X-Git-Url: https://git.gag.com/?p=fw%2Faltos;a=blobdiff_plain;f=doc%2Fmicropeak.xsl;h=91126ce520a366d1842a4a52da70a06a91a7f1de;hp=556700c089e3de8ae08354bcea584a812c06e6f1;hb=c8866fbae2b00b1d7a7ddf89a3f971a75d3dcd60;hpb=f7d2613bb0a6ab1c63e3f6252a3a2358fdfbc691;ds=sidebyside diff --git a/doc/micropeak.xsl b/doc/micropeak.xsl index 556700c0..91126ce5 100644 --- a/doc/micropeak.xsl +++ b/doc/micropeak.xsl @@ -30,6 +30,20 @@ Initial release with preliminary hardware. + + 1.0 + 18 November 2012 + + Updates for version 1.0 release. + + + + 1.1 + 12 December 2012 + + Add comments about EEPROM storage format and programming jig. + + @@ -70,7 +84,8 @@ NAR #88757, TRA #12200 preparing a soft cushion of wadding inside a vented model payload bay. Wherever you mount it, make sure you protect the barometric sensor from corrosive ejection gasses as those - will damage the sensor. + will damage the sensor, and shield it from light as that can + cause incorrect sensor readings. @@ -115,8 +130,7 @@ NAR #88757, TRA #12200 - Recover the data. Turn MicroPeak off for a couple of seconds - (to discharge the capacitors) and then back on. MicroPeak + Recover the data. Turn MicroPeak off and then back on. MicroPeak will blink out the maximum height for the last flight. Turn MicroPeak back off to conserve battery power. @@ -141,14 +155,13 @@ NAR #88757, TRA #12200 to keep conductive material from coming in contact with the exposed metal elements. - The barometric sensors used in MicroPeak is - sensitive to sunlight. Please consider this when - designing an installation, for example, in an air-frame with a - see-through plastic payload bay. Many model rockets with payload bays - use clear plastic for the payload bay. Replacing these with an opaque - cardboard tube, painting them, or wrapping them with a layer of masking - tape are all reasonable approaches to keep the sensor out of direct - sunlight. + The barometric sensor used in MicroPeak is sensitive to + sunlight. Please consider this when designing an + installation. Many model rockets with payload bays use clear + plastic for the payload bay. Replacing these with an opaque + cardboard tube, painting them, or wrapping them with a layer of + masking tape are all reasonable approaches to keep the sensor + out of direct sunlight. The barometric sensor sampling ports must be able to "breathe", @@ -204,7 +217,7 @@ NAR #88757, TRA #12200 Lithium Battery The CR1025 battery used by MicroPeak holes 30mAh of power, - which is sufficient to run for over 15 hours. Because + which is sufficient to run for over 40 hours. Because MicroPeak powers down on landing, run time includes only time sitting on the launch pad or during flight. @@ -266,6 +279,118 @@ NAR #88757, TRA #12200 serve to further protect the switch from launch forces. +
+ On-board data storage + + The ATtiny85 has 512 bytes of non-volatile storage, separate + from the code storage memory. The MicroPeak firmware uses this + to store information about the last completed + flight. Barometric measurements from the ground before launch + and at apogee are stored, and used at power-on to compute the + height of the last flight. + + + In addition to the data used to present the height of the last + flight, MicroPeak also stores barometric information sampled + at regular intervals during the flight. This information can + be extracted from MicroPeak through any AVR programming + tool. + + + MicroPeak EEPROM Data Storage + + + + + + + Address + Size (bytes) + Description + + + + + 0x000 + 4 + Average ground pressure (Pa) + + + 0x004 + 4 + Minimum flight pressure (Pa) + + + 0x008 + 2 + Number of in-flight samples + + + 0x00a … 0x1fe + 2 + Instantaneous flight pressure (Pa) low 16 bits + + + +
+ + All EEPROM data are stored least-significant byte first. The + instantaneous flight pressure data are stored without the + upper 16 bits of data. The upper bits can be reconstructed + from the previous sample, assuming that pressure doesn't + change by more more than 32kPa in a single sample + interval. Note that this pressure data is not + filtered in any way, while both the recorded ground and apogee + pressure values are, so you shouldn't expect the minimum + instantaneous pressure value to match the recorded minimum + pressure value exactly. + + + MicroPeak samples pressure every 96ms, but stores only every + other sample in the EEPROM. This provides for 251 pressure + samples at 192ms intervals, or 48.192s of storage. The clock + used for these samples is a factory calibrated RC circuit + built into the ATtiny85 and is accurate only to within ±10% at + 25°C. So, you can count on the pressure data being accurate, + but speed or acceleration data computed from this will be + limited by the accuracy of this clock. + +
+
+ MicroPeak Programming Interface + + MicroPeak exposes a standard 6-pin AVR programming interface, + but not using the usual 2x3 array of pins on 0.1" + centers. Instead, there is a single row of tiny 0.60mm × + 0.85mm pads on 1.20mm centers exposed near the edge of the + circuit board. We couldn't find any connector that was + small enough to include on the circuit board. + + + In lieu of an actual connector, the easiest way to connect to + the bare pads is through a set of Pogo pins. These + spring-loaded contacts are designed to connect in precisely + this way. We've designed a programming jig, the MicroPeak + Pogo Pin board which provides a standard AVR interface on one + end and a recessed slot for MicroPeak to align the board with + the Pogo Pins. + + + The MicroPeak Pogo Pin board is not a complete AVR programmer, + it is an interface board that provides a 3.3V regulated power + supply to run the MicroPeak via USB and a standard 6-pin AVR + programming interface with the usual 2x3 grid of pins on 0.1" + centers. This can be connected to any AVR programming + dongle. + + + The AVR programming interface cannot run faster than ¼ of the + AVR CPU clock frequency. Because MicroPeak runs at 250kHz to + save power, you must configure your AVR programming system to + clock the AVR programming interface at no faster than + 62.5kHz, or a clock period of 32µS. + +