man down IDEA

thanks in advance.

My idea is to make Arduino act like a man down monitor. just at thinking stage and coming stuck.

I'm thinking of using a mercury tilt switch with 10K pulldown, to then control a timer.

movement detected == YES == TIMER reset

movement detected == NO == if no movement for 10secs (do something)

I also need a long press to reset TIMER if movement is detected after the 10secs,
basically continues to flash LED SOS, until human interaction.

can this be done as i was originally going to use a 555 somehow.
I'm new to this so be gentle...

many thanks

can this be done


i was originally going to use a 555 somehow.

You will need more than one I suspect.

"can this be done "
I suspect your real question is "can this be done using an arduino".
If that assumption is right, then the answer is YES.

Is this device to be worn on a human, 24/7?
What does it do in the case of "man down"? flash a light, call 911, or what?

I'm thinking of using a mercury tilt switch

Problem is that it is illegal to use a mercury switch in Europe. I used to be in a place that made them professionally and we had to design the mercury tilt switch out. We used a ball tilt switch but had reliability problems getting a contact.

I suspect your real question is "can this be done using an arduino".

I suspect the real question is "can you give me the code to do this".

Jack wp:
This is going to be used in a diver umbilical torch, to auto flash an LED if a diver loses consciousness.

It's apart of a bigger idea to control a 10w LED.

Grumpy-Mike: thanks for pointing out the legals of mercury. I'll switch to a ball bearing type.

I'm thinking about using the timer function but not sure how to go about it.

It's getting the switch to trigger the timer. Is confusing to say the least

As for giving me code, i would like a little help yes but, a jumping off point would be nice.

I've all ready got the code working for selecting led brightness with one switch.


The small print at the end of the Atmel datasheets says
Atmel’s products are not intended, authorized, or warranted for use as components in applications intended to support or sustain life.


This is merely a proof of concept idea

It’s not going to sustain life just a method of attracting attention of dive buddy.

If it is a diver then he can be any way up and "falling" does not obey the normal rules. Are you sure he is going to fall "right" enough to be detected?

With the amount of weight a diver carries they will sink.

I'm thinking about making the 'light head' slightly negatively buoyant to make it harder for the tilt switch to register, this way as the diver is moving about, swimming, exploring whatever.

Divers arm will sink a little bit
No movement after ten secs off goes the LEDs

What Mike said… I know when I dive, I can easily be in any position relative to gravity, and remain there for some time. Especially when I do cage-less shark dives, motion can attract attention and that is a bad thing, especially if you look tasty. The man down alarms we use in emergency services will go off every 30 seconds or so even if you’re just standing still, you need to frequently and repeatedly swat the thing to keep it from going off. I don’t see this being practical nor a good idea in a dive situation, as the ‘proper’ dive position is usually with your arms crossed in front of you.

Under what scenarios are we diving in?

If we’re in a situation where direct contact from your dive buddy is not practical (cave or wreck diving), then you should be using radio comms to maintain contact. In these scenarios, a blinking light is pointless as the victim/diver is already obscured by whatever was preventing you from maintaining line of sight contact. That’s why we use ropes/tethers.

If we’re in an open water situation, there’s no excuse for not being close enough to your dive buddy to see if they are in distress. And again, if the water is cloudy enough that you can’t see your buddy, then a light will not be that effective. That said, buddies do drift away sometimes, chasing giant turtles or whatever. But when that happens, it should only be momentary, and the pair should reunite ASAP.

With everything involved with a dive, I think a positional trigger will either be always going off, or never going off. The motion of the water, or the movement caused by an unconscious body as it slowly settles to neutral buoyancy will prevent the sensor from tripping. On the flip side, if those are accounted for, the body would have to settle out before it trips, and by then it could be too late.

I think, if your intent on building such a device, you need to change your mechanism. A couple of ideas, some practical, some not:

  • Monitor the air flow and breathing rate. Only the most fit divers would have air consumption rates near their unconscious levels while alert, even then a couple quick puffs on the regulator would reset the counter.

  • Add a pressure plate to the mouthpiece. An unconscious diver would relax their mouth, and then the counter would start. If they’re just a calm diver, a quick lite chomp would reset the timer.

Anything you build, though, would need an auditory warning before the alarm is triggered. Firefighters have a couple few chirps from their alarms before it goes crazy. An audible chirp underwater would be very noticeable by the diver, and they could easily perform the reset action. Sound carries a looong way underwater, so you wouldn’t need a powerful source to alert the wearer.

With the amount of weight a diver carries they will sink.

Only if their BC is set to a negative buoyancy.

