I have recently embarked on creating my own 2 Team Score Counter. There a few out there for sale but with some time to kill I thought it would be more fun creating my own. This is my first time using an Arduino. I have done some programming back in the day but have no experience in electronics. It has been a lot of fun so far. I purchased a starter kit and have used what was in the starter kit to create a prototype. It is a simple design with a plus and minus button for each team and a reset button. A 1/2 Inch - 4 Digit - 7 Segment - Common Cathode LED came with the starter kit so that is what I have been using. Digit 1 and 2 are used to keep track of Team 1's Score and Digit 3 and 4 are used to keep track of Team 2's score. I am using two instances of the SevSeg library to control the LEDs and each team's score. Everything in the prototype works great and I am happy with the code and how it functions.
I would like to create a bigger version of this (bigger LEDs). I thought I could order larger LEDs and use the same general circuitry but I can not get the LEDs to work. Since the original 4 Digit LED in the starter kit was Common Cathode I ordered 5 Inch Common Cathode LEDs. Ultimately I would like Team 1's score to be Red and Team 2's score to be Blue. From the datasheet provided for each I believed that they would run off of 5V and 20mA. I have been unsuccessful in getting the larger LEDs to work.
Thinking that maybe the LEDs were defective, I contacted the supplier and the only response I received was that the Red LED needs 6V and the Blue LED needs 9V. After doing some research I believe that I can use the 9V 1A wall wart that came with the starter kit and then use the Vin pin on the Arduino to get the 9V needed for the Blue LED (if it actually needs 9V). Again I have no experience with the electronics side and I am not sure what needs to be done to make these work.
I have attached my existing circuit that works with the 1/2 Inch - 4 Digit CC LED. There is also a diagram of the circuit with the (2) 5 Inch CC Red and (2) 5 Inch Blue LEDs. I have also attached the datasheets from the supplier.
Any suggestions, comments, feedback on what I need to do to get these larger LEDs working would be greatly appreciated.
Generally you need a high current/high voltage shift register (TPIC6B595) to sink current thru common anode LEDs to light them.
If they are common cathode LEDs then a high current high voltage shift register (MIC5891) is used to source into the segments to light them up.
Your parts are both common cathode.
If you look at the datasheet, you can see each segment is made of multiple LEDs in series. Vf is for the different colors, and there is a current.
So for a power supply you will need # LEDs in series x Vf of the LEDs for voltage level.
Then there is a spec on the current for a string of LEDs. Brightness numbers are given at 20mA.
Two LEDs in parallel will need 40mA. 7 LEDs in series need 7 x Vf for voltage, plus a little more so a current limit resistor can be used.
With a Vf of 2.5V, x 7 = 17.5V. Assume a 20V supply is used.
Then Resistor R needed of (20V - (7 x 2.5))/current of 0.04A = 62.5 ohm (Vs - Vf)/I = R
The resistor will dissipate (20 - (7 x 2.5) * .04A = 0.1W P = IV, so normal 1/4W rated resistor is all you need.
Each segment needs 40mA, so: 40mA/segment x 7 segments/digit x # digits = how much current the power supply needs to supply.
.04 x 7 x 8 = 2.24A @ 20V for this example and 8 digits, all showing the #8 at the same time.
CrossRoads has calculated figures for the red digits, but the blue digits will need even higher voltages, as those segments also have 7 pairs of leds, probably around 27~28V. To avoid having separate psu for red and green, you will need to calculate the series resistors based on that higher voltage.
You should contact the supplier again. Either they gave you incorrect information about the displays, or the wrong data sheets.
Can you return these digits to the supplier for at least a partial refund? If so, I would recommend that. These displays are not suitable for beginners.
Thank you both for your input! I had a feeling there was more involved than how I was interpreting the specs and what the supplier was telling me. Unfortunately with the cost of shipping it will be cheaper for me to just keep them and eat the cost, hopefully I will learn enough to put them in production one day.
I still would like to see the project through and have some sort of usable device when its all said and done. I will do some more research and try to find some suitable alternatives. I will take a look at 2", 3" and 4" LEDs to see if they will possibly fall within the specs of being able to be used in my current setup.
