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RF controller relay help

Discussion in 'Radio and Wireless' started by Henry Glen, Aug 30, 2015.

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  1. Henry Glen

    Henry Glen

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    Aug 30, 2015
    Hi;

    I'm not very tech savvy but I have been doing my research and reading about general electronics so that I can build a simple, RF controlled, valve-type device. Essentially, the issue that i have is that I have an RF transmitter and receiver. I am looking for some sort of a device (as small as possible) that will function like a switch once it receives the signal from the RF receiver (sent originally from the RF transmitter) to activate a very small motor which will turn a valve. The RF transmitter will be about a foot or two away. I was reading that an RF controller relay may be the answer but, if it is, I have some questions. Thanks for any help that you may provide. Sorry if my description is insufficient.
     
  2. AnalogKid

    AnalogKid

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    Jun 10, 2015
    There are many small remote control modules on ebay, some with 1 to 4 buttons and 1 to 4 relays. You don't give any details about voltages, currents, etc. But you can check them against the relay specs. If the relay can't handle it, use the remote control module relay to control a larger relay, and let that one control the motor.

    ak
     
  3. Old Steve

    Old Steve

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    Jul 23, 2015
    What sort of RF transmitter and receiver do you have? Pics maybe?
    RF noise and false triggering are likely to be a problem.

    You could use a PT2262 remote control encoder IC connected to the transmitter, which allows you to set an address code to avoid false triggering, then a PT2272 remote control decoder IC connected to the receiver, with it's code set to that of the transmitter. The PT2272 comes in several versions, both momentary or latching, with different numbers of data outputs - 0 data, 2 data, 3 data - - - - 6 data.
    There are 12 tri-state IO pins and those not used for data set the address. ie With no data, there are 12 address pins, with 2 data there are 10 address pins, etc.
    The latching version is probably best for your application. I've only ever used the momentary type, but I would assume that the latching version latches 'on' (high) when the code is received the first time, then 'off' (low) when it is received the second time, and so on.

    I have nothing else to do right now, so to show how this could be done, I'll scribble up a couple of quick schematics using the 2 data version and post them shortly. (You only need to use one of the 2 data pins for your purpose.)

    Meantime, I've uploaded the PT2262 and PT2272 datasheets for you to check out.

    Edit: Sorry AnalogKid, We were typing at the same time. Essentially, those modules use the same PT series chips and may be the way to go.
     

    Attached Files:

  4. Henry Glen

    Henry Glen

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    Aug 30, 2015
    Holy crap! You guys are great! I've put up two pics of the Geetech 433 Mhz Tx Rx pair, and the servo motor I am using. Now I am using a breadboard and I plan to keep Tx at 3V so as to not send a signal around the block. I was considering Arduino but in the end, I'm not sure Arduino is what I need...not to mention that I dont believe I can figure out how to apply it. This device will be a simple miniature "water damming" device that stops the flow of a small current of water when the TX sends a signal to the RX, and the RX activates the servo motor attached to a mechanical valve. The dam would be manually reset afterwards. The servo is 4.5V-6V.

    Old Steve: thank you very much for the schematics. I'll be applying these as best as I can. I'm certain I'll have questions! Thanks.
     

    Attached Files:

  5. Old Steve

    Old Steve

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    Jul 23, 2015
    Henry, the PT2262 needs a minimum 4V, but the strength of signal is unimportant with a coded 3^10 setup, since nothing else will respond to the signal. My schematic suggests a 12V supply, a small 23A battery, but anything above 4V would do the job.
    Here's the transmitter schematic. (Receiver to follow shortly.)
    Transmitter.JPG
     
  6. Old Steve

    Old Steve

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    Jul 23, 2015
  7. Old Steve

    Old Steve

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    Jul 23, 2015
    Henry, in my haste I forgot to put a protection diode across the relay, to protect the transistor when the relay turns off. I suggested a 1N4002, but any 1N400x diode would do, or even a 1N4148.
    Here it is:-
    Protection Diode.JPG

    I just looked more closely at your motor. It complicates things, being an RC servo. A servo needs a pulse stream to operate, so none of what I've done will do you much good. You will need to go to a much more complicated system if you stick with that servo. It may not have enough torque for the application, either.
    You could use a small, geared DC motor to turn off the valve, possibly. Then the above diagrams would work.
    Otherwise, you may need that Arduino or another microcontroller to run the show and some study of programming.
    (In my defense, your initial post said it was a small motor.)

