It’s rare in 2023 for an instrument to be entirely analog, instead it’s more normal for a front-end to feed the analog-to-digital converter (ADC) in a microcontroller. Typically the front-end will do the job of transforming whatever the output range of the sensor is, and present it to the microcontroller in whatever range it accepts. [David] had exactly this problem with a pH sensor, and rather than buy an expensive module to do the job he designed his own.
The sensor in question produces a relatively tiny voltage of -0.414 to +0.414 volts, and requires a very high input impedance. A FET input op-amp is selected, with the ground of the sensor shifted upwards into the positive range by a voltage divider. This then feeds a second op-amp that amplifies the resulting DC voltage for the microcontroller input.
This circuit is an especially simple op-amp application, and is a typical one for a sensor interface where a DC voltage needs to be brought into range of a microcontroller. If you’re not used to op-amp circuits then take a look, this type of analogue circuit is not difficult and might just save your butt some time.
Want to know more about simple op-amp circuits? Have we got the video for you!
Taking the form of an Arduino mega-shield that supports a pH meter, a spectrophotometer, and a PID-controlled hot plate, [M. Bindhammer]’s design has a nice cross-section of the instruments needed to start biohacking in your basement. Since the shield piggybacks on an Arduino, all the data can be logged, and decisions can be made based on the data as it is collected. One example is changing the temperature of the hot plate when a certain pH is reached. Not having to babysit your experiments could be a huge boon to the basement biohacker.
