I am trying to make a pulse train generator that should output current pulses of 10-30mA. The time scale of the pulse is in the range of a few seconds to milliseconds. I mean, the pulse on time can be 1 sec, 0.5 sec or down to 1ms and off time is also comparable to on time. How do i make it?

 

http://williamson-labs.com/555-tutorial.htm

and/or

http://www.uoguelph.ca/~antoon/gadgets/555/555.html