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Topic: Signal inverter (Read 1 time) previous topic - next topic

Docedison

#5
Feb 03, 2013, 05:56 pm Last Edit: Feb 03, 2013, 06:25 pm by Docedison Reason: 1
Where is the base bias for T1?, T2 is now on as it's emitter is lower than it's base so collector current can flow to the emitter... From Where? current cannot flow from the emitter, it's grounded. and there is no pull-up on T1's base. How is T1 ever turned on?.

Bob

This was a question I used on an employment exam for prospective electronics technicians... If the prospect got this question right, I'd read his resume, if not it got 'filed'.
(I missed it once in the late 70's, applying for a job that I didn't get)
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

cargol

Sorry, Sorry,

I try to explain again.

I'm trying to activate a relay from the output of  Arduino UNO

The 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 put

I've tried everything and no way to activate the relay coil . If  is activated, then there is no way to disable

The program with leds  works correctly.

Someone has the outline of a circuit to do this.

thank you very much

Miquel

Docedison

@ Miguel; Senor, there are many relay tutorials available from the net... Adafruit, SparkFun.... and even the playground here. I have found that If I search Google I can get a whole lot of answers and I just pick the one that fits my situation best. I don't have to post the question here and try to deal with a great many people who don't fully understand the Question... ?Por Que?, Senor. The added advantage is that you can do it in your native tongue.

Bob
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

Papa G


Where is the base bias for T1? How is T1 ever turned on?.

Bob


When the emitter of T2 is greater than two diode drops higher than ground, i.e around 1.4V, the emitter-base junction of T2 is reverse biased but the base-collector junction of T2 is forward biased by virtue of the 4K7 resistor connected to +5V. This biases T1 into saturation and its output drops to near ground.

Papa G


Sorry, Sorry,

I try to explain again.

I'm trying to activate a relay from the output of  Arduino UNO

The 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 put

I've tried everything and no way to activate the relay coil . If  is activated, then there is no way to disable

The program with leds  works correctly.

Someone has the outline of a circuit to do this.

thank you very much

Miquel


Miguel, do what retrolefty said. Replace the 1K resistor with your relay coil. You must use a base resistor. If your relay doesn't have one internally, then put a reverse-biased diode (Cathode towards your positive voltage) across its coil.

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