Once upon a time, touch buttons in equipment were a tribute to fashion. The very fact that there was no need to press the button, but only to touch it, aroused delight among users. Today, such buttons have become so commonplace that hardware designers use them even less often than in the past.
Instructions
Step 1
Purchase a K561LA7 or K561LN2 microcircuit. The first allows you to implement up to four touch buttons, the second - up to six.
Step 2
Check out the pinout of the K561LA7 microcircuit:
- 1 element: 1, 2 - inputs, 3 - output;
- 2 element: 5, 6 - inputs, 4 - output;
- 3 element: 8, 9 - inputs, 10 - output;
- 4th element: 12, 13 - inputs, 11 - output.
Step 3
Check out the pinout of the K561LN2 microcircuit:
- 1 element: 1 - input, 2 - output;
- 2 element: 3 - entrance, 4 - exit;
- 3 element: 5 - entrance, 6 - exit;
- 4th element: 8 - entrance, 8 - exit;
- 5th element: 11 - entrance, 10 - exit;
- 6th element: 13 - entrance, 12 - exit.
Step 4
Please note that on both microcircuits, the seventh pin is for connection to the common wire, and the fourteenth is for supplying the positive pole of the power supply (from 3 to 15 V). The supply voltage of the microcircuit should be equal to the supply voltage of those logical nodes to which it is connected, it is even desirable that they are powered from a common source.
Step 5
To make a touch button from any of the logic elements of the microcircuit, first, if the element has two inputs, connect them together. Then connect the input (or the point of connection of the inputs, depending on the element) to the positive power bus through a resistor with a resistance of about two megohms. Place two sensors side by side on the front panel of the instrument. Connect one of them with a short conductor to the input of the element or the connection point of its inputs, and the other with an equally short conductor to the common wire of the device.
Step 6
When no one touches the sensor contacts, a logical zero is present at the output of the corresponding logic element (since its input is connected to the power bus through a resistor, or, as they say in jargon, "pulled up", which corresponds to one, and the element is an inverter). If you touch both sensor contacts at the same time, the input of the element through the skin resistance, which is much less than the corresponding parameter of the resistor, will be connected to the common wire, which corresponds to a logical zero. And at the output of the element, a level corresponding to a logical unit will appear, which will hold out until the finger is removed from the sensors.
