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Just continuing a discussion started in a pic from Sauraen. I asked if he noticed any problems driving that many LEDs, the answer was that everything worked out fine. Psykhaze asked about 74HC541, but this is implemented in the Core to take the load off the MCU driving the SRIO lines. (For better results resistors should be added at the 541 outputs to control the impedance/attenuate reflections.) Also, some degree of PWM control is possible in LED matrices but of course limited by the 1/8 multiplexing. There are LED driver chips as mentioned, but they run over SPI. The beauty of shift register designs is (as mentioned) wide availability, but from a programming perspective the usage is also very simple -- once the matrix driver is written -- just send a series of bits and latch in a regular cycle; the low processor overhead is easily predictable. While the standard BLM uses 220R /13mA peak for red LEDs, the BLM 16x16+X is driving blue LEDs with 56R, so more like 35mA peak. Of course only one 595 output will be on at a time with 1/8 multiplexing. Still, turning multiple LEDs on drops the supply voltage, so much so that I needed a power up delay to allow the logic to stabilise, and a local buck-boost regulator helped. My feeling is the "high" current demands put on the anode drivers could do with some improvement. From the current sink side, this is already solved by using NPN bipolar transistors. The row scanning means 8 or even 16 LEDs could be on at a time, but that's no problem for the transistor. An N-channel MOSFET would likely do a better job, but these are a bit more expensive with lower availability, and are more prone to ESD. Another common method is to use a ULN2803 (8-channel Darlington) current sink. The issue is the extra PN junction has the effect of raising 0V/ground, which in turn can cause problems triggering the DIN side, especially if the supply starts to sag/droop. It seems fine to use a plain old 595 output to drive LED anodes at low current. But what about higher current LEDs, or organ pipes? The simplest method might be to use a common emitter PNP with base and collector resistors. If a higher source voltage was needed, a cascaded NPN/PNP would work. (If a PNP had 12V supplied to the emitter and 5V switching on the base, it would never turn off.) Getting fancier, there are chips numbered 2981 which act as source drivers. The UDN2981 is from Allegro (availability isn't great); the MIC2981 can be ordered at Mouser with good stock levels at the moment. So maybe that's the answer. TPS2080/2081/2082 (dual) and TPS2085/2086/2087 (quad) look okay as chip-based MOSFET high side drivers. There are shift registers with better sinking capability (e.g. TPIC6595), but there's only one I've seen for sourcing: MIC5891. On paper it looks good (have to check the programming), but the pinout is different -- actually nicer than 595 IMO -- and I'm a bit wary of using "specialist" chips for long-term availability. Now I've got all of those part numbers down I can close most of my browser tabs :-)