Diver Dave's 3 sensor PP02 meter

OK, Divers: Here's what we've been waiting for. It's a 3-sensor PP02 meter that plugs into a P-Connector, meaning that it's plug-and-play into anyplace where a Draeger Oxygauge would fit. This is an upgrade to my old Franken-Rig for now, and will be an integral part of Franken-Son, a new rebreather that I'm building right now. The bottom line is that I was diving Franken-Rig with one PP02 meter, and that aint cool. So, I got down to brass-tacks and made something that I've been thinking about for about three years now.

Before we get to the tour, I want to give an unsolicited plug to Mark Monro. Mark has made up a series of circuit boards to allow people to build their own PP02 meters. He's got 1 sensor ones, 3 sensor ones with the battery in the display, 3 sensor versions with a remote battery, and a new one out that replaces a Mark-15 secondary. I chose the 3-sensor version with the battery in the display. Although this makes for a slightly bulkier display, I wanted it to be a simple 1-component meter, so I can move it from rig to rig without difficulty. Next, I'll build up a 3-sensor one with a remote battery, to save some space in the display. Mark's kits are great, and he's a good guy (and a recent visitor to the Diveshop of Horrors). He's got a nice website, PP02.com, and I suggest that you avail yourself of his information. I buy my 02 sensors from Pat Duffy, who has some excellent information on his Oxycheq Website. It's nice to keep our business among friends, and Mark and Pat are both members of our Rebreather List family.

Here's Mark's kit. It's a circuit board, 3 digital meters, 3 resistors, 2 magnetic switches, 3 trim potentiometers, a terminal block, and a battery holder. It's everything you need to build the meter, and he includes excellent instructions. Even a soldering-fool like myself can get this together without difficulty. But, and this is a *big* but, the kit is a LONG way away from being a complete meter. You'll need to figure out how to house it, and how to set up your sensors. That's the fun part!

The plan, as it seemed, was to figure out a way to house the displays in a length of acrylic tube, keep it all waterproof, and feed 3 sets of sensor data to the housing. This is definitely a machine-shop job. McMaster-Carr has the tube in their catalog. Once it was in hand, all it needed was a quick edging on the sander. I squared it off, and got rid of the burrs left from the chop-saw that was used at the supplier. Yes, that's cat-food on the bench. No, my wife hasn't sent me into the garage to live, that's for the old orange cat that's my tried-and-true companion through many of these adventures.

The tube is 1 1/2 inch diameter, with a 1 1/4 inch inside diameter. Here I've stuck a simple plug into one end. I was seeing how concentric the inside diameter was, and it turned out to be OK.

Well, no sense beating around the bush: Let's get the hacksaw out and hack off a few inches of black Delrin. This is also available from McMaster-Carr, and is great stuff. It's easy to machine, tough, and is my favorite material for making up rebreather parts of various sorts. You want 1 1/2 inch stuff if you want to make a system like this. It matches the outside diameter of the acrylic tube perfectly, and we'll use it later to make the sensor holder.

No joke, folks: This is the tool that you need to make one of these meters. A lathe, and the ability to use it, is *the* main set of stuff that you need to build rebreathers and all sorts of other neat stuff. This is an old 9" South Bend toolroom lathe, and has been a trusted friend for many years. Lathe's aren't all that expensive, and even the cheap Chinese imports are OK for casual use. Learning to use them is a story in itself, but trust me: Once you master one you'll be a better person. Not only that, you'll have cool stuff that you have made that all of your friends will want to steal from you. Having a lathe means never needing to buy your own Pizza on Saturday night, since all your dive-buddies will be hanging around asking you to make cool stuff for them to use.

Non-Commercial Plug: I learned how to use a lathe by trial and error, as well as by asking a few questions from experienced machinists when I got stumped. I did OK. This Christmas, Santa (My Wife), did well by buying me a series of excellent video-tapes on lathe-use from the American Gunsmith Institute. AGI has produced video-courses for Gunsmiths for years. With the overlap between Gunsmithing and Machine-Shop work, they developed a course on the Lathe, and a second one on the Milling Machine. The lathe course is *excellent*. I confirmed that many of my self-taught techniques were the correct ones, learned some shortcuts, and learned how to do a few things that I had not yet attempted. If I had gotten these tapes earlier, I would have saved a couple of years of experimentation. So, if you decide to buy a lathe, buy this course first. You'll thank me for the advice. As soon as I buy a Milling Machine, I'll buy their milling course too.

