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The MARS Altimeter Project - Update November 2006

I will be doing another pcb revision and build this winter. The circuit will be unchanged but some improvements in trace layout will be made. This unit has been flown several times now and has proven to be pretty robust. If you are interested in getting one, let me know so I can get an idea of how many boards to order. This is a non-committal indication, I am just trying to get an idea. The units will be assembled and tested. Cost will be between $50 and $65. Email your interest and questions to: jderimig@rochester.rr.com

The goal of this project is to give our members a low cost way to get into dual deployment electronics and learn at the same time. The target cost would be in the area of $35.Low cost does not mean a stripped down unit. Since I will be using this altimeter for my flights, I did not want to skimp on any functionality.

Well we have a full season of flights and learned somethings to modify the design a little. Here is what we learned...

    1. The algorithm and circuit works well, no changes need to be done there.
    2. Keeping separate power rails (9v and 5v) for the firing circuit and logic introduced a subtle failure mode if the power comes up noisily like twisting wires for arming. This has been corrected with a software modification and tuning the storage capacitance on both rails.
    3. Through hole mounted components are more susceptible to damage due to handing and “rough” flight events like catoing motors. Surface mount is the way to go at the expense of assembly for DIYers.
    4. Separate battery option for pyro channel has low value for most applications, should be using low current matches.

Given these learnings and others, here are the modifications for the MARS Altimeter Version 2.

    -Eliminate the separate pyro battery option and its connector.
    -Use surface mount for most components (except micro)
    -Provide integrated option for arming switch
    -Enable up to 8 options via dipswitch (mach timing, alt selection and ground test mode)
    -Add extensive ground plane for further noise suppression.
  • Dual deployment controller.
  • Ultra reliable operation.
  • 2 selectable main altitude settings
  • Mach timer
  • Record peak altitude and velocity
  • Extensive self-test, continuity, battery and sensor health.
  • Can fit inside 38mm airframe.
  • Ground test mode

Cost Update: (as of 9/18/2006)

Parts and PCB Board: $45.00
Assembled and tested: $65.00

On the left side of the board is the 4 terminal power connector. The battery connects to position 1 and 2, the altimeter arming swtich attaches to position 3 and 4. At the top of the board is a Schottky diode for polarity protection along with the two energy storage capacitors, one for each ps rail.

Next a column of SMD resistors highlights the MPX4115 signal conditioning.  On the right side of the board are the pyro channel connectors which is driven by the dual Hexfet smd capable of supplying 10A per pyro channel.

Here is a picture of the new MARS altimeter.
Improvements from previous version is extensive use of SMD (surface mount devices) which are more mechanically rugged than through hole leaded components. Also the board can be coated with a laquer that will protect the componets from corrosive ejection charge residue in the event of ebay leaks.