Brigadoon - An Occasional Corner on the Internet
Construct Ground Temperature Array
Designed by Mark Little
Now that the sensors have been built and calibrated, it is time to to put things together into the array module that will be put into the ground. The first decision is how to bring the cable into the pipe through the end cap. Ideally, a socket should be mounted in the end cap. This allows the array to be installed without the cable getting in the way and it is easier to replace the cable if it gets damaged later.
However, in some cass, this is not practical, so an alternative is to use a waterproof gland to allow the cable to directly enter the pipe holding the sensors with perhaps a waterproof connector a short way along the cable exiting the pipe. For Australian constructors, waterproof glands can be obtained from many suppliers, such as Jaycar Electronics where the electronic components can be obtained, although this example will use an 8-pin mini-DIN plug and socket.
The 8-pin mini-DIN plug and socket are being used because I was able to obtain them very cheaply. They suffer from two disadvantages: (1) They are not weatherproof and they will need to be weatherproofed after installation and testing; (2) The socket is designed to be soldered into a Printed Circuit Board (PCB) to hold it in place. Since this connector is going to be mounted in the end cap of the pipe holding the temperature sensors, a fixing method will need to be developed.
Pin Wire Colour (nominal) Length Function
1 Yellow 20cm 10cm Temperature (analogue signal 10mV/°K)
2 Green 30cm 20cm Temperature (analogue signal 10mV/°K)
3 Black 70cm Power and Signal Earth Connection.
4     Not Connected
5 Red 70cm +5V Power Rail
6 White 60cm 50cm Temperature (analogue signal 10mV/°K)
7     Not Connected
8     Not Connected
Take the end cap and mark the center of the cap and drill a hole just smaller that the diameter of the DIN socket. Adjust the size of the hole so that the connector can be firmly pressed into the cap (but don't do it yet!).
Solder wires to the socket pins according to the wiring list below, if you are using individual wires. As an alternative, if you have multi-wire ribbon cable available, you can use a length of ribbon cable trimmed to five (5) wires instead. Whatever cable you use, make sure that there is enough clearance for the wires and the temperature sensor to slide through the tube.