Please suggest a best and reliable switch circuit

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I am using a MC14060BCP as a oscillator and counter. A 3.XXXMhz crystal
is being connected to pin 10 and 11 with RC circuit. However, I need a
switch that once I simply press the button, it goes to 3.XXXMhz
crystal. If I press the same button for 5 second, it can be switched to
another crystal , which is 4.XXXMHz. I think a reed relay which draw
20mA is required to swtich from 3.XXX and 4.XXX MHz crystal. Any
suggestion for a safety and reliable circuitfor my reference. Thanks

 

[[email protected]]

I am using a MC14060BCP as a oscillator and counter. A 3.XXXMhz crystal
is being connected to pin 10 and 11 with RC circuit. However, I need a
switch that once I simply press the button, it goes to 3.XXXMhz
crystal. If I press the same button for 5 second, it can be switched to
another crystal , which is 4.XXXMHz. I think a reed relay which draw
20mA is required to swtich from 3.XXX and 4.XXX MHz crystal. Any
suggestion for a safety and reliable circuitfor my reference. Thanks

If I were doing it, I would make two oscillators. One at each
frequency. That could be done with one 74HC04UB. Then I'd switch the
oscillators into the 14060 with a quad NAND gate wired as a data selector. How
to get the selection level, pushbutton or simple SPDT switch, is left as an
exercise for the ambitious student.

Jim

 

[[email protected]]

Thank you so much for your advise, cause other chips are CMOS, any
suggestion other than 74HC04UB? How about using two MC14060, then
using a flip-flop to switch the clock to next stage. Which solution
would perform better?

 

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Sorry for my mistake. 7404 actually is a CMOS .

 

[Pooh Bear]

I am using a MC14060BCP as a oscillator and counter. A 3.XXXMhz crystal
is being connected to pin 10 and 11 with RC circuit. However, I need a
switch that once I simply press the button, it goes to 3.XXXMhz
crystal. If I press the same button for 5 second, it can be switched to
another crystal , which is 4.XXXMHz. I think a reed relay which draw
20mA is required to swtich from 3.XXX and 4.XXX MHz crystal. Any
suggestion for a safety and reliable circuitfor my reference. Thanks

You actually want to switch crystals ?

Wrong approach. It takes time ( millisecs ) for oscillators to start up so
you won't get a nice transition.

Just run the crystals is individual oscillators round an inverter. Intel
does a nice app note on crystal oscillators btw.

http://www.intel.com/design/mcs51/applnots/230659.htm

The oscillator outputs can then be gated for use as the counter clock. NO
relays.


Graham

 

[[email protected]]

I am totally convinced not to use realy. Thank you so much,
I am searching information to build a gate for the purpose of press the
button once, it turn on one crystal, If I press it for over 5 seconds,
it would turn on other crystal. Any advise will be highly appreciated.

 

[ehsjr]

I am totally convinced not to use realy. Thank you so much,
I am searching information to build a gate for the purpose of press the
button once, it turn on one crystal, If I press it for over 5 seconds,
it would turn on other crystal. Any advise will be highly appreciated.

Conceptually, this is what you want to do, if I understand
it: Press the pushbutton and immediately set the flipflop
to high to select XTAL1, but if you hold the pushbutton
down for 5 seconds, the FF is reset and at that time XTAL1
is deselected and XTAL2 is selected. In other words, you
are not looking for a 5 second time where neither XTAL1
nor XTAL2 is selected. If I understood it correctly, the
circuit below should work for you.

---- ------ +---[Relay]--Vcc
PB----+----------|NAND|----|SET | /c
| | | | FF |---|
| | | | | \e
[R1] +-| | +-|Reset | |
| | ---- | ------ Gnd
+---+--[Zd]--+---------+
| | |
[R2] [C1] [R3]
| | |
+---+--------+---Gnd

When you press PB the NAND output goes high and the FF is set
so its output goes high. When C1 charges through R1 to the
zener voltage, the NAND goes low bringing the set low.
The reset goes high, resetting the FF, so the FF output goes
low. R1 and C1 set the time it takes to reach the Zener
voltage. R3 ensures the second NAND pin & the reset pin are not
"floating" when the charge is below the zener voltage. R2
discharges C1 when the pusbutton is released.

