Resonators and Crystals - Help Request
#1
Posted 03 October 2011 - 08:31 AM
I have a 3 pin resonator with built in capacitors. I have placed this component in the circuit for the crystal and the two capacitors. I have a 1M resistor across the invertor (horizontal resistor in the diagram) and a 2K2 resistor for the other resistor. The invertor is provided by a 74LS04 and the whole circuit is powered by 5V.
The circuit is built on breadboard (could this be a problem?) as I'm experimenting
I am expecting to see a 4MHz square wave coming out of the invertor but when I connect the scope to the circuit I am getting nothing.
Can anyone see any obvious problems or point me to a good resource to help me learn a little more about these circuits?
Thanks in advance,
Mark
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#2
Posted 03 October 2011 - 08:42 AM
http://cds.linear.co...Note/an12fa.pdf
It is much stable than any other.
However, I always used crystals (3 to 5MHz), and never any resonators.
For freqs relatively low (less than 10MHz), the crystal/resonator is working on the primary harmonic. Some crystals/resonator released for 20-30MHz (and over), may works on third or fifth harmonic. In this case is much harder to make it oscillating properly.
Cheers
#3
Posted 03 October 2011 - 08:45 AM
Thanks for the hint - I'll look at it later today. I'm not precious about using a resonator - crystal will be fine. I really just need to get an external clock up and running.Mark, I have tested with success, many times, the circuit in fig. 1d
http://cds.linear.co...Note/an12fa.pdf
It is much stable than any other.
Regards,
Mark
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#4
Posted 04 October 2011 - 05:35 PM
The circuits in the document all have different crystals in them - does this mean that the circuit is "tuned" to a specific range of values?Mark, I have tested with success, many times, the circuit in fig. 1d
http://cds.linear.co...Note/an12fa.pdf
It is much stable than any other.
However, I always used crystals (3 to 5MHz), and never any resonators.
I have wired up the circuit in 1d using a crystal rated at 8MHz (smallest value crystal I have) at the moment. I am getting a wave form which is not very square out of the circuit and the frequency is about 8 MHz. Just out of interest I swapped out the crystal and dropped in a ceramic resonator and got a slightly better wave form.
I did make one modification, I fed the output through a not gate to buffer the output - this also had the effect of squaring the wave off a little more.
So back to the questions - should I use circuit 1c (instead of 1d) if I am using a 10Mhz crystal?
Thanks in advance,
Mark
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#5
Posted 04 October 2011 - 05:51 PM
#6
Posted 04 October 2011 - 06:02 PM
I started working on this on Saturday afternoon and I had 74LS04's but not a HCMOS equivalent. Basically, I was using what I had to handAnyway, why are you using LS and not HCMOS?
Thanks for all the help,
Mark
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#7
Posted 06 October 2011 - 06:50 AM
#8
Posted 06 October 2011 - 07:03 AM
#9
Posted 06 October 2011 - 07:22 AM
#10
Posted 06 October 2011 - 07:30 AM
This is where I started with the TLC - I used an astable 741 for the clock - not fast and a bit crude but I knew I could get the circuit working at 40-70KHz. Fast enough to prove the concept before moving on to new principles - hence this thread. I knew I needed to be able to generate good clock signals.If you were talking about the TLC, my suggestion is still to make one step a time. I'd first try to use a well-known clock source, such the Netduino PWM, afterward you may refine the circuit with a good (and faster) oscillator.
Bit off topic - I'm expecting to be posting some code on the TLC5940 later this week, possibly the weekend. I'll be including a schematic and some description of the operating principles - including the clock circuit. I just need to work on the code at the moment.
Mario - thanks for the help on this topic.
Regards,
Mark
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