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The WinThermO Monitor Sensor Units are based on the high quality, accurate and sensitive Dallas DS1621 temperature sensing ICs. Two different circuits are given here - in both the sensor chip communicates with the WinThermO Monitor application through the PC's serial (RS232) port. However, in Design 1 power for the sensor chip is obtained from the PC's serial port itself, but in Design 2 it is obtained from the PC's USB port. These Sensor Units are simple to construct (suitable for those with even basic electronics assembly experience), simple to operate ('plug n play' with the feature-packed WinThermO Monitor application) and very cheap (around $20 to make for Design 1, and somewhat less for Design 2). The results however are every bit as good as temperature monitoring hardware/software combos costing hundreds - and you don't have to look far to find those (here's one: TempElert. Asking price $129 for the cheapest serial port sensor unit and $99 for the application!) |
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Sensor Design 1 |
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| All parts should be readily available from
any electronics components store, except perhaps the LM2936Z-5 Voltage
Regulator, which can be obtained from Futurlec,
and the DS1621 sensor chip, which can be obtained from Farnell.
The component count is small enough for everything to fit onto a piece of
stripboard (also known as 'veroboard' - which has conducting strips of
copper on one side), inside the DB9 casing itself, giving you a
self-contained WinThermO Air Sensor 'dongle'. If you'd like the sensor chip
to be on a lead so that it can be placed on/attached to objects to monitor
their surface temperature, you can use up to 1.5m of 4-strand ribbon cable
between the board in the DB9 casing, and the sensor chip in it's own little
housing.
To make a Fluid Sensor for monitoring non-corrosive fluids up to around 90°C, you need to mount the chip in a fluid-proof housing. Note: Before you solder everything up, you may wish to initially simply breadboard the circuit (which only takes a few minutes to do), plug it into the PC and launch WinThermO Monitor, as a 'proof of concept', and to familiarize yourself with everything the application can do. As an alternative to sourcing the parts yourself and constructing on stripboard, you can obtain a complete kit from Erlich Industrial Development. It'll cost more than doing it yourself, but this way you get everything you need (including a pre-etched and labeled PCB) from the one source. You can even order just the PCB, and pre-wired sensor chips on leads are also available. |
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Sensor Design 2 |
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| This design dispenses with the Voltage Regulator componentry of Design 1, resulting in the dual benefits of fewer components, and providing you an alternative if you have trouble obtaining the LM2936Z5. The only 'downside' with this is that you're tying up another PC port (since the regulated 5V is drawn from the USB port), and you need to be sure that you have connected the +5V and Gnd pins of the USB Plug to the sensor circuit the right way round, otherwise the PC may be damaged. Please refer to the Plug Pin-Wire Color table below. Place C1 as close to the DS1621 sensor chip as possible. | |||||||||||||||||||||
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Constructing A Fluid Probe |
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| If you want to be able to monitor the temperature of fluids, the sensor chip needs to be in fluid-proof encasing before you dunk it. This section shows one way to do this. The trick is to use a potting compound, which is usually polyurethane or silicone-based, and provided as a resin and hardener. | |||||||||||||||||||||
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