DECO BRAIN HANS HASS, the first dive computer

DECO BRAIN HANS HASS, the first dive computer
Andrea Campedelli

Produced by the Divetronic company of Liechtenstein, the Decobrain I computer is firstly marketed in 1982 with the support and sponsorship of Hans Hass. This is the first real dive computer available for the large recreational diver stalls. Although technically it is not a dive calculator, but a decompression device based on five sets of tables with 8 compartments, developed by dr. Bühlmann of Zurich university, it is able to supply data for multilevel dives; this is what differs it from simple table readers, that are only able to allow the execution square dives. Decobrain computer was a big news; it was also able to calculate altitude dives; in fact, each set to tables was used for a different altitude interval from 0 to 2500 meters at sea level. An important thing is that it used a power source composed by an NiCd rechargeable battery pack, which allowed about 80 hours of continuous functioning, with one complete charge. The road for the future development of dive computers was opened.

fig. 1 - Deco Brain prototype 1980 fig. 2 - Deco Brain prototype 1981

When turned on, the first operation that executing on the surface was to read the ambient pressure; this allowed it to determine which one of the five tables to use. Watching the instrument underwater, it was appreciated its large quadrant, where you could clearly read current depth, dive time, ascent time and time of the first decompression stop. Now we try to describe its functioning, remarkably simple and intuitive both while diving and on the surface. Let us imagine to dive; we are two minutes at the limit of non-decompression: in our Decobrain’s display, in the window of the decompression stop two zeros begin to flash, to advise that you must ascend to stay within the non-decompression curve. At this point, let us suppose we ignore this information, entering in the decompression mode: the display changes the information, to show the depth of the first stop as well as the decompression time.  

fig. 3 - The Deco Brain

Ended the dive, on the surface it is shown both the maximum depth reached and the dive time, together with the surface interval and desaturation time needed to eliminate all residual nitrogen. Decobrain I allowed also to make repetitive dives in all safety, giving information on decompression based on the interval time of the chosen table, depending on the ambient pressure detected at the beginning. But its incredibly unique characteristic was that, since it was based on table reading, Decobrain I allowed to make multi-level dives. Also, if it seems a paradox, this was made possible with the integration, into the decompression calculations, of the repetitive group designators of the chosen table, that is the coefficients used to indicate the residual nitrogen quantity present in the diver’s body at the end of the dive. The problem coming from the use of this “trick” to consider the repetitive group is that it considers only compartment of the decompression model, in our case that one of 80 minutes, while no one of the other seven compartment is considered in the calculation of the repetitive groups of the table. To consider that Decobrain I had an operative limit of 70 meters, not given by its parts or a limit imposed by the constructor, but from the depth limit of the tables used.

fig. 4 fig. 5


In 1985, Divetronic market a new model remarkably like its previous one, in its shape but different in its heart; this time not based on table reading but a true and real calculator of the decompression model. In fact, the heart of this new Decobrain is the ZHL-12 decompression model with 16 compartments, with 12 coefficients and periods from 4 to 635 minutes, developed by Dr. Bühlmann. This unit has big differences, among them the possibility to use it for altitude dives up to 4500 meters on sea level, and the fact that it sets its M values (critical over saturation limits in the single tissue compartments) based on the determined pressure. Its functioning is like the previous model; during diving, the instrument showed depth, dive time and remaining no-deco time, flashing when diver is within five minutes from the end of the non- decompression time. In a decompression dive, the first stop is shown with ascent time, while maximum dive depth is shown two times per minute, for two seconds. Ascent speed led begins to flash if 10 meter per minutes are exceeded. On the surface, when the unit was turned on, the atmospheric pressure in millibars was shown, together with a scrolling of decompression limits from 9 to 30 meters. After the dive: maximum depth, bottom time, no-fly time, total time to eliminate residual nitrogen from compartments. Later, because of some cutaneous irritation cases, together with Dr. Max Hahn a change was made to the ZHL-12 decompression model, modifying the values of some medium tissues, so that to make the original model more precautionary. After these observations, we can summarize the story of the first mass diving computer. Decobrain was produced in two versions, Decobrain I and Decobrain II, implemented with 3 software versions, that are:

