Stan,
I have been playing with the MP3 player, amp module, and speaker. I have it working fine (other than the startup pop). However, now comes the problem. As you had recommended, I am powering the amp/speaker with the 5VDC supply direct. I wrote a short Arduino program to turn an output pin high for 5 sec. and then low for 5 sec. I tried connecting the MP3 player directly to the output pin and got nothing. I looked at the spec.s for the Arduino and at one site it says 20ma max. at 5V VCC. I measured the MP3 current when powered at 5V direct and it varied between 21 and 19ma--seemed like it should have worked a little; but nothing. So, plan 2. I connected one of my 3904 transistors with the player connected to the 5VDC supply and grounded through the transistor. Used a resistor splitter for the base with 10K to ground and 1K to the base and each end of the resistors connected to the Arduino output pin. The speaker is noisy when the transistor is off and plays poorly when it's on. I measured the voltage drop across the player when powered and it's only 3.8V. I checked the spec.s on the 3904 and it says it can sink 170ma max. With 5VDC direct to the player it works fine. I don't understand what is going on. I know there is a voltage drop across the transistor, but it I measured it and it's very low (maybe 100mv). Do I need to lower the base resistor (currently 1K) to more fully turn on the transistor?
Ken
