# TeleMetrum History
## v0.1 ##
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. All
v0.2 boards were hand-assembled by Bdale.
The v0.1 board was
significantly different than later versions, in both mechanical and
circuit terms.
* 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
* 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
* a dual LED instead of just one attached to the CPU
The v0.1 artwork had three issues, two of which required physical rework
on each board, all of which 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 as pdf copies for easy reference:
* [schematic](v0.1/telemetrum.pdf)
* [pcb artwork](v0.1/telemetrum.pcb.pdf)
* [bill of materials](v0.1/telemetrum.bom)
## v0.2 ##
These are photos of our second version. All v0.2 boards were hand assembled
by Bdale:
Lots of things were different from v0.1. Perhaps the biggest change was
integrating a Venus GPS receiver and a passive patch GPS antenna. This
required stretching the board length to 2.75 inches, and changing the layout
to put through-hole parts on the opposite side from
the surface mount parts. While we were at it, things were rearranged to put
tall parts near the center and not on the board edges so that boards could
be mounted in smaller diameter tubes.
Another significant change was adding a "companion" port, intended to support
expansion boards but also possible to use as a programming interface. With
a suitable cable, the presence of the companion port allowed any TeleMetrum
board to be used to re-program any other TeleMetrum or TeleDongle
board. Elimination of the discrete temperature sensor and second LED were
necessary to free up the pins needed for the companion interface.
We also changed to a different flash memory chip with 1 megabyte of storage.
Issues with the v0.2 boards included:
* The passive GPS antenna turned out to have disappointing performance due
to our many PCB geometry constraints.
* The initial voltage regulator on v0.2 boards was a 100mA part. Once we
realized how much power the GPS receiver needed to achieve initial lock,
we switched to a 150mA part.
* The reset circuit worked well for the cc1111 but was marginal for the GPS
chip .. sometimes the board would have to be power cycled several times
to get the GPS to come up correctly.
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)
## v1.0 ##
These are photos of our third version, which was our first production
build. By the time we understood what we wanted to change in v0.2, things
worked
well enough that every time we went to a launch someone would ask about
buying boards from us. So in January 2010, Keith and Bdale made the decision
to produce enough boards to sell some to others. These were sold between April
and December 2010, and performed very well.
The changes from v0.2 were fairly small. The value of the reset capacitor
changed to increase the probability of the GPS chip coming up correctly, and
we moved to using a Taoglas amplified patch antenna attached to the U.FL
connector instead of the passive GPS patch antennas.
There were really only two issues with the v1.0 boards that annoyed us. The
first was
that the reset circuit still wasn't satisfying. The GPS chip would sometimes
fail to initialize, particularly in hot weather. The second was that
fluctuation of the 3.3 volt power rail correlated with radio transmission
induced noise patterns in the accelerometer data.
The schematics and PCB artwork for this version are on the v1.0 branch in
our git repository, here are pdf copies for easy reference:
* [schematic](v1.0/telemetrum.pdf)
* [pcb artwork](v1.0/telemetrum.pcb.pdf)
* [bill of materials](v1.0/partslist.csv)
## v1.1 ##
These are photos of v1.1, which rightfully looks very similar to v1.0. These
boards were sold through most of 2011.
There were several changes in v1.1:
* different flash memory part due to supplier availability problems. It turned
out that 2 megabyte chips were cheaper than 1 megabyte, so the size doubled.
* updated reset circuit to improve reliability at temperature extremes
* changed the GPS antenna footprint to eliminate the large through-hole
originally intended for use with a passive patch
* irq line eliminated from the companion port
* an additional resistor divider added to allow sampling the 5V supply
With an associated software change, being able to sample the 5V and 3.3V rails
made it possible to factor out almost all of the coherent noise from the
accelerometer data seen with v1.0 boards.
The one big problem with v1.1 boards turned out to be that they would
sometimes reset during flight, usually when firing pyro charges. Bdale
wrote a [blog entry](http://www.gag.com/bdale/blog/posts/RF_Immunity.html)
that explains in some detail what we finally learned was causing this.
For those who don't have ready access to the gEDA suite, here are pdf snapshots
of the files for Production PCB version 1.1 in more easily readable form.
* [schematic](v1.1/telemetrum.pdf)
* [pcb artwork](v1.1/telemetrum.pcb.pdf)
* [bill of materials](v1.1/partslist.csv)
## v1.2 ##
This is our current production version, first made available for sale on
Christmas day 2011.
Changes from v1.1 include:
* changed to 70g accelerometer from Analog Devices since Freescale MEMS parts
are still unavailable following the Japanese earthquake and tsunami.
