OverviewThe basic block diagram is shown below:
555 TimerThe 555 astable board uses a 555 timer in its astable configuration. This means that it outputs a square wave or a series of high and low signals. The speed that the signal goes high and low is set by the capacitor C1 and variable resistor R3. The board is designed to make a tone so will be switching quickly on and off which is just what’s required for the 7 segment dice. The purpose of the 555 timer is to generate a clock signal whenever the switch is pressed. When this happens the 7 segment will be clocked through the various numbers. The circuit diagram of the 555 astable circuit is shown below:
CounterThe counter selected is a binary coded decimal four bit up down counter (4510B). This means that it can either count up from zero to nine or down from 9 to 0 and that the output of this is indicated in binary.
|CE||Count Enable (active low) Low = Counting functionality enabled High = Clocking the count line has no effect, the previous value is held||Low|
|CP||Clock in - causes the count to either go up or down by one||To the 555 timer output|
|UP / DN||Up / Down Mode Low = down High = up||Low|
|MR||Master Reset (active high) Low = normal operation High = hold the device in a reset state, where CP, PL and outputs Q3 to Q3 are disabled||Low|
7 Segment converterThe final step in the process is to turn the binary encoded number into outputs that can drive a seven segment display. This is done with a BCD to seven segment converter IC, specifically the 4511B. This part has four input lines in BCD format and 7 output lines to drive the seven segments on the number. A few extra control lines are present as follows:
|LT||Lamp Test (active) Low = Turns all segments on, for test purposes High = Normal operation||High|
|BI||Blanking (active low) Low = turns all segments off High = displays the required number The blanking pin can be used with a high speed variable width square wave to provide a dimming function||High|
|LE||Latch Enable Low = Normal operation High = previously displayed number is latched and held||Low|
Connecting the boardsThe following diagram shows how the Kitronik 555 astable board should be connected to the 7 segment display board:
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