Replacing the Clock Resistor – Process and Example

Many children's toys that make electronic sounds contain a 'clock resistor'. This is a discrete resistor that is usually a surface mount component, and regulates the playback rate (pitch and speed) of the sound and all other time-based functions, including aspects like LED flashing rate and triggering interval of button inputs.

To locate the clock resistor:

  • Remove the circuit from the housing of toy
  • Continuously make sound with the toy. 
  • During audio playback, run fingers over the components and listen to any variations in playback rate. 
  • Narrow down this change to one component (or the connection between two point on the board). 


Once the clock resistor has been found, a number of different modifications can be made:

  • A physical pot can be added to the circuit at the two points where a change of pitch was detected. The physical pot will only change the playback rate up (and not down). 
  • The clock resistor can be removed by desoldering carefully. The clock resistor can then be replaced with a physical pot - the middle leg and one outside legs are connected to the two points where a change of pitch was detected.
  • Instead of using a physical pot, a light dependent resistor can be used. 
  • Instead of using a physical pot, a flex sensor can be used.  
  • Instead of using a physical pot, a digital potentiometer can be used.
  • Instead of using a physical pot, a series of pots wired as a sequencer can be used.

In the example shown below: 
  • The circuit board of the toy is removed from the housing
  • The clock resistor is located
  • The clock resistor is removed via desoldering
  • Two new connections are soldered on in place of the clock resistor. This is achieved by added some solder to each point on the circuit board, and the inserting a small wire per connection. 
  • Note how much of a playback rate change can take place when the clock resistor has been removed 
  • A light dependent resistor is added, and now controls the playback rate