The dive computer is now in the final phase.

After many small projects, there is now a plan.

Images, hardware and software will follow soon.

Universal AVR ATmega board

For many new projects, is a universal board useful as a development platform.

Therefore, the board has been generated, a ATMega (32/64), 2 OP-Amp’s and includes a display.


The op-amps are wired back to the amplification of small signals (eg O2 sensors) with amplification factor of 20.

As Shown are 2 × 16 × 16 or 4 line LCD display is used.

For input two keys are available (eg for a menu).

An ISP programming header is also present, may be programmed directly from AVR Studio.

For output signals are 6 ports brought out.

A 5 V voltage regulator is also provided, as well as the wiring of the internal reference voltage for the AD converter

The ATMega is powered by an external crystal of 8Mhz

Ansicht der Universalplatine, links die CPU Platine mit allen I/O’s, rechts die Anzeige 4×16 Zeichen LCD Universalplatine

O2 sensor measurement chamber

Selbstbau eines O2 Sensoren Testers

From the project OLED HUD came the idea to build one O2 sensors tester.
O2 sensors age with time (galvanic cell) and thus have no more linear characteristic. Especially in the range of pO2> 1.0 Curves then fall flat, or the sensor reaches 1.6 pO2 not even the final value.

To test this, sensors may therefore be a pressure-tight measuring chamber in and out with compressed air (max 9 bar of regulators) is applied. The pressure increase is a fixed flow allows small to (pressure increase over time).

The sensors are measured while the electronics and values on the display graphically illustrated them. This allows linearity and full scale (1.6pO2) is determined to be very good.

What features are realized

  • Indication of the measured chamber pressure
  • Display of three sensors
  • Representation of the measurement graphically in real time
  • Display of measurement for each sensor (stored values, offline replay)
  • Start and stop of measurement
  • Termination of the measurement

The first consideration was now the chamber with oxygen filled. Good idea, but has a hook :-) is because in the time in which the measuring chamber filled to 100% oxygen, there is no increase in pressure in the chamber (ambient) only when the chamber is closed (solenoid valve) causes a pressure increase, which can then be recorded and the pressure sensor. This results in pO2 = 1.0 to no curve on the display. (Y = const pressure, x = sensor value rises)

So now air was selected as the measuring medium. The pressure chamber is closed and the pressure continues to rise (Y-axis pressure is increasing with time). In a final value of about 9 bar, the sensors should then reach a pO2 of 9 x 12:21 = 1.89 pO2. This results in a series of measurements can, the pressure increase delayed by a needle valve (about 0.5 liters per minute).

The O2 sensor electronics.Everything is still on an experimental board. The display is 160 × 160th  Processor is a ATMEGA32 AVR. On display also is the pressure sensor. This is yet replaced by another (10bar).
The display in detail.  It can be seen, the coordinate system.  Among them, in real time, pressure and displays the three sensor values.
View of the measuring chamber (still in its raw state), the material is milled from extra thick, because it can withstand a pressure of 9 bar is. Messkammer

homemade OLed HUD for CCR Rebreather

Why building a HUD itself?

The HUD on the market are usually implemented with one or more single or multi-colored LED’s. An article on rebreatherworld.com came the idea of a HUD from a miniature OLED build.


I found them in a large auction house and obtained a 0.95 “color OLED graphic. It uses the SSD1331 controller for which there was already finished in the net libraries (www.microcontroller.net).

Served as control electronics, the circuit foundation stone of the dive computer.  However, it should all fit in a “can” of TecMe.
Therefore, the circuit has been realized in SMD.

In the can even fit a standard battery LiIo what the power supply of course easier.

What features has the OLED_HUD

  • The operation is done inside the enclosure via a “joystick” to perform the “Select”, “up”, “down”, “Yes”, “No”.
  • Manual brightness adjustment of the display
  • Displays battery voltage
  • Display height above sea level (barometric altitude formula)
  • Display of three oxygen sensors in a large font
  • Show the cell voltage in a small font
  • Calibration with Air
  • Calibration with 100% O2
  • Altitude mode selection in 500m steps
  • Power off (Sleep Mode)

The display then changes its colors of pO2:

RED: is <0.65 and> 1.5

YELLOW: when> = 0.65 to <1.1 and> 1.3 to <= 1.5

GREEN: when> = 1.1 and <= 1.3

The heading “pO2” will change your color accordingly, being always the “most” dangerous color appears.

The OLED HUD electronics.
The display in detail. It is attached to a Dolphin mouthpiece. Possible to see the three sensors in pO2 (red) behind the sensor voltages.