Review of Add-On Circuit to Existing Circuit

[djsfantasi]

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?

 

[cowboybob]

Here is a schematic of the design for the displays

The schematic image didn't make it.

 

[alec_t]

The schematic image is ok here, but the calculations diddn't make it.

 

[djsfantasi]

Ok, can you see it now?

 

[eTech]

I see the schematic and calculations ok.

What transistors did you use? Need to know the DC gain.

 

[cowboybob]

Interesting. In Foxfire, nothing. In Chrome, calculations but still no schematic. Some sort of settings issue, maybe.

 

[djsfantasi]

Interesting. In Foxfire, nothing. In Chrome, calculations but still no schematic. Some sort of settings issue, maybe.

Try one more time. I rewrote the post.

I see the schematic and calculations ok.

What transistors did you use? Need to know the DC gain.

The transistor used is no longer available. A similar one, BC546, can be found here at DigiKey. I am driving it into saturation with 1/10th the LEDs current, which can be seen in the calculations.

 

[gophert]

You could use a cd4511 BCD to 7-segment driver. Then use a 4-bit dip switch to set your locked values. That way, you can have one board design for all numbers and add on to 9 terminals.

 

[cowboybob]

Can see it all, now. Thanks.

Everything (using the BC546-50) looks fine to me.

Sim'ed gives equivalent numbers.

<EDIT> Looked at your "Jeopardy" lock-out article - very nicely done. I assume this is updating it so as to display a number, rather than just a lit LED for the successful contestant bashing on the "Signaling Device" (Push Button in Alex talk... ).