Construction

I built the circuit on a double sided full length card for an XT slot (62 contacts), with 3-hole copper patches. A card like this, eventually including buffering and address decoding circuitry, is also called a prototype card. Included in the ADDA10.ZIP archive is a board layout sketch, showing the approximate IC positions (if I should build the board a second time, I would shift the whole setup to the right, creating more space for input signal shaping circuitry close to the connector). I wire-wrapped the board. Because the holes in the card were too large for standard wire-wrap pins I used parts of 36-pins rectangular SIL blocks. The circuit occupies about one third of the card space, leaving plenty of room for the addition of a programmable amplifier, a multiplexer or analog signal shaping circuitry (e.g., filters). These additional components can be programmed from the unused I/O addresses $302 and $303.

To minimize noise, correct grounding is important. The AD7569 has one digital ground (DGND), and two analog ones (#math32#AGND_DAC and AGND_ADC). These have to be connected to each other as close to the IC as possible. The common connection is called ;SPMquot;STAR GND;SPMquot; in the diagram. This prevents the fluctuating supply current from influencing the #math33#AGND_DAC and AGND_ADC grounds. Other connections to the analog grounds are made directly to the pins. It is possible that using IC's from the HCT instead of the LS series reduces noise because of the much reduced power consumption.

The 5 V power supply is decoupled to ground in some places with 100 nF ceramic capacitors, and all unused inputs are tied low.