Advice About Over-Driving LEDs


We usually stay within the recommended Amperage with LEDs, but multiplexed displays provide an interesting opportunity to push them outside of that range. Because multiplexing scans a set of LEDs, they are not on all of the time. If your multiplexing setup allows you to remain within a certain time frame and duty cycle they can be driven past the constant current specifications. [Bryanduxbury] decided to take a look at the best way to overdrive LEDs.

The example that he gives is that his 30 mA constant current rated parts can accept up to 185 mA but only for 0.1ms with a duty cycle of 10%. If you know how to apply these figures you can get them to shine much brighter. This becomes especially useful when your multiplexed display already has the light off for the majority of the time because the resulting average luminosity will be much higher. His side-by-side test is shown above. With a current limited LED on the left of each color group, a multiplexed LED driven at normal voltage in the middle, and multiplexing with overdrive on the right.

The biggest drawback that [Bryan] mentions is that if your firmware hangs for more than the spec’ed time you’ll definitely fry these diodes.

Stripping DRM From OverDrive Media Console EBooks


[Armin Tamzarian’s] local library recently started lending eBooks via the OverDrive Media Console system. He checked out a couple of books, which got him thinking about how the copy protection scheme was implemented. He wondered what recourse users had if they wanted to view a book they have already checked out on a different, or unsupported piece of hardware.

His research centers around Adobe’s ADEPT digital rights management scheme, which is used to protect the books offered on loan by OverDrive. The topic is broken down into three parts, starting with an introduction to the EPUB file structure, the OverDrive Media Console, as well as the aforementioned ADEPT DRM scheme.

The second part takes a close look at the OverDrive Media Console itself, where he uses the ineptkey and ineptepub utilities written by [I♥CABBAGES] to pull the RSA cipher keys from the EPUB data he uncovered. When he then tries to strip the ADEPT DRM layer from his books however, he discovers that OverDrive is using a non-compliant version of the ADEPT standard, which renders existing tools useless.

The final part of [Armin’s] discussion digs even deeper into the OverDrive Console’s inner workings, where he finds that the OverDrive Media Console stores quite a bit of information in an SQLite database. After a bit of digging, he finds all the data he needs to strip the DRM from his books. [Armin] also took the time to wrap all of his findings up into a neat little tool called OMCStrip, which as you may have guessed, strips the DRM from ADEPT-protected eBooks with ease.