Adding a Shearwater to a KISS

The Shearwater is a computer produced by Bruce Partridge at Shearwater Research, it is a full mixed gas computer with triple cell monitoring which can be integrated into the KISS system. The computer has four modes:

open circuit mixed gas: the simplest system, enter your gases, put a cylinder on your back and dive
closed circuit mixed gas: as above but the computer will calculate what you are breathing based on the set-point which you tell it you are using
CCR with single cell monitoring: as above but instead of basing deco calculations on a setpoint which you have told it that you will maintain, it reads the ppO2 from a single cell somewhere in the loop and calculates your deco based on what you told it you were using for diluent.
CCR with 3 cell monitoring: this monitors all three cells on the rebreather as well as doing all the deco functions

If you want to use the last two options then you need to figure out some way of connecting the computer to the loop somehow. On the KISS this isn't necessarily the easiest thing in the world to do. Bruce does sell a complete system which includes a whole new kidney and the computer hooked straight up to it. However this isn't a cheap option and it is possible to save a bit of money by trying something else.

If you have a new KISS then it is a fairly straightforward process: strip out all the wiring from the kidney leaving just the kidney with three cable glands; you need to drill holes between the centre dome and the domes to the left and right so that the new wiring can pass through; blank off two of the cable glands, the simplest way is to get a small piece of stainless or brass rod the same diameter as the cable and fit it into the glands then blob a load of aquasure either side. I bought a blank kidney which was then drilled and tapped with two M12x1.5 holes and had the connecting holes between the domes drilled in. I also have an old 1st gen kidney which has had one of the hose barbs removed, the hole enlarged and tapped to M12x1.5 and the other two barbs blanked off. More about what this is for later.

This is the kidney I started with. It is a blank kidney without any of the normal connections for the KISS displays or any of the millwork to the top surface of a standard kidney. Two holes have been drilled on the front face of it and these have been tapped for a M12x1.5 thread.

This is the underside. It looks fairly standard but what is hard to make out in the picture is that there are a couple of channels drilled between the left and right cell domes into the centre dome.

Next fit the cable gland. I have used IP68 environmentally sealed glands from Rapid Electronics. These glands are also rated to 5bar of pressure on top of the IP68 designation (Rapid do glands with a higher pressure rating but they start at M16 thread and as the kidney is at ambient pressure then the 5bar rating should be adequate). The strain relief collar should be fitted to the Shearwater cable now.

The other gland is there only to blank off the spare hole. It has been packed out and blocked with sealant. What I didn't think of at this stage was that the ADV swivel would sit right in front of it so it had to be cut down later.

Prepare some molex connectors with the ground leads fitted. If you look at the top of the connector with the guides pointed up (so it looks like a U) then the ground lead is on the left with R22D cells. I've done three but I actually only needed two.

Fit one in the cell dome furthest from the cable gland and pass the wire through the channel and into the centre dome. Pass that again into the next channel into the cell dome closest to the gland. Insert another molex into the middle dome, pass the cable through the channel and into dome next to the gland. If you have used the same colour wire as I have then mark which is which.

Fit the Shearwater cable through the gland and decide what length you want it. Cut the outer sheath away then strip away the inner braided wire sheath and finally the inner plastic film sheath.

Seperate out the wires. This is now the hard part, you need to identify which wire should connect to which cell. If you are monitoring three cells then the Shearwater reads one wire from each of the cells and a common ground lead, so the computer uses four wires. If you are using a Shearwater cable from Tecme then it has seven cores so obviously three of these are useless, one is the ground lead and three are the cell leads. On the Shearwater website it describes the pin layout for the Fischer connector to the computer, however it is pretty useless as there are seven pins on the Fischer connector and there is no diagram of which is which.

You now need to identify which lead is which. On mine, the ground was blue and the cell wires were green, white and brown. This may or may not be the same as yours. How I did it:

- take a cell and fit a molex with two leads coming out with stripped ends
- switch on the Shearwater and put it into external cell monitoring mode. It will read 0.00 on all three cells
- connect the cell leads to any two of the cable cores
- switch the computer to millivolt mode
- look for a reading on one cell
- if you get a reading then note which cores they were
- work your way through the other five cores

With a bit of trial and error you can work out which is the ground lead and which are the cell leads.

If you haven't lost the will to live by this point then it's probably a good time for a beer. Now that you have ID'd which are the good cores and which are dead, cut back the dead ones.

