The PC (personal computer) is an IBM Industrial PC-AT with an Intel 80286 microprocessor. The IBM Industrial PC-AT is packaged in a 19" rack-mount case. I think that the power supply is a little bigger than the standard PC-AT power supply and the fan has an air filter.
The PC controls the brewing system through an ADIO (Analog/Digital Input/Output) board. The ADIO board is an IBM DACA (Data Acquisition and Control Adapter).
The DACA offers three analog voltage ranges,
I use the 0 to 10 volt range.
The DACA offers 12-bit resolution. This means that the analog voltage range is represented by 4096 discrete levels, or approximately 409 levels per volt for the ten volt (absolute) ranges and 204 levels per volt for the 20 volt (absolute) range.
The DACA offers four channels of analog voltage input. I use the four analog inputs as,
The DACA offers two channels of analog voltage output. I don't use the analog output.
The DACA offers a 16-bit binary input port. This means that the DACA can monitor the status of up to 16 two-state (on or off, open or closed, high or low, …) devices. I use one of the 16 bits to monitor a mash float switch.
The DACA offers a 16-bit binary output port. This means that the DACA can control the status of up to 16 two-state devices. I use eight of the 16 bits to control,
The DACA offers a one-channel, 16-bit counter. I don't use the counter.
I didn't exactly choose the IBM Industrial PC-AT or the IBM DACA for the brewing system. I acquired the two for about $30.
The 80286 microprocessor provides more than enough horsepower to control the brewing system. The biggest drawback is that it's about 190 MHz and 32 M bytes of memory shy of running Windows 95. And while I'm not the biggest fan of Windows 95, it is the de facto standard PC operating system.
The biggest shortcoming of the IBM DACA is the number of analog inputs. Refer to the section on Future Enhancements for plans to extend this functionality.