| iButton Temperature Datalogger | |
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| What is an iButton?
It's a small monitoring devices, about the size of a coin and resembling a fat button battery. Originally designed for monitoring the temperature of perishable or delicate goods in transit. Perhaps you need to move a container of frozen fish from one end of the country to the other and you need to be sure that the shipment wasn't allowed to thaw. Pack an iButton or two with the fish and have the recipient read the buttons to check the thermal history of the shipment. |
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| Why use them for monitoring growing temperatures?
If you only get to see the data after the event, then it's probably too late for your plants?
True. But they do provide a cheap and easy method for recording historic temperatures and planning heating/cooling setups. You will need another system that somehow alerts you to unwanted temperature changes (eg a small weather monitoring system) or you need to consider a more sophisticated iButton setup where the buttons communicate continuously with a datalogging PC. |
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| How do they work?
The buttons are programmed from a PC and set to record a temperature every 1 to 255 minutes. A total of 2,048 readings may be taken before the device either stops recording or starts overwriting the existing data. Taking a reading a minute the iButton will record for about 1.4 days, at a reading every 4.25 hours the device will record for almost a year. The inbuilt battery should last for about ten years or 1 million readings which ever comes first. |
iButton, holder and PC interface hardware. |
| Where can I buy them?
You can buy iButtons and the necessary PC interface from Maxim or Tech Supplies. The iButton Datalogger Starter Kit from Tech Supplies is a good starting point as it gives you everything you need to get going (1x iButton, 1x Plastic holder, 1x serial interface and connector and 1x CDROM with Windows software and user manual). You will need to provide a PC running Windows 95/98/ME/NT/2000/XP, a CDROM drive and a spare serial port. |
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| What else?
The Hygrochron temperature/humidity logger iButton - search the Maxim site for "DS1923". Look here also for other types of iButton. |
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