Pull the cable out until the outer sheath is just inside the dome. Tighten the strain relief down on to the gland to secure the cable. If your gland has a torque setting on the data sheet then use it because some are very easily broken.

Hook the Fischer cable up to the Shearwater, switch it on and make sure it is in external cell monitoring mode.

If you haven't already done so then you need to ID which lead corresponds with which cell on the display. It doesn't really matter but it does make a bit of logical sense if the cells are in the same sequence on the Shearwater display as they are on the KISS head. Fit a molex with two leads on to a cell, hook the cell's ground to the Shearwater ground and the other to one of the cell leads.

Check the Shearwater and note which position it lights up on the display. Depending on whether or not the Shearwater has previously had a good calibration then you may not get a reading, if this is the case then switch to millivolt mode.

When you have ID'd which wire is which then mark it and insert it into the correct dome.

Crimp a pin on to the cell lead nearest the gland. On the other two, crimp pins on to the ends of the cell leads and fit them into the molexes which have been previously fitted to the ground leads.

Splice the two ground leads together.

Splice in the ground lead from the Shearwater cable into the other grounds. If you can get away with it then crimp a pin on the end and fit the bundle of wires into the last molex. I couldn't get a secure connection this way so I ended up splicing a short lead on to the ground wire bundle, putting a load of solder on the joint and then a lump of heatshrink on top with a blob of aquasure. I crimped a pin on to the other end of the lead and fixed that into the molex.

And there is the end result. You should have three molex connectors in three domes.

Hook up the three cells and switch on the Shearwater. You should get a reading on all three cells. It doesn't really matter what the readings are at this stage as long as they are there. If the Shearwater hasn't been calibrated then there may not be any reading. Either way, switch it to millivolt mode and check the values. You should be getting in the region of 10.5mV on each cell. Blow some O2 onto each cell, the mV should get up to 49-50.

Fit the cells into the head. Fit the o-rings on to the turrets of the kidney then fit the kidney on to the head. With the rebreather fully assembled do a positive check and watch for leaks round the gland.

With the Shearwater switched on, flush the loop with oxygen and do a calibration on the Shearwater. Disconnect the exhale hose and breathe from the DSV, forcing fresh air into the loop. Check that the Shearwater display drops back to the 0.21 (or thereabouts).

So that's it, you now have triple cell monitoring on the KISS. Things I don't like: I'm still not convinced about doing away with the three independant cells of the CK. I don't like that the Shearwater uses a common ground lead, if that goes then I lose all my cells. I don't like that there are only two decimals on the display, the flickering third digit on the Jetsam displays tells you that they are still working. On a system that relies on some digital processing of the signal then I'm slightly uncomfortable that I don't have anything telling me it is still working. The displays stay too steady for me. It is also one seriously big brick.

I bought the Shearwater as a replacement for the Jetsam displays which I found were becoming increasingly unreliable. I also wanted something backlit for cave diving on a scooter -- my old displays are the original non-backlit versions which are just about impossible to scooter with if you are in the dark. The deco calculation was a bonus but I can live without it (managed fine for three years on the CK before) so the display function was my primary motivation for shelling out. But since fitting the Shearwater I am not convinced that it is the right tool for the job. I know a lot of people will disagree with me but I don't think it is a primary display if you don't have anything else. I'm not sure I'd be comfortable with just a HUD as a secondary display either, to me it's a graphic and easily readable supplement to the primary.

Hence the reason for having the other kidney modifed. My next plan is to fit a Shearwater cable to it and use either a triple or double Jetsam display as a secondary. The other option is single cell monitoring by the Shearwater and retain a double Jetsam display.

