Clock signals through a Transistor

[cerkit]

Consider a scenario:

* Microcontroller (Raspberry Pi in this case)
* Oscillator output (in this case it's just a simple 40106 single oscillator)
* Transistor
* Trigger signal (from GPIO pins of Raspberry Pi)

I'd like to be able to send the signal of the oscillator through the transistor so it can be triggered by the microcontroller.

Is this possible or do I need to look at it differently?

Will this have an impact on the oscillator (something tells me the transistor will alter the signal in some way).

If not a transistor, what's the best way to gate the output of an oscillator?

Should I use the transistor between the "loop" resistor on the oscillator and the output pin?

Maybe between the capacitor to ground and the "input" pin of the oscillator?

Thanks in advance for any insight.

[PHOBoS]

yes a transistor can work, downside is that the output wil be floating when turned off so you might need an extra pulldown resistor. Better would
be to use an AND gate since you are using digital signals, or probably even better: make the oscillator using a schmitt trigger NAND gate (CD4093).
You can find an example of those here

[wackelpeter]

[PHOBoS]

a switch like a 4016 or 4066 would work, but since the output of the
oscillator is a digital signal an AND gate would be more suitable.

[wackelpeter]

well that's true, since you have a defined logical level, high or low at the output, when you want to use the oscillator for further logic implementations...

guess with a switch you had to pull down it's output when you want it to use the same way, as otherwise it wouldn't be a defined logical level.

[cerkit]

Thanks for the assistance. I just happened to have a 4093 on hand, so I hooked it up based on your suggestion.

However, I'm still using the 40106 as the oscillator and the 4093 as a simple gate.

Could you take a look at my blog post on the subject and let me know if my description of how/why this works is correct? I may have some of the details wrong in my description, especially as it deals with the output of the gate (I'm still a little unclear of what I'm getting as an output from the gate as I haven't bought a meter, yet). I'm connecting the output pin of the gate to a PNP transistor that controls a +3v source to an LED.

Would a -5v output form the NAND gate trigger the transistor? I guess in this case, evidence points to a yes if what I understand about the relationship between my 40106, the diode, the 4093, and the transistor is correct.

Thanks again for all of your help.

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2016-12-11 16_58_10-GatedOscillatorSchematicWithPinHighIndicatorLEDNoGrid.png
Description:	This is the schematic that I created to describe the circuit that I put together based on using a 40106 and a Raspberry Pi to trigger a 4093 NAND gate to flash an LED.
Filesize:	41.4 KB
Viewed:	376 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

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[Grumble]

You could also use one of the gates of the 4093 to make an oscillator while controlling the oscillator with the second input.

[PHOBoS]

yep, that's what I meant when I mentioned "make the oscillator using a schmitt trigger NAND gate (CD4093)"

as for the GatedOscillatorSchematicWithPinHighIndicatorLEDNoGrid I'd use an AND gate for that function, but I guess a NAND will work if
you invert the output. You don't need the diode on the input (pin2) of the NAND gate and if you do you should add a pullup resistor to +5V.
I am not sure if Q2 will be happy with 5V on the Base and 3.3V on the Emitter and I would also put a resistor (10K or so) in series with the
Base. If you do want to use a NAND gate instead of an AND gate you could use another one as an inverter instead of the transistor but that
also depends a bit on what you want to drive with it. You could drive the LED straight from that gate's output if you increase the resistor
value a bit and if you really need 3.3V to drive something else you could just add a voltage divider to the output.

[Blue Hell]

Q1 needs a base resistor too - both Q1 and Q2 will blow up when their base goes to ground. Oh, CMOS driven, Q2 will survive and so will the CMOS port, but it's really a short circuit (in both cases).

[Grumble]

[PHOBoS]

Checked the blog and the only thing that doesn't seem to be correct is "(with a negative 5v - a behavior of the NAND gate)"
The output will be either high (Vcc) or low (0V/GND) it will not be negative. (at least not on a single supply) Although you could
regard GND as the negative rail but it is not -5V.

[cerkit]

[cerkit]

[Grumble]

As you can see in this drawing the logic high for a cmos powered at 5 volt is 3.5 volts, and that is to high for your raspi gpo signals.
So the circuit will not work. (Well, not reliable anyway)

[Blue Hell]

[cerkit]

[cerkit]

[gdavis]

I'm a little late to the party so I haven't read the whole thread in detail, sorry if I missed something, but in your latest schematic, why the 5V instead of just putting everything on 3.3V?

Why is R2 there?

[cerkit]

[gdavis]

[cerkit]