URIx USB Radio Interface 9095 Features  Easy radio connections  High quality audio  CM119 audio controller  Low cost  PTT, COR, CTCSS  7 GPIO  +6dB gain op-amp  Full RF filtering Description URI allows a standard land or mobile FM radio to be connected to a host computer via USB interface. Potential radios include amateur, business, public service/safety, GMRS, citizens band, and many others. The host computer requires appropriate software to drive the device such as app_rpt with chan_usbradio. These applications currently run under Asterisk/Linux. URI may be used for remote radio control or can link two or more radios in repeater mode. Audio can be passed through VOIP/Ethernet. Many radios provide an interface connector for external access. These signals can be easily connected to the URI’s standard DB-25 connector. The URI contains the C-Media CM119A, a high-quality full-duplex USB audio controller. One channel of receive audio is provided along with two channels of transmit audio. Radios that have separate voice and CTCSS signals are supported. Optionally, the second audio channel may be used as a line monitor. URI has dedicated input pins for CTCSS and COR, and an output pin for PTT. There are also 7 general purpose I/O pins that may be controlled by software. Each audio output channel is fed through a 3- pole low-pass filter with a 4KHz cutoff frequency. The filter outputs are AC coupled through 10µF bi-polar capacitors. This allows low-frequency CTCSS signals to be passed un- attenuated when driving a low impedance device. The filter outputs may be DC coupled if desired by installing internal jumpers. DMK Engineering Inc. 2908 Oregon Ct. H3 Torrance California 90503 Tel: 310.544.1222 Fax: 310.693.0753 info@dmkeng.com www.dmkeng.com Description Continued… If the radio requires high input drive levels, an on-board 6dB gain amplifier is provided. An external 12 volt DC power source is needed to power this amplifier, if needed. If this gain is not needed, no external power is required. If desired, a 1K-bit 93C46 serial EEPROM may be used to store radio-specific configuration data. Internally, the URI circuit board provides space for a surface-mount version of this part, but this is normally not installed. Instead, the EEPROM interface signals are brought out to the DB-25 connector in such a manner that a DIP part may easily be soldered directly to the pins. This way if the URI device is changed, the stored configuration data will remain with the cable attached to the radio. Table 1. Connector Pin Assignments Pin No. Name Description 1 PTT Push to talk, open collector output to radio transmitter, maximum off state voltage 45V, maximum on state current 0.75 amps 2 GPIO1 General purpose input or output (note 1) 3 GPIO2 General purpose input or output (note 1) 4 GPIO4 General purpose input or output (note 1) 5 GPIO5 General purpose input or output (note 1) 6 GPIO6 General purpose input or output (note 1) 7 CTCSS_DET Input, diode isolated, continuous tone-coded squelch system detect (note 2) 8 COR_DET Input, diode isolated, receive (carrier operated relay) detect (note 2) 9 MIC_IN Direct low-level audio input to CM119, must be AC coupled (note 3) 10 GPIO7 General purpose input or output (note 1) 11 GPIO8 General purpose input or output (note 1) 12 AOUT AC coupled output from 6dB gain amplifier 13 GND Ground 14 +5V 5 volts DC power output from USB bus 15 EEP_CS EEPROM chip select control 16 EEP_CK EEPROM serial clock 17 EEP_DI EEPROM data input 18 EEP_DO EEPROM data output 19 GND Ground 20 GND Ground 21 MIC_AC Audio input, line level, AC coupled 22 LEFT_OUT AC coupled left audio output, 4KHz bandwidth 23 RIGHT_OUT AC coupled right audio output, 4KHz bandwidth 24 AIN AC coupled input to 6dB gain amplifier 25 AVDD 12 volt DC power input required for 6dB gain amplifier 1 Note 1: Absolute maximum voltage on all GPIO lines is from -0.3 to 5.5V. Maximum current is ±8mA. Note 2: Absolute maximum voltage on CTCSS and COR is -0.3 to 40V. Maximum current is ±4mA. Note 3: Absolute maximum voltage on MIC_IN is from -0.3 to 5.5V. A Note about USB Hubs USB hubs are not recommended. However, if a hub must be used, make sure it is rated at USB 2.0 High Speed. Some hubs are USB 2.0 compliant but are rated only at Full Speed (12Mbps) not High Speed (480Mbps). Do not connect any USB 1.x devices to either the same external hub or to the host computer’s internal root hub. The URI radio interface connector is a standard female 25-pin D-shell. The recommended mating connector is the Amphenol G17S2510110EU or equivalent. This connector is available from both Digi-Key and Mouser Electronics. Application Information Audio I/O. In most applications audio inputs and outputs should be AC coupled. Large value non-polarized capacitors are provided on-board to pass low frequency CTCSS signals. If desired the audio outputs may be DC coupled by installing zero ohm jumpers on the circuit board. Please contact the factory for more information. The MIC_AC input in addition to providing AC coupling also has an 18dB attenuator. This brings line level signals down to the low-level microphone level signals required for the CM119. LEDs. The URI has two LEDs, one on either side of the USB connector. The green LED on the left is on when the URI is powered from the USB bus. When the app_rpt application is running this LED flashes. The red LED is on when the PTT signal is active. 6dB Gain Amplifier. An optional on-board 6dB gain amplifier is provided for radios that need more than the 1.7 volt rms maximum signal available from the standard outputs. To use this amplifier, an external 12 volt power source must be connected to pin 25 and ground to pin 13. The op-amp is the National Semiconductor LMC7101. This amplifier features very low noise and distortion, high speed, rail-to-rail inputs and outputs. Absolute maximum supply voltage on pin 25 is 16 volts. An external jumper should be installed on connector J1 from either pin 22 (left) or pin 23 (right) to the amplifier’s input on pin 24. The boosted audio output is then taken from pin 12. 2 PTT. This open drain output is active low and requires an external pull-up resistor. In the on state it may sink up to 0.75 amps. In the off state the line may be pulled up to a maximum of 45 volts. COR/CTCSS. These two inputs are diode isolated and require an external pull-up resistor. A logic high must be between 3.5 and 40 volts. A logic low must be between -0.3 and +0.3 volts. 3