Example Applications (cont’d)

5 of 5

ELM415

ELM415DSA

Elm Electronics – Circuits for the Hobbyist

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A variation of Figure 2 is shown in Figure 3. It uses

series resistors on the pushbutton inputs, and has also

had its autorepeat function modified slightly.

This circuit assumes that the pushbuttons are to

be mounted at a distance from the ELM415, which is

why the series resistors have been added. This is a

good practice to follow whenever working with CMOS

circuits that might be exposed to electrostatically

induced charges, as could be the case due to the extra

wiring for the switches. The resistors help to limit

induced currents which will flow through the IC’s

internal protection diodes during a discharge, and in

doing so reduce the chance of latchup problems.

Generally, we recommend that protection resistors be

installed close to the IC whenever wiring is to extend

from the circuit by more than about twelve inches.

Figure 3. Controlling a digital potentiometer (with rapid down)

The other difference between the circuits of

Figures 2 and 3 is the connection between pins 5 and

6. This can best be explained by considering that in

Figure 3, due to the internal pullup resistor on pin 6,

function). When the Down button is pressed, the

autorepeat function will remain enabled, and multiple

pulses will be output. When the Up button is pressed,

however, it will pull both pins 5 and 6 low, disabling the

autorepeat and allowing only a single pulse to be

generated. This is useful if one wants the user to

explicitly press a button for each advance in one

direction, but will allow a rapid transition to a ‘safe’

position when the other button is pressed. This may be

a desireable feature if controlling the temperature in a

heater circuit, for example.

2

3

4

7

6

5

8

1

Down

Up

1

2

3

4

8

7

6

5

AD5220

1K

Ω

1K

Ω

Our final example shows how easily one can use

the

ELM415

as

a

‘one-shot’

or

monostable

multivibrator in a reset circuit. Often one has the need

to reset a circuit using a pushbutton, but multiple

2

3

4

7

6

5

8

1

Reset

Reset

Output

Figure 4. Manual reset circuit

resets due to bouncing switches would be an

annoyance. Using the circuit of Figure 4, one can

generate a single clean reset pulse whenever the

pushbutton is pressed. If the circuit needs a negative-

Hopefully this has provided you with several ideas

for using the ELM415 in your next project. Have you

considered using it to reset a timer whenever a contact

closes, or to count switch closures, or to determine an

object’s direction based on the order in which the two

switches operated…