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Looking for a comparable RELAY — Parallax Forums

Looking for a comparable RELAY

Brian CarpenterBrian Carpenter Posts: 728
edited 2009-07-27 02:43 in Propeller 1
i have a PIC circuit that we are currently using that all runs at 5v. i want to convert the project to the Propeller. We are using a Clare optomos relay http://www.clare.com/home/pdfs.nsf/www/CPC1218_R04.pdf/$file/CPC1218_R04.pdf . Its control voltage is 5-12 v any suggestions on replacements for 3.3volts??

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Comments

  • mctriviamctrivia Posts: 3,772
    edited 2009-07-27 01:25
    a transister to run higher voltage rail.

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  • Mike GreenMike Green Posts: 23,101
    edited 2009-07-27 01:33
    There are reed relays and solid state relays that operate at 3.3V and will run directly off a Propeller I/O pin. Look at DigiKey's website for models. I don't have the model # handy, but there's one SPST reed relay I used with a 3V coil voltage and about 12-15mA coil current.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-07-27 02:20
    Brian,

    Are you using it to switch AC or DC?

    -Phil
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-07-27 02:43
    Brian,

    If you're driving the relay coil in a pull-down configuration, you might well be able to drive it directly from the Prop with 5V on the anode end. The reason is that most IREDs have at least a 1.2V voltage drop. That leaves 3.8V. The body diodes in the Prop won't begin to conduct until the input voltage is above 3.9V. So with the Propeller pin floating, there should be little more than leakage current going through the IRED. When the Propeller pin is set as an output and pulled "low", the IRED/resistor combo will see at least the 3.75 volts it needs to turn the relay "on".

    Now, there's the little issue of the relay's spec'd minimum turnoff voltage, which is 1.0V. 5V - 3.9V is 1.1V, which is above that. To keep everything within range, you could add another diode in series with the Propeller pin, which drops the "off" voltage to 0.5V and the "on" voltage to 4.4V. Both are well within the relay's specs.

    -Phil
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