Primary Display

This is the primary display for the Mk15. When everything is perking along as it should, the green "O" in the center is lit up. If the partial pressure of O2 in the loop begins to creep up, the High 1 lights up. If it creeps too low, the Low 1 lights up. If the PPO2 levels get really high, the H for High alarm lights up and if they drop really low, the L for Low Alarm lights up. If the electronics have determined that one of the sensors is reading out of range, the Alarm light to the extreme left lights up. The Velcro strap keeps the display attached to the divers left wrist and even has an extra flap to cover the lights for stealth mode.

The one thing you definitely do not want to see are all of the lights lit up at once. This is called a Christmas tree and is an indication that water has somehow entered the electronics and shorted things out. Very bad - but not fatal.

Secondary Display

The secondary display is one of the great features of the Mk15. It allows the reading from each one of the sensors to be displayed individually reading out directly in PPO2. Even if the battery is dead and the primary electronics crap out, you can still know your PPO2 and fly the unit manually. The round switch on the left end selects which sensor you are reading. In this case, I am reading sensor 3 and it reads a PPO2 of .2. The + position at the top lets you read the battery voltage.

Electronics Pod

This is the brain of the Mk15. The electronics pod houses the battery that powers the unit along with all of the electronics that make the decisions.

Electronics Pod

Here is the electronics pod removed from the unit.

Bendix

The electronics pod has four Bendix connectors feeding into it. One carries the signal from the sensors in the Center Section. The second is the output signal to the Primary Display. The third carries the signal from the switch, which turns the unit on and off. The fourth carries the signal and power to the solenoid, telling it when to fire.

Bendix

Close-up of one of the Bendix connectors. There is an o-ring seal just inside the connector that seals to the male portion of the connector. Even if the connector floods or the male connector isn't even attached, the water will not get into the inside of the pod. The pins will short out but the rest of the electronics will hopefully survive to live another day.

Bleed Screw

The bleed screw in the cap allows the pressure inside the pod to be vented as the cap is sealed into place. The bleed screw also has to be removed to get the cap off. The cap forms a very tight seal with an o-ring and the pressure from the cap closing has to be vented in order to get it into place. Don't forget to screw this baby down tight when you prep your rig for diving. One good piece of advice is to remove the screw entirely instead of just loosening it to vent the pressure. With the screw missing you won't think that the pod is sealed and it is the last thing staring at you as you close the case.

Battery

This is the battery that powers the electronics. It is relatively low tech being several AA batteries soldered together. The big power drain on the Mk15 is the solenoid. I have a low power solenoid waiting to go into this rig as soon as the new electronics arrive.

Follow this link to information on the making of this battery.

Battery Chamber

With the battery removed, you can see the rest of the battery chamber. This chamber is sealed from the rest of the electronics with an additional bulkhead. Even if you forget to tighten the bleed screw (above) the only thing you will kill is the battery. The center screw is removed to access and calibrate the electronics. They are pretty well protected and you have to screw up a lot of things to actually flood the electronics chamber.

Bendix Open

The Bendix going to primary display is connected to the electronics pod. The red band showing indicates that the connector is not completely seated.

Bendix Sealed

With the red band covered up, a clear indication is given that the connector is properly seated.