Saturday, May 14, 2016

Quick PCB: TCXO Breakout

I'm back with another Quick PCB. This one is a little breadboard-compatible breakout board for inexpensive temperature-compensated crystal oscillator (TCXO) modules commonly found on eBay.

Need a TCXO frequency reference for your breadboard project?
This might be a good option for you.


There are some good, inexpensive TCXO modules on eBay that come in the slightly unusual package shown above. This breakout board allows you to mount one of the modules onto the small PCB and adapt it to standard 0.1" breadboard-compatible headers. I have also included a few optional SMD components. There are spots for a power LED, a bypass capacitor on the supply rail, and a capacitor on the control voltage input.

Some of these modules don't actually have a control voltage input on pin #1. Typically they have a small trimmer on top for adjusting the frequency, which is probably more useful for how these are commonly used. If you have access to a disciplined frequency reference such as a GPSDO, you should allow the module to warm up for 24 hours and then trim the frequency.

I have tested this board with two such TCXO modules from eBay. One is a 20MHz Raltron unit that is quite useful for microcontroller projects. You could also use a D flip-flop to divide it to 10MHz. The other is a 14.4MHz Rakon unit. Other modules in the same package will work. I honestly don't know what the package is called, so if YOU do please let me know in the comments below.

Assemble Your Own

Eagle Files: Shared on Github
TCXO Breakout Board: Order PCBs on OSHPark!

TCXO Breakout Board Schematic

TCXO Breakout Board Layout
Sharp-eyed readers will note this has been updated from the boards shown above.
The circuit is the same but the layout is much cleaner.

Parts List:

TCXO Module: Raltron RTX0230LC, Rakon VTX0525-14.4MHz, or similar
C1: 100nF 0603 SMD
C2: 10nF 0603 SMD (Only necessary if your module has VFC on pin #1)
R1: 1k 0603 SMD (or adjust value to change brightness of LED)
PWR LED: 0805 SMD (color of your choice)
Headers: Four 2x1 0.1" standard male headers (snap off from breakaway strips)

Note: The outer-most pins on each header are not connected to anything. They are just there for stability on the breadboard.

Sine to Square Wave?

Many of these modules output a relatively weak sine wave. However, you probably need a logic-level square wave for your project. You can use the circuit shown below to convert the sine wave output to a square wave. Note that you may need to adjust the resistor divider values based on the output signal of your module and the inverter you use. The peak-to-peak output from the TCXO needs to extend past the High and Low logic thresholds of the inverter to successfully trigger it. The divider also adjusts the duty cycle of the output.

Use a schmitt inverter chip with TTL-compatible inputs. I use 74LVC chips exclusively for my projects. 74ACT is another good series. If you want to be really old school, find those 74Fs in the junk box.

A typical circuit for converting a sine wave signal to a logic-level square wave. 

Wrap Up

I hope this little breakout board is useful to you! Tweet me a pic @sync_channel if you build one into a project.

Thanks for reading!

- Dan W.


  1. Another great project, Dan. Thanks, also, for the sine to square hints. I'm going to play around with that circuit to simplify what I'm currently using.

  2. Great work. Many thanks Dan. Should be great for most microcontroller projects.