You can use the output from the FF to select your XTAL -
high selects XTAL1 and low selects XTAL2. A diode or FET
or relay switch circuit can be used for that.

Ed

 

[[email protected]]

I'd appreciate your advice. Please frogive me for being lack of
knowledge in electronic. Is ther any CMOS intergrated with both NAND
gate and Flip-Flop. My board space is very limited. I am thinking if it
possible to use two single chip oscillators then feed their output to
the data selector. Thanks anyhow.

 

[ehsjr]

I'd appreciate your advice. Please frogive me for being lack of
knowledge in electronic. Is ther any CMOS intergrated with both NAND
gate and Flip-Flop. My board space is very limited. I am thinking if it
possible to use two single chip oscillators then feed their output to
the data selector. Thanks anyhow.

Sure - you could use a CD4011 quad nand. Cross
connect two of the nands and you have a flipflop.

Ed

 

[Jim Thompson]

Sure - you could use a CD4011 quad nand. Cross
connect two of the nands and you have a flipflop.

Ed

Wouldn't a J-K flop do what you want?

...Jim Thompson

 

[[email protected]]

http://www.doctronics.co.uk/4011.htm#bistable

That link provides a very useful 4011 application that i can make use
of it.

 

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Hi Ed,

I connect the circuit as you descripted. Using Nand gate to trigger the
FF. The FF output is high once it is powered on. Not press the buttom.
However, it meets the requirement of press for 5 seconds FF Q trun low.

 

[ehsjr]

Hi Ed,

I connect the circuit as you descripted. Using Nand gate to trigger the
FF. The FF output is high once it is powered on. Not press the buttom.
However, it meets the requirement of press for 5 seconds FF Q trun low.

When Q is low, does it go high when you press the button for
1 second?

Perhaps I misunderstood. You have two xtals: a 3.xxx and a 4.xxx.
You want to select the 3.xxx with a short press on the button,
and the 4.xxx with a long press. The FF has to power on in
one state or the other.

Do you really need 3 states?
1) No xtal selected
2) 3.xxx selected
3) 4.xxx selected

OR do you need it to power up with the 3.xxx selected

OR can you never get Q to go high, once it has gone low?

Ed

 

[ehsjr]

Hi Ed,

I connect the circuit as you descripted. Using Nand gate to trigger the
FF. The FF output is high once it is powered on. Not press the buttom.
However, it meets the requirement of press for 5 seconds FF Q trun low.

Meant to ask you to post your circuit in my earlier reply.
Ed

 

[ehsjr]

ehsjt, Thank you so much for your help.

Actually, I need 3 stage:
1. Press the button once(trigger it on), it select 3.XXMHz and turn on
a red LED.
2. Press the same button for 5 seconds, remains on and select 4.XXXMHz.
a,d turn on yellow LED.
3. Press the button again(trigger), it turns off the clocks feed to the
op amp and turn off LED.

Actually, there is a MC4013 in the existing circuit handling the
triggering to select the 3.XXXMHz oscillator clock feed through to the
op amp through another MC4013.
Therefore, I can make use of the existing 4013 to trigger the newly
added oscillator selector. The MC4013 can also trun off the both
oscillator and LEDs

I can use the spare MC3346 transistor array in the existing circiot to
drive the LEDs on and off..

Does it work??

Thanks

Ok that changes things. Use a 4017 decade counter.
Conceptually:
Run the pushbutton through a debounce to put a high into the
clock input. When the counter is reset, 0 is active (high).
(If you want, you could put a LED on it to indicate standby mode.)
Press once, and 1 becomes active. Press the second time, and 2
becomes active. Press the third time, and 3 becomes active. Tie 3
to the reset pin; tie the reset pin to 0V through 10K. When 3
becomes active, the counter resets to zero. Use the 1 and 2
outputs to control xtal selection & light the LEDS.

You get 3 states - counter 0 or 1 or 2. You can use
1 to control the 3.xxx, and 2 to control the 4.xxx
Does that do what you want?

Ed