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  1. BobK

    How to wire a LED

    If the light is a single LED with a resistor designed to work from 12V it will probably work as is from 9V but at a lower brightness. To bring it up to full brightness, you would lower the value of the series resistor that is already there. A 9V battery will be able to drive a single 20ma Led...
  2. BobK

    Voltage Multiplier Design

    It is not a voltage multiplier you want, it is simply an amplfier. An opamp is the approriate device to use. The gain of an opamp can be set by the ratio of two resistors. Use an amplifier with a gain of 41.7 and you will get a reading of 1mV / lb. Bob
  3. BobK

    SMD Soldering

    Get a small conical tip. Use a magnifier, I use one on a headband that you can flip in and out. Use a solder paste syringe. Squirt a bit of solder on each of the pads. Use tweezers to place the part (not the kind from your medicine cabinet, really sharp pointed ones designed for this...
  4. BobK

    Testing Volts and Amps in my Circuit

    If you have a single LED and resistor, then add a second LED in parallel, the current will increase but not double. This is because the increased current through the resitor lowers the voltage across the two LEDs, and LEDs current is very sensitive to the voltage across them. Bob
  5. BobK

    Working on getting a Pierce Oscillator to Oscillate

    What you would hear if you tuned the frequency it is oscillating at is the radio going very quiet. It will be near 1000 on the AM dial. Bob
  6. BobK

    Working on getting a Pierce Oscillator to Oscillate

    The scope is probably aliasing, which means it is showing a wavefofm that is a complex interaction between the sampling frequency / phase and that of the input. which means maybe it is oscillating. Do you have a multimeter with a frequency function. That would tell you something. Bob
  7. BobK

    Working on getting a Pierce Oscillator to Oscillate

    your PC scope is useless at RF frequencies. How do you know it is not oscillating? I am not an expert on RF circuits, but your inductor seems way too high. As for breadboardiing an RF oscillator, I have made 100Mhz oscillators work on a breadboard. bob
  8. BobK

    Control circuit

    Don't build any circuits until this condition is remedied! Bob
  9. BobK

    n00b question about input and output of a guitar effects box

    Revesing the input and output of an electronic circuit makes as much sense as trying to water your lawn by forcing water into the tiny holes on the sprinkler head. Bob
  10. BobK

    TQFP package PIC18F4520 programming using pickit 3

    Yes. This is expained in the PICkit 3 user's guide. You will have to connect: 1. both Vdd / Vss pairs to power and ground with a 100nF capacitor at each pair. 2. MCLR, PGC, and PGD to the PICkit 3. 3. PGM to ground. Bob
  11. BobK

    How do I switch a 220 Volt incandescent lamp from a PIC

    There are opto-isolated triacs in a single package. That would simplify things a little. Bob
  12. BobK

    How to heat a wire.

    Oops, make that supercapacitor! The 36A seconds is of course way overkill, I just threw out some numbers. The 0.02 in wire in the link above required 4A to heat. And it would certainly heat in less than a second. So lets do some numbers, say we went with charging just to 1.5V and we...
  13. BobK

    How to heat a wire.

    I have to disagree. An LR44 button cell has a capacity of 150maH. Use that to charge a capcitor at say 10ma for 1 hour and you could then produce 10 * 3600ma = 36 A for 1 second. And you could do this 15 times. Bob
  14. BobK

    Merry Christmas and a happy new year

    Happy Solstice! Bob
  15. BobK

    Squeeze that battery

    Let me see if I understand what you are asking. You have a battery driving some load. The battery lasts for some number of hours. But what you want is to use the same battery to drive more power into the load (brigher light, faster running motor, louder sound, etc), and have the battery last...
  16. BobK

    Make a "blinker" for LED panel?

    Hard to tell without the actual datasheet for the LEDs. But, for comparison, here is a single 5W LED at 660nm that puts out up to 1W of radiant power. http://www.ledengin.com/files/products/LZ1/LZ1-00R200.pdf This would be enough to give you 60mW /cm^2 in a 2inch circle. The panel you...
  17. BobK

    Buffer or pre-amp?

    A buffer typically has no voltage gain. An amplifier typically, does. Bob
  18. BobK

    Capacitors

    You can make a non-polaraized capacitor from polarized capacitors by putting 2 of them in series back-to-back. The resultant capacitor is 1/2 the value of each capacitor. I have tried several times to understand why this works, but it escapes me. If you search the net, you will find multiple...
  19. BobK

    Very noisy BLDC Circuit.

    Do you have a flyback diode on the motor windings? Bob
  20. BobK

    Can you ID this transformer

    There appear to 2 red and a black wire on the secondary. 17-0-17 seems like a reasonable guess. Bob
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