My name is Greg Winn I am a web developer, specializing in web application development. Take a look at some of my projects, then drop me a line.

Latest Posts

LED Resistor Calculator Posted on 27 July 2015.
TI-99/4A Starting with the Keyboard Posted on 24 June 2015.
Rebuilding a TI-99/4A Posted on 20 May 2015.
Watchdog Arduino Posted on 01 December 2014.
extconf.rb failed Posted on 30 November 2014.
Winn A1 now on Amazon Posted on 05 September 2014.
Bootloading an ATTiny85 Posted on 24 August 2014.
Winn A1 coming very soon Posted on 15 August 2014.
Rails API CORS Posted on 20 April 2014.
Using yStock Posted on 21 April 2013.
Active Merchant Posted on 17 October 2012.
Deployment with rubber Posted on 20 August 2012.

View older articles.

My Gems

Most of my projects can be followed on Github (@gregwinn)


This is a wrapper for the Lnkdto API. This gem gives to access to both single url and batch url requests.

Gem Version Build Status


This Ruby gem named Ystock will pull stock information such as price, volume, and change from Yahoo! & Google Finance.

Gem Version Build Status Coverage Status

LED Resistor Calculator Posted on 27 July 2015

LED Resistor Calculator on a TI-Nspire CX CAS

Single LED only, not ment for use with series/parallel arrays.

Recently I needed to calculate a bunch of LED current limiting resistor values for different colored LED’s. In order to quickly do this I created a simple TI BASIC program that runs on my TI-Nspire CX CAS calculator based on the math used to calculate the value.

The Math

This very simple math problem will give you the current limiting resistor value for any LED!

# R = The Resistor value

R = (VCC - Forward Voltage) / Forward Current

The program asks 3 questions:

  • VCC -> The input voltage going to the LED.
  • Forward Voltage -> The voltage the LED allows through.
  • Forward Current -> Current needed to make the LED light up!



Let me know if you have any questions or edits.

Checkout the Gist, or the GitHub Repo.