Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Help with a wireless relay control modification circuit

Help with a wireless relay control modification circuit

Help with a wireless relay control modification circuit

I will start by describing the problem, then I will propose my solution. I hope that someone here can first, tell me if my idea would work, and secondly, help me find what I would need to put it together.

The problem:

I have purchased a simple 12 channel remote relay system for about $20.00. It is a hand held transmitter with an antenna that works at 315MHz. The receiver is a board with 12 relays on it, one for each button on the transmitter. It all works. If you push button #3 on the transmitter, Relay #3 closes. The same with all the other buttons. This is not latching. It is in momentary mode, as I need it to be. Each relay will stay closed for as long as the button is being held down. As soon as the button is released, the relay opens again. What I need for it to do is to allow me to press and hold down a given button. Let's say button #3. While still holding that button down and keeping relay #3 energized, I want to also press and hold Button #4. I want relay #3 to remain energized since button #3 is still depressed. I also want relay #4 to become energized at the same time because I am pressing down Button #4 as well, and so on. Unfortunately, it does not work that way. If any one button is pushed, pushing any other additional button at the same time does nothing. Apparently, it is only capable of transmitting a single button closure at a time. I need no restrictions on the number of buttons pushed.

What I am using it for:

Instead of just pushing the buttons on the transmitter, I have wired 2 joysticks and a couple of extra buttons all mounted on a panel to the switches on the transmitter. Moving the joysticks controls 2 large mechanical arms that can move up and down and out to the side and back. These actions must be able to happen at the same time requiring up to 6 connections to be needed simultaneously if I am moving both arms and pushing a couple of the buttons at the same time which would be quite likely. The relays control coils in pneumatic valves which control cylinders that move the arms. The motion is dampened so it is not very fast moving.

My Proposed solution:

On the panel which I have built with the joysticks and the buttons, I add a circuit board that does the following:

1. scans all my switches multiple times a second to see how many connections are being made at any given time and which connections they are

2. Give me an output that will send a sequence of quick 'pulses' to close the switches on the transmitter one at a time, rapidly scrolling through all the switches that are currently closed on the panel until the state changes. As an example, If I am holding my joysticks in a manner which would cause buttons #3, #4 and #5 to all be closed at the same time, I would want this new circuit to close switch #3 for a few milliseconds then release it, then close switch #4 for a few milliseconds, then release it, then close switch #5 for a few milliseconds, then release it, then go back to close switch #3 again and continue that rotation until its scan of my panel determines that a different combination of switches are now closed and adjust its output accordingly.

The result of this would be that the transmitter would only be transmitting a single closure at a time, but they would be so rapid that the end result of appearing to move two or more pneumatic pistons at the same time would result.

The timing of the scanning and how long each output is held on before moving to the next would need to be adjustable in case the transmitter and receiver can't communicate as quickly as the information is moving. It also needs to stay on long enough for the physical relay to actually close and start to activate the coil of the valve before it goes off.

I can see a problem where the relays and valves wear out prematurely because now instead of closing the relay and valve once for 5 seconds, the relay and valve have actually been cycled many times in that same time span. If we slow this down to only dividing each second up into 5 parts, much longer durations than one might initially program for, this might be a good compromise. If each step in the 'Rotation' of the output stayed closed for 200 milliseconds, it would mean that if 4 switches were closed at the same time, it would cycle through all of them and hit the first one a second time all within a second, which would be less wear and tear on the relays and valves and would still probably look like smooth enough motion at the output. This is all for visual effect. It does not have to be precision at all. The fewer switches being held down at a time, the quicker it more pulses per second each relay gets.

I hope I have explained what I need adequately and that someone out there can help me. Please feel free to ask questions.

I can buy a transmitter/receiver combination that will do this, but it will cost between $600 and $800! I hope this would be a cheap, simple solution to this problem and might be helpful to others in a similar situation as myself.

RE: Help with a wireless relay control modification circuit

The simplest way forward is a single board computer such as an Arduino. There are many similar products, and everyone's opinion of the best depends on which one they happen to have used lately. For that reason the Arduino is far superior to any of the others (<- joking).

For the transmitter / receiver link, there are again plenty of choices. For low power short range, they're very cheap. Same with I/O, interface, relay boards.

Then mix in some software. It's a very straightforward project, but I'd still allow several days if you're starting from scratch.

RE: Help with a wireless relay control modification circuit

So is there no way to do this without replacing the entire system I already have? I didn't really want to buy another transmitter and receiver or relay board. I already have all those. I just wanted something that would feed the transmitter I have in the manner I explained. Can that be done?

What I really wanted was to build a system that didn't involve any proprietary programming or custom parts. I won't be involved in this project going forward, and I wanted to provide the people who would have to maintain this with a basic system that anyone could repair simply by buying another piece off the shelf. It doesn't look like that's possible, but if I can retain as many of the simple, off-the-shelf components as possible, that would be best.

Thank you for the suggestion. I am familiar with the Arduino boards and software to a point, but I have never used one or made my own project with one.

RE: Help with a wireless relay control modification circuit

Quote (HB)

I add a circuit board that does the following: 1. scans all my switches multiple times a second ... 2. Give me an output that will send a sequence of quick 'pulses' ...

My suggestion was aimed (more or less) at the above added circuit board. Rather than adding an expensive custom circuit board, instead use several extremely inexpensive off-the-shelf cards. You could reuse the radio circuits, but that might be more trouble than it's worth (can't tell based on what you've provided).

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close