Devlog #01

Overview

So MCU board schematic is done. Nothing too crazy, but there are a few interesting things.

Fan connectors

I put 4 connectors for fans. Why? Well, I may not need that many but they might come in useful. I need 1 connector for a pump and 1 for aio fans. Maybe I’ll use 3rd one for chassis fan and 1 will be as a spare.

There isn’t a lot more to say about it. After all its just a PCB with an MCU just like any other. The difference between this one and any other lets say nucleo board is just in special connectors, eeprom and temperature sensor.

Devlog #04

Overview

I added a menu and fully finished Ohm’s law calculator.

Menu

From the menu you can now select what calculator you want to use. For now there aren’t too many options but there will be more in the future.

Ohm’s Law Calculator

This section is now fully finished! You have to select what to calculate, input all remaining parameters and click Calculate.

Devlog #03

Overview

So Ohm’s Law calculator is finished! You can select what to calculate and it will do just that.

Language support

As you can see everything is translated and has no impact on performance.

Further plans

I still have to add a few calculators. I was thinking about:

• Voltage divider
• Capacitor filter for bridge rectifier
• Transmission lines

Devlog #02

Overview

I finished language manager. Adding translations is now quite easy. Just add a file and that’s it. Languages can be changed at runtime but it still has a few problem.

New Font

With addition of a new font all characters are displayed correctly. It now supports latin + cyrylic and of couse greek. And whatever else is in the font by default.

Ohm’s Law Calculator

Ohm’s law section is starting to take shape.

Maintenance

Also I refactored a lot of code, cleaned up big files, moved code into function and different files.

Devlog #01

Overview

I started working on a calculator that would help hobbyist with their electronic projects. Whenever I am designing a project, I use online calculator for many things: Ohm’s Law, Voltage Divider, Transmission Line. These are just the most common. With this project I intend to make it simpler by combining all of these calculators into one.

Language & GUI Library

I decided to write the project in C++, because it’s my favorite language. As for the GUI Library I went with Dear ImGui with glfw and opengl3.

Language support

This project is meant to be multilingual, so I decided to make this system first. Languages are stored as text files with .lang extension. Language Manager load text form this file and stores it in a map. This way adding new languages is very simple.

Here you can see a quick demo showing that ImGui is working.

Devlog #01

I started working on the project and well… it’s a lot. The electronic part seems simple, but there is so much more.

Requirements

Before diving deeper intro the project I would like to set some basic requirements:
Max Voltage: 60V
Max Current: 50A
Max Power: 2kW

Architecture

I decided to split it into a few boards. To handle power up to 2kW I need to be very careful about it. There will be 12 IRFP250N power Mosfets split into 4 separate boards. All will be connected to control board and power management board. You can see schematic of the mosfet board below.

Cooling

And now the most important part. Mosfets can dissipate up to 2kW. That’s a lot. And I mean a LOT. My electric space heater has the same power rating. If cooling isn’t done properly the device will fry. That’s why I decided to use water cooling. The idea is to slap one of those big AIOs like in PCs to a copper block and mount 12 transistors onto the block. This way the heat will be quickly transferred away from the mosfets and with help of a few powerful server fans it should be good enough. (Well not for my ears, but I’ll accept it I guess)

Anyway, everything starts coming together. I will soon start designing control circuitry. It all looks quite nice and I am excited to continue this project!

Devlog #05

The design step is finished!

I fully designed the PCB. The precision section is separated from the rest, PSU is far away and everything looks nice.

Digital section

I added an STM32, it tracks uptime, manages calibration data, measures temperature, measures heater current and all 15V rails. It can be connection to a PCB via USB.

Silkscreen

I left a few text fields on the silkscreen in order to write down initial LM399 voltage and other stuff: temperature during calibration, date and Serial Number.

Devlog #04

— PCB —

I added shielding for the precision section. All that’s left to do here is to route power, but I will do that after I route the PSU.

— PSU —

I added a 3.3V regulator for an STM32. It will use 1 16V transformer and make: 15V for reference, 15V for heater, 5V and 3.3V.

— MCU —

I am planning to add an STM32G431. To it I’ll connect and EEPROM that would store some calibration data, like date and drift.

Devlog #03

I have mostly finished reference. I’ll tell you a few interesting things about it.

— Schematic —

Not much changed. I simply added footprints. But the thing I have to point out is the added filter. I decided to go with 50ohm resistor, 10uF aluminum cap and 100nF MLCC cap.

— Stackup —

I went with a 4-layer board. That allowed me to have a dedicated ground plane on second layer. It will improve the performance.

— Layout —

I tried to keep everything together, so all the parts will have similar temperature. Also the reference part will be on opposite side of the board compared to PSU.

That would be all. It looks like I will soon finish this project, but that will take me just a little more time.

Devlog #02

— Power Supply —

I made schematic for power supply.
To make 15V for the zener, I decided to go with LT3045 and 7018 for a pre-regulator. 7818 will help with noise and ripple. Also LT3045 cannot handle input voltage so 7818 steps it down first, then it is regulated to 15V.

— Transformers —

I decided to go with 2 DP-241-4-20 20V transformers. The datasheet states that it has low capacitive coupling, which is crucial for such precision standard. Higher capacitance between windings means higher common mode currents, that could potentially make measurement inaccurate. This specific type of transformer has been tested by Marco Reps in his Extreme Isolation video, with quite good result. This transformer has lower leakage that Fluke 732A. which is much better than any standard based on LM399.
It is a 20V transformer, so after rectification there will no more than 28V - voltage drop on rectifiers without a load. That’s why pre-regulator is necessary, otherwise it would fry the main LDO.
Also I used low leakage diodes as the rectifier.
The heater supply isn’t too interesting - just a 7815.
I am wondering whether I should switch to 16V transformers or not. I am not concerned about ref supply, since it draws very little current. What may be a problem is the heater supply, but i will have to do some more calculations.

Devlog #01

I am making a precision 10V Standard based on LM399.

— Reference schematic —

I managed to make a schematic for the reference, gain stage and calibration resistors. The output can be calibrated by soldering required jumpers that connect trim resistors.
I want to achieve sub 5ppm stability, so the resistors for the gain stage must be precise and stable.

— Power supply —

Now I should focus on power supply. The heater will be powered from a separate source. Another important thing about building the PSU is isolation. It has to be isolated from mains quite well so leakage currents will not mess up the measurements. Capacitance between transformer windings is a problem.