Is it possible to create an Add a switch for R.C

Discussion in 'The Projects Forum' started by Jure George, May 20, 2010.

  1. Jure George

    Thread Starter Active Member

    Dec 28, 2008

    I am involved with Surface and submarine remote control, 75 mHz, FM only. What I have been thinking about making is a set of external switches to physically add to one channel of my transmitter. I would disconnect that control pot inside the transmitter and add the wires from the keypad. Say from a transmitter stick, up is a signal wire, down is a signal wire and black is ground.

    I would be interested in either 8 or 16 functions from the keypad to the matching receiver that would be connected to the transmitter`s receiver on that channel now dedicated for this use. The individual either 8 or 16 functions could be set to momentary, as long as that keypad button is pressed or latched, you press the keypad number once to start the function then again to stop it.

    The unit would be powered from the main battery, 6v to 12v. and there needs to be a power on LED indicator as well. Each channel should be able to run a max. of 1 A, small d.c motor, radar, turn on LED`s or a sound system or smoke system or motor for the anchor etc. Also there should be No effects on the receiver circuit if the main battery is disconnected, once setup is done to the user likes, it should stay in the receiver until the user changes the settings through dip switches for each channel.

    Can anyone help me with a working circuit and a source for the needed keypads, either 8 button or 16 ? I have checked into the Hobby suppliers and one has the unit I am interested in BUT that person`s product has a high failure rate with POOR customer service etc. and the other supplier is VERY expensive.

    Can this be done without PIC technology, as I have NO knowledge of PIC`s and the programing needed to make them run. Regual I.S, Tansistors and Programmed EEPROMS, I could pay for.

    Please let me know if anyone knows of a working curcuit and sources of special parts.

    Thanks Again for Your Help.

  2. jpanhalt


    Jan 18, 2008
    I think what you are proposing is possible, if I understand what you mean. Let me describe how it might work and see if that is what you mean.

    The stick you your transmitter controls the pulse width for a particular channel. You want to create digitally the equivalent pulse width for various positions (up to 16) and each width would correspond to operating a particular switch. A mechanical analog would be if the servo operated a rotary switch, so each predefined position would be a different set of contacts.

    That system would not allow each function to be independent. That is, you could turn on #1 or #3, but not at the same time easily -- a combined function of 1 and 3 "on" could be assigned to another switch.

    Does the stick control a potentiometer or optical encoder? Let's assume it is a pot. So, you need a way to digitally create various currents or voltages. Look at the datasheet for the LM317 voltage regulator. At the bottom of page 22 of the National version (, you will find a schematic for digitally selected outputs. A similar approach using transistor logic could give you the step currents/voltages you need. It could also be done with a PIC or other MCU, but you said you did not want to do that.

    I think the receiver end might be a little more difficult. Since you will essentially be sending fixed positions to the servo, a mechanical solution might be the easiest (i.e., a rotary switch). Otherwise you will need a decoder that will convert the pulse width on the servo channel to a specific switch action. There are certainly non-MCU ways to do that, but I cannot give you a schematic for one from memory.

    Before getting into a more lengthy response, please let us know if this is the right concept. How complicated do you want it to be? Is a mechanical solution OK? Are MCU's out of the question or only an aversion?

    Last edited: May 21, 2010
  3. Markd77

    Senior Member

    Sep 7, 2009
    Or for the transmitter side just buttons and a range of fixed resistors all in parallel, maybe with a high value resistor in parallel depending on if the transmitter works with the pot disconnected.
  4. Jure George

    Thread Starter Active Member

    Dec 28, 2008

    Sorry for not getting back to you sooner. Yes the Transmitter pot is disconnected and the transmitter keypad has its three wires soldered to the trace positions where the pot was soldered. The numerical keypad with either 8 or 16 functions has resistors of unknown value( to me ) connected to it.

    I am not affraid of PIC circuitry, I just don`t know how to program it, if someone can program it, for a few PIC`s, then I would go that rout as well. Again keeping the receiver circuit as small as possible is important.

    The keypad connected to a Transmitter, would be joined to the one channel that the pot was removed from. The receiver for the keypad would be plugged into the receiver channel that the transmitter pot was removed from. So the keypad #1 button would be seen on the receiver then that signal goes through the " channel expander receiver " and that circuit board would have a row of dip switches, one side is latch mode - function is on until same #1 is pushed to turn off OR Toggle mode, function only works while pushing #1 button. The same channel expander board has a row of screw terminals to connect either 8 OR 16 items to it to be controlled.

    The channel expander receiver can have several things operating if latched then you can turn On #1 and then turn on #5 then turn on #8 etc and go back and turn off whatever plus also Toggle what ever function you want according to your list of functions and devices.

    The channel expander receiver would get its power from the main battery 6v upto 12v max. There should be a way for the channel expander receiver to maintain the setup of function mode ( Toggle / Latch ) if main power is lost, dead battery or battery unplugged for storage or replacement etc. The circuit I have seen that operates in this form has an EEPROM, Transistors and a few other I.C that I do not recognize. I can get their I.C numbers if that helps BUT this circuit has HAD LOTS of Failures and due to VERY POOR customer service, its not worth buying from that person, who created that circuit.

    I would like to have my own for a few ships and submarines that I would like to have this capability. IT would be alot cheaper then buying a Large Channel Radio System for.

    I hope this detail gives you a better idea of what I am looking for and someone can help me with a working plan set. Also if you can program the a PIC to do what I need, with the custom program, I would pay for that PIC.

  5. Jure George

    Thread Starter Active Member

    Dec 28, 2008
    Hi again

    Is anyone still working on this, I hope ?

  6. Jure George

    Thread Starter Active Member

    Dec 28, 2008

    I hope someone here can help me with this. I would like to keep this alive and hopefully I will hear from someone with a working circuit.

    Thanks Again for everyone`s help.

  7. SgtWookie


    Jul 17, 2007
    Jure George,

    I think people have given up on helping you.

    You propose a complex set of requirements for a project, and you expect someone else to do it for you; and then when you change/modify your requirements in mid-stream, you expect the modifications will be implemented.

    Even if the modifications ARE implemented, you appear to abandon the project and start making requests for help on new projects.

    What would be the point in making a design for you, and telling you where to get the parts, when you aren't going to complete it anyway?

    I'd rather spend my time helping people that actually want to learn something.

    Now if you change your mind and decide that you actually DO want to learn something, then start here:

    You can skip modules 18, 23 and 24.
  8. MMcLaren

    Distinguished Member

    Feb 14, 2010
    Jure George,

    Can you provide a link to the "expensive" off-the-shelf solution you mentioned?

    Can you post pictures of your rudderless submarine, please?

    Regards, Mike
    Last edited: Jun 27, 2010