This barometric apogee sensor was built as more reliable rocket apogee sensor than the UV sensor while still keeping the things as simple as possible … nevertheless this barometric apogee sensor is quite universal and could find different applications in the amateur rocketry. The specifications are:
– barometric apogee detection
– high noise immunity through hardware and software filtering
– false start condition detection
– ignition at apogee – Jumper is OFF
– ignition at 100m above the ground after the apogee was reached – jumper is ON
– 1 high current output
– 3 seconds on-time
– igniter integrity indicator
– low current consumption – about 11mA
– 8v to 12v power supply
– 7.4v LIPO can be used with small modification
– 4.5gr weight
– 23x15x10 mm size
The electrical schematic is very simple and all components are easily obtainable. If the sensor is to be used with a 7.4v LIPO battery then D3 should be replaced by a 0 Ohm resistor or bridge. Keep in mind that R3 and D2 which represent the igniter integrity circuit allow about 2mA to flow through the load at all time – normally this is not a problem, but if you have a really sensitive igniter you can increase the R3 value up to 8-10 kOhm and further reduce the current.
As you can see this barometric apogee detector have very small dimensions – about the size of a SIM card and only 4.5 grams. Due to its small dimensions and functionality it could be used to open the parachute at apogee, it could be used in dual parachute systems to open the second parachute at 100m above the ground, it can be used for recovery of rocket stages etc.
The actual use of the sensor is very simple:
– If the jumper is removed, then the sensor will turn switch on the output at apogee, if the jumper is present then sensor will fire when 100 meters above the ground after the apogee are reached.
– If the LOAD LED is on when the igniter is connected then the circuit is not interrupted. If the LOAD LED is off when the igniter is connected then there is something wrong with the igniter.
– When you switch on the device, a solid ST LED means that the device is still looking for stable basic pressure and it is making calculations. The maximum time that it could take to finish all calculations is about 30 seconds and you should not launch the rocket while the device is making calculations.
– Once the calculations are finished (it could take up to 30 seconds but no more than that) the ST LED will start blinking slowly meaning the device is ready for launch but no rocket launch is detected.
– When the rocket is launched and the apogee barometric sensor detects this, the ST LED will start blinking fast which means the device is in flight mode and looking for apogee or 100m above the ground after apogee in order to fire the output.
The high noise immunity and faulty start trigger prevention is achieved by using high data averaging rate, low ADC resolution (10 bits ADC) and the following logical decision algorithm:
The necessary firmware for the microcontroller and the PCB manufacturing files are attached here: