Wireless Serial Data Logger

A machine that reports what it is doing over a serial port is common, and what it reports is usually only seen while somebody is watching a terminal. The moment the session ends the information is gone, and the fault that happened at three in the morning has left no trace of what preceded it. A serial logger exists to keep that record.

What makes this one different from a cable and a terminal program is that the record is stored on a card and reachable over a network at the same time, so it can be watched while it is being made and collected afterwards.

Product overview

The module presents two serial ports to the equipment and records what passes through them to a TF card, with the option of a clock so that entries carry a time from the module itself. It reports onward over Wi-Fi to a user-defined destination, either as UDP datagrams or as MQTT messages, and it can raise its own access point where no network exists.

Two versions differ only in the clock and in the cell that holds it. Both are supplied as bare boards rather than in enclosures.

How the logging works

Data arriving on either serial port is captured by the module and written to the card, with a timestamp added by the host or by the on-board clock depending on the version. Because the card holds the record continuously, a message that fails to reach the network is not a reading that is lost; it is still on the card and can be read later.

The network side is separate from the recording. A small web page served by the module shows the state of the device, and the host application reads the live and historical logs, changes the configuration, and can map the incoming data onto a conventional serial port on the computer so that existing software sees the equipment exactly as if it were cabled directly.

How to select the right logger

Settle three things in order. First, whether the log needs a time of its own: if the equipment runs unattended and the record has to stand by itself, the clock version is the one, and the standard version is adequate where the host is always present. Second, how the data is to leave the site, since that decides whether the module joins an existing network, raises its own access point, or reports to a server over a wide-area link.

Third, how much is expected of the card. The material warns that some cards are not recognised, and it does not state the maximum size accepted or the throughput at the highest baud rate, so a duty that pushes a great deal of data through both ports at speed should be confirmed against the module rather than assumed.

Measurement limitations and selection considerations

The record is only as good as the card in it. The card is the place the log lives, and a card that stops being recognised stops the record without stopping the equipment, which is the failure that is hardest to notice. The material’s own warning about card compatibility is the practical form of that risk.

Two further limits are worth stating plainly. The board is supplied bare, so any environmental protection is a property of the enclosure it is installed in rather than of the product. And the certification identifiers were removed from the material at source while the photograph shows marks on the radio shield; until a conformity statement is supplied, the page claims none, and the discrepancy is recorded rather than resolved by assumption.