A leading radio broadcasting company required a reliable, small, cost-effective solution for monitoring and control at transmitter sites. In addition to the dense I/O requirements, the customer requested that the design allow for easy upgrade or replacement of the single-board computer. Sealevel designed a custom Relio system providing a variety of serial, analog, and digital I/O that can be queried or send alerts via the internet or a standard telephone connection.
A fanless, diskless system capable of running under Windows XP Embedded or Linux was specified. To minimize rack space used, a 1U (1.75) 19″ rackmount enclosure was desired. A significant amount of I/O is required to accomplish the monitoring and control needed to ensure quality AM and FM radio transmissions:
- 64 Digital Outputs (24VDC @ 250mA)
- 64 Isolated Digital Inputs (5VDC – 30VDC)
- 24 14-bit Analog Inputs (0-10VDC)
- Dual 10/100BaseT Ethernet
- Four USB 2.0 Ports
- Four RS-232/422/485 Serial Ports (Software Selectable)
- Voice Modem with DTMF
- Power and Status Indicator LEDs
The Sealevel Solution
For maximum flexibility and cost-effectiveness, a Mini-ITX form factor was chosen for the single-board computer. The 1.3GHz VIA processor used provides excellent computing capabilities with minimum power dissipation and does not require a cooling fan. To accommodate the 1U enclosure, high-density SCSI connectors were chosen to expose the analog and digital I/O signals on the rear of the chassis. Cables connect the system’s I/O to an external termination board with easy to use removable screw terminal connectors. The computer is silkscreened with the customer’s name and logo (not shown) to customize the appearance.
Key Design Challenge
Interfacing I/O Requirements to the Mini-ITX Single Board Computer
Mini-ITX is a proven form factor supported by a number of vendors. However, Mini-ITX boards typically offer minimal I/O expansion options, usually one PCI slot. To meet this customer’s application requirements, Sealevel engineers designed a custom I/O board that interfaced to the SBC via an internal USB connection. The I/O board includes a microcontroller that polls the analog and digital I/O and communicates with the host via USB. This design fulfills the requirement for easy processor upgrade or replacement since the I/O board is not mechanically dependant on the SBC in any way. The USB connection provides a fast, reliable interface that allows the I/O to be polled at a 100ms scan rate using the software driver provided by Sealevel.