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5 VDC power supply on a Board of Education Rev. B — Parallax Forums

5 VDC power supply on a Board of Education Rev. B

nboucqueynboucquey Posts: 3
edited 2006-03-05 00:04 in Learn with BlocklyProp
Hello,

I am using a Board of Eductaion Rev.B for a new project.
For this project, I have only a 5VDC power supply available.
Can I connect the +5V directly to the Vdd pin without to connect the 6-9VDC power input?

Many thnaks in advance,

Nicolas

Comments

  • Andy Lindsay (Parallax)Andy Lindsay (Parallax) Posts: 1,919
    edited 2006-03-04 17:30
    Nicolas,

    It really depends on the supply, and some voltmeter testing may be in order.

    If it's a good 5 V supply that actually stays at 5 V, then yes.

    If it's the kind of 5 V supply that starts out at maybe 8 V, and drops down to around 5 V at maximum current draw, then no. However, for this kind of supply, you may actually be able to connected to the Vin input. So long as its output voltage does not drop below around 5.5 V, the system will keep running.

    Andy
  • nboucqueynboucquey Posts: 3
    edited 2006-03-04 17:57
    Andy,

    No, the supply is very accurate and delivers 5 V.
    My concern is about the way to connect the 5 VDC to the Board of Education.
    Are you sure it is not bad to connect 5V to the Vout pin of the LM2940?

    Another solution is to use the normal power input with more than 5 Volt and to use the Vdd to drive my relay coil.
    Then I am not sure the current deliver will be sufficient to drive all the relays (7).


    Nicolas
  • Andy Lindsay (Parallax)Andy Lindsay (Parallax) Posts: 1,919
    edited 2006-03-04 22:27
    Actually, it depends on the vintage of your Board of Education. You can supply the BASIC Stamp's Vdd via a socket on the serial Board of Education Rev B and Rev A. It also works with the BASIC Stamp HomeWork Board. It will not work with the serial Board of Education Rev C, or any USB Board of Education.

    Here's a better way. Use a 6 to 9 VDC supply on the Board of Education. Then, use the separate 5 V supply for the relay system. So long as the relay system's ground is tied to the Board of Education's Vss, the transistors that drive the relays will be able to correctly receive the high/low signals sent by the BASIC Stamp's I/O pins.

    Optoisolators would remove the need for even the common ground.

    Also, here are a couple of links to take a look at for equipment that you may find useful for driving multiple relays:

    http://www.parallax.com/html_pages/products/industrial/industrial.asp
    http://www.parallax.com/html_pages/products/boards/efx.asp
  • Andy Lindsay (Parallax)Andy Lindsay (Parallax) Posts: 1,919
    edited 2006-03-05 00:04
    NOTE. Do not tie the positive supplies together, just the grounds (Vss to relay board ground).
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