I started a new thread for this question. Related threads and the schematic are here:
http://forum.allaboutcircuits.com/showthread.php?t=61894
I just breadboarded this thing including all the recommended changes ( thanks guys ) including .33uf / .1uf caps on the 7805 voltage regulator plus decoupling caps on every IC. I also have 100uF caps across VIN/GND and VOUT/GND on the voltage regulator. I am using 51 Ohm resistors on the LEDs and 220 Ohm resistors on the base of each transistor.
I was building this up slowly testing as I went when I added the 2nd TPIC6C595. I started to get what looked like flicker. I figured something wrong with my multiplex code, but that is not it.
The problem turns out to be a fluctuation in the voltage when all the LEDs are on at one time. I don't have an oscilloscope or any good tools, but on the voltmeter it looked like the voltage was swinging between 5.0 and 4.8 volts. When the flicker goes away the fluctuation also goes away.
I can make the fluctuation go away by increasing the supply voltage to the voltage regulator or drastically increasing the capacitance between Vcc and Gnd. I was using a 9V supply, going to 12V makes the problem go away, or adding 3300uF will let me run at 7.5V with no visible flicker.
What is going on here? Can I counter this problem without increasing the supply voltage or adding such large caps?
http://forum.allaboutcircuits.com/showthread.php?t=61894
I just breadboarded this thing including all the recommended changes ( thanks guys ) including .33uf / .1uf caps on the 7805 voltage regulator plus decoupling caps on every IC. I also have 100uF caps across VIN/GND and VOUT/GND on the voltage regulator. I am using 51 Ohm resistors on the LEDs and 220 Ohm resistors on the base of each transistor.
I was building this up slowly testing as I went when I added the 2nd TPIC6C595. I started to get what looked like flicker. I figured something wrong with my multiplex code, but that is not it.
The problem turns out to be a fluctuation in the voltage when all the LEDs are on at one time. I don't have an oscilloscope or any good tools, but on the voltmeter it looked like the voltage was swinging between 5.0 and 4.8 volts. When the flicker goes away the fluctuation also goes away.
I can make the fluctuation go away by increasing the supply voltage to the voltage regulator or drastically increasing the capacitance between Vcc and Gnd. I was using a 9V supply, going to 12V makes the problem go away, or adding 3300uF will let me run at 7.5V with no visible flicker.
What is going on here? Can I counter this problem without increasing the supply voltage or adding such large caps?