Sine Systems RFC-1/B - Page 28

Telemetry
U7 is a differential DC amplifier with a gain of 5. The voltage at U7 pin 6 should be five times
the DC voltage between pins 4 and 5 of J3. The A-D converter is contained in U5 which must
be replaced if defective.
Relay Panel Output
U6 is an octal source driver. Pins 1 through 8 are the inputs and pins 18 through 11 are the
outputs. J3 pins 6 through 11 should contain the address of the currently selected channel
in positive logic binary form with pin 11 being the most significant bit. J3 pins 12 and 13
should go high when the appropriate control function is initiated.
Telephone Line Interface:
When the RFC-1 is not in use, both RY1 and RY2 are "off." When the RFC-1 is in use from a
remote telephone, RY1 is "on" and RY2 is "off." When the RFC-1 is in use from the local
telephone, RY1 is "off' and RY2 is "on. ” U1 provides gain and isolation for the audio signals
going to and from the telephone line. OC1 detects ring voltage and hang-up pulses.
Local Telephone
The "Telephone" jack on the front panel of the RFC- 1 is connected to an internally generated
DC source in the "Local Control" mode. This supplies the power to the local telephone and
allows it to generate tones with its keypad. The DC power supplied by the RFC-1 is at a lower
voltage than would normally appear on a standard telephone line. However, with extensive
field use, only one telephone has been found that would not generate tones reliably with the
DC power supplied by the RFC-1. This particular telephone was a low cost telephone
purchased as a discount retailer. Consequently, if the "Local Control" button is pushed and
"OK" is heard on the telephone but the telephone will not generate tones reliably, try a
different telephone. The best type of telephone to use is one that has good sidetone
suppression of the DTMF tones. This eliminates the annoyance hearing loud tones while
calibrating. In the high RF fields near AM transmitters, the simple, "non-electronic"
telephones work the best. In particular, the original "2500" series AT&T telephone is virtually
"bullet proof' when it comes to RF and its sidetone suppression is very good also.
DTMF Decoder
U2 decodes the DTMF signals. Pins 16, 17, 18 and 1 are the "8, 4, 2, 1" weighted binary
outputs corresponding to the detected DTMF signal. Pin 14 goes high when the data is valid.
The binary output number corresponds directly to the entered key numbers except that the
"0" key outputs a "10" output (1010), the "*" key produces an "11" output (1011) and the "#"
key produces a "12" output (1100).
Low Voltage Interrupt
U3 is a low voltage interrupt (LVI) device which resets the microprocessor and prevents it from
operating if the supply voltage drops below about 4.5 volts. Pin 1 should normally be high.
3.01.1
Troubleshooting and Repair
page 7.4