Problem when MB64e running from USB power

Testing/Troubleshooting
1

Hello to All!

I hope that some of you have experience regarding this issue, which I am facing with at the moment.

I built a midibox64 with 1 core 8, 1AIN, 2DINs, 1DOUT, and a PIC USB module.

First I built into the core module the 7805 voltage regulator, everything worked fine.

Now I soldered out the 7805 from the module to try the whole system’s working from my laptop’s USB power.

It is working, but in some cases random midi events are sent.

I placed 100nF capacitors near to all shift registers on AIN, DIN, DOUT modules, and to the power input of the USB module.

What I already tried:

  • replace the USB cable to a good quality shielded cable >>> less random event, but still occurrs

  • disconnect the laptop’s PSU >>> it had no influence to this

  • disconnect the mouse, and using only the touchpad on the laptop >>> sporadic random events still occurred

I suspect some noise on the USB power. All integrated circuit have its own capacitor, so I have no other idea what else should I do.

Can somebody help me to solve this?

Thank you in advance for everyone!

2

It could help to add a small resistor (e.g. 10 Ohm) in serial to the 5V power input of the core module + a 1000..2200 uF bypass cap in parallel between ground and +5V *behind* the resistor (at J2)

(in fact you could just re-use C2 by soldering the pins to J2 with small wires)

I did something similar with the AINSER64 module with success: much less ripple noise :slight_smile:

See also this schematic: http://www.ucapps.de/mbhp/mbhp_ainser64.pdf

Best Regards, Thorsten.

3

It could help to add a small resistor (e.g. 10 Ohm) in serial to the 5V power input of the core module + a 1000..2200 uF bypass cap in parallel between ground and +5V *behind* the resistor (at J2)

(in fact you could just re-use C2 by soldering the pins to J2 with small wires)

I did something similar with the AINSER64 module with success: much less ripple noise :slight_smile:

See also this schematic: http://www.ucapps.de/mbhp/mbhp_ainser64.pdf

Best Regards, Thorsten.

Thanks Thorsten for your quick answer!

I’ll try it tomorrow, and write here the result.

Thank you once more :slight_smile:

4

Hello Thorsten,

the small resistor in series with the +5V not worked, because the core module did not boot in. All leds are lighting, and nothing happens.

But I realized a big mistake what I made… As I mentioned I soldered out the voltage regulator, and because of this the buffer capacitor C5 on the core module wasn’t in contact with the power line… So the filtering was not appropriate.

Now I cutted the + line which comes from the bridge rectifier, and I put a bridge between the VREG in and out points.

Now everything works fine, random events could not be observed.

Anyway, thanks for your help :slight_smile: