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how to control power to an oscillator

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ulot

New Member
Hi, i have an oscillator circuit that i'm using for a project
i built this circuit after so many various tires to control power to the oscillator circuit (a pierce oscillator)
However, it doesn't seam to work fine.

The trigger input is coming from a microcontroller, when i test the circuit with a scope, it seams to work,cos as i set the input high, the oscillator waveform is producted, when i set it low, it goes out.
but inside the main circuit, with the input triggered by the microcontroller, it doesn't work, except i connect the power directly the VCC what other method can i use to control

ive attached the schematic of the design
thank you.
 

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ericgibbs

Well-Known Member
Most Helpful Member
hi,
A ULN has a Darlington type, open collector output.

When you pull 0V to the 7404 it will only pull to approx 1.5V.

Why do you need to switch the 0V as well as the +Vcc to the IC..??

Also what are the resistor values on the pnp.?
 
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ulot

New Member
i don't have to switch vcc and ground, i just want to control the oscillator, i've tried using a notgate buffer to switch, it didn't seam to work, i've also tried a number of ULN connections, all don't seam to work, i just need something that workds.

What other circuit can i use to do this?
 

ericgibbs

Well-Known Member
Most Helpful Member
i don't have to switch vcc and ground, i just want to control the oscillator, i've tried using a notgate buffer to switch, it didn't seam to work, i've also tried a number of ULN connections, all don't seam to work, i just need something that workds.

What other circuit can i use to do this?
hi,
Post the circuit that you are trying to control.
 

ronv

Well-Known Member
Most Helpful Member
I think it may be that there is nothing to "pull" the output of the transistor to ground when it is turned off. Add a resistor to ground there.
 

ulot

New Member
Hi, the circuit i'm trying to control is just the VCC pin of a hc7404, which i use to design a pierce oscillator (which is tested and working fine)

i designed the above using proteus but the problem with proteus is it doesn't give the HC7404 in full DIP package so i can simply connect this output to the VCC pin.
 

ericgibbs

Well-Known Member
Most Helpful Member
Hi, the circuit i'm trying to control is just the VCC pin of a hc7404, which i use to design a pierce oscillator (which is tested and working fine)

i designed the above using proteus but the problem with proteus is it doesn't give the HC7404 in full DIP package so i can simply connect this output to the VCC pin.
hi,
If it works OK in simulation, why not build the circuit on a project board.??
I would advise not to switch the 0V [pin7] of the 7404, leave that connected to 0V.
You should drive the pnp transistor into saturation in order to give the maximum voltage to the 7404, [pin14]
 
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