I'm trying to build a large display with 4 custom giant seven segment led numbers. I think I have a decent plan, but I'd like to get some input before I go and spend a bunch of money on something that might not work. I'm especially looking for input on the schematic in the file called "scoreboard wiring.png". I know it's going to be a ton of pieces and soldering, but I'm okay with that.
requirements -
4 digits
able to control each segment of each digit separately
pwm to adjust brightness of entire display
my idea for how to do it -
25 green leds per segment * 7 segments per digit = 175 leds per digit
175 leds per digit * 4 digits = 700 leds
5 constant current drivers driving 5 leds each per segment
3.2V per led * 5 leds per driver = 16V
700 leds / 5 leds per driver = 140 drivers
140 drivers * 20mA per driver = 2.8 A
18V 6A power supply
shift registers turn on constant current drivers for each segment
1 mosfet acts as low side switch for all constant current drivers to allow pwm dimming of entire display (without eating up a lot of computing time doing pwm over the shift registers)
datasheets for components in schematic -
NTD4858N Power MOSFET http://www.onsemi.com/pub_link/Collateral/NTD4858N.PDF
2N3904 NPN General Purpose Amplifier http://www.fairchildsemi.com/ds/2N/2N3904.pdf
TC74HC595AP 8-Bit Shift Register http://www.toshiba.com/taec/components2/Datasheet_Sync//151/397.pdf
questions -
Is this a retarded plan? (If so, can you suggest something better, or at least tell me why it's dumb?)
Will the circuit do what it's supposed to?
Will it let me control each segment individually?
Will the leds get the proper voltage and about 20mA of current with this circuit?
Will this circuit let me dim the display with pwm?
Will this burn down my house if I build it?
Do you have any suggestions on improving this project?
Did I leave anything out?
Any comments are appreciated. I want to do this right, so even if there is small stuff wrong, I'd like to know. Thanks for the help!
requirements -
4 digits
able to control each segment of each digit separately
pwm to adjust brightness of entire display
my idea for how to do it -
25 green leds per segment * 7 segments per digit = 175 leds per digit
175 leds per digit * 4 digits = 700 leds
5 constant current drivers driving 5 leds each per segment
3.2V per led * 5 leds per driver = 16V
700 leds / 5 leds per driver = 140 drivers
140 drivers * 20mA per driver = 2.8 A
18V 6A power supply
shift registers turn on constant current drivers for each segment
1 mosfet acts as low side switch for all constant current drivers to allow pwm dimming of entire display (without eating up a lot of computing time doing pwm over the shift registers)
datasheets for components in schematic -
NTD4858N Power MOSFET http://www.onsemi.com/pub_link/Collateral/NTD4858N.PDF
2N3904 NPN General Purpose Amplifier http://www.fairchildsemi.com/ds/2N/2N3904.pdf
TC74HC595AP 8-Bit Shift Register http://www.toshiba.com/taec/components2/Datasheet_Sync//151/397.pdf
questions -
Is this a retarded plan? (If so, can you suggest something better, or at least tell me why it's dumb?)
Will the circuit do what it's supposed to?
Will it let me control each segment individually?
Will the leds get the proper voltage and about 20mA of current with this circuit?
Will this circuit let me dim the display with pwm?
Will this burn down my house if I build it?
Do you have any suggestions on improving this project?
Did I leave anything out?
Any comments are appreciated. I want to do this right, so even if there is small stuff wrong, I'd like to know. Thanks for the help!
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