SiTech molded keypads are used on countless electronic devices from security panels to cell phones. The technology behind them is simple but elegant and understanding how they work will help you design the right keypad for your device.
Basic Keypad Function
Regardless of the device, the function of molded keypads is basically the same. The keypad is placed over a circuit board with each key over a broken circuit. When a key is pressed, the circuit is completed and the device reacts to the action.
An individual key is made of silicone rubber. It is mounted to a silicone membrane or web that holds it in place and resists downward pressure. As the user presses a key, the membrane will give way under the pressure and allow the key to come into contact with the circuit, a distance of a millimeter or less. On the underside of the key is a conductive surface which will complete the circuit. When the key is released, the membrane springs back and the key is ready for another press.
Understanding Membrane Design
The function of the membrane may seem simple but its characteristics vary over different molded keypads. The membrane provides the tactile feedback, the “click” users feel, that is so important in proper control design. Different membrane designs give stronger or weaker clicks as desired.
Many devices can take molded keypads with weaker clicks. Any control that will see slow, occasional control presses and is accompanied by visual or auditory cues will be fine with less tactile feedback. However in many cases users require a stronger response. Molded keypads used on security access panels should have strong clicks since users won’t see their code displayed as they key it in. Cell phones are another good example since rapid texting is easier if each key gives a strong click.
Choices in Contact Materials
SiTech offers our clients a variety of choices in conductive surfaces. The most common material is carbon and two popular choices are the pill and painted contacts.
Sicoate IV pills have a long life and will usually outlive the molded keypads they are used on. They have low resistance so don’t interfere with circuit function. However they are about a half a millimeter thick which is too thick for some control panels. They also come in a limited choice of shape and some clients need more versatility.
At the other end of the contact spectrum we use carbon that is painted on in a layer a few microns thick. These contacts are thin enough to be used in the smallest spaces and can accommodate any shape desired. However their thin profile also means high resistance and that can be a problem for some circuits.
We offer other choices in between those two to fit the needs of a wide range of custom keypads. Consult with our staff and we can guide you in designing the ideal controls for your project.