Looking for help to review the schematic for my flight computer PCB

Thread Starter

jjagani22

Joined Mar 22, 2021
2
Hello everyone!
The board I am creating is a flight computer for a model rocket that has a barometric pressure sensor (BMP280) and an Inertial Measurement Unit (MPU-6050) to measure orientation, acceleration, and altitude. Additionally, the computer is designed to control 2 servos, as well as 4 separate "Pyro Channels", which use N Channel MOSFETS to drive a high current through a nichrome wire attached between 2 alligator clips, which are electrically connected to the board via a 2 pin screw terminal. Lastly, the board will have an SPDT on and off switch. The board will be powered by a 12 V LiPo Battery, whose voltage will be regulated down to 5 and 3.3 volts for different components. Before getting the board manufactured, I am also looking to add a buzzer and a few tri-color LEDs (the brighter the better) in order to add some visual flair, but I am having trouble finding SMD packages for these components, so any recommendations would be much appreciated. I am still in high school, so I have no formal EE education at all, and this is the first time I have expanded beyond the breakout boards, so I am fully expecting to see mistakes, and if you see any please point them out to me

20210322_162244.jpg
This is the wiring from the Teensy 3.5 to the I2C sensors and to the regulated 5V power supply. Each I2C data line (SDA & SCL) has 4.7k Ohm pull-up resistors to 3.3V to prevent the data lines from going low when the sensor is not transmitting data ( I think). I didn't actually calculate these values but read online on Sparkfun that they should work. Pins 3-6 are connected to pyro channels, and pins 8 and 9 are connected to the servos
20210322_162225.jpg
This is a voltage regulator that takes the 5V power supply and regulates it down to 3.3 V for the sensors. I was originally using this because I was planning not to use a development board and use the processor as a standalone, but after I couldn't figure out how to program a standalone processor (help would be appreciated), I switched to the Teensy, which can regulate down to 3.3 V for me, so I probably don't need this anymore

20210322_162229.jpg
This is another Voltage regulator (the well-known 7805), that takes the 12V from the battery and regulates it down to 5V. I am pretty sure, from what I remember that 12 V is close to, or higher than the maximum input voltage for the Teensy, so I decided to be safe and regulate it down. The reason I am using a 12V battery is because I want to be able to use this board in things other than rockets as well, like robots, so I need the extra power to keep them running for extended periods of time. The circuit is just copied from the datasheet

20210322_162234.jpg
These are the servo headers for both servos on the rocket, and they will just be 0.1" male header pins in a row of 3, connected to pin 8 and 9 of the teensy.

20210322_162237.jpg
Now this on and off switch is something I am rather worried about. I could not find that many wiring examples of using an SPDT switch for on/off, so I built the circuit off my own intuition. I thought this would work, but now I realize that no matter what position the switch is in, power will be drawn from the battery. How do I make an on-off switch that doesn't actually draw power in the off position?. I read online that it is not good to keep pins floating, so I felt like I needed to connect the other side. Not sure if I make any sense, but help would be appreciated.


20210322_162200 (2).jpg
This is the BMP280, a barometer which has popularity as a breakout. I just copied the circuit from the datasheet, but if there is any tip or anything anybody has for working with this sensor it would be great

20210322_162208 (2).jpg
This is the MPU6050, the raw sensor without any breakout. Again, basically just copied the datasheet and tried to follow all the electrical specifications. However, if anybody has tips for me, I would gladly take them

20210322_162217 (1).jpg
This is 1 of 4 pyro channels on the computer. This is basically how it works. 5V are passed from the MCU GPIO pin into an N channel MOSFET with a very low RDSon, and the high current is sent out a screw terminal block into a nichrome wire, which is not pictured below. The 10k pull-down resistor is there to prevent the MOSFET from accidentally activating, and the 510 ohm current limiting resistor is there to prevent the MOSFET from trying to pull too much current from the MCU pin in the instant it is activated

What I am really worried about is the fact that I might need some passive components or other things that I might not know how to use, and that will cause a failure in my circuit. However, if you see ANYTHING wrong or even slightly concerning please tell me as it would really help me out. Thanks!

Datasheets and parts: Note that I have not used some parts yet (like the buzzer and LED) Also this doc is like half notes so don't mind some of it

 

sagor

Joined Mar 10, 2019
439
Not sure your 1117 3.3V regulator will work as shown, you are blocking the 5V and 3.3V DC by those capacitors. I assume you meant to put those caps to ground from each leg, not in series with the voltage. (and you are grounding your 5V and 3.3V with that diagram)
 

Thread Starter

jjagani22

Joined Mar 22, 2021
2
Not sure your 1117 3.3V regulator will work as shown, you are blocking the 5V and 3.3V DC by those capacitors. I assume you meant to put those caps to ground from each leg, not in series with the voltage. (and you are grounding your 5V and 3.3V with that diagram)
Oops, I see now, thank you for taking the time to point that out!
 

Hemi

Joined Mar 17, 2012
20
Your FRAM memory is SPI while the rest of your sensors are I2C, is that intentional? FWIW, I was about to log about 30 readings per second to standard I2C EEPROM using a pretty slow MCU.
 
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