555 Signal Generator Kit

In the circuit diagram above, we have a 555 Timer IC in astable configuration operating as a multi-vibrator with a fixed frequency, which the manufacturer has not disclosed for some reason. My first thought was, why on Earth would anyone want a signal generator with a fixed frequency? Surely, one of the most important aspects of a signal generator is that you can adjust the frequency and amplitude of the waveforms. Unfortunately, in this kit, there is only one preset at the output end to adjust the amplitude of the waveform. So there I was scratching my head trying to figure what application this circuit could possibly have besides being educational and for simply looking at waveforms.

Looking at the circuit, it occurred to me, as it would for any GCSE electronics student, that the value of resistors R1 and R2 should determine the frequency of the signals. If we were to replace R2 with a variable resistor of value say 200 kΩ and a fixed resistor of 1 kΩ, then we should be able to get a wide range of variable frequencies. The fixed 1 kΩ resistor ensures that the minimum resistance between pins 7 and 6 will not be less than 1 kΩ. Hobbyists usually have a box full of different variable resistors that they could choose from; therefore, it was not a big issue, considering I get all these components in the kit for almost nothing.

There does not seem to be much information regarding the voltage requirements of the circuit, however the NE555 IC can accept supply voltages between 4.5 V and 16 V. It seems to work fine on a single PP3 9 V battery though.

This Article Continues...