Elospeed LedPreResistor 2.3

by Elospeed

🇩🇪 Deutsche Anleitung: LIESMICH.md

Website: elospeed.github.io/LedPreResistor · Download: latest release

LedPreResistor calculates the series resistor for one or more LEDs. It is the new edition of the freeware tool LED Pre-Resistor (Delphi 7, 2004), rebuilt from scratch in Lazarus: a single 64-bit Windows exe, no installer, no extra packages. Since 2.2 there is also a native Linux version.

What it does

• Live calculation while you type: supply voltage, forward voltage, LED current and number of LEDs in series.
• Nearest standard value from the E12, E24 or E96 series (always the next higher value, so the LED never gets more current than planned).
• Real current and power in the resistor, in the LEDs and in total, plus a recommended resistor rating (⅛ / ¼ / ½ / 1 W) with a warning above 50 % load and an estimated temperature rise.
• Colour bands of the resistor (4 bands, 5 bands for E96) and a schematic with all values at the components.
• "How it is calculated" panel that walks through the calculation step by step with your own numbers.
• Presets for red, yellow, green, blue, white and infrared LEDs, or your own forward voltage from the datasheet.
• LED preview: a 5 mm LED in the chosen colour with anode, cathode and flat side labelled.
• Blink circuit tab (since 2.3): NE555 astable (optionally with a diode across R2) or a two-transistor multivibrator (BC547). Calculates frequency, on/off times and the LED series resistor from the parts, or the timing resistors from a desired frequency and duty cycle. The preview blinks at the calculated rate, with schematic, "How it is calculated" and checks (supply range, output current, transistor saturation, base reverse voltage).
• LED info "The LED" built in (F1, opens in your browser, also offline).
• Copy the result with Ctrl+Shift+C. Comma and dot both work as decimal separator.
• English and German: starts in German on a German Windows and in English everywhere else; View → Language switches at any time (saved in LedPreResistor.ini next to the exe, on Linux in ~/.config/LedPreResistor/).

Example: 12 V supply, one white LED (3.2 V), 20 mA → 440 Ω calculated, 470 Ω (E12, yellow-violet-brown-gold), 18.72 mA real current, 164.8 mW in the resistor → use a ½ W resistor.

LedPreResistor is a one-person hobby project. If it helps you, you can buy me a coffee on Ko-fi ☕. Entirely optional, the tool stays free either way. The program never asks; there is just a small "Buy me a coffee" button in the status bar.

Getting started

1. Download the ZIP from the latest release and unzip it anywhere.
2. Start LedPreResistor.exe. Nothing to install. Windows SmartScreen may warn because the exe is not signed: "More info" → "Run anyway".
3. Optional: compare the SHA-256 checksum with the one in the release notes (certutil -hashfile LedPreResistor.exe SHA256).

Linux (x86_64, native GTK2 build):

1. Download LedPreResistor-<version>-linux-x86_64.tar.gz from the latest release and unpack it.
2. Run ./LedPreResistor in the unpacked folder. It needs GTK2, which most desktops already have (otherwise: sudo apt install libgtk2.0-0, sudo dnf install gtk2 or sudo pacman -S gtk2).
3. Optional: ./install.sh adds the program to your application menu (no root, into ~/.local), ./install.sh --uninstall removes it.

Building

Lazarus 3.8 (FPC 3.2.2), LCL only:

lazbuild -B --os=win64 --cpu=x86_64 --ws=win32 src/LedPreResistor.lpi   # Windows
lazbuild -B --ws=gtk2 src/LedPreResistor.lpi                            # Linux
linux/pakete-bauen.sh <version> ausgabe                                 # Linux tar.gz

Every pull request and every push to main is built automatically for Windows and Linux by GitHub Actions (.github/workflows/build.yml).

Repository layout

Path	Content
src/	Lazarus project and units
src/lang/	Translations (German / English)
tests/	Unit tests of the calculation (FPCUnit, run by every build)
docs/	Project overview, development log, ideas, test builds (German)
docs/legacy/	Original Delphi 7 source code from 2004, for reference only
docs/design/	Approved design draft (open the HTML file in a browser)
linux/	Linux packaging: menu entry, install script, readme, pakete-bauen.sh
site/	Project website (GitHub Pages, English and German)

License

MIT, see LICENSE.