Conductor Identifier Circuit

Ralston18

Titan
Moderator
1) Where are the "two wires"?

2) What is the purpose of "L1" with respect to your intention or understanding?

3) S1 does not appear to be anything other than a simple manual switch.

Best if you explain more about the overall circuit and the individual component functions.

I think I know what the intended circuit design is to do but it is really your assignment.

Once you get to the point where you can explain the purpose/function of each component then you will know yourself whether the circuit is correct or not.

 

UnforgivenGamer

Reputable
Dec 15, 2014
133
0
4,710

The purpose of the two wires were to act as a switch, when you touch the two wires to a conductive material, it would close the circuit and light up the LED. So I figured I could just show that with a switch rather than having two wires that go off into nowhere. L1 is the LED that should light up when the circuit is closed. BT1 is a 9V battery. I'm now thinking that S1 should be connecting directly to the LED rather than looping around it
 

Ralston18

Titan
Moderator
Probably two simple arrows each labeled "Test Probe" would be sufficient/acceptable. Clarity matters.

Now explain what is expected happen with respect to Q1 and Q2 if or when there is conductivity between the test probes versus no conductivity/open. Why are the transistors in the circuit?





 


He's using a pair of cascaded PNP transistors to pass a small current out through the transistor base when the switch is closed by a conductive material. This small current is amplified at the transistor collector (for PNP Ie = Ic + Ib) which passes through a current limiting resistor and finally through an LED. The second transistor increases the current amplification, thus increasing the device's sensitivity to greater resistances.

<There, fixed the quoting for you>



 

Ralston18

Titan
Moderator
Agree. Nicely stated. Thank you.

However, my hope/intent was to get something like that from the OP.

Do not know if OP has any means to test his design. Hopefully his EE class has a lab.

Kids in the family have "Snap Circuit" kits - can come up with all sorts of things when they play with it. [OPED: However, the recommended age(s) may need to be a bit higher I think.]

Anyway, just happy to see anyone trying to do "hands on" science, engineering, math, etc..