10mhz timebase osc

Thread Starter

radioshack5209

Joined Nov 25, 2020
68
hello

I made this 10mhz osc but the square wave o/p is very noisy. The 74LS390 counter on the o/p won't count.
I used 1K resistors and 10mhz hc49/u xtal. Any help would be very much appreciated.
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MrChips

Joined Oct 2, 2009
23,897
I think you do not mean 10mHz. That is very different from 10MHz.

Depends what you mean by "very noisy". Do not expect a perfect sine or square wave.
What do you mean by the 74LS390 counter would not count? That could happen for other reasons that have nothing to do with the clock signal.

Show us your physical setup and the oscilloscope waveforms.
Show us also the circuit schematic of your counter.
 

Papabravo

Joined Feb 24, 2006
16,472
An 'LS' gate has very poor linear amplifier characteristics, and the TTL inputs are 'sourcing' current. This configuration will work better with a CMOS part, but maybe not all that well at 10 MHz.
 

Thread Starter

radioshack5209

Joined Nov 25, 2020
68
I would recommend using inverters that have Schmitt trigger inputs -- i.e., 74xx14 instead of 74xx04.
Thanks I will do that. My scanner stopped working so I can't show my schematic for the counter wiring. Is it possible for someone to
show how the 74LS390 should be wired in order to divide by 100? I have a feeling the diagram that I found has an error.
thx
 

Thread Starter

radioshack5209

Joined Nov 25, 2020
68
Thanks I will do that. My scanner stopped working so I can't show my schematic for the counter wiring. Is it possible for someone to
show how the 74LS390 should be wired in order to divide by 100? I have a feeling the diagram that I found has an error.
thx
Thanks for the 74LS390 wiring diagram?!
 

Ian0

Joined Aug 7, 2020
2,612
I would recommend using inverters that have Schmitt trigger inputs -- i.e., 74xx14 instead of 74xx04.
Don't do that - you can't get a Schmitt trigger biassed as a linear amplifier, so it won't oscillate.
Also, it must be a CMOS type - the bipolar device don't make good linear amplifiers
By all means buffer the output with Schmitt triggers (CMOS or TTL)
 

WBahn

Joined Mar 31, 2012
26,398
Don't do that - you can't get a Schmitt trigger biassed as a linear amplifier, so it won't oscillate.
Also, it must be a CMOS type - the bipolar device don't make good linear amplifiers
By all means buffer the output with Schmitt triggers (CMOS or TTL)
Yeah, I was thinking of a difference kind of oscillator.
 

Thread Starter

radioshack5209

Joined Nov 25, 2020
68
Yeah, I was thinking of a difference kind of oscillator.
I have no CMOS devices at this point. My oscillator produces a 9.925 MHZ square wave with 6.1% + overshoot and
17.0% - overshoot. If I put 74LS14 on the oscillator, I get a 9.889 MHZ square wave with 2.3% + overshoot and
25.2% - overshoot. So I am not sure what to do. I get much cleaner square waves from a 555 but can't achieve
a 10 MHZ output. I need to get a wiring diagram for the 74LS390 as a bi-quinary divide by 100 as well but it is
no where to be found on the internet.
 
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Ian0

Joined Aug 7, 2020
2,612
Have you got a MOSFET? With a resistor from drain to V+ you can use the same circuit. Gate = input, Drain = output.
Is the overshoot real? Not something to do with a misplaced earth clip or un-calibrated probe?
 

Thread Starter

radioshack5209

Joined Nov 25, 2020
68
A single 74HCU04 will work perfectly in the Pierce oscillator circuit at 10MHz.
https://en.wikipedia.org/wiki/Pierce_oscillator
R1 = 10M
C1, C2 = 22pF
hi:
I can get my hands on 74HC04 and 74HCT04 s are they okay?
Will they directly interface with TTL?
Do I need to buffer the o/p with a schmitt trigger if so, does it need to be CMOS?
I still can't find a hookup diagram for 74LS390 as divide by 100.

thx
 

Ian0

Joined Aug 7, 2020
2,612
The 74HC04 will probably work in the oscillator. Theory says it might not, but practice generally says it does. (I've made a NAND gate work)
Both will drive TTL.
TTL will drive the HCT, but maybe not the HC (again, it generally does)

If you want the divide-by-100 to be a nice square-wave then you need the bi-quinary circuit. If you want to use the outputs as BCD then use the BCD circuit.
To make it divide by 100 connect the Qa output to clock B (bi-quinary); or the Qd output to clock A (BCD).
 

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Ian0

Joined Aug 7, 2020
2,612
Actually, you could really do with a sine-wave from the first stage. It will rarely be perfect, but it will be a lot better than that!
Then buffer the sinewave with a few more inverters until it gets square.
 
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