What is an easy way to write a two switch Lock out routine for a piece Equipmen

sam_sam_sam

Here is what i want to do

So feet and hands are not where the· Equipment··can hurt you

I want to use two switch that are depend on each other with two inputs to a Basic Stamp and ..........

Which Basic Stamp would be the Right choice and why ???

I want it so that each switch has to make with in a second of each other to be·valid

other wise lock out is in forced and you must start again

I am just looking for ··s for now

Where·I work at we are having trouble with this· piece of Equipment·and the cost of this board is $1500
it also dose other functions besides the one i have here

One this that is bad with this setup is that it send 120 volt to the switch for safety switches




Both Switch Must make with in ONE Second
Switch 1
Switch 2

If not then both switchs must be released and start over

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··Thanks for any··that you may have and all of your time finding them

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Sam

Post Edited (sam_sam_sam) : 9/30/2008 1:38:07 AM GMT

Searider

I suspect that any of the processors can easily do the 1 sec timing you suggest. There are some unanswerd questions that I have.
What is the specification of the output when a sucessful two switch sequence is made?·


There may also be simpler ways to accomplish your goal.
If this is just to ensure that it takes two hands to activate thus ensureing that both hands are not in/on the equipment. Why not just put two N.O. momentary switches in series and mount them about 1 foot apart from each other?

You could also make the curcuit you descript with a a few simple components like an RC circuit that closes a releay. If both switches are pressed before the releay closes then you activate the equipment. If not, then you have to wait for capacitor to discharge.

Also look at LM555 timers.




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Searider

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sam_sam_sam

Searider

Thank You for your reply

I have to ask you something

You could also make the circuit you descried with a a few simple components like an RC circuit that closes a relay.


How would do this set up with capacitor and two relays

If both switches are pressed before the relay closes then you activate the equipment.
If not, then you have to wait for capacitor to discharge.
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··Thanks for any··that you may have and all of your time finding them

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Sam

kelvin james

You could use an AND GATE like the 7408. The link shows how to do it with transistors also.



http://hyperphysics.phy-astr.gsu.edu/hbase/Electronic/and.html


If the timer is necessary, you could run an additional output from each switch to the stamp, and start a conditional timer loop that has to be met before the and output would become active. So the stamp would wait for button press 1, it starts a 1 second timer waiting for button press 2, if not, go back and wait again for button 1. If condition is met, then allow input from and gate / output from stamp to be sent to machine.

Post Edited (kelvin james) : 10/4/2008 4:51:43 PM GMT

kelvin james

On second thought, since there is a liability issue involved with a possibility someone could get hurt, i would not do to it at all. No doubt it would work, but if you design and implement it, the reponsibility falls on you, unless you get a legal statement otherwise from your employer. If the machine is the dangerous type, a safety light curtain ( break beam ) should be used around the access point, to prevent any possible accidents.

stamptrol

kelvin is right; there could be some liability issues if you just go ahead and modify a safety system.

However, you can work with your Dept of Labour inspector and get him/her to help you test and accept the modifications.
More complicated procedure to be sure, but the owner of the business will thank you in the long run.


The issue is that the two buttton system must also reject a scenario where the operator ties down one button. These circuits
are also called "anti-tie-down" circuits for that reason.

Cheers,

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Tom Sisk

http://www.siskconsult.com
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GICU812

Yea, I had to explain to the guys at radioshack what an AND gate was last time I went in there. That wasnt so supprising as having to explain it to the guy at the electronics specialty store I went to when RS didnt have it. That was just disturbing. They have hundreds if not thousands of ICs in stock, and the guy doesnt know what an AND gate is.

sam_sam_sam

I want to Thank every one that has reply ed to this post

I had not thought of this part I am gald that you brought this up and thank you for it

Tom Sisk

However, you can work with your Dept of Labor inspector and get him/her to help you test and accept the modifications.
More complicated procedure to be sure, but the owner of the business will thank you in the long run.

This one thing I was going to add to it which it dose not have now

The issue is that the two button system must also reject a scenario where the operator ties down one button. These circuits
are also called "anti-tie-down" circuits for that reason.





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··Thanks for any··that you may have and all of your time finding them

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Sam

hippy

Putting aside the legal and liability issues it's an interesting challenge. Perhaps not so much in an algorithm in detecting a second button has been pressed within a certain time frame but in determining when a fault has occurred or where a deliberate attempt to circumvent the process has been instigated ( that tie-down etc ). Preventing false triggering as much as recognising the legitimate.

It is perhaps more an exercise in failure mode analysis than anything else. Consider one potential fault - the switch has become disconnected and the input is floating and appearing to flip high and low; pressing just the one switch in those circumstances could lead to a false recognition of valid trigger.