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  1. Hero999

    Semi-high resolution thermometer/data logger

    Don't confuse resolution with accuracy. They are different things. Of course it's possible to make a thermometer with a resolution of 0.001oC but it won't be necessarily be any more accurate than a cheap one with a resolution of 1oC Over what temperature range? Getting a high accuracy over a...
  2. Hero999

    Phase shift detection circuit

    It's made by lots of other manufacturers. Mouser has a lot in stock. http://www2.mouser.com/Search/Refine.aspx?Keyword=6N138&FS=True
  3. Hero999

    Current monitor/sensor

    http://www.allegromicro.com/en/Design-Center/Technical-Documents/Hall-Effect-Sensor-IC-Publications/Method-for-Converting-a-PWM-Output-to-an-Analog-Output-When-Using-Hall-Effect-Sensor-ICs.aspx http://www.cnblogs.com/shangdawei/p/3312084.html http://www.avr-asm-tutorial.net/avr_en/AVR_ADC500.html
  4. Hero999

    Capacitor charging using low voltage supply

    How is the circuit physically constructed? Is it small and compact or are there lots of long leads and wires? Did you read pages 10 & 11 on the data sheet on inductor selection? http://cds.linear.com/docs/en/datasheet/3639fd.pdf
  5. Hero999

    Use 2v Signal to Control 12v LED strip

    I doubt the circuit is capable of driving a relay. You can probably connect the base to the output of the circuit which drives the LED. It will already have a current limiting resistor for the LED which should also be fine for a transistor. The ZTX690 is widely available. Digikey and Rapid...
  6. Hero999

    Use 2v Signal to Control 12v LED strip

    That's odd. The ON semiconductor datasheet lists a maximum IC of 800mA but Hfe is only specified at 300mA, Hfe > 60 VCE = 1V. http://www.onsemi.com/pub_link/Collateral/BC337-D.PDF 600mA with a forced beta of 30 doesn't seem unreasonable but a heatsink would be a good idea. Don't forget the...
  7. Hero999

    Current monitor/sensor

    The easiest way to do that is to have two circuits: one to charge the battery and another to discharge it. A single pole RC filter is not enough to convert PWM to a steady DC voltage. You need to use two poles or more to get the voltage anywhere near smooth.
  8. Hero999

    Capacitor charging using low voltage supply

    That inductor doesn't seem to be what you want. Can you post a schematic of the whole circuit.
  9. Hero999

    Use 2v Signal to Control 12v LED strip

    It's more likely that each LED has a series resistor to limit the current and the LED foward voltage is 2V. If you remove an LED, you'll probably find the voltage increases to 3V. The BC337 might do. It's specified with a minimum Hfe of 40 when IC = 500mA and VCE = 1V...
  10. Hero999

    Use 2v Signal to Control 12v LED strip

    The 2V signal is probably only 2V because it has an LED across it which is driven off 3V with an appropriate series resistor. You need find out how the LEDs are wired before you can interface with the board.
  11. Hero999

    minimum reliable low currents

    The question doesn't make any sense. a) What's the leakage current of the capacitor? b) How good is the ammeter? c) What's the speed? Logic family?
  12. Hero999

    Dry Box Battery Charger

    Draw what you mean. The most important thing is the wire is rated to carry the current.
  13. Hero999

    Capacitor charging using low voltage supply

    It's the energy stored, rather than the capacitance which is important. E = 0.5CV2 Doubling the voltage quadruples the energy storage, given the same capacitance. A 5mF capacitor charged to 100V will be storing twice the energy as a 10mF capacitor charged to 50V and it's likely it will be...
  14. Hero999

    Dry Box Battery Charger

    A fuse is mandatory and the cable must be rated to carry the current rating of the fuse. The box must be vented when the battery is charged, to avoid the build up of hydrogen gas which is explosive.
  15. Hero999

    Capacitor charging using low voltage supply

    Why not use a 100V capacitor, then you can utilise the power more efficiently and don't need any over-voltage protection?
  16. Hero999

    Old led 7 seg pinout

    It's not an LED display. It's a vacuum fluorescent display. The chance are you won't be able to find the data sheet.  You'll need to experiment to find the pin out. http://rctractor.proboards.com/thread/60
  17. Hero999

    Capacitor charging using low voltage supply

    How long does it need to last for? I hope you're aware that you will not be able to charge the capacitor and draw 5V at 20mA at the same time. Before you said the transformer charges the capacitor to 90V when nothing is connected to it, then it drops to around 50V when a 22k resistor is...
  18. Hero999

    Capacitor charging using low voltage supply

    You didn't say anything about a buck converter before. How much current do you need to draw? What's the point of increasing the voltage to 50V then reducing it to 5V? According to the datasheet, the LTC3639 can work up to 150V so as long as the capacitor is suitably rating you don't need to...
  19. Hero999

    Capacitor charging using low voltage supply

    The TL431 is not an ordinary zener diode. It's an op-amp with a buit-in voltage reference. Unfortunatly its maximum voltage rating is 0nly 36V so a transistor is used to buffer it. http://www.ti.com/lit/ds/symlink/tl431.pdf
  20. Hero999

    PCB Etching Problems

    Not all UV lamps are equal. Ideally you need a black light, like the type used in insect killers but the short used in discos will do. Ambient light, including the shorter visible wavelengths (blue and violet) can expose the board. Once exposed, the PCB shouldn't be exposed to any light at all...
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