UV-meter design
Introduction
LUVI is a simple design for a handheld UV-meter with an Erythema sensitivity curve. It uses as much as possible ready-made components and will need a minimum amount of soldering.
Early ideas on how to design the LUVI UV-meter that may be helpful to see the design choices that have been made and the different issues that have been looked at when making the design, are described at
Components
UV-sensor
Display/voltmeter
- Murata 3½ Digit, LCD Display Digital Panel Voltmeter DMS-20lcd-1-5-c
- Application notes
- DMS Application note 3: Analog Common and Reference in-out
- DMS Application note 12: Signals with Zero Offsets
-
DMS Application note 2: Input Configurations, Power Supplies, and Ground Loops
- All models have an internal, 1- 2 microfarad, filter capacitor connected across pin 1 (+5V SUPPLY/+BATTERY) and pin 3 (5V RETURN/ –BATTERY) to attenuate high-frequency noise.
From AN 3:
For 5V-powered meters, ANALOG COMMON will be approximately 2 Volts above pin 3 (5V RETURN). If the 5V power supply were to suddenly drop down to 4V, however, ANALOG COMMON would then only
measure 1 Volt above pin 3.
Pin 1 (+5V SUPPLY/+BATTERY), not pin 3, should always be used as the reference point if measuring ANALOG COMMON.
So Vcc-Vana_com = 3V (i.e. with Vcc=5V: Vanacom - Gnd = 2V). This 3V is used for the voltage divider to create Vref (Uref = Vrefin - Vana-com). Reading is ((Input_Hi - Input-Lo) / Uref) * 1000. So full scale of 2000 is twice the Uref.
External reference circuits should be designed so that the current drawn from pin 10 is maintained between 50 and 200 microamps.
Using a Voltage divider calculator (Voltage input = 3V, adding RV1 to R2 or to R1), gives the following range of Uref.
EDL-00001 | R1 | RV1 | R2 | Uref = Vref_in - Vana_com | Iref | Comment |
---|---|---|---|---|---|---|
V2-0 | 2k | 5k | 17k4 | 0.25V - 0.86 V | 3V/24k4 = 120 uA | Original, as in schematic |
V2-1 | 2k | 5k | 8k87 | 0.40V - 1.32V | 3V/15k87 = 189 uA | Allows for more sensitive sensors |
V2-2 V2-3 |
2k | 20k | 2k | 0.25V - 2.75V | 3V/24k = 125 uA | Allows even larger range, up to UVI scale |
Printed Circuit Board
- Holds
- UV-sensor mounted on a separate PCB to allow a 90 degrees angle to have opening at the front-side of box
- Diode for protection against battery reversal
- Ultra-stable 5 Volt reference voltage IC that powers all components
- Resistors and multi-turn potentiometer for the full-scale adaptation and calibration
- Resistors and multi-turn potentiometer for the zero-reading calibration
- Connector for pushbutton
- Wires to the 9V battery clip
- Display/voltmeter
- Needs careful adjustment in height when soldering. 3D-printed template for assembly is designed
Box
-
Camdenboss
-
45 Series
- CHH451PBK - 45 Series enclosure, handheld electronics enclosure ABS
- 117.5 mm x 72.5 mm x 25.5 mm
- Integrated 9V battery compartment with clip
- Silicon rubber boot as option (delivered with each LUVI) CHH451PBK
- Dedicated rubber protection: CHH451BBK - 45 Series rubber boot, Size 1, Black
-
45 Series
- Design
- Factory-made cutouts for display, pushbutton and UV-sensor
- Factory-printed customisation
Various
- 9V battery
- Screen protector
- 3mk FlexibleGlass
- Factory-cut to the exact size of the display (22.3 mm x 35.1 mm)
Erik van der Bij - 17 February 2023