Clarification Needed "Rocket Model"

Other Hardware General Electronics
1

Hello everyone, I'm working on the electronics bay parts of a rocket model of a university project, the rocket will NOT have any control surfaces, and our objective is purely scientific (to get data from the launch such as pressure, temperature, altitude, velocity, etc.).
Introduction:
Until now, I have been working on the different models we will need, I have not yet proceeded to the coding part. Below you will find the schematics that I have been drawing, It is still an ongoing work.

Schematics
Schematics3903×2464 100 KB

and the following list of items
Power Rating.pdf (42.8 KB)
As you see in the schematics, we have two servomotors that are controlling the valves, the GY-521 as a Gyroscope and Accelerometer, BMP280 for atmospheric pressure measurements, MAX6675 amplifier with a thermocouple K-Type, EBYTE E32 transceiver chip, and SD card. Our power source will be a Lipo 7.4V, 1050 mAh.
I would like for the sensors to make the measurements and then to store the data locally on the SD card, and transmit the data via the transceiver to a ground station and have live telemetry.
Questions:
1- In the schematics I added the voltage regulators to switch from 7.4V to 3.3V and 5V, however as I understand the linear voltage regulator will waste the difference in voltage as heat, which will really affect the efficiency of my batteries, so I'm thinking maybe better to use dc-dc converters, however the duration of the launch will be for few minutes so the system wont be hooked up for a long period of time. can anyone advise about this please. 2- I connect all the peripherals powers to the regulators, and only the data communication to the controller correct? and only 1 power line from the regulator to the board to power the controller. can you confirm this.
3- I'm worried about the maximum current that can be passing through the controller, as per the datasheets for Arduino nano max current per pin is 40 mA, and recommended not to exceed 20 mA. but since we only have data lines between the controller and peripherals and the power will be directly through the voltage regulator and the battery, I do not need to worry about the mA level on the controller?
4- There is still the 2 pressure transducer that are not present in the schematics, I'm thinking on using the Wika A-10 model. and the use a current to voltage converter to read the analog data from 4-20 mA to 0-3 V. is this the best way to connect the pressure transducer?
5- I'm confused on how to connect the Lora antenna and the SD card holder, as u see I have the SD without the serial communication and the antenna with both SPI and serial interfaces, I'm not sure about the right way of wiring if I want to transmit the data and store it locally on the SD.
And a last point regarding the logic level shifters of the peripherals, from the data sheets of all the sensors it is written that they are compatible with 3.3 V and 5 V so I avoided adding logic level shifters, is it ok or we need to add them?

Thank you all for the help.

Need help in ground station to rocket model communication
Need help in ground station to rocket model communication
2

You ask for qualified theoretical analysis that would take a lot of time to perform.
No helper will be able to guarantee anything.
Sum up the need for currents and build powering circuits accordingly, and put them to the test. Be prepaired for redesigning parts.

3

Hello everyone, I'm working on a university project, and I have a Lipo battery 7.4V, 1050 mAh I need to connect this to several sensors(Pressure, Temperature, Gyroscope, and servos) and Arduino nano board. I was thinking on adding voltage regulators to switch from 7.4V to 3.3V and 5V, however as I understand the linear voltage regulator will waste the difference in voltage as heat, which will really affect the efficiency of my batteries, so I'm thinking maybe better to use dc-dc converters, noting that the duration of the usage will be for few minutes so the system wont be hooked up to power for a long period of time. can anyone advise about this please? is it worth it to use a dc-dc connection or just go with voltage regulators?
Also as a good habit I should connect all the peripherals powers to the regulators, and only the data communication to the controller(nano board) correct? and only 1 power line from the regulator to the board to power the controller. can you confirm this please?
Thanks!

4

Not exactly. You cannot connect the servos power input to the Arduino unless you want to fry the Arduino. The servos need to go directly to the battery, it can be the power input to the Arduino if you are using Vin. My preference would be to use a SEPIC (Buck/Boost) converter and set it for about 7.5V out and feed that to Vin. This will maintain a steady voltage over the battery power cycle. You can use this voltage to power the servos, there performance will remain constant. I like the additional filtering I get when using the Arduinos on board regulator. If the combined total of the other sensors is less then 50mA use the 5V pin on the Arduino. You will need to adjust the current on the servos to make it work properly. Caution with this configuration you will have a stable system well below the discharge point of the battery discharged voltage. Good Luck.

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If the setup will be used only for a few minutes, battery lifetime is irrelevant.

Servos require 4.8 to 6V (not 7.4V) at large currents (1 Ampere per small servo, like SG-90 and 2.5 A per large servo, like MG996R) and should be powered separately. Don't forget to connect all the grounds.

To connect 3.3V sensors to a 5V Arduino, bidrectional logic level shifters are required.

1 Like
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@samba220, please do not cross-post. Threads merged.

7

Indeed. The 7805 is a poor choice in this application for several reasons. Plenty of more suitable, modern options are available.

Also, don't apply 5V to the "Vin" pin of the Arduino, but to the 5V pin instead.

Indeed.

