ELM401
Example Application
Figure 4 below shows how the ELM401 might be
used with a microprocessor. Power for the ELM401
has been obtained from the microprocessor circuit,
and a small capacitor has been added to ensure that
the supply is filtered. The positive supply has been
shown simply as VDD, since the ELM401 will operate
with any voltage from 2.0 to 5.5 volts.
That’s about all there is to using the ELM401 in
your circuit. Connect pullup resistors to your rotary
encoder signals, connect the encoder signals to the
ELM401, then connect the ELM401 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 circuit uses 10 KW pullup resistors with the
rotary encoder signals in order to convert the signal
from the dry contacts into one that swings from VDD to
VSS. The momentary pushbutton contact from the
encoder is treated no differently than the ones from the
encoder wheel. Since both ICs share the same supply,
they can be directly connected as shown.
VDD
VDD
VDD
your microprocessor
VDD
port pins
0.01µF
10 KW
10 KW
10 KW
1
2
3
4
8
7
6
5
A
B
Sw
rotary
encoder
C
Figure 4. Connecting the ELM401 to a microprocessor
ELM401DSB
Elm Electronics – Circuits for the Hobbyist
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