Using the 555 timer as a LED flasher.
The 555 timer is a very versatile chip I’ve used it in hundreds of circuits. This little chip is so handy that I purchase the in lots of 100 or more. It is simple to wire up and requires few components to work. Below I will show just two of the many uses this chip has. I recommend using an 8 pin socket in your board. Then plug the 555 into the socket. This allows you to change the chip should it fail or become shorted.
Here the 555 timer is used to flash a single LED at a fixed rate. The flash rate is determined by R1. A 100k pot can be used to make the flash rate variable. The center lead on the pot must be used for one of the connections. You can use the pin to the left or right of the center lead for the other connection. The total current draw needs to remain less than .050 ma.
This circuit can be used to drive a relay for higher current draws. When using this circuit to drive a relay you must use a diode across the relay coil to protect the circuit. The diode should be reversed biased. See example below.
Example of diode protection
This method can be used with switching transistors as well. The current flow is pointing toward the positive.
In this diagram the 555 chip is used to flash 2 LEDs. The voltage on pin 3 is toggled high then low to flash LED 1 then LED 2. As with the circuit above the same current draw limitations apply. This circuit can also be connected to 2 relays using the protection circuit above. The pot is used to control the flash rate.