Category: Note to Self

Note to self: HC-05 bluetooth-to-serial modules need a pull-up resistor on the TX pin

I ran into some trouble today getting an HC-05 bluetooth-to-serial module to communicate with my Trimble Resolution T GPS receiver.

The ResT will send some data automatically once per second, but needs to be polled to send other data. Lacking the polling packet, weird things happen.

Some devices have built-in pull-up resistors so the module works fine, but the ResT doesn’t. The HC-05’s TX pin is open-drain, so without a pull-up it does nothing, causing confusion. Putting a >1k pull-up to 3.3v on that pin works wonders.

See https://mcuoneclipse.com/2014/03/30/getting-bluetooth-working-with-jy-mcu-bt_board-v1-06/ for more details.

Note to Self: Raspberry Pi & Motorola Oncore UT+ setup

This is the first of (hopefully) several “notes to self”. They are intended as a record of my various tinkerings and processes that I’ve learned. Although publicly readable, they’re meant as notes to myself in the context of my personal setup and are not really intended as complete “how-to” guides. If you find it useful, awesome! If not, sorry.

The version of NTPd packaged in Raspbian Jessie doesn’t have support for PPS (why?!) or the Motorola Oncore driver enabled. It needs to be recompiled to support those options. The Oncore hardware is quite old, so I understand them not wasting a bit of space by enabling the Oncore driver at compile-time (though really, disk space is cheap and abundant), but no PPS? C’mon.
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