[Alt-photo] 365 nm. UV-Densitometer. Part 2a of 7.
e.camerling at tiscali.nl
Wed Nov 13 10:48:29 UTC 2013
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
That is the delay needed for the measuring signal to the S & H circuit
in IC2 B (11) an outgoing pulse (10) with ~8,2 msec. for the S & H
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
To be continued next week.
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