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Making a serial cable for a Telaire CO2 sensor

If you have the version of sensor without a display, you need a serial cable to change settings like the CO2 setpoint and log the CO2 level.

The Telaire 800x series CO2 sensors are popular for growers because they let a person make their own InfraRed CO2 controller very cheaply. They are easy to use because they have an internal relay that can directly control a CO2 dosing solenoid valve.

The Telaire 800x sensors come in versions with and without a display. The 8001 has no display and is cheaper and more common (about US$50 on ebay in USA). The versions with display are at least twice the price and don’t come up very often.

This is an 8001:


Unfortunately without the display none of the following is made available to you :
• Display of CO2 level in PPM
• Change the CO2 setpoint, which by default is 1000ppm
• Turn off ABC logic

However, if you have a PC with a serial port, you use a special interface cable to completely reconfigure the sensor using Telaire’s ‘UIP’ software.

The serial cable from the PC plugs into the Telaire sensor at the bottom using RJ45 connector, as used on Ethernet cables.


Making the cable

A serial cable from Telaire will cost you US$50, but you can make your own if you know how to use a soldering iron.

what you will need:

  • Soldering iron and solder
  • Wire cutters
  • Ethernet ‘CAT5’ patch lead (has RJ45 plugs on each end), at least 1m long, wouldn’t try to make it longer than 20m
  • A FEMALE, ‘DB9’ connector that can have wires soldered on to it

All these parts are available from an electronics store like

This is the front and back view of the required DB9 connector, so you know what to buy:


You can see the pin numbers are marked on the front and back.

Step 1
Cut one end off the patch lead

Step 2
Hold the Telaire so that the buttons are facing upwards and the RJ45 socket is facing towards you. Look into the RJ45 socket and you can see 8 contacts, counting from the left, let’s call them pins 1, 2, 3..8 (See photo above)

Step 3
Plug the other end of the patch lead that still has a connector into the Telaire sensor

Step 4
Using the photo, write down which wire colours in the patch cable connector mate with pins 1, 2 and 3 on the Telaire. This is hard to do because you have to look closely inside the plug.

If you can’t see the wires at all, it may help to know what colours are in an Ethernet cable (not in any order):
• Orange
• White with orange stripe
• Green
• White with green stripe
• Blue
• White with blue stripe
• Brown
• White with brown stripe

In my case, pin 1 went to orange/white, pin 2 went to orange and pin 3 went to green/white.

Step 5
At the other end of the RJ45 cable (where you cut off the connector), strip off about 25mm of the outer insulation.

Step 6
Separate the wire colours that correspond to pins 1, 2 and 3, leave these but cut the other wires short.

Step 7
Solder pin 3 of the RJ45 to pin 5 of the DB9 connector.

Step 8
Solder pin 2 of the RJ45 to pin 2 of the DB9 connector.

Step 9
Solder pin 1 of the RJ45 to pin 3 of the DB9 connector.

In my case:

Now you have a serial interface cable.

The UIP software is hard to find on Telaire’s website but you be able to find it on the net somewhere. It looks like this:


As you can see there are a lot of settings you can change, but what you really want is for the ABC logic to be off and set the relay set point to 1500 PPM.

The software is self explanatory. Make sure you have the right serial port, if it doesn’t work check your wiring. Change settings as required then press Update.

by enn
editor: Pure

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