Building a Type-K Thermocouple to Pasco Capstone Adapter
Welcome to the Type-K Thermocouple to Pasco Capstone Adapter project page hosted by Walla Walla University. This project was developed and is maintained by Dr. Tom Ekkens. If you have comments or suggestions please send email to firstname.lastname@example.org. This page was last updated on June 7, 2022.
Some years ago, Pasco sold a Type-K temperature interface (CI-6526) to connect a Type-K probe to the Science Workshop 750. That design has been retired and replaced by the Pasport design. If it necessary to use the Science Workshop connection instead of the Pasport, an adapter can be constructed using the following process.
The Electrical Design
The electrical system is very simple – the AD595AQ chip does all the work. An op-amp in follower configuration and a low-pass filter complete the hardware. Power is supplied by the Science Workshop through the 8 pin DIN connector. In spite of the notation on the schematic at left, the op-amp used was the LF411. It turns out almost any pin-compatible op-amp will work so use what is on hand. The five smallest capacitors can tolerate considerable variation in value. The board seems to work the same for 100 nF capacitors as it does with 220 nF capacitors. The electrolytic capacitor can be in the range of 100 uF to 120 uF and possibly higher.
The board file (Click for file) was sent out for fabrication since it is a two-sided board. A generic 8-pin DIN cable and Type-K socket complete the connections to the board. The picture of the completed board is shown below. Each chip was soldered directly to the board to minimize loose connections but a socket could be used if desired.
The 3D-Printed Case
The final piece of the project is a case to hold the circuit board and minimize cable strain. A 3d-printed case fabricated from PLA works well. ABS or Resin cases would also work. The top (Click for STL) and bottom (Click for STL) are held together by four #2 sheet metal screws about 1/2" long. These screws also hold the circuit board in position.
The Completed Adapter
The completed adapter is shown at the left. It works just about like the original part from Pasco. There are variations of noise and calibration offsets with each AD595 chip so buying a few extra chips and cherry-picking the best ones is recommended.