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  1. pebe1

    the finer points of electronics - I

    If I may add to Kevin's comments: There is a circuit that would not only supply inverse reactive current for use in unilateral phase detractors, but would also be capable of automatically synchronizing cardinal grammeters. Such a circuit is the "turbo-encabulator." Basically, the only new...
  2. pebe1

    the finer points of electronics - I

    As Audioguru has already explained, the 'ground' in a circuit is merely a reference point against which all other voltage nodes in the circuit are measured.  It does not push or pull anything. It may or may not be connected to true ground (earth), or to the earthing point in an electric mains...
  3. pebe1

    Simple voltage regulator

    Kevin, if you are referring to your first circuit in this thread, it cannot work. The Vbe of the Darlington will always be around 1.5V so the voltage across the 20K resistor will be about 135mV. Ignoring the input offset, the two input voltages of the op-amp must be the same, so the output...
  4. pebe1

    advantages/disadvantages of auto-ranging DMMs

    Every time you use an auto-ranging meter it goes through the timewasting procedure of starting at the highest range and then scaling down through the ranges until it finds a range suitable for display, so there is little risk of damaging the meter by over-voltage/current. If you move your probe...
  5. pebe1

    Re: Free Schematics for electronic surveillance

    These are the faults I found: The timer is described in the parts list as ‘a standard NE555 timer chip’. It is powered by 2 x 9V batteries. But that is the absolute maximum voltage rating for many of these chips, and exceeds the 16V absolute maximum of a Fairchild or Contek NE555. R4 is shown...
  6. pebe1

    Re: Free Schematics for electronic surveillance

    Just checked the site out of curiosity and looked at the Tracker, TT5. It has faults on it - I wonder if this is typical of the other circuits?
  7. pebe1

    My first project - A simple regulated power supply 30V

    If it’s not too late to change direction, have you considered going down the switch-mode route? My ageing 28V 2A power supply (using 2N3055) is now getting past its ‘sell-by’ date, so I intend to make a new one using ready made inexpensive modules from ebay. I already have an HP laptop power...
  8. pebe1

    turning my old arc welder into a mini spot welder

    It seems logical to eliminate the welder transformer if you can and connect the micro tranny straight to the mains. There are plenty of ways of making a spot welder from one. Go to Youtube and look for 'Spot welders'
  9. pebe1

    microcontrol/ electronics related project Needed.

    How about a robotic lawn mower?
  10. pebe1

    Need ideas for a secure short range (3m) wireless system.

    You could use a micro to send 3 bytes of data every 5 seconds via a small Tx like those from RF Solutions. That would give you almost 17million combinations of code. By the time you got on to your bike the Rx would have received the code and disarmed the bike. If it received no further codes in...
  11. pebe1

    help for rpm measurement

  12. pebe1

    pnp vs npn?

    You are splitting hairs. Audioguru is right. Base current is controlled by the value of the base bias resistor. Current through the base emitter junction will cause a collector current equal to base current times beta. Both of those currents will flow through the emitter. It makes no...
  13. pebe1

    Need information on mouse eltronics

    Try this link. The info you need is towards the bottom of the page. http://pinouts.ru/data/Serial9_pinout.shtml
  14. pebe1

    Voltage level shifting

    Hi Windoze, Here's an op-amp which may do you. It goes rail-to-rail on its input and output. http://www.datasheetarchive.com/search.php?search=lt1782&sType=part I'd like be interested in your final solution when you get it all going. Best of luck.
  15. pebe1

    Voltage level shifting

    I have read them, so what have I missed? Please read my PM.
  16. pebe1

    Voltage level shifting

    I cannot see how this more complex arrangement is better than Staigen's proposal in his post #6. Or have I missed something?
  17. pebe1

    NiMH Battery Pack Charger

    This is a very good link to batteries. http://www.batteryuniversity.com/parttwo-33.htm
  18. pebe1

    Voltage level shifting

    Now you have said what the purpose of the project is, could I suggest an alternative? How about a dedicated micro just for this data input. Input would be to the A/D convertor section of this micro reading the 2.5v to 5v. Compare the digital readings obtained with a lookup table that will give...
  19. pebe1

    Voltage level shifting

    Hi Staigen and Enac, You are both right. With input=5v, inv input=5v, output =5v and no current flows through the resistors. With input = 2.5v, inv input=2.5v, output=0v because current flows through both resistors and giving equal voltage drop across each. So inv input is 2.5v below +rail...
  20. pebe1

    How to make RPM counters

    They use their timer to measure the time between two interrupts, then calculate the RMP from that.
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