2.1 for Decobrain I, which was a table calculator but, by means of a “trick”, it was also able to calculate multi-level dives.
2.2 for Decobrain II, the computed implemented with a real and serious algorithm, the ZHL-12 able to calculate all dive parameters in real time.                                   
2.3 for Decobrain II, the compuer with ZHL-12 decompression model modified by Dr. Max Hahn.

fig. 6 - The number P2-2 on the Eprom indicates the version

Since “not all doughnuts turn out with a hole”, several flooding problems arrived for Decobrain computer too. The cause was the poor manufacturing of the case used for the last series, due to an effort to reduce production costs. This proclaimed its premature production ending, at the end of 1986.

fig. 7 - Example of tables stored in Deco Brain I


This is an extract of the interview to Decobrain designer, taken from Dive Inside. The original text was shortened, mentioning only the main parts concerning Deco Brain computer.
In the long, original text, the systems used by recreational divers in the first ‘80s are mentioned, and the distrus of Deco Brain when it was presented in 1982. Jürgen Hermann,
born in Liechtenstein, tells how he discovered diving when he was young. After years of diving, he realized that the decompression scheme of the SOS analogical decompression instrument, at the top in that period, did not precisely represent the dive reality while, who used tables rarely followed them scrupulously; most of the time, people had to trust unprecise instruments or used badly for depth and time calculations. At the end, following realizations of Jürgen Hermann are mentioned, in cooperation with other dive computer manufacturers, such as MicroBrain Pro, than DC 11, DC 12 and Trac for Scubapro.

Jürgen Hermann

Dive Inside:  Jürgen, when you were at the University, did you think that you were able to build a dive computer?
Jürgen Hermann: Yes, my wish to improve things in this sector perfectly completed my professional choice; the coincidence was that at Zurich University Professor Bühlmann had a teaching post in hyperbaric medicine. He developed the dive table with his name for the Swiss Army, with which we all dived. In 1980, I changed my dissertation in programming this calculation model in one of the first intel processors.

DI:  So, Decocomputer became the subject of your dissertation?
JH: Yes however, at first, Professor Bühlmann refused. He thought it was impossible that nobody else before me tried to do it. He could not support this project. I had to find another dissertation.

DI: How did you succeed?
JH: I went to look for the person responsible of the laboratory of the pressure chamber at the University, Mr. Benno Schenk. Being an engineer, he knew well the Bühlmann calculation model; he was extremely excited about my idea so, he gave me all data of ZHL-12 calculation model. In the frame of my dissertation, I succeeded to optimize this calculation program, adapting it to the Intel 80C48 microcomputer, just born at that time.

DI:  How did you succeeded to replicate the complicate ZHL-12 calculation model?
JH: I had to write the multiplication, the division and the in- and e- functions, the Taylor series, etc. as an own mathematic library for the 80C48, to be able to numerically calculate and integrate the differential equations of ZHL-12 system. I also had to widen the 8-bit calculation range of 80C48 to a code level with 16-bit and 64-bit results, to maintain a sufficient calculation precision. After I programmed all this, I reached the capacity of 4 Kbyte Rom so, professor Bühlmann prophecy could have happen if, at this point, I was not making a small but innovative invention that, still today is used to amplify the interval of the addresses of a computer. I invented the Memory-Bank-Switching with which I could externally multiply the addressable deposit of 80C48; at this point, I added an external 8 Kbyte Rom memory, with which I widened the 80C48 deposit from 4 to 12 Kbyte. This space was enough to host the rest of the program. Intel welcomed my Memory-Bank-Switching in their application manuals, and this motivated me a lot.

DI: Today’s processors are 10.000 times volte more powerful; why modern dive computers essentially do not have more capacity of Deco Brain?
JH: Since when Intel entered in the market in 1981 with 8040 and I transferred my Dekocomputer program in it, building its hardware with the pressure sensor, signal amplifier, A/D convertor and indicator, not much changed in the calculation model.

