LEDs & Power
About & Help

TC420 Programmable LED Time Controller

Welcome to TC420.net. Here I'm going to show you how to set-up and use the TC420, and pass along any tips or bugs I've found along the way. I want to make this site a great resource for fish keepers wanting to install DIY LED lighting in their aquarium.

Please note: I do not manufacture the TC420, nor am I associated with the people that do.

NULL Mode Problem

A lot of people have been contacting me all with the same problem. The symptoms are:

  • You plug in the TC420 via USB
  • You upload the mode(s) and test the mode(s) with the play button in the PLed software and it works fine
  • You disconnect the USB but the mode(S) does not run, no lights come on
  • If you switch the power off then on, the mode(s) disappear and NULL is displayed on the screen

Fix Options

There are 2 options for you if you have this problem. The first option is to return the TC420 to your supplier as faulty and hope your replacement is a working version.

The second option is to update the device yourself. You can contact the manufacturer and they will sell you a device to update the processor in your TC420, however these may be sold out temporarily. From discussions I've had with people, the issue seems that there was an issue when the device was programmed. It was initially thought to just be the firmware, but this is not the case.

Please find all the details on this page.

NOTE: Please do not update your firmware unless your TC420 has the error above.

About the TC420

The TC420 is a simple, programmable time controller that can alter the brightness of up to 5 channels, each channel supporting a maximum of 4 amps. As an idea of what this can run, my Dad is using a single TC420 to control the main and sump lights on two marine aquariums, a 4' 400 litre system and a 2' 110 litre system.

The controller is programmed by a PC via a USB connection. The controller then performs the desired changes via it's 5 control ports. Input to the unit should be via a regulated power supply rated at 12v to 24v, but make sure the power supply is rated at the same voltage as your LEDs, or that you have a converter to make it safe.

The TC420 uses Pulse Width Modulation (PWM) to alter the brightness of the LEDs, as it is a very energy efficient way to do it. What this means is that the TC420 flashes the LEDs on and off extremely quickly to change how bright the LEDs appear; this happens in hundredths of a second. Each "flash" of the LED has what's known as a duty-cycle, and this determines how long the LED is on and off. Imagine our controller takes 20000 microseconds to complete 1 cycle and our duty is set to 25%, the LED will be on for 5000 microseconds, and then off for 15000 microseconds. The longer the off time, the dimmer the LED's brightness.

I hope this guide gives you a good head start for using the TC420 with your aquariums. This site will be growing as I learn more; I will be adding features, calculators, videos, and guides to make using the device even quicker and easier for you. If you would like to drop me any feedback, please visit the About TC420.net page.