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by tubular
Sun Jul 27, 2014 12:58 pm
Forum: Add-ons
Topic: Preliminary B+ HAT (Hardware Attached on Top) docs/specs
Replies: 106
Views: 32648

Re: Preliminary B+ HAT (Hardware Attached on Top) docs/specs

rpdom, yes, if its critical to use a particular gpio pin for its alt function, then the stack order also matters. Keep in mind I'm only 'stacking' the extended 9 gpio pins, the original 26 pins carry through as usual. If your board is the first in the stack, there may be away to grab your desired (c...
by tubular
Sun Jul 27, 2014 10:42 am
Forum: Add-ons
Topic: Preliminary B+ HAT (Hardware Attached on Top) docs/specs
Replies: 106
Views: 32648

Re: Preliminary B+ HAT (Hardware Attached on Top) docs/specs

Here's one way to implement the stack, with the ability to easily carry signals straight through (for the original 26 pins), or stagger GPIO so they don't conflict (for the new 14 pins). https://www.dropbox.com/s/frsr0y6ver7hqi1/2014-07-27%2009.55.46.jpg The female header is a 'passthrough' type, th...
by tubular
Sat Jul 26, 2014 11:38 am
Forum: Add-ons
Topic: Preliminary B+ HAT (Hardware Attached on Top) docs/specs
Replies: 106
Views: 32648

Re: Preliminary B+ HAT (Hardware Attached on Top) docs/specs

Let me get some mock-ups together of how to do it
by tubular
Sat Jul 26, 2014 10:27 am
Forum: Add-ons
Topic: Preliminary B+ HAT (Hardware Attached on Top) docs/specs
Replies: 106
Views: 32648

Re: Preliminary B+ HAT (Hardware Attached on Top) docs/specs

Sorry what I mean by "can" is that it is _able_ to be solved in the software domain (GPIO mapping). However the stack does separate out the GPIO on a board by board basis By way of example say you have an SPI ADC (requires 1 chip enable, + the SPI already on the 26way connector), and a stepper motor...
by tubular
Sat Jul 26, 2014 10:05 am
Forum: Add-ons
Topic: Preliminary B+ HAT (Hardware Attached on Top) docs/specs
Replies: 106
Views: 32648

Re: Preliminary B+ HAT (Hardware Attached on Top) docs/specs

There's no doubt the HAT spec will be a big step forward. Its good to understand some of the logic behind what you've already looked at, so thanks for that. I realise its important to maintain compatibility with existing 26 way boards. What I'm proposing is just to use the new 9 GPIO pins in a 'stac...
by tubular
Sat Jul 26, 2014 9:29 am
Forum: Add-ons
Topic: Preliminary B+ HAT (Hardware Attached on Top) docs/specs
Replies: 106
Views: 32648

Re: Preliminary B+ HAT (Hardware Attached on Top) docs/specs

James Adams wrote:
we couldn't/can't make bullet-proof electically by simple means
What were the main issues you struck, James? Too much capacitance caused by more boards in the stack? Electrical loading? Other aspects?

What sort of max data rate can the SPI interface run to currently?
by tubular
Sat Jul 26, 2014 8:05 am
Forum: Add-ons
Topic: Preliminary B+ HAT (Hardware Attached on Top) docs/specs
Replies: 106
Views: 32648

Re: Preliminary B+ HAT (Hardware Attached on Top) docs/specs

The eeproms contain the information about the gpio used. From the Pi point of view, it can determine what (extended) gpio routes to which board, up to 4 deep. Capacitance wise there is another way to do it without long routes and alternating direction. However I'll duck into work and get some capaci...
by tubular
Sat Jul 26, 2014 4:37 am
Forum: Add-ons
Topic: B+ Perfboard pattern (mounting holes)
Replies: 2
Views: 2780

Re: B+ Perfboard pattern (mounting holes)

PiPb_mech_perfboard.png Hopefully this is useful. I would start with (just under) a 2.5" x 2.2" rectangle of perf board. Cut along the holes of the perfboard. It will fit nicely as full 65mm width still works but is close to ethernet RJ45 jack. The lower two holes could be drilled with ~3mm drill b...
by tubular
Fri Jul 25, 2014 11:09 pm
Forum: Add-ons
Topic: Preliminary B+ HAT (Hardware Attached on Top) docs/specs
Replies: 106
Views: 32648

Re: Preliminary B+ HAT (Hardware Attached on Top) docs/specs

Hi James I've been working on a solution to the "stack" problem - photo at this link https://www.dropbox.com/s/myyuq34h4ew1qg2/2014-07-24%2011.07.32.jpg It works by using the new extra 9 gpio as a "stack" - plug in boards take one or more pins from the stack and the rest shuffle down in numerical gp...

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