+
+## Problems ##
+
+* The CC1111F32 is a 36-pin QFN package, which necessitates reflow
+ soldering. Since we needed to reflow solder anyway, and because TI used
+ them in their reference design, we went a little crazy and used 0402
+ passive parts everywhere. That means working under a microscope to
+ place parts! Without an inspection microscope, loading and testing these
+ boards might be impossible.
+
+* The addition of on-board GPS in v0.2 means that the total power consumption
+ can exceed the rate at which we draw power from the USB interface,
+ particularly when the GPS is in cold start mode. This means a battery must
+ be attached during operation, and also that the battery will only charge
+ effectively from USB when the board is turned off.
+
+## History ##
+
+### v0.2 ###
+
+These are photos of our second version, which included the integrated Venus
+GPS receiver, but with a passive patch antenna that turned out to have
+disappointing performance due to our many PCB geometry constraints. It also
+used a voltage regulator with less capacity which we felt was marginal for
+supporting the companion boards we have planned:
+
+<a href="v0.2/cimg5164-cropped.jpg"> <img src="v0.2/cimg5164-thumb.jpg"></a>
+<a href="v0.2/cimg5171-cropped.jpg"> <img src="v0.2/cimg5171-thumb.jpg"></a>
+
+Other than cleaning up the silkscreen, the differences between v0.2 and our
+current v1.0 boards were really quite small:
+
+* 100ma LDO regulator instead of the current 150ma part
+* no C38 footprint
+* different value for C36 reset capacitor
+
+The schematics and PCB artwork for this version are on the v0.2 branch in
+our git repository, here are pdf copies for easy reference:
+
+ * [schematic](v0.2/telemetrum.pdf)
+ * [pcb artwork](v0.2/telemetrum.pcb.pdf)
+ * [bill of materials](v0.2/partslist.csv)
+
+### v0.1 ###
+
+And this is a photo of our original board with serial port for off-board GPS,
+without the big off-board 1000uF cap from the original ejection circuit:
+
+<a href="v0.1/loadedpair.jpg"> <img src="v0.1/loadedpair-thumb.jpg"></a>
+
+The differences between v0.1 and later boards were substantial:
+
+* 2.5 x 1 inch board with all parts mounted on one side
+* 4-pin PicoBlade serial port connector for attachment of external GPS module
+* USB connector projected approximately 3mm over the edge of the board
+* Debug connector used 4 IC socket pins on 100 mil centers
+* no companion board interface
+* 50ma LDO regulator on early boards, later boards used a 100ma part
+* [Microchip 25LC1024](http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en520389) CMOS serial EEPROM instead of DataFlash
+ * 128k x 8
+ * SPI interface
+* [Microchip MCP9700A](http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en027103) discrete temperature sensor
+* used 1000uF electrolytic capacitor charged to 5V for pyro supply
+* two LEDs instead of one attached to CPU
+
+The elimination of the discrete temperature sensor and second LED were
+necessary to support the companion board interface added in v0.2.
+
+The v0.1 artwork had three issues, two of which required physical rework
+on each board. All of these issues were fixed in v0.2.
+
+* The USB connector footprint was placed wrong, so that the
+ connector hung out over the edge of the board instead of being
+ flush.
+* We needed chip select on the SPI memory. To fix that, we gave up the
+ ability to put the accelerometer into self-test mode and used that
+ GPIO line to pull chip select on the memory, which required two
+ cuts and two jumpers.
+* The igniter sense circuits each needed a second resistor to
+ complete the voltage divider so our 3.3V CPU ADC could read the
+ 5V ejection voltage. This was fixed by changing two resistor
+ values, and tacking two additional resistors onto the board
+ with jumpers to ground.
+
+The schematics and PCB artwork for this version as of the working-v0.1 tag
+are available here are pdf copies for easy reference:
+
+ * [schematic](v0.1/telemetrum.pdf)
+ * [pcb artwork](v0.1/telemetrum.pcb.pdf)
+ * [bill of materials](v0.1/telemetrum.bom)
projects / web / altusmetrum / blobdiff