The C Programmer’s Guide to the Mosaic Handheld

Chapter 13

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Customizing Your Handheld Instrument

Your Handheld comes with 17 I/O signals including timer controlled digital I/O, 8 lines of 8-bit A/D, and two serial ports.  You can further customize its I/O by:

Adding WildCards for virtually any kind of I/O;

Routing any I/O signals to the Handheld’s DB-25 connector;

 Filtering and/or protecting any of the I/O; and,

Adding custom circuitry.

Using the Personality Board to Customize I/O

The Handheld’s Personality Board allows you to place your own custom circuitry into the Handheld, to mount WildCards for custom-off-the-shelf I/O, to route any of the Handheld’s signals to its DB-25 connector, or to filter, protect, or condition any of its I/O signals.

Figure 13‑1 shows the Personality Board.  On the left is prototyping area you can use to mount custom sensors, actuators or to include your custom circuitry.  On the right are field connections for up to four WildCards.  Each of the field connectors for the WildCards is mirrored with a sea of holes to provide access to any of the field signals. Corresponding hole patterns for the DB-25 connector and the Processor Board’s native I/O are provided so that you may point-to-point wire from any I/O signal to the DB-25 connector.

The Personality Board includes protection circuitry for you to use to protect up to eight signals.  This protection circuitry comprises SIDACtor overvoltage protection devices mated with current-limiting resistors. The schematic for the protection devices is found on the “Protection” page of the Handheld Schematic.

Figure 13‑2 and Figure 13‑3 show the internal and external dimensions of the Handheld.  There is considerable volume between the Personality Board and the Handheld’s back shell.  This volume is roughly in the shape of two adjacent cubes, one of approximately 17.7 in³ (4.0” x 3.4” x 1.3”) available for mounting Wildcards or your custom hardware, and another of 5 in³ (appx. 1.5” x 2.8” x 1.2”) over the prototyping area.  Even if you fill the Handheld with four Wildcards, there is still the sizeable prototyping area available for your custom devices.

Figure 13‑1  The Personality Board showing room for custom circuitry on the left, and protection circuitry in the center.

Routing I/O Into the Instrument

Figure 13‑1 shows that the Personality Board includes a hole pattern corresponding to the DB-25 signals, labled “DB-25 Connections”. All the DB-25 lines are routed for you from the connector to these holes.  You may point-to-point wire on the Personality Board from any of the WildCard field headers, the Port A and E Connections, or your custom circuitry to these holes.

Using Compact Flash

Using Other WildCards

Plugging in WildCards

Connecting to the Field Headers

Routing signals to the DB-25

Installing signal protection circuitry (include schematic)

Mounting Additional Components

Figure 13‑2  The Handheld’s external dimensions  (in inches).

Figure 13‑3  The Handheld’s internal dimensions (in inches).

Using the Prototyping Area

Accessing the Motherboard’s I/O

Adding circuitry, power supplies

Adding Components, Sensors, Actuators, Probes

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