Rs232 example, excessive ripple on power supply

Other Hardware General Electronics
1

I simply followed this example

If I test the 5v from the Arduino, I see on the oscilloscope a normal 5v plus a little ripple, but if I attach the 5v and GND to the breadboard I get this :

https://dl.dropboxusercontent.com/u/1186728/IMG_20130612_110800.jpg

The 5v supply has :

  • 4.88 V average
  • 333.6KHz frequency
  • 4.64 Vpp
  • 3.36 Vmin
  • 8 Vmax

The connections are correct, but the rs-232 cable is not connected and also the tx and rx from arduino are not connected. It is just the max 3323 with all the stuffs around. Is it normal? What could be the cause?

2

Try connecting a ceramic capacitor, value 0.1uF or greater, between pins 15 and 16 (Vcc and ground) of the MAX3323, as close to the chip as possible.

3

PS - there is an error in the tutorial. The 3rd capacitor listed should be connected between pin 2 and ground, not pin 1 and ground.

4

PPS - I just spotted another error in the tutorial. If you are using polarized capacitors, then the one between pin 6 and ground must have its negative side connected to pin 6, not to ground.