Strowger invented an automatic exchange allowing connections between telephone lines to be made electromechanically without requiring a plug board. Initially just used within exchanges its reach was soon extended to the telephone by the addition of a dial.
Almon Brown Strowger was born on 26 May 1839 at Penfield, New York, USA.
Strowger was convinced that the local manual telephone exchange operators were sending calls to his competitor rather than his business and was so motivated to invent an automatic system.
Strowger’s design consisted of a device to create a train of electrical pulses corresponding to each digit (this evolved into the rotary dial telephone). At the exchange the pulses drove a rotating arm of a switch to step between 10 possible contact points. The switches were cascaded to deal with a second digit to provide 100 possibilities, then a third for 1000 possible connections.
Strowger died in 1902.
US 447,918 “Automatic Telephone Exchange” 10 March 1891.
Click here to read the original patent
Did You Know?
The original STD code assignment:
1 = End of short code
2 = A, B or C
3 = D, E or F
4 = G, H or I
5 = J, K or L
6 = M or N
7 = P, Q, R or S
8 = T, U or V
9 = W, X, Y or Z
0 = O or Start of code
| London | 01 | |
| Birmingham | 021 | B = 2 |
| Edinburgh | 031 | E = 3 |
| Glasgow | 041 | G = 4 |
| ... | ||
| Aberdeen | 0224 | AB = 22 |
| Bedford | 0234 | BE = 23 |
| ... | ||
| York | 0904 | YO = 90 |
Whilst automatic exchanges were introduced from the 1880s subscribers could only direct dial others on the same local exchange. All distance calls had to be placed via the operator by giving the required exchange/place name and number.
In the United Kingdom to help the operators remember the exchange codes, each was based on the name of the town by using letters assigned to the digits. These codes evolved into the STD (Subscriber Trunk Dialling) Codes (or area codes) introduced from 1958. The last UK manual exchange was phased out in 1976.
