Dual 555 Circuit for Sound Generation

326

03:12:12

Exp. 16d  Fig. 16-18 from Make Electronics 3rd Ed.

Background:    Left 555 Timer (LT) is in astable mode and its output is linked to a speaker (represented by the 8 ohm resistor).  The  555 timer on right (RT)) is supposed to control LT.  The control pin of the LT is linked to the output of RT.   

There are 3 Potentiometers:  
P1 on bottom L controls the pitch of the tone generated by LT;     
P2 around middle adjusts the frequency and speed of modulation in the control pin of timer LT.   If turn P2 down = vibrato sound; if turn P2 up, alarm sound;
P3 on bottom R controls the speed of modulation of timer RT. 

published 4 years ago

jason9

4 years ago

Are you sure pin 7 of RT should be connected directly to the capacitor (and thus pins 6 and 2)? This essentially ensures that the discharge time of the capacitor is as short as possible (nearly instantaneous) meaning that the output of RT is high almost 100% of the time regardless of the position of P3. Double check the schematic to be sure you’ve copied it to EC correctly, and pay special attention to the 555 timer pin connections. If you’re sure everything is copied correctly, then perhaps there is an error in the schematic. If that is the case then you can fix the circuit by adding a resistor to pin 7 of RT. You can experiment with different values to find what works best.

SewerDoc

4 years ago

Thanks Jason 9. Pin 7 should not have been linked directly the the capacitor. I think this probably happened when I was moving the capacitor and the wires automatically changed. The wiring for Pins 6 and 7 of the RT are now correct. Tomorrow I will recheck everything. At least now I am getting a small change in the speaker when I alter P3.

matthewg811

4 years ago

I can see why you chose the title help this thing is crazy

SewerDoc

4 years ago

I double checked the schematic and everything looks to be wired as per the book. I wish this program had 2 missing features: 1) a working simulated speaker; and 2) the ability to add text labels to the circuits to make every thing more understandable.

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