I have designed a program to count the frequency and time period of the pulse generated by a 555 timer IC using PC Parallel port. I’ve connected a base of BC547 (NPN) transistor to the output pin (no. 3) with a resistor of multiple values to the IC and its emitter to the common ground. Parallel port Input pin is connected to the Collector and its ground pin is also connected to the common ground. As shown:
R1 = 1440 Ohms; R2 = 3.3 M Ohms; C1 = 1 micro farad.
So the; time period of ON pulse = time period of OFF pulse = 2.2 sec.
When I connect LED to output pin it shows right value but when I connect transistor it displays wrong values. In this ratio:
Greator Resistor = Greator Time period; Lessor Resistor = Lessor Time period.
I don’t know how to connect right resistor to display the right values.
The circuit is powered by 6volt @ 250mA power supply.
If there is any equation for this purpose please provide here.