It's called a "resistor". Yes, should work OK. 150 ohms would give 3V at 30mA.

Looks like you have a problem there, or actually several.
You've now got the LoRa connected with both UART and SPI to the Nano. I'd select either. Preferably UART, because the SD module you use apparently has no chip select (CS) pin, so it'll be problematic combining it on the same SPI bus with other devices. I understand there are other types of SD card modules out there that do not have this limitation. Either way, you could still use this one and then use UART to 'talk to' the LoRa module (assuming you have verified it supports this in the functionality you require).
However, keep in mind that debugging your system through the Serial monitor in the Arduino IDE also relies on the hardware UART (tx/rx pins, d0 and d1 on the Nano). This may (but does not necessarily) result in challenges when debugging your program with the LoRa module in place.
There are plenty of controllers (e.g. ESP32) that have several hardware UARTs. You can also run a 'Software serial", which is an emulated UART, on the Nano for the LoRa.

No need for logic level shifters then, assuming you accurately interpreted the datasheets. I've not verified.

Depends though; if these are little MG90 type servos, they will run OK from 5V and in fact should not be run >6V.
So it depends on what servos are used.

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Thank you for your reply.

This is the link of the servomotors we’ll be using.
Regarding level shifters, as I understood if the peripherals are powered by 5V and the nano is 5v logic, then we can proceed without using level shifters? The data sheets of the peripherals states that they are compatible with 3.3v and 5v. In case we connect a peripheral to a 3.3v power in that case we need to add a logic level shifter only correct?

9

Thank you for the reply. Can you provide some alternative models in place of the 7805?
Yes the wiring will be directly to the 5V pin.

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I was thinking on using something like the following:

Since I wont be using a breadboard I was avoiding to add resistors in the wiring and stick to modules. Does this work? Or you have a recommendation?

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Regarding this point, I proceed in connectingvthe Lora antenna only using the UART and I think I’d better find a different SD module with CS to share same SPI bus. Using this approach should make if feasible to transmit data of the sensors to the ground station using the Lora antenna, and save the sensors’ data on the SD card?

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The thing you linked to will not convert a 4-20mA signal to a voltage, no. Just use a resistor. There are plenty of ways to work one into your project that don't involve a breadboard. How about soldering it? Otherwise use some kind of clamp terminals.
Or look for a module that consists of a PCB with a single resistor on it; I'm sure they exist, silly as they would be.

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https://www.google.com/search?q=buy+5v+buck+converter
Take your pick.

Sure.

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Thanks a lot rsmls! you have been really helpful!
I will proceed with a resistor and solder it on, I can use the 250 ohm for 0-5 V output? can you please confirm.

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I've never used the dc-dc buck converters before, as I understand they can either be step up or step down? and they can have different output but a fixed input? so for my case I need to get a 7,4V input and that has an option of step down to 5V output?

16

Indeed, that should work.

However, a better approach is to not use 5V as the reference voltage for your analogRead. Instead, if you use something like a Nano, use the 1.1V internal reference. This prevents all manner of annoying accuracy problems because of power supply variations (e.g. USB power vs. external power supply).

Scale your 4-20mA signal to fit this range; let's say you want 0-1V range. This gives 50R; the closest common value is 47R.

Or both. You want step-down. Step-up is usually called "boost".

Indeed. You'll find that the input voltage on most regulators covers a broad range; your 7.4V input won't be a problem. And modules with 5V output are very common, indeed. Just keep an eye on which product you actually order; it's common that the same type of module is offered in variants with different output voltages, so be sure to select the correct one.

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Thank you for the helpful suggestion. I will attempt to do that.
Can you advise though if I can use the internal reference of 1.1V on a specific pin without affecting the rest of the sensors?
Also as a general view of the schematics I sent do you have any recommendation other than what we discussed to make it better? should I add any circuitry protection? change any of the wiring?
Much appreciated!

18

You can switch between the different references in your code as desired. However, I'd suggest using the same reference for all inputs and simply scale down any signals that exceed the 1.1V range with a simple resistor divider.

However, I don't see any other analog signal sources in your schematic. Note that the 1.1V reference bit applies to analogRead only, so ADC inputs. It doesn't affect digital signal levels.

There appear to be some loose ends still. Your 'batter fuel gauge' IC is unconnected. So is the I2C multiplexer, but it doesn't seem to be needed anyway in your current setup. And if you encounter the scenario where you'd need one, I'd consider switching to a different microcontroller with more than one I2C bus.

I'd recommend adding some pullup resistors (e.g. 4k7 or 3k3) on both SDA and SCL for the I2C bus.

In terms of protection, I always like to put a fuse on the power input to the system, but most people don't in the kind of system you're building. The Arduino has a fuse onboard.

19

Thank you @rsmls , I'm working on updating my schematics.

I will revert back soon.
Much appreciate the help.

1 Like
20

For the Motor Control, Is it better to use something like the "Adafruit DRV8871 Brushed DC Motor Driver Breakout" to control the motor, or there is no need and I can just connect it to the "PWM" pins on the nano board?