Australian Rocketry

A bit more firmware work recently, nothing too exciting mostly additions to CLI functionality.

- dtmf simulator: allows the simulation of dtmf tones being sent. syntax: dtmf<space>a<space>b<space>c<space>d<space>e<cr>. where a c b d e etc are individual numbers (1 to 16) representing a 4 x 4 keypad. These are fed straight into the dtmf processor as though they were received by the radio etc

- output channel direct drive: allows one of the output channels (1 to 4) to be 'turned on' for a 1s period. syntax: out<space>x<cr> where x is 1 to 4

- gps status: dumps current gps parameters. syntax gps<cr>

- power monitor status: lists values from power monitor board/ "Smart Disconnect". syntax pwr<cr>

- overall system status: dump of all system parameters and values. syntax ??<cr>

Also added a short beep upon receipt of any valid DTMF value.

Example terminal screen grab from cli



Still a few bugs to iron out....

Updated version of user guide here, gives a bit of insight into how it all works.

https://drive.google.com/file/d/12FasdV2VqZdyatxcFXeAZWLK_hbI0Xgm/view?usp=sharing

strud wrote:Hi Matt, where did you see the 4MV battery? (units are mV by the way)

The numbers written together on the screen shot wasn’t ware these were 3 separate readings...

Time for an update on this, it's been too long...

So Drew has been kind enough to fly the rev0.1 and rev0.2 versions of hardware, each using a variant of the MTK3339 chipset with built in patch antenna.

The results have been not great for these, even for the second unit (which had GPS Uart RX connected) when in avionics mode. Altitude performance was the biggest issue, but really the performance during boost also not great.

I sought feedback from others who have tried using these for rocketry applications and it seems these are not the units to use......

So I bit the bullet and went with a ublox module (like I should have from the start...) and pulled off one of the MTK3339 modules and replaced it with one of the ublox neo-6m hobby boards and seperate patch antenna. This was sent over again to Drew in WA to see if we could fly it on the last launch of the year but unfortunately it was cancelled due to fire risk etc...

Here are a few pics of how this lash up layout looks in my HPV4PoC av-bay





Plan is to incorporate one of these new ublox all in one modules into the design on the next iteration:

https://www.u-blox.com/sites/default/files/SAM-M8Q_ProductSummary_%28UBX-15027452%29.pdf

On to the firmware features;

When time permits, have been adding some useful features:
- configurable DTMF command latching eg allowing a particular command to trigger an output or change that stays on/off until the command is issued again when it is toggled. Need this to turn on loads such as cameras etc
- Configuration parameter editing via CLI which will be compatible with a GUI app later
- Smart switch/power monitor filtering - ignoring of false results eg zeroes returned if I2C comms is corrupted, running average filter etc

Also discovered an issue of interference of the supply line feeding back out from the radio module. With the ferrite bead in place (right at the power supply pin for the radio module) a 330mVpp 145MHz signal was found during Tx! Those modules have basically no power line fRF filtering inside....

This will need a low pass filter such as this added:

https://www.murata.com/en-global/products/productdata/8796766699550/ENFE0002.pdf

In the meantime, the addition of a 1uH series inductor has cut that pollution down from 330 to 72mVpp.....

Oh and I received a bunch of ESP32 WROOM modules so that I can make a version with these instead of the rather large hobby breakout boards. The overall height can be reduced dramatically but may force me to have an offboard antenna....




Now that I have a new DSO, will be looking into other parts of the board for EMI issues before I commit a new board design to be made.

Next iteration of board done, including the following changes and additions:

1. ublox SAM-M8 GPS module with integrated patch antenna
2. RF blocking filter (T) on Radio power supply pin
3. PTT fet gate pull down resistor (was seeing the PTT input being pulled low during programming etc)
4. Baro sensor for altitude measurement: https://www.te.com/commerce/DocumentDel ... ng=English
5. Bosch BMX160 IMU (triaxial accel, gyro and magnetometer) https://au.mouser.com/datasheet/2/783/B ... 509610.pdf

github repo for Bosch sensor : https://github.com/BoschSensortec/BMI160_driver (note this is what Bosch recommend to use with some #define changes)

Both new sensors are on the I2C bus.



Will send off to fab and order the sensors shortly.

So while I'm waiting for the the boost converter and RocTrak 0.3 boards to arrive, I have got the 'draft' design of the 2.0 version done.

This is using an ESP32 WROOM module instead of the devkit type boards, meaning the overall height comes down a LOT. I've also replaced the DTMF chip with the SSOP package (much smaller) and gone with a SMD crytstal package (much lower profile) AND put all of the components on the topside of the board.









To get most items on the top side (except radio module and RF LPF (much better for reflow operations) things are pretty tight in some areas & I have gone with a 4 layer board to make the task achievable.(may be possible with 2 layer but MUCH more awkward) AND having a full ground plane is much better given the significant RF electrical sources on board.

Unfortunately not really any opportunity to make the board any smaller since all components are now on the top side, and the radio module dominates the board width.

Have added the baro sensor and Bosch IMU mentioned in the previous post as well.

Still need to review (especially the RF section between antenna and radio RF pin since having a ground plane at the different depth has changed the impedance) and resolve some of the DRC issues I have (mostly clearances) before contemplating getting this made.

Have the first RocTrak rev0.3 together now, and firmware modified to utilise the ublox SAM-M8N module

Top side:

ublox SAM-M8N module (to the right of the SMA connector) is the main change here, but have also gone from a large tantalum to 3x 100uF ceramic caps for the radio supply bulk capacitance (left side of the bottom left corner of the ESP32)



Closeup of ublox module. Note this had to be reflowed since the package has no exposed pads



Bottom side:
Addition of 2 new sensors (above crystal)
- Measurement specialties baro pressure sensor( right, looks like a little metal can)
- Bosch IMU (left - very small black)
Addition of supply line RF blocking filter for radio (above top right corner of radio tin can)



Did find one very hard to see board bug which I can only blame myself for - somehow Vcc was not connected to the DTMF decoder, the very last bit of a track to the bypass cap was not present.... don't know how the DRC missed that.

So I made use of the ublox library provided by sparkfun: https://github.com/sparkfun/SparkFun_Ublox_Arduino_Library
Not much work really to get that going, but still quite a bit more to go to optimise the configuration of the module.
Currently setup to use the ubx protocol only ie not NMEA. This ublox proprietary protocol is binary and has a LOT more capability/functionality than what you can get from the NMEA implementations. Have it reporting at 5Hz for now and setup for Avionics +4g mode.
Since I have not included a backup battery or local eeprom/flash for it, the gps will be configured upon startup.

Now starting on incorporating the libraries for the two new sensors. These will primarily be used to detect the flight status but also will allow for vehicle attitude determination. All of these metrics will be added to the log entry, saved in the SPIFFs within the ESP32.