# Simple circuit with logic need

Joined Feb 27, 2010
249
I am making vacuum lifts, and I want to put a little safety light on them.

My question is how to do it best to work off battery power (3vdc). Both switches you see are mechanically activated contacts.

What I want-

Initial state shall have no switch activated, and have no parasitic draw (for battery life when not in use). No lights shall be on.

When both the High Pressure switch and the Vacuum switch are triggered, the green light shall be ON. This means it is OK to lift.

When either the High Pressure switch, or the Vacuum switch is cut off, the green light should go OFF, and the red light should come ON. This means the lift lost source pressure, but is still holding vacuum by the reserve tank.

When both switches are cut off, the circuit returns to initial state. (both lights off).

Is this feasible with basic components? I have been racking my brain on this, and not sure if I am over thinking it.

http://schematics.com/project/vacuum-safety-light-59374/

#### MrChips

Joined Oct 2, 2009
27,101
You could do this if the switches had additional contacts. You would use three-way switches.
Since it is unlikely that you have additional contacts the only other solution is to use additional logic, relays, or PLC.

Joined Feb 27, 2010
249
I forgot to mention the reason I was having problems was because I don't have NC contacts. NO only.

And I have looked for other vacuum switches, they just don't make very many kinds.

Yes, if I had NC contacts on the switches, it would be easy.

If I went the PLC route, which pic chip do you think would suit me best? I am most worried about battery life, although I believe I would activate it by a vibration sensor switch, and then have it time out after 5 minutes or so.

#### eetech00

Joined Jun 8, 2013
3,418
HI

See attached.

eT

#### Attachments

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#### MrChips

Joined Oct 2, 2009
27,101
You can do it with CMOS digital logic chips. However, it will require a couple of chips, one MC14070 quad XOR and one MC14071 quad OR.

#### WBahn

Joined Mar 31, 2012
27,372
I am making vacuum lifts, and I want to put a little safety light on them.

My question is how to do it best to work off battery power (3vdc). Both switches you see are mechanically activated contacts.

What I want-

Initial state shall have no switch activated, and have no parasitic draw (for battery life when not in use). No lights shall be on.

When both the High Pressure switch and the Vacuum switch are triggered, the green light shall be ON. This means it is OK to lift.

When either the High Pressure switch, or the Vacuum switch is cut off, the green light should go OFF, and the red light should come ON. This means the lift lost source pressure, but is still holding vacuum by the reserve tank.

When both switches are cut off, the circuit returns to initial state. (both lights off).

Is this feasible with basic components? I have been racking my brain on this, and not sure if I am over thinking it.
This part doesn't make any sense:

When either the High Pressure switch, or the Vacuum switch is cut off, the green light should go OFF, and the red light should come ON. This means the lift lost source pressure, but is still holding vacuum by the reserve tank.

First, this includes the case in which BOTH switches are cut off. Do you mean "When one switch is off but the other is on"?

If so, then does the high pressure switch being on while the vacuum switch is off also mean that the "lift lost source pressure, but is still holding vacuum by the reserve tank."?

I think you need to spend a moment making sure that your needs are very clearly thought out and expressed.

You have four states. What do you want the lights to do for each of the four?

pressure=OPEN; vacuum = OPEN=> red = OFF; green = OFF
pressure=CLOSED; vacuum = CLOSED => red = ?; green = ?
pressure=OPEN; vacuum = CLOSED => red = ON; green = OFF
pressure=CLOSED; vacuum = CLOSED => red = OFF; green = ON

I have no idea how a vacuum lift system works. Is it even possible for the vacuum switch to be closed if the pressure switch isn't? If not, then that line could be treated as a "don't care" state which makes the resulting circuit much simpler.

Joined Feb 27, 2010
249
This part doesn't make any sense:
WBahn, sorry, I wrote that wrong. I was initially going to make a "dont care" circuit (just lights on a switch), but it's a lot better for the user of the lift to have the lights work logically. If both lights were on all the time, and only went out when their corresponding pressure was lost, the user probably wouldn't notice the change right away- and seconds will matter in this case.

The lift uses a venturi to create a vacuum from a high pressure, high cfm source. For reference, this is approx 100psi around 8cfm to create -15hg of vacuum on a suction pad. There is a small (a few cubic inches) reserve tank that is on the vacuum line to hold a reserve suction, and is isolated by a check valve from the source. This allows the lift to hold vacuum for a few seconds even if the source pressure is lost. Problem is, if the user doesn't realize the source pressure has dropped to a dangerous level, the vacuum could let go and the lift would drop the load. These loads are 500lb+ stones, and could ruin someones life if they fell on them.

That is why I want logic between the green and red states. I want it to be very clear to the user that a dangerous situation is occurring, so they can get out of the way immediately.

It should state as follows-

pressure=OPEN; vacuum = OPEN=> red = OFF; green = OFF (no parasitic drain in this mode)
pressure=CLOSED; vacuum = CLOSED => red = OFF; green = ON
pressure=OPEN; vacuum = CLOSED => red = ON; green = OFF
pressure=CLOSED; vacuum = OPEN => red = OFF; green = OFF

If I make the CMOS circuit, as MrChips suggests, to do this, I believe I would have to have a time-out feature to cut off the parasitic drain of the circuit. I could do this with a vibration switch on a 555 timer (or just buy a module off ebay that does this).

Last edited:

Joined Feb 27, 2010
249
HI

See attached.

eT
This is what I was going to do... however I am worried the battery drain would be too much using relays. I have been looking for solid state relays, miniature ones, that might be better suited than coils.

