djsfantasi
Member
I'm updating an old project of mine (link to Game Show circuit). I want to add some wireless keychain remotes to trigger the lockout. And I want to have a better output than a single LED. I decided to use large (1"H) 7-segment displays, hardwiring each of the four to display a number from 1 to 4. This would be an add-on to the existing circuit, which switches one of four lines to ground. I want each line to switch on one 7-segment display.
I was hoping that I could get a second pair of eyes, to review my calculations. I haven't picked out the final display yet, but used the following values to make some initial calculations, obtained from the datasheet of a candidate display.
Iseg 0.020 A
Vcc 9 VDC
Vf 1.8 VDC
Here is a schematic of the design for the displays.
Based on the above assumptions, I determined that I needed a 390 resistor for each segment.
The numbers 1 - 4 have varying number of segments lit. from 2 segments for a '1', '4' requires 4 segments and '2' and '3' require 5 segments lit. From this, I calculated the total current for each digit. Which led me to determine the value of the base resistors (at 1/10th the total current).
Below is a screenshot of the Excel spreadsheet I used.
Can anyone comment on my approach and confirm my calculations and design?
I was hoping that I could get a second pair of eyes, to review my calculations. I haven't picked out the final display yet, but used the following values to make some initial calculations, obtained from the datasheet of a candidate display.
Iseg 0.020 A
Vcc 9 VDC
Vf 1.8 VDC
Here is a schematic of the design for the displays.
Based on the above assumptions, I determined that I needed a 390 resistor for each segment.
The numbers 1 - 4 have varying number of segments lit. from 2 segments for a '1', '4' requires 4 segments and '2' and '3' require 5 segments lit. From this, I calculated the total current for each digit. Which led me to determine the value of the base resistors (at 1/10th the total current).
Below is a screenshot of the Excel spreadsheet I used.
Can anyone comment on my approach and confirm my calculations and design?
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