ASR-1 Hardware Integration

In addition to reading the sections below, be sure to refer to the ASR-1 Data Sheet.

ASR-1 Layout Checklist

1. Bypass capacitor placement
  a. Place the bypass caps near to the VCC pin (pin 6) on the same layer as ASR-1, with the lowest value cap closest to the pin.
2. Ground pour
  a. Pour ground under the whole part and tie into ground pins:

Ground

3. RF Layout
  a. RF trace should be routed as 50ohm .
  b. If using more than 2 layers board stackup, it is a good idea to open ground under the RF line to increase the RF trace width and reduce its insertion loss.
  c. Antenna should be routed to the RF trace as 50ohm as well.
  d. Antenna return loss should be equal or better than -10dB.

ASR-1 Schematic Checklist

Link to PDF of checklist.

1. Mode
  a. Is your device in standalone or companion mode? If it is in companion mode, skip to Interface
2. GPIOs
  a. Are the devices connected to your GPIOs compatible with VCC_SIP?
  b. Are the signals open-drain, or do they need pull-resistors?
  i. If so, they can be configured using the Afero Profile Editor to support this.
3. A/D converters and/or comparators
  a. Do you want to reference to VCC_SIP?
 

i. If not, you need to connect a voltage reference to AREF (pin 5)

4. Interface
  a. SPI
  i. SPI is connected with the host micro as a slave device.
  1) SPI_SCLK is driven by the host micro
  2) SPI_CS is driven by the host micro
  3) SPI_MOSI is driven by the host micro
  4) SPI_MISO is driven by ASR-1
  b. UART
  i. UART is connected to the host as a two-wire interface.
  1) UART_HOST_RX is driven by the host micro
  2) UART_HOST_TX is driven by ASR-1
  c. Control (RESET_B and HOST_INT_B)
  i. RESET_B is driven by the host micro.
  ii. HOST_INT_B is driven by ASR-1.
  iii. It is possible to configure these lines as open-drain to share them with other peripherals. In that configuration, they need pull-up resistors (10K is fine).
  d. Is host VCC higher than 3.6V? If not, move on to power supplies.
  e. If your host VCC is higher than 3.6V, you need to add level-shifters.
    i. Add push-pull level-shifters on serial lines. Feel free to use bidirectional level-shifters, or standard single-directional level-shifters.
  ii. Add open-drain level shifters on RESET_B and HOST_INT_B if you are using them in that mode.
5. Power Supplies
  a. Level
  i. VCC_SIP must be between 2.1-3.6V. That is the operating range for ASR-1.
b. Decoupling
  i. There must be a 22uF bulk cap on VCC_SIP.
  ii. There should be a 6.8pF decoupling cap on VCC_SIP.
6. RF
  a. RF trace should be controlled 50ohm impedance.
  b. Plan for a Pi matching network placeholder by having shunt (DNI), Series 0ohm, shunt (DNI) for possible antenna matching (see picture below).
  c. If RF connector is used, add a placeholder for ESD diode in case it was needed (shunt DNI pad).

Pi Network

Pi Network

7. Manufacturing
  a. In order to program your profile into your device, you must pin out the following pins to test points:
  i. Pin 12 (RES1)
  ii. Pin 13 (RES2). You must be able to short pins 12 and 13 to program a profile to ASR-1.
  iii. Pin 14 (DBGUARTRX). This is should be tied to the TX line of your programming fixture.
  iv. Pin 15 (DBGUARTTX). This should be tied to the RX line of your programming fixture.

ASR-1 Layout Guidelines

RF Design Guidelines

  • The RF TRX pad is a 50ohm controlled impedance. The module is internally matched to provide a 50ohm output impedance. Furthermore, the module is matched to provide a good robustness against load condition. Since each design can have some impedance impairments (PCB material, RF lines impedance mismatch, PCB PADs, etc.), it is recommended to have a Pi matching network placeholder between the RF output and the antenna. the placeholder matching network can be used to match the module output to the antenna if needed.
  • The RF trace between the module and the antenna should be impedance controlled to a 50ohm. tradeoffs between μstrip line and striplines should be considered. μstrip line provide the best power handling and least insertion loss, while stripline structure will provide the best isolation and protection to the RF line. depending on the PCB layout customer can choose between μstrip line or stripline structure. if μstrip line structure is chosen, try to have ground planes with ground VIAs on both sides of the line on the layer that hosts the RF line.
  • The module RF pad is designed to be between 2 ground pads to give the best isolation between the RF and the digital/power pads.
  • Avoid 90° corners while routing the RF line, instead use arcing and 45° turns to avoid RF reflections and impedance impairments.
  • Place 6.8pF caps at the DC lines of the module to decouple any unwanted 2.4Ghz frequency components.

Antenna Design Guidelines

  • The Afero team can assist the customer with the antenna design if needed, Afero team can offer various PCB antenna designs to reduce cost, or external antenna designs if PCB antenna was not feasible.
  • Antenna impedance should be as close as possible to 50ohm and have a return loss of -10dB or better
  • The higher the antenna efficiency the better range should be expected and more battery life can be optimized by reducing the Tx power while meeting the range requirements. Afero recommends a target of 50% or better efficiency.
  • If long RF trace is needed between the module and the antenna, place a Pi network placeholder at the module and at the antenna during the first build. Once boards are available and matching is done customer can remove the unwanted matching components to reduce BOM cost.

ASR-1 Manufacturing Guide

  1. Request a signed profile from Afero.
  2. Boot the device and retrieve the following from debug output via serial port (38.4Kbps, 8N1):
    1. 6-byte or 12-byte Association ID
    2. 8-byte Device ID
    3. 1-byte Company Code
  3. Store the Association ID and Device ID in a file to send to Afero for device activation.
  4. Put ASR-1 into profile injection mode by tying pins 12 and 13 of ASR-1 together (RES1 and RES2).
  5. Send device profile binary to device via UART.
    1. Connect to USB serial port running with comm port parameters (38.4Kbps, 8N1, No Flow Control).
    2. Send signed profile.
    3. Program will output OK if success, or NG (Not Good) if failure.
  6. Use the 6-byte or 12-byte Association ID to create a QR code. For more details, read Generating QR Codes.
  7. Once the profile has been programmed, ASR-1 will begin broadcasting BTLE advertising packets at whatever interval has been set in the profile. The customer can measure the RSSI of the advertising packets (vs. a golden unit) to determine if the RF chain has been assembled correctly.

Generating QR Codes for Afero Products

Refer to Generating QR Codes for details.