Insight - How DIP Switch works

DIP switch can be defined as an array of simple two terminal On-Off electromechanical switches (Single Pole Single Throw) that are commonly used in electricity operations. The word DIP is an acronym for Dual In-line Package which means that the electrical contacts are in two rows. DIP switches are surface mountable and are used in those applications where multiple numbers of switches are involved in output generation. For instance, in a universal remote control, the DIP switch is used to set the frequency according to the device that is being operated. On a computer motherboard, DIP switches help in optimizing the clock speed and configuration settings according to the type of processor mounted.

Depending on the number of miniature switches in the array and the application, DIP switches can be rotary, slide contact, rocker contact etc. Let us explore the skeletal innards of one such device.

Fig. 1: Image Showing a DIP Switch

Outer Structure

Fig. 2: Outer Structure of a Sliding Type DIP Switch

Shown in the image above is a sliding type DIP switch. It is a combination of 8 switches and hence has total 16 pins equally divided into two rows, thus making it a 16 pin Dual In-line Package Switch (DIP). It is similar to an IC in its shape and size so that it can be easily mounted on a PCB. The switches are made of flexible materials like polyamide (Nylon) that can withstand operational jerks when switching rate is high. The casing is made of heat-resistant thermoplastic polymer made from polybutylene terephthalate and also contains a flame retardant epoxy.

Fig. 3: Top View of DIP Switch Showing Sliders and ON Position

From the top view, sliders and the ON position can be seen. The plastic casing has guide-ways on its top that contain the sliders. The frame dimensions have to be precise so that the sliders can be exactly placed over ON and OFF states.

Fig. 4: Bottom View of DIP Switch Showing its Various Parts

The bottom view of the switch shows the connecting terminals of the DIP bound to the structure with the help of a strong adhesive. The connecting leads are made of bronze over which tin is coated.

Internal Construction

Fig. 5: Internal Structure of DIP Switch Showing its Contact Pins

The removal of top casing and the switch sliders reveals the switch array. The black base over which the contacts are placed is made of same material with which the casing has been made. The contact pins are made of bronze. In order to protect the pins from corrosion, they are plated with gold. The choice of coating material is often dependent on ratings of the switch, gold being preferred for dry, low power situations. Also, they are dipped into sulfide so that the contact resistance is least affected by chemicals present in the atmosphere. Sulfides are known to deposit quickly on a metal surface and change its contact resistance. But their deposition slows the reaction rate with which other chemicals can interact with the metal. Hence, they serve as efficient protector of the metal contacts.

Fig. 6: Dissected View of DIP Switch Part

For every switch, a pair of contact pins is there. In each pair, one contact is flexible while other is stationary. All the switches are contact isolated from each other so that no output variations are there. The flexible part has a leaf spring shape which helps in optimizing the slider in terms of force required to switch position from 0 to 1. Whenever a slider is switched from 0 to 1 position, the flexible part bends down to establish contact with the stationary contact.

Pins & Switching

Pins

Fig. 7: Types of Pins—Leaf Spring and Stationary Contact Pins

Separately shown above are the flexible pin and the stationary contact pin of the switch. The leaf spring is formed from the same plate with which the connecting pin is formed on the part following the right angled bend. The farthest end of this leaf spring is curved outwards to have maximum contact area with the fixed contact.

Switching

Fig. 8: Switch ON and OFF Mechanism

When pushed to 1 (ON) position, the slider moves to that curved part of the flexible pin which pushes the leaf spring down, establishing contact between the two plates. When the slider moves back to its 0 (OFF) position, the restoring force of the leaf spring restores it to the neutral, open condition.

Based on the application, electrical configuration for a DIP Switch is determined in terms of current, voltage and power ratings. As they are used for On-Board configuration, these settings are pre-defined in a range making them application dependent. The ratings are life tested by manufacturers and signify the recommended working conditions. Paying no heed to such ratings can lead to problems like self-welded switches, electrical arching while switching etc.

Dip switches have been used in electronics since a long time and even though faster CMOS based switching circuits have arrived, former are still in trend in MSI and LSI circuits. The output in a DIP switch is strictly dependant on what slider positions to “On”. Thus the combination of switches can be used to generate various outputs which in turnreduce the hardware requirement by a significant amount.