Pt100 Reader: README

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+ PT100 Reader
+============
+
+* Serial link for data output and calibration setting
+* 200 uA sensing current
+* Default range is +- 50 degrees, can be extended by changing one resistor and the conversion polynomial in the uC
+* Two measurements of the same channel take about 8 ms, before the current is switched off again to keep self-heating at a minimum.
+* The sensors are connected in 3-wire mode: The middle pin of the connector is wired to one pin of the PT100 sensor, the outer two pins are connected to the other side of the sensor.
+* PT100 sensor can be plugged either way, no polarity needs to be checked.
+* The offset of each channel and the global gain can be calibrated manually and corresponding values are stored in the uC memory.
+
+
+
+Serial Data
+-----------
+All measured data is output on a serial interface, running at 38400 8N1. The FT232 adapter board can be used to connect to a USB on any PC. The data format is as follows:
+
+All datagrams are 11 ASCII characters long, the last one being a newline (\n), e.g. "AB12345678\n". Data generated by a uC starts with an 'A' ("answer"), data sent by the controlling PC starts with a 'W' ("write"). The second letter marks the type of the message (T: temperature, I: board information, E: Eeprom configuration data, R: Reload configuration).
+The first digit is the board address: The first board connected directly to the PC is board 0. If more boards are chained, each subsequent one increases its address by 1. The second digit is the channel number and only used in the temperature words: Channel 0 to 7 are the 8 PT100 inputs as labelled on the board. Channel 8 delivers the temperature of the ADC on the board. The remaining 6 digits are word dependent, all data is given in hex digits:
+* AT: If the third digit is '1', no sensor is connected. The last 5 digits contain the temperature in mK
+* AI: An arbitrary version string of the board
+* WE: Digits 3 and 4 are the register address, Digits 5 to 8 are its contents (16 bit)
+* WR: No data, fill with '0'
+
+
+Configuration Memory
+--------------------
+| Address | Content |
+| 0x0 - 0x7 | Per-channel offset calibration. The relation is about 0x10 for a change of 0.08 degrees centigrade.|
+| 0x9 | Current and gain calibration. Nominal value is 0xd260. The value is calculated as 2**29/gain/current[nA] |
+| 0xa | Conversion rate. Gives the time between starting two conversion (of all channels) in units of 2ms |
+| 0xb | LCD enable. Set to 0 to disable output on the display, 1 enables data output |
+| 0xc | Averaging. Number of samples to take before sending the averaged value on USB and updating the display |
+
+
+Display
+-------
+The display shows temperatures of even channels in the left column, odd channels in the right. Negative values are displayed in red. Using the display slightly reduces the sample rate due to the time needed to update the readings. The display is only updated after enough samples are taken to provide the required amount of averaging.
+
+-- 
+Jan Michel