Dangerous Prototypes Open Source Hardware

Bus Pirate v4 production problem

December 06, 2010, 10:16:06 am

Here's the problem for this project There's always issues moving from prototype to production, and the great part about doing the small test batch is that they are worked out now rather than while people are waiting for a preorder.

Kevin assembled the prototype and programmed it with the v4 firmware posted in the other thread.

Symptoms:
*It isn't seen at all by the PC
*No OSC on the crystal

We verified:
*power supply (duh)
*MCLR resistor and voltage
*usb->PIC connection
*PIC type (http://search.digikey.com/scripts/DkSea ... 06-I/PT-ND)
*PIC orientation
*Vcore capacitor solder
*I verified the firmware on my v4 hardware, and sent another copy of the test firmware

And now, Kevin has gone through a whole change:
*change PIC
*Crystal
*soldered a new PCBA manually

I'm kind of stumped, so I'm opening it up. Any suggestions?

All the current BPv4 stuff is in SVN.

Re: Bus Pirate v4 production problem

Reply #1 – December 06, 2010, 10:20:48 am

I figured it out

BOM has 0.1uF on the crystal. Duh. My fault, apologies all around.

Re: Bus Pirate v4 production problem

Reply #2 – December 06, 2010, 10:34:41 am

[s:]With the proto you had an issue with Vdis:

http://dangerousprototypes.com/forum/in ... 31#msg8431

I don't think it is the issue, but better safe then sorry [/s:]

Re: Bus Pirate v4 production problem

Reply #3 – December 06, 2010, 04:06:06 pm

[quote author="ian"]
I figured it out

BOM has 0.1uF on the crystal. Duh. My fault, apologies all around.
[/quote]

noob question: I notice that many of the AVR designs use a ceramic resonator instead of a crystal and loading caps.   It it a difference in the MCU design or a just a per (board) designer's preference?

Re: Bus Pirate v4 production problem

Reply #4 – December 06, 2010, 04:18:47 pm

I think the resonator is cheaper, but less accurate. This design pretty much requires a real crystal because the USB needs a pretty precise frequency.

Re: Bus Pirate v4 production problem

Reply #5 – December 07, 2010, 03:02:15 pm

i have had usb designs that used resonators successfully, you just need to find a supplier that carries a higher tolerance part.