I could not have guessed better 1KHz & 1.5KHz sound perfect. This morning first thing I did was change the 8 ohm speaker to this tiny little micro watt speaker and "WOW" the circuit works excellent. I moved the 2 NE555P to the other circuit board along with the 100 ohm resistor and same 8 ohm speaker and it does not work? Only things that is actually different is duty cycle is much closer to 50% online calculator says 53% for 1KHz and 55% for 1.5KHz. These 2 NE555P were working good on the TTL book siren circuit board with this 100 ohm resistor and the same 8 ohm speaker. Maybe the green color capacitor should be orange? Now that I think of it online 555 calculator resistor values are not even close to TTL book resistors values that might be a good place to start tomorrow. I used online calculator to get the resistor values maybe it is wrong. Ohm meter shows nothing is shorted and all connections are good. I can remove 555 #1 and 555 #2 still not work. I can not find any reason for the circuit to not work. Only reason I used these variable resistors it was quick and easy to dial in the exact resistance I need and not spend 2 hrs search for fixed resistors and soldering several fixed resistors together to get close as possible to the value I need. Only thing I have not done is replace variable resistors with fixed resistors. Every things ohms good and tests good but it does not work. If I put R7 and the speaker on the 555 circuit I built last week with the 12v batteries it works even if I swap out the 555 on this board that is not working. With battery connected no sound comes out of the speaker. Combined resistance of R3 R4 R5 are correct. I ohm out all 8 pins of the IC socket to make sure them connect from front to back and solder connected are good to all the resistors, caps, ground, and + connection. 555 #1 runs so I removed it and put 555 #2 in its place and it runs. The board is finished but second half of the circuit does not run. Bear in mind that CMOS circuits are static-sensitive, so don't go dancing around in nylon knickers on synthetic carpet before handling them. It is advisable to use a 14-pin socket for the IC if you are unused to soldering ICs. The result is an oscillator, with the output snapping between high and low, i.e a square-wave.Īs for wiring this IC, the +ve supply voltage goes to pin 14 and the ground (0V) connection is pin 7. The output voltage can be used to charge a capacitor via a resistor, and the voltage developed across the capacitor can be fed back as the input signal. If the signal then goes lower the output stays low until the input goes below 3V and at that point the output goes high (5V). If the signal input (whether a sinewave or not) goes above 4V the output goes low (0V). The thresholds will typically be about 4V and 3V.
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