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gps.md

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GPS receivers

With a PC, it's generally more convenient to use GPS receiver that has its own case, rather than one that is designed to be put inside a case with a computer. This allows you to see the blinking PPS LED.

My top recommendation is the BG7TBL TS-1: this provides a high-quality timing receiver, in a separate case, at an inexpensive price.

BG7TBL TS-1

This became available in 2023. Internally, it uses the u-blox LEA-M8T module. This is a single band module.

It provides a PPS signal on an SMA connector at 3.3V (as required by the i210/i225).

I got mine on AliExpress for $77. It's also available on eBay.

The power connector is standard 5.5x2.1mm DC barrel connnector, which accepts 5V-12V and requires only 0.3A, so can easily be powered via a dumb USB to DC 5V cable. However, the board doesn't have a battery, so powering it from the PC over USB means that a PC power cycle requires a cold start of the GPS.

It provides RS232 DB9 female connection to the UART port on the LEA-M8T. It can be connected to a PC that does not have a serial port by using an USB 2.0 to RS232 DB9 male converter cable.

Many GPS receivers being sold from China are fakes. But I am confident the one I got is not. The idea behind this product is to repurpose timing modules originally manufactured for Huawei cellular base stations. These timing modules are available on eBay for about $50 or less, but they require some hard-to-find parts to wire up properly.

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ArduSimple simpleRTK2B M.2 ZED-F9P

The simpleRTK2B M.2 fits into a M.2 E-key slot, which is the kind of slot PCs have for Wifi cards.

The module is a u-blox ZED-F9P. It's designed for precise positioning (RTK), but it also supports time mode. This is a dual band (L1/L2) module. It's a step up in both price and performance from the LEA-M8T used in the TS-1.

The USB port on the ZED-F9P will be exposed as a USB device in Linux, typically /dev/ttyACM0.

If you are using the ZED-F9P purely for timing purposes, you might want to downgrade to firmware HPG 1.12, since that version is the last version that provides the quantization error in UBX-TIM-TP messages (at least versions 1.13 and 1.32 don't provide this).

Note that this needs a dual band antenna for best performance.

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ZED-F9T USB Dongle

The GNSS OEM Store (in Latvia) sell a USB dongle with a ZED-F9T inside. It has two SMA connectors: one for the antenna and one for PPS output. The case is semi-transparent and has a PPS LED. There are two versions: one is L1-L2 dual band, and the other is L1-L5 dual band.

It's quite bulky and is likely to block adjacent USB ports. I recommend using it with a short USB A 2.0 male to female extension cable.

This option is very convenient and the ZED-F9T is the best available timing GPS receiver (as of 2023), so it's a good option, but it is expensive (€220).

In this photo, the lower SMA connector is for the antenna.

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In-case module with USB-to-TTL converter

This is the cheapest option. It combines

  • a GPS module, with the following properties
    • very cheap
    • very small
    • not a fake
    • no case
    • TTL-level pins
    • 0.1" (2.54mm) pins compatible with Dupont connectors
    • PPS pin
    • SMA female antenna connector
    • default speed of 9600 baud (ts2phc in LinuxPTP 3.x only supports 9600 baud)
  • a USB to TTL converter

Suitable boards are available very cheaply, so this is the cheapest option.

These need to be wired up as follows:

Color GPS pin USB to TTL pin i210 pin
black GND GND -
red VCC VCC -
green TXD RXD -
white RXD TXD -
yellow PPS - SDP0
grey - GND GND

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In the photo, I'm using

Note that two GND connections are needed to the USB-to-TTL converter, and the Waveshare converter has two GND pins, which makes it the convenient choice here.

The Waveshare converter comes with a cable with Dupont connectors, but it is likely to be too short. I'm using some separate Dupont female-female jumpers to wire things up.

This shows the rear when it's fully assembled. The GPS antenna is attached directly to the SMA connector on the module. I've used a M3 female magnetic screw to attach the module to the backplate. This setup is rather vulnerable to the antenna cable being yanked: I recommend clamping the antenna cable to the table.

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