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I have a sensor (HC2A-S3A), which provides analog and digital output signals. The digital interface is UART (19200 baud, protocol RoASCII). Can I use a USB to Serial TTL Converter (chipset: FTDI FT232RL) to connect the sensor to a computer?

My idea would be (but I don't know much about electronics) to connect V+ to VCC, GND, RXD, and TXD, respectively. Also, I guess RTS and CTS on the converter side have to be short-circuited. Would this work?

Sensor USB Converter
Sensor pinout USB converter pinout
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  • \$\begingroup\$ Have you checked the instruction manual and datasheets? \$\endgroup\$
    – liaifat85
    Commented Apr 28 at 17:15

3 Answers 3

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Should be fine. However, noting that while the sensor datasheet says it operates at 3.3 to 5 V, there is also a note saying "calibrated @ 3.3 V". You might consider using one of the 3.3 V variants of the USB-to-serial converter for best results.

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  • \$\begingroup\$ Thanks! I did not mention that I use a cable with a built-in voltage regulator and tinned ends (type E2-05XX-ACT), which requires 5 to 24 VDC supply voltage, so I guess the adapter I linked should be fine. Many Thanks! \$\endgroup\$
    – Pontis
    Commented Apr 28 at 14:23
  • \$\begingroup\$ @Pontis Wrong assumption and thus wrong adapter for your regulated voltage. \$\endgroup\$
    – Justme
    Commented Apr 28 at 14:50
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Also, I guess RTS and CTS on the converter side have to be short-circuited.

RTS and CTS are hardware handshake signals itended to support flow control. Communication software such as PuTTY normally allows configuration of which flow control option is used. E.g. Selecting the serial flow control scheme in the PuTTY documentation contains:

The ‘Flow control’ box allows you to choose what type of flow control checking is used on the serial line. The settings are:

  • ‘None’: no flow control is done. Data may be lost if either side attempts to send faster than the serial line permits.
  • ‘XON/XOFF’: flow control is done by sending XON and XOFF characters within the data stream.
  • ‘RTS/CTS’: flow control is done using the RTS and CTS wires on the serial line.
  • ‘DSR/DTR’: flow control is done using the DSR and DTR wires on the serial line.

The HygroClip2 ADVANCED Humidity Temperature Probes manual says the following in the UART interface description:

Flow Control : none

Therefore, providing what ever software is run on the computer for communication allows the flow control to be set to "None" there should be no need to short-circuit RTS and CTS on the converter side.

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  • \$\begingroup\$ Thanks for all the details! Silly question: how do I correctly "deactivate" the pins of a cable with tinned ends, which I'm no longer using (apart from using a splicing connector)? \$\endgroup\$
    – Pontis
    Commented Apr 28 at 14:30
  • \$\begingroup\$ @Pontis Perhaps use some heatshrink or wrap with electrical (insulating) tape. \$\endgroup\$
    – Chester Gillon
    Commented Apr 28 at 14:47
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You said you are using an adapter cable with built-in regulation to 3.3V supply for the sensor.

Therefore the sensor communicates with 3.3V voltage on TX/RX pins, and you need an USB serial adapter with matching 3.3V TX/RX voltage, as using 5V may damage your sensor.

If you can find an adapter which outputs 5V USB supply but uses 3.3V for TX/RX logic voltage, it would be a standalone solution.

You don't generally need the RTS/CTS pins of the USB adapter so they can be cut off, but it depends on which program you intend to use and how it wants to use the RTS/CTS pins and if it requires them to be connected in some way.

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  • \$\begingroup\$ Many thanks! That's tricky: Delock states nothing about supply for its 3.3 V converter, however the vendor Reichelt specifies 5V for VCC and 3.3 V for LVTTL. I guess I have to buy and measure ... \$\endgroup\$
    – Pontis
    Commented Apr 28 at 15:19
  • \$\begingroup\$ @Pontis The Delock unit seems to be just a cable made by FTDI. You will get better data sheets from FTDI, the Delock data sheets seem useless. \$\endgroup\$
    – Justme
    Commented Apr 28 at 15:29
  • \$\begingroup\$ Delock indicates the same FTDI chipset (FT232RL) for both of its converter versions (5V and 3.3V), and the chipset supports all kinds of voltage. For the cable from FTDI itself TTL-232R-3V3-WE its clearly stated, but its hard to find a vendor which ships in reasonable time ... \$\endgroup\$
    – Pontis
    Commented Apr 28 at 15:47
  • \$\begingroup\$ @Pontis A lot of brands sell FTDI manufactured cables. Look at FTDI data sheets and buy the cable from any vendor that matches the FTDI part number. \$\endgroup\$
    – Justme
    Commented Apr 28 at 17:05

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