frequency probes are used for imaging small, superficial structures at shallow depths and high resolution. Powerful low-frequency probes are required for imaging at greater depths,
The frequency probe enables ”listening in’ to the speed of a computer. It is, however, also suitable for use with other digital circuits because it makes high frequency audible so that signal can be conveniently monitored.
A 12-bit counter serves as a frequency detector. The signal measured in a computer or digital circuit is divided by 1024 and is output at pin 14. It is then used to control a transistor, T1, which in turn drives piezo buzzer Bz1
The scale factor has been chosen to convert MHz into KHz, so that the clock frequency of say an XT computer will be heard as a shrill 8 kHz tone. If higher frequencies need to be monitored scale factors of 2048 and 4096 can be obtained by connecting R2 to pin 15 or pin respectively. If an HCT circuit is used the measuring limit is some tens of MHz. For frequencies <4 MHz, a standard Type 4040 may be used: that has the advantage that the supply voltage need not be exactly 5 V. The supply connections and the probe are best made from flexible wire terminated into crocodile clips.