555 Circuits II
Some useful circuits using the LM555 IC. (11/26/2006)
Timer with 555.
This circuit can be used to activate a relay for two or three minutes. Pressing the switch the relay will be activated. Changing the 1M resistor with a variable resistor you can vary the time. The 0.01 capacitor is important because it prevents any false triggering.
The circuit will work OK with 6 Volts without any modification. If you want to use 9 or 12 Volts, you need to change the relay with a 9V or 12V relay. Using this circuit with 120 VAC is not recommended, however, using the right parts and the right isolation, will be not a problem.
The aplications for this circuit may vary, for example: Bouce-free switch, A three-minutes light to walk thru a dark area, A timer-activated faucet to save water, etc. Any project that needs only a few minutes of power will be perfect for this circuit. Ever if you have an old microwave with the broken electronic control, you can replace it with this timer (using the right hi-current relay).
This is a simple oscillator with multiple resistors in serie. When you press any switch, the circuit starts oscillating. You can user variable resistors instead the 1k resistors. Using variable resistors you will be able to tune the frecuency for each note. You cannot be able to press two keys at the same time because the frecuency will change. To make an electronic organ capable to press many keys at the same time, you may need to use thirteen 555 ICs.
Is ok to use 9 to 12V as power but it may be quite loud. I do not recommend to use a power supply as it may cause electrical shock. Also a "hum" will be audible while it is in use.
Dual Led Flasher.
This circuit can be used to attract the attention. Long time ago I used this circuit to "light" a cap, Later, I used it to light a button. (After I started to use the PIC 12C508, I stopped using this circuit).
Any LED color can be used, even white LEDs. For white, blue or violet LEDs you may need to increase the voltage or reduce the LED resistor.
PWM with 555.
I alredy posted a web page with this circuit. I displayed the schematic here just for the records.
Any of these circuits can be used as a "tester" also. If you recover some 555 ICs from another projects, you assemble any of this circuits using a 8-pin IC base.