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  1. BobK

    Drive two relays based on input voltage.

    Thanks, it should have been "than using a perfect...". Fixed Bob
  2. BobK

    Drive two relays based on input voltage.

    Yes, but if the 5V is off, the output voltages are also off by the same ratio. So deriving the set points from the 5V makes it more accurate than using a perfect voltage reference. Bob
  3. BobK

    transistor pairing? or not?

    Feedback takes care of differences between the two output transistors. Are there matched power MOSFETs available? Bob
  4. BobK

    Drive two relays based on input voltage.

    AK is assuming that the voltages coming from the stick are absolute, not dependent on a 12V electrical system that might vary between 12 and 14V, If the voltages from the stick vary with input voltage, the reference should be derived from the positive rail. Bob
  5. BobK

    Bench power supplies! [help!]

    Any linear regulator going down from Vin to Vout will waste exactly the same amount of power. The formula is Pwaste = (Vin - Vout) * Iout You can save a little by using a low dropout regulator, which will allow you have a smaller Vin, but if you are going up to 30V anyway, but normally use...
  6. BobK

    I'm a Carpenter, not an Electrical Engineer

    Here is how I see carpenter vs. woodworker or cabinetmaker: Carpenter's tools: Chop saw Contractor saw Nail gun Hammer Drill / driver Tape measure level square Woodwoker / Cabinetmaker's tools: Good table saw, preferably with induction motor Band saw with re-saw capability Jointer Planer...
  7. BobK

    I'm a Carpenter, not an Electrical Engineer

    Unless you build your guitars out of 2x4's I would say you are woodworker, not a carpenter. Bob
  8. BobK

    3.2v LEDs 12v battery

    If they are stealing resistors, they must be quite desperate! Bob
  9. BobK

    Simple latching switch for a pcb

    I am not sure I understand what you mean by latching. This usually refers to a pushbutton that you push once for on and again for off. Yet you mention slide switches, which you slide to one side for on and to the other for off. Does the switch really have to be a latching switch (as I...
  10. BobK

    3.2v LEDs 12v battery

    Do the Chinese suppliers on Ebay ship there? They are a good source for parts like resistors, but it can take weeks for shipping. Bob
  11. BobK

    Choice of PCB drill and stand (Dremel?)

    I use a Dremel tool and the drill press stand you show and I find them to be about perfect for PCB drilling. No complaints. My wife and I have both used Dremel tools for various purposes for a long time and have never had one burn out. People who say that are most likely misusing it. Bob
  12. BobK

    3.2v LEDs 12v battery

    Yes, buying those resistors will make it work, even if you do not use them in the circuit. :rolleyes:
  13. BobK

    How do i use these thingys?

    Yes, he is right, I now see that I did have the emitter and collector reversed. I was looking at his revised drawing, and of course, they were correct there :oops: Bob
  14. BobK

    I need to hire someone for a logic design

    Supplying AC would reverse the chemical reaction 60 times a second, so no corrosion. But if the circuit only conducts when hit by a bubble and the current is kept low, I think corrosion might not be a problem with DC. Bob
  15. BobK

    3.2v LEDs 12v battery

    You have the right idea with series and parallel, but you have it backwards. What you need is 3 strings of 3 in series with a resistor in each string. Then you parallel those three strings. The resistor has to drop 12 - (3 * 3.2) = 2.4V at 20mA of current. Use Ohms law to calculate the...
  16. BobK

    mini christmas lights

    It sounds like the replacement bulbs want more current than the originals. It could pass a small current without lighting. Can you test and original bulb and the replacement for current draw at 2.4V? Bob
  17. BobK

    How do i use these thingys?

    I don't think so, is it a PNP. I simulated it and it does work. Bob
  18. BobK

    How do i use these thingys?

    Here is a circuit that might work: Q1 can be any PNP switching transistor. R2 should be as shown for a red LED, lower (maybe 68) for a white LED. This assumes 20mA LEDs. R1 will adjust the sensitivity, try a range of 1K to 10K. If you have a 10K pot, you can use that, and adjust it. As far...
  19. BobK

    RF signal strength

    It is odd that it only works at 2m. I have two cars with remotes and they both work at as much as 30m. Holding they high in the air will also increase the operating distance. Bob
  20. BobK

    I need to hire someone for a logic design

    Dave, That is exactly what he suggested in his post. As well a low voltage supply for the logic (batteries.) He also want a set off period after each on period. Bob
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