Question

(7432 integrated circuit question)

Here is the problem and solution:
http://i.imgur.com/vaRfLZn.jpg

I just wanted to ask about the resistor's "purpose". Why was that 150 Ω resistor placed where it is? What would happen to the 7432 integrated circuit if the resistor were removed ror had it's value reduced or increased?

Any input would be greatly appreciated!

Answer 1

or* not ror

Answer 2

This question is more suited for the Engineering group, but anyway...

The resistor is not necessary for the 7432, but for the LED. WIthout the resistor, the output voltage wouldn't be what you'd expect it to be, since the voltage over an LED is 0.7 V IIRC. The voltage over the resistor is the supply current - 0.7 V (for a high output), causing a current to flow and the LED to light up. With a smaller resistor, the LED will burn brighter (U=IR, R going down means I must be going up).

Answer 3

Okay so the value 150 Ω is not important as in the book could have used any other value and, it's just the brightness of the LED that changes but there is no fixed, standard definition as to how bright the LED needs to be for a 7432 integrated circuit as long as the voltage of the 7432 integrated circuit and across the LED is 0.7 V on a high bit (1) and 0 V on a low bit (0), right? Or no?

Answer 4

Yeah. The only function of both the LED and the resistor is as an indication light as to whether or not the ouput is high.

Answer 5

Thanks. Just to say for you to know, the 7432 integrated circuit uses a 5-V dc power supply. :)