Rotary Decoder – 2 wire 2x Interface


The ELM402 is an 8 pin integrated circuit that is used to convert the signals from a rotary encoder into a series of up and down output pulses. 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 ELM402, as this is all performed within the integrated circuit. After debouncing the encoder signals, the ELM402 then determines the direction of shaft rotation, and generates the appropriate pulses at the Up or Down output pins. The duration of these pulses can be selected for either 0.2 or 2.0 msec.

The ELM402 provides 2x decoding of a rotary encoder signal. If your application requires 4x decoding, please see the ELM403 (it is identical to the ELM402 in every respect, except that it provides 4x decoding).


  • 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 decoding
  • Startup delay timer
  • High current drive outputs

Connection Diagram

( PDIP or SOIC, top view )
ELM402 connection diagram

Block Diagram

ELM402 block diagram


The ELM402 data sheet (ver A, 54K):

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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 (ELM402P + ELM402SM) for the calculation.


Select the desired integrated circuit package type, then the quantity desired, before adding it to your shopping cart. Quantity discounts will be applied as appropriate.