Watering programmer

[arsana]

Dear friends:

I would like to ask you for your help in the following:

I have a programmer for watering my garden that is far from it. The plastic tube that conducts the electric wires from the programmer to the electrovalves is blocked and is impossible to add more cables or even to pull them for using as a guide. Now, there are 2 electrovalves that are controlled by 3 wires from the programmer (one mass). The problem is that I would like to add 2 more electrovalves. As it is impossible to add two cables, I am wondering if you see any method to convert the signal that generates the programmer for four valves (the programmer can control up to 4 valves) in a binary code who travels along one of the cables. Then, in the garden demodulate the signal convert back in a signal for 4 electrovalves. The other cable should be used to provide the supply for the valves (26 volts AC).

Thank you very much for your help

Arturo

 

[Hero999]

What do you mean by programmer?

Do you mean you employ a programmer to water your garden? Perhaps you should employ a gardener.

Are you talking about a PLC (Programmable Logic Controller)?

 

[3v0]

I am wondering if you see any method to convert the signal that generates the programmer for four valves (the programmer can control up to 4 valves) in a binary code who travels along one of the cables. Then, in the garden demodulate the signal convert back in a signal for 4 electrovalves. The other cable should be used to provide the supply for the valves (26 volts AC).

Thank you very much for your help

Arturo

Am I correct that you have 3 wires to work with. It is possible to get what you need but maybe not exactly the way you wanted to do it.

Use a microcontroller on the controller side to sense the state of the original controller outputs/wires. This info is sent over the first wire to another microcontroller on the other end of the cable. This microcontroller is on a board with 4 relays that control the valves.

The 2nd wire is used to power the microprocessor. relay board, and valves. The 3rd is ground.

This is not a hard problem if you know how to program microcontrollers. The materials are not too expensive.

If you used this board you would only have to build and program the one one the controller side.

**broken link removed**

This is all rather speculative and since you did not specify how long the wires were one can not tell if it exceeds what can be done with RS232. Also note that this would be an open loop system. Not way to tell if the relay board ever got the command. But it could work.

A 4th wire would be a big help.

 

[mroberts]

OK, so it currently has 3 wires controlling 3 valves, and can control them independantly - effectively parallel control.

Without adding any more wires, doing what you want to do with result in you only being able to switch on one valve at a time, and you will only be able to control 3 valves (assuming one wire is a ground, and there are only two signal wires):

00: All valves off
10: Valve 1
01: Valve 2
11: Valve 3

You can do this with a binary / BCD to decimal decoder - it will take your two input lines, and activate one of 4 outputs depending on the values of the inputs.

You'll need some simple filter circuitry to handle the different current requirements - you're looking at very low currents for the IC, but you'll somehow need to harness the high current capability of the lines to power the valves at the end.

The other problem will be how the valves are controlled - does it pulse them to switch them, or are they "on" while voltage is being supplied.

You'll need to work out how it's sending the signals.

 

[3v0]

Now, there are 2 electrovalves that are controlled by 3 wires from the programmer (one mass). The problem is that I would like to add 2 more electrovalves.

OK, so it currently has 3 wires controlling 3 valves, and can control them independantly - effectively parallel control.

It has 2 valves controlled by two wires and a ground.
He wants to add 2 valves for a total of 4.

Your solution only handles 3 valves.

If this is the sort of sprinkler system I use the valves use simple selonides to turn them on and off. No latching. This seems to be the case because a latching system would require another wire.

 

[arsana]

Thanks

Dear Hero999, 2963 posts, 8.7 posts per day. All your posts are so interesting as your reply to this thread?. I can see thousands of things to do with 24 years of age more interesting than this. In any case, yes, I meant a Programmable Logic Controller.

3v0: Thank you very much for your answer. The wires are +- 30 meters long. Is it too long?


mroberts: The valves are on while they receive voltage. I think that my main problem is that the valves work with AC. If not, I could use the polarity with respect to ground to send 4 different signals (++, +-, -+, --) using only two wires. At the valves end, with diodes, I could send the signal to the correct valve.

Thank you

 

[Hero999]

Lol, I am by no means the most prolific poster on this forum; I believe that title goes to Nigel and audioguru.

 

[3v0]

3v0: Thank you very much for your answer. The wires are +- 30 meters long. Is it too long?

