This small flight computer is the same computer as my MINI FLIGHT COMPUTER (BREO M) but it has two more powerful MOSFET transistors instead of the small ones I used on BREO M and the mounting holes are 4 at the corners instead of 2 in the middle which makes it much easier to solder and to install in the rocket.
In order to fit the two larger D-PACK MOSFETs I had to increase the width with 5 mm so the new dimensions are 60x20x15 mm. Nevertheless, BREO N still has the same excellent functionality as BREO M. The main characteristics are:
– Barometric altitude measurement up to 18km
– High g acceleration sensor
– 40 samples per second / 13 bit ADC
– 3.5 minutes recording time
– Igniters connectivity check for both channels (LEDs for each channel will show the status of the igniter)
– USB connection
– 7.5 to 16 VDC power supply with on-board ON-OFF switch
– 10A (40A pulse) MOSFET for each channel
– Selectable on-time for each channel (between 0.1 and 5 seconds)
– Each channel has igniter connectivity feedback for back-up purposes (one channel can substitute the other in case a defective igniter is detected during flight)
– 2 individually programmable outputs where each output can be set up for one of the following events:
1.DISABLED – Output won’t fire
2.TIME – Fire after the time elapsed (in seconds)
3.ALTITUDE – Fire as soon as the predetermined altitude is reached (in meters)
4.APOGEE-IMMEDIATELY – Fire at apogee
5.APOGEE-TIME DELAY – Fire n seconds after apogee
6.APOGEE-ALTITUDE – Fire at a predetermined altitude after the apogee has been reached (in meters)
7.STAGE BURNOUT – Fire as soon as the initial acceleration falls below 1 (motor burnout)
As I said compared to BREO M, the new flight computer, BREO N is slightly larger and about 50% heavier (12gr instead of 8gr) because of the MOSFETs.
The schematic for BREO N remains the same:
Of course the PCB is different:
The firmware which has basically three main parts – USB part, on-the-field maximum altitude calculation and the flight mode is the same as for BREO M.
And regarding the PC software, the both devises share the same program.
The flight computer passed so far the testing in my improvised barometric chamber and I hope soon to be tested in a real flight.
RocKI (http://kia-soft.narod.ru) mentioned a situation where a false start condition could trigger the flight computer. As a result the computer could be fooled and the ejection charge could be fired untimely. This situation arises when the electronic bay is tidily closed and the next bay is mounted on the top by pressing it down. This acts much like a piston and temporarily increases the pressure in the electronics bay. As soon as the pressure starts falling down to equalize with the surrounding pressure and if this is combined with a strong shaking of the rocket, then the start detecting algorithm will be fooled that the rocket is launched.
To avoid this problem I made some modifications in the firmware start detection algorithm – now it is much harder to have a faulty start triggering. However as a result of the new algorithm you should allow about 30 seconds between switching on the flight computer and launching the rocket. This time is necessary for the flight computer to make some additional calculations. Launching before those 30 seconds have elapsed could result in faulty initial calculations and this could have detrimental consequences.