Background:
I've started down a project where I want to drive three honkin' large 7-segment LED displays. These digits use a ~8V supply to drive them (I'm not going to use the decimal point). I can definitely verify that the digits barely turn on until at least 6V. I am currently using an 8V voltage regulator to step down from 13.8V (this is going in a vehicle):
https://www.kingbrightusa.com/product.asp?catalog_name=LED&product_id=SC23-11SRWA
I was going to use the MAX7221 LED display driver to run them with the LEDcontrol library:
https://www.maximintegrated.com/en/products/power/display-power-control/MAX7221.html
According to the 7221 datasheet, to run a 2.3" display requires the use of a MAX394 switching circuit, some individual MOSFETs, and a +5/-5 voltage supply for the MAX394. This forum post mentions using a MAX681 to get +10/-10 out of +5V, but I need half that. The product information indicates the MAX681 is a "doubler", so would supplying +2.5V to it produce a +5/-5 output?
https://forum.arduino.cc/t/can-you-...itive-voltage-out-of-the-same-source/101213/7
This app note talks about ways to drive common anode displays (I currently have common cathode ones but I can reorder anode ones if it simplifies things):
https://www.maximintegrated.com/en/design/technical-documents/app-notes/1/1196.html
This is also a lot of extra circuitry just to drive some digits and a significant extra cost. The 1.5" 7-segment LED display looks like it can operate at 3.8-4.6V:
https://www.kingbrightusa.com/category.asp?catalog_name=LED&category_name=KC1-Digit 1.5in&page=1
There's also a 1.8" one, but it requires 5.4-6.9V:
https://www.kingbrightusa.com/category.asp?catalog_name=LED&category_name=KC1-Digit 1.8in&page=1
That being said, this comment in this thread indicates that the 7221 is a current device, and not a voltage device, but, still:
https://forum.arduino.cc/t/max7219-voltage-to-low-0-2v/880284/10
Questions:
1. Can the MAX7221 drive the 1.5" LED display directly? The 1.8"?
2. If I want to use the 2.3" digits and need to run the MAX394 + MOSFETs, what is the right/best way to get +5/-5? Somehow I don't think a pile of voltage regulators is the right choice.
3. Is there a simpler way to run the 2.3" LEDs?
I've started down a project where I want to drive three honkin' large 7-segment LED displays. These digits use a ~8V supply to drive them (I'm not going to use the decimal point). I can definitely verify that the digits barely turn on until at least 6V. I am currently using an 8V voltage regulator to step down from 13.8V (this is going in a vehicle):
https://www.kingbrightusa.com/product.asp?catalog_name=LED&product_id=SC23-11SRWA
I was going to use the MAX7221 LED display driver to run them with the LEDcontrol library:
https://www.maximintegrated.com/en/products/power/display-power-control/MAX7221.html
According to the 7221 datasheet, to run a 2.3" display requires the use of a MAX394 switching circuit, some individual MOSFETs, and a +5/-5 voltage supply for the MAX394. This forum post mentions using a MAX681 to get +10/-10 out of +5V, but I need half that. The product information indicates the MAX681 is a "doubler", so would supplying +2.5V to it produce a +5/-5 output?
https://forum.arduino.cc/t/can-you-...itive-voltage-out-of-the-same-source/101213/7
This app note talks about ways to drive common anode displays (I currently have common cathode ones but I can reorder anode ones if it simplifies things):
https://www.maximintegrated.com/en/design/technical-documents/app-notes/1/1196.html
This is also a lot of extra circuitry just to drive some digits and a significant extra cost. The 1.5" 7-segment LED display looks like it can operate at 3.8-4.6V:
https://www.kingbrightusa.com/category.asp?catalog_name=LED&category_name=KC1-Digit 1.5in&page=1
There's also a 1.8" one, but it requires 5.4-6.9V:
https://www.kingbrightusa.com/category.asp?catalog_name=LED&category_name=KC1-Digit 1.8in&page=1
That being said, this comment in this thread indicates that the 7221 is a current device, and not a voltage device, but, still:
https://forum.arduino.cc/t/max7219-voltage-to-low-0-2v/880284/10
Questions:
1. Can the MAX7221 drive the 1.5" LED display directly? The 1.8"?
2. If I want to use the 2.3" digits and need to run the MAX394 + MOSFETs, what is the right/best way to get +5/-5? Somehow I don't think a pile of voltage regulators is the right choice.
3. Is there a simpler way to run the 2.3" LEDs?
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