DI: When you dived with your computer for the first time, and how did it look like?
JH: I had to house the electronics, that was built in 2 circuits (one circuit for the indicator and one for the calculator) together with the pressure sensor in a case resistant to pressure. I commissioned the case to be milled from an aluminum block; I glued its glass; I installed the on-off button and one charging connection. I put the accumulator under the button and indicator circuits. I had dived with it the first time in autumn of 1980, in Walenstadt lake in West Switzerland, then in Portofino in Italy.

 DI: How did you present your dive computer to professor Bühlmann and when?
JH: I did it at the end of October of 1980, in the laboratory of the pressure chamber of the Zurich university. Schenk and I submerged the Decocomputer in a water basin near a porthole inside the chamber, and we left it there “diving”. Professor Bühlmann established the dive profile, and he was astonished when the small aluminum box precisely indicated all data.  No-stop times, single decompression times, decompression stops, total ascend time, depth, and dive time. Also, the alarm of the ascent speed of 10 m/min correctly blinked becoming faster and faster until he bicame a constant red light at 20 m/min.

DI: What happened next?
JH:  In the summer of 1981, I founded the Divetronic AG company in Liechtenstein, completing the first 6 prototypes. In autumn, I took these prototypes to Spoga show (today called ISPO) in Koln. This first small series was housed in a case, specifically developed by Hugyfot. At Spoga, I exposed this situation to the dive team because I wanted to evaluate people’s interest of its possible sale. I also tried to understand this interest through a questionnaire in Aquanaut magazine. Results were encouraging so, I found several companies in Liechtenstein that funded me with money in exchange of Divetronic AG shares. With this money, I began producing Decocomputer in 1982, under the name of “Hans Hass Deco Brain”.

DI: How professor Hans Hass was involved?
JH: Hans Hass played a particularly important role. Firstly, after a presentation of 2 hours he gave me a check of 100.000 francs, saying: “This will help you to find other investors”. Subsequently, he created the needed trust, supporting me as my mentor and promoter. Without him I would not have founded Divetronic AG; I would not have overcome confusion and problems that followed, until our financial success. We were pioneers. We faced table, clock, and depth gauge.

DI: Did you have further problems in the next Deco Brain development?
JH: It soon resulted that the simple Bühlmann model for limited dives brought to DCS 1, with skin rushes characteristics of these case. So, I informed Doctor Max Hahn of Aquisgrana university, and transferred the calculation model in the Max calculator, which succeeded to study and improve it.  The Bühlmann/Hahn table was born. This new algorithm was adopted in the manufacturing of Deco Brain; at the end, he also found professor Bühlmann’s approval.

DI: When Deco Brain was produced? Were there manufacturing problems?
JH: Deco Brain was produced in Switzerland at the “Keller Druckmesstechnik“in Winterthur, while I was working in California to new development and new chips. When, in 1985, the case production passed to a more economic one in plastic, suggested to make cost savings, we found a contact crack from stress, for example, with soap, shampooing or big surges of temperature. It was a disaster. We received the 30% of returns of all instruments made with the new plastic, with defective cases and wet electronics; we had to sustain the exorbitant costs of substitutions and reparations; not to talk about our image damages! As a result, in 1986 we suspended the Deco Brain production.

DI: When your fist competitor arrived in the market?
JH: In the USA, in 1984, it arrived in the shops Edge of Orca. It was a mere noDecocomputer, that is it did not calculate the possible decompressiion. In case of deco obligation, it only announced the Sad (Safe Ascent Depth) or Ceiling, that is the possible ascent depth where divers had to stop for a non-indicated time. If the diver did not stop, ascending directly to the surface, the instrument gave error and blocked. The Edge of Orca was the only competitor for many years. In 1986, Orca bankrupted and was acquired by Oceanic that, in 1987 marketed its own dive computer that was also a noDeco calculator.

DI: When Uwatec arrived with Aladin?
JH: At the end of 1986. Its first version was only a noDecocomputer. Deco Brain was substituted only by Micro Brain Pro, that was marketed in 1988. It was Decocomputer fully valid. Uwatec followed in 1989 with its Aladin Pro.