Digital Designs and Scientific Hardware - Open-Source Lab: How to Build Your Own Hardware and Reduce Research Costs - page 221

Similar to the open-source environmental chamber in Chapter 4 and the open-source color-
imeter in the previous section, the pHduino operates as a stand-alone unit using an LCD to
display the pH and the temperature data like any commercial pH meter. Again, similarly, you
can control it using a computer by USB port in addition to loading up the firmware. For this
design, the signal gain (slope) and the signal offset are adjusted manually by trimpots and the
signal is compensated by a temperature sensor. Unlike other examples in this topic, this partic-
ular design can be more expensive than the low-end commercial pH meter bench instruments
that are mass produced due to the tool's vast collection of applications. However, the pHduino
has significant advantages, which provide it with superior value. It is interfaceable, program-
mable, expandable, and, of course open and free, so you are free to adapt it to your specific
application without paying additional money to a vendor. As it develops and matures, simil-
ar to other areas of complex open-source scientific tools, making and, specifically, printing it
from functional materials should reduce costs below those that can be manufactured conven-
tionally and sold.
The printed circuit board (PCB) layout is shown in Figure 6.63 , the electronic schematic is
shown in Figure 6.64 , and the Arduino shield details are shown in Figure 6.65 . The completed
pHduino is shown in Figure 6.66(a) with details in Figure 6.66(b) .
FIGURE 6.63 The printed circuit board (PCB) layout of the pHduino.