Hello.
So, I noticed something strange with my circuit, and while I can "work-around" it, I'd like to understand what's going on.
I took my LED display project to school so I could use their DC power supply. I found that my project works (MCU runs, the LEDs light up as expected, etc...) if I connect it to an already on 3.5v to 4.0v. If I ramp up the voltage, it seems to get stuck, If the voltage goes much above 4v, it seems to stop working, and I have to disconnect the power supply and lower it back to 4v.
My current block diagram:
+--------------------+ | 8x8 RGB LED matrix | | Common Cathode per | | row | | | | | +--------------------+ |||| ||||||||||||| 8||| 24 anode pins Row| ||||\|||| \|||| Select |||| \|||| \|||| pins |||| \|||| \||||| |||| RED| \GRN| \BLU| |||| |||| \|||| \|||| |||| [TLC5916]-[TLC5916]-[TLC5916] |||| |||| [54HC238] |||| || |||| || |||| [20MHz xtal][2 caps for 20MHz resonance] || |||| ||| \\ [ATTiny84 MCU] -========-/The way that this works is that each of the TLC5916 chips sink current (if all on, that's 24 times current sink from the chips) from the specific PIN which is "active" on the 54HC238.
Though the RED is configured for lower current (it is brighter than the green and blue for the same current).
I built this before I understood how transistors work and can be applied.
As far as I know, all my chips are rated to run at 5v. The only thing I can think of is maybe the constant current sinks are drawing more current from the 54HC238 than it supports, and is causing it to stick?
If I limit the current from the power supply, the starts moving all over the place of course, but the circuit seems to continue working. At first I thought the crystal oscillator wasn't working at the voltages, but the oscilloscope at school shows a great sine wave at 20MHz with a peak-to-peak of 5v, regardless of VCC voltage.
I'm wondering if I need to use transistors (MOSFETs maybe) with the gate connected to the output of the 54HC238. Thoughts?
Thanks for any comments/suggestions/thoughts.