# 3 Switch LOGIC Circuit

Discussion in 'Homework Help' started by johncena, Aug 29, 2010.

1. ### johncena Thread Starter Member

Aug 15, 2010
32
0
We need to setup a 3 switch wherein if more than 2 switch are open, the LED will light. Materials should only be 2 transistor NPN and 2 PNP transistors, LED , resistors and wires. If switch is off it will generate negative volt, else, it will give +5 volts ( There is also a separate - and +5 volts source aside from the switches) (Switches are from the Digital trainer). It doesn't matter where LED will glow very bright, as long as there is a light on led, it counts as on.

Is it possible to make a circuits with only 2 NPN and 2 PNP transistors?

Last edited: Aug 29, 2010
2. ### hgmjr Moderator

Jan 28, 2005
9,030
214
What have you been able to come up with on your own so far?

hgmjr

3. ### johncena Thread Starter Member

Aug 15, 2010
32
0
still unsuccessful. I made 3 AND gates and 1 OR gate (without doing the required limited transistors). But the output is wrong

4. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Have you drawn up a truth table? It is then possible to make a network to match.

Can you use diodes, or are transistors it?

5. ### johncena Thread Starter Member

Aug 15, 2010
32
0
Here:

0 0 0 = 0
1 0 0 = 0
0 1 0 = 0
0 0 1 = 0
1 1 0 = 1
1 0 1 = 1
0 1 1 = 1
1 1 1 = 1

No diodes, just Transistors as a Basic ON and OFF switch (General Purpose Transistors)

6. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Just a suggestion, whenever you make a logic diagram use a sequential count. Patterns show up better too.

0 0 0. 0
0 0 1. 0
0 1 0. 0
0 1 1. 1
1 0 0. 0
1 0 1. 1
1 1 0. 1
1 1 1. 1

Ever study how to build a Schmitt trigger using transistors? You may be able to set up a voltage comparator threshold using resistors and transistors.

7. ### Georacer Moderator

Nov 25, 2009
5,151
1,266
I really can't see how this can be materialized. Give me 6 npn's and 4 pnp's and sure, I 'll do it, but with such a tight budget I'm at a loss.