buttonpullup
This problem is decades old but I do not see a direct answer to it on this site. I want the following:
This circuit just allows to check the state of the button from inside the micro-controller. Nothing fancy. My questions:
It's a silicone rubber keypad. They're usually custom-made for the application (MOQ in the thousands or more if a mold has to be made).
They require a matching PCB that is either gold-plated or printed with a carbon paint in order to form the key patterns. The rubber keys have a conductive silicone bit molded into the back of the keys that bridges the PCB interdigitated pattern so that the switch is closed (the resistance is not nearly as low as with a switch that has metal contacts, but plenty good enough for a microcontroller to detect). The buckling of the key gives a tactile feel that is appropriate. Sealing against the environment (water, finger oils etc.) is not great, but acceptable for many applications.
Excellent choice if you're making a large quantity of a product, not so practical if you're only making a few hundred pieces or fewer.
In my opinion it should work. If you are afraid of the charge rate of C1, you can add a resistor between S1 and +5V. This way, you limit capacitor's loading rate.
By the way, you can simulate your circuit on LTspice, it's a free and helpful software.
Best Answer
First, a lot of microcontrollers and digital signal controllers will have internal pull up resistors. Here's an example, an Atmel ATMega164.
There will typically be a register that allows the internal pull ups to be turned on and off. Due to variations in the fabrication process, these internal pullups come in a very wide range, and are not a good choice if you need very close control over current draw in ultra low power applications. If keeping component count low is important, this is an easy way to do it. Using internal pull ups for hardware debounce would not be a good idea, since it's not possible to predict their exact value.
Whether the 100\$k\Omega\$ value is adequate depends. If it's just a switch that will be periodically flipped by a user, then 100\$k\Omega\$ would be a good choice for minimizing power consumption. For things that are going to switch more rapidly, such as rotary encoders, the process I would go through is
So if the maximum sink current per GPIO pin were 10 mA and operating at 5V: \$R=\dfrac{V}{I}=\dfrac{5V}{10mA}=500\Omega\$. Keeping this R value small as possible will allow for the sharpest edges and highest switching frequencies.