* reset controller changed from 3.15 to 3.00 volt trip point
* bypass cap added to LDO input
* pyro circuit resistor values tweaked to eliminate a glitch that at least in
theory made it possible for pyro charges to fire at power on. We never saw
a problem, but the change was easy and obvious.
Lots of things were different from v0.1. Perhaps the biggest change was
integrating a Venus GPS receiver and a passive patch GPS antenna. This
required stretching the board length to 2.75 inches, and changing the layout
to put through-hole parts on the opposite side from
the surface mount parts. While we were at it, things were rearranged to put
tall parts near the center and not on the board edges so that boards could
be mounted in smaller diameter tubes.
Another significant change was adding a "companion" port, intended to support
expansion boards but also possible to use as a programming interface. With
a suitable cable, the presence of the companion port allowed any TeleMetrum
board to be used to re-program any other TeleMetrum or TeleDongle
board. Elimination of the discrete temperature sensor and second LED were
necessary to free up the pins needed for the companion interface.
We also changed to a different flash memory chip with 1 megabyte of storage.
Issues with the v0.2 boards included:
* The passive GPS antenna turned out to have disappointing performance due
to our many PCB geometry constraints.
* The initial voltage regulator on v0.2 boards was a 100mA part. Once we
realized how much power the GPS receiver needed to achieve initial lock,
we switched to a 150mA part.
* The reset circuit worked well for the cc1111 but was marginal for the GPS
chip .. sometimes the board would have to be power cycled several times
to get the GPS to come up correctly.
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)
## v1.0 ##
These are photos of our third version, which was our first production
build. By the time we understood what we wanted to change in v0.2, things
worked
well enough that every time we went to a launch someone would ask about
buying boards from us. So in January 2010, Keith and Bdale made the decision
to produce enough boards to sell some to others. These were sold between April
and December 2010, and performed very well.
The changes from v0.2 were fairly small. The value of the reset capacitor
changed to increase the probability of the GPS chip coming up correctly, and
we moved to using a Taoglas amplified patch antenna attached to the U.FL
connector instead of the passive GPS patch antennas.
There were really only two issues with the v1.0 boards that annoyed us. The
first was
that the reset circuit still wasn't satisfying. The GPS chip would sometimes
fail to initialize, particularly in hot weather. The second was that
fluctuation of the 3.3 volt power rail correlated with radio transmission
induced noise patterns in the accelerometer data.
The schematics and PCB artwork for this version are on the v1.0 branch in
our git repository, here are pdf copies for easy reference:
* [schematic](v1.0/telemetrum.pdf)
* [pcb artwork](v1.0/telemetrum.pcb.pdf)
* [bill of materials](v1.0/partslist.csv)
## v1.1 ##
These are photos of v1.1, which rightfully looks very similar to v1.0. These
boards were sold through most of 2011.
There were several changes in v1.1:
* different flash memory part due to supplier availability problems. It turned
out that 2 megabyte chips were cheaper than 1 megabyte, so the size doubled.
* updated reset circuit to improve reliability at temperature extremes
* changed the GPS antenna footprint to eliminate the large through-hole
originally intended for use with a passive patch
* irq line eliminated from the companion port
* an additional resistor divider added to allow sampling the 5V supply
With an associated software change, being able to sample the 5V and 3.3V rails
made it possible to factor out almost all of the coherent noise from the
accelerometer data seen with v1.0 boards.
The one big problem with v1.1 boards turned out to be that they would
sometimes reset during flight, usually when firing pyro charges. Bdale
wrote a [blog entry](http://www.gag.com/bdale/blog/posts/RF_Immunity.html)
that explains in some detail what we finally learned was causing this.
For those who don't have ready access to the gEDA suite, here are pdf snapshots
of the files for Production PCB version 1.1 in more easily readable form.
* [schematic](v1.1/telemetrum.pdf)
* [pcb artwork](v1.1/telemetrum.pcb.pdf)
* [bill of materials](v1.1/partslist.csv)
## v1.2 ##
This is our current production version, first made available for sale on
Christmas day 2011.
Changes from v1.1 include:
* changed to 70g accelerometer from Analog Devices since Freescale MEMS parts
are still unavailable following the Japanese earthquake and tsunami.
* reset controller changed from 3.15 to 3.00 volt trip point
* bypass cap added to LDO input
* pyro circuit resistor values tweaked to eliminate a glitch that at least in
theory made it possible for pyro charges to fire at power on. We never saw
a problem, but the change was easy and obvious.