Figure 8 below shows how the ELM407 might be

used with a digital potentiometer (in this case, a Dallas

Semiconductor/Maxim DS1804).

Pullup resistors of 10 K

Ω are used with the rotary

encoder to provide voltages for the A and B inputs.

Power for the ELM407 and the DS1804 has been

supplied from a common source (it must be between

2.7V and 5.5V for the DS1804), and a small capacitor

has been added to ensure that the supply is filtered.

The DS1804 data sheet does not recommend any

value for the size of this capacitor (0.01 µF is fine for

the ELM407), but some digital potentiometers do

specify a larger capacitor size (typically 0.1 µF). You

may need to increase the size of the capacitor,

depending on the chip that you use.

The ELM407 output lines are directly connected to

the DS1804 inputs, but we have added two 10 k

Ω

Example Application

Figure 8. Connecting the ELM407 to a DS1804

10 of 10

ELM407DSA

Elm Electronics – Circuits for the Hobbyist

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ELM407

pullup resistors to ensure that the Chip Select and the

after power up. This may not be absolutely necessary

(as the 3 wire port of the DS1804 is not active for

about 50 msec after powerup), but it does not hurt to

add it – other chips may not have such a start up

timer.

That’s about all there is to using the ELM406.

Connect pullup resistors to your rotary encoder,

connect the encoder signals to the ELM407, then

connect the ELM407 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!

0.01µF

1

2

3

4

8

7

6

5

10 K

Ω

10 K

Ω

A

B

rotary

encoder

C

10 K

Ω

DS

1804

1

2

3

4

8

7

6

5

H

W

L

10 K

Ω