    Edit: Just thinking about it, instead of the relay, the PT2272 could enable a pair of NE555 or similar timer chips to produce the required pulse stream. The first could produce the 50Hz time base, with the second triggered by the first, generating the pulses to move the servo in the required direction.
     
    Last edited: Aug 31, 2015
    Arouse1973 likes this.
  8. Henry Glen

    Henry Glen

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    Aug 30, 2015
    Wow! Thanks a lot Steve. I have to admit that this is above my understanding but I have a friend that can help understand all of this. As we put it together, I will definitely be soliciting your advice and knowledge. Thanks a lot. Apologies for saying that it was a small motor. In my defense, I am new to all of this and am trying to learn. So you think that to move the damming valve, we would need a DC motor? I looked at a small 3V DC motor today as an alternative but the folks at Frys said the Servo motor in the pictures was what I needed. According to the specks on the back of the package, it says that it could pull up to 1.5 Kg.cm. By the way, do you know of a site that I can purchase gears that I can mount on the servo or DC motor (since I may have to go that route)? also, what is pulse streaming and why would that complicate things?

    No programming for me. I am trying to keep this as simple as possible. I think programming is beyond me.
     
    Last edited: Aug 31, 2015
  9. Old Steve

    Old Steve

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    Jul 23, 2015
    No problem. Glad to help in any way I can. I just got back into electronics after some years off, so it's all good practice. Luckily for you, one of my first projects involved RF remote control using the PT2262 and PT2272 chips.
     
    Arouse1973 likes this.
  10. Henry Glen

    Henry Glen

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    Aug 30, 2015
    Thanks. I added a little more to my prior post regarding pulse stream, and the amount of torque for the servo motor. The servo motor will drop a hatch (from top to bottom, of sorts), to stop the water flow with a current strength of what comes out of a kitchen sink. Is the servo still not enough?
     
  11. Old Steve

    Old Steve

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    Jul 23, 2015
    Sorry, I can't definitively answer that, although it will probably have enough torque. It's really a matter of trying it, then going to a larger servo if it doesn't, I guess.

    Regarding the pulse stream question, a servo is driven by a stream of pulses at 50Hz, with 1.5mS pulses centring the servo, longer pulses moving it in one direction and shorter pulses moving it in the other direction. It's not just a matter of connecting a voltage to make it move like with a DC motor.
    Another point is that a 360 degree servo can only turn 360 degrees and no further. That's why I originally suggested a geared DC motor. I assumed that the valve would require more than one turn.

    I think I can picture your 'damming' valve, but a drawing would help.
     
    Last edited: Aug 31, 2015
  12. Henry Glen

    Henry Glen

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    Aug 30, 2015
    I think that the switch to a DC motor will probably be needed. After reading more about servos and microcontrollers, it appears that programming is a main aspect to get the device to function despite it being, in theory, a simply little toy.
     
  13. Old Steve

    Old Steve

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    Jul 23, 2015
    As mentioned in the edit of my last post, if you do a quick sketch of your valve setup, I'll think about it tonight and see what I can come up with. I don't think that you necessarily need to go as far as a micro and programming, but we'll see.
     
  14. Henry Glen

    Henry Glen

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    Aug 30, 2015
    The valve assembly is not unlike that of a transmission system of a pickup truck. Transmission connects and rotates a drive shaft which connects to a rear differential. Only, in this case, there is no rear differential, but a valve. The motor will function like a transmission, either directly connected to the valve, or connected to a type of "shaft" that connects to the valve, as a drive shaft connects to the rear differential - and naturally rotate. I will draw a picture and scan it soon to help clarify. Thanks Steve.
     
  15. Old Steve

    Old Steve

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    Jul 23, 2015
    That sounds much better. I was picturing something like this:-
    Damming gate controller.JPG

    And if more than one turn of the shaft is needed, a servo is definitely out.
     
