts or repels. Insulators can hold a charge, it just cannot move easily along the insulator as it would in a conductor. Bob
  2. BobK

    Fix 250 watt Dayton Plate Amp or Convert 400 Alpine Car Sub Amp for Home Use

    You cannot get 400W into a speaker with 12V. So you car amp boost the voltage up to probably something like ±40V. Now, when you are going to run from mains (120VAC) down to 12V then back up to ±40V this is wasteful. It would be better to go directly from the mains to ±40V and skip the part in...
  3. BobK

    silly idea

    Um, Donkey, were you sober when you posted? Bob
  4. BobK

    Identification help

    2210 would be 221 Ohms would it not? 221 x 10^0 Bob
  5. BobK

    Assistance with Transistor Theory

    Yes, it is an analogy. Basically, I am trying to say that if you have two variables and a function that maps one to the other, either one can be said to control the other. Specifically, the Vbe and Ib are related by an equation, so you can think of either as controlling the other. Bob
  6. BobK

    Cool circuit plotter with conductive ink

    Yes, but I want one for other purposes anyway! When I get it (probably after I retire next year) I will try it out. Bob
  7. BobK

    Circuit Schematic Design Software

    +1 on Express PCB. I use it for my all my DYI boards. I have also used Eagle and have many problems with it: As someone else said the libraries are too large, and badly organized making them difficult to search. Making a new component has me pulling my hair out every time I attempt it. And...
  8. BobK

    MOSFET H-bridge, weird effect...

    I have a robot car that I built the bridges from dual P-N MOSFETs which cost me 25 cents for each H-bridge bridge. You can't get much cheaper than that. Bob Edit: Here are the MOSFETS I am using. I bought 100 at 12.1 cents each...
  9. BobK

    MOSFET H-bridge, weird effect...

    I just did a simulation with BJTs and it does conduct, but in a manner that will destroy the transistor, which is why you should always have flyback diodes across each transistor. Here is the circuit, simulating an H-bridge with both lower transistors (NPN) biased on, and a motor that has been...
  10. BobK

    PIC24FJ256GB106 Acheiving maximum speed.

    Here is an example of setting up the PLL on a dsPIC33FJ128GP802 chip, which is similar to 24FJ... This is starting with an 8MHz crystal. void init_clock() { /* Set up clock at 25.6 Mhz */ _PLLPRE = 8; // PLL pre divider of 10 (it is +2) = 0.8Mhz _PLLDIV = 126; // PLL multiplier of 128 (it is...
  11. BobK

    PIC24FJ256GB106 Acheiving maximum speed.

    Read the oscillator section of the datasheet. It is quite complex. To get full speed, you have to write code to set up the PLL. Bob
  12. BobK

    analog clock on ntsc display

    Most microcontrollers would not have enough RAM to do what Harald is suggesting, i.e. have a frame buffer. Even a very low resolution 320x200 monochrome display would require 8K bytes of RAM, which is high, for a microcontroller, though not out of the question. To go to 640x400 and even 3 bit...
  13. BobK

    Cool circuit plotter with conductive ink

    A better idea would be to use a 3D printer to put down plastic on a copper clad board, then etch it. The accuracy of 3D printers is much higher than they achieved. Bob
  14. BobK

    MOSFET H-bridge, weird effect...

    You didn't get the braking effect with the BJT bridges because there is not short circuit when, for instance, the bottom two transistors are on and the top ones are off. But with MOSFETs, one will conduct from source to drain through the body diode. BJT bridges often have diodes placed like...
  15. BobK

    Assistance with Transistor Theory

    Laplace: Look at this nifty device called the lever. If I push on the long side of the lever, I can control a much larger weight on the other side of the lever. LvW: No, your pushing on the long end of the lever is not controlling the weight, it is the multiplied force on the other side of...
  16. BobK

    Wireless Voltmeter probes?

    Hey Chris, Haven't seen you in a while. Welcome back! Bob
  17. BobK

    LM358 Breathe light

    You can create a non-polarized capacitor of 1/2 X uF by tying the - terminals of two X uF capacitors together, and using the two + terminals as the terminals of the non-polarized capacitor. Bob
  18. BobK

    Novice needs help with three phase motor controller

    Sorry, posted to wrong thread! Bob
  19. BobK

    Novice needs help with three phase motor controller

    You can make a non-polarized 100uF capacitor by connecting together the - leads of two 200uF capacitors and using the two + leads as the leads of your non-polarized capacitor. I know it is counter-intuitive, but it really does work. Bob
  20. BobK

    Wireless Voltmeter probes?

    Yes, I understand. My point was that under some conditions, i.e. having a common ground, the voltage between the two points can be measured without putting the two probes of the measuring device on the two points, but rather by making a separate measurement between each of them and the common...
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