The Frequency Probe Is a Tiny Tool for Measuring Frequency or Voltage

When working with electronics, there are times when you’d like to know the frequency output by a device. Although an oscilloscope is more than capable of this task, such a thing might be a bit overkill, and with a few notable exceptions, you can’t put one in your pocket.

For his latest Technoblogy project, David Johnson-Davies created the Frequency Probe that won’t replace your oscilloscope, but will give a visual indication of frequencies between around 1Hz to 5MHz, as well as voltage — and comes in a package about the size of one’s finger.

The Frequency Probe runs on an ATtiny84A microcontroller, along with a 128x32 I2C OLED user interface and a small LiPo battery. For measurement, one lead plugs into ground and a dressmaking needle is attached to the unit's PCB as the probe.

Besides its tiny form factor, a notable feature of Johnson-Davies' design is how it actually measures frequency. As explained in his write-up, one can either measure the time between pulses in an “interval mode,” or count the number of pulses that occur within a time period in a “frequency mode.” Interval mode is more accurate at lower frequencies, while frequency mode is more accurate at higher frequencies. This device is actually able to switch between these two modes as needed, giving it an accuracy of better than 0.3% over its measurement range.

Code and PCB design files can be found on GitHub, and the project is on OSH Park if you’d like to order one directly.