Rf transmitter with 2 receivers

[crazybry79]

I have another thread on here about AFADs (automatic flagge assistance devices). Basically, they are trailers that get parked on the side of the road and replace a human flagger. (Stop / slow guys)

In order to make these work, they need to be remote controlled. I have very limited Rf experience, and minimal electronics experience.

Here's what I need to do....
I have 2 trailers 1000' apart. The operator will sit in the middle and operate both AFAD trailers via remote. Each trailer needs to receive 3 channels - one for "stop" one for "slow" one for "horn".

I require the Rf distance be 1000' minimum range. Even though the operator is 500' away, I want a safety margin.

I've searched online, and I've found various remote controls, 3 - 4 channels and more. But I am having problems finding a setup with one controller, and 2 receivers.

In a perfect world, I'm looking for a remote that has...(abs I realize they won't be labled, stop, slow, etc)
(1) stop button
(2) slow buttons
(1) horn button
The stop button would send a signal to BOTH AFADs every time it's pressed.
Each slow button would have its own trailer.
The horn button would send a signal to both AFADs.

Possible? Am I barking up an expensive tree?

 

[Osmium]

Totally possible because, you know, complete systems are available "off the shelf" http://www.autoflagger.com/products/autoflagger-76/

I have to ask, why are you re-inventing this particular wheel? I understand if this is a fun project, but if you're looking to save time/money/hassle then this path is unlikely to achieve any of those.

 

[crazybry79]

The link that you have there, is very similar to what I'm building. The modem 76 you have shown I'd the bare bones basic stop/slow (S/S) model. They offer a red/yellow as well.

I am building a hybrid of both - no other manufacture builds that hybrid. Plus, the bare bone 76S/S is $19,900 plus delivery - that's for one. I will have less than $2k into my entire setup, minus Rf equipment. That's for a pair or AFADs.

That's why I'm reinventing the wheel.

 

[Osmium]

OK. In that case...

You need a microprocessor controlled transmitter and two microprocessor controlled receivers.

The idea is that the transmitter sends messages out to both receivers. The receivers are designated 1 and 2. Each message sent consists of an ID and a command. The ID can be 0 meaning "This is for both of you" so both receivers respond to that message. Otherwise, receiver 1 responds to messages with an ID of 1, and 2 with an id of 2. The commands are Stop, Slow or Horn represented by a command code of, say, 1, 2 and 3.

Typical messages:

01 = Stop to both
11 = stop 1
23 = horn on 2
12 = slow on 1

And so on. The transmitter/receiver modules can be something like https://www.linxtechnologies.com/en/products/modules/lr-rf-transmitter-receiver

The microprocessors can be anything that is easily interfaced to the tx/rx modules.

The transmitter is enclosed in a small case with the buttons as you've described.

You'll need some help in the form of an electronics hobbyist/engineer who is used to dealing with microprocessors and can program the (very simple) messaging system outlined above.

You may need to add a small amount of complexity to improve reliability eg: Sending the message several times for each button press, including some extra parity information in the messages to reduce the possibility of false triggering.

 

[crazybry79]

Ok. After first read of your post - totally lost.

Now I've re-read it, and makes sence.

I'll look around for more info on micro controllers and the like.

Every adventure is a new page! That's why I love it!

 

[Osmium]

This could be a good place to start: https://www.linxtechnologies.com/en/products/modules/kits/lr-rf-transmitter-receiver-eval

It's pretty well a complete solution in an assembled kit - buttons included! Check out the user guide.

 

[Osmium]

Thinking about it some more. I'm not sure how much those evaluation kits cost; you'll need to ring and check it out. However, if they could supply an extra receiver eval board and antenna you would have potentially a complete solution. There are 8 buttons. If you set up both receivers so that they respond identically to the one transmitter, then you could use 4 of the buttons as follows:

B1 Stop - Both receivers go into stop mode
B2 Slow Rcvr1 - Receiver 1 goes into Slow mode, Receiver 2 ignores (just don't connect this output on receiver 2)
B3 Slow Rxvr2 - Receiver 2 goes into Slow mode, Receiver 1 ignores
B4 Horn - Both receivers go into Horn mode

Job done... mostly...

 

[Osmium]

Hope that was clear. If not...

Each receiver has 8 outputs. Those outputs go high whenever a corresponding button is pressed at the transmitter. Both receivers behave identically. Output 1 goes high on both when the transmitter button 1 is pressed. Same for all the other buttons. Both receivers are connected such that output 1 always makes the AFAD go into STOP mode. Both receivers are connected so that output 4 makes the AFAD go into Horn mode. Outputs 2 and 3 are treated differently. Receiver 1 only uses output 2 to go into SLOW mode and output 3 is not connected. Receiver 2 uses output 3 to go into SLOW mode and output 2 is not connected.

Make sense?

 

[Osmium]

and furthermore...

Because you don't want both AFADs to go into slow mode, 'cos that would be bad... If at, for example, receiver 1 you made the STOP mode trigger if Output 1 OR Output 3 went high (so that'd be an OR gate). For receiver 2 it would be Output 1 OR Output 2. You might need some logic at the transmitter so that if both SLOW buttons are pressed together it either sends nothing or sends STOP.

 

[Osmium]

actually... just put all the logic at the receivers. leave the transmitters as is.

 

[Osmium]

I think this is the logic...

B1    B2    B3    B4    AFAD1    AFAD2
1    X    X    X    STOP    STOP
X    X    X    1    HORN    HORN
0    1    0    0    SLOW    STOP
0    0    1    0    STOP    SLOW
0    1    1    0    NOP    NOP

X = Don't care
NOP = No operation = do nothing (or could be STOP)

 

[Osmium]

Hi Crazy,

I don't know where you're at with this but I've found these eval kits on digi-key: http://www.digikey.com/product-detail/en/EVAL-418-LR/EVAL-418-LR-ND/670150

At that price, you could order two kits and then add the enclosures, extra logic and so on for under $400 (my estimate) for the finished RF solution - which, in my book, is not bad at all. You might be able to do better.

Anyhow, have fun and let us know how you go.