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.

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:

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.

To calculate the LED resistor, I used \(R_{LED}=\frac{V_{cc}-V_{f}}{I_{seg}}\)

To calculate the base resistor, I used \(V_{base}=V_{cc}-0.6\)

Then, I calculate the base resistor as follows: \(R_{base}=\frac{V_{base}}{I_{base}}\),

where \(I_{base}=I_{total}/10\)

\(I_{total}=n*I_{segment}\)

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:

Iseg 0.020 A

Vcc 9 VDC

Vf 1.8 VDC

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.

To calculate the LED resistor, I used \(R_{LED}=\frac{V_{cc}-V_{f}}{I_{seg}}\)

To calculate the base resistor, I used \(V_{base}=V_{cc}-0.6\)

Then, I calculate the base resistor as follows: \(R_{base}=\frac{V_{base}}{I_{base}}\),

where \(I_{base}=I_{total}/10\)

\(I_{total}=n*I_{segment}\)

Can anyone comment on my approach and confirm my calculations and design?

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