Hardware Development
The circuit was developed using Labcenter™ ISIS schematic capture software, a component of Proteus VSM, which provides animated drawing objects for integrated software and hardware testing (see Appendix E for details). When the circuit had been tested by simulation, a stripboard implementation was devised (Figure 13.4). This layout was designed for an earlier version of the board using the pin-compatible PIC 16F877A chip, with a common anode display, so slight modifications would be needed to implement the TEMCON2 circuit in Figure 13.3.
A demo target system was constructed of this original design, with two filament lamps as the heaters, operating from a high-current 5 V supply. A 5 V central processing unit (CPU) fan was fitted as the cooling element, and the temperature sensors were arranged symmetrically inside the enclosure. The wiring of the target hardware is shown in Figure 13.5. Note that there is a sensor output on the fan that could be used to monitor the actual fan speed, if a suitable interface were added to convert the fan sensor pulse to TTL (transistoretransistor logic) levels. The vent was not physically implemented in this test hardware.
The photograph of the finished system (Figure 13.6) shows the simulator at the right of the picture, with the ICD module (enclosed in ABS box) connected to the ICPD connector on the TEMCON board. Five-volt power supplies and a host PC would complete the system. When final hardware testing was completed, an application board was created using Labcenter ARES™ printed circuit board (PCB) layout software, shown in Figure 13.7. This incorporated an on-board þ5 V supply for operation from a mains adapter.