# How to calculate the resistors and capacitors for an amplifier circuit [duplicate]

Here is an amplifier circuit that I was given in a previous question:

They told me to use this for an experiment for using magnetic fields for nearby communication instead of radio frequency. Here is the link to it. How do I figure out what values for all of the components I should use, Is there an equation? Lets just give an example, I want a 9v input, and I want the output to turn on if the voltage on the input is greater than .1 volts AC. How would I make the circuit do this?

• The circuit above is the canonical AC coupled common emitter amplifier which is typically used as a linear amplifier, not a switch that "turns on" when the input is above some level. – Alfred Centauri Apr 9 '13 at 19:26
• so what should i use for a switch that turns on above a certain level? – skyler Apr 9 '13 at 19:31
• Edit you question to reflect what you're trying to do, I have an answer but I need to make sure I understand what you're asking first. – Matt Young Apr 9 '13 at 19:37
• ok i edited it. – skyler Apr 9 '13 at 20:16
• You still show an AC amplifier yet you ask for it to 'turn on' at a DC level. More editing is definitely needed! – Wouter van Ooijen Apr 9 '13 at 20:19