Discussion in 'Homework Help' started by Kid347, Sep 7, 2016.

1. ### Kid347 Thread Starter Member

Aug 14, 2015
68
0
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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2. ### dl324 Distinguished Member

Mar 30, 2015
4,264
844
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.

3. ### Kid347 Thread Starter Member

Aug 14, 2015
68
0
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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4. ### dl324 Distinguished Member

Mar 30, 2015
4,264
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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.

5. ### Kid347 Thread Starter Member

Aug 14, 2015
68
0
All I have is a 8 ohm speaker. but as of now I get no sound at all from my speaker.

6. ### dl324 Distinguished Member

Mar 30, 2015
4,264
844
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?

7. ### Kid347 Thread Starter Member

Aug 14, 2015
68
0
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.

8. ### dl324 Distinguished Member

Mar 30, 2015
4,264
844
$\small P = \frac{V^2}{R} = \frac{6.5*6.5}{8} = 5.3W$
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.

9. ### Kid347 Thread Starter Member

Aug 14, 2015
68
0

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?

10. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,512
1,348
Here's 10 seconds of the diagram in action. The potentiometers are set at 50%. Turn your audio down ....

Last edited: Sep 8, 2016
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