halleffector
Member
In this circuit http://www.z80.info/z80test0.htm is 470 ohms really correct for the LEDs?
Assuming a green LED draws 20 mA at 2.1 forward voltage, giving the CPU 5 volts (and assuming 5 volts makes it out on the address pins, should not this be R = (5 - 2.9) / 0.02 = 145 ohm? I attempted to build the circuit just as it is, using green LEDs, but it does nothing. I'm assuming I've made a mistake, but the 470 ohms confuse me.
Assuming a green LED draws 20 mA at 2.1 forward voltage, giving the CPU 5 volts (and assuming 5 volts makes it out on the address pins, should not this be R = (5 - 2.9) / 0.02 = 145 ohm? I attempted to build the circuit just as it is, using green LEDs, but it does nothing. I'm assuming I've made a mistake, but the 470 ohms confuse me.