• Introduction
• Wiring diagram
• Wire choices
• Components chosen
• Summary

Introduction

Hi there!

In this post we will present how we created circuitry and wiring for the Envidrawer project. We will also underline issues we faced and our solutions to them! Let's get started

Because this project requires varying voltages, from 3.3 V for sensors, through 5 V for RPi and the water pump, finishing at 12 V for LEDs and fans, we had to be ingenuous with our designs and do somewhat complicated circuitry by ourselves. First of all because the project requires a considerable amount of current, we decided to go for a more sturdy one, which could be reused in a different project and provide proper protection for our devices (as a few of them will be directly connected to it). The PSU can provide up to 20 amps of current and outputs 12 V.  In the table below currents for each of the loads are listed.

Wiring diagram

For those who are already eager to see the most important part of this post - the wiring, here it is!

The diagram presents all vital components of the project with appropriate pin assignments on the Raspberry Pi. Sensors will be connected to remaining pins or hooked up to the I2C bus in a future post. Right now they are being mounted

Wire choices

Choosing the proper wire gauge was also essential, as the currents we are working with are not in milliamp ranges but rather in full amps for the power devices. Therefore we had to do some research on the topic. Interestingly, most websites are concerned with the current propagation in the free air, rather than in an encasing making the wire choice more expensive (because of thicker wires).

Nevertheless, basing on two websites, we chose wires that would provide a safe margin of current that can pass through them.

Below you may see pictures of several wired-up components of our system as well as several ways in which we connected the wires.

The power supply unit wired up and operational

M3 Loophole connectors for easier cable mounting on the PSU

Automation hat connected and operational

DC Motor control L298N H-bridge with all 4 outputs wired up

Cables covered with heat-shrink tubes. This way they are more resistant to any damage and most importantly isolated.

Components chosen

Although we could build the H-bridge and the DC-DC step down converter by ourselves, we decided to stick to the pre-built PCB's which are very common and cheap. However, we built quite a complex control circuit by ourselves (which proved to be a thrilling experience, and a challenging undertaking!)

Although we had a 2 channel H-bridge it proved to be quite unsafe and simply put badly designed (for higher steering voltages than powering, the steering signal would be lost resulting in no control over the bridge!) - more information about it here

The DC-DC converter circuit could also be much simpler (for example LM350, but it would require a heatsink and not a small one ), following with the trend we chose more modern component and one which can be reused.

Summary

It might seem simple, but proper wiring, planning the connections and making everything work took us a lot of time In the upcoming post we plan to elaborate on the design and all the nuances of designing your own analog electronic circuits (which takes even more time) and some challenges that arose during this busy holiday season. See you soon!

Jakub & Szymon & Michał