• 1889: The uniselector switch was invented by Almon B. Strowger, who was a frustrated undertaker in Kansas City, Missouri. Strowger was angry that a competitor had installed a switchboard that allowed operators to listen in on his calls, and he set out to create a system that would prevent this from happening.
• 1891: Strowger’s invention was patented, and he began to manufacture and sell uniselector switches. The switches were quickly adopted by the telephone industry, and they soon became the standard for routing calls in automatic exchanges.
• 1915: During World War I, uniselector switches were used in military communications systems. The switches were able to handle the high volume of calls that were required during the war, and they played a critical role in the Allied victory.
• 1940s: During World War II, uniselector switches were used in Japanese cipher machines. The switches were used to encrypt and decrypt messages, and they were essential to the Japanese war effort.
• 1950s: After the war, uniselector switches continued to be used in telephone exchanges and other communications systems. However, they began to be replaced by electronic switches in the 1960s.
• Present day: Uniselector switches are no longer used in commercial applications. However, they are still used in some specialized applications, such as radio control systems and industrial control systems.

Uniselector switches, also known as stepping switches, were electromechanical devices used in early telephone systems for routing and switching calls. Here is a detailed overview of the history and key points about uniselector switches:

1. Invention and Development:
   • Uniselector switches were invented by Arthur Pollen in the early 1900s as a solution for automating telephone switching operations.
   • The first practical uniselector switch was developed by the British Post Office in the 1920s.
   • It was further improved and refined by several engineers and manufacturers during the 1930s and 1940s.
2. Operation:
   • Uniselector switches consist of a rotating arm or rotor that moves in discrete steps to select a particular contact or position.
   • The rotor has multiple contacts arranged in a circular pattern and is driven by an electric motor or other mechanical means.
   • Each step of the rotor corresponds to a specific position or contact within the switch.
3. Contact Arrangement:
   • Uniselector switches typically had two sets of contacts: one for the input circuit and one for the output circuit.
   • The input circuit contacts were connected to the incoming telephone lines, while the output circuit contacts were connected to the desired outgoing lines or other switching elements.
4. Selection Mechanism:
   • A set of control magnets or solenoids was used to control the movement and positioning of the rotor.
   • The control magnets would energize or de-energize based on the switching requirements, causing the rotor to step to the desired position.
5. Switching Capabilities:
   • Uniselector switches were primarily used for connecting and routing calls between different telephone lines or exchanges.
   • They allowed for manual or automatic selection of desired connections, enabling telephone operators or automatic switching systems to establish connections.
6. Advantages:
   • Uniselector switches were relatively simple and reliable compared to earlier manual switching systems.
   • They provided efficient call routing and helped streamline telephone operations.
7. Limitations:
   • Uniselector switches were mechanical devices prone to wear and tear, requiring regular maintenance and occasional replacement.
   • They had limited switching capacity and were eventually surpassed by more advanced electronic switching systems.
8. Evolution and Replacement:
   • Uniselector switches paved the way for further advancements in telephony, leading to the development of crossbar switches and ultimately electronic switching systems.
   • Crossbar switches, introduced in the 1940s and 1950s, offered higher capacity and improved reliability, gradually replacing uniselector switches in telephone networks.
9. Legacy and Historical Significance:
   • Uniselector switches played a crucial role in the early days of telephone systems, contributing to the automation and efficiency of call switching operations.
   • They served as a foundation for subsequent advancements in telecommunication technology.

In summary, uniselector switches were electromechanical devices used in early telephone systems for routing and switching calls. They offered a significant advancement over manual switching methods but were eventually replaced by more advanced electronic switching technologies. Nonetheless, they hold historical significance in the evolution of telephony and automation of call routing.

1. Manual Switchboards: Before the uniselector switch, telephone calls were manually routed by operators using switchboards. This system was prone to errors and inefficiencies.
2. Almon Brown Strowger: Almon Brown Strowger, an undertaker from Kansas City, Missouri, invented the uniselector switch in the late 19th century.
3. Automation of Call Routing: Strowger designed the uniselector switch as an automated alternative to manual switchboards.
4. Electromechanical Design: The uniselector switch used electromechanical components, including a rotating vertical shaft and spring-loaded metal brushes, to establish connections between telephone lines.
5. Call Routing Process: When a person dialed a number, electrical pulses were sent to the local exchange, directing them to the appropriate uniselector switch. The switch stepped through the contacts until a connection was established.
6. Advantages: The uniselector switch offered faster and more reliable call routing, reducing the need for human operators and increasing the efficiency of telephone networks.
7. Impact and Advancements: The uniselector switch was a significant advancement in telecommunications technology. It paved the way for more sophisticated automatic switching systems, such as crossbar switches and digital switches.
8. Replacement: Over time, electronic switching technologies gradually replaced the uniselector switch. These newer systems provided increased capacity, faster call processing, and additional features.
9. Legacy: Despite its replacement, the uniselector switch holds a special place in the history of telecommunications as a crucial step towards automated call routing and the evolution of telephone networks.