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Photo A hookup he CES 51GSA-II is an automatic microprocessor-controlled telephone interconnect (autopatch) that provides telephone access to mobile and portable radios operating in simplex, half-duplex, and full-duplex modes (see sidebar for explanations of these modes). But it's more than an autopatch. With built-in 10 capability, ii can operate as a repealer controller, and has provisions for limited remote control of external devices as well.

Out Of The Box

The first thing I learned about the Smartpatch M was that you have to be careful not to drop it when you open the shipping box, or you couid be limping around for a while. It's enclosed in an expensive looking 16 gauge steel cabinet ihai weighs almost four pounds!

Also packed with the interconnect, I found a DTMF [Touchtone) encoder for programming the unit, ihree cables, and a 27-page manual marked "Preliminary"1 that had a picture of an earlier version paten on the front cover

After unpacking, I immediately grabbed a screwdriver and took the cover off the patch You need to do this to make the connections since there are no rear panel connectors. You have to run the connecting cables through a cutout in the rear panel to a screw terminal block inside the unit inside is a well laid oui double-sided circuit board ^ith a lot of trimmer potentiometers and jumpers. More about those later There was no silk screen on the board, but various components were identified by lettering etched in the copper itself \ found it interesting that none ot the lOs were labeled, fUlP U2, etc.) The manual, however, has a parts layout diagram that serves this purpose.

I always like to look at the bottom of boards

. View of the Smartpatch tt with enclosed DTMF encoder and cables.

Photo B. Inside view of Smartpatch li for "OPS" components and jumpers These usually are extra parts added to correct problems found after the PC board has been made There was one jumper and seven components on the bottom of this board.

The front panel of the interconnect sports four indicator LEDs—power noise, pit, and connect—and two push button switches, power and connect The program jack in the center of the front panel accepts a DTMF

programming pad connection. See Photo A,

The Circuit

The brain of the CES 51 OSA-ll is a MOSTEK 38P70 microprocessor. This is a piggyback type of micro in which the program ROM plugs directly onto the top of the microprocessor itself. It's an expensive way to go. This minimizes board space and complexity, however, and eliminates several memory interface components. Also, it makes it easy to upgrade software later, A watchdog timer automatically resets the processor should some type of glitch send the processor wandering off into never-never land. There is also a Power-On Reset (PQR) circuit to get the micro started properly when power is applied.

Customer programmed parameters are stored in an 8 pin, XICOR 2404-type 512 byte EEPROM This EEPROM can hold data even with power removedf and can be easily erased and reprogrammed electrically w ihout using ultraviolet erasers and expensive EEPROM programmers.

The Smartpatch II uses the powerful CMOS chip, the MITEL MTB880 DTMF transceiver for decoding and generaiing touchtones (DTMF). It has an onboard call progress tone fitter which delects various phone line signals, such as diat tone, busy signals, etc. It also has a microprocessor bus interface. Quite impressive for a 20 pin chip! The 510SA-It uses all of these features.

The phone line interface consists of a hybrid transformer coupler circuit for full duplex operation The traditional holding coil is replaced by a three-transistor current sink circuit. Optically isolated ring detection and "off hook" detection circuits are included Diode bridges eliminate polarity sensitivity when connecting continued on p 35

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