# Rocket Talk - Arduino-based radio flight data

### Help Support The Rocketry Forum:

#### OverTheTop

##### Well-Known Member
TRF Supporter
A comment regarding oscillator/crystal vulnerabilities due to high g. In all my rocketry electronics designs I stick with internal RC oscillators since these are pretty much immune to these issues. The loss in accuracy is inconsequential I think and considering the improvement in robustness then its a no-brainer for me.
In the spectrometers I design I sometimes use RC oscillators in the various modules. They can be trimmed to within about +/-2% (for the ATMega328) at the factory and if that is sufficient then it makes sense to use. Other modules require more accuracy and I am now switching to MEMS oscillators for newer designs.

#### AllDigital

##### Well-Known Member
Thanks for all the great feedback. I received the Teensy 4.0 and have been putting it through some tests. It is so crazy fast. I have a short program that just increments a counter and checks for 1000ms timer to display a count. When I run it on the Teensy 4.0 I get 8,109,923 increments a second (wow!). On the ESP if I run it straight up on one core I get 763,000. On both cores and then added together, I get 1,364,624. So, for my purposes, the new Teensy is 6X faster than the ESP32 in a much smaller package. That said, I really like the ESP32's dual core framework, so I can do sampling on one core and housekeeping (logging, transmitting, etc) on the other core without worrying about single-threaded delays impacting sampling.

#### cerving

##### Owner, Eggtimer Rocketry
TRF Supporter
I'm not surprised that you get a "better" graph out of the lower-G accelerometer on a 4G test... the steps are smaller, so the filtered output will be cleaner. That's a problem with using a high-G accelerometer in a low-G application... the resolution dictates that your steps will be higher, so it will look noisier. Of course, once you hit 17G all bets are off with the low-G accelerometer, so some altimeters use both a low-G 3-axis accelerometer and a high-G z-axis accelerometer. You use the low-G one for calibration on the ground, and in flight you use the z-axis high-G accelerometer along with the low-G for x-y readings.

#### OverTheTop

##### Well-Known Member
TRF Supporter
How about filtering the data by normally using the lower rated device and then take the feed from the high-g device when limits are exceeded? You may need to watch out for discontinuities when blending the two and have some sanity checks in place on the data.

#### AllDigital

##### Well-Known Member
How about filtering the data by normally using the lower rated device and then take the feed from the high-g device when limits are exceeded? You may need to watch out for discontinuities when blending the two and have some sanity checks in place on the data.
That is my plan. I want to fly with both. I'll use the 16G for regular flight monitoring (tilt, apogee, etc), but I'll also log the 200G x,y,z, so I can see the extremes in the post flight data. The processor I'm using can easily read both at 500Hz (likely 3X faster) and log to SD card, so there is not much overhead.

#### Robz82

##### New Member
I've not read all the post from top to bottom but coming from a scratch building drone background there are a lot of drone flight computers on the market that are cheap and have inputs for GPS telemetry etc. Might be worth looking at a few of those.

#### strud

##### Active Member
The MTK3339 was mentioned early in this thread, has anyone flow these in a rocket and got good results?

A few flights of our RocTrak board that uses these has shown the altitude to be unreliable with lat and long to be pretty good, even in Avionics mode.

Wanted to get some feedback from others before we commit to another GPS module (probably one from Ublox)

details of the project here: RocTrak thread

#### mikec

##### Well-Known Member
Some people claim the MTK works all right. I've had bad experiences and will never use them again; no reason not to use Ublox IMHO.

#### strud

##### Active Member
Some people claim the MTK works all right. I've had bad experiences and will never use them again; no reason not to use Ublox IMHO.
Thanks mikec, Performance on the ground seems very good but in the air lock seems to be lost earlier and altitude upon landing is often at least 1000ft off and hence causes me to lose confidence in altitude at other times in the flight....