Wednesday, March 14, 2012

Prop TCVCXO PCB

I have been watching/testing the 10MHz TCVCXO that I installed to replace the master clock on the Propeller (see previous posts). The stability is better than I had hoped, but the installation was NOT as good. I just soldered the TCVCXO onto the Propeller Protoboard where pads were available, but spacing was not optimal as solder bridges where necessary to make it fit. It was a jury-rig just to do some initial test.

Now that I had time to think about how it should be mounted, I decided to build a small PCB to hold the the parts; TCVCXO, by-pass cap, two fixed resistors, a variable tuning resistor, and a output cap.

Schematic on CircuitLab
Keeping with my on-going project goal, I wanted it to be as small as my ability allow. The results was a PCB that is 0.453 inches by 0.492 inches. The circuit will stand on three legs/pins which insert into mating sockets. I installed the sockets on the Prop Protoboard using existing holes, which provide 3.3v, ground and the clock input.

If the TCVCXO can not to be used, or if I want to use the original crystal, it can be re-inserted. Only the three pin-sockets were necessary and they can be abandoned.

DipTrace Layup
I will have the board made by a commercial PCB vendor, but for a quick test, I resorted to my tried-and-true Toner Transfer Method.
Circuit at Different Stages of Toner Transfer
I made more than one copy, Just in case Murphy was Watching

Components Loaded and Ready to Install
Some things just looks Ugly, when you get TOO close.
The TCVCXO PCB,
Two Fixed Resistors and Pot in Foreground
10MHz TCVCXO Center
Two Cap's in at the Far Edge
Using the board, is just a matter of changing the clock parameters and plugging the TCVCXO in.
TCVCXO Installed on the Prop Protoboard
It Sets Just Below the Edge of the LCD
I was easy to do, and it works GREAT!

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