Auxiliary and Analog Interfaces
RTC Coin Cell Interface
Overview
The RTC Coin Cell Interface provides coin-cell backup power to the OEM modem's real-time clock, allowing calendar time to be retained across main-battery power cycles.
Electrical Connections
All signal directions are relative to the OEM modem. Refer to the digital board connector locations figure for the connector's physical location.
| Pin Number | I/O | Pin Name | Notes |
|---|---|---|---|
1 | P | RTC_VBAT | RTC battery backup voltage supply, 1.0–5.0 V, nominal 3.0 V |
2 | P | GND | Board ground |
Hardware Components
The RTC Coin Cell Interface uses a Molex PicoBlade connector, P/N 0510210200, or equivalent. The recommended contacts are Molex P/N 0500798000, suitable for 26–28 AWG wire.
| Part Number | Manufacturer | Description |
|---|---|---|
0510210200 | Molex | PicoBlade 2-position connector receptacle, 1.25 mm pitch |
0500798000 | Molex | PicoBlade 26–28 AWG sockets |
2002181900 | Molex | PicoBlade hand crimp tool |
2149202211 | Molex | Pre-crimped PicoBlade lead, 75 mm length |
CODEC Input/Output Interface
Overview
The two CODEC Input/Output Interface connectors provide up to four analog inputs and four analog outputs in addition to the standard acoustic transducer interface.
Electrical Connections
All signal directions are relative to the OEM modem. Refer to the digital board connector locations figure for the connectors' physical locations.
Each headphone line output is single-ended and AC-coupled through a 47 µF capacitor. The resulting high-pass cutoff is f3dB,HPF = 1 / (2π × 47 µF × RLOAD). Full-scale output voltage is 0.5 V RMS.
By default, CODEC inputs are single-ended: only CODECn_LIN1 and CODECn_RIN1 are used, while CODECn_LIN2 and CODECn_RIN2 are unused. Full-scale input voltage is 0.5 V RMS. Each input is AC-coupled through a 0.1 µF capacitor; depending on the software-selected CODEC input impedance, the high-pass cutoff can be 159.2 Hz, 79.6 Hz, or 39.8 Hz.
For the differential-input option, which increases full-scale input voltage to 1 V RMS, contact info@popotomodem.com. The maximum CODEC input and output sample rate is 192 ksps, supporting frequencies up to 96 kHz.
| Pin Number | I/O | Pin Name | Notes |
|---|---|---|---|
1 | P | VSYS_5V | +5 V out when unit is powered up |
2 | O | CODECx_HPL | Headphone line output, left channel |
3 | O | CODECx_HPR | Headphone line output, right channel |
4 | I | CODECx_RIN2 | Analog line input 2, right channel |
5 | I | CODECx_LIN2 | Analog line input 2, left channel |
6 | I | CODECx_RIN1 | Analog line input 1, right channel |
7 | I | CODECx_LIN1 | Analog line input 1, left channel |
8 | P | GND | Board ground |
Hardware Components
Each CODEC Input/Output Interface uses a Molex PicoBlade connector, P/N 0510210800, or equivalent. The recommended contacts are Molex P/N 0500798000, suitable for 26–28 AWG wire.
| Part Number | Manufacturer | Description |
|---|---|---|
0510210800 | Molex | PicoBlade 8-position connector receptacle, 1.25 mm pitch |
0500798000 | Molex | PicoBlade 26–28 AWG sockets |
2002181900 | Molex | PicoBlade hand crimp tool |
2149202211 | Molex | Pre-crimped PicoBlade lead, 75 mm length |
Mating Cable Notes
Attach or detach the interface only while power is disconnected from the OEM modem to avoid electrical damage.
Analog Line Input Interface
Overview
The Analog Line Input Interface accepts an analog signal into the receiver pathway. The transducer receiver is normally digitized at separate 43 dB and 12 dB gains; using analog line input disconnects the transducer from the 12 dB pathway.
Move the Analog Input Selection Jumper from pins 1/2 to pins 2/3 before using this interface.
Electrical Connections
The interface is single-ended and AC-coupled through a 10 µF capacitor with a 10 kΩ input resistor, producing a 1.59 Hz high-pass cutoff and approximately 10 kΩ pass-band input impedance. Gain is −1 V/V with an intentional 123 kHz low-pass roll-off. The full-scale ADC input is 5.32 V peak-to-peak.
Refer to the analog board connector locations figure for the connector's physical location.
| Pin Number | I/O | Pin Name | Notes |
|---|---|---|---|
1, SMA center | I | LINE_IN | Analog line input |
2–5, SMA shell | P | GND | Board ground |
Hardware Components
The Analog Line Input Interface accepts any standard SMA cable. One example is TE Connectivity P/N CSE-SGAM-305-SGAM.
Analog Line Output Interface
Overview
The Analog Line Output Interface provides an analog signal from the transmitter pathway.
Electrical Connections
The transmitter pathway contains a two-channel stereo DAC. The left channel drives the Transducer Interface and the right channel drives the Analog Line Output Interface. The line output is single-ended and DC-coupled, with a minimum supported load of 32 Ω and a full-scale output of 1.58 V RMS.
Refer to the analog board connector locations figure for the connector's physical location.
| Pin Number | I/O | Pin Name | Notes |
|---|---|---|---|
1, SMA center | O | LINE_OUT | Analog line output |
2–5, SMA shell | P | GND | Board ground |
Hardware Components
The Analog Line Output Interface accepts any standard SMA cable. One example is TE Connectivity P/N CSE-SGAM-305-SGAM.