I don't really understand for what this first resistor is needed. Could someone explain me this? Would my solution work?
No I don't think so... There is no base bias on the second transistor (it should be a PNP) the first transistor is cut off when the emitter is high when it's low there is nothing at the collector for it to work with. This is a conceptually bad adaptation of a ttl gate input.Bob
Where is the base bias for T1? How is T1 ever turned on?.Bob
Sorry, Sorry,I try to explain again.I'm trying to activate a relay from the output of Arduino UNOThe relay is 12 Volts and I have other of 9 volts. The transistror I use is a 2N222A and I do not know that I have emitter resistor to putI've tried everything and no way to activate the relay coil . If is activated, then there is no way to disableThe program with leds works correctly.Someone has the outline of a circuit to do this.thank you very muchMiquel
@ PapaG, You are right I would Never thought of using a switched diode to do what can be done perfectly well with a single transistor. The circuit so intrigued me that I took a very careful look at it, simulated and then built a 2 transistor inverter. I apologize to You and Lefty and all involved for my fat mouthed insistance. The circuits posted by the OP are both inverters but one requires a current sink to change state and the other requires a current source to change state. Neither circuit as drawn will work very well as has been noted the first missing a resistor in the base and and the second one with a not so obvious fault. The second circuit will only work reliably if the input is held below about .5 volts, hang a Si diode from the input to ground cathode grounded and you have a thermometer... If you heat the diode gently.. 100 C, the switch turns off. Below that temperature with the emitter @ .65 Volts the switch is still on and if you heat both transistor and diode equally nothing happens the switch is still on. Not a very ideal circuit where a logic low is specified to be above the level that will cause the switch to turn off. In practice most of the time it will work But if there is even a small breadboard ground differential which is real easy to do it will fail and fail with temperature too.Bob