Can someone help me with this electronic schematic?

Question

I need to know which wires that lead away from the 9volt battery are supposed to be positive and which ones are supposed to be negative.

The schematic is at...

http://www.instructables.com/file/FHEWL9TFD80BUXE/

Answer 1

The Positive terminal is marked +9V and has 3 connections.

The Negative terminal is marked with ground symbols (upside-down Christmas trees) and has 2 connections.

The schematic has a serious mistake.  It will not work as drawn.  It will activate the siren all the time, and light on the photocell will not make any difference.  The only way it can work is if you do NOT make the bottom +9V connection to the battery. Short the 5K wiper arm to the 5K end and connect that to the 2N3904 base terminal, but do NOT connect that wire to +9V.  

If you did connect 2N3904 base to +9V and 2N3904 emitter to -9V (ground), you blew up the 2N3904.  Try again with a new one and DON'T make that one +9V battery connection.

Answer 2

I ran into this same schematic a month or so ago.

It is the worse drawn schematic I ever saw.

either the 3 leads on the +9 point are all at the + terminal of the battery or perhaps one of them is the - terminal.

Assuming the former, then this applies +9 directly to the base of the transistor which will blow it up.

Assuming the later, that the lower of the 3 terminals is the - terminal of the battery, then you wind up grounding the base of the transistor and it will never turn on.

No, no matter how I look at it, it doesn't make sense. Scrap it and find a different schematic that makes sense.

Answer 3

First off, the schematic is defective, as the battery is shown incorrectly, but in any case these guys are right, all 3 wires connected to the battery (+9V) are posative.  The ground symbol (in two places, on the left and right side of the circuit):

-------

-----

  ---

   -

is the negative of the battery.

Answer 4

All the 3 connections are in parallel with the positive side of the battery... the wire with the ground sign is connected to the negative side...... (the ground sign is the one at the upper rightmost part of the schematic....^^

Answer 5

This is the solution to the schematic.

Please note that none of the wire coming from circle+9v is NEGATIVE!! And please follow this.

1- Assumed that the circle " +9V" is all positive 9V dc.

2- The 1000uF capacitor needs to be wired across 9 V supply.( 9V + and -).

3- Bottom of circle + 9V needs to be DISCONNECTED from circle +9V.

4- The end of photocell having " Chrismast tree upside down" needs to be wired to +9V battery ( instead to Negative), the transistor's emitter needs to be connected to ground in order to bias this transistor.

5- This transistor can only drive a 12V piezoe instead a siren!  If you want it to drive a siren, you need a relay ( Siren uses more current than this transistor can handle).

You will have a perfect circuit, which is "here comes the lights , so does siren .Get up and go to work!".