Let's make chips fly! First step is to face off the Delrin. This is going to be an end plug.

Next step is to turn the plug so it fits into the inside of the tube. You want a close fit, as it will be O-Ring sealed and you do *not* want it to leak. Get that dial-caliper out and learn how to read it.

O-Ring grooving is an acquired skill. You'll need to grind a special tool to make the cut, and get both the width and the depth exactly correct. Professionals know that one O-Ring will provide reliable sealing. That's why I used two on each end-cap! Hey, I'm not a professional, and it only took another few seconds to cut the second groove. Most of the time was spent grinding the tool.

Of course, once I had the grooves cut, I needed to pay a visit to the "Rebreather Parts Manufacturing Material Supply", better known as Sears Hardware. They have every O-Ring ever made in the plumbing section.

Now, holding the board in the tube so it doesn't float around in there requires that you cut grooves across the face of the two end plugs so that they hold the board. That's a job for a milling machine. Problem is that I don't happen to have one of those handy. What I do have is this little gizmo for my lathe, a Palmgren milling adapter. This fits the toolholder and allows the work to fit where the cutting bits are normally mounted. Then you mount the milling cutter in the chuck of the lathe and mill away. It works fine for what I do, and costs several thousand dollars less than a vertical milling machine.

So, here's one of the slots being cut. This slot is about 1/3 the way up from the bottom of the tube, if you held the tube horizontally and looked at the edge of the board as it lays in the interior of the tube.

There are two ways of connecting the housing to the sensors. One way is to simply run a length of hose between the two using hose fittings, and then run wires through the hose. This keeps the housing at ambient pressure, Bad news is that if you flood the loop, bye-bye to your electronics. The second way is to use a strain-relief, like this one. These fit into a threaded hole and will pass a cable through the bulkhead while keeping it waterproof. These are easier to use and actually are cheaper than the fittings needed for an ambient pressure system.

The key to getting a good waterproof system using a strain relief is to use good cable. You want a braided shield cable, which will have a fairly rigid diameter. This way the strain relief can grip the circumference of the cable tightly, and make a waterproof seal. Buy good cable. This stuff cost me $8.00 a foot.

I used a 6 conductor cable of 1/4 inch outer diameter. You can use a common ground wire with 3 sensors, meaning that you only need 4 conductors, but due to the design of my sensor holder, I needed dedicated pairs to each sensor. I used the red, white, and black wires for ground, and the blue, green, and orange for sensor voltage.

The next little project was to make a clone of an Oxygauge sensor holder, so it would simply plug into a P-Connector. This was another piece of Delrin, machined and O-Ring grooved as required. Here, it's about half done.

Here was another decision point: The Teledyne K1-D sensor fits the diameter of the P-Connector as shown. But, to use it like this would have meant that I needed to solder the sensor wires on, and I wanted it to be field serviceable without a soldering iron. So, I elected to orient the sensors with the faces parallel to the connector, not as shown.

