Resistor Question

Thread Starter

Ticrandall

Joined Dec 31, 2021
40
I have very limited electric knowledge, so I appreciate your patience! I was tasked with fixing a shuffleboard scoreboard. Picture attached. The original ic was damaged and not replaceable from the company. So, I used an arduino and lots of wires and reused the board/lights to 'remake' the board. I worked with a guy that did the programming. They're 7 segment numbers. Each number shares common positive. The guy I worked with had me solder resistors in before each number, brown black black purple gold. The problem, the lights are much to dim. With out the resistor the lights are plenty bright. Not knowing much about electronics though, with no resistor will that burn out the lights is my question and if so what should I use as a resistor to make sure that the lights are bright enough?
 

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dl324

Joined Mar 30, 2015
14,323
Welcome to AAC!

Without a schematic, we can't even guess.
  1. What is the supply voltage?
  2. How are the LEDs connected? Are they a matrix, or are they driven individually?
  3. Are transistors being used for column/row or anode/cathode drivers?
  4. How is the Arduino connected?
The guy I worked with had me solder resistors in before each number, brown black black purple gold. The problem, the lights are much to dim
Did he provide you with a schematic? The color code you gave doesn't make sense. Gold as the last band indicates a 5% tolerance, so the purple band would be extraneous.
With out the resistor the lights are plenty bright. Not knowing much about electronics though, with no resistor will that burn out the lights is my question and if so what should I use as a resistor to make sure that the lights are bright enough?
I can't visualize what "before each number" means from your description.
 

sghioto

Joined Dec 31, 2017
3,061
brown black black purple gold
If it's a five band color code that would be 1000 megohms, no wonder they are dim, just joking :DMost like they are 10 ohm resistor. Can you post a photo of the resistor?
If they are 10 ohm resistors you could try replacing them with a smaller value until the desired brightness.
 
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Thread Starter

Ticrandall

Joined Dec 31, 2021
40
Thank you for the reply's! Ok.. Attached are more pictures to hopefully help explain what I am trying to say!.
Supply to arduino mega is 9v. This is a double sided board, so there are 8 - 7 segment numbers, each segment has 25 leds. I have 4 numbers connected together and plugged into a 5v socket on the Arduino. The wires you see are soldered to each segment of the 7 segment number, and then plugged into an arduino socket.

PXL_20210812_003939087.jpgPXL_20210810_121640622.jpgPXL_20211230_235718751.jpgPXL_20210806_213150807.jpg
 

Thread Starter

Ticrandall

Joined Dec 31, 2021
40
Welcome to AAC!

Without a schematic, we can't even guess.
  1. What is the supply voltage?
  2. How are the LEDs connected? Are they a matrix, or are they driven individually?
  3. Are transistors being used for column/row or anode/cathode drivers?
  4. How is the Arduino connected?
Did he provide you with a schematic? The color code you gave doesn't make sense. Gold as the last band indicates a 5% tolerance, so the purple band would be extraneous.
I can't visualize what "before each number" means from your description.
No schematic.. this is.. cobbled together, mostly the guy that helped me just wrote the code to make the lights light up as they are supposed to.
 

sghioto

Joined Dec 31, 2017
3,061
Agree with AlbertHall, a 470 ohm 1% resistor but it appears the resistors are in series with the common anode side of the LED display. Problem with that is the display will vary in brightness depending on the number of segments lit.
If that's not a problem try changing the resistors to 220 ohms, Red-Red-Black-Black-Brown. Or connect two of the 470 ohm resistors in parallel.
 

Thread Starter

Ticrandall

Joined Dec 31, 2021
40
Agree with AlbertHall, a 470 ohm 1% resistor but it appears the resistors are in series with the common anode side of the LED display. Problem with that is the display will vary in brightness depending on the number of segments lit.
If that's not a problem try changing the resistors to 220 ohms, Red-Red-Black-Black-Brown.
Ideally would like them to be the same brightness, so all numbers are the same brightness.
 

dl324

Joined Mar 30, 2015
14,323
Ideally would like them to be the same brightness, so all numbers are the same brightness.
Given the way that the LEDs are wired, you can't even expect to get uniform brightness within a digit. In some cases, you have 4 LEDs in parallel without ballast resistors, and others that can be driven independently. It's a poor design.
 

sagor

Joined Mar 10, 2019
677
Also remember that the Arduino 5V supply cannot power too many external devices. As well, the I/O pins of the Arduino are limited to a maximum current per pin and per port. In many cases, you cannot drive 8 LEDs from one port all at the same time without using a buffer/driver in between.
Without a schematic, hard to tell if you are overloading the Arduino. You should be using some form of buffer driver to drive the LEDs.
 

sghioto

Joined Dec 31, 2017
3,061
With a 9 volt supply you could wire the LEDs in a series arrangement with a ULN2003 driver. The logic from the Arduino would need to be reversed plus re-building the display board. Similar to the schematic below.
1640980269972.png
 

Thread Starter

Ticrandall

Joined Dec 31, 2021
40
Given the way that the LEDs are wired, you can't even expect to get uniform brightness within a digit. In some cases, you have 4 LEDs in parallel without ballast resistors, and others that can be driven independently. It's a poor design.
Perhaps. After completing this I found a several other better ideas. However, The original design had all leds share a single common positive. So, they had it working with one resistor for all.
 

dl324

Joined Mar 30, 2015
14,323
However, The original design had all leds share a single common positive. So, they had it working with one resistor for all.
That doesn't make it a good design.

If you're a manufacturer selling a million widgets, saving a few cents on each unit adds up.

Cheap LED flashlights have many LEDs in parallel without ballast resistors or a current limiting resistor. Having a cascading failure is good for business. They'll just change their name and sell the same crap.
 

Thread Starter

Ticrandall

Joined Dec 31, 2021
40
With a 9 volt supply you could wire the LEDs in a series arrangement with a ULN2003 driver. The logic from the Arduino would need to be reversed plus re-building the display board. Similar to the schematic below.
View attachment 256543
Way over my head, appreciate the reply though.
There are 8 numbers, 25 leds per number, plus a few other lights. Two prongs per light, plus the resistor, that's over 400 solder points. Not feasible for this project. That's why we used the current set up and kept the common positive. When applying direct 5v to the number, all segments are equal brightness - But I fear that will burn them out quickly.
 

Thread Starter

Ticrandall

Joined Dec 31, 2021
40
That doesn't make it a good design.

If you're a manufacturer selling a million widgets, saving a few cents on each unit adds up.

Cheap LED flashlights have many LEDs in parallel without ballast resistors or a current limiting resistor. Having a cascading failure is good for business. They'll just change their name and sell the same crap.
Ha.. quite true. I guess in the 50s they were still worried about penny pinching! Perhaps one reason they are no loner in business.
 
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