LEDs & Power
About & Help

About TC420.net

Welcome to TC420.net. The idea behind this site is 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 do not manufacture the TC420, nor am I associated with the people that do.

I started using the TC420 Programmable LED Time Controller to add a sunrise/sunset effect to my LED lit aquariums. As there was not a lot of information about the TC420 and I found a few issues with it so I created a video to show how I set up the controller on my bedroom aquariums. The video got a lot of views and a lot of questions, so I created a page on my personal web site to show how to set up the TC420 in detail and answer any questions that have been asked in the YouTube comments. That page quickly grew to monstrous proportions, so it has now morphed in to this full site. This is my instructions and guides for the TC420 Programmable LED Time Controller.

About Me

I'm Darren and I live in the South of England. I have been keeping fish on and off for about 26 years. I started with a tiny 12" x 8" x 8" tank with a air pump powered filter, but have progressed over the years to bigger and better things. I currently have 4 working aquariums (3 tropical freshwater and 1 marine) and am working on my biggest project yet, a 6' marine reef tank with pretty much everything being DIY. As well as my own aquariums I help my Dad with his 2 marine tanks and pond.


I'm always interested in hearing your thoughts on the site as well as any questions or suggestions, so please feel free to drop me a message with the form below. If you have a question, please read through the relevant pages first, as I do get a lot of questions for things that are already on the site. I also have a Questions & Answers page and Bugs & Problems page which may also have the answer for you quicker than sending me a message. If not, please feel free to send me a message.
Please note, I am happy to try and help with using the TC420, but I am not technical support and do this in my own time. If you think your TC420 is faulty, please try contacting your supplier first.

PLEASE NOTE: I will not be replying to emails about the null mode error, as it is covered in detail on this page. I will also not be replying to emails about downloading the software, it can be downloaded here. If there is an error page, it may have been downloaded too many times for the day, so try again later.

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.