The MagPi Issue 26

Page 27

A (7) to an appropriate value. While working with an oscilloscope you should always be aware about the settings of the instrument and the expected voltages in the circuit.

Is this NE555 timer IC still working?

Fig. 3: Measuring +5V on the GPIO pins 2 and 6 of the Raspberry Pi

Look at the main screen of the BitScope DSO (1 ). The x-axis is the line in the middle and has small vertical lines to sub-divide each square. This is our 0V line. But our yellow beam is in the middle of the third square above the x-axis. Because we know there is a voltage of 5V between pin 2 (the plus pole) and pin 6 (the minus pole), and we set the channel control to 2V per Div, so the horizontal line indicates exactly this voltage. In Fig. 4 I have inserted an extra scale in red on the y-axis to help you interpret the screen.

In our next experiment we want to find out if a NE555 timer IC is still functional. This IC is often used when a clock signal is required. For this experiment we need: • 2x 1 K resistors (R1 , R2) • 0.1 F capacitor (C1 ) • 1 0 nF capacitor (C2) • NE555 timer IC (IC1 ) • small breadboard • test leads provided with the BitScope Micro Fig. 5 shows the circuit diagram and Fig.6 shows you how to implement this circuit on a breadboard.

Fig. 5: Circuit diagram of the clock generator

Fig. 4: Measuring +5V between the Rasperry Pi GPIO pins 2 and 6.

You may get a reference measurement with your multimeter, if you like. Could we measure other and higher voltages than 5V? Sure, but what about our input range? We have to change the input range with the channel control for Channel

Fig. 6: Implementation on a breadboard


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