Misc. Circuits: 555 Monostable Multivibrator Demo + Scoposcopy

The 555 timer chip is a very versatile little bit of kit. Here I demonstrate the basic Monostable Multivibrator circuit using the 555.

The 555 is triggered by a short button press, and turns on an external circuit (mosfet, light bulb) for a set amount of time, determined by the timing components (a resistor and capacitor.) By adjusting the values of the R and C, just about any duration can be set, from milliseconds to many minutes. Here I’m using values that give me about 6 seconds of ON time (100k and 47 uF).

The oscilloscope is used to show the relationship between the button press, the charge on the timing capacitor, and the output pulse from the 555’s Pin 3 output, which drives the mosfet Gate.

For more information about this application, google “555 multivibrator” for circuits and general info and data sheets. There are several variants of the 555 available, both CMOS and TTL compatible. Here I’m using an NE555P version but any one will work in this circuit.

Thanks for watching, and Merry Christmas !

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