X-Git-Url: https://git.gag.com/?a=blobdiff_plain;f=doc%2Fmicropeak.xsl;h=aa1adaef9f57a2bc64d34033c301abe3662dd3a5;hb=d663da13db60e1200535282ee1a0ea6305cad98c;hp=556700c089e3de8ae08354bcea584a812c06e6f1;hpb=f7d2613bb0a6ab1c63e3f6252a3a2358fdfbc691;p=fw%2Faltos
diff --git a/doc/micropeak.xsl b/doc/micropeak.xsl
index 556700c0..aa1adaef 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.
@@ -217,10 +230,10 @@ NAR #88757, TRA #12200
with the negative battery terminal.
- Shipping restrictions prevent us from including a CR1025
- battery with MicroPeak. Many stores carry CR1025 batteries as
- they are commonly used in small electronic devices such as
- flash lights.
+ Shipping restrictions may prevent us from including a CR1025
+ battery with MicroPeak. If so, many stores carry CR1025
+ batteries as they are commonly used in small electronic
+ devices such as flash lights.
@@ -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 Ã
+ 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.
+
+