ELM406
Example Application
Figure 7 below shows how the ELM406 might be
used with a digital potentiometer (in this case, a Dallas
Semiconductor/Maxim DS1804).
pullup resistors to ensure that the Chip Select and the
Clock lines rise to the VDD level as quickly as possible
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.
Pullup resistors of 10 KW are used with the rotary
encoder to provide voltages for the A and B inputs.
Power for the ELM406 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 ELM406), 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.
That’s about all there is to using the ELM406.
Connect pullup resistors to your rotary encoder,
connect the encoder signals to the ELM406, then
connect the ELM406 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!
The ELM406 output lines are directly connected to
the DS1804 inputs, but we have added two 10 kW
VDD
VDD
VDD
VDD
0.01µF
10 KW
10 KW
10 KW
10 KW
1
2
3
4
8
7
6
5
VDD
1
2
3
4
8
7
DS
A
B
1804
rotary
encoder
6
5
H
L
C
W
Figure 7. Connecting the ELM406 to an DS1804
ELM406DSA
Elm Electronics – Circuits for the Hobbyist
9 of 9
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