The Broadcast Tools SCR-8 III is one of those devices that doesn't attract much attention, but once you have a use for it, it becomes one of those many critical tools for operating a radio station. Simply put, this unit is a GPI-to-serial interface. It converts eight opto-isolated inputs into a 38.4kb/s RS-232, RS-422 or RS-485 serial stream and also converts serial stream data into SPDT, 1A relay closures. If an identical unit is connected to the serial connection it's essentially a relay extender. Multiple units can be chained to offer a 32 input × 32 relay integrated control system.
This device is most often used to transmit closures between remote locations. One example is a station that has satellite receivers at the transmitter site and needs a way to send automation closures to the studio. Use of a serial path via the STL, T1 or even a pair of auto-dial modems can allow stations to tie the satellite automation closures as if the receiver were sitting at the studio. Other uses abound however. The units can be configured to offer any function that needs relay control. If the device is paired with the Broadcast Tools ESS-1 those serial signals can be transmitted over IP.
The applications extend beyond using two units to relay closures between locations. Because the output is a standard serial ASCII or binary protocol, software and automation systems can be programmed to read the closures or drive the relays directly. Simple computer applications can be used to drive the equipment to switch an antenna pattern at a scheduled time, start an analog network recorder or even start the morning coffee.
Performance at a glance
Eight opto-isolated inputs
Eight SPDT, 1A relays
Logic functions via microprocessor and
Front-panel input and relay status LED indicators
Expandable to 32 inputs × 32 outputs
Plug-in euroblock screw terminals
The SRC-8 III is a new version of the original SRC-8, which had similar functions. The III version features front-panel indicators for the closures being sent and received. There are also LEDs to show data traffic in each direction. Both of these tools are critical during set-up and troubleshooting. The unit can be mounted in the Broadcast Tools RA-1 shelf and is sized so that three will fit in a standard 1RU space. It's also useful for wall or desktop mounting.
Opto and relay wiring is easy using the Euroblock terminals. These are the plug-in type terminals that allow the screw-down connections to remain in place if the unit needs to be removed for service. The RS-232 connection is via the DB9 connector. There's a jumper setting for the pin-out so there's no need to make a special cable to connect it or a null modem to connect them back-to-back. The RS-422 is connected on Euro screw terminals just like the optos and relays. Although the device typically comes configured for 38.4kb/s speed, there are jumpers that offer lower speeds of 2400, 4800 and 9600. Other speeds are available by special order. The unit operates on 9Vac through the ubiquitous wall-wart but this power arrangement allows a small device footprint and a UL listing. There is an available USB interface for PCs without a standard serial port.
Put into use
My earliest application of the device was to get a next event command from a remote studio to an automation system and to feed an on-air light back to the studio. This was easy to manage but during setup I noticed that the user manual (available online) had the complete ASCII and binary command reference. After a quick test using hyperterminal, I discovered how easily it could be controlled. I also discovered how the device could be used to log events as well. One of my collegues, Ron Stephan, jotted down a quick application that we used with the device to log closure events and relay signals as they passed through network systems. Using the SRC-8 and an available PC we tracked GPI events as they were received, retransmitted and confirmed. Those results were saved in a text file that was correlated with the program schedule to help isolate an intermittent failure. This became an invaluable tool for tracking intermittent problems throughout complex systems.
My first purchase was for two units. Within weeks I started ordering more as applications presented themselves for remote control, monitoring and control extension. Every time I purchased one as a spare, I found that it was needed for an application. I think I ordered the spare unit at least four times within a few months. Once you start using this valuable tool, you'll find even more ways to use it — not just for extending closures, but for simple direct PC control. It's a powerful tool to integrate the increasingly complex and automated operation of radio stations.
Thomas is president of Thomas Media Systems, Bloomfield Township, NJ.
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