Search results

Search Forums New Posts
  1. (*steve*)

    Digital Potentiometer and Power Supply

    Since you have an even number of these, I'd run pairs in series. Do you have a link to the datasheet for the digital pot? A simpler approach may be to set the voltage to the max for the elements and use a microcontroller and a mosfet to vary the power using pwm. An advantage of this is that...
  2. (*steve*)

    Voltage Divider to control Current in a Circuit

    Cells in series have different but equally serious problems. if the cells differ in capacity, one will (if you only look at the pack voltage) get damaged by virtue of being over charged and over discharged. This will lead to the failure of the pack, possibly in a pyrotechnic fashion.
  3. (*steve*)

    LED's and constant current

    Go ask the wizard for the resistor value for 5 LEDs in series. The 6.8 ohm resistor is too small to be effective in limiting the current. This is covered in the resource on driving LEDs.
  4. (*steve*)

    Low voltage cutout help

    Yeah, adding a transistor would probably help, especially if you modify the relay. Also your schematic does not show a diode connected across the relay (which is required to protect the transistor (or op-amp) that is switching the relay. edit: a 9V to 12V relay would probably be what you're...
  5. (*steve*)

    Low voltage cutout help

    The problem (or at least one problem) is that the relay is being driven directly by the output of an op-amp which may not be able to provide the extra current.
  6. (*steve*)

    Voltage Divider to control Current in a Circuit

    I guess the question is whether 2.8V (or whatever you decide is the discharge limit) is sufficient to operate the device.
  7. (*steve*)

    Auto Channel Search With Antenna TV

    antenna tv? Do you mean broadcast free to air stations? and your tv doesn't have an antenna socket? what inputs does it have?
  8. (*steve*)

    LED's and constant current

    I'm not sure what you mean by #4. can you post the schematic?
  9. (*steve*)

    Voltage Divider to control Current in a Circuit

    a voltage divider won't work. you could use two batteries in series followed by a regulator. for efficiency a switch mode power supply would be best. you could also use a single battery followed by a boost switchmode regulator. whatever way you go, you need to be very careful you don't...
  10. (*steve*)

    Low voltage cutout help

    that circuit should turn on and off at the same voltage. if it requires a substantially higher voltage to turn the relay on, you may need a more sensitive relay.
  11. (*steve*)

    Today's Salvage Haul

    Even if you never use the parts, it's great practice for when you need to desolder something.
  12. (*steve*)

    Digital Potentiometer and Power Supply

    the digital pot will probably not work correctly if any of the voltages on the digital pot terminals are outside the power supply rails for the chip.
  13. (*steve*)

    3 Position switch - how does this work?

    ok, reading your images again, this switch cannot be used since, rather than having a "both off" position it had a "both on" position.
  14. (*steve*)

    Bridge rectifier melted.

    It's hard to tell. Perhaps the original design was for a three phase delta wound generator?
  15. (*steve*)

    Creating a variable wien bridge oscillator

    if you go for a lamp stabilized wien bridge oscillator like the hp200, be sure to use a cheap op-amp, not a really good one. HP have a really good paper describing why distortion is actually required for good stability. the feedback loop if you use a lamp (and possibly a thermistor) is...
  16. (*steve*)

    Generating Multiple Frequencies

    what are inches? So, is your problem locating where the bb gun was pointing, or lighting up a LED behind that point? I'm not sure how the 100 LEDs thing relates to the former, or would be particularly useful for the latter. how big is the target and how accurately do you need to position the...
  17. (*steve*)

    pull down resistor for npn relay driver

    thread nothing special, but I wonder if the base resistor you're using isn't a bit on the high side. it's ok if you're switching a load of about 3 mA. A more typical value might be in the order of 1k or so for a relay drawing 50mA or thereabouts. oh, and do you have a diode across the relay coil?
  18. (*steve*)

    pull down resistor for npn relay driver

    you haven't attached a schematic, but I assume you have a common emitter circuit with a base resistor and no emitter resistor. a resistor from the base to ground that is about 10 times the base resistor will do what you want.
View older results
Top