[Alt-photo] 365 nm. UV-Densitometer. Part 2a of 7.

[Erich Camerling]

The clock-factory.   (Part 1)

Definition : two different pulses for the UV-Densitometer
    - clockpulse 1 for the UV-LED  ~ 10 msec.
    - clockpulse  2 for the Sample & Hold amplifier. This pulse must 
start ~1 msec. later
      and stop ~1 msec  before clockpulse 1.
    - refresher time must be ~128 msec.
    - power supply :  = 5 V. The PCB uses a 470 µF capacitor as an 
buffer and a 6 V zenerdiode for protection.
    - every IC has a 0,1 µF capacitor between "+" and "0"

The wiring diagram starts with a "local oscillator" : 74HC4060 (IC1) and 
a  4.194304 MHz  crystal.
The resulting pulse is connected to the second 74HC4060 (IC3) as divider.
The outgoing pulse starts the 74HC4538 (IC 4 A/B).
One of the outgoing signals  from IC 4 B (10) is connected to the next 
4538  (IC 2A).
That IC starts simultaneously with the rising side from this signal and 
gives a pulse of
~1 msec.
That is the delay needed for the measuring signal to the S & H circuit 
and starts
in IC2 B (11) an outgoing pulse (10) with  ~8,2 msec. for the S & H 
measuring time.

Connections :
    You need 2 screw terminal blocks with each 3 connectors.

    X1-1 : pulse 21 msec (not used)
    X1-2 : pulse 10 msec for the UV-LED
    X1-3 : pulse   1 msec starting simultaneously with X1-2
                                          (will not be used but is the 
delay between X2 -3 and X1-2)

    X2-1 : + 5 V
    X2-2 :    0 V
    X2-3 : pulse (8,2 msec) for the S & H.

When you give a + 5 V  on R 10 via a switch you stop the pulse train for 
the UV-LED.

To be continued next week.