I just got back from a trip to China where I purchased 4 large digits as well as the large digit drivers. I have followed [this SparkFun tutorial on hooking them up and tried the One Large Digit example. To my surprise, nothing worked. The large 7-segment display did not light up at all. The text in the console is working fine but nothing is happening in my circuit. I tried using a different 7-segment display with a different large digit driver but it still didn’t work. I used the exact code of the tutorial by copying and pasting it in my IDE so I highly doubt that that is the issue. I am using an Arduino Uno
Is there something I am doing wrong? I have used a multimeter and my soldering job looks fine (all connections work).
Here are a few ideas I have as to what might be wrong, let me know if you think these are issues:
-The voltage I measured using a multimeter on the 12V port of the large digit driver and that is distributed to the 7-segment display after using a 12V power supply to the Arduino and plugging the driver into Vin was 11.3V. Would this cause the display not to light up? (there is not even a low light that gets turned on)
-When looking at the back of my large 7-segment display the part number is KDS-80011-7 while the one in the example pictures in the tutorial is KDS-60011-7. Would this difference be the cause?
-Having bought the parts in China, I believe they are knockoffs. Is there a security measure (like a missing circuit element on the large digit driver) that SparkFun uses to avoid knockoffs? (I’ve already had that issue with Adafruit)
Yes, the difference between the KDS-80011-7 and the KDS-60011-7 is, in addition to the size, the forward voltage drop, due to more LEDs being in series in each segment.
I found a datasheet for the bigger display at https://eleshop.jp/shop/g/gE3K124/ Not sure if this is the one you have, but it states that the forward drop is 18v. Given the 20 ohm resistors on the large driver board and the roughly 6 ohms of series resistance in the TPIC6C595, 60mA would drop 1.5v or so. Therefore, you would need to feed the 12v terminal on the board with 19.5 volts. If you don’t have an adjustable power supply, try a laptop brick; they tend to be in the 19 to 19.5 volt range. If you only have a larger power supply (say a 24v one), you could use that but would need to either change the resistors on the large driver board or add series resistors between the board and the display.
Thank you very much! Since the Arduino can only take maximum 12V I would need to power the driver through the 18V separately, correct? Does the driver have a maximum voltage?
I finally managed to get my hands on a DC power supply. I set the voltage to 19.5V and connected it to the 12V pin on the driver. But there are still no numbers getting displayed on my 7-segment display. I keep getting an HTTP error while uploading the images so here is a link to them:
Those are definitely knock offs, but we don’t omit anything from our design so if someone copied it, the board should work. You might check your display to verify the pinout make sure it’s a common anode display and not a common cathode. (Our design is common anode) If our example code isn’t working and the the displays are common anode, there might be a counterfeit or defective IC on your boards.
Thank you for your response. Is there a way to check if its common anode or common cathode? Also, if it is common cathode, is there a way to make it compatible with the driver?
You would need to remove the driver board from the display and figure out the pinout. If the common lead is positive and connecting negative to each segment’s pin lights them up, you have a common anode display.
If the common lead is negative and connecting positive to segment pins lights them up, you have a common cathode display.
You’d need to add additional electronics to the driver (or use a different driver) to convert your driver to common cathode.