Hi Garrett my compliment for your italian understanding
The ShiftBrite is not defective, it will operate from 5.5V to 9V, though 6V to 7V are preferred. It has an internal regulator for 5V internal logic, and constant current sink drivers. Ballast resistors are not needed at that voltage range because the current sink drivers will be able to regulate that amount of excess voltage.
I don't say that the shifbrite are definitely defective, but i say that maybe an issue regardig the absence of the ballast resistor, again from the A6281
The voltage on the outputs should be kept in the range 1 to 3 V.
If the voltage goes below 1V, the current will begin to rolloff as
above 3 V, the power the driver runs out of headroom. At V
OUT dissipation may become a problem, as each output contributes
V × I of power loss in the output sink driver. Typically the
OUT LED power supply nominal voltage is chosen to keep the output volt-age in this range. Alternatively, series resistors can be added to
dissipate the extra power and keep the output voltage within the
the simplified shema of one SB is thi for what i can understand
PS+ 5 to 9V )-------|>|------(A6281 OUTn)----------(GND
So suppose i set PS 9 V , the RED Led have a forward voltage of 2.1 and 20mA of forward current:
- where go the over voltage 9-2.1=6.9V how can absorbe its? may be the allegro chip so this means 150mW to dissipate for it
- what about this statement in the spec of allegro chip "The voltage on the outputs should be kept in the range 1 to 3 V. " here we have 6.9V we are out of the range
Adding a capacitor may be a good idea but in practice it has not been necessary.
i don't know if it is not necessary but for sure is a very good practice.
The 10 ShiftBrites that ale914 had were connected to 12V, and later attached to a 9V source without connecting the GND wire. This can cause incorrect voltages on the TTL communication lines. I have sent 10 replacement ShiftBrites to ale914 for free.
ther was a misunderstanding, i never connect to 12 V i use a 9V battery and yes the GND at certain moment disconnect. you are right this can for sure cause a damage to the allegro chip, this i why i start to investigate it and found the possible issue regarding the ballast resistor i explai above.
I very thanks you for the refound of the new SB and i'm sorry if you feel my point as an attack to you or your SB, i only try to understand better how your SB works, i guess that a perfect SB is good for the community and also for you.
Sorry italians guy for the english.