Find a solution for LED intensity variation

[daveythacher]

LED brightness varies as a function of temperature, manufacturing and usage. Currently there is no automatic process for doing this without computer vision. It is possible for LEDs to do this on their own, however I do not have access to such LEDs. I can make something like them but those are cost prohibitive.

[daveythacher]

It should be noted the following issues have already been considered to be less of an issue:

• Serial Bandwidth
• Par capacitance
• Power stability
• Multiplexing/Refresh
• Signal Integrity
• Inrush current

The main issues found:

• LED driver temperature
• LED temperature
• LED intensity
• Ground stability
• Response time of LED

A dynamic digital signal processing control loop is required to maintain stability of the output intensity. The bandwidth of this control loop likely forbids multiplexing with high contrast. A dedicated coprocessor will likely be required, such as a custom neopixel. Current neopixels are not believed to operate fast enough or reliably enough to be considered. This will mean most LED displays should be single scan and that multiplexing is a pointless cost optimization.

An alternative to the neopixel is a custom LED which sinks heat to a substrate. This may support multiplexing with DSP module, however this is not believed to work with most SRAM based LED drivers. It may be possible to support hardware PWM drivers using this approach but that would be a conjecture.

[daveythacher]

Such digital signal processing would need to model multiple dimensions of intensity without direct measurement. Therefore neopixel is the preferred approach. (Direct measurement and compensation.)

• LED intensity can vary as a function of power rail/cable, LED driver ground pin and/or PCB traces/planes.
• LED intensity can vary as a function of LED temperature from previous refresh and/or frame.
• LED intensity can vary as a function of LED driver temperature from previous multiplex.
• LED intensity can vary as a function of manufacturing.

[daveythacher]

Note neopixels should provide a means of error detection using a boundary scan based test approach. Thereby allowing them to fail to an observable error state by default. This requires multiple types of fault detection to prove operation of the control plane.