3 button rf remote

Discussion in 'The Projects Forum' started by seesoe, Apr 27, 2011.

  1. seesoe

    Thread Starter Active Member

    Dec 7, 2008
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    hello, im working on a 3 button rf remote control system, that will control 3 solenoid valves.

    i found this page and i would like to build it, however i need to build 6 of these systems and the project is already getting expensive. i couldn't find a good price for the RLP434A and TLP434A that they use.

    i did find this though, could i just swap them? or would i have to make changes to the schematics? if so what kind? im not sure how to calculate all that kind of stuff:confused:

    also here is the solenoids that the receiver will be switching (im 80% sure i saw they had 6v versions too). the receiver shows that after the led i can connect a 5v relay, but i don't really want to use relays for the whole thing. couldn't i run the 6v solenoids directly instead of the relays? or would i need some sort of transistor setup? if so how?

    thank you for any feedback!
    seesoe
     
  2. russpatterson

    Member

    Feb 1, 2010
    351
    16
    Have you seen this product? http://www.sparkfun.com/products/8602

    You have to source 400mA to turn on those solenoids. The output pins on your pic will only source 20mA. So you could use transistors to switch the solenoids. Read up on transistors in the e-books section on this site. I think they call it a common emitter setup. Make sure your transistors will handle more than 400mA. Quick overview: connect the ground of your solenoid to the NPN, BJT transistor (like a 2n2222) collector and then the emitter to ground of your circuit. Put a series resistor between the pic pin and the base (like 10k).
     
    Last edited: Apr 27, 2011
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Ahhh, you'll need more base current to saturate the 2n2222 than the uC can provide.
    Ib=Ic/10, and since the desired Ic=400mA, Ib needs to be 40mA, or twice what the PIC can source.

    You'll probably be better off using a logic level MOSFET to sink current from the solenoid.
    An IRLD014 or IRLD024 will easily handle that much current. Digikey.com carries them.
     
  4. seesoe

    Thread Starter Active Member

    Dec 7, 2008
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    @russpatterson i saw the main site that had those before, but 24 bucks is way to expensive, i need to build 6 pairs of these, and the transmitter isn't going to be used as a fob, and i need it as small as possible

    im buying from allied, the only mosfet they have is the irld024, and the cheapest:p

    i attached the mosfet version of the schematics, how did i do? would i still need the 10k resistors with the mosfets?

    the mosfets could handle 60v at 2.4a max correct? so if i were to use the 12v valves, could i just supply the mosfet's S with 12v like i did in the second schematic?

    thanks
    seesoe
     
  5. Pencil

    Active Member

    Dec 8, 2009
    271
    38
    Your MOSFETS are upside down.

    You will need "protection diodes" on the relays.

    Try this.
     
    Last edited: Apr 28, 2011
  6. seesoe

    Thread Starter Active Member

    Dec 7, 2008
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    yeah, but im not going to use any relays.

    so like this?
     
  7. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    You need reverse EMF diodes across plain solenoids too.

    Switching any type of inductive load will create reverse EMF.
     
  8. seesoe

    Thread Starter Active Member

    Dec 7, 2008
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    im not sure i fully understand where to put the diodes, would it be like this?
     
  9. russpatterson

    Member

    Feb 1, 2010
    351
    16
    You're pic can only source 20mA so I think your resistor between your i/o pin and gate needs to be about 150 Ohm. Assuming I've got the diodes in right, you can take a look at this schematic, the MOSFET for the motor control is in the upper right. http://2.bp.blogspot.com/-fcShHZt2i...TRF5g/s1600/2-12-11+Solar+Board+Schematic.png

    Doesn't Allied have a $50 minimum or something or you pay huge for shipping? If you're not worried about performance you can get outdated stuff for really cheap through electronics goldmine and all electronics.
     
  10. russpatterson

    Member

    Feb 1, 2010
    351
    16
    It could be that I'm not understanding something but the solenoids you posted were 12V. Is the curly inductor looking thing in your schematic the solenoid(s)? I think Pencil's schematic looked closer. Imagine your MOSFET as a switch that's going to interrupt the ground connection of your solenoid. So 12V goes to the positive lead of the solenoid valve; and your circuit's ground to the negative lead (only you put the MOSFET between ground and the negative lead so you can control when current flows through the solenoid and opens it up).
     
  11. Pencil

    Active Member

    Dec 8, 2009
    271
    38
    Part of this whole confusion is due to the fact that in the original design
    (the one being copied), the relay was being triggered by the output
    of the uC (microcontroller) going low (sinking, being grounded).
    The OP has chosen N-Channel MOSFETS which will require
    that the output of the uC to go high (sourcing) to trigger the relay.

    It also appears to me (sorry if I am mistaken) that the
    OP does not quite understand the operational differences between
    the "switching" of a MOSFET as compared to the "switching" of a relay.
    If this is the case, keep posting you'll get the help you need.
    If this is not the case I hope I did not offend.
     
    Last edited: Apr 28, 2011
  12. Pencil

    Active Member

    Dec 8, 2009
    271
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    Does this help?
     
  13. seesoe

    Thread Starter Active Member

    Dec 7, 2008
    99
    0
    @russpatterson, at first i thought i could get my hands on 6v valves, however i talked to the supplier and he confirmed i wouldn't be able to, in this case i will for sure be using the following valves 12vdc at 450ma.

    yes the curly inductors are the solenoid valves. haha yes you are correct, allied requires $50 min, im now ordering everything from digikey.


    @Pencil, my knowledge with this is very limited, i do understand the relays, but i dont understand MOSFET types.

    so your saying the MOSFET selected aren't correct? what would i use then?

    im trying to control this solenoid


    on a side note, the original circuit being copied; if the pic only supplies 20ma, then they are missing resistor transistor and diode between the uC pin and relay right?


    i posted the 12v version of what im working on, what needs to be done from there.
    - the 10 resistor before the MOSFET needs to be changed to 150 ohms
    - check that the diodes are correctly placed
    - figure out the correct MOSFET and setup

    thank you for all the help thus far!
    seesoe
     
  14. seesoe

    Thread Starter Active Member

    Dec 7, 2008
    99
    0
    sorry i just saw your post before i posted mine, let me update it and see if i understand.

    thanks
     
  15. seesoe

    Thread Starter Active Member

    Dec 7, 2008
    99
    0
    yes that was very helpful, thank!

    i made 2 versions, i feel like something is wrong with the diode setup in the first version, and i believe i corrected it in the second?
     
  16. Pencil

    Active Member

    Dec 8, 2009
    271
    38
    The MOSFETS are O.K.
    Operation of uC needs to be altered from original (easy change in program).

    Maybe their relay drew less than 20mA. The PIC 12f509 can only sink 25mA per I/O pin.
    Another theory is that they are driving that poor uC to an early grave
    by pushing the outputs beyond recommended limits.
     
  17. Pencil

    Active Member

    Dec 8, 2009
    271
    38
    Look below.
     
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  18. seesoe

    Thread Starter Active Member

    Dec 7, 2008
    99
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    resistor value?
     
  19. Pencil

    Active Member

    Dec 8, 2009
    271
    38
    No.

    Look how {output>>>>resistor>>>LED>>>>ground} is configured.
     
  20. seesoe

    Thread Starter Active Member

    Dec 7, 2008
    99
    0
    oh ok lol, sorry i didn't see that, i thought it was the same as the original, its flipped because the way we are using the mosfet's?

    what do you mean by (operations need to be altered from the program)?
    do you mean flip the pin's low/high?
     
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