Counters - Counts up from 0 to a certain number and starts over. Binary arithmetic (1s and 0s) is used in counting upwards. It is an example of a more complex digital circuit.
- Reload http://lushprojects.com/circuitjs/
- Choose Circuits → Sequential Logic → Counters → 4-bit Ripple Counter
- Watch the output change. What is the highest count value?
- What is the input “CLK”? What does it remind you of?
74393 Counter Chip - One counter that has a lot of functionality in one easy-to-use package. As with the 555 timer, when placing the 74393 in the breadboard, it is important that the little half circle points upwards, otherwise it will be on backwards.
However, most digital chips work on 5V or less - the battery we are using is 9V. As a result, we need to "regulate" the voltage from 9V to 5V. To do this, we must add a diode.
The Zener Diode, pictured here, regulates the voltage going into our 74393 chip. The current flowing from the positive to negative end is clamped at 0.8V. The current flowing from negative to positive is clamped at 5V, just what we need for the 74393.
Thus, we place the zener so that current seems to flow from - to +, simply to increase its junction potential. When placing a zener diode on a breadboard, the negative end should go in first, followed by the positive.
- Reload http://lushprojects.com/circuitjs/
- Choose Circuits → Diodes → Zener Diodes → Voltage Reference
- Right click on voltage source → Edit → DC Offset = 9V
- Right click on 500 Ω resistor → Edit → Rresistance = 250 Ω
- Right click on zener diode → Edit → Zener voltage = 5.1 V
- What is the lowest value of resistance for the second resistor that keeps the voltage at 5V? Edit the 10k resistor with different values and see if the graph labeled "5.19V out" changes value from 5.19 to something else. What does this mean? (Answer: The lowest resistance value is roughly 460 ohms Every circuit that we connect to this voltage source effectively “lowers” this resistance. This is so that it will be able to power a circuit involving both the 555 timer and 74393, which will be created on the next page)
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