- The left connector is six screws which connect to your power supply and analog-to-digital converter. From top to bottom these are:
- V+: Something like 5V. As long as the power supply provides a clean voltage larger than the output you need, the exact numbers don't explicitly matter. The maximum voltage between V+ and V- is a function of the dual op-amp you use.
- V-: This can be shorted to ground through SJ1 if you don't need to measure temperatures below 10C, otherwise apply something like -5V.
- Tcold: This is a 10mV/C signal of the cold junction reference on the circuit board. Useful if you also want to measure the ambient temperature. If you expect the ambient temperature to be below 0C, you will need to install a 10k resistor in R5, which is otherwise unneeded.
- CH1: 10mV/C signal of the first thermocouple to be fed into a volt meter or ADC.
- CH2: 10mV/C signal of the second thermocouple, also to be somehow measured.
- The right connector is for the two K type thermocouples. The polarity is important! Make sure you get the positive wires in the positive terminals, which are marked in the silk screen. I expect the thermocouples to be terminated with bare wire, so if they come ending in HPC connectors or otherwise, you just need to get a screw driver and disassemble those.
- 7x 0.1μF capacitors (in 0.1" packages) (Digikey) C1-C7
- 5x 2 position, 0.2" spaced wire-to-board terminal blocks (or any other way to get four and six positions) (Digikey) J1, J2, J3, CH1, CH2
- 2x 255k 1% resistor (Digikey) R1, R2
- 2x 1k 1% resistor (Digikey) R3, R4
- 2x 100 ohm multiturn trimpot (Digikey) R6, R7
- 2x 8DIP IC socket (Digikey)
- 1x LT1025 DIP (Digikey) U1
- 1x LTC1051 or any other dual low-offset op-amp. (Digikey) U2
- Optionally 1x 10k resistor - R5
ITead Studio's prototype PCB service, which is a very interesting service. $14 out the door got me 10 copies of my sub-5cm x5cm board, and two random other boards of other person's design. They're decent boards... There is definitely some problems with drilling accuracy, but it doesn't look like any of the holes are too problematically off-center. If you're planning on using this service for a board design, I suggest pushing all your masks out a few more mil than you really need for through-hole.
it's a stepper motor driver for a CNC mill. The other board is a little baffling; it seems to be some sort of surface mount breakout / some sort of LED bar / random stuff. Pretty baffling...
PCBs in stock: 5
If you would like to make any changes, or use this design in a larger project, or just have boards fabricated yourself, the entire design is licensed CC BY-SA, noting that the original schematic is heavily based on Linear's datasheet application note. Download the Eagle/Gerber files here.