The battery-powered circuit in Fig 1 detects 295-nm UV radiation, which is dangerous to eyes and skin. Be sure to protect yourself and your coworkers against this radiation.
The battery-powered circuit in Fig 1 detects 295-nm UV radiation, which is dangerous to eyes and skin. Be sure to protect yourself and your coworkers against this radiation.
To operate the device, press switch S1 and hold it closed for at least 2.2 sec. A start pulse applied to IC4 starts the 2.2-sec measuring cycle. Pin 3 of IC4 resets the 4040 binary counter, IC5.
UV radiation at 295 nm generates a current in the R1107 vacuum photodiode. This photo current charges C1 in a linear fashion. Size C1 to suit your application; values should range from 5 to 20 pF. IC1 is a high-impedance buffer amplifier, and IC2 is a noninverting amplifier having a gain of ~20.
The amplified, linearly increasing voltage triggers 555 timer, IC3. If the ramp voltage reaches two-thirds of the supply voltage of IC3, IC3 generates an output pulse into pin 10 (CLK) of the 4040 counter, IC5, and discharges C1 via IC3's Pin 7. This cycle repeats until IC4 times out and its Pin 3 goes low. The counter IC5 holds the radiation count and drives the LED array.
If the sensor detects no 295-nm radiation, the counter nonetheless displays 1 bit. This single count verifies that the battery can still power the circuit. (DI #1629)