Figure 7 below shows how the ELM404 might be

used with a digital potentiometer (in this case, an

AD5220 from Analog Devices).

Pullup resistors of 10 K

Ω are used with the rotary

encoder to provide voltages for the A and B inputs.

Power for the ELM404 and the AD5220 has been

supplied from a common source (it must be between

2.7V and 5.5V for the AD5220), and a small capacitor

has been added to ensure that the supply is filtered.

Note that the output lines are directly connected to the

AD5220 inputs, but we have added a 10 k

Ω pullup

resistor on the CS line, to ensure that it rises rapidly to

This may not be absolutely necessary in this case (as

the AD5220 setting only changes on the falling edge of

the clock signal), but it does not hurt to add it.

That’s about all there is to using the ELM404.

Connect pullup resistors to your rotary encoder,

connect the encoder signals to the ELM404, then

connect the ELM404 to the controlled circuit. Use a

common supply for all the devices, and add a small

bypass capacitor across the supply line. The controlled

devices can be digital pots, microprocessors, or almost

any circuit that will accept CMOS signals. Enjoy!

Example Application

Figure 7. Connecting the ELM404 to an AD5220

9 of 9

ELM404DSA

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

ELM404

0.01µF

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10 K

Ω

10 K

Ω

A

B

rotary

encoder

C

10 K

Ω

AD

5220

1

2

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8

7

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5

H

W

L