| Molded keypads are used on devices such as | | | | Molded keypads that see occasional use, such as |
| television remote controls and cell phones. These | | | | a TV remote, work well with a weak click. Button |
| switches are simple in design and understanding | | | | presses aren't rapid and the user has plenty of |
| their function makes it easier to request the right | | | | time to react to the key press without needing |
| keypad for your application. | | | | the tactile feedback. However molded keypads |
| The Basic Key Structure | | | | that are used more often, such as those used for |
| Molded keypads are mounted over a printed | | | | sending text messages, require a stronger click. |
| circuit. Underneath each key is a broken circuit | | | | Users press keys very rapidly, often pressing the |
| that is completed when the key is pressed. As | | | | same key many times in succession. A tactile |
| the circuit is completed, the electronics can detect | | | | response registers with the user long before the |
| and react to the key press appropriately. | | | | character appears on the screen, allowing for |
| Each key is a bead of silicone rubber held over | | | | faster operation. |
| the circuit by a web or membrane, also made of | | | | Contact Materials |
| silicone. A conductive pill is mounted underneath | | | | There are a number of choices for the |
| the key to complete the circuit when pressed. | | | | conductive surface on the underside of each key. |
| The space between this pill and the circuit is small, | | | | Each has advantages depending on the application. |
| generally on the order of a millimeter. | | | | The most popular choice is the carbon pill. Circular |
| When the key is pressed, the web collapses and | | | | or oval discs of carbon about a half-millimeter |
| the key falls allowing the conductive pill to come | | | | thick are mounted to the bottom of the key. |
| into contact with the circuit board. When pressure | | | | They have a long life, typically more than 10 |
| is released, the web causes the key to spring | | | | million activations, so usually outlive the device. |
| back into its original position for another stroke. | | | | They have very low resistance however they |
| The Webbing and Snap Ratio | | | | come in limited shapes and some keypads require |
| Design of the web is an important aspect of | | | | a thinner contact. |
| molded keypads because it is the source of the | | | | Other molded keypads use contacts printed with |
| click - the tactile feedback users experience when | | | | carbon ink. They are only a few microns thick so |
| a button is pressed. The design of the web | | | | work in even the tightest space and can be |
| affects the activation force, the strength required | | | | created to accommodate any shape. However |
| to depress the key, and the contact force, the | | | | they carry substantially higher resistance than pills |
| effort required to keep a key depressed. The | | | | which can be a problem. |
| difference between these two forces determines | | | | An experienced manufacturer of custom keypads |
| how strong a click the user gets when pressing | | | | can help you decide what features are right for |
| the button. | | | | your project. |