My first post, I hope I have select the right topic and am asking an appropriate question.
I am designing a "Kitchen Sink" project that demonstrates the use of three boards (Nano, Pico, and ESP32), three data transmission protocols (UART, I2C, and SPI), and three communication protocols (LoRa, WiFi, and BLE), with multiple sensors and controllers.
I have made power connections across the boards keeping in mind the need for a common ground, use of an external power supply, and the use of a level shifter.
Posting a Fritzing circuit diagram with just the power connections. This is an updated version from the original post based on initial comments, please read comments with that in mind. I wanted to see if I could get this validated or get feedback if I am doing something wrong.
Ok, got it. The label is placed over the wire for lack of space but it refers to the rail. The red wire is not connected to the label. I forgot to mention but I have used red wires for 5V and orange wires for 3.3V.
A simple annotated schematic would make this much easier to follow. The batteries, at 1.5V each, do not provide sufficient voltage. Additionally, the processor pin numbers are not legible.
Without a schematic, it’s difficult to determine if you need a level shifter. If this is for I²C, simply use pull-up resistors to the 3.3V power supply. This ensures the signal levels stay within the I²C specification, and the 5V Arduino will work correctly.
Remember, I²C lines are open-collector (or open-drain) outputs. They do not source power; instead, they only switch to ground.
I would say I am an advanced beginner so still figuring out best practices. To @lastchancename as well, Fritzing seemed like the easiest option, have been considering taking a look at KiCad or Eagle but haven't gotten around to it yet. The schematic view in Fritzing seems messed up, not sure how to get it right. Would appreciate any help there (alternative to Fritzing and/or the best way to represent circuits for beginners).
Coming back to the original ask, thank you for all the feedback so far, and my response below:
Have updated the diagram: moved the label from top of the red wire and added a label to the batteries. They are supposed to be 3.7V each.
I felt the processor pins (except the power and ground) are not relevant to this review. But even otherwise, not sure how to impove legibility with Fritzing image export (tried 600 dpi if that helps).
Since I am not able to provide a schematic, best I can do is to share that the level shifter is to connect a LoRa SX1278 module which has a 3.3V op voltage to a Nano. So that's SPI. But will look into your feedback on I2C, need to understand that better.
My primary ask still is to make sure my power connections are good such that all components work ok (for example, I had not used a common ground in my first version, which I learnt later).
Also, maybe another clarification will help: this is a slightly overloaded approach to illustrate all concepts as a learning project. It may not be the best implementation for a production project where you would simply choose the best matches for boards and components.
I get that. But if someone were to follow the thread they would know that this is an updated diagram based on the feedback given. Also the changes are rather minor (just labels, and a battery I had missed).
I am not a fan of posting mutiple versions of a diagram since then comments can get even more confusing if everyone is not consistently referring to the latest.
This is also a common occurrence in StackOverflow where the original post is changed based on the comments. As long as it is mentioned in the thread that there was an update, it works. But if this forum prefers a different approach I will try to follow that going forward.
It is not the thread followers that get confused, it is anybody reading the thread later
Look at the diagram in your original post where you ask for comments on it then read my reply. Does it make sense ?
If you make changes to a post that already has comments made about it then the least that you can do is to make it clear in the revised post that it has been changed
I agree, and I usually don’t spend much time on Fritzing diagrams. Power and ground are two of the most critical aspects of a circuit, and they must be clearly shown. My earlier comment about the batteries was unnecessary because your diagram doesn’t properly indicate what’s what; most labels are missing.
What you’ve provided is a wiring diagram, not a schematic. Also, keep in mind that many people don’t have the specific parts you’ve pictured and won’t take the time, as I did, to look them up.
Finally, avoid using the 3.3V and 5V pins on the Arduino as a power supply. These are not designed to power external components reliably.
This might help: Gil's Crispy Critter Rules for Processor Hardware:
Rule #1: An Arduino is NOT a Power Supply!
Rule #2: Never connect anything inductive (motors, speakers) directly to an Arduino!
Rule #3: Avoid connecting or disconnecting wires while the power is on.
Rule #4: Do not apply power to any pin unless you are certain of what you're doing.
Rule #5: Do not exceed the maximum voltage ratings.
Rule #6: Many Arduinos cannot power transmitters directly.
Rule #7: Before powering your project, take a break and double-check the wiring.
LaryD’s Corollaries:
Coro #1: When starting out, add a 220Ω resistor in series with both input and output pins to protect against shorts.
Coro #2: Invest in a Digital Multi-Meter (DMM) to measure voltages, currents, and resistance.
Note: Violating these rules can turn your Arduinos into crispy critters. For optimal performance, keep your wires under 25 cm (10 inches).
Additional Tips:
The L293 motor driver, though common, is inefficient as it can lose around 3V as heat when driving both legs of a motor. Consider using a motor driver with MOSFET outputs to reduce heat loss and conserve battery power.
One more takeaway for me from all the comments is that the diagram that I thought was very clear is actually not so. Need to understand how to create a schematic.
Let me work on this and will post an update with what I come up with.
There are many out there free of charge. I use one of the more popular ones called KiCad. It is not as easy as some of the others but it is full blown with no limitations on what you do. There are a lot of libraries available, again free. They do ask for a donation when downloading but it is not required.
I’ve been using it for several years, and I still learn something new every time I use it. One of its most powerful features is that the footprints are stored in a separate library from the components. This adds a lot of versatility, especially when creating custom parts—which is easier than it might seem.
I went looking to see which was more popular and found this: KiCad is currently more popular than Eagle, especially since Eagle is being discontinued by 2026, leading many users to switch to KiCad for its free and open-source features. KiCad has a larger user base and more resources available for learning and support.
