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Controlling relays with prop — Parallax Forums

Controlling relays with prop

VGVG Posts: 32
edited 2009-05-14 05:12 in Propeller 1
Hi there,
1. How can I turn on a relay (5V coil voltage) with Prop signal (3.3V only)?

2. How many maximum relays I can control individually with one prop (are there any·AMP restrictions from prop)?

Thanks in advance.

Sincerely,
Venkata.

Comments

  • mctriviamctrivia Posts: 3,772
    edited 2009-05-14 04:31
    you can pull in a 5v relay by using a transister see http://www.kpsec.freeuk.com/trancirc.htm for schematics.

    the only limit to the number is the 50mA max load on each pin.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    My new unsecure propmod both 1x1 and full size arriving soon.
  • Mike GreenMike Green Posts: 23,101
    edited 2009-05-14 05:01
    There are some nice reed relays on the market that have a 3V coil voltage and require only 20mA to turn on. They do need a protective diode reverse connected across the coil, something like a 1N914.

    Refer to the Propeller Datasheet, page 25 for the current restrictions for the Propeller. The max. current for each pin is 40mA and the max. total current for the whole Propeller is 300mA.
  • rjo_rjo_ Posts: 1,825
    edited 2009-05-14 05:12
    VG...

    Just because it says 5V on the package doesn't mean that you can't use your prop to drive it directly... it is worth a try.

    My favorite relay is a 5V RadioShack reed relay. At one time, I use them for almost everything. Your prop has enough umph in it so that you can put a diode in and the relay will still work.
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