Adjusting my Knowledge of Schematics

A little while ago, I posted about learning new things about schematic design. In short, I followed a tutorial that encouraged clear schematics by using many net labels in the place of drawing out wires. In particular, they connected net labels directly to the PCB, and had everything defined separately from that. However, I’ve come to find out that this is a bit of a debate in the hobbyist electronics world. I was reading the following post on Reddit that shows an example of the discussion in the comments:

A Reddit thread where someone posts their schematic, which makes heavy use of net labels. The discussion about this in the comments was quite educational for me.

The discussion centered around the balance between clean and clear schematics. Separating everything out with net labels will certainly make schematics clean, as there will be a minimum of crossed wires or cramped symbols. However, the downside is that this will reduce clarity. I followed a suggestion in the comments and tried to trace a signal through the schematic. I have to admit, it was pretty tricky – I checked a pin, and then read the net label, followed by having to scan the schematic to find that net label again, only to see that there were two other net labels involved. As a result, it was pretty tricky to see what the internal connections were.

It seems there’s a pretty clear divide on the topic, as evident in the discussion as well. Some people will say that leaving as many wires in the schematic will aid readability, although they’ll also say a schematic should have as few crossed wires as possible. The consensus seems to be that some common sense should be applied in choosing when to use labels. In the case of this schematic, there’s an example of a label being used for no reason at all, apparently, as this person points out:

This user identifies three components that are right next to each other on the schematic, but connected via labels rather than wires.

I can wholly understand their comment here. These components were literally adjacent to each other and nothing else, and connecting them via cables would cause very little trouble at all (one connection to ground would have crossed over a signal wire but that’s it).

In the case of my Pomdoro schematic, I’m thinking that I may have doubled up on methods to clean up my schematic. For instance, I used both buses, wire labels, and global labels. I could have stuck with only wire labels, and perhaps adding buses to still draw a line but collate the five wires into one. Furthermore, it makes sense to me to separate out the power section of the schematic. It’s a functionally separate part from the main schematic. The same goes for the ISP programmer – it’s a side issue to the main function of my device. However, I’d also separated out the LEDs from the microcontroller, even though that’s the main point of my entire Pomodoro timer.

Figure 1: The Pomodoro Schematic

It’s a good lesson for when I make the hamster cage lighting system. I’m not bothering to rework this schematic again, but if I would, I now know what I’d do better.

  1. I’d edit the ATtiny84 symbol to put PB3 on the left side of the symbol. After all, it’s an input to the microcontroller, so it makes sense to me that the signal goes from left to right.
  2. I’d not use net labels for TimerLeds and PomodoroLeds, but rather use the bus wire to connect the LEDs somewhere to the right of the ATtiny84.
  3. I’d use the small versions of the symbols to create a little more space on the schematic.
  4. I’d have the wires on PA5 and PA6 connect directly to the relevant switches. Those are their main functions, after all, whereas the MISO and MOSI are secondary connections and should be branches off that.
  5. Similarly for PB3, where I’d have it connect directly to the RST label, and have the pull-up resistor be a branch upwards.

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