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Scoreboard Last update 20 december 2001

Relais box

The function of the relais box is dual. To code BCD code (4 wires) to 1 out of 10 (10 wires) and to amplify the current from about 30 mA to 1 Amp. There are 32 relais for 8 display characters needed because 4 relais control 1 character. If the bulbs are 100 mA each and there are about 15 bulbs on simultaneously, the current is 1.5 Amps. In reality the bulbs burn not at full strength, so the current is less. relais box

It is easy to see that when none of the relais have been activated the current can flow from the plus sign upper left via the relais contacts to the wire of figure 0 top right. When now relais 1 is activated (BCD 0001), the current will flow to cipher '1'.

To prevent having relais 1 to many contacts, something has been changed with the control of relais 1 and 4. As soon as relais 8 is activated, relais 1 is not any more activated with BCD=1, but relais 4. So the wire of '9' is not connected to relais 1 (where an extra contact would be needed) but to relais 4.

Normally telephone relais are mounted on strips. One may construct a wooden box which fits around 8 strips and on every strip 4 relais.

When open telephone relais are used, it is necessary that the rear of the display unit is closed with a dust tight cloth. In my case an old billiards cloth and pins.



Relaisbox. Right front a small part of the display. The white turnswitches (left front) are not in use.