Re: [Oap-discuss] issue reading odometry

[Dafydd W. <daf...@gm...>]

Hi Scott,

The new version looks fine.

The problem you encountered (power pins on ICs not being connected) is
common, because parts in gEDA component libraries with hidden power pins
often use different terminology for the power lines.

More often than not, I've found this is a problem when, for example, one
library part calls its hidden power pins GND and Vcc, while another use the
terminology 0V and +5V (there are other variations too, like Vdd, Vss etc.).

The only way to be sure everything's connected properly is to eyeball the
netlist, and look for orphaned nets.

To fix it, I usually just add the necessary nets in one corner of the
schematic (for example, I connect a net called Vcc to +5V), and then the
next time the netlist is generated, it should combine those nets.

Occasionally, I find a schematic library part doesn't have the power pins,
but that's just a bug in the part, and it can be fixed by adding the
necessary hidden power pins to the part.

The new library part you've created is better from the standpoint of
someone who's actually building the circuit, because it shows exactly
what's connected to where, but my own preference in schematics is for
composite parts containing gates and latches to show those gates and
latches individually to aid understanding of how the circuit works. It's a
bit more work to make sure that all the hidden nets are connected, but I
just prefer to do things that way.

Regards,
Dafydd.



2013/11/23 Scott Crawford <rob...@gm...>

> Hi Dafydd,
>
> The gEDA gsch2pcb tool relies on the schematic pins and network to create
> the pcb traces.
>
> I've created a new 78HC74 symbol and updated the mcm schematic.   Would
> you please review the new version?  The pdf and image formats are available
> from the community wiki:
>
> http://www.openautomaton.org/index.php/MCM
>
> Thanks for your help.
> --scott
>
>
> On Tue, Nov 19, 2013 at 1:14 AM, Dafydd Walters <daf...@gm...>wrote:
>
>> Hi Scott,
>>
>> Yes, pin 14 should be connected to +5V and pin 7 should be connected to
>> GND (0V).
>>
>> It's customary not to show the power supply pin connections of ICs on
>> circuit schematics to avoid clutter, but you mustn't forget the power when
>> laying out the PCB :-)
>>
>> Regards,
>> Dafydd.
>>  On 19 Nov 2013 02:35, "Scott Crawford" <rob...@gm...> wrote:
>>
>>> Hi Dafydd,
>>>
>>> I'm not receiving valid odometry data from the "read_odometry" function
>>> in oap-motor.c.  However, the i2s_smbus_read_block returns exactly 5 bytes.
>>>
>>> Can  you tell me if pin 14, Vcc, on the 74HC74 (U3 and U4) need to be
>>> connected to +5V?
>>>
>>> Some references:
>>> 1. 74HC74 datasheet for a 74HC74 with preset and clear:
>>> http://www.fairchildsemi.com/ds/MM/MM74HC74A.pdf
>>>
>>> 2. odometry input signals
>>> http://www.openautomaton.org/index.php/MCM
>>>
>>> 3. Your original oap 0.1 schematic and my rework for pcb design are here:
>>> http://www.openautomaton.org/index.php/Schematics
>>>
>>> Thanks for your help.
>>> --scott
>>>
>>>
>>>
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