# Newbie needs help with 555 basics

Discussion in 'The Projects Forum' started by Decafinate, Mar 7, 2011.

1. ### Decafinate Thread Starter New Member

Mar 7, 2011
3
0
Hello,

I presently power a relay with a 9v battery thru a microswitch. I need to delay the relay for a fraction of a second... 50ms -100ms or so. I am trying to find the right capacitor(s) and resistor combination to accomplish this. I need the relay to be delayed and then have power until switch is released. I am real green at this so please be patient. If you know a simple 555 wiring diagram and can help calculate the c r values, I would greatly appreciate it. Thanks in advance.

Mar 24, 2008
20,772
2,540
3. ### Decafinate Thread Starter New Member

Mar 7, 2011
3
0
Mr. Marsden,
Thanks for the quick reply. I am super green and apologize for not understanding the different types of caps and their sizes to be able to attempt to follow the diagram, any additional help would be greatly appreciated. I quess I need types and sizes to try.
Thank you.

4. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Did you follow the original link? It goes through a typical monostable, you can even build it if you get the parts.

100 ms is not very long, are you trying to debounce the switch? What is the delay for?

As for values, the formula could not be simpler.

0.1 seconds = 1.1 R C

Pick a resistance, say 10KΩ.

The capacitor would 9.09µF. A 10µF cap would work well.

Use a 0.1µF cap for C2 (again, it is in the link), and 470Ω for R1 for the transistor. Likely a 2N2222A will work for the transistor, but I don't know the relay you're using, so maybe not. CR1 can be a 1N4001 through 1N4007 diode (it is absolutely necessary).

While the schematic does not show it, you probably need a 100µF cap near the power supply leads to insure the circuit works correctly.

5. ### ve3bbn New Member

Mar 7, 2011
2
0
Since you are working with 9v, why not keep it simple by using a 6 volt relay fed with a resistor and put a 100uf cap across the relay to act as your delay. By using the proper (try different) value of R*C you will have your delay. This is a very simple way of achieving your results. Depending on the coil inductance and resistance you simple start with a 100 ohm resistor and 100ufd cap and adjust either or both untill you get your proper time.

cheers David

6. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
You do realize the math works? Math is pretty fundamental to electronics.

7. ### Decafinate Thread Starter New Member

Mar 7, 2011
3
0
Thanks for guidance. As you can tell I know very little about electronics.
I drag race slot cars and my controller limits the power to the DC motor as it takes off using the first microswitch at the bottom of the trigger pull is a second microswitch that triggers a 12v automotive relay with a 9v battery. the time from the first microswitch to the second microswitch is now determined by how fast you pull the trigger. I am trying to remove that variable with a delay timer. any advice is welcomed.