The attached schematic shows what I went back and did, mainly to educate myself… two LED’s, one connected to 5V and one connected to GND, with respective resistors, and then a simple sketch to confirm that HIGH and LOW are used the reverse of each other to light the two LED’s. Taking Grumpy_Mike’s comments (since I never found a tutorial or simple example showing it) I wired up two LED’s and tested the two possible configurations to better understand what’s going on. Is there some distinct reason to choose or prefer common cathode or common anode over one another? Now that I have done a lot more homework and reading, please allow me to re-ask my original question… Offloading the multiplexing to the MAX7219 seems like a real performance benefit of using that chip. I need to send step signals to a stepper motor and want a pretty clean "loop", while displaying a pot setting on the 4-digit display (with an occasional analogRead and display update).
the multiplexing handled by the chip doesn't bog down the Arduino. Or just use the single digit approach to make my own.īTW, a comment I haven't read yet, but I'm sure has been made, is one of the features that makes the MAX7219 appealing for my application. I'll have to keep poking around, or maybe just give up and use one slightly larger or slightly smaller. It looks like Liteon makes one, but it's non-stock at Digikey. Right after I hit the last post, I continued my search for 0.3" 4-digit displays. I don't see any 0.3" displays on their site though.
Yes, I can see you've been around a while, but also your answers, no matter how dumb the questions, or how new the member, seem universally helpful and informative. Given the way the MAX7219 works, it looks like I can just make my own 4 digit display, using discrete CC digits, and connecting them like the attached image (borrowed from Nick Gammon's page Gammon Forum : Electronics : Microprocessors : Interfacing LED displays with the MAX7219 driver), creating my own 12-pin-equivalent part to multiplex from the MAX7219. I am trying to match a device that has 0.3" 4 digit displays, but I haven't been able to find a similar 4 digit display in that size, and in fact the one I'm trying to match has discrete digits soldered onto its PCB. But the other approaches like the 595's weren't so obvious with regard to CC/CA preferences or ease of use/programming. In the case of multiplexing with the MAX7219, that sort of answers one of the original questions, as it only works with common cathode displays. I have now read a lot more about the 595's and MAX72xx's too. I think I have read at least another 300 posts now (many, many of them with your answers in them!), and I'm starting to understand the issues a little better. Thanks CrossRoads for the pointers and ideas.
#COMMON ANODE VS COMMON CATHODE HOW TO#
I am trying to figure out how to make a cascaded 4 digit counter, using 7-segment digits, but I'm stumped with what to order/buy to get going.
In trying to read data sheets for devices like TPIC6B595's and 74xx595's, it is very hard for a beginner to understand why and when to select a common cathode or common anode type of device. I am sure this is also closely related to the equally confusing (to me) notion of "sinking" or "sourcing" from Arduino pins. internal pull-ups, or overall power requirements to drive the LED segments, or less complicated programming logic) Is it easiest to use common cathode or common anode devices with an Arduino? Is there some simple explanation/example somewhere to help understand why one might be easier/better than the other when using an Arduino? (e.g. A little additional explanation in examples like the "ShiftOut" tutorial would be really useful for beginners. common cathode or common anode? I don't seem to be able to find much helpful information with my searches to differentiate between the two. Sorry for the beginner question, but I am very confused about which is easiest when working with an Arduino for things like 7-segment displays.
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