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I have an idea for little project where I want to log weight changes (standalone) on a bee hive, preferably low-cost.

Now there's a lot of cheap temperature loggers on the market, for example this one: Temperature Data Logger on ebay.

Is it possible to connect a load cell to this or any other generic temperature logger, provided that I apply the right amplification to get the load cell to work in the same output range as the temperature sensor? Or is a temperature sensor output radically different from a load cell output? I have no problem with using a formula to convert the temperature values to kg values.

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Almost certainly the output from a load cell is a Wheatstone bridge whereas the output from a temperature sensor is typically a single-ended two-wire configuration that offers a resistance change with temperature or maybe a constant current output like the AD590.

This likely means that the load cell would need to be buffered with an instrumentation amplifier followed by a voltage to current generator if you are lucky to find that the temperature logger you have uses a device similar to an AD590 then you are OK - it can be done.

However, if your temperature data logger expects the input sensor to be a thermocouple of platinum resistance type gauge then you won't be successful.

Added to this, you need to provide an excitation voltage to a load cell - it is a four wire device; two wires are excitation supply and two wires are its output.

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  • \$\begingroup\$ Thanks, that's really informative! I guess that even if the input sensor is of the platinum resistance type (which sounds the most likely) I might be able to bypass the circuit somewhere as the logging functionality will be the same. I'll just start by ordering a logger and checking what it comprehends. Am I correct in assuming that the excitation voltage needs to be very precise (i.e. batteries might not do the trick?) \$\endgroup\$ – Ewout Sep 25 '13 at 8:58
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    \$\begingroup\$ Excitation does need to be constant but can usually be any value from a volt upwards. If battery powered then the lower the better (and use a voltage reference circuit for it) but lower means smaller signals so try and figure a way of using an instrumentation amp but watch power rails - the inputs need to work close to power rails if the excitation voltage is low. \$\endgroup\$ – Andy aka Sep 25 '13 at 9:03

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