  16. Old Steve

    Old Steve

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    Jul 23, 2015
    Here's one possible solution using a geared DC motor , only a crude first draft so far:-
    (This uses a 'no data' version of the PT2272, with the Vt (valid transmission) pin operating the motor to close the valve.)

    Geared Motor Controller.JPG
     
  17. Henry Glen

    Henry Glen

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    Aug 30, 2015
    Wow. Thanks Steve for the great diagrams. I don't need to send a pic now. haha. Question: Q2 and Q3 are forward and reverses switches or buttons? Also, how small can we get these components to be? We have a small space to put this together within, and then hide it with some sort of housing unit. Also, how do we program the relays to provide enough energy to rotate the valve, say 90 degrees, or 180 degrees, or full 360? I ask because we want to measure current flows when the gate is open at certain heights
     
  18. Henry Glen

    Henry Glen

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    Aug 30, 2015
    Also, I have a question: the Rx and Tx pair I am getting are 433 mhz. Will there be any issues for the IC 2272 and IC 2262 respectively?
     
  19. Old Steve

    Old Steve

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    Jul 23, 2015
    Ready for a long reply? :-

    Q1 turns on the relay that operates the motor in the forward direction, (closing the valve), and Q3 turns on the relay that operates the motor in the other direction. Q2 senses the current flowing through the motor via R7, so that when the valve reaches the end of it's travel in each direction, stalling the motor and therefore increasing the current through the motor, it will be switched off.
    (Relays aren't 'programmable' as such, they're just voltage-controlled switches that are operated by a lower current/voltage than that being switched.)
    The only button in my circuit, apart from the one on the transmitter, is the one labelled "Re-open Valve".

    Regarding size, that would depend on whether it was made with surface-mount or through-hole components. Some parts are not shown in that schematic. ie A 5V regulator, bypass capacitors, terminals for off-board connections.

    All up, using through-hole components, the receiver would need a circuit board about 50mm square, with the tallest components about 20mm tall. The (1-button) transmitter board as shown in my earlier drawing could be tiny, about 40mm x 25mm, even using through-hole components.
    Also, for the receiver some sort of power-supply would be needed, capable of supplying enough current for the motor and voltage(s) for the motor and relays, (and logic via a 5V regulator).

    Having said all that, until now you haven't mentioned the need to stop it at various points to measure the (water) current, you only mentioned closing the valve by RF control and re-opening it manually.
    The circuit I drew up cannot do what you want, because it is intended to only fully open or fully close the valve.

    So, you're right back where you started, I'm afraid. You'll need a much more complicated setup to do what you want. Most likely, a fair-sized stepper motor would be needed to get enough torque and have the sort of control that you require, with a micro-controller running things, and a minimum 2 data bits PT2272, maybe the 3 or 4 data bit version, to allow the transmitter to 'tell' the receiver where the operation must stop. ie 1/4 open, 1/2 open or fully open.

    The 433MHz question isn't an issue. The PT2262 and PT2272 don't actually 'see' the transmitter frequency, only the internal oscillator frequencies as set by the resistors connected across their 'OSC1' and 'OSC2' pins - 3.3MΩ for the PT2262 and 680KΩ for the PT2272.
    (The 2 systems that I've already designed and built using PT series chips both operate using 433MHz TX/RX pairs.)

    This gets more and more complicated by the minute, and while it could be done, it requires a great deal more design and development (and programming) time than you might think, along with the associated mechanical aspects.
    You'll need to get yourself a microcontroller, a programmer and associated compiler and study up on micro programming. A stepper motor is even harder than a servo to run.

    Another point I noticed is that you say "90 degrees, or 180 degrees, or full 360". So your valve only needs to be turned 360 degrees to go from fully open to fully closed, or does it need more than one turn to achieve this? Describing an auto drive-train gave me the impression that it would be a fairly typical 'gate' valve, requiring several turns of the shaft.

    Edit: Out of interest, too, how are you planning to measure the water current flow?
     
    Last edited: Sep 1, 2015
  20. Henry Glen

    Henry Glen

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    Aug 30, 2015
    Thanks again for the info, Steve. Believe it or not, we're just attaching a hose to the assembly and we will use a speedometer type device with a little milling wheel on the end to see how fast it flows. This isn't anything spectacular. :D NEvertheless, it's a fun little project.
     
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