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  1. BobK

    Crystal 3.2768 to 3.57954

    The way you have written it, it is probably wrong. I would expect 3.2768 to mean 3.2 MHz. But clock crystals are usually 32.768 KHz. This is a number that, when run through 15 flip flops will produce a 1 Hz signal. Look for a 32.768KHz or 32768 Hz crystal. I think this is probably what...
  2. BobK

    PCB

    Osh Park. $5 per square inch for 3 boards. They only accept Eagle or Gerber files, though. http://www.oshpark.com/ Edit: I just realized this is $40 per board, so not that much different. Bob
  3. BobK

    Tiny85 and LDR Analogue Read

    You would not need a bootloader. If you program the chip directly, you can access any of its features that way. I would think there would be example code on the AVR site, but I am a PIC guy, so I couldn't tell you for sure. Bob
  4. BobK

    Heat Sink for a LM4780?

    The C/W rating of a heat-sink tells you how may degrees C the temp will rise per Watt of dissapated power. So the lower the number, the more heat it can dissapate. For example. if you are dissapating 10W the 1.5 C/W will rise in temp by 15C, the 2.5C/W will rise by 25C. Bob
  5. BobK

    pic16f84a doubt

    But only if it is powered with 5V. Inputs cannot be more than 0.3V above Vdd or they will feed power into the chip through the protection diodes. Bob
  6. BobK

    [newbie] Powering car horn?

    Using a siren is illegal if you are in the U.S. and probably elsewhere. Bob
  7. BobK

    bipolar stepper motor driver selection

    I assume that it is 2 phase bipolar motor with 4 wires, right? If so, a quad half-bridge driver is what you are looking for, like SN754410, which can handle 1A. Or you can do the same thing (but limited to 800mA) with 4 2N2222 and 4 2N2905 eight diodes and 4 resistors for less money! Bob
  8. BobK

    How to design a sallenkey highpass filter

    Yep, DC is as low as you can go. Bob
  9. BobK

    USING A CELLPHONE AS REMOTE CONTROL

    They could find that easily enough. Bob
  10. BobK

    Math: Geometric Progression

    As I read your wording it is not a geometric progression, it is increasing by 6 thousand each day. (This should be in homework help) Bob
  11. BobK

    How to design a sallenkey highpass filter

    I would not call the signal in your image a DC pulse signal. Any changing signal can be considered an AC signal with a DC offset. The DC offset will be lost going through a highpass filer. Bob
  12. BobK

    dual power: battery or regulator

    Diodes do not "eat" current, the same current that goes in, goes out. They do drop the voltage a bit though. A Schottky diode drops less than a normal diode, usually less than 0.5V at their full rating. At 50uA, the voltage drop will be much lower, probably more like 0.2V. Lowering the...
  13. BobK

    need help in controlling the voltage in a circuit

    I am going to guess that the problem is that you are simply using a voltage divider with the LDR and a resistor and feeding it to the base of a transistor. If you use a comparator instead, it will work much better, it will snap to the full voltage once the threshold is crossed, and they have...
  14. BobK

    Calculating gain of an OPAMP

    The word bandwidth here is misleading, it is not the range of frequencies as you have assumed in your calculation, but the upper limit of the frequencies that you need to amplify. In any case, at 3.5Hz you are not going to have any problems with any opamp. Bob
  15. BobK

    LED and 555 timer help

    The 555 chip cannot switch mains circuits by itself. Bob
  16. BobK

    Wireless trigger for LEDs and buzzers

    Do you have a PICKIT 2? It has a 4-bit logic analyzer feature that you could use for that. Bob
  17. BobK

    Controlling DC Lego motors with an old Blackberry?

    The problem is that phones are not USB hosts. The boards would expect a host. Bob
  18. BobK

    LED and 555 timer help

    They must be UV or infrared LEDs, because I don't see anything :) Bob
  19. BobK

    Controlling DC Lego motors with an old Blackberry?

    Does it have to be a phone? A laptop or desktop computer would be easier. There are boards available for about $20 that plug into USB and allow you to control a number of inputs and outputs to the real world. There might be something similar for a phone, but I do not know about it. Bob
  20. BobK

    Controlling DC Lego motors with an old Blackberry?

    Yes, it is doable, but not something for a beginner. Bob
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