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  1. BobK

    Drive A 5w Led

    If you apply 6V you may well burn another one. LEDs cannot be reliably run from a voltage source, the current would be too varisble. You had the right idea with the constant current source. You just need one that can run in the range of 6 to 7 volts. And you do need a hear sink if you want...
  2. BobK

    LED strips for vanity/accent lighting?

    Lumens measure the total light output in all drections, unlike candella. The angle of view does not affect lumen measurements. The total illumination provided by a bulb or strip putting out 100 lumens is the same, though the spatial distribution will be different. It is also adjusted...
  3. BobK

    LED strips for vanity/accent lighting?

    That is not my experience at all. The LED bulbs I have bought appear to provide more illumination to me than their stated incandescent equivalent. On the other hand, Lumen raytings of raw LEDs from Ebay are almost certainly way overstated. I doubt that that is the case with the very...
  4. BobK

    12 V motor loss of power

    Have you tried supplying power directly to the motor to see if it runs correctly? Bob
  5. BobK

    PWM Control with Shift Register Support for 3w White LED's

    The ones I have are all 3 under one lens, but it is clear. They are in an application were there is an outside diffuser. The key things you need to look for in the MOSFET are: 1. Current capability. Allow at least twice what you need. 2. On resistance. The lower the better, but for...
  6. BobK

    OP-amp help

    Agree. Not enough info yet. Your comparator idea might work in any case if it is basically the frequency that matters, which seems likely. Bob
  7. BobK

    OP-amp help

    Hmm. The diagram posted by the the thread starter indicates a coil and magnet are used for the pickup, which means the signal might really be AC. It also explains why the signal might degrade. A Hall effect signal would not likely degrade to a lower output voltage, but if clearances changed...
  8. BobK

    Different 12v DC power sources

    No. If there is no other connection between the two transformers, no current can flow. If the two have a common ground, and if that was the - of the first transformer and the + of the second, you would have 24V on the light. If the two minuses are connected together it will work, but what is...
  9. BobK

    OP-amp help

    The OP said it needed to send a 6 to 8V AC signal. (probably means square wave, which I am guessing the frequency indicates the vehicle speed). He just wants to amplify the <5V signal he is currently getting. Bob
  10. BobK

    PWM Control with Shift Register Support for 3w White LED's

    Here is a fine one: http://www.mouser.com/ProductDetail/Diodes-Incorporated/DMG2307LQ-7/?qs=sGAEpiMZZMshyDBzk1/Wi/D7Em5shE8qzFcwKhDCLpqxghky/WLlwg== 134mΩ at -4.5V 3.1A at that gate voltage. $0.35 for 1 $2.66 for 10 Bob
  11. BobK

    PWM Control with Shift Register Support for 3w White LED's

    Nope, no good. This part requires 10V to turn on. This is what you are looking for in the datasheet RDS(on) Static drain-source onresistance VGS = -10 V, ID = -5 A 0.13 0.16 Ω When they do not characterize Rds(on) at 5V (or less) it is most likely not going to work at 5V. The Vgs threshold...
  12. BobK

    OP-amp help

    The pollution control stuff is probably using the vehicle speed in its calculations. Or, maybe it is used to detect the smog test and change the operation of the engine, ala Volkswagen? Bob
  13. BobK

    PWM Control with Shift Register Support for 3w White LED's

    The WS2811 has outputs that are constant current sinks, so they are active low, which means using a P channel MOSFET is correct. You will also need a pullup resistor to 5V on each channel to turn the MOSFET off. Since the output is trying to sink a constant current, I am not sure what happens...
  14. BobK

    Education: Transistor as a Switch

    I think I screwed up. I looked at the 4069 datasheet and the min input for logic high is 4V, it will not work at 3.3V, Instead you could use 74HCT04, which can work with a 2V input. Make sure the T is there in the part number, that is what specifies the lower logic level, Bob
  15. BobK

    Education: Transistor as a Switch

    The 3 LEDs are not in series, so their voltages do no add. Each of the anodes should be connected through its own resistor to the collector of a PNP transistor with the emitter to 5V, just like your schematic. The base will be driven, through a resistor, by the output of an inverter, with the...
  16. BobK

    Education: Transistor as a Switch

    With a PNP transistor the voltage is still with respect to the emitter, and a negative voltage turns it on. In you example, the emitter is at 5V and the battery is at 1.5V so, it has -3.5V applied to the base resistor, which turns it on. Bob
  17. BobK

    Education: Transistor as a Switch

    Okay, if you need to interface to a signal that is active high, you will need an inverter for each color. You can use a CMOS hex inverter (CD4069), which has 6 of them in a single 14 pin IC. Bob
  18. BobK

    Is this dc adapter safe to plug into my keyboard instrument

    Okay, assuming you can get the correct one. Bob
  19. BobK

    Is this dc adapter safe to plug into my keyboard instrument

    Yep, the polarity is reversed. And I don't think the plug is right, it looks to me like the inner connector on jack (keyboard) is smaller than the inner connector on the plug (power supply) Do you have a vernier caliper? To get this to work you need to get the correct plug and rewire it to...
  20. BobK

    PWM Control with Shift Register Support for 3w White LED's

    That looks like a good option, which basically does exactly what I was proposing without requiring any programming. Only drawback is you have to send 3 bytes for each light. On the other hand, you could use one WS2811 (and 3 MOSFETS) to control 3 of the LEDs if that made any sense. Bob
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