		Here's Mark's kit. It's a circuit board, 3 digital meters, 3 resistors, 2 magnetic switches, 3 trim potentiometers, a terminal block, and a battery holder. It's everything you need to build the meter, and he includes excellent instructions. Even a soldering-fool like myself can get this together without difficulty. But, and this is a big but, the kit is a LONG way away from being a complete meter. You'll need to figure out how to house it, and how to set up your sensors. That's the fun part!
		The plan, as it seemed, was to figure out a way to house the displays in a length of acrylic tube, keep it all waterproof, and feed 3 sets of sensor data to the housing. This is definitely a machine-shop job. McMaster-Carr has the tube in their catalog. Once it was in hand, all it needed was a quick edging on the sander. I squared it off, and got rid of the burrs left from the chop-saw that was used at the supplier. Yes, that's cat-food on the bench. No, my wife hasn't sent me into the garage to live, that's for the old orange cat that's my tried-and-true companion through many of these adventures.
		The tube is 1 1/2 inch diameter, with a 1 1/4 inch inside diameter. Here I've stuck a simple plug into one end. I was seeing how concentric the inside diameter was, and it turned out to be OK.
		Well, no sense beating around the bush: Let's get the hacksaw out and hack off a few inches of black Delrin. This is also available from McMaster-Carr, and is great stuff. It's easy to machine, tough, and is my favorite material for making up rebreather parts of various sorts. You want 1 1/2 inch stuff if you want to make a system like this. It matches the outside diameter of the acrylic tube perfectly, and we'll use it later to make the sensor holder.
		No joke, folks: This is the tool that you need to make one of these meters. A lathe, and the ability to use it, is the main set of stuff that you need to build rebreathers and all sorts of other neat stuff. This is an old 9" South Bend toolroom lathe, and has been a trusted friend for many years. Lathe's aren't all that expensive, and even the cheap Chinese imports are OK for casual use. Learning to use them is a story in itself, but trust me: Once you master one you'll be a better person. Not only that, you'll have cool stuff that you have made that all of your friends will want to steal from you. Having a lathe means never needing to buy your own Pizza on Saturday night, since all your dive-buddies will be hanging around asking you to make cool stuff for them to use. Non-Commercial Plug: I learned how to use a lathe by trial and error, as well as by asking a few questions from experienced machinists when I got stumped. I did OK. This Christmas, Santa (My Wife), did well by buying me a series of excellent video-tapes on lathe-use from the American Gunsmith Institute. AGI has produced video-courses for Gunsmiths for years. With the overlap between Gunsmithing and Machine-Shop work, they developed a course on the Lathe, and a second one on the Milling Machine. The lathe course is excellent. I confirmed that many of my self-taught techniques were the correct ones, learned some shortcuts, and learned how to do a few things that I had not yet attempted. If I had gotten these tapes earlier, I would have saved a couple of years of experimentation. So, if you decide to buy a lathe, buy this course first. You'll thank me for the advice. As soon as I buy a Milling Machine, I'll buy their milling course too.
		Let's make chips fly! First step is to face off the Delrin. This is going to be an end plug.
		Next step is to turn the plug so it fits into the inside of the tube. You want a close fit, as it will be O-Ring sealed and you do not want it to leak. Get that dial-caliper out and learn how to read it.
		O-Ring grooving is an acquired skill. You'll need to grind a special tool to make the cut, and get both the width and the depth exactly correct. Professionals know that one O-Ring will provide reliable sealing. That's why I used two on each end-cap! Hey, I'm not a professional, and it only took another few seconds to cut the second groove. Most of the time was spent grinding the tool. Of course, once I had the grooves cut, I needed to pay a visit to the "Rebreather Parts Manufacturing Material Supply", better known as Sears Hardware. They have every O-Ring ever made in the plumbing section.
		Now, holding the board in the tube so it doesn't float around in there requires that you cut grooves across the face of the two end plugs so that they hold the board. That's a job for a milling machine. Problem is that I don't happen to have one of those handy. What I do have is this little gizmo for my lathe, a Palmgren milling adapter. This fits the toolholder and allows the work to fit where the cutting bits are normally mounted. Then you mount the milling cutter in the chuck of the lathe and mill away. It works fine for what I do, and costs several thousand dollars less than a vertical milling machine.
		So, here's one of the slots being cut. This slot is about 1/3 the way up from the bottom of the tube, if you held the tube horizontally and looked at the edge of the board as it lays in the interior of the tube.
		There are two ways of connecting the housing to the sensors. One way is to simply run a length of hose between the two using hose fittings, and then run wires through the hose. This keeps the housing at ambient pressure, Bad news is that if you flood the loop, bye-bye to your electronics. The second way is to use a strain-relief, like this one. These fit into a threaded hole and will pass a cable through the bulkhead while keeping it waterproof. These are easier to use and actually are cheaper than the fittings needed for an ambient pressure system.
		The key to getting a good waterproof system using a strain relief is to use good cable. You want a braided shield cable, which will have a fairly rigid diameter. This way the strain relief can grip the circumference of the cable tightly, and make a waterproof seal. Buy good cable. This stuff cost me $8.00 a foot.
		I used a 6 conductor cable of 1/4 inch outer diameter. You can use a common ground wire with 3 sensors, meaning that you only need 4 conductors, but due to the design of my sensor holder, I needed dedicated pairs to each sensor. I used the red, white, and black wires for ground, and the blue, green, and orange for sensor voltage.
		The next little project was to make a clone of an Oxygauge sensor holder, so it would simply plug into a P-Connector. This was another piece of Delrin, machined and O-Ring grooved as required. Here, it's about half done.
		Here was another decision point: The Teledyne K1-D sensor fits the diameter of the P-Connector as shown. But, to use it like this would have meant that I needed to solder the sensor wires on, and I wanted it to be field serviceable without a soldering iron. So, I elected to orient the sensors with the faces parallel to the connector, not as shown.