2 diff. time delays in 1 RC network

[vandyo]

Hi
Wondering how i might have diff. delays by using 2 diff. size resistors in my RC.
I know you can have 2 together in series but i was thinking of having one to provide a very short delay whenever the board starts up due to a power change, and another one that would occur whenever the restart was due to a reset button that pulls pin2 low on the LM555 & restarts everything.

I am running the IC as a monostable (oneshot). Pin2 & 6 are connected and pin7
is open. The output feeds another 555 but no other affect.

I have tried steering diodes but unsuccessfully, but may be my lack of knowledge. Anyone know if this could be done with transistors and/or diodes?

Have inc. image Any help appreciated

[/img]

 

[erikl]

For a long reset, you connect pin2 to GND, and then open the connection. For the short reset, you connect pin2 to GND via a resistor (in the order of .5 .. 1 Mohm) and then open the connection. This means, C1 will not be decharged totally down to GND level, but only somewhere in between. Depending on the 555's trigger level and the size of this a.m. resistor you can adjust the short reset time duration.

 

[VVV]

I think this circuit does what you want: at power up it will create a pulse given by R2C1, while in normal mode the time constant will be that given by R1C1.

With the given values you will get a 0.1ms pulse at power up and 13.2s when you discharge C1.