Lab Clock DIY

04-26-2007 Clock

There is no any clock in my lab, so I DIY one, using SCM (AT87C51) fused with a few lines of codes. I want to thank Backfire (zealous fan of Mao Zedong, USSR and Nazi lover, another orthodox Marxist, military and weapon expert, badminton athlete, physicist, part-time AFM assistant of the institute. Fields of interest: photovoltaic material and solar cell, organic/polymeric light-emitting diode, nano-architecture and self-assembled monolayer) for guiding me all the way during the fabrication of this clock. He told me to read textbooks of digital logic circuits, assembly language, and manual of the MCS-51 series SCM (I had already known something about analogue circuits and Visual Basic/C programming), and guided me during practically assembling the devices in order and debugging the system.

Now let's have a look at the clock (photos are available in my Picasaweb album. Click the album cover on top left). Besides the main SCM, I use a buffer (74LS244P) and a series of triodes to drive the segment and digit select lines, respectively, of the 7-segment LED arrays. Two INT inputs (buttons) are employed responsible for date/time display switching and date/time setting functions. Wires on the backside of the circuits board and their junctions are immobilzed by hot melt adhesive.

As a chemist I do the chemical part of job by myself of course. Two rubber stoppers is attached to a poly(methyl methacrylate) (PMMA) board synthesized via radical polymerization initiated with benzoyl peroxide (BPO) and molded into a plain board of the same size as the circuit board (notice there is no bubble in this board which is generally quite hard to achieve in terms of bulk polymerization). Then the PMMA board is attached to the backside of the circuit board as a back cover, the two lateral walls of the clock made of as-received foam of ethylene vinyl acetate copolymer (EVA). The inside of the PMMA board is covered with a paper displaying the circuit diagram of the clock system. Ethyl-2-cyanoacrylate (ECA) based adhesive is empolyed wherever needed.

The system need a DC supply of about 4.5-6V to work. To meet this condition I use a AC/DC adapter which is the schoolwork of a friend of Backfire. The clock runs well, with less than 1s error per day compared with my computer clock. Moreover, the LEDs make it visible in dark ambiance, a very useful feature sometimes.