JamesBourne

Let me rather say what I'm trying to do: I want to create a sine wave of 140Hz with the frequency as accurately as possible. This will be played through on a 3.5mm earphone. My current idea is to use a 555 to create 140Hz as accurately as possible and filter the square wave to sine. I'll be happy to use another oscillator as long as the frequency can be accurately controlled. I want to run the circuit off the small rechargeable battery so that it's small and portable. If you have any other suggestions or ideas on achieving this, I will be happy to listen.

I'm currently building a project that generates a frequency using a 555 timer. Since the power requirements are low, I thought of using a small, rechargeable battery. After dismantling one of those "battery-less" shake flashlights, I found a Ni-MH 40mAh 3.6V battery inside. My problem comes with the voltage. The 555 requires at least 5V to operate and the battery usually gives 3.1V after a quick shake and 2V after leaving the light on for a few hours. I have read that you can use a charge pump to raise the voltage, but the IC used to do this also requires 5V! So, if possible, how can you raise the voltage about 3 times without using IC's? Schematics will be much appreciated. Thanks

Hi again, I read a about the filters as you mentioned (RC filter) in your answer and have gotten some results. I am posting my solution thoroughly, just to make sure I'm heading in the right direction as I'm still a newbie in electronics. On Wikipedia I found the following equation under RC circuit: f=1/2πRC After crunching the numbers where f must equal 140Hz and C=10uF I got R=114Ω. I used Electronics Workbench to simulate the circuit with the calculated values (3 pole as you suggested). (See "sine wave output.JPG") I used the square wave input (+5V) with an offset of +5V (to create the output form of 555) and got a good sine wave but with a new problem. As you can see the output wave is also being offset by +5V. Is it possible to reduce the offset to 0V? If so, how? Thank you for your help.

Hi everyone, I am building a circuit that will produce a sine wave as output. I am using a 555 timer (astable) to create a frequency of 140Hz. This produces a square wave with an amplitude of about +5V. Note that voltage is 0V and +5V (not -5V and +5V). My problem is that I do not know how to turn the square wave into a sine wave. I have read on various sites that you can use capacitors and inductors to filter the signal to produce a sine wave, but calculations and explanations are nowhere to be found. Please help.