Completed Project!

This project was quite more complex than all my previous ones, and it turned out to be even more complex than I expected. So, I decided to firstly make a block diagram for the whole project.

Alright, the STM32F407 was at the center. Then the F103 was supposed to program the F407. It further had a USB port (for the F407) and a JTAG header (for flashing the debugging firmware onto it). Then the F407 was also connected to a USB port, utilizing it’s USB-OTG powers.

Alright next, I have two DRV8701E motor drivers. I couldn’t use the widely available, cheap L293D
motor driver as it was too underpowered. Later, though I decided to keep only one motor, to reduce complexity. I didn’t remove it from the block diagram or power budget, so that I could upgrade whenever I wanted to. The motor driver needed 4MOSFETs each, and then it was connected to a plug to be connected to motors.

I also needed a ADC. For that, I decided to go with the ADS112C04PW/PWR. They are drop in replacements with near-identical specs.

For Ethernet, I chose the DP83826 and the MII interface as I didn’t require much high speeds. It is connected to a RJ45 connector with in-build magnetics.

Then comes the audio section. I firstly have a DAC that can connect to both Stereo speakers and a headphone jack. Then, I have a MIC for voice input.

Alright, so with so many components, I can’t use just any power supply due to the high current. So along with the block diagram, I decided to make a power budget too.

I firstly started with a +12V I/P connector. Then, I added the two motors that draw 3A each. After that came my +3V3 buck converter. To the buck converter, I connected the F407, F103, CH340C, DP83826, ADS122, DAC and Mic.

I referred to each of their datasheets to get the peak current they can draw. The peak current is the maximum current a chip can safely draw while the average current is the current it draws under normal use. The peak current usually happens during power on and when it is activating a new peripheral. So when calculating power, the peak current is always used.

I then added all the peak currents to get roughly 475mA. To calculate the input current, we need to first calculate the output power.

Output power = Vout * Iout
= 3.3 * 0.475
= 1.5675W

Input Power = Vin * Iin
= 12 * Iin

Efficiency = 90%
=0.9

Output power = Input Power * Efficiency
1.5675 = 12 * 0.9 * Iin
Iin = 1.5677/10.08
= 0.1555A
= 155.5mA

Now, the total IP current is (2 * 3) + 0.1555 = 6.2A. For this, I’ll take a margin of 25%, so
(6.2 * 0.25) + 6.2 = 8A. The closest standard power supply current is 10A, so I finally came at +12V/10A for my I/P connector.

Now, I also designed the schematic page for each of the listed part, and also made a PCB, but even though I want to, I can’t devlog it here as I’m reaching the max characters limit here. Though I can say that the datasheets were my best friends throughout this project, especially the pin description, typical application diagrams, and the recommended layout sections. I don’t know why I can’t like refer to links and then journal my work, like I can in Lapse. But I later realised that devlogs had to be written as soon as I synced Lapse with Hackatime, which I will keep in mind from next time. By the way, thinking of Lapse, to journal my work properly for this project, I’ll use Forge. This project was originally meant for Forge, to be honest, but when I got to know about the 30 hour certificate, I created a Stardace project too.