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Using Relays with the propeller — Parallax Forums

Using Relays with the propeller

Greg LaPollaGreg LaPolla Posts: 323
edited 2009-02-06 00:30 in Propeller 1
I am in the initial stages of the design to use a propeller to control a gas valve and a pump. I have sourced the following:

Still deciding on which one also open for a better solution if someone has one

www.crouzet-usa.com/catalog/_caso.shtml
www.crouzet-usa.com/catalog/_ga8.shtml

both of these relays will work on 3 volts so I should be good there. Here is where I get lost. I am still learning in this area. Do I need a resistor or something here to protect the propeller? should I put a resistor between the input pins?

I also noticed that the controller board that parallax sells uses mosfet on the high voltage lines, does that accomplish the same thing ?

I will also be using the thermocouple interfaces available from the store.

I am currently using 2 of these to get the job done, however they are limited in scope to 1 step. I would like to start by simply replacing them with my propeller project, then enhance it after the basics are complete.

Does anyone have any input on whether I should go for a prototype board or a PE Kit to start with?

Thanks in advance

Greg

Comments

  • mctriviamctrivia Posts: 3,772
    edited 2009-02-05 06:05
    i would use spin studio to start with most versitile.

    As for relays you should always put a diode in reverse across the coil terminals to protect circuitry attached to the relay. Most likely the propeller can not provide enough current to directly activate the relays so you should use a transistor or mosfet to act as a switch providing direct current from the power rail but you can check the specs of the relay to see.
  • Mike GreenMike Green Posts: 23,101
    edited 2009-02-05 06:38
    Your links are to solid-state relays. These are not true relays and have no coil so they don't need a protective diode. Their input circuit, if you look at the datasheet, is an LED with a built-in resistor. You can connect the input directly to a Propeller output. They draw a maximum of 16mA according to the datasheet. The total Propeller current is up to 300mA, so you can drive several of these without exceeding the total current limit.
  • mctriviamctrivia Posts: 3,772
    edited 2009-02-05 06:39
    guess i should have looked at the links. solid state relays are a lot easier.
  • hinvhinv Posts: 1,255
    edited 2009-02-05 15:42
    Hi Mike,

    Thanks for pointing out the current maximums, but I believe the manual says not over 100mA for a group of pins. The obvious question then, which I have not seen answered in the book, is what are the groupings of the pins.
    Thanks so much for your help. They should give you a propeller avatar.

    Doug
  • Bobb FwedBobb Fwed Posts: 1,119
    edited 2009-02-06 00:20
    Actually, from the v1.1 datasheet: "General purpose I/O Port A. Can source/sink 40 mA each at 3.3 VDC."
    With a max across all pins not exceeding 300mA.
    Didn't see anything about groups of pins.
  • Mike GreenMike Green Posts: 23,101
    edited 2009-02-06 00:30
    The groups of pins limit applies to the SX and PIC processors used in the Stamps, not the Propeller.
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