Rotary Decoder – 2 wire Interface


Quantity Pricing

The following are the unit prices, as you vary the quantity purchased:






All prices are in Canadian dollars. We use the total number purchased (ELM408P + ELM408SM) for the calculation.


The ELM408 is an 8 pin integrated circuit that is used to convert the output from a rotary encoder into two signals (chip select, and up/down) that can be used to control various devices. The low power CMOS technology used ensures that only a very small current is required over the entire 2.0 to 5.5 volt operating range.

There is no need for external filtering or debounce circuits with the ELM408, as this is all performed within the integrated circuit. After debouncing the encoder signals, the ELM408 determines the direction of shaft rotation, and then generates the appropriate outputs. A write sequence can also be generated if the Write Enable input is at a high level when the outputs are generated.

The ELM408 provides both 2x and 4x decoding of a rotary encoder signal. See the Output Waveforms section for more information.


  • Digital audio potentiometer controls
  • Variable voltage or temperature circuits
  • Positioning controls
  • Tuning circuits


  • Low power CMOS design
  • Wide supply range – 2.0 to 5.5 volts
  • Complete debouncing of the encoder inputs
  • No external filtering needed
  • 2x and 4x decoding
  • Can generate a write sequence
  • Startup delay timer
  • High current drive outputs

Connection Diagram

( PDIP or SOIC, top view )
ELM408 connection diagram