Although I have several Arduino boards for quickly bread boarding a project, I've not used a commercial Shield before, so I'm still learning some Arduino basics.
I ordered a couple GLCDs off eBay for a different project and came across this cool looking Arduino Multi Function Shield for $2 USD.
It appears that many suppliers offer this generic, open source, Shield.
It has a 4 digit, 7-Segment LED display with two SPI serial to parallel shift registers chips for the hardware driver interface, (MC74HC595A chips), (plus a piezo, 4 LEDs, 3 PB switches, and a 10K pot).
I searched around a bit and found a schematic for the Shield, and as best I can tell with a quick look it seems to match the actual Shield I actually have.
I've posted the portion of the schematic that shows the 7-Seg display and its driver below.
My concern is that neither the schematic nor the PCB appear to have current limiting resistors in series with the 7-Segmend display's LED segments.
So, does one assume that the software driver is scanning the segments very quickly, with a low duty cycle, and that both the display and the MC74HC595A can tolerate a 5V Vcc without current limiting?
I don't see any resistors on the Shield, either.
Obviously buyer beware!
So I don't have a formal data sheet for the 7-Segment displays, unfortunately.
This seems a little odd to me, not having any current limiting resistors.
Any thoughts on this?