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ELM415

Up/Down Interface

Elm Electronics 

ELM415

Example Applications

Figure 1 shows the ELM415 used to interface two

pushbutton switches to an ELM310 stepper motor

controller, so that the motor position can be manually

controlled. For simplicity, the stepper motor and its

drive transistors are not shown in the diagram. Notice

that pin 5 has been tied to VDD in order to enable the

automatic repeat function, allowing the motor to move

‘continuously’ if a button is held down. Also, because

there are internal pullup resistors, the two pushbuttons

have been connected directly to the inputs without

further support circuitry.

Using the ELM310 to control a stepper motor has

many advantages – low cost, low power, and ease of

use, for example. The disadvantage, however, is that

the integrated circuit is capable of responding very

quickly to input signals. This could result in multiple

steps of the motor, and perceived erratic motor

operation, if the input were not ‘debounced’ by a circuit

such as the ELM415.

A

+5V

1

8

To winding

+5V

2

7

B drive circuits

5

4

3

6

C

Clockwise

6

3

7

2

+5V

8

1

4

5

D

Counter

clockwise

Figure 1. Controlling a stepper motor

The circuit of Figure 2 is very similar to the one

above, but it uses an Analog Devices AD5220 Digital

Potentiometer as the controlled device. The up and

down buttons are used to ‘move’ the wiper between

the two ends (pins 3 and 6). As shown, when stepped

in the Up direction, the AD5220 moves the wiper

towards the pin 3 end of the pot, while Down moves it

towards pin 6.

The AD5220 expects to have a Count signal that

is normally low, pulsing to a high level in order to

change the resistance, so pin 4 is connected to a low

(VSS) level, as shown. Some devices, such as the

Maxim MAX5160, require an inverted Count output,

which can be provided by simply tying pin 4 to VDD

instead of VSS.

Up

Down

VDD

5

6

7

8

4

3

2

VDD

1

VDD

1

8

2 AD5220 7

3

6

4

5

Figure 2. Controlling a digital potentiometer

ELM415DSA

Elm Electronics – Circuits for the Hobbyist

< http://www.elmelectronics.com/ >

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