The RS232 standard suggests 15 meters or less but there is a very good chance you could get it to work well at 30, it has been used over much longer runs. It depends on how much noise is on the cable. Also the slower you run the signals the longer the cable can be.

You could test this with a PC. Take two wires off the controller and hook one to pin2 and another to pin3 of a DB9 and plug them into the serial port. Connect the same wires togither on the valve end. Use hyperterm to send characters. The echo you see on the screen will be what you get back. A better test would be to write a program that did the same.

This does not have to be fast. To use the above board you need to run at 9600 baud. If you use a board that allows you to pick the baud rate you could run much slower if needed, like 300 buad.

Since this is open loop I would send each command multiple times to be safe. Esp off commands.

Are you up to this ?

 

[picasm]

If it all runs on 26V AC,could you consider moving the programmer into a weather-proof box next to the valves and then you would only need two wires for the power?

 

[Pommie]

Why not change the valves to 12V ones and use the 2 halfs of the 26VAC to control 2 valves through 1 wire (plus ground). See attached.

Mike.

 

[3v0]

If it all runs on 26V AC,could you consider moving the programmer into a weather-proof box next to the valves and then you would only need two wires for the power?

This gets my vote. If the OP has valves at other locations and can not move the controller then he can just add another controller at the site in question. It is a lot less work then what I suggested. It also has the advantage of putting the controller closer to the areas being watered.

 

[arsana]

Picasm: This is one option. I am a medical doctor and so nothing to do with electronics. However, I love electronics and I thought that this exercise would be very nice for a beginner like me. I will try a more "elegant" solution and finally, if it fails, I probably will choose your option, thanks.

Pommie: The reason to divide the garden in several zones is that usually the water pressure is not enough for watering all the garden at once. I do not have enough water pressure for watering two zones at the same time. Thanks.

3v0: I will try your solution, thank you

 

[ljcox]

Why not change the valves to 12V ones and use the 2 halfs of the 26VAC to control 2 valves through 1 wire (plus ground). See attached.

Mike.

You could use 26 Volt DC rather than AC and thus Mike's solution would work.

But I don't know whether the valves can be used on DC. Does anyone know?

 

[Pommie]

Pommie: The reason to divide the garden in several zones is that usually the water pressure is not enough for watering all the garden at once. I do not have enough water pressure for watering two zones at the same time. Thanks.

I think you misunderstood what I was suggesting. The circuit I posted earlier will take 2 outputs and drive 2 valves independently through 1 wire. Or, it will drive 4 valves through 2 wires plus 1 return/common wire. There is no need for 2 valves to be on at the same time. This may even work with the existing valves if suitable capacitors are put across each valve.

Look at the circuit again and if it doesn't make sense then post back and I will explain how it works.

Mike.

 

[justDIY]

You could use 26 Volt DC rather than AC and thus Mike's solution would work.

But I don't know whether the valves can be used on DC. Does anyone know?

the lawn sprinkler valves I've tinkered with are rated for a 24vac system but work fine with 12vdc. It's just a simple solenoid that moves a plunger, give it enough energy and it does its job. I figure they specify the 24vac because it carries a lot better over 100's of feet of cable than lower voltage DC would.

 

[arsana]

Pommie: sorry for the misunderstanding. Your idea looks fine, now that I have looked at with attention. I will test if valves open with half tension. Regarding the post from ljcox, I think that this solution only will work with AC ¿?¿?

Thanks

 

[Pommie]

As far as I am aware, this will only work with AC. I think what Len meant was to smooth the rectified AC at the valve end using capacitors.

I would just try it as drawn and if it isn't reliable add capacitors until it is. Let us know how it progresses.

Mike.

Mike.

 

[ljcox]

No, I did mean DC, see attachment.

 

[Pommie]

How do you turn ON V1 and V2 at the same time? Using AC you get fully independent operation of 4 valves through 3 wires.

Mike.

 

[ljcox]

How do you turn ON V1 and V2 at the same time? Using AC you get fully independent operation of 4 valves through 3 wires.

Mike.

MIke,
He only wants one valve on at a time.

Pommie: The reason to divide the garden in several zones is that usually the water pressure is not enough for watering all the garden at once. I do not have enough water pressure for watering two zones at the same time.