Pushbutton Ideas

klittle · Jun 21, 2010

i have a project with 28 push buttons that basically enable 28 valves but how do i enable the valves in the order that the buttons are pressed? if three people push buttons only one valve can be turned on at a time and they have to come on in the order they were pushed?

Karsten · Jun 21, 2010

Totally impossible!

Let's say 35 persons are pushing the buttons randomly at a random time.

Or are there any other limitations that you would like to inform us of?

bits'bytes · Jun 21, 2010

Hi klittle,

if I am understanding all, I would do it like this:

- you scan all buttons in one cycle
- for each button pressed, you put the corresponding number into a fifo
- in a second task you check the fifo
- if there is a number (or more numbers) inside, you pick the first and handle the corresponding valve.
- if the valve is finished, check if there is more in the fifo.

br
bb

James Mcquade · Jun 21, 2010

assuming there is only one operator pushbutton station, if you have a plc, then get a touch screen. on an AB pv600 for example, you can only push one cell at a time.

BACK TO THE MAIN POINT,
you have asked a very vague question. We need more details.
what is this application, what does it control, WHAT HAPPENS IF A VALVE IS TURNED ON OUT OF SEQUENCE, how to reset machine,
safety issues?

Yes, you can do what you asked, but we can't do it without a lot more information.

regards,
james.

L D[AR2P#0.0] · Jun 21, 2010

Simplify the problem down to 2 push buttons/Valves

If you can describe the functionality required, it will be easier to then extend it to many pushbuttons.

klittle · Jun 21, 2010

this is a system that delivers an ice/water mixture to 28 stations with a button at each station. when the button is pushed the corresponding valve opens then there is a delay and the pump turns on for a time set through a HMI for each valve then the pumps turns off and after a delay the valve closes. the system can only deliver to one station at a time but they have requested that if a button is pushed while someone else is requesting ice then that will be the next station that is enabled. which would be fine if there were only 2 buttons but there are 28 buttons. the sequence is determined by the order in which the buttons are pushed and some buttons may never be pushed on a shift.

bernie_carlton · Jun 21, 2010

You haven't identified a controller. If I were using an Allen Bradley unit I would use the FIFO Load and FIFO Unload commands.

The FIFO Load would be enabled when a button was pressed. It would place the identifier for that button into the FIFO array.

The routine controlling the valves/pump would watch for any entry in the array. If there was it would perform an FIFO unload to get the identifier, go through the actuation and timing routines for that identifier, then go back to looking for an entry in the FIFO array.

klittle · Jun 21, 2010

thanks Mr. Carlton i am looking at how to do that and i think i can make it work. i have not yet used a FIFO but i think i under stand how it works.

L D[AR2P#0.0] · Jun 21, 2010

What is to happen if you press Button 1 and then press it again whilst the delivery sequence is in progress - do you get another delivery of ice/water immediately after the first one ?

klittle · Jun 21, 2010

L D[AR2 said:
What is to happen if you press Button 1 and then press it again whilst the delivery sequence is in progress - do you get another delivery of ice/water immediately after the first one ?

no i will not use the Input directly they will have to hold the button down for a time and i will latch in a bit and if the bit is latched in the button will not do anything.

bkottaras · Jun 21, 2010

L D[AR2 said:
What is to happen if you press Button 1 and then press it again whilst the delivery sequence is in progress - do you get another delivery of ice/water immediately after the first one ?

Regardless of latchingor using a delay this is a legit question.
Assume the station pumps ice at this point and the operator holds the button down for a certain amount of time.
The system has to re-supply another batch?
Besides the FifO solution posted which solves the push button sequence issue, you'll have to do a lot of coding to make the system function as intented.

TConnolly · Jun 21, 2010

Getting only one valve to turn on at a time is a pretty simple bit hack if you assign the priority to the least significant bit or most significant bit.

For example, J := I AND (NOT (I-1)) will always leave you with just one bit set in word J and that bit will be the least significant bit from I. Other bit hacks give you different bits. Google "bit twiddling hacks" to get a number of different ways to do it.

You should be able to use a combination of that and the FIFOs Bernie mentioned to do what you need.

klittle · Jun 25, 2010

i got it working at least on my desk with the plc and HMI by forcing inputs on.

thanks for the help!

shooter · Jun 25, 2010

you can do it without memory just the first one button is seen.
by ld 1 andnot 2 andnot3 etc.
ld2 andnot1 andnot3 etc.

or by memory so that way the valve will be open if none is pushed.

Pushbutton Ideas

klittle

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