For some reason, when they built a lot of the buildings in the early to mid 90’s, they decided it would be a good idea to wire the entire building with Fiber Optics to every desktop, thinking technology would catch up. Enter Present day: Apparently technology has caught up in every regard except for the cost efficiency of a fiber card in every PC and laptop in the building (Have you ever tried to order a laptop with a fiber optic network interface?). Fiber to Ethernet converter boxes are what a lot of I.T. shops are using to get around that nuance. There is one inherent problem: They don’t last very long. Here is a picture of the circuit boards that came out of a bunch I am in the process of salvaging:

Note the white circles and arrows. Each of these has a 25 MHz crystal oscillator running the clock. Something I have not determined is whether this is an ordinary crystal oscillator or a TCXO (Temperature Controlled Crystal Oscillator). Anyone who is not familiar with the difference between an oscillator and a TCXO need not be afraid. Crystals, by nature, are affected by temperature. The resonant frequency can change (sometimes drastically) with the addition or subtraction of heat. TCXO’s resolve this fundamental problem by providing corrections to the shift in frequency using analog sampling of the output and compensating accordingly.

The challenge with identifying it correctly is that there is virtually no data on the internet for this part, and both types of oscillators can look exactly alike! (For those interested, they are all MMD MB050HA) If anyone knows, please inform me.

Either way, these are all getting reclaimed and thrown in the junk box for a future project! 25 MHz is not ideal for any microcontroller clock, but with a little convincing I could probably turn it into something on one of the HF ham radio bands. Happy circuit bending!

No Comments »

No comments yet.

RSS feed for comments on this post. TrackBack URL

Leave a comment

You must be logged in to post a comment.