Sunday, July 1, 2012

Aktakom Oscilloscope and the 555 timer

Schmitt Trigger as a Signal Generator The 555 timer makes for a great way to illustrate how different waveforms can be created using a Schmitt trigger. Rather than just being used for timing, the LM555 IC chip can be used like a function generator or even for creating a pulse width modulation (PWM) signal.

This is all good and well for the electronics hobbyist, but what good is it if you don't have a nifty oscilloscope to play around with? Of course you want to be able to see the different signals generated by the 555 timer when you mess around with the different threshold, trigger, and discharge pinouts. You can change the waveform, the frequency, and even the duty cycle when incorporating the 555 timer into a signal generator circuit. This is done with different resistors, capacitors, and/or diodes.

You can view your output of the circuit by making an LED blink at different rates with various RC time constants, but it would be much cooler to see it on a real oscilloscope right? I know the oscilloscopes you have seen before at school or at work are extremely expensive, and most of us cannot afford them for hobby or home use. I had this same problem throughout my entire time when studying robotics engineering at SPSU until I found the perfect solution for me. I figured that others may have the same problem, so I wanted to share my find. It is the Aktakom ADS-2022 digital storage oscilloscope, and you can check out the video on how I use a 555 timer as a signal generator and what it looks like on that oscilloscope. You will also find there that you can buy it for a really great price, and it has a very large screen for easy visibility.

The 555 Timer and a Variable RC Time Constant = Throbbing LED

Here is the video of the LM555 circuit I built to make the LED flash at different rates using capacitors, resistors, and a potentiometer. The variable resistance allows you to change the RC time constant to control the speed of the flashing.

When you hook up this circuit to the Aktakom oscilloscope, you will see the signals generated by the LM555. The output signal is a digital square wave where the frequency can be changed. This is because of the built in Schmitt trigger that causes the output to only be HIGH when the capacitor is charging. When it has reached a certain peak and the lower voltage threshold beyond the peak is reached, the Schmitt trigger throws the digital LOW signal as the capacitor discharges.