wiki/ news/ 1999-04-11/ data

LV1 Flight Data from April 11th, 1999

From the original flight of LV1, with the LV1 PIC17C74 flight computer and no low pass filters (!) or anything on the LV1 IMU. Yeeeuch.

Here's some comments from the original assembly code on the raw data output:

; Whenever the TX buffer is empty, we simply fill it with the right byte for the
; data frame. The downlink uses the 1200bps modem chip run at 2x it's rated speed
; (using a 2x crystal). This gives us 2400bps which is actually 240Bps. We would like
; to send down status, pressure and temperature at a slow data rate (2 - 10 Hz) and
; the IMU data at as high a rate as possible. After struggling with the problem, this
; seems a pretty optimal solution for a single frame:
;   00 00 00 [T] [TP] [P] {IMU} {IMU} {IMU} {IMU} {IMU} {IMU}
; where {IMU} = [Z] [ZX] [X] [Y] [YA] [A] [B] [BG] [G]. Note that each sensor reading is
; 12 bits long so the upper nibbles are stored in a common byte ([ZX] for examples).
; Each frame is 60 bytes which gives a frame rate of 4 Hz. So we get header, Pressure
; and temperature at 4Hz. The IMU data we get at 6 IMU points * 4Hz = 24Hz. Note that
; this doesn't download FC status yet.

; The frame is 60 bytes long which at 2400bps, or 240bytes/sec, is 250ms
;        2) UplinkFlg > 0 will cause the Uplink Command header to be sent
;           and at the end of ther header will set UplinkFlg = 0.
;    3) FCS = 1 sends down OneGee and BaseAlt. instead of P and T
; Normal: [00] [00] [0<FCS<F] [T]       [TP]         [P]       {IMU 1} ...   {IMU 6}

First came the 6 byte header:

 Uplink command header:  00 00 [15] [OLD FCS] [UPLINK CMD] [NEW FCS]
 FCS = 1 (on pad, not armed) header: 00 00 [01] [OneGeeL] [OneGeeH:BaseAltH] [BaseAltL]
 NORMAL Header Frame - 00 00 [1<FCS<16] [T] [TP] [P]

And then came the 54 byte IMU data:

 IMU Frame #1 - [z] [zx] [x] [y] [ya] [a] [b] [bg] [g]
 IMU Frame #2 - [z] [zx] [x] [y] [ya] [a] [b] [bg] [g]
 IMU Frame #3 - [z] [zx] [x] [y] [ya] [a] [b] [bg] [g]
 IMU Frame #4 - [z] [zx] [x] [y] [ya] [a] [b] [bg] [g]
 IMU Frame #5 - [z] [zx] [x] [y] [ya] [a] [b] [bg] [g]
 IMU Frame #6 - [z] [zx] [x] [y] [ya] [a] [b] [bg] [g]