Help needed dout

[besh]

Hello, this is my first midibox project and I have a problem with the dout module.

My mb64 start sometimes , sometimes not. If I put my finger on the sc/rc input of the dout

module the box get started. I tested all buttons and all leds, they are working. Do I have to drill

a hole in my midibox to get it started by putting my finger on the rc/sc line???

[TK.]

Do I have to drill a hole in my midibox to get it started by putting my finger on the rc/sc line???

No!!! ;)

This issue could be related to the wire impedance.

How many DOUT modules are connected together, and how long are the cables?

Best Regards, Thorsten.

[besh]

Hi Thorsten,

There are 2 dout modules connected to 60 Leds.

The longest cables to the Leds are about 50 cm.

Is that maybe to long?

[TK.]

No, thats uncritical.

Hm, strange... it sounds like there is a power problem, e.g. Vss and/or Vdd between core and DOUT module not connected. This could cause such effects as well.

Did you already check the connections between core and DOUT modules?

Best Regards, Thorsten.

[besh]

After turning mad,could the problem be that I have not grounded the case?

Now with ground it seems to work.

EDIT: No it has nothing to do with grounding I ve to search again.

Edited September 13, 2010 by besh

[besh]

There are only 3.85 Volt on the line to dout module and if I touch the rc/sc line it goes up to 5 Volt.

Mysterious.

[TK.]

Do you mean MBHP_CORE::J8:Vd with the "line"?

Best Regards, Thorsten.

[besh]

Yes, J8 Vd 3.8 Volt, and then with putting finger 5 Volt.

And sometimes midibox do start, sometimes not, wihout any schematic.

Edited September 13, 2010 by besh

[TK.]

Ok, looks like a bad soldering joint at the core module - check the track which goes to the J8:Vd pin.

Best Regards, Thorsten.

[besh]

Looks like you were right. Thanks a lot.

[TK.]

Great! :)

Best Regards, Thorsten.

[besh]

Ahhrrgg, on either way it dont work. 10 times or more turning on, all is fine.

next time turning on all leds or only a some are burning but midibox dont start.

The voltage on J8 Vd is too low. I proved all soldering an see no problem.

Why is the starting prodcedure randomized?

Edited September 14, 2010 by besh

[TK.]

What is the voltage at J1 and J2? Maybe your PSU isn't strong enough?

Best Regards, Thorsten.

[besh]

The voltage at J1-2 is about 7,6Volt.

If I try to press more then one button together the midibox reset.

It must be some voltage problem without pic and all leds burning

the Voltage at dout module is only 4 Volt.

[besh]

It works! After trying two differnt psu which were dc with over 500mA ,I tried a ac psu and it works now.

thanks for your patience. But why it works now, I dont know.

[TK.]

alright! :)

somehow this makes sense to me: the power consumption depends on how many LEDs are active at once.

Normally a single LED consumes up to 20 mA, but the current draw is already limited to ca. 10 mA via the 74HC595 and 220 ohm resistor.

let's say you've connected 64 LEDs, makes up to 640 mA!

So, your previous PSU was definitely not strong enough.

during power-on it can happen that all LEDs are active for a short moment (ca. 100 mS, you won't notice this), as long as the 74HC595s are not initialized.

putting a finger on a floating line (SC is floating during these 100 mS) will probably avoid that the LEDs are active during this startup phase, maybe because you are grounding a SC by doing so.

however, good that you found the reason!

best regards, thorsten.