Joined Feb 20, 2016
4,200
I know I'll get howled down, BUT this is a real Arduino project.
And they are dirt cheap!
$2 US or less will get you one and you can play around with the logic to your heart's content. Adding timeouts and delays. Pressure sensors, displays, servos to control stuff...... Here is a 3.3V one... http://www.ebay.com/itm/1PCS-Pro-Mi...869445&hash=item2a56eb969b:g:FSwAAOSwBahU~u5b But you could try something like this.. . The added diode above the red will make the on volts too high for the red led to light when the green led is on. When the switches are open. the red led will light, and when they are both closed, the green led will light. You will probably have to test leds to get the correct ones as the forward voltages vary quite a bit. Use high intensity leds if you can. Limiting it to 3V can make it a bit harder, but have a go. Last edited: Thread Starter #### trader007 Joined Feb 27, 2010 249 I know I'll get howled down, BUT this is a real Arduino project. And they are dirt cheap!$2 US or less will get you one and you can play around with the logic to your heart's content. Adding timeouts and delays. Pressure sensors, displays, servos to control stuff......
Here is a 3.3V one...
http://www.ebay.com/itm/1PCS-Pro-Mi...869445&hash=item2a56eb969b:g:FSwAAOSwBahU~u5b
oh... i didnt know they went down that small. So the battery drain would be minimal wouldn't it? I want to keep this under 100ma total load (lights and the circuit logic). My led's will run about 25ma each.

Joined Feb 20, 2016
4,200
You can put the Arduino in sleep mode if you want to save power, but the total current will be way under 100mA and use high intensity LEDs and run at lower current. See the circuit I added to the above post as it may work.
But I'd advise you to have a go at the Arduino version as it will be a good learning project.

#### MrChips

Joined Oct 2, 2009
27,101
I forgot to mention in my previous post that the minimal solution is to use a small (8-pin) CMOS microcontroller.

There are MCUs other than the Atmel ATmega328 (Arduino) that draw lower currents.

With both LEDs off, the current drain is less than 1μA.
High efficiency LEDs have significant brightness at 1-2 mA.

As dendad points out, you can implement any logic you desire, including flashing LEDs, LED off after a given delay, or slow flash to conserve battery power.

Joined Feb 27, 2010
249
Ok I like the ATmega328

This post points out why its a good choice, if you use sleep states and small modifications

http://www.home-automation-communit...n-atmega328p-for-a-year-on-coin-cell-battery/

Also for reference, the LED's will only be on for maybe a couple hours a day total. The lifts are only used when stones are being lifted onto and off of saws. Otherwise they just sit there doing nothing.

I could run the ATmega off a lithium 9v that would probably run it for months before it needs changing.

#### eetech00

Joined Jun 8, 2013
3,418
This is what I was going to do... however I am worried the battery drain would be too much using relays. I have been looking for solid state relays, miniature ones, that might be better suited than coils.
Hi

Your description in post #7 indicates that the failure of this circuit to operate correctly has the potential to cause bodily injury or even a fatality.
So the circuit, in my opinion, should be "failsafe". While there are many ways to implement this logic, the most simple, is the use of relays.
I used to work in the railroad industry where failsafe design was commonly used. Failsafe circuits can be designed using solid state electronics (digital chips, microcontrollers, etc.) but they require very sophisticated design techniques and circuits (most are patented).

just my opinion.

eT

Joined Feb 27, 2010
249
But you could try something like this..
.View attachment 130855

The added diode above the red will make the on volts too high for the red led to light when the green led is on.
When the switches are open. the red led will light, and when they are both closed, the green led will light.
You will probably have to test leds to get the correct ones as the forward voltages vary quite a bit.
Use high intensity leds if you can.
Limiting it to 3V can make it a bit harder, but have a go.

This was my very first thought when I decided I needed these lights. It's crude, but for such a simple project it might be best. I might try this. The only issue is when the lift is not being used, both lights need to be off... and I dont want them to use a switch to turn the circuit on because they won't do it. It would need to be tied to a vibration switch that latches the circuit on for a set period (say a few minutes).

Joined Feb 27, 2010
249
Hi

Your description in post #7 indicates that the failure of this circuit to operate correctly has the potential to cause bodily injury or even a fatality.
So the circuit, in my opinion, should be "failsafe". While there are many ways to implement this logic, the most simple, is the use of relays.
I used to work in the railroad industry where failsafe design was commonly used. Failsafe circuits can be designed using solid state electronics (digital chips, microcontrollers, etc.) but they require very sophisticated design techniques and circuits (most are patented).

just my opinion.

eT
Well right now they have no safety lights. They just go by feel, noise, and they never position themselves in harms way. The lights are just added visual cues, but you might have a point because if I give them lights they will probably rely on the lights... and trust them too much...

#### MrChips

Joined Oct 2, 2009
27,101
Your simplest solution is to connect each switch to individual LEDs through a series resistor.
Both LEDs must be ON for normal safe operating mode.

Joined Feb 27, 2010
249
Your simplest solution is to connect each switch to individual LEDs through a series resistor.
Both LEDs must be ON for normal safe operating mode.
I fear two things with that-

one, people would get confused what one light on, one off would mean (even if I labeled them)
two, during a long busy day, it would not be immediately noticeable if one light goes out. However, a bright green light that changes to red is easily noticed.

#### MrChips

Joined Oct 2, 2009
27,101
I fear two things with that-

one, people would get confused what one light on, one off would mean (even if I labeled them)
two, during a long busy day, it would not be immediately noticeable if one light goes out. However, a bright green light that changes to red is easily noticed.
How about, in addition to two RED LEDs, one on each switch, a single GREEN LED when both RED LEDs are ON.
This can be implemented with one transistor.