When I get to my planned depth, I usually try to set my BC for neutral, if not very slightly positive. But it's situational really.

One other comment.

You might want to add an louder auditory alarm to the LED for when the alarm is triggered. Depending where you have the device, it may be obscured from the rest of the party by the diver themselves. Ie, the body is going to block the light.

Add a higher powered sound, like a constant warble, to the alarm. Again, since sound carries well, it shouldn't need that much power.

Telling sound direction is nearly impossible under water for humans (In my experience at least), but at the very least every body within a few hundred meters will be made aware of a diver in distress situation. And maybe, if you're lucky, some friendly local animals will come over to investigate :).

And perhaps adding a float that gets released.

Great practical advice there +1

I've already had the lamp machined, and it's setup as a simple on/off lamp with a 10watt LED.

I understand that because its theoretically possible its not likely to be practically possible.


UK based wreak diving in the SEA, so not always the best of vis.

I wouldn't of considered using an audible warning to warn the diver all hell was about to kick off.

I certainly never considered using it as an additional warning feature.

I'm not liking the idea of having a tethered automatically deploy-able float as this could left the diver therefore adding to the problem of having to preform a lift.

you've now got me thinking about how a drift dive would impact on the unit triggering.

I'm not liking the idea of adding a pressure plate to a DV as that means routing wire from the divers mouth to the unit.

and how would i go about monitoring breathing rates?

Problem is that it is illegal to use a mercury switch in Europe. I used to be in a place that made them professionally and we had to design the mercury tilt switch out. We used a ball tilt switch but had reliability problems getting a contact.

Right now, unfettered idiotic Political Correctness about Mercury is the least of Europe’s problems. :astonished:

Well, come to think of it, maybe Political Correctness in some ways is actually the problem.

Grumpy-Mike: thanks for pointing out the legals of mercury. I'll switch to a ball bearing type.


I am surprised no-one has mentioned it, or did I just miss it?

The sensor you actually need to use is an accelerometer and/ or gyroscope.

Paul_B, are idea has my really intrigued I’ll have a look into those thank you.

I just had an idea of adding a flow sensor between the reg and hose, to sense the movement of air, but then comes problems with safety when high oxygen rate diving.

so i started thinking about about sensing the turbulence within a DV hose whilst the diver is breathing.
i think a similar device to a knock sensor used in cars.

I actually think a pressure switch would be easier than monitoring the air flow. I know I would hesitate using a system where my air supply might potentially fail (as home built projects tend to do every now and then), leaving me at 100ft with no air.

You need an audible warning, or else there could be many false alarms as the diver was not aware they were in a position that would trip the alarm. I'm thinking a chirp no louder than lightly tapping your knife on the tank (That's how we signal for attention to other divers).

Like Paul said, a gyroscope/accelerometer is the way to go, IF you stick with a motion based system. I really think though you'll never be able to calibrate it sufficiently to avoid it constantly or never going off. As you know, you're basically flying, constantly in motion.

For prototypes, you could apply the pressure switch to the mouthpiece and run the wires out the mouth. For the final product, though, I think you would need to get into silicon molding and have the wires and switch molded into the mouthpiece, with the wires coming out after the ziptie. That way the diver isn't inconvenienced by them.

A pressure switch may run into issues with, well, pressure. As you descend, will the water pressure trip the switch?

You have my interest piqued macca.

Doing a little research, I cannot find an already commercially available version of this idea. That may be because it's impractical/impossible. If you get one to work, you may have a legitimate product on your hands.

SCOTT makes a variety of PASS alarms that are air "powered" for SCBA's. You may want to take a look at them for ideas.

I may have to patent the idea quickly then lol.

I dont think its a system people would use or even buy.

It's likely to be an impossible idea to make function. But saying that it makes me want to make it even more

You are of cause right about an incorporated sensing device failing and then blocking air flow, it way I considered something external to the diver. Device on the hose but I'll pick up a small bite sensor and see where it takes me.

But I still can't figure out how to get the timer to work and not lock up other functions.

I still wish to add a small LCD to display battery charge remaining time.

The LCD is for the main battery which is powering the torch? You could do that but adding that kind of complexity just for a battery monitor seems excessive. Since it's underwater, the number of penetrations through the main housing must be minimised at all costs. I would try to think of solutions that use the main LED, such as 4 flashes means >75%, 3 flashes means >50% and so on. I would even try to avoid adding another button, maybe a double-tap on the main button triggers this battery-flashing mode.

The "not locking up" problem with the code will be solved by applying the principles in Several things at the same time Once you've read the first two posts in that thread, come back here if there are any more questions about that method.