has anyone used a thermocouple k type with arm or specificaly LPC2148 ?
looking for code or ideas etc , i was thinking of using an AD 595 but wondered if it was realy needed
also looking for hooking up a halleffect to measure RPM ( Tacho )
thanks all
Dave
http://datasheets.maxim-ic.com/en/ds/MAX6675.pdf
Check these out! Pretty sweet. Whatever IC or schematic you choose make sure you use something with cold junction compensation for accurate results.
The MAX6675 senses and corrects for the changes in
the ambient temperature with cold-junction compensation.
The device converts the ambient temperature
reading into a voltage using a temperature-sensing
diode. To make the actual thermocouple temperature
measurement, the MAX6675 measures the voltage from
the thermocouple’s output and from the sensing diode.
The device’s internal circuitry passes the diode’s voltage
(sensing ambient temperature) and thermocouple
voltage (sensing remote temperature minus ambient
temperature) to the conversion function stored in the
ADC to calculate the thermocouple’s hot-junction temperature.
Don’t forget that the voltage out of a Thermocouple is also a non-linear function and must be accounted for (usually by a lookup table).
I’m using AD7708 16bit ADC to measure J and K thermocouples and the ‘cold temperature’ via a thermistor. This gives me pretty good results, but don’t forget that if you need 1ºC resolution, the 10bits internal ADC is not enough, and use of specific IC’s probably will be more expensive.
So if it is a one-off project, better you go with Maxim’s solution, otherwise could be better to use an external ADC and some math.
Guillem.