	This is the kidney I started with. It is a blank kidney without any of the normal connections for the KISS displays or any of the millwork to the top surface of a standard kidney. Two holes have been drilled on the front face of it and these have been tapped for a M12x1.5 thread.
	This is the underside. It looks fairly standard but what is hard to make out in the picture is that there are a couple of channels drilled between the left and right cell domes into the centre dome.
	Next fit the cable gland. I have used IP68 environmentally sealed glands from Rapid Electronics. These glands are also rated to 5bar of pressure on top of the IP68 designation (Rapid do glands with a higher pressure rating but they start at M16 thread and as the kidney is at ambient pressure then the 5bar rating should be adequate). The strain relief collar should be fitted to the Shearwater cable now. The other gland is there only to blank off the spare hole. It has been packed out and blocked with sealant. What I didn't think of at this stage was that the ADV swivel would sit right in front of it so it had to be cut down later.
	Prepare some molex connectors with the ground leads fitted. If you look at the top of the connector with the guides pointed up (so it looks like a U) then the ground lead is on the left with R22D cells. I've done three but I actually only needed two.
	Fit one in the cell dome furthest from the cable gland and pass the wire through the channel and into the centre dome. Pass that again into the next channel into the cell dome closest to the gland. Insert another molex into the middle dome, pass the cable through the channel and into dome next to the gland. If you have used the same colour wire as I have then mark which is which.
	Fit the Shearwater cable through the gland and decide what length you want it. Cut the outer sheath away then strip away the inner braided wire sheath and finally the inner plastic film sheath.
	Seperate out the wires. This is now the hard part, you need to identify which wire should connect to which cell. If you are monitoring three cells then the Shearwater reads one wire from each of the cells and a common ground lead, so the computer uses four wires. If you are using a Shearwater cable from Tecme then it has seven cores so obviously three of these are useless, one is the ground lead and three are the cell leads. On the Shearwater website it describes the pin layout for the Fischer connector to the computer, however it is pretty useless as there are seven pins on the Fischer connector and there is no diagram of which is which. You now need to identify which lead is which. On mine, the ground was blue and the cell wires were green, white and brown. This may or may not be the same as yours. How I did it: - take a cell and fit a molex with two leads coming out with stripped ends - switch on the Shearwater and put it into external cell monitoring mode. It will read 0.00 on all three cells - connect the cell leads to any two of the cable cores - switch the computer to millivolt mode - look for a reading on one cell - if you get a reading then note which cores they were - work your way through the other five cores With a bit of trial and error you can work out which is the ground lead and which are the cell leads.
	If you haven't lost the will to live by this point then it's probably a good time for a beer. Now that you have ID'd which are the good cores and which are dead, cut back the dead ones.
	Pull the cable out until the outer sheath is just inside the dome. Tighten the strain relief down on to the gland to secure the cable. If your gland has a torque setting on the data sheet then use it because some are very easily broken.
	Hook the Fischer cable up to the Shearwater, switch it on and make sure it is in external cell monitoring mode.
	If you haven't already done so then you need to ID which lead corresponds with which cell on the display. It doesn't really matter but it does make a bit of logical sense if the cells are in the same sequence on the Shearwater display as they are on the KISS head. Fit a molex with two leads on to a cell, hook the cell's ground to the Shearwater ground and the other to one of the cell leads.
	Check the Shearwater and note which position it lights up on the display. Depending on whether or not the Shearwater has previously had a good calibration then you may not get a reading, if this is the case then switch to millivolt mode.
	When you have ID'd which wire is which then mark it and insert it into the correct dome.
	Crimp a pin on to the cell lead nearest the gland. On the other two, crimp pins on to the ends of the cell leads and fit them into the molexes which have been previously fitted to the ground leads. Splice the two ground leads together.
	Splice in the ground lead from the Shearwater cable into the other grounds. If you can get away with it then crimp a pin on the end and fit the bundle of wires into the last molex. I couldn't get a secure connection this way so I ended up splicing a short lead on to the ground wire bundle, putting a load of solder on the joint and then a lump of heatshrink on top with a blob of aquasure. I crimped a pin on to the other end of the lead and fixed that into the molex.
	And there is the end result. You should have three molex connectors in three domes.
	Hook up the three cells and switch on the Shearwater. You should get a reading on all three cells. It doesn't really matter what the readings are at this stage as long as they are there. If the Shearwater hasn't been calibrated then there may not be any reading. Either way, switch it to millivolt mode and check the values. You should be getting in the region of 10.5mV on each cell. Blow some O2 onto each cell, the mV should get up to 49-50.
	Fit the cells into the head. Fit the o-rings on to the turrets of the kidney then fit the kidney on to the head. With the rebreather fully assembled do a positive check and watch for leaks round the gland. With the Shearwater switched on, flush the loop with oxygen and do a calibration on the Shearwater. Disconnect the exhale hose and breathe from the DSV, forcing fresh air into the loop. Check that the Shearwater display drops back to the 0.21 (or thereabouts).