ELM404
Example Application
Figure 7 below shows how the ELM404 might be
used with a digital potentiometer (in this case, an
AD5220 from Analog Devices).
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!
Pullup resistors of 10 KW 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 kW pullup
resistor on the CS line, to ensure that it rises rapidly to
the VDD level as quickly as possible after power up.
This may not be absolutely necessary in this case (as
VDD
VDD
VDD
0.01µF
10 KW
10 KW
10 KW
1
2
3
4
8
7
VDD
6
5
1
2
3
4
8
7
6
5
AD
5220
A
B
rotary
encoder
H
L
C
W
Figure 7. Connecting the ELM404 to an AD5220
ELM404DSA
Elm Electronics – Circuits for the Hobbyist
9 of 9
www.elmelectronics.com
ELM [ ELM ELECTRONICS ]
