You might be an electronic engineer if… (VI)

… you can’t find quite the AVR development kit you need, so you make your own.

Completed "Timeserver" development board

The board was designed as a first foray into embedded Internet and is intended, ultimately, to act as an NTP server using an external MSF radio receiver as a time and frequency reference.  It features:

• A principally through-hole approach, for neatness, IC socketability and ease of routing.
• A 1 Amp dual linear power supply (5V, 3.3V) with over-voltage protection (once T1 arrives from the supplier…) and a logic-level mains frequency output for use as a timing reference.
• An ATMega128A 16 MHz microcontroller — chosen for its simplicity and the availability of a cheap (£10) programmer/debugger.  The ATMega128A is well supported by the GNU toolchain so no expensive proprietary compiler is needed.
• 64kB SRAM to expand the ATMega128A’s on-chip 4kB, which would be a little restrictive for TCP/IP and Ethernet.  A 74573 latch, used for address expansion, hides underneath this chip.  The SRAM is actually 128kB, wired as a 64kB part.  A future tweak might be to make the whole memory available to the AVR by using the (currently grounded) excess address line as a software-driven page select line.
• 128kB FLASH (IC1) for holding static data such as web pages and images.
• An Ethernet interface provided by a Microchip ENC28J60 together with an RJ45 socket featuring integrated magnetics.
• Frequency/Data input and output interfaces (two BNC connectors).
• A 34-pin IDC header for connection to a back-lit LCD (16×2 line text display, not shown).

Here is the schematic.

I have much work to do on the software, insofar as it does not yet exist.  The board does, however, produce stable 5V and 3.3V supplies and doesn’t consume an unexpected amount of current (always a good sign).  My JTAGICE Mk.1 (clone) also finds and identifies the microcontroller, which must therefore be happy.

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