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Clever Way To Interface Basic Stamp with 3.3v Device — Parallax Forums

Clever Way To Interface Basic Stamp with 3.3v Device

G McMurryG McMurry Posts: 134
edited 2011-03-06 23:29 in BASIC Stamp
Sorry, I don't have the answer, but I am asking the question. I have exactly 1 device that I would like to interface with my BS2 that is 3.3v. It is the XPort Pro Ethernet Adapter. It needs 3.3v supply at 220ma and then is serial in and out at the same level.

I would assume I can use a to-92 package regulator for the power supply. I would like to NOT use a giant IC for the other levels.

First, will the BS2 see 3.3v data? If so, I can then just use a couple of resistors to create the 3.3v to send to the device from the BS2

THANKS --

Greg

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2011-03-04 21:25
    Yes, the BS2 will work with data from a 3.3V device. Usually you look in the datasheet for the device and find the value of Voh (voltage output high). For a 3.3V device, this is commonly 0.3V below the supply voltage (Vdd-0.3V). The BS2 uses a PIC16F57 microprocessor whose datasheet shows a minimum Vih (voltage input high) of 2V.

    Going the other way, the BS2 will produce a high voltage of about 4.3V. You could put two silicon diodes in series with this to drop the voltage by 2 x 0.7V = 1.4V which would bring it into the range of acceptable voltage for a 3.3V device or you could use a voltage divider like 1K Ohms : 3.3K Ohms to provide about a 1.2mA load and 3.3V or less out.
  • G McMurryG McMurry Posts: 134
    edited 2011-03-04 21:33
    Thanks Mike -- You always have great ideas....

    Greg
  • Mike GreenMike Green Posts: 23,101
    edited 2011-03-04 22:00
    Be careful about the regulator. Your Ethernet Adapter needs 220mA and I don't think you'll find any TO-92 regulators with that kind of current output.
  • G McMurryG McMurry Posts: 134
    edited 2011-03-05 08:28
    You're right about the regulator, I already thought about that.

    If I use a couple of 1n4148 diodes would I also use a pull down resistor?

    voltage%20converter.jpg
  • Mike GreenMike Green Posts: 23,101
    edited 2011-03-05 08:41
    Good idea!
  • MoskogMoskog Posts: 554
    edited 2011-03-06 23:29
    You can also take a look at this long lasting thread from a few years ago discussing interfacing 5V to the Propeller:

    http://forums.parallax.com/showthread.php?85474-How-to-safely-interface-a-5v-signal-to-the-propeller
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