# Need help reading schematics

#### Kid347

Joined Aug 14, 2015
70
I am new to electronics and have been trying to teach myself for over a year now, and one of my big hurdles is reading schematics. I have attached a schematic of a kit that I purchased and I am stuck. Here is what confuses me about schematics. Connections to multiple components, if it is simply connect pin 1 to ground I am fine. But when it shows pin 1 connecting to pin 8 which also connects to to +5v and a capacitor to ground I am lost.
If you look at the schematic that I attached my questions are:

1. looking at IC on the left it shows pin 7 going to R1 which connects to C2 which connects to pin 8 which connects to pin 4 then it goes to 5v. this is where it gets confusing to me, I just don't understand the logic of how these components should be connected. I have a half dozen beginner electronics books but none of them explain how these multiple connections work.
2. looking at the IC on the right same thing does pin 7 connect to 5v through R3? does VR2 connect to pin 7 and to R3 then to 5v? does pin 8 connect to pin 4? which then goes to C6 then to ground? and I am really clueless with the speaker connected to D1 which goes to 5v? and to Q1.
3. but I am real clear on the IC555 on the left that pin 1 goes to ground, and pin 5 goes to ground through C3.
Well I am hoping that someone can clear this up for me. As it is really a hurdle that has brought my learning of electronics to a halt. Thank you in advance.

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#### dl324

Joined Mar 30, 2015
12,807
All of the lines are called "nets" or sometimes "nodes" (as in nodal analysis). All components on the same net are, naturally, connected to each other. The order in which they're connected usually isn't significant since, by definition, all components on a net are connected.
looking at the IC on the right same thing does pin 7 connect to 5v through R3?
Yes
does VR2 connect to pin 7 and to R3 then to 5v?
Yes
does pin 8 connect to pin 4? which then goes to C6 then to ground?
Yes

You understood the connectivity, but didn't trust your understanding.

and I am really clueless with the speaker connected to D1 which goes to 5v? and to Q1.
The speaker is being treated as an inductive load and D1 protects Q1 from back EMF generated when Q1 is turned off and the magnetic field in the inductor collapses.

#### Kid347

Joined Aug 14, 2015
70
All of the lines are called "nets" or sometimes "nodes" (as in nodal analysis). All components on the same net are, naturally, connected to each other. The order in which they're connected usually isn't significant since, by definition, all components on a net are connected.
Yes
Yes
Yes

You understood the connectivity, but didn't trust your understanding.

The speaker is being treated as an inductive load and D1 protects Q1 from back EMF generated when Q1 is turned off and the magnetic field in the inductor collapses.
can you take a look at what I have done so far, and let me know what changes I need to make. also I have no idea how to hook up the speaker.

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#### dl324

Joined Mar 30, 2015
12,807
I don't trace breadboards. Just make sure you follow the schematic.
have no idea how to hook up the speaker.
Wire + to the supply and - to the transistor. Though I don't think polarity matters unless you have multiple speakers and want them to be in phase.

Make sure the resistance is 32 ohms or larger.

#### Kid347

Joined Aug 14, 2015
70
I don't trace breadboards. Just make sure you follow the schematic.
Wire + to the supply and - to the transistor. Though I don't think polarity matters unless you have multiple speakers and want them to be in phase.

Make sure the resistance is 32 ohms or larger.
All I have is a 8 ohm speaker. but as of now I get no sound at all from my speaker.

#### dl324

Joined Mar 30, 2015
12,807
All I have is a 8 ohm speaker. but as of now I get no sound at all from my speaker.
Note 2 on the schematic said to use 32 ohms or larger.

What supply voltage are you using? What is it's current capacity?

Can you calculate the resistance and wattage needed to substitute an 8 ohm speaker?

Do you know what the power rating is for your 8 ohm speaker?

#### Kid347

Joined Aug 14, 2015
70
Note 2 on the schematic said to use 32 ohms or larger.

What supply voltage are you using? What is it's current capacity?

Can you calculate the resistance and wattage needed to substitute an 8 ohm speaker?

Do you know what the power rating is for your 8 ohm speaker?
I am using a DC power supply and I starter out using 6.5 volts, I do not know what the current is.
the speaker I am using is rated 8 ohms and 0.5w
I will look for a 32 ohm speaker tomorrow, I thought it would be alright to use the 8 ohm for a short period of time, but now all I get is very slight static for a second or two. Not even close to a siren. and just wanted to say thanks for all the help.

#### dl324

Joined Mar 30, 2015
12,807
the speaker I am using is rated 8 ohms and 0.5w
$$\small P = \frac{V^2}{R} = \frac{6.5*6.5}{8} = 5.3W$$
That's a lot more than your speaker can handle.
Not even close to a siren.
I'm not sure what you're expecting in terms of volume. I built something similar 40 years ago and it wasn't what you'd call ear piercing.

#### Kid347

Joined Aug 14, 2015
70
$$\small P = \frac{V^2}{R} = \frac{6.5*6.5}{8} = 5.3W$$
That's a lot more than your speaker can handle.
I'm not sure what you're expecting in terms of volume. I built something similar 40 years ago and it wasn't what you'd call ear piercing.

Do you think that my circuit is correct, but my speaker can't handle the output? Is it possible that with the proper speaker my circuit will work?

#### JoeJester

Joined Apr 26, 2005
4,390
Here's 10 seconds of the diagram in action. The potentiometers are set at 